Sedimentary and tectonic evolution of the Vena del Gesso basin … · 2017. 7. 2. · Marco...

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GSA Bulletin; April 2003; v. 115; no. 4; p. 387–405; 16 figures.

Sedimentary and tectonic evolution of the Vena del Gesso basin(Northern Apennines, Italy): Implications for the onset of the

Messinian salinity crisis

Marco Roveri†

Dipartimento di Scienze della Terra, Universita di Parma, Viale delle Scienze 157A, 43100, Parma, Italy

Vinicio ManziFranco Ricci LucchiDipartimento di Scienze della Terra e Geologico-Ambientali, Universita di Bologna, Via Zamboni 67, 40127, Bologna, Italy

Sergio RoglediENI-Agip Division, Via Emilia 1, 20097, San Donato Milanese, Milano, Italy

ABSTRACT

The integration of field and subsurfacedata permits a substantial revision of thesedimentary evolution of the Vena del Gessobasin, a thrust-top basin in the NorthernApennines where shallow-water primarygypsum deposits related to the Messinian sa-linity crisis were well developed and pre-served. As inferred from lateral and verticalfacies changes within the underlying deep-marine turbidites of the Marnoso-arenaceaFormation, evaporite precipitation occurredin a basin bounded to the north and to theeast by a thrust-related anticline activelygrowing since the late Tortonian. Both gyp-sum deposition and subsequent deformationwere strongly controlled by evolving paleo-bathymetry driven by tectonics. Primarygypsum precipitated in a shallow, silled ba-sin, while in the adjacent deeper and largerforedeep basin, organic-rich shales were de-posited. Gypsum deposits underwent severepostdepositional deformation related tolarge-scale gravitational collapse, as a resultof a regional uplift event, also coincidentwith the end of the evaporitic phase. Alongthe inner, shallower-dipping limb of the an-ticline bounding the basin, large-scale, poor-ly deformed gypsum slabs moved downslopealong a detachment surface developed at thecontact with the underlying euxinic shales,forming both extensional and compressionalfeatures and showing an overall southwest-ern vergence. The identification of a south-

† E-mail: [email protected].

southwest–dipping paleoslope, here pointedout for the first time, suggests that the de-formational features affecting the gypsumunit were probably driven by gravity andnot by active thrusting, as thought up tonow. The steeper frontal limb of the anti-cline promoted the transformation of gyp-sum slides into debris flows and turbiditecurrents that deposited their load in the ad-jacent deeper basin. This gravitational de-formation was sealed by postevaporitic up-per Messinian Lagomare deposits. Thesedimentary history of the Vena del Gessobasin suggests that the Messinian salinitycrisis in the Apennine foredeep, as well as inthe Balearic, Tyrrhenian, Sicily, and EasternMediterranean Basins, was tightly linked totectonic processes. The large-scale, postde-positional collapse of primary evaporitic de-posits is a widespread feature in the Medi-terranean basins, and it may have alteredthe original stratigraphic relationships insome places. This finding has potentially im-portant implications for a correct paleoen-vironmental reconstruction of the onset ofthe Messinian salinity crisis.

Keywords: Messinian salinity crisis, Apen-nine foredeep, thrust-top basins, evaporites,slope instability, physical stratigraphy.

INTRODUCTION

The Tortonian–Messinian succession of theApennine orogenic wedge records the fragmen-tation and closure of the Marnoso-arenacea

foredeep basin during the longer-term thrust-front propagation and concurrent depocentermigration toward the foreland (Ricci Lucchi,1986). This process implied the formation ofsmall thrust-top basins; some of them werecharacterized during the Messinian by the de-position of shallow-water, primary evaporites(mainly selenitic gypsum), coeval with theLower Evaporites of Mediterranean marginalbasins (Krijgsman et al., 1999a, 1999b). How-ever, because of subsequent tectonic defor-mation, these basins are rarely preserved; theVena del Gesso basin is a valuable exception.It is worth noting that most of the Messinianevaporitic rocks occurring in the Apennineforedeep are actually deep-water clastic de-posits derived from the dismantling of pri-mary evaporites and their resedimentationthrough gravity flows (Parea and Ricci Lucchi,1972; Ricci Lucchi, 1973; Roveri et al., 2001;Manzi, 2001).

The name ‘‘Vena del Gesso’’ indicates acontinuously outcropping gypsum belt elon-gated in a northwest-southeast direction forsome 15 km in the western Romagna Apen-nines (Fig. 1). This area offers spectacular andimpressive outcrops of selenitic gypsum. Ex-tensive studies carried out in the 1970s led tothe formulation of the sedimentary model forthe cyclical deposition of primary seleniticgypsum (Vai and Ricci Lucchi, 1977). Sub-sequent work focused on related topics con-cerning the origin of postdepositional defor-mation affecting the gypsum unit (Marabiniand Vai, 1985), the late Messinian mammalianfauna found in karstic dikes cutting the unit’s

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388 Geological Society of America Bulletin, April 2003

ROVERI et al.

Figure 1. Schematic geologic map of the Romagna Apennines with the reported main stratigraphic and tectonic features of the studyarea. The Cusercoli and tetto formations are informal units easily recognizable in the field throughout the Apennine foredeep; their usehas been proposed by Roveri et al. (1998) to replace the less specific Colombacci Formation. The Gessoso-solfifera Formation is informallysubdivided into lower-rank lithostratigraphic units (shallow- and deep-water members [mb]), following Roveri et al. (1998). VdG—Venadel Gesso basin. Abbreviations of unconformity-bounded stratigraphic units: p-ev2—postevaporitic unit 2; p-ev1—postevaporitic unit 1.

upper part (Costa et al., 1986; De Giuli et al.,1988; Marabini and Vai, 1988; Landuzzi andCastellari, 1988), and the cyclostratigraphy oflower Messinian euxinic shales underlying theevaporites (Vigliotti, 1988; Krijgsman et al.,1999a, 1999b; Vai, 1997; Negri and Vigliotti,1997; Negri et al., 1999).

Despite these valuable contributions, thetectonic and sedimentary history of the Venadel Gesso basin, as well as its relationshipswith the adjacent areas, were not investigatedin detail and still remain poorly understood.In this paper, based on new field observationsintegrated with subsurface data (wells andseismic profiles), we propose a new geologicmodel for the Vena del Gesso basin that pro-vides a unifying explanation for the complexof sedimentary and deformational featurescharacterizing the upper Tortonian to lowerPliocene successions. Besides some obviouslocal implications, this model provides some

thoughtful insights into the general geologicproblems related to the Messinian salinity cri-sis at a Mediterranean scale.

Many still-open problems in the big Mes-sinian puzzle are related to the virtually un-known nature of evaporitic and preevaporiticdeposits lying below the deepest Mediterra-nean basins (McKenzie, 1999). Primary evap-orites occur in many marginal, shallow-waterbasins, but both the sedimentary processes in-volving evaporite deposits and their strati-graphic relationships with deeper depositionalsettings are poorly understood, mainly be-cause of (1) the poor preservation of manyMessinian successions that often makes re-gional geologic reconstructions very difficult,and (2) the fact that some areas (like theApennine foredeep) have been overlooked inthe past, as a result of their ‘‘anomalous’’stratigraphic characteristics, thought to be not

fully representative of the Messinian salinitycrisis.

The most puzzling feature of the Messinianevaporites is that these shallow-water depositsare sandwiched between deeper-water sedi-ments through apparently continuous contacts.This fact has been very attractive for the geo-logic scientific community; the studies of theearly 1970s led to the reconstruction of one ofthe most fascinating geologic histories. Sev-eral lines of evidence led to the formulationof the successful ‘‘deep desiccated basin mod-el’’ of Hsu et al. (1972). The initial model andits subsequent modifications (Muller and Hsu,1987; Hsu, 2001) envisage the total desicca-tion of the Mediterranean basin, considered tohave a physiography similar to the present-dayconfiguration, as a result of the closure of theAtlantic gateways (the Betic-Rifian corridors).Evaporite precipitation (Lower Evaporites)followed a long phase of progressively re-

Geological Society of America Bulletin, April 2003 389

SEDIMENTARY AND TECTONIC EVOLUTION OF VENA DEL GESSO BASIN, NORTHERN APENNINES, ITALY

duced deep-water circulation and consequentdevelopment of dysaerobic seafloor conditionsin the Mediterranean Sea, responsible for thewidespread deposition during the early Mes-sinian of organic-rich laminites (Tripoli For-mation, euxinic shales).

The main controversies around this modelinvolved the timing of Messinian events andthe stratigraphic relationships between mar-ginal and basinal evaporites at a Mediterra-nean scale. These actually form two distinctevaporitic bodies separated by a great erosion-al unconformity, deeply cutting the marginalevaporites. In deeper basins, such a surfacewas traced to the base of a very thick evapo-ritic suite. On the basis of such observations,a two-step model for the Messinian salinitycrisis has been proposed (Clauzon et al.,1996): evaporite deposition started in the mar-ginal basins and progressed only later into thedeepest Mediterranean basins, following thecomplete closure of the Atlantic connectionsthat caused a dramatic sea-level drop of 1500–2000 m. This huge sea-level fall led to thedevelopment of the great intra-Messinian ero-sional surface, mainly through subaerial, flu-vial processes (Ryan and Cita, 1978); the mainrivers cut deep canyons along the shelves andslopes of the desiccated Mediterranean Sea(Rhone, Nile, Ebro; Clauzon, 1982). Thealready-mentioned Apennine foredeep‘‘anomaly’’ is due to the fact that its deepestpart did not undergo total desiccation; thisanomaly has usually been explained by invok-ing its complete isolation from the Mediter-ranean and the consequent development of itsown positive hydrologic budget (Cita andCorselli, 1990).

Before the connections with the Atlanticwere catastrophically reestablished at the baseof the Pliocene, the Mediterranean was partiallyrefilled with brackish to fresh waters comingfrom the Paratethys, a large nonmarine basinplaced to the east, in the present-day Black Seaarea (postevaporitic Lagomare phase). Duringthis final phase of the Messinian salinity crisis,some minor, nonmarine evaporites locally de-veloped (Upper Evaporites).

The timing of Messinian events proposedby Krijgsman et al. (1999a), on the basis of adetailed astronomically calibrated cyclostra-tigraphy, pointed out their remarkably syn-chronous character throughout the Mediterra-nean, despite the different geodynamic anddepositional settings represented in the studiedsections (Sicily, Spain, Apennines). In partic-ular, the onset of Lower Evaporite depositionhas been dated at ca. 5.96 Ma and its end at5.6 Ma. These dates raise important questionsabout the nature of the Lower Evaporites, es-

pecially concerning the actual paleodepth ofevaporites formed in the deepest basins(Krijgsman et al., 1999a). Moreover, thisstudy does not support the hypothesis sharedby many authors that the connections betweenthe Atlantic and Mediterranean were ultimate-ly controlled by eustasy (Kastens, 1992; Clau-zon et al., 1996). The obliquity-driven, glacio-eustatic sea-level falls of oxygen isotopestages TG22 and TG20, thought to haveplayed an important role in the Messinian sa-linity crisis, postdate and predate, respective-ly, the base of the Lower Evaporites and theintra-Messinian unconformity related to theisolation and desiccation of the Mediterra-nean. Instead, a complex interplay betweenprecession-induced climatic changes super-posed on longer-term tectonic processes in theMediterranean area has been suggested bythese authors as the main factors controllingthe Messinian salinity crisis (Krijgsman et al.,1999a).

