Glaciogenic and related sedimentary rocks: Main lithochemical features. Communication 1. Late...

ISSN 0024�4902, Lithology and Mineral Resources, 2010, Vol. 45, No. 4, pp. 377–397. © Pleiades Publishing, Inc., 2010.Original Russian Text © A.V. Maslov, 2010, published in Litologiya i Poleznye Iskopaemye, 2010, No. 4, pp. 423–445.

377

INTRODUCTION

Three great climatic stages are distinguished in theEarth’s history. The Archean was mainly the glacier�free stage. Only rare glacial episodes occurred in theLate Archean, Early Proterozoic (Paleoproterozoic),and Early–Middle Riphean (Mesoproterozoic).Finally, the third stage spanning the Late Riphean–Vendian (Neoproterozoic) and Phanerozoic was char�acterized by frequent and periodic glaciation epochs.It is suggested that these stages were caused by gradualcooling of the Earth’s surface due to the slow changeof its thermal balance (Chumakov, 2004).

Several “great” glaciations have been distinguishedin the Earth’s history among glacial periods of differ�ent scales. They were characterized by the largestabundance of glaciers and related deposits. The firstglaciation occurred in the terminal Late Riphean(~740 Ma ago). The second, Early Vendian glaciationtook place ~600 Ma ago. The third, Late Ordovicianevent, reached maximum at ~ 440 Ma. The fourthgreat glaciation was identified in the Late Paleozoic(maximum ~290 Ma ago). The fifth subglobal�scaleevent was the Late Cenozoic glaciation with culmina�tion in the Pleistocene (Chumakov, 2004).

Glacial deposits and problems of their formationare widely discussed in literature (Chumakov, 1978,1984; Zubakov, 1990; Klimat…, 2004; Spencer, 1971;Kennett, 1977; Hambrey and Spenser, 1987;Earth’s…, 1981; Harland, 1964; Stanistreet et al.,1988; Kirsechvink, 1992a, 1992b; Smith et al, 1993;Golonka et al., 1994; Eyles and Young, 1994; Meertand Van der Voo, 1995; Hoffman et al., 1998; Hoffmanand Schrag, 2002; Narbonne and Gehling, 2002;Trompette, 1996; and others). In the last 20–25 years,

numerous works of foreign authors (Nesbitt andYoung, 1982, 1984; Nesbitt et al., 1996, 1997; Fedoet al., 1997; Young, 1983, 1991, 1995, 2001, 2002;Young and Nesbitt, 1985; Visser and Young, 1990; andothers) were mainly focused on the consideration oflithochemical features of glaciogenic deposits,whereas this aspect did not receive proper attention inRussia. Data reported in this paper and obtained byanalysis of the chemical composition of glaciogenicand associated deposits of wide age range fill this gapto some extent.

This work is based on literature data on the chemi�cal composition of glaciogenic and associated depositsof different ages (Late Archean, Early and Late Prot�erozoic, Early and Late Paleozoic, and Late Ceno�zoic), and our original data on Early Vendian rocks ofthe Middle Urals. The analyzed chemical composi�tions were compared with that of the average PAAS(Taylor and McLennan, 1985). We also analyzed theCIA values for these rocks. Note that CIA = 100 ×Al2O3/(Al2O3 + CaO* + Na2O + K2O) (Nesbitt andYoung, 1982).

The CIA value based on the molecular amounts ofpetrogenic oxides with correction for CaOcarb can serveas criterion for estimating the paleoclimatic condi�tions (Nesbitt and Young, 1984, 1989; Fedo et al.,1996, 1997; McLennan et al., 1993; Nesbitt et al.,1996; Colin et al., 1998; Corcoran and Mueller, 2002;Scheffler et al., 2003; Rieu et al., 2007a, 2007b). HighCIA values reflect the preferential removal of mobilecations (Ca2+, Na+, and K+) relative to stable phases(Al3+ and Ti4+) during the chemical weathering underwarm humid climate. Low CIA values suggest analmost complete absence of chemical weathering.

