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Journal of Foraminiferal Research,v. 31, no. 4, p. 287–293, October 2001

PALORBITOLINA LENTICULARIS FROM THE NORTHERN ADRIATIC REGION:PALEOGEOGRAPHICAL AND EVOLUTIONARY IMPLICATIONS

ANTUN HUSINEC

Institute of Geology, Sachsova 2, PO Box 268, HR-10000 Zagreb, Croatia

ABSTRACT

Samples bearing Palorbitolina were obtained fromthree localities on the islands of Cres and Losinj in thenorthern Adriatic. Although a relatively small number(�60) of specimens were studied, the size of the embry-onic chamber and test diameters of Palorbitolina lenti-cularis indicate a Lower Aptian age. This is confirmedfor the Adriatic carbonate platform by the presence ofLower Aptian index taxa. Both embryonic chamber andtest diameter variation are pronounced. No change wasobserved concerning the relationship between strati-graphic horizon and the embryonic chamber diameter.A proportional relationship between the size of the em-bryonic chamber and the test was determined.

These data show that before it appeared on the Adri-atic carbonate platform, Palorbitolina already colonizedthe predominantly mixed clastic-carbonate environ-ments of the Mediterranean, as has been suggested byVelic & Sokac (1978). Although an essentially westwardswater circulation during the late Barremian and earlyAptian probably aided Palorbitolina in colonization ofthe Tethyan realm, it can neither explain the simulta-neous existence of Palorbitolina in different and remoteparts of the Tethys nor its dispersal, which must havebeen very rapid.

INTRODUCTION

In the Adriatic region, as in the wider Tethyan realm, thespeciesPalorbitolina lenticularisis found at numerous lo-calities, occasionally forming the bulk of the deposit. Thisstudy focuses on the northern Adriatic islands of Cres andlosinj, where carbonate platform deposits range from theEarly Neocomian to the Senonian (Fucˇek and others, 1995).Biozonation of the Aptian, Albian and Cenomanian platformcarbonates in this area is based on the orbitolinids (Husinecand Velic, 1998; Husinec and others, 2000).

Although P. lenticularis is a well-known species, and inspite of the fact that for most fossil populations a relation-ship between size and age must be assumed (Brenchley andHarper, 1997), the relationship between its dimensions andage is poorly understood. Hofker Jr. (1963) was the first onewho clearly showed gradual increase of the diameter of thedeuteroconch from the Upper Barremian to the Lower Ap-tian. His measurements were made exclusively on axial sec-tions of several specimens found in the same layer. Theauthor reported minimum value of 110�m for the UpperBarremian and maximum value of 350�m for the LowerAptian specimens. Arnaud-Vanneau (1968) studied five dif-ferent populations ofP. lenticularisand distinguished twoarchitectural modifications: reduction in size of megalos-

E-mail: antun.husinec@zg.hinet.hr

phaeric forms and progressive enlargement of microsphericindividuals. Schroeder (1975) indicated gradual increase ofthe diameter of the embryonic areas from the Upper Bar-remian to the Lower Aptian/Upper Aptian boundary, withits maximum value reaching 200�m. Cherchi and others(1978) pointed out that specimens with an embryonic cham-ber diameter of 240–300�m belong to the latest Early Ap-tian. Very important research in this area was done by Gusˇic(1981). He used the increase in the size of the embryonicchamber in successive populations ofP. lenticularisto dis-tinguish different evolutionary stages within the phyleticline of the species, which enabled him to divide the UpperBarremian-Lower Aptian sequence in the absence of strati-graphically more indicative forms. Recently, Cherchi andSchroeder (1999) investigated the Late BarremianPalorbi-tolina from Northern Somalia. Their results exhibit embry-onic chamber diameters ranging from 160 to 260�m.

The measured values of both the embryonic chamber andtest diameters in this study agree with the age determinedon the basis of microfossil association and clearly indicatethe Lower Aptian.