A complete discussion of all the open prob-lems related to the Messinian salinity crisis iswell beyond the scope of this paper. We limitthis paper to the possible larger-scale impli-cations of our interpretation of the Vena delGesso basin succession as far as the onset ofthe evaporite phase and the relationships be-tween shallow- and deep-water settings areconcerned.

GEOLOGIC SETTING

The Romagna Apennines, extending fromthe Sillaro valley to the west to the Marecchiavalley to the east (Fig. 1), are part of thenortheast-verging Northern Apennine arc andis characterized by an exposed belt of silici-clastic deposits of early Miocene to Pleis-tocene age, overlying buried Mesozoic toCenozoic carbonates, only reached by com-mercial exploration wells. This sedimentarysuccession formed above the Adria plate, rep-resenting the lowest structural unit of theApennine orogenic wedge (for an updated re-view of the Apennine geology, see Vai andMartini, 2001).

To the west of the Sillaro valley, this tec-tonostratigraphic unit is covered by the Lig-urian nappe (Fig. 2), a chaotic complex of Ju-rassic to Eocene deep-marine sedimentaryrocks and slabs of their oceanic crustal base-ment (Castellarin and Pini, 1989). This me-lange formed during the Late Cretaceous Al-pine compressional phases and wassubsequently (during the Apennine orogeny,in post-Oligocene time) thrust over the Adriaplate (Kligfield, 1979; Boccaletti et al., 1990).During its movement, deep- to shallow-water

sediments also accumulated above the Ligur-ian complex, forming the so-called Epiligurianunits.

The uppermost structural unit cropping outalong the Po Plain side of the Romagna Ap-ennines consists of the Langhian to TortonianMarnoso-arenacea Formation turbiditic com-plex (Ricci Lucchi, 1975, 1981). This unit,.3500 m thick, is detached from its lowerMiocene carbonate basement along a flat basalthrust and shows a deformational style domi-nated by fault-propagation folds, forming im-bricated structures in some places (Capozzi etal., 1991; Benini et al., 1991; Farabegoli et al.,1991). The inner part of the Marnoso-arenaceaFormation has been overridden by a stack ofolder turbiditic units (Macigno, Cervarola, andModino Formations) along a thrust front ap-proximately corresponding to the present-daywatershed (Fig. 1). Northeast-verging thrustsin the southern belt of the chain are rectilinearfeatures elongated in a northwest-southeast di-rection (Fig. 1). The axes of the thrust foldsplunge toward the northwest and the southeastapproaching the Sillaro and Marecchia val-leys, respectively. These two valleys roughlycorrespond to the axis of tectonic depressionsoccupied since the late Miocene by the ad-vancing Ligurian nappe.

The Apennine foothills consist of a gentlenorth-northeast–dipping monocline of Messi-nian to Pleistocene deposits resting above theMarnoso-arenacea Formation. Seismic datashow that the outermost front of the Apenninethrust belt lies in the subsurface of the PoPlain (Pieri and Groppi, 1981; Castellarin etal., 1986, Castellarin, 2001), where severalramp anticlines are buried by a thick succes-sion of marine Pliocene–Pleistocene deposits.

The Romagna Apennines are split into twosectors (western and eastern) by the Forlı line(Fig. 1), a deformational zone characterizedby reverse faults oriented obliquely to theApenninic trend (north-northeast–south-southwest). This tectonic feature played a pri-mary role in the geologic evolution of thearea, at least since the late Tortonian (RicciLucchi, 1986). In a northwest-southeast crosssection, flattened at the Miocene/Plioceneboundary (Fig. 2), dramatic facies and thick-ness changes can be observed particularlywithin the Messinian succession, caused bythe structural high related to the Forlı line.

Subsurface data permit a better definition ofthe tectonic framework of the area. One of theburied ramp anticlines of the western sector(Riolo anticline, Fig. 1) turns its axis from anorthwest-southeast to a north-south directionand merges with the outcropping structuralhigh associated with the Forlı line. As a con-


ROVERI et al.

Figure 2. Schematic geologic cross section roughly parallel to the Apennine front (see location in Fig. 1) and connecting the mainMessinian depocenters; the section is flattened at the Miocene/Pliocene boundary. Note the strong thickness change of the Messiniansuccession across the Forlı line. Abbreviated formations: GS—Gessoso-solfifera; MA—Marnoso-arenacea. Abbreviations of unconfor-mity-bounded stratigraphic units (synthems): p-ev2—postevaporitic unit 2; p-ev1—postevaporitic unit 1; T2—Tortonian–Messinian; MP—Messinian–Pliocene.

sequence, a single east-northeast–verging ar-cuate structure, of which the Forlı line repre-sents the eastern lateral ramp, can bereconstructed (Fig. 1). This anticline, plungingwestward below the Ligurian nappe along theSillaro valley, bounds the Vena del Gesso ba-sin to the north and to the east. The originalbasin extension to the west and to the southcannot be reconstructed owing to the Liguriannappe cover and the post-Messinian erosion.

STRATIGRAPHY

From a lithostratigraphic point of view (Fig.3), the Langhian to Pliocene sedimentary suc-cession of the Romagna Apennines is classi-cally subdivided into four formations (Vai,1988):

1. The Marnoso-arenacea Formation(Langhian–Messinian), made up of deep-watersiliciclastic turbidites mainly derived from Al-pine sources, is the infill of a large foredeepbasin elongated in a northwest-southeast di-rection, whose depocenter shifted throughtime, following the northeastward propagationof the compressional front. The upper part ofthis unit mainly consists of slope mudstones(informally named ‘‘ghioli di letto’’ by older

authors) containing minor turbiditic sand-stones and chaotic bodies; these rocks are inturn overlain by a thin horizon characterizedby cyclically interbedded organic-rich lami-nites and mudstones, informally referred to as‘‘euxinic shales’’ (upper Tortonian–lowerMessinian). Like the coeval Tripoli Formationin Sicily and Spain, such deposits, consistingof organic- and diatomite-rich laminites (Ped-ley and Grasso, 1993; Sprovieri et al., 1996b;Sierro et al., 1999; Bellanca et al., 2001), re-cord the paleoceanographic changes that her-alded the Messinian salinity crisis. The eux-inic shale unit, straddling the Tortonian/Messinian boundary, spans a 1.5 m.y. timeinterval, characterized by well-defined biom-agnetostratigraphic events; their calibrationwith astronomical cyclicity allowed a detailedchronostratigraphy to be established (Krijgs-man et al., 1999a, 1999b; Vai, 1997).

2. The Gessoso-solfifera Formation (Mes-sinian), is made up of both primary and clas-tic, resedimented evaporites with interbeddedorganic-rich shales, deposited during the evap-oritic and postevaporitic stages of the Messi-nian salinity crisis.

3. The Colombacci Formation (upper Mes-sinian), consisting of siliciclastic sediments

derived from Apenninic sources, was depos-ited in both shallow and deep, brackish orfreshwater basins developed during the finalphase of the Messinian salinity crisis (Lago-mare stage).

4. The Argille Azzurre Formation (lowerPliocene) is made up of mudstones depositedin a relatively deep marine environment. Theylocally encase conglomerate and sandstonebodies and small, isolated carbonate platforms(locally named Spungone).

A few attempts to establish a physical-stratigraphic framework of the study area havebeen carried out so far. The most completestratigraphic scheme has been provided byRicci Lucchi and Ori (1985) and Ricci Lucchi(1986), within a general synthesis of the sed-imentary evolution of the Apennine thrustbelt, taking into account both tectonism andeustasy as controlling factors. Creation of thisphysical-stratigraphic framework resulted in thedefinition of several large-scale, unconformity-bounded units (called depositional sequences)recognizable in different domains of theApennine Chain and thus led to a unifyingpicture of Apennine evolution (Fig. 3).

The stratigraphic framework has subse-quently been slightly revised (Roveri et al.,



Figure 3. Stratigraphic scheme (A) adopted in this work, and (B) a more detailed frame-work for the Messinian deposits showing the possible stratigraphic relationships betweenmarginal and basinal settings of the Apennine foredeep (based on Roveri et al., 1998,2001; chronology of Messinian events from Krijgsman et al., 1999a). Abbreviations ofunconformity-bounded stratigraphic units (synthems) are explained in Figure 2, exceptfor the following: LP—lower Pliocene; eP—early Pliocene; M—Messinian. GPTS—geo-magnetic polarity time scale. Hypotheses a and b are discussed in the text (see columnslabeled ‘‘main foredeep a’’ and ‘‘main foredeep b’’).

1998, 2001; Manzi, 2001), particularly for theMessinian interval. In this paper we adopt aphysical-stratigraphic scheme that substantial-ly derives from these studies (Fig. 3). The Tor-tonian to lower Pliocene succession is subdi-vided into three main large-scale synthemsthat record regional-scale phases of tectonicdeformation of the Apennine orogenicwedge. From base to top, they are the T2 (up-per Tortonian–lower Messinian) synthem(termed a ‘‘sequence’’ in Ricci Lucchi, 1986),the MP (upper Messinian–lower Pliocene)synthem, and the LP (lower Pliocene) syn-them; the names adopted for such units derivefrom those of their basal unconformities.These large-scale units can be further subdi-vided into lower-rank unconformity-boundedstratigraphic units and lithohorizons of region-al significance delimited by minor unconfor-mities and flooding surfaces (Roveri et al.,1998; Fig. 3).

In the next sections, the stratigraphic unitsare described. The depositional characters ofthe western and eastern sectors of the Roma-gna Apennines separated by the Forlı line arecompared as well.

T2 Synthem (Late Tortonian–Messinian)

The base of the T2 synthem corresponds toa sharp vertical change in the sedimentary fea-tures (facies character, sandstone-body geom-etries, and overall stacking pattern) of theMarnoso-arenacea Formation turbiditic sys-tems. During the previous stages (T1 sequenceof Ricci Lucchi, 1986), turbiditic deposits werecharacterized by tabular geometries, high lat-eral continuity, and transitional bases, suggest-ing deposition by unconfined flows runningparallel to the basin axis (i.e., in a northwest-southeast direction) along a nearly flat sea bot-tom (Ricci Lucchi, 1981, 1986). In the T2 syn-them, sandstone bodies show erosional bases,poor lateral continuity, coarser mean grainsize, and various sedimentary structures (e.g.,basal scours, cut-and-fill, and water-escapestructures; Ricci Lucchi, 1981) that suggestrapid deposition from low-efficiency flow, i.e.,flows that were not able to fully segregatetheir grain populations as a result of topo-graphic constriction (Mutti et al., 1999). Suchchange of geometry and facies characters ofturbidites implies the creation of erosional de-pressions cut by large-volume turbiditic flowsand subsequently filled by smaller-volume,confined flows forced to rapidly deposit theirsediment load. This scenario has usually beenrelated to a regional phase of uplift and basinnarrowing (Ricci Lucchi, 1981, 1986), but thetectonic structures involved in the generation


ROVERI et al.