Glaciogenic and Related Sedimentary Rocks: Main Lithochemical Features. Communication 1. Late Archean and Proterozoic

A. V. MaslovZavaritskii Institute of Geology and Geochemistry, Uralian Division, Russian Academy of Sciences,

Pochtovyi per. 7, Yekaterinburg, 620075 Russiae�mail: [email protected]

Received July 20, 2009

Abstract—Lithochemical features of the Late Archean, Paleoproterozoic, and Neoproterozoic glaciogenicand related sedimentary rocks around the world are considered. Based on comparison with the average Post�Archean Australian Shale (PAAS), it is shown that the bulk chemical composition of diamictites reveals nospecific lithochemical characteristics that would undoubtedly suggest their formation under cold climaticconditions. The chemical index of alteration (CIA) frequently applied in different paleoclimatic reconstruc�tions should be considered as additional (though sufficiently important) tool, because its values for each ana�lyzed object show significant variations mainly controlled by local factors.

DOI: 10.1134/S0024490210040061

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LITHOLOGY AND MINERAL RESOURCES Vol. 45 No. 4 2010

MASLOV

Hence, they can be considered indicators of coldand/or arid climate.

The CIA value varies in the following range: from30 to 45 in unaltered basalts, 50 in unaltered granitesand feldspars, 75 in muscovite, 75–85 in illite andsmectites, and 100 in kaolinite, chlorite, and gibbsite.According to (Nesbitt and Young, 1982), the stronglyweathered tropical clays are characterized by CIAmore than 80. Average cratonic shales, such as Post�Archean Australian Shales (PAAS), North AmericaShale Composite (NASC), Russian Platform ShaleComposite (RPSC), and others have CIA within 70–75. Glacial mudstones show significantly lower CIA(~60–65), while CIA values in the Pleistocene tillsrelated to physical (“mechanical”) weathering aloneare around 50. The ternary Al2O3–CaO+Na2O–K2Odiagram (A–CN–K diagram) is considered the mostinformative tool for estimating CIA (Nesbitt andYoung, 1984).

The CIA parameter can be significantly influencedby the grain�size composition of sediments and thecomposition of rocks eroded on paleodrainages. Forinstance, the coarse�grained rocks with higher feld�spars/clay mineral ratios relative to other rock typeshave generally lower CIA values (Visser and Young,1990). At the same time, compositional variations andproportions of clay minerals are controlled by differ�ences in the provenance composition or hydraulicsorting during transportation. In order to minimizethis influence, we commonly used data on composi�tion of the finest�grained rocks (mudstones, silty mud�stones, and shales), in particular, composition of thesilty mudstone matrix of diamictites for glaciogenicdeposits. Since loss on ignition (LOI) lacks positivecorrelation with CaO, the high CaO content indicatesthat rocks contained less weathered material ratherthan carbonate phase (Rieu et al., 2007a). In contrast,the positive correlation of CIA with geochemical indi�cators, such as Zr/Ti, La/V, Th/Sc, or La/Sc (Taylorand McLennan, 1985), testifies that CIA variations insedimentary sequences were caused by changes of rockcomposition in source areas rather than “climatic sig�nal.”

LATE ARCHEAN AND EARLY PROTEROZOIC (PALEOPROTEROZOIC)

It is believed that reliable information on glacia�tions in the Early and Middle Archean is absent (Chu�makov, 2004; Eyles, 2008). First traces of glaciationswere identified in South Africa among rocks of theLate Archean Witwatersrand and Mozaan supergroups(Young et al., 1998). It is suggested that the Witwa�tersrand Supergroup contains the products of pied�mont and mountain glaciers, while the MozaanSupergroup comprises a blanket of glacial deposits.