DEPOSITIONAL ENVIRONMENT OFPALORBITOLINA LENTICULARIS

Due to its eurytopic character,Palorbitolina lenticularishad a circum-global distribution during the Upper Barre-mian-Lower Aptian; hence, the species is found in variousdepositional environments. Rey (1975) concluded that it wasliving in the infralittoral zone, both in agitated reefal settingsand backreef muds. Arnaud-Vanneau (1975) considered itas a form tightly linked to vegetation-covered substratescharacteristic of clayey-to-carbonate muddy deposits. Alter-natively, Masse (1976) has suggested that it reflected deepercircumlittoral conditions. Arnaud-Vanneau (1980) recordedoccurrences in both infralittoral and circumlittoral environ-ments. Three main settings were recognized by Arnaud(1981): circumlittoral (finely bioclastic limestones), openmarine infralittoral (caprinid calcareous muds) and ‘‘marlychannels’’. Velic(1988) defined its environment as lagoon-to-subtidal-to-restricted shoals with patch reefs and back-reef; i.e., shallow infralittoral. Banner and Simmons (1994)have suggested that the depth ranged from 5 to 60 m, witha preferred range of 10–60 m. Vilas and others (1995) point-ed out five major distinctive depositional environments: lit-toral zone, coastal zone, platform interior, outer platformand outer shelf. In the study area of the northern Adriatic(the islands of Cres and Losˇinj), Palorbitolina is foundwithin a protected, low-energy subtidal environment thatwas affected and modified by storm events.

METHODS

Samples bearingPalorbitolina were obtained from threelocalities on the islands of Cres and Losˇinj in the northern

288 HUSINEC

PLATE 1Palorbitolina lenticularis (BLUMENBACH). (1–3) Axial and (4) oblique section through megalospheric embryonic apparatus, sample CK-4,

magnification�42.

TABLE 1. Embryonic chamber diameter (ECD) ofP. lenticularisspecimens from samples CDB–35-38/4, CK–1A-4 and LP–1-15.

Samples NumberMean ECD

(�m)Standarddeviation Range (�m)

CDB–35-38/4CK–1A-4LP–1–15Total

16201854

261.3255.5322.8279.6

40.4835.032.746.9

200–330200–320260–370200–370

Adriatic. The samples were cut to maximize the number ofaxial (vertical) sections of embryonic apparatuses (Plate 1).The embryonic chamber diameter of the speciesP. lenti-cularis was measured for 54 specimens, while test diametermeasurements were made on 56 specimens. The limitednumber of measurements was a consequence of the veryhard lithology (generally massive and compact limestones)from which it was difficult to obtain appropriate sections.Many of the tests were destroyed and some embryonic ap-paratuses were separated from their tests, which made itimpossible to take both of the measurements on a singlespecimen. Samples were obtained at three sites:

Dragozetici – samples CDB-35 through CDB-38/4.Foursamples were obtained from the wackestones (thickness 35m) deposited in a protected, low-energy subtidal environ-ment. The age of these samples is Lower Aptian. This canreliably be concluded due to the presence ofVoloshinoidesmurgensisandPraeorbitolina cormyiin association withP.lenticularis. The embryonic chamber diameter ofP. lenti-cularis was measured for 16 specimens (Table l, Fig. 1),

and the test diameter was measured on 25 specimens (Table2, Fig. 2).

Krizice – samples CK-1A through CK-4.Five sampleswere taken from the 7.40 m thick sequence of wackestones,gastropod floatstones and grainstones (tempestites). The ageof this sequence is Lower Aptian, which can be concludedfrom the association of the following species:Palorbitolinalenticularis, Praeorbitolina cormyi,andP. wienandsi.Theembryonic chamber diameter of the speciesP. lenticulariswas measured on 20 specimens (Table 1, Fig. 1), and testdiameters were measured for 14 specimens (Table 2, Fig.2).

Losinj Punta – samples LP-1 through LP-15.Fifteensamples were collected from a very thick sequence (46.30m) of massive wackestones-floatstones interbedded withrudstones and tempestites. The association ofPalorbitolinalenticularis, Praeorbitolina cormyi, P. wienandsi, Orbito-lina (Mesorbitolina) lotzei,and Voloshinoides murgensisreliably indicates early Aptian age. The embryonic chamberdiameter ofP. lenticulariswas measured in 18 specimens(Table 1, Fig. 1), and the test diameter was measured for 17specimens (Table 2, Fig. 2).

RESULTS

Embryonic chamber diameter data are summarized in Ta-ble 1 and Fig. 1. Pronounced variation in the size of theembryonic chamber diameter occurred among specimensfrom each locality. The maximum value of embryonicchamber diameter was 42% larger than the minimum value

289PALORBITOLINA LENTICULARIS

FIGURE l. Histogram of embryonic chamber diameters.

TABLE 2. Test diameter ofP. lenticularis specimens from samplesCDB–35-38/4, CK–1A-4 and LP–1–15. Measured values are roundedto whole mm.