Figure 4. (A) Panoramic and (B) closer view of the lower Fontanelice channelized system,Santerno valley. (A) The thickness and geometry of the lower Fontanelice ‘‘channel’’ con-trast with those characteristics of the underlying sandstone lobes of the T1 group. (B) Cut-and-fill feature within the lower ‘‘channel’’; note the abrupt onlap of thick to very thicksandstone beds above the scour wall.

of the observed sedimentary features havenever been identified.

Western SectorT2 synthem deposits show some differences

across the Forlı line. In the western sector,they crop out only in the Santerno-Sillaroarea. They are represented by the well-knownFontanelice ‘‘channels,’’ two turbiditic sand-stone bodies confined within large-scale ero-sional depressions and separated by a mud-stone horizon (Ricci Lucchi, 1968, 1969,1975, 1981; Figs. 4A, 4B). The lower body(Fig. 4A) has a slightly concave-upward, ero-sional base and a thickness of ;30 m. Thefirst fill is cut by a second erosional surface(Fig. 4B), which forms a depression filled bythick sandstone beds, characterized by ero-sional bases, massive to crudely horizontallylaminated divisions and rippled, commonlyclimbing, tops. Mudstone divisions are eithervery thin or absent, and amalgamated beds arecommon, especially in the lower part of thescour fills. The upper erosional surface deep-

ens toward the southwest, i.e., normal to themain paleocurrents. As a result of the expo-sure, the control in a downcurrent direction ispoor, but these bodies disappear within a fewkilometers.

The upper channelized body (Figs. 5A, 5B)is completely encased in mudstones (ghioli diletto) and is larger and thicker than the lowerone. Like the lower body, its basal surfacedeepens toward the southwest, and a spectac-ular onlap toward the northeast of sandstonefill can be observed in the section almost nor-mal to the paleocurrent direction (Fig. 5A).The erosional surface is much deeper than thatof the lower system, almost reaching its top.The composite fill consists of clean, fairlywell sorted conglomerates that form smallbars at the bottom and at least two distinctsandstone bodies in the upper part (Fig. 5B).Pebble composition indicates an Alpine prov-enance (Ricci Lucchi, 1969), and the con-glomerates’ facies character (degree of or-ganization, etc.) suggests that they representthe coarser-grained load laid down by large-

volume gravity flows bypassing this area anddepositing the bulk of their sediment loadmore downstream (i.e., to the southeast).Sandstone beds of the upper part of the ‘‘chan-nel’’ fill show facies characters similar tothose of the lower system.

The upper Fontanelice system is overlain bya prevailing mudstone unit (ghioli di letto)with interbedded minor turbiditic sandstonebodies, more preserved to the west and form-ing an overall thinning-upward sequence (Fig.5B). Toward the southeast, minor bodies dis-appear; in the Santerno river section, the mud-stone unit instead contains a chaotic slumpedhorizon, up to 50 m thick, characterized bysandstone olistoliths, likely derived by minorturbiditic bodies (Fig. 6). The slumped hori-zon is capped by an ;50 m thickness of theorganic-rich euxinic shales, here attaining athickness of ;50 m. Sedimentation ratesthrough the euxinic shales are plotted in Fig-ure 7 and are discussed subsequently.

The T2 synthem is topped by the primaryin situ Messinian evaporites of the Gessoso-solfifera Formation, which form a continuousbelt from the Sillaro to the Lamone valleys(Fig. 1). A maximum thickness of 150 m isattained in the central area of the sector (Fig.8). Like the underlying euxinic shales, gyp-sum deposition was cyclical, probably con-trolled by periodic changes of orbital parame-ters (Vai, 1997; Krijgsman et al., 1999b). Upto 16 small, decameter-scale-thick, shallowing-upward cycles—each recording the progres-sive evaporation of shallow lagoons (Vai andRicci Lucchi, 1977)—have been recognized.The typical cycles are characterized by thevertical superposition of six main sedimentaryfacies, five of them made up of gypsum; eachcycle starts with basal organic-rich shales, de-posited in shallow lagoons below the wavebase; these shales are overlain by stromatolitesreplaced by gypsum and, in turn, by well-stratified selenitic gypsum. The size of sele-nite crystals usually decreases upward; thischange is thought to be related to the pro-gressive evaporative drawdown and increasingsalt concentration of the lagoon. The upperpart of each cycle is characterized by clasticgypsum deposits (gypsarenites, chaotic selen-itic breccia). These deposits are thought to berelated to a phase of subaerial exposure anderosion, leading to strong gypsum reworkingby waves or torrential streams action (Vai andRicci Lucchi, 1977).

A progressive vertical change in the thick-ness and facies distribution within the individ-ual cycles can be observed; the upper cyclesare thinner than those at the base, and the rel-atively deeper-water facies units are signifi-



Figure 5. The upper Fontanelice ‘‘channel.’’ (A) The classical view looking north with theclear onlap of sandstone beds against the basal erosional surface. The sandstone body isencased in slope mudstones containing an intrabasinal slump (see also Fig. 6); (B) Generalview of the upper ‘‘channel’’ looking west from the east side of the Santerno valley. Thebasal erosional surface deepens toward the southwest, and the channel fill is compositewith alternating sand- and mud-rich bodies onlapping toward the northeast.

cantly less well developed than the clastic fa-cies. This change suggests that an overall‘‘regressive’’ trend is superposed on the smaller-scale, higher-frequency cyclicity; this longer-term trend culminates with the great erosionalunconformity that cuts the uppermost gypsumunit and marks the base of the overlying MPsynthem. An angular unconformity is associ-ated with this surface (Vai, 1988), clearly in-dicating its tectonic nature. It is well knownfrom regional geologic studies that the intra-Messinian event is one of the most importantin the evolution of the Apenninic orogenicwedge, marking a significant migration of thewhole compressive front and associated fore-deep basin toward the foreland, i.e., the PoPlain.

Along this surface, evidence of prolongedsubaerial exposure (karstic dikes filled by con-tinental deposits rich in mammal fossils) hasbeen found in the Monticino section, near Bri-sighella (Costa et al., 1986; De Giuli et al.,1988). The erosion associated with the Mes-sinian/Pliocene unconformity increases to-ward the southeastern end of this sector (La-mone valley), where the evaporitic andpreevaporitic Messinian deposits are com-pletely missing.

Deformation of the Primary Evaporites ofthe Vena del Gesso Basin

The gypsum unit is characterized in thewestern sector by extensional and compres-sional deformations (Marabini and Vai, 1985),with rotated blocks (Fig. 9A) and shallowthrust faults (Fig. 9B), partially also affectingthe top of the underlying euxinic shales (shearplanes observed by Krijgsman et al., 1999b).All these deformational features emanate froma detachment surface in the upper part of theeuxinic shales (Marabini and Vai, 1985). Thegypsum deformation processes, not involvingeither the overlying or underlying units, haveusually been referred to as thin-skinned tec-tonics related to strike-slip movements alongnortheast-trending faults, leading to the for-mation during the latest Messinian of a com-plex framework of structural highs and de-pressions (Marabini and Vai, 1985).

From west to east, the deformation showsdifferent characteristics. To the west (Santerno-Sillaro sector, Fig. 10), the gypsum unit isgreatly reduced in thickness and more discon-tinuous and is characterized by both compres-sive and extensional deformations. Rotationallistric faults affect the gypsum unit on the leftbank of the Santerno River (Borgo Tossigna-

no; Fig. 9A), whereas farther to the west(Monte Penzola), a shallow thrust fault is re-sponsible for the vertical repetition of the low-er gypsum cycles (Figs. 5, 6). All these struc-tures indicate a west-southwest vergence (Fig.9B). Traces of transformation of gypsum toanhydrite (due to higher lithostatic loadingduring burial) and subsequent rehydrationhave been observed in the westernmost edge(Sillaro-Santerno valleys, S. Lugli, 2001, per-sonal commun.).

To the east (Sintria valley, Fig. 10), the de-formation is more severe. Here the gypsumunit forms a complex tectonic structure madeup of at least three thrust sheets with a south-west vergence (Fig. 9B; Marabini and Vai,1985). Thrust faults emanate from a flat de-tachment surface in the upper part of the un-derlying euxinic shales. The latter containscattered blocks of chemosynthetic carbonateswhose origin is related to methane-rich fluidventing (informally referred to as ‘‘calcari aLucina’’ by older authors; see Ricci Lucchiand Vai, 1994; Taviani, 1994, 2001; Conti andFontana, 1998).

The central sector shows a minor degree ofdeformation. The gypsum unit is only cut bysubvertical normal faults (Fig. 8). The Montedel Casino section, where the upper part of theeuxinic shales is characterized by abundantshear planes (see Krijgsman et al., 1999b), be-longs to this sector.

Eastern SectorThe T2 synthem in the eastern sector of the

Romagna Apennines is significantly different,especially in its upper part. The basal uncon-formity, here only slightly erosional, is tracedalong the base of a thick pile of tabular tur-biditic sandstone bodies, made up of thick-bedded, coarse to very coarse and pebblysandstones, with common amalgamated bedsand basal scours. Mud-draped scours andwater-escape structures are also common. TheSavio turbidite system, cropping out discon-tinuously in the Savio valley (Fig. 2), has acomposite nature with up to five sandstonebodies vertically stacked to form an overallfining-upward sequence with a maximumthickness of some 200 m. Although not easyto assess because of the exposure conditions,the close physical and genetical relationshipof such turbiditic deposits with the channel-ized bodies of the western sector (Fontanelicesystems) is here suggested on the base of fa-cies and regional geologic considerations.

As in the western sector, these sandstonebodies are overlain by a mudstone unit, but inthe eastern sector, they are more developedand contain two huge chaotic bodies separated


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Figure 6. Panoramic view of the upper part of the T2 strata along the west side of the Santerno valley. The intrabasinal chaotic bodywith sandstone olistoliths is overlain by the upper Tortonian–lower Messinian euxinic shales. On top is the deformed gypsum of theGessoso-solfifera Formation; note the lateral ramp of a shallowly northeast-dipping thrust cutting gypsum unit at Monte (M.) Penzola.

Figure 7. Sedimentation rates and subsidence trends in the euxinic shales from differentsections of the Romagna Apennines (names of locations 1–5 labeled in Fig. 10) comparedwith the coeval Tripoli Formation of the Falconara-Gibliscemi sections of Sicily; the uni-form upward decrease of sedimentation rate matched with paleobathymetric data suggestsan overall uplift during the preevaporitic phase; note also that beside this general verticaltrend, absolute values also decrease from west to east in the Vena del Gesso basin, sug-gesting larger uplift to the southeast (Monticino section).

by an undisturbed muddy horizon, 400 mthick. The chaotic bodies are made up of bothintra- and extrabasinal deposits (Lucente et al.,2002), and their thickness reaches ;300 m.

Also in this sector the T2 synthem is toppedby an organic-rich unit corresponding to theeuxinic shales of the western area; the unithere is thicker (100 m) but with a less evidentlithologic cyclicity owing to a higher terrige-nous content. As in the western sector, theTortonian/Messinian boundary lies at the baseof this unit, just above the upper chaotic body.