Sections of the Upper Archean (3.07–2.72 Ga)(Armstrong et al., 1991) Witwatersrand Supergroupinclude several diamictite levels (Stanistreet et al.,

1988; Beukes and Cairncross, 1991; Smith, 2007). Inparticular, these rocks are known in the Promise, Cor�onation, and Africander formations of the West RandGroup (Fig. 1). The mica�rich matrix in the diamic�tites of the Coronation Formation occupies 30–40%.It is mainly made up of the clasts of sedimentary rocks.Granites account for less than 1% fragments. Occa�sionally, matrix accounts for as much 75% (Huberet al., 2001). The diamictites of two other levels con�tain up to 50–55% of the goethite�rich mylonitizedmatrix. The predominant clasts in the matrix arequartz and quartzites, while cherts and potassic feld�spars account for approximately 5%. Fragments ofgranitoids, gangue quartz, crystalline schists, andshale occur are subordinate (Huber et al., 2001).

Median contents of the major rock�forming oxidesin diamictites of the Coronation Formation calculatedfrom data (Huber et al., 2001) are presented in Table 1.The CIA value in them varies from 53 to 84. This isalso reflected in fairly high (~18) standard deviation.Diamictites of two other formations have slightlylower CIA values (77 and 74, respectively). As com�pared to PASS, the diamictites from the CoronationFormation depleted in TiO2, Al2O3, and K2O, whereasthe CaO content significantly varies and is signifi�cantly lower than in the average PAAS in two of threeanalyzed samples (Fig. 2a).

The glacial deposits are much wider spread in theEarly Proterozoic (Early Paleoproterozoic, 2.4–2.2 Ga). The predominance of glaciomarine depositsamong them points to the cover nature of glaciations(Chumakov, 2004). According to Young (2004), theglacial deposits of this time were mainly formed at thepassive craton margins.

One of the most prominent examples of such rocksis the Paleoproterozoic Huronian Supergroup (Fig. 3).North of the Great Lakes, the Huronian sections con�tain three glacial levels: Ramsay Lake, Bruce, andGowganda formations. The Gowganda Formation(~2.3 Ga) is the most known among the glacial levelsof the Huronian Supergroup. The formation is repre�sented by mudstones with extremely thin lamination,which resembles that in the Pleistocene varved clays(Lindsey, 1969; Young and Nesbitt, 1985), and mas�sive diamictites. In the opinion of many researchers,the presence of dropstones confirms the glaciogenicorigin of the mudstones.

As compared to the composition of the upper con�tinental crust (Wedepohl, 1995), the fine�grainedrocks of the Gowganda Formation are enriched in Feand strongly depleted in Ca (Young, 2001). They lacksigns of K�metasomatism, which was possibly causedby relatively low permeability of the rocks. The higherCIA in the mudstones of the Gowganda Formation(~64) as compared to that in the Pleistocene glacio�genic deposits (39–48) suggests significant contribu�tion of the weathered recycled material in these rocks.Mudstones of the Gowganda Formation are alsomarked by the low Sr content, which is atypical of the


GLACIOGENIC AND RELATED SEDIMENTARY ROCKS 379

Pleistocene varved clays and attributed to the moreintense weathering in the Paleoproterozoic (Nesbittand Young, 1982; Kasting, 1987, 1993; Young, 1991).

In the sequence of the Huronian Supergroup, rocksof the Gowganda Formation are underlain by sand�stones of the Serpent Formation (Fig. 3) characterizedby the predominance of plagioclase. Some authorssuggest that these sufficiently exotic rocks were formedby erosion of plagioclase�rich complexes. At the sametime, the results of lithochemical studies (Fedo et al.,1997) suggest that the presence of plagioclases in rocksof the Serpent Formation is related to less intenseweathering in the paleodrainage areas at that time ascompared to the epochs of formation of other sandysequences of the Huronian Supergroup (Young andNesbitt, 1985; Eyles and Young, 1994).

The Serpent Formation is mainly represented bysandstones, with the subordinate role of shales andsiltstones (Fig. 4). Its thickness varies from tens ofmeters to almost 2000 m (Young, 1983; Zolnai et al.,1984). The rocks were subjected to both potassic (illi�tization of kaolinite) and sodic (albitization of plagio�clases) metasomatism (Fedo et al., 1997).

Based on the analysis of paleocurrents, sourcerocks of the Serpent Formation were presumablytonalites, granites, supracrustal rocks and their meta�morphosed analogues from the Archean SuperiorProvince (Long, 1995; Card, 1979; Feng and Kerrich,1992).