Samples Number

Mean testdiameter

(mm)Standarddeviation Range (mm)

CDB–35-38/4CK–1A-4LP–1–15Total

25141756

4.03.44.84.1

1.10.91.11.2

1.8–6.42.1–5.33.0–6.51.8–6.5

FIGURE 2. Histogram of test diameters.

within the Losinj Punta samples (LP) and 65% larger thanthe minimum value in the Dragozetic´i samples (CDB).Comparing all samples within the study area, the maximi-mum value for the embryonic chamber diameter was 85%larger than the minimum value. Similar observations weremade by Gusˇic (1981) in his study ofP. lenticularis fromBosnia-Herzegovina and Slovenia. Nevertheless, no changewas observed concerning the relationship between strati-graphic horizon and size of the embryonic chamber diam-eter.

The mean embryonic chamber diameter ranged from255.5�m for the specimens from the Krizˇice samples (CK)to 322.8�m for the specimens from the Losˇinj Punta (LP)samples. The mean embryonic chamber diameter calculatedfrom all sample specimens was 279.6�m.

The total range of the embryonic chamber diameter cal-culated from all sample specimens was 200–370�m. Ac-

cording to Gusˇic (1981), both the range and value of themean embryonic chamber diameter ofP. lenticularis arecharacteristic of the late Early Aptian. The microfossil as-sociation observed in the investigated area, combined withthe stratigraphy, also implies an Early Aptian age.

Test diameter data are summarized in Table 2. The vari-ation of the test diameter within specimens from each lo-cality was even more pronounced than the embryonic cham-ber diameter. The maximum value of test diameter was133% larger than the minimum value within the Dragozetic´isamples (CDB) and 150% larger than the minimum valuein the Losinj Punta samples (LP). Comparing all samplestogether within the studied area, the maximimum value for

290 HUSINEC

FIGURE 3. Geographic distribution ofPalorbitolina lenticularisduring the Lower Aptian (114–112 Ma). 1� shallow platform, 2� basin, 3� slope or shelf-edge/slope boundary, 4� palaeolatitude, 5� present-day coastline, 6� additional locating marks, 7� Palorbitolina lenticularis.Palaoegeographical map simplified after Masse and others (1993a).

the test diameter was 250% larger than the minimum value.The mean diameter of all the tests was 4.1 mm and themeasured values were predominately between 4 and 5 mm(Fig. 2). Although this measured character, unlike the em-bryonic chamber diameter, is strongly influenced by the en-vironment (e.g., Vilas and others, 1995), the data yielded aproportional relationship between the diameter of the em-bryonic chamber and the diameter of the test.

PALEOGEOGRAPHICAL AND EVOLUTIONARYIMPLICATIONS

Although Hughes (1998) concluded thatHeterosteginaandOperculinapossibly represent modern analogues for or-bitolinids, it is most likely that such do not exist. Recentlarger foraminifera are adapted to life in oligotrophic, nu-trient-deficient conditions (Murray, 1991), where light andwater energy are considered to be the most important factorscontrolling their distribution (Hottinger, 1980, 1983). How-ever, as previously mentioned,Palorbitolina lenticularisisa eurytopic species.

It is almost impossible to enumerate all the known local-ities in the Mediterranean region whereP. lenticularis isfound. It is known from the northwestern Atlantic (Sen Gup-ta and Grant, 1971; Schroeder and Cherchi, 1979), Mexico(Meza, 1980; Pantoja-Alor and others, 1994; Gonzalez-Ar-reola and others, 1996) and Venezuela (Arnaud-Vanneau,written communication, 1999). In Africa, besides the Med-iterranean region, it is found in Ethiopia (Bosellini and oth-ers, 1999), Somalia (e.g. Bosellini, 1989; Luger and others,1990; Cherchi and Schroeder, 1999) and Tanzania (Peyber-nes, 1982), which is the only locality in the present-daysouthern hemisphere.Palorbitolina lenticularis is alsofound in Israel, Lebanon and Syria (Saint-Marc, 1970),Yemen (Cherchi and others, 1998), Oman (e.g. Simmons,1994; Simmons and Hart, 1987; Masse and others, 1998),and the United Arab Emirates (Witt and Gokdag, 1994; Vah-renkamp, 1996). It is also recorded from Iran (Mehrnusch,1973; Ricou, 1976; Shakib, 1990), Afghanistan (Montenat

and others, 1982), Tibet (Marcoux and others, 1987;XZBGM, 1993), India (Cherchi and others, 1984), Borneo(Hofker, 1963; Yuwono and others, 1988) and the Phillipi-nes (Wolcke and Scholz, 1988).