Primary evaporites are totally absent in theeastern sector. Instead, a thick complex of re-sedimented evaporites made up of a completesuite of gravity-flow deposits—ranging fromthin-bedded, gypsum turbidites to huge olis-tostromes containing large blocks of primaryselenitic gypsum—is preserved. These evap-orites were deposited in relatively deep wa-ters, well below the wave base, as suggestedby the observed sedimentary structures (Pareaand Ricci Lucchi, 1972; Ricci Lucchi, 1973;Roveri et al., 2001; Manzi, 2001; for deep-water evaporite sedimentation, see also Schla-ger and Bolz, 1977). Interbedded mudstoneshave a moderate organic content, decreasingupward. No evidence of subaerial exposure orany angular unconformities has been found inthis unit. Moreover, despite the fact that thesedeposits are well stratified, a clear cyclicalpattern cannot be recognized, pointing to amore random style of sedimentation, stronglydifferent from that of the primary evaporites.All these characteristics make the detailed cor-relation with the Messinian succession of thewestern sector a quite difficult task.

In order to better define the genetic rela-tionships between primary and resedimented



Figure 8. Panoramic view of the Gessoso-solfifera Formation in the central, less deformed sector, of the Vena del Gesso basin. Gypsumbeds are cut by small normal faults leading to the lateral juxtaposition of upper, thinner cycles and lower, thicker ones (looking northfrom Tossignano; location in Fig. 10).

Figure 9. Panoramic view showing two contrasting examples of deformation affecting theGessoso-solfifera Formation. (A) Rotated blocks along the west side of the Santerno valleyat Borgo Tossignano (location in Fig. 10). (B) The three small northeast-dipping thrustsheets of Monte Mauro (Sintria valley; see location in Fig. 10). Abbreviations ofunconformity-bounded stratigraphic units (synthems): TM—Tortonian–Messinian; MP—Messinian–Pliocene.

gypsum facies, Roveri et al. (1998, 2001) andManzi (2001) suggested that the erosional un-conformity of the western sector could betraced into a correlative conformity either atthe base or within the resedimented evapo-ritic complex of the eastern sector. As a con-sequence of this interpretation, the wholeGessoso-solfifera Formation of the eastern

sector (or at least part of it) belongs to thepostevaporitic phase and can be included inthe overlying MP synthem as in the ‘‘mainforedeep a’’ column of Figure 3 (see hypoth-eses illustrated by columns labeled ‘‘mainforedeep a’’ and ‘‘main foredeep b’’ in thestratigraphic diagram of Fig. 3).

According to hypothesis a of Figure 3, the

time equivalent of primary evaporites in theeastern area is to be found in the upper partof the local euxinic shales. As a general rule,no stratigraphic studies have ever been carriedout on deep basinal Messinian successions ofthe Mediterranean, either because they areburied at great depths below the seafloor orbecause they are not recognized in the field.The Apennine foredeep offers such a uniqueopportunity to observe both the shallow andrelatively deep Messinian depositional settingsand compare them in field-based studies. Inthe upper part of the euxinic shales of the east-ern sector, preliminary biomagnetostratigraph-ic data (Manzi, 2001) indicate the presence ofa very organic rich, barren horizon that doesnot occur below the primary gypsum unit ofthe western sector (and also not below theLower Evaporites of Sicily and Spain). Wethink that this horizon represents a good can-didate for being correlated to the primaryevaporites, as their deeper-water counterpart.

The implications at Mediterranean scalefor the Messinian salinity crisis of such astratigraphic model will not be discussed inmore detail here. What we would emphasizeis the strong tectonic component superposedto the Apennine foredeep intra-Messinianunconformity.

MP Synthem (late Messinian–EarlyPliocene)

This synthem shows the most dramatic fa-cies and thickness changes across the Forlıline. Its general characters will be only brieflysummarized here; for more detailed descrip-tions the reader can refer to Roveri et al.


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Figure 10. Detailed geologic map of the Vena del Gesso basin with indications of the main subsurface features. The locations of wellsand seismic lines are also shown. Abbreviations of unconformity-bounded stratigraphic units (synthems): LP—lower Pliocene; MP—Messinian–Pliocene; TM—Tortonian–Messinian. RB1—Riolo Bagni 1 well.

(1998, 2001), Bassetti (2000), and Bassetti etal. (1994). We emphasize here that this groupcontains the Miocene/Pliocene boundary, asupraregional synchronous surface markingthe sudden reestablishment of fully marineconditions in the Mediterranean (Hsu et al.,1972; Iaccarino et al., 1999).

Western SectorDeposits of this unit are very thin and can be

separated in two minor lithohorizons by theMiocene/Pliocene boundary. The uppermostMessinian deposits consist of clays containing ahypohaline faunal assemblage of para-Tethyanaffinity (Lagomare fauna). Small lenses of

sandstones occur locally, and near the top amicritic horizon, locally named ‘‘colombac-cio,’’ is commonly present. As in many otherareas of the Apennine foredeep where the suc-cession is continuous, the Miocene/Plioceneboundary is generally heralded by a charac-teristic dark, organic-rich horizon, whose ori-gin is still poorly understood.

Lower Pliocene deposits of this synthemconsist of a thin unit (only 2 m in the San-terno section, according to Colalongo et al.[1982] and Cremonini et al. [1969]) of deep-marine mudstones draping the entire area.Detailed biostratigraphic studies carried outin the Santerno and Monticino sections show

that a large hiatus is associated with the LPregional unconformity marking the top ofthis synthem; the LP unconformity occurs inthe upper part of the Gilbert Chron (Fig. 3A)and is related to the advance of the Apenninecompressive front; this event is recorded inthe Sillaro-Santerno area by the sudden ap-pearance within deep-marine clays of coarse,chaotic deposits (pebbly mudstones and debrisflows) derived from the Ligurian units (Cre-monini and Ricci Lucchi, 1982). The smallthickness of lower Pliocene deposits of theMP synthem in this area is essentially relatedto the strong erosion associated with the LPunconformity.



Eastern SectorThe main outcrops of the upper Messinian–

lower Pliocene synthem occur in two largesynclines (Giaggiolo-Cella and Sapigno syn-clines in Fig. 1), possibly corresponding toformer basins separated by topographic highsrelated to minor tectonic structures. From alithostratigraphic point of view, this synthem,according to Roveri et al. (1998, 2001; Fig.3B, hypothesis a) consists of a basal complexof resedimented evaporites and organic-richshales (deep-water member of the Gessoso-solfifera Formation in Fig. 3B). This complexis overlain by a thick (up to 600 m) successionof upper Messinian Lagomare deposits (Col-ombacci Formation), made up of terrigenoussediments derived from Apenninic sources;these in turn are overlain by the Pliocene fullymarine Argille Azzurre Formation.

Physical features (minor unconformities,key beds, cyclical stacking pattern) define adetailed stratigraphic framework, useful for re-gional correlations (Roveri et al., 1998). Thesuccession can be subdivided into two units(p-ev1 and p-ev2 in Fig. 3; see Roveri et al.,2001) separated by a minor unconformitymarking important paleogeographic and struc-tural changes.

The lower unit (p-ev1) only occurs in struc-tural depressions and consists of resedimentedevaporites overlain by a thick, monotonousmuddy section containing minor sandstonebodies and showing an overall coarsening-upward trend. An ash layer, dated at ca. 5.5Ma (Odin et al., 1997), represents an excep-tional lithostratigraphic marker throughout thewhole Apennine foredeep basin that allows usto trace the unit across different subbasins(Bassetti et al., 1994; Ricci Lucchi et al.,2002).

The upper unit (p-ev2) consists of cyclicallystacked coarse-grained fluviodeltaic systems,vertically arranged in a backstepping se-quence. This unit is thicker in structural de-pressions but also overlies and seals all thepreviously uplifted and subaerially exposedareas. Geologic cross sections clearly showthe onlap of this unit against the Forlı highand the progressive upward decrease of thick-ness and grain size of the fluviodeltaic sedi-ments (see Figs. 2 and 3). Paleocurrents andfacies changes (Manzi, 1997; Roveri et al.,1998) show that the entry points of such flu-viodeltaic systems were located along the For-lı line. Coarse-grained bodies are regularly in-terbedded with muddy units containing threelimestone horizons (locally named ‘‘colom-bacci’’); the upper one, as in the western sector,lies just below the Miocene/Pliocene boundary,also here marked by a dark, organic-rich hori-

zon. The basal Pliocene deposits here have thesame facies character as in the western sector(epibathyal mudstones), but their thickness isgreater because of the less-developed erosion-al character of the overlying LP unconformity.

SUBSURFACE DATA

The assessment of northeast to southwestfacies changes and geometrical relationshipsamong the different stratigraphic units is nor-mally prevented by the limited width of theoutcrop belt in the western sector. Seismicprofiles and well data made available by ENI-Agip Division overcome this problem. A gridof dip and strike seismic profiles of good qual-ity, shot in the lower reaches of the valleys,has been studied in detail (Fig. 10). Some pro-files reach the outcrop area of the Marnoso-arenacea Formation and Gessoso-solfiferaFormation, allowing integration of field andsubsurface data.

The gently northeast-dipping, outcroppingmonocline is clearly imaged in seismic pro-files. The unconformity separating the T2 andthe MP synthems is easily recognizable, as aresult of the high-amplitude reflector associ-ated with the gypsum and angular relation-ships between the underlying and overlyingunits (Figs. 11, 12). A thrust-related anticlineinterrupts the regular monoclinal attitude ofthe T2 synthem and older Marnoso-arenaceaFormation deposits (Fig. 11, SL-2 and SL-3).The northwest-trending anticlinal axis lies ;6km northeast of the gypsum outcrop belt. TheMessinian/Pliocene unconformity has astrongly erosional character (e.g., Fig. 11, SL-2 and SL-3), and the gypsum reflector disap-pears along the southern flank of the anticlineapproaching the crest (e.g., Fig. 11, SL-1, SL-2 and SL-3). The unconformity lies at ;1500m depth at the crest of the anticline and isoverlain by a seismically transparent unit thin-ning toward both to the southwest (the outcropzone) and the northeast, with maximum thick-ness along the southwest flank of the structure.The upper boundary of this transparent unit,erosional along the monoclinal ramp, becomesmore conformable above the anticline core.The seismic unit above this upper unconfor-mity is characterized by high-amplitude re-flections regularly dipping toward the north-east; they can be traced to the outcrop zoneinto Pliocene deposits.

The northeast limb of the anticline is char-acterized by a highly deformed belt, corre-sponding to the thrust-fault zone (Fig. 11, SL-1, SL-2 and SL-3). The seismic succession inthe footwall consists of parallel, regular re-

flectors, subhorizontal or gently dipping to-ward the southwest (Fig. 12).

The anticline has been drilled in the pastfor hydrocarbon exploration; wells are distrib-uted along its axis and are particularly abun-dant in the Santerno valley (Fig. 10), wherethe flanks of the structure have also beenexplored (Fig. 13). The anticlinal crest con-sists of Tortonian turbiditic sandstones ofthe Marnoso-arenacea Formation (Fig. 11,SL-2; Fig. 13). Although the available strati-graphic data from wells do not allow an ac-curate age determination of these deposits, theabsence of a thick mudstone interval equiva-lent to the upper Tortonian–lower Messinianinterval occurring in the outcrop belt indicatesthat these turbiditic deposits could be olderthan the T2 synthem. However, this sandstoneunit is abruptly overlain by lower Plioceneclays, corresponding to the transparent unitrecognized on seismic profiles (Fig. 11, SL-2). Detailed biostratigraphic studies carriedout on these wells show that the Pliocene de-posits overlying the MP unconformity still be-long to the MP synthem (Fig. 3); well corre-lations also show that these deposits onlap thesouthern flank of the anticline (Fig. 11, SL-2;Fig. 13). The upper erosional surface is theLP unconformity; its erosive character in-creases away from the anticlinal crest towardthe southwest, i.e., the outcrop belt. As a con-sequence, the Pliocene deposits of the MPsynthem are much thicker above the anticlinethan in outcrop. Significantly, no trace of ei-ther primary selenitic gypsum or postevapor-itic deposits of the MP synthem have beenfound in the anticline crest or in the upper partof its flanks (Fig. 11, SL-2; Fig. 13).