In the Al2O3–CaO*+Na2O–K2O, i.e., (A–CN–K) diagram, data points of fine�grained rocks of theSerpent Formation define a near�linear field indicat�ing that the nonweathered source rocks contained pla�gioclase and K�feldspars in the ratio of 5: 1 (Fedoet al., 1997).

Median contents of the major rock�forming oxidesin the fine�grained rocks and sandstones of the Ser�pent Formation calculated using data in (Fedo et al.,1997) are shown in Table 1. The PAAS�normalizedpatterns show that mudstones of the Serpent Forma�tion are characterized by notably lowered contents ofCaO, whereas the Na2O and K2O contents are oftenhigher than those in PAAS (Fig. 3b). As compared tothe PAAS, sandstones of the Serpent Formation aredepleted in TiO2, Al2O3, Fe2O3, MgO (Fig. 3c), andoften CaO. The median Na2Osample/Na2OPAAS andK2Osample/K2OPAAS ratios are 1.29 (minimum 0.64,maximum 3.51) and 0.73 (minimum 0.45, maximum1.58), respectively.

Based on the REE and trace�element distributionpatterns in the sandstones and fine�grained rocks ofthe Serpent Formation, 80% of the source area wereoccupied by tonalites (this fact explains the significantamount of detrital plagioclases in the sandstones),while granitic rocks accounted for ~ 20%. The under�lying and overlying rocks were derived from paleod�rainage area of approximately the same composition.Thus, source areas during accumulation of the Ser�

Formation

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1

2

3

4

5

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7

8

9

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Fig. 1. Schematic section of the West Rand Group of theWitwatersrand Supergroup, simplified after (Smith, 2007).(1) Gravelstones; (2) quartzites; (3) quartz wakes;(4) alternation of shales and siltstones; (5) magnetiteschists; (6) banded iron formation; (7) diamictites;(8) lavas; (9) unconformity.

380


MASLOV

Table 1. Median contents (%) of major rock�forming oxides and CIA values in the glaciogenic and associated deposits of theCoronation, Gowganda, Serpent, Port Askaig, and Mineral Fork formations

Components

Coronation Formation, diamictites

Gowganda Formation*

SerpentFormation, mudstones

SerpentFormation, sandstones

Port Askaig Formation, diamictites

Mineral Fork Formation, diamictites

Mineral Fork Formation, mudstones

Md SD Md SD Md SD Md SD Md SD Md SD

SiO2 71.00 2.17 60.31 61.7 8.01 80.50 6.71 52.21 12.35 72.83 7.62 60.36 6.97

TiO2 0.54 0.09 0.67 0.59 0.27 0.09 0.10 0.51 0.15 0.55 0.14 0.945 0.16

Al2O3 11.30 2.44 17.56 17.68 4.13 7.44 3.52 8.45 1.49 9.13 2.57 18.48 3.00

Fe2O3tot 8.08 2.23 8.65 4.33 2.94 0.80 0.83 4.57 2.67 4.74 2.58 6.26 3.06

MnO 0.07 0.03 0.08 0.03 0.03 0.01 0.02 0.07 0.02 0.06 0.04 0.04 0.04

MgO 2.26 2.41 3.10 2.49 1.74 0.64 0.52 5.42 2.36 3.03 1.09 2.63 0.57

CaO 0.04 2.12 0.9 0.35 1.05 0.18 1.49 8.70 5.05 1.47 1.10 0.37 1.17

Na2O 0.19 0.14 3.07 2.13 1.29 1.55 0.96 0.34 0.61 0.87 0.37 0.60 0.56

K2O 1.88 0.65 3.24 5.80 2.26 2.71 1.18 2.71 0.66 2.73 0.81 5.14 0.83

P2O5 0.05 0.04 0.17 0.18 0.07 0.07 0.02 0.12 0.16 0.10 0.04 0.18 0.05

L.O.I. 3.01 2.27 2.64 2.59 1.74 1.00 1.14 14.43 6.68 2.09 1.21 3.39 1.28

Total 99.70 0.29 100.40 99.97 0.49 99.47 0.33 99.19 0.35 99.54 0.36 99.59 0.51

CIA 83 18 64 62 5 53 9 70 5 60 8 71 6

n 3 9 23 13 21 9 14

Note: Hereinafter: (Md) median; (SD) standard deviation, (n) number of analyzed samples; (*) arithmetic mean.