Orbitolinids were perhaps the most significant larger fo-raminifera of the Lower Cretaceous Tethys. Paleogeographicfactors were one of the host factors which limited their dis-tribution (Moullade and others, 1985).Palorbitolina lenti-cularis, which is one of the most important species, has aworld-wide distribution in Cretaceous carbonate platformsduring the Lower Aptian (Fig. 3), when a global sea-levelrise resulted in a series of transgressions in the wider peri-Mediterranean area. The sea-level curves from Watts andSteckler (1979) and Watts (1982) in Williams (1988) sug-gest a global sea-level rise of nearly 10 m during this period,while Sahagian and Holland (1991) calculated it as up to25 m. During this time carbonate platforms and warm seasoccupied vast areas between palaeolatitudes 35�N and 35�S,except on the Pacific side of America where carbonate plat-forms are only documented from the northern hemisphere(Masse and others, 1993a, 1993b). Water temperature wasapproximately the same as or warmer than today (27–32�C),as suggested by Barron (1984, 1986), while overall salinitieswere 20% higher (Southam and Hay, 1981). The palaeo-geographical reconstruction and the position of the equatorimply an essentially westwards flowing circulation with aminor poleward deflection due to the land barriers fromSoutheast Asia and Africa (Masse and others, 1993b). Al-thoughP. lenticulariscould have migrated with the help ofthe westward and poleward flowing currents, it cannot ex-plain the dispersal of this species which must have beenvery rapid.Palorbitolina simultaneously existed in the LateBarremian, not only in what is today the Mediterranean re-gion, but also in the Arabian Peninsula (Simmons and Hart,1987; Scott, 1990; Witt and Gokdag, 1994; Simmons,1994), Northern Somalia (Cherchi and others, 1993, 1998;Cherchi and Schroeder, 1999) and Venezuela (Arnaud-Van-neau, written communication, 1999).

291PALORBITOLINA LENTICULARIS

Palorbitolina lenticularis originated fromValserina, arelatively small orbitolinid genus exhibiting an eccentricallysituated embryonic apparatus (Schroeder, 1993), which was,according to Cherchi and Schroeder (1973), geographicallyrestricted to SW Europe (Jura Mountains, Subalpine Chains,Provence, eastern Pyrenees and Sardinia). However, differ-ent species ofValserina have previously been foundthroughout the Tethyan realm: Hungary (Bodrogi, 1999),Oman (Simmons, 1994), Northern Somalia (Cherchi andothers, 1993, 1998; Cherchi and Schroeder, 1999), and evenas far as Venezuela (Arnaud-Vanneau, written communica-tion, 1999). These widespread occurrences seem to excludePalorbitolina evolution by allopatric speciation. During theUpper Barremian,P. lenticularis colonized most of theMediterranean region. The data from the Apennines (e.g.Chiocchini and others, 1984; Luperto-Sinni and Masse,1986; Raspini, 1998) and the Adriatic carbonate platform(e.g. Velic and Sokacˇ, 1978; this paper) show thatPalor-bitolina reached this region later than the rest of the Med-iterranean, where mixed clastic-carbonate environments pre-dominated. This environmental control is further suggestedby findings ofPalorbitolina in the mixed Upper Barremianenvironments of the neighboring area of Central and EasternBosnia in the Inner Dinarides (Gusˇic, 1981; Velic, 1988).Finally, according to Cherchi and Schroeder (1980), a directdescendant of the phylogenetical lineageValserina primi-tiva–V. broenimanni–V. charollaisi–V. transiens–Palorbi-tolina turbinata – P. lenticularis(Schroeder, 1993; Schroe-der and others, 1999; see also Caus and others, 1990) isPalorbitolinoides hedini.Previously it was found only inLadakh (India), Afghanistan and Tibet (Cherchi and others,1984; Marcoux and others, 1987), in the realm that corre-sponds to the ‘‘Cimmerian Continent’’ (S¸engor, 1981). It isprobably the result of the isolation ofPalorbitolina lenti-cularis in these areas that produced the subsequent replace-ment byPalorbitolinoides hedini.

ACKNOWLEDGMENTS

The study greatly benefited from the numerous discus-sions held with Dr. I. Velic´ and Prof. Dr. I. Gusˇic. Both alsothoughtfully reviewed an early version of the manuscriptand made valuable suggestions. The author gratefully ac-knowledges Prof. Dr. A. Arnaud-Vanneau and Prof. Dr. E.Caus for their constructive reviews and comments that havegreatly improved the manuscript, and Dr. A. S. Hendersonfor improving the English. I thank Dr. R. E. Martin for hishelp in final preparation of the manuscript. This researchwas carried out during work on the geological map of theRepublic of Croatia (scale 1:50.000), project No. 0181-0101, sponsored by the Ministry of Science and Technologyof the Republic of Croatia. I thank the Institute of Geology,Zagreb, for financial support.

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Received 1 November 2000Accepted 28 February 2001