Primary gypsum has been encountered inthe Riolo Bagni 1 well (RB1 in Figs. 10, 11,12), drilled in an axial depression of the an-ticline. Seismic profiles indeed show in thisarea a strong reflector draping the anticlinalcrest (Fig. 11); this reflector is discontinuous,and the extension of gypsum above the anti-cline is limited to a small area that is alignedwith the segment of the outcrop belt wheregypsum deposits show the lowest degree ofdeformation.

DISCUSSION—THE TECTONIC ANDSEDIMENTARY EVOLUTION OF THE

VENA DEL GESSO BASIN

The data just presented permit a reconstruc-tion of the sedimentary and tectonic history ofthe Vena del Gesso basin, whose generalstratigraphic framework is schematicallyshown along a west-northwest–east-southeastsection in Figure 14. Basin evolution can be


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Figure 11. Line drawings of dip-parallel seismic profiles in the Vena del Gesso basin (see traces in Fig. 10) showing a buried thrust-related anticline (Riolo anticline). In SL-1, note in the lower left, the deep thrust involving the Mesozoic carbonate succession. Note alsothe deeply eroded Marnoso-arenacea Formation on the southwest limb of the anticline and the occurrence of gypsum above its crestonly in profile SL-3. A synthetic stratigraphy of the Riolo Bagni 1 well (RB1; see location in Fig. 10) is shown in the upper right.Formations: GS—Gessoso-solfifera; MA—Marnoso-arenacea. MP—Miocene–Pliocene; LP—lower Pliocene; p-ev1—postevaporitic unit1. TWTT—two-way traveltime.

subdivided in several steps related to discretetime slices (see Fig. 15).

Late Tortonian: First Evidence for SubtleTopographic Relief

Facies and geometry characteristics ofsandstone bodies of the Fontanelice channel-ized systems imply the lateral confinement ofturbiditic flows running from the northwest tothe southeast in a progressively narrowing ba-sin. The geometry of the erosional surfaces

suggests the creation of limited topographicrelief to the northeast, possibly elongated in adirection parallel to the basin axis. We arguethat such subtle seafloor topography is the firstevidence of the growth of the Riolo anticline(Fig. 15A). The early growth of this structureis not substantiated by clear wedging of stratain the outcropping succession; however,slightly converging seismic reflectors charac-terize this unit in the subsurface (Fig. 11).Such weak geometric evidence for uplift islikely related to very slow and subtle move-

ments compensated by high sedimentationrates (for more on this item, see Argnani andRicci Lucchi, 2001). Nevertheless, the ongo-ing modifications of seafloor topography lefta strong imprint on the facies characters ofturbidite systems. The larger-volume flows,accelerated by lateral constriction, increasedtheir erosional power and cut large-scale ero-sional features; we expect their sediment loadto be deposited farther downcurrent, i.e., to thesoutheast, to feed the Savio turbidite system.The thick, often amalgamated and structure-



Figure 12. Line drawing of a strike-parallel seismic profile (see trace in Fig. 10) along the anticlinal axis. The strong reflectors associatedwith Mesozoic carbonates clearly show the overall westward plunge of the structure. TWTT—two-way traveltime.

Figure 13. Schematic cross section, flattened at the MPl2/MPl3 boundary (early Pliocene),along the Santerno valley from the outcrop area (Santerno section, see location in Fig. 10)to the crest of the Riolo anticline, e.g., along the SL-2 profile up to the intersection withSL-4 (Fig. 11). This section clearly shows the paleotopography just before the early Pli-ocene tilting (LP unconformity); thickness and stratal relationships of upper Tortonianand Messinian units suggest a paleoslope dipping toward the southwest. Abbreviations:LP—lower Pliocene; p-ev2—postevaporitic unit 2; M/P—Miocene–Pliocene; T/M—Tor-tonian–Messinian; mbsl—meters below sea level.

less sandstone beds of ‘‘channel’’ fills weredeposited by smaller volume flows during thesubsequent recessional phase of the system;they can actually be considered as deposition-al lobes formed in a confined basin.

Several sandstone bodies (up to four withupward-decreasing thickness) are verticallystacked to form a clear backstepping sequence(Fig. 5B). This trend is probably due to the

growth of the anticline, but changes in the vol-ume of sediment delivered by the source area(i.e., the Alps) cannot be ruled out. The pro-gressive growth of the anticline along thefrontal and lateral ramp (i.e., the Forlı line)split the former foredeep into two differentsubbasins: an uplifting basin to the west (thefuture Vena del Gesso basin), gradually dis-connected from the main foredeep and cut off

from the main pathway of turbidite flows, anda subsiding basin to the north and to the east,still reached in the late Tortonian by turbiditycurrents fed by Alpine sources.

Independent Evidence for Uplift Duringthe Late Tortonian and Early Messinian

Paleobathymetric reconstructions based onbenthic foraminifera from the Monte del Ca-sino section (Kouwenhoven et al., 1999; Vander Meulen et al., 1998, 1999) provide inde-pendent evidence for the uplift of the westernsector during the late Tortonian and earlyMessinian. Calculations show a steadily de-creasing sedimentation rate associated with aprogressive shallowing-upward trend (Fig. 7).

Early Messinian sedimentation rates fromthree sections aligned in a northwest-southeastdirection show absolute values regularly de-creasing toward the southeast (Monticino sec-tion; Figs. 14, 15B), indicating an additional,more local effect to the general trend. The lat-ter is common to other basins of the Mediter-ranean area and is usually related to thechanging paleoceanographic conditions her-alding the Messinian salinity crisis, promotingthe widespread development of organic-richdeposits in deep-water settings. Setting apartthe meaning of such a regional trend, still farfrom being fully understood, we concentratehere on the specific depositional setting of thisstudy area. Euxinic shales formed through theslow settling of biogenic and very fine-grainedterrigenous particles from (1) hemipelagic‘‘rain’’ and (2) low-density, turbiditic currents.The observed decrease of sedimentation rateis essentially due to the suppression of the ter-rigenous component; this change can be bestrelated to the deactivation of sediment sourcesdue to large-scale climatic or eustatic events,but also to the progressive cutoff of an uplift-


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Figure 14. General geologic and stratigraphic model of the Tortonian–Pliocene succession of the Vena del Gesso basin along a west-northwest–east-southeast section, flattened at the lower Pliocene and showing all the depositional and deformational features describedin the text. M/P—Miocene/Pliocene boundary; T/M—Tortonian/Messinian boundary.

ing seafloor area from bottom-seeking turbid-ity currents; the two hypotheses are not mu-tually exclusive, and their combination ismore than likely, especially considering thepaleobathymetric data based on foraminifera(Kouwenhoven et al., 1999).

Such considerations and the reconstructedlate Tortonian–early Messinian paleogeo-graphic setting imply that the observed addi-tional southeastward decrease in the sedimentrate is due to a topographically more elevatedsoutheastern area, corresponding to the cul-mination of the ramp anticline related to theForlı line, developed during the Messinian. Tothe east of the Forlı line, both the thicknessand sandstone/shale ratio of upper Tortonian–lower Messinian deposits are much greaterthan in the western area, suggesting highersubsidence and sediment input (Fig. 15B).

Evaporite Deposition

During the evaporitic phase of the Messi-nian, the role of the Riolo anticline is clearlydefined. Primary, shallow-water evaporites(selenitic gypsum) deposited in a barred basin(Vai and Ricci Lucchi, 1977) only occur to thewest of the Forlı line (Fig. 15C).

The abrupt vertical facies changes from theeuxinic shales to the overlying shallow-water

evaporites implies a dramatic relative sea-level fall, on the order of several hundreds ofmeters, occurring in a very short time span(according to Krijgsman et al., 1999a). How-ever, its amplitude cannot be easily deter-mined in the Vena del Gesso basin because ofthe absence of reliable paleodepth indicatorsin the uppermost euxinic shales.

The overall aggradational stacking patternof shallow-water primary gypsum cyclesclearly indicates that climatically forced, cy-clic evaporite deposition occurred during arelative sea-level rise. The longer-termshallowing-upward trend superposed onsmall-scale cycles suggests a gradual upwardreduction in the amount of accommodationspace created. The evaporites are cut by anerosion surface showing evidence for subaer-ial exposure. This unconformity can be tracedto the southeast on the culmination of thestructural high associated with the Forlı linelateral ramp, where lower Pliocene sedimentsdirectly overlie the Marnoso-arenacea For-mation or the Tortonian mudstones. The samesituation can be reconstructed in a southwest-northeast direction from seismic and welldata; the latter show that above the anticlineculmination, gypsum is normally absent, withthe notable exception of a small area (below

the Riolo Terme village, Fig. 10), coincidingwith an axial depression.

Whether these vertical trends were mainlycontrolled by eustasy or by tectonics is verydifficult to assess. We are well aware that, ac-cording to most models, Messinian events arethought to imply dramatic eustatic changes,far exceeding the amplitude and velocity oflocal tectonic movements. As far as the Apen-nine foredeep succession is concerned andtaking into account the fact that the main Mes-sinian events were not coincident with globalsea-level cycles (Krijgsman et al., 1999a), theobserved stratigraphic evolution appears to befully consistent with the regional tectonichistory.

Thickness and Facies Distribution ofPostevaporitic Deposits

Messinian postevaporitic deposits showdramatic thickness differences across the Forlıline (Fig. 2). To the west, above the upliftedand subaerially eroded gypsum, only a thin,mainly fine-grained unit occurs; this unit oflatest Messinian age is conformably overlainby the lower Pliocene deep-marine deposits.To the east of the Forlı line, postevaporitic de-posits occur in different subbasins with thick-nesses of .600 m. Two units with different



Figure 15. Sketches showing the evolution of Vena del Gesso basin from the late Tortonianto early Pliocene. See text for explanation; s.l.—sea level; b.l.—base level; M/P—Miocene/Pliocene boundary; M–P—Miocene–Pliocene strata; LP—lower Pliocene strata; p-ev1—postevaporitic unit 1.

stacking patterns can be recognized: (1) thelower unit (p-ev1) comprises the resedimentedevaporites (Figs. 15D, 15E) at its base and ismainly made up of fine-grained terrigenousdeposits. It has an overall progradationalstacking pattern and a shallowing-upwardtrend. This unit only occurs in structural de-pressions and was deposited during the upliftphase, as suggested by minor unconformitiesand evidence for slope instability. (2) The up-per unit (p-ev2; Fig. 15E) is made up of cy-clically stacked fluviodeltaic systems, show-ing an overall backstepping pattern. This unitonlaps the basin margins and tends to coverall the previously uplifted structures (Fig. 2).Its uppermost part lies above the culminationof the Forlı line and extends all over the Venadel Gesso basin. The geometric characteristicsof the unit point to the unit’s deposition duringa phase of relative base-level rise (at that time,the Mediterranean area was disconnected fromthe ocean and a complex array of endorheiclakes occupied the more depressed areas),more likely controlled by tectonic quiescenceand generalized subsidence that lasted untilthe early Pliocene. As an alternative to explainthe observed vertical facies trends, a mecha-nism must be envisaged for the progressiverefill of the basin with fresh to brackish waterprior to the earliest Pliocene marine flooding.