pent Formation did not contain any unique rocks. Inaddition, the REE distribution patterns in the under�lying (Pecors Formation) and overlying (GowgandaFormation) rocks are highly similar to those of theSerpent rocks (McLennan et al., 1979). Thus, thegreat amount of detrital plagioclase in sandstones ofthe Serpent Formation is related to the specific weath�ering settings during their accumulation (Fedo et al.,1997).

Remarkable example of glaciogenic deposits arediamictites from the Makganyene Formation ascribedto the Paleoproterozoic Transvaal Supergroup (Gri�qualand West Basin) (Polteau et al., 2006). The Mak�ganyene Formation is made up of the massive tocoarsely bedded diamictites, sandstones, shales,banded iron formations (BIF), and stromatolite bio�herms. The diamictite clasts mainly consist of sedi�mentary rocks: sandstones, cherts often displayingconspicuous glacial striations, BIFs, and occasionalcarbonate rocks. The composition of diamictite clastsshows strong variations depending on their location inthe Griqualand West Basin. Rocks of the Makganyene

Formation are overlain by the pillowed basaltic andes�ite lavas of the Ongeluk Formation with the Rb–Sr ageof ~2.22 Ga (Cornell et al., 1998). In general, the bulkchemical composition of the Makganyene diamictitesis close to that of the underlying BIF, but the Al2O3 andTiO2 contents are higher. From the base to top of theMakganyene Formation, the contents of MnO, MgO,and CaO in the diamictites increase, while Fe2O3decreases. It is suggested (Polteau et al., 2006) that thegrowth of MgO and CaO contents is related to theincrease of carbonate component in the diamictites.The average contents of SiO2, Al2O3, and CaO are 55–59, 4–7, and 6–8%, respectively. The content of totaliron (as Fe2O3) reaches 17–22%, while the N2O andK2O contents are typically no more than 0.5%.

In the northern part of the Griqualand West Basin,volcanics of the Ongeluk Formation are overlain byrocks of the Voelwater Subgroup subdivided into theHotazel and Mooidraai formations, which also con�tain diamictites and BIF with a substantial carbonatecomponent. Diamictites of this level are characterizedby a relatively fine�grained structure. They contain

Fig. 2. PAAS�normalized major�element distribution patterns for the glaciogenic and associated rocks. (a) Coronation Forma�tion, Upper Archean Witwatersrand Supergroup; (b, c) Serpent Formation of the Paleoproterozoic Huronian Supergroup:(b) mudstones, (c) sandstones; (d) diamictite matrix of the Port Askaig Formation; (e, f) Neoproterozoic Mineral Fork Forma�tion: (e) diamictites, (f) mudstones); (g, h) Neoproterozoic Fiq Formation in the Wadi Sahtan area: (g) diamictites, (h) mud�stones; (i) diamictites of the Fiq Formation in the vicinity of the Wadi Mistal; (j) fine�grained diamictite matrix and mudstonesfrom the Ayn Formation of the Neoproterozoic Mirbat Group, southern Oman.



10

1

0.1

(а) (b)

(d)

(f)

(h)

(j)

10

1

0.1

(c)

10

1

0.1

(e)

10

1

0.1

(g)

10

1

0.1

(i)

SiO2 TiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O P2O5 SiO2 TiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O P2O5

Аргиллитыформации Айн

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MASLOV

small rounded carbonate clasts (up to 2 cm in size)embedded in a stilpnomelane�rich matrix. The pres�ence of dropstones indicates that the diamictites areglacial formations (Kirschvink et al., 2000). The pro�portions of SiO2, Fe2O3, and MnO in the diamictitesof the Hotazel Formation are similar to those in theBIF from the lower part of the Transvaal Supergroup.At the same time, their major element composition isclose to the average composition of the Makganyenediamictites. In rare cases, the content of total iron ismore than 40%, while SiO2 is less than 40%.