Southwest-northeast seismic profiles showthat the thin p-ev2 occurring in the Vena delGesso basin onlaps toward the northeastagainst the southern limb of the Riolo anti-cline and is absent on its crest (Fig. 11). Afterthe emergence following the evaporitic phase,the structural high bounding the basin wasprogressively submerged and leveled in thelate Messinian; it ceased to be a topographichigh during the early Pliocene, when mainlyfine-grained, deep-water sediments again ac-cumulated above its culmination, as clearlydemonstrated in both the outcrop area and inthe subsurface (Santerno river wells).

Early Pliocene Tilting

Lower Pliocene deposits of the MP synthemare very thin in the outcrop area of Vena delGesso basin and thicker above the buried Rio-lo anticline. Well data also show that the hi-atus associated with the overlying LP uncon-formity decreases along the southern limb ofthe anticline and disappears above its culmi-nation (Fig. 13). This geometry means thatlower Pliocene deposits preserved below theunconformity are progressively thicker in anortheast direction.

Moreover, a careful evaluation of outcropand subsurface data shows that within the


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northeast-dipping monocline, lower Pliocenedeposits have higher dip angles than those ofthe Marnoso-arenacea Formation (Figs. 10,16). This finding can only be explained by ad-mitting the existence of a Messinian–early Pli-ocene paleoslope dipping toward the west andthe southwest that was subsequently tilted andinverted during the early Pliocene. The southand western sectors of the Vena del Gesso ba-sin, topographically more depressed duringthe Messinian, were uplifted and eroded,while the northern sector was contemporane-ously affected by higher subsidence. A pos-sible explanation for such northeastward tilt-ing is the movement of a deeper thrust fault,detached along the base of Mesozoic carbon-ates (Fig. 11, SL-1) and possibly also involv-ing the basement. This important tectonicevent, dated at 4.2 Ma (and represented by theLP unconformity), marks a significant propa-gation of the Apennine thrust front toward thePo Plain area and a concomitant generalizedadvance of the allochthonous Ligurian nappe(Ricci Lucchi, 1986).

The Gravity vs. Tectonic Nature ofEvaporite Deformation in the Vena delGesso Basin

We think that the existence of a paleoslopedipping toward the west and southwest duringthe late Tortonian–early Pliocene interval,here suggested for the first time, is well sub-stantiated by the sedimentary history of theVena del Gesso basin and could explain thedeformational features affecting the primaryevaporites as being mainly related to large-cale gravity processes. Cross sections modifiedfrom Marabini and Vai (1985) show the ge-ometry of the deformation (Fig. 16), and theirclose relationship to the southwest-dipping pa-leoslope that can be easily reconstructed byremoving post-Messinian deformation throughthe flattening of lower Pliocene deposits. Thestrong mechanical contrast between the rigidgypsum and the underlying, more plastic, or-ganic-rich euxinic shales created the condi-tions for the development of a weak layer attheir boundary, which acted as a very efficientdetachment surface. Renewed uplift during theintra-Messinian phase triggered gliding oflarge gypsum slabs along this surface on thesouthern, shallower-dipping limb of the anti-cline. On the frontal limb, characterized by asteeper profile, movement of gypsum slabswas accelerated, and they were transformed bybreaking up along the slope, leading to moreevolved deposits (debris flows, turbidites).The observed change in type and degree ofdeformation along the outcrop belt can be re-

lated to a different magnitude of translation ofgypsum slabs along the paleoslope; in this re-spect, it is worth noting that in the central, lessdeformed sector of the Vena del Gesso basin,gypsum layers are preserved in an axial de-pression of the anticline. The gravity-drivendownslope translation of primary gypsumslabs also implies a somewhat important ver-tical-movement component; rough and pru-dent calculations based on the reconstructedpaleoslope show that such vertical displace-ment could be ;150–200 m for a translationin the order of 1–2 km.

As a consequence, a word of caution isneeded when interpreting in terms of dramaticpaleobathymetric changes the ‘‘abrupt’’ verti-cal transition from euxinic shales to primaryevaporites observed in the Vena del Gesso ba-sin. The amplitude of the relative sea-levelfall, if any occurred, associated with the onsetof evaporite deposition, could have been farless important than usually thought. At a larg-er scale, this observation could resolve the ap-parent contradiction deriving from the syn-chronous development of Lower Evaporitesabove sediments of greatly variable paleo-depth, as implied by the cyclostratigraphicmodels (Krijgsman et al., 1999a). This syn-chronous development represents one of themost puzzling problems of the Messinian sa-linity crisis, as previously discussed; however,considering the peculiar mechanical propertiesof Messinian rocks and the high tectonic mo-bility of the Mediterranean area during thistime interval (Meulenkamp and Sissingh,2001), large-scale, gravity-driven gypsum-slabsliding and related gravity-flow deposits couldbe widespread features in other Mediterraneanbasins (Roveri et al., 2001). Many other Med-iterranean basins, tectonically active duringthe Messinian (Tertiary Piedmont Basin, Si-cily, Tuscany, Greece, Spain), are character-ized by the common occurrence of collapsefeatures affecting the Messinian evaporites ata variable scale (Ghibaudo et al., 1985; De-cima and Wezel, 1971; Kontopoulos et al.,1997; Michalzik, 1996; Testa and Lugli,2000). Nevertheless, the larger-scale implica-tions of such deposits have not been thor-oughly investigated yet. Besides the correctpaleodepth estimate of the local base of LowerEvaporites successions, the experience derivedfrom the Apennine foredeep supports the hy-pothesis that evaporitic deposits occurring indeepest subbasins of the Mediterranean couldactually have been deposited in deep waters(Krijgsman et al., 1999a) through precipitationfrom deep brines and/or, we suggest, throughclastic resedimentation processes.

Pierre et al. (2002) have suggested that the

huge sea-level drop related to the Mediterra-nean desiccation caused gas hydrate dissocia-tion in late Tortonian reservoirs of the LorcaBasin (Spain), thus triggering large-scale fail-ure processes. This mechanism is undoubtedlyplausible and can explain sedimentary insta-bility without the need for tectonic processes;however, in the example of Pierre et al., noMessinian evaporites were apparently in-volved in failures and this missing featurecaused some problems in the correct deter-mination of the age of such events. In theApennine foredeep, carbonate bodies relatedto methane-rich fluid venting are largely dif-fused at several stratigraphic levels throughoutthe whole Miocene succession (Ricci Lucchiand Vai, 1994; Conti and Fontana, 1998). Asin the Lorca Basin, chemosynthetic carbonatebodies also occur in the euxinic shales of theVena del Gesso basin, just below the de-formed gypsum unit. A specialized molluskfauna is often associated with these bodies,indicating that fluid venting at the sea bottomwas already active during the early Messinian(Taviani, 1994, 2001). The areal distributionof the carbonate bodies is revealing: In theVena del Gesso basin, they only occur in thesoutheastern sector (Sintria valley); like sim-ilar bodies occurring at other stratigraphic lev-els, they are most commonly associated withstructural culminations. Gas hydrate couldwell have played a role in triggering massmovements of gypsum slabs in the Vena delGesso basin; however, the distribution of thecarbonate bodies suggests that tectonic upliftlikely provided the conditions for theirdissociation.

CONCLUSIONS: IMPLICATIONS FORTHE ONSET OF THE MESSINIAN

SALINITY CRISIS

The sedimentary and tectonic history of theVena del Gesso basin clearly illustrates thecomplex evolution of a thrust-top basin, fromthe early growth of its bounding thrust to thefinal tectonic uplift. In such a geologic con-text, the deposition of Messinian primaryevaporites—which occurred during the finalstage of a long-lasting uplift phase affectingthe whole Apennine thrust front—seems tohave been intimately controlled by the tecton-ic history of the region and not merely—or, atleast, not only—the result of the superpositionof remote events (closure and reopening of theAtlantic gateways).

Evaporite deposition and subsequent defor-mation were both locally controlled by tecton-ics and the evolving basin morphology. Thegrowth of a structural high led to the forma-



Figure 16. (A) Gypsum slide blocks of the Sintria valley (based on Marabini and Vai, 1985, section D). (B) The present-day interpretation;M/P—Miocene/Pliocene unconformity; p-ev2—postevaporitic unit 2. (C) When removing the Pliocene to Holocene deformation, asouthward-dipping late Messinian paleoslope appears. MA—Marnoso-arenacea. The steepening of such a paleoslope during the intra-Messinian tectonic phase triggered large-scale slope instability phenomena and promoted the collapse and accumulation of huge gypsumslabs.

tion of a small basin, isolated from the main-land and with reduced connections with themain basin. Evaporites were deposited withinthis shallow basin; the deeper and wider fo-redeep basin was characterized by depositionof organic-rich shales. Subsequent uplift andtilting led to the collapse of the gypsum unitin the late Messinian.

A point that we want to stress here is thetectonic nature of the base of the local LowerEvaporites; this fact probably has negligibleeffects on the chronostratigraphy, as the in-trastratal deformation does not produce sig-

nificant stratigraphic elisions or duplications.This interpretation could have a far-reachingeffect on paleoenvironmental reconstructions,as primary gypsum deposits were fragmentedand eradicated from their original substratumand translated downslope. As previously dis-cussed, depending on the extent of translation,gypsum might be superposed onto sedimentssomewhat bathymetrically deeper than thoseon which they were deposited; the estimatedvertical displacements are in the order of 150–200 m. This result implies that the amplitudeof sea-level drop at the onset of the Messinian

salinity crisis, as inferred from the abrupt su-perposition of the Lower Evaporites to theeuxinic shales, could be considerably smallerthan generally thought.

As for the ultimate processes triggeringlarge-scale slope instability and mass move-ments, we think that, also taking into accountthe possible role of other factors—for ex-ample, the gas hydrate dissociation related tohigh-amplitude sea-level falls (see Pierre etal., 2002)—the contribution of the Mediter-ranean structural evolution in controlling theMessinian stratigraphy has been somewhat


ROVERI et al.

overlooked in the past and should be re-considered.

ACKNOWLEDGMENTS

We are greatly indebted to R. Flecker and ananonymous reviewer for their thorough revisionsthat led to a significant improvement of the manu-script, to W. Schlager, Associate Editor of the GSABulletin for his thoughtful suggestions and contin-uous encouragement, and to M. Eberle for final ad-justment of the text. A. Argnani, M.A. Bassetti,A.M. Borsetti, G. Ghibaudo, W. Krijgsman, S. Iac-carino, F. Lirer, C.C. Lucente, E. Mutti, M.E. Rossi,M. Taviani, E. Turco, L. Vigliotti, and G. Villa arealso gratefully acknowledged for the helpful discus-sions and suggestions during different steps of ourwork. Financial support for this study was providedby a 2000 grant from the Italian Ministry of Uni-versity and Research (title of the project: The Apen-nine foredeep record of Messinian salinity crisisevents: regional synthesis of outcrop and subsurfacedata and Mediterranean scale implications).

REFERENCES CITED

Argnani, A., and Ricci Lucchi, F., 2001, Tertiary turbiditesystems of the Northern Apennines, in Vai, G.B., andMartini, I.P., eds., Anatomy of an orogen: The Ap-ennines and adjacent Mediterranean: Dordrecht, Neth-erlands, Kluwer Academic Publishers, p. 327–350.

Bassetti, M.A., 2000, Stratigraphy, sedimentology and pa-leogeography of upper Messinian (‘‘post-evaporitic’’)deposits in the Marche area (Apennines, central Italy):Memorie di Scienze Geologiche, v. 52, p. 319–349.

Bassetti, M.A., Ricci Lucchi, F., and Roveri, M., 1994,Physical stratigraphy of the Messinian post-evaporiticdeposits in the central-southern Marche area (Apen-nines, central Italy): Memorie della Societa GeologicaItaliana, v. 48, p. 275–288.

Bellanca, A., Caruso, A., Ferruzza, G., Neri, R., Pierre,J.M., Sprovieri, M., and Blanc-Valleron, M.M., 2001,Transition from marine to hypersaline conditions inthe Messinian Tripoli Formation from the marginalarea of the central Sicilian Basin: Sedimentary Geol-ogy, v. 140, p. 87–105.

Benini, A., Farabegoli, E., and Martelli, L., 1991, Strati-grafia e paleogeografia del Gruppo di S. Sofia (altoAppennino Forlivese): Memorie Descrittive della Car-ta Geologica d’Italia, v. 46, p. 231–243.

Boccaletti, M., Calamita, F., Deiana, G., Gelati, R., Massari,F., Moratti, G., and Ricci Lucchi, F., 1990, Migratingforedeep-thrust belt system in the northern Apenninesand southern Alps: Palaeogeography, Palaeoclimatol-ogy, Palaeoecology, v. 77, p. 3–14.

Capozzi, R., Landuzzi, A., Negri, A., and Vai, G.B., 1991,Stili deformativi ed evoluzione tettonica della succes-sione neogenica romagnola: Studi Geologici Camerti,Volume Speciale (1991/1), p. 261–278.

Castellarin, A., 2001, Alps-Apennines and Po Plain–frontalApennines relationships, in Vai, G.B., and Martini,I.P., eds., Anatomy of an orogen: The Apennines andadjacent Mediterranean: Dordrecht, Netherlands, Klu-wer Academic Publishers, p. 177–196.

Castellarin, A., and Pini, G.A., 1989, L’arco del Sillaro: Lamessa in posto delle ‘‘Argille Scagliose’’ al margineappenninico padano (Appennino bolognese): Memoriedella Societa Geologica Italiana, v. 39, p. 127–141.

Castellarin, A., Eva, C., Giglia, G., Vai, G.B., with a con-tribution of Rabbi, E., Pini, G.A., and Crestana, G.,1986, Analisi strutturale del Fronte Appenninico Pa-dano: Giornale di Geologia, v. 47/1–2, p. 47–75.

Cita, M.B., and Corselli, C., 1990, Messinian paleogeog-raphy and erosional surfaces in Italy: An overview:Palaeogeography, Palaeoclimatology, Palaeoecology,v. 77, p. 67–82.

Clauzon, G., 1982, Le canyon messinien du Rhone: Une

preuve decisive du ‘‘desiccated deep-basin model’’(Hsu, Cita et Ryan, 1973): Bulletin de la Societe Geo-logique de France, v. 24, p. 597–610.

Clauzon, G., Suc, J.P., Gautier, F., Berger, A., and Loutre,M.F., 1996, Alternate interpretation of the Messiniansalinity crisis: Controversy resolved?: Geology, v. 24,p. 363–366.

Colalongo, M.L., Ricci Lucchi, F., Guarnieri, P., and Man-cini, E., 1982, Il Plio–Pleistocene del Santerno (Ap-pennino romagnolo), in Cremonini, G., and Ricci Luc-chi, F., eds., Guida alla geologia del margineappenninico padano: Guide Geologiche regionali dellaSocieta Geologica Italiana: Bologna, Societa Geolo-gica Italiana, p. 161–166.

Conti, S., and Fontana, D., 1998, Recognition of primaryand secondary Miocene lucinid deposits in the Apen-nine Chain: Memorie di Scienze Geologiche di Pa-dova, v. 50, p. 101–131.

Costa, G.P., Colalongo, M.L., De Giuli, C., Marabini, S.,Masini, F., Torre, D., and Vai, G.B., 1986, Latest Mes-sinian vertebrate fauna preserved in a paleokarst-neptunian dike setting (Brisighella, Northern Apen-nines): Le grotte d’Italia, v. 12, p. 221–235.

Cremonini, G., and Ricci Lucchi, F., 1982, Guida alla Geo-logia del margine appenninico padano: Guide geolo-giche regionali: Bologna, Societa Geologica Italiana,248 p.

Cremonini, G., Elmi, C., and Monesi, A., 1969, Osserva-zioni geologiche e sedimentologiche su alcune sezioniplio-pleistoceniche dell’Appennino romagnolo: Gior-nale di Geologia, v. 35, p. 85–96.

Decima, A., and Wezel, F.C., 1971, Osservazioni sulle eva-poriti messiniane della Sicillia centro-meridionale:Rivista Mineraria Siciliana, v. 22, p. 130–132.

De Giuli, C., Masini, F., and Torre, D., 1988, The mammalfauna of the Monticino quarry, in De Giuli, C., andVai, G.B., eds., Fossil vertebrates in the Lamone val-ley, Romagna Apennines, International Workshop:Continental Faunas at the Mio-Pliocene Boundary:Faenza, Italy, March 28–31, 1988, Field Trip Guide-book, Gaenza, Litografica, p. 65–69.

Farabegoli, E., Benini, A., Martelli, L., Onorevoli, G., andSeveri, P., 1991, Geologia dell’Appennino Romagnoloda Campigna a Cesenatico: Memorie Descrittive dellaCarta Geologica d’Italia, v. 46, p. 165–184.

Ghibaudo, G., Clari, P., and Perello, M., 1985, Litostrati-grafia, sedimentologia ed evoluzione tettonicosedi-mentaria dei depositi miocenici del margine sud-orientale del Bacino Terziario Ligure-Piemontese(Valli Borbera, Scrivia e Lemme): Bollettino della So-cieta Geologica Italiana, v. 104, p. 349–397.

Hillgen, F.J., and Krijgsman, W., 1999, Cyclostratigraphyand astrochronology of the Tripoli diatomite formation(pre-evaporite Messinian, Sicily, Italy): Terra Nova,v. 11, p. 16–22.

Hilgen, F.J., Bissoli, L., Iaccarino, S., Krijgsman, W., Mei-jer, A., Negri, A., and Villa, G., Integrated stratigraphyand astrochronology of the Messinian GSSP at OuedAkrech (Atlantic Morocco): Earth and Planetary Sci-ence Letters, v. 182, p. 237–251.

Hsu, K.J., 2001, Gaia and the Mediterranean Sea: ScientiaMarina, v. 65, p. 133–140.

Hsu, K.J., Ryan, W.B.F., and Cita, M.B., 1972, Late Mio-cene desiccation of the Mediterranean: Nature, v. 242,p. 240–244.

Iaccarino, S., Castradori, D., Cita, M.B., Di Stefano, E.,Gaboardi, S., McKenzie, J.A., Spezzaferri, S., andSprovieri, R., 1999, The Miocene/Pliocene boundaryand the significance of the earliest Pliocene floodingin the Mediterranean: Memorie della Societa Geolo-gica Italiana, v. 54, p. 109–131.

Kastens, K.A., 1992, Did glacio-eustatic sea level drop trig-ger the Messinian salinity crisis? New evidence fromOcean Drilling Program Site 6754 in the TyrrhenianSea: Paleoceanography, v. 7, p. 333–356.

Kligfield, R., 1979, The Northern Apennines as a collision-al orogen: American Journal of Science, v. 279,p. 676–691.

Kontopoulos, N., Zelilidis, A., Piper, D.J.W., and Mudie,P.J., 1997, Messinian evaporites in Zakynthos, Greece:Palaeogeography, Palaeoclimatology and Palaeoecol-ogy, v. 129, p. 361–367.

Kouwenhoven, T.J., Seidenkrants, M.S., and Van derZwaan, G.J., 1999, Deep-water changes: The near-synchronous disappearance of a group of benthic fo-raminifera from the late Miocene Mediterranean: Pa-laeogeography, Palaeoclimatology, Palaeoecology,v. 152, p. 259–281.

Krijgsman, W., Hilgen, F.J., Raffi, I., Sierro, F.J., and Wil-son, D.S., 1999a, Chronology, causes and progressionof the Messinian salinity crisis: Nature, v. 400,p. 652–655.

Krijgsman, W., Hilgen, F.J., Marabini, S., and Vai, G.B.,1999b, New paleomagnetic and cyclostratigraphic ageconstraints on the Messinian of the Northern Apen-nines (Vena del Gesso Basin, Italy): Memorie dellaSocieta Geologica Italiana, v. 54, p. 25–33.

Landuzzi, A., and Castellari, M., 1988, A new vertebratesite from late Messinian karst holes, Santerno Valley,W Romagna, in De Giuli, C., and Vai, G.B., eds.,Fossil vertebrates in the Lamone valley, Romagna Ap-ennines, International Workshop: Continental Faunasat the Mio-Pliocene Boundary: Faenza, Italy, March28–31, 1988, Field Trip Guidebook, Faenza, Litograf-ica, p. 70–74.

Lucente, C.C., Manzi, V., Ricci Lucchi, F., and Roveri, M.,2002, Did the Ligurian sheet cover the whole thrustbelt in Tuscany and Romagna Appennines? Some ev-idence from gravity emplaced deposits: Memorie dellaSocieta Geologica Italiana, Volume Speciale no. 1,p. 393–398.

Manzi, V., 1997, Analisi di facies dei depositi messinianipost-evaporitici tra il Fiume Bidente ed il Fiume Sa-vio: Tra Corbara e Pieve di Rivoschio (Appenninoromagnolo) [M.S. thesis]: Bologna, Italy, Universityof Bologna, 124 p.

Manzi, V., 2001, Stratigrafia fisica, analisi sedimentologicamicroscopica e caratteri magnetostratigrafici dei de-positi connessi all’evento evaporitico del Messiniano(F. ne Gessoso-solfifera l.s.) [Ph.D. thesis]: Bologna,Italy, University of Bologna, p. 1–72.

Marabini, S., and Vai, G.B., 1985, Analisi di facies e ma-crotettonica della Vena del Gesso in Romagna: Bol-lettino della Societa Geologica Italiana, v. 104,p. 21–42.

Marabini, S., and Vai, G.B., 1988, Geology of the Monti-cino Quarry (Brisighella, Italy) stratigraphic implica-tion of its late Messinian Mammal Fauna, in De Giuli,C., and Vai, G.B., eds., Fossil vertebrates in the La-mone valley, Romagna Apennines, InternationalWorkshop: Continental Faunas at the Mio-PlioceneBoundary: Faenza, Italy, March 28–31, 1988, FieldTrip Guidebook, Faenza, Litografica, p. 39–52.