The CIA value calculated from the data in (Polteauet al., 2006) for diamictites of the Makganyene For�mation without any corrections varies from 21 to 72,while the CIA value in diamictites of the Hotazel For�mation is ~9 due to extremely low Al2O3 content(median 4.81, minimum 4.34, maximum 6.58%).

As compared to the average PAAS, diamictites ofthe Makganyene Formation have lower contents ofTiO2, Al2O3, Na2O, and K2O, while the median con�tents of Fe2O3, MgO, and CaO are 3.15, 1.76, and4.53 × PAAS, respectively. The similar pattern is alsotypical of diamictites of the Hotazel Formation,except for SiO2 depletion.

No traces of glaciations were established at higherlevels of the Lower Proterozoic, Lower Riphean, andmajor portion of the Middle Riphean (Chumakov,2004; Eyles and Young, 1994; Braiser and Lindsay,1998; Crowell, 1999; Eyles, 2008). In contrast, sincethe Late Riphean, the glaciations became much more

frequent than in previous epochs and some cyclicity isrevealed in this process.

LATE RIPHEAN AND VENDIAN (NEOPROTEROZOIC)

According to Eyles (2008), a significant part of theNeoproterozoic glacial rocks was localized among theglaciomarine and debris�turbidite marine sequences,which were accumulated in the riftogenic basins. Con�tinental tillites and related deposits are of limitedabundance.

In the Northwest Europe, the British–Irish Cale�donides contain Neoproterozoic Dalradian Supergroup(Fig. 5). Its basal levels have an age of 800–840 Ma(Highton et al., 1999), while zircons from ash interbedin rocks of the uppermost Southern Highlands Groupare dated by the U–Pb method at 601 ± 4 Ma (Demp�ster et al., 2002). Rocks of the Dalradian Supergroupare overlain by the Cambrian Leny limestones (Tan�ner, 1995). The Dalradian section is subdivided intothree glacial units: the Port Askaig Formation, theInishowen�Loch na Cille beds with ice�rafted debris,and the Stralinchy�Reelan Formation consisting ofdiamictites and ice�rafted sediments (Spencer, 1971;Panahi and Young, 1997; Condon and Prave, 2000;McCay et al., 2006). The Port Askaig Formation is

Group Formation

Ell

iot

Lak

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ough

L

ake

Qui

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Lak

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tBar River

Gordon Lake

Lorrain

Gowganda

Serpent

EspanolaBruce

Mississagi Pecors

Ramsey Lake

McKim

Matinenda

1000 m

1

2

3

4

5

6

7

Fig. 3. Schematic stratigraphic column of the HuronianSupergroup, after (Fedo et al., 1997). (1) Diamictites,(2) siltstones, (3) sandstones; (4) volcanic rocks;(5) shales; (6) dolomites; (7) limestones.

50 m

20 m

(a) (b)Gowganda Formation

Espanola Formation

1

2

3

4

5

6

7

8

Fig. 4. Sections of the Serpent Formation in the (a) ElliotLake and (b) Whitefish waterfalls areas, after (Fedo et al.,1997). (1) Diamictites, (2) conglomerates, (3) gravel�stones; (4) sandstones; (5) shales; (6) limestones; (7) dia�bases, (8) unexposed intervals.



located in the Dalradian section, 7–10 km below theash beds dated at 601 Ma, and is likely correlated withthe Sturtian glaciation (~700 Ma). The Stralinchy�Reelan Formation is located approximately 3–5 kmbelow the beds correlated with rocks dated at 601 Ma(McCay et al., 2006). It is made up of the diamictitesand dropstone�bearing rocks. These rocks are overlainby the Cranford sediments, whose carbon isotopic sig�natures are similar to that of the cap carbonates over�lying the Marinoan