McKenzie, J.A., 1999, From desert to deluge in the Med-iterranean: Nature, v. 400, p. 613–614.

Meulenkamp, J.E., and Sissingh, W., 2001, Circum-Mediterranean late Miocene to early Pliocene tecton-ics and paleogeography, in Agustı, and Oms, O., eds.,Late Miocene to early Pliocene environments and eco-systems: 2nd EEDEN (Environment and EcosystemsDynamics of the Eurasian Neogene): Sabadell, Spain,Plenary Workshop, 15–17 November, 2001, Abstractvolume, p. 47.

Michalzik, D., 1996, Lithofacies, diagenetic spectra andsedimentary cycles of Messinian (Late Miocene)evaporites in SE Spain: Sedimentary Geology, v. 106,p. 203–222.

Muller, D.W., and Hsu, K.J., 1987, Event stratigraphy andpaleoceanography in the Fortuna-basin (southeastSpain): A scenario for the Messinian salinity crisis:Paleoceanography, v. 2, p. 679–696.

Mutti, E., Tinterri, R., Remacha, E., Mavilla, N., Angella,S., and Fava, L., 1999, An introduction to the analysisof ancient turbidite basins from an outcrop perspec-tive: AAPG Continuing Education Course Note Se-ries, no. 39, 61 p.

Negri, A., and Vigliotti, L., 1997, Calcareous Nannofossilbiostratigraphy and paleomagnetism of the MonteTondo and Monte del Casino sections (Romagna Ap-ennines, Italy), in Montanari, A., Odin and, G.S., Coc-cioni, R., eds., Miocene stratigraphy—An integratedapproach: Amsterdam, Elsevier, p. 478–491.

Negri, A., Giunta, S., Hilgen, F., Krijgsman, W., and Vai,G.B., 1999, Calcareous nannofossil biostratigraphy of



the M. del Casino section (Northern Apennines, Italy)and paleoceanography conditions at times of late Mio-cene sapropel formation: Marine Micropaleontology,v. 36, p. 13–30.

Odin, G.S., Montanari, A., and Coccioni, R., 1997, Chron-ostratigraphy of Miocene stages: A proposal for thedefinition of precise boundaries, in Montanari, A.,Odin, G.S., and Coccioni, R., eds., Miocene stratig-raphy—An integrated approach: Amsterdam, Elsevier,p. 597–629.

Parea, G.C., and Ricci Lucchi, F., 1972, Resedimentedevaporites in the Periadriatic trough (upper Miocene,Italy): Israel Journal of Earth-Sciences, v. 21,p. 125–141.

Pedley, H.M., and Grasso, M., 1993, Controls on faunaland sediment cyclicity within the Tripoli and Calcaredi Base basins (late Miocene) of central Sicily: Pa-laeogeography, Palaeoclimatology, Palaeoecology,v. 105, p. 337–360.

Pieri, M., and Groppi, G., 1981, Subsurface geologicalstructure of the Po Plain, Italy: Pubblicazione 414,Progetto Finalizzato Geodinamica, C.N.R., 13 p.

Pierre, C., Rouchy, J.-M., and Blanc-Valleron, M.-M.,2002, Gas hydrate dissociation in the Lorca Basin(southeast Spain) during the Mediterranean Messiniansalinity crisis: Sedimentary Geology, v. 147,p. 247–252.

Ricci Lucchi, F., 1968, Chanellized deposits in the middleMiocene flysch of Romagna (Italy): Giornale di Geo-logia, v. 36, p. 203–282.

Ricci Lucchi, F., 1969, Composizione e morfometria di unconglomerato risedimentato nel flysch miocenico rom-agnolo (Fontanelice, Bologna): Giornale di Geologia,v. 36, p. 1–47.

Ricci Lucchi, F., 1973, Resedimented evaporites: Indicatorsof slope instability and deep-basins conditions in Per-iadriatic Messinian (Apennines foredeep, Italy) inMessinian events in the Mediterranean: KoninklijkeNederlandse Akademie van Wetenschappen, Geodyn-amics Scientific Report no 7, colloquium held inUtrecht, March 2–4, p. 142–149.

Ricci Lucchi, F., 1975, Miocene paleogeography and basinanalysis in the Periadriatic Apennines, in Squyres,C.H., ed., Geology of Italy: Tripoli, Petroleum Explo-ration Society of Lybia, v. 2, p. 129–236.

Ricci Lucchi, F., 1981, The Miocene Marnoso-arenacea tur-bidites, Romagna and Umbria Apennines, in RicciLucchi, F., ed., Excursion guidebook: Bologna, Italy,2nd International Association of Sedimentologists Re-gional Meeting, p. 229–303.

Ricci Lucchi, F., 1986, The Oligocene to Holocene forelandbasins of the northern Apennines, in Allen, P.A., andHomewood, P., eds., Foreland basins: InternationalAssociation of Sedimentologists Special Publication 8,p. 105–139.

Ricci Lucchi, F., and Ori, G.G., 1985, Field excursion D:Syn-orogenic deposits of a migrating basin systems inthe northwest Adriatic foreland, in Allen, P.A., ed.,Foreland basins, Excursion guidebook: Fribourg, Ger-many, International Association of Sedimentologists,p. 137–176.

Ricci Lucchi, F., and Vai, G.B., 1994, A stratigraphic andtectonofacies framework of the ‘‘calcari a Lucina’’ inthe Apennine Chain, Italy: Geo-Marine Letters, v. 14,p. 210–218.

Ricci Lucchi, F., Bassetti, M.A., Manzi, V., and Roveri, M.,2002, Il Messiniano trent’anni dopo: Eventi connessialla crisi di salinita nell’avanfossa appenninica: StudiGeologici Camerti, (in press).

Rio, D., Raffi, I., and Villa, G., 1990, Pliocene–Pleistocenecalcareous nannofossil distribution patterns in thewestern Mediterranean, in Kastens, K.A., Mascle, J.,et al., eds., Proceedings, Ocean Drilling Program, Sci-entific results, Volume 107: College Station, Texas,Ocean Drilling Program, p. 513–533.

Roveri, M., Manzi, V., Bassetti, M.A., Merini, M., and Ric-ci Lucchi, F., 1998, Stratigraphy of the Messinianpost-evaporitic stage in eastern Romagna (northernApennines, Italy): Giornale di Geologia, v. 60,p. 119–142.

Roveri, M., Bassetti, M.A., and Ricci Lucchi, F., 2001, TheMediterranean Messinian salinity crisis: An Apennineforedeep perspective: Sedimentary Geology, v. 140,p. 201–214.

Ryan, W.B.F., and Cita, M.B., 1978, The nature and distri-bution of the Messinian erosional surface—Indicatorsof a several-kilometers-deep Mediterranean in theMiocene: Marine Geology, v. 27, p. 193–230.

Schlager, W., and Bolz, H., 1977, Clastic accumulation ofsulphate evaporites in deep water: Journal of Sedi-mentary Petrology, v. 47, p. 600–609.

Sierro, F.J., Flores, J.A., Zamarreno, I., Vazquez, A., Utrilla,R., Frances, G., Hilgen, F.J., and Krijgsman, W., 1999,Messinian pre-evaporite sapropels and precession-induced oscillation in western Mediterranean climate:Marine Geology, v. 153, p. 137–146.

Sprovieri, R., 1992, Mediterranean Pliocene biochronology:A high resolution record based on quantitative plank-tonic foraminifera distribution: Rivista Italiana di Pa-leontologia e Stratigrafia, v. 98, p. 61–100.

Sprovieri, R., Di Stefano, E., and Sprovieri, M., 1996a,High resolution chronology for late Miocene Mediter-ranean stratigraphic events: Rivista Italiana di Paleon-tologia e Stratigrafia, v. 102, p. 77–104.

Sprovieri, R., Di Stefano, E., Caruso, A., and Bonomo, S.,1996b, High resolution stratigraphy in the MessinianTripoli Formation in Sicily: Paleopelagos, v. 6,p. 415–435.

Taviani, M., 1994, The ‘‘calcari a Lucina’’ macrofauna re-considered: Deep-sea faunal oases from Miocene-age

cold vents in the Romagna Apennine, Italy: Geo-Marine Letters, v. 14, p. 185–191.

Taviani, M., 2001, Fluid venting and associated processes,in Vai, G.B., and Martini, I.P., eds., Anatomy of anorogen: The Apennines and adjacent Mediterranean:Dordrecht, Netherlands, Kluwer Academic Publishers,p. 351–366.

Testa, G., and Lugli, S., 2000, Gypsum-anhydrite transfor-mations in Messinian evaporites of central Tuscany(Italy): Sedimentary Geology, v. 130, p. 249–268.

Theodoridis, S., 1984, Calcareous nannofossil biozonationof the Miocene and revision of the helicolith and dis-coasters: Utrecht Micropaleontological Bullettin,v. 32, p. 1–271.

Vai, G.B., 1988, A field trip guide to the Romagna Apen-nine geology, The Lamone valley, in De Giuli, C., andVai, G.B., eds., Fossil vertebrates in the Lamone val-ley, Romagna Apennines, International Workshop:Continental Faunas at the Mio-Pliocene Boundary:Faenza, Italy, March 28–31, 1988, Field Trip Guide-book, Faenza, Litografica, p. 7–37.

Vai, G.B., 1997, Cyclostratigraphic estimate of the Messi-nian stage duration, in Montanari, A., Odin, G.S., andCoccioni, R., eds., Miocene stratigraphy—An inte-grated approach: Amsterdam, Elsevier, p. 463–476.

Vai, G.B., and Martini, I.P., eds., 2001, Anatomy of an or-ogen: The Apennines and adjacent Mediterranean:Dordrecht, Netherlands, Kluwer Academic Publishers,632 p.

Vai, G.B., and Ricci Lucchi, F., 1977, Algal crusts, autoch-thonous and clastic gypsum in a cannibalistic evapo-rite basin: A case history from the Messinian ofNorthern Apennines.: Sedimentology, v. 24,p. 211–244.

Van der Meulen, M.J., Meulenkamp, J.E., and Wortel,M.J.R., 1999, Lateral shifts of Apenninic foredeep de-pocentres reflecting detachment of subducted litho-sphere: Earth and Planetary Science Letters, v. 154,p. 230–219.

Van der Meulen, M.J., Kouwenhoven, T.J., van der Zwaan,G.J., Meulenkamp, J.E., and Wortel, M.J.R., 1999,Late Miocene uplift in the Romagnan Apennines andthe detachment of subducted lithosphere: Tectono-physics, v. 315, p. 319–335.

Vigliotti, L., 1988, Magnetostratigraphy of the Monticinosection 1987 (Faenza, Italy), in De Giuli, C., and Vai,G.B., eds., Fossil vertebrates in the Lamone valley,Romagna Apennines, International Workshop: Conti-nental Faunas at the Mio-Pliocene Boundary: Faenza,Italy, March 28–31, 1988, Field Trip Guidebook, Fa-enza, Litografica, p. 61–62.

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Sedimentary and tectonic evolution of the Vena del Gesso basin … · 2017. 7. 2. · Marco...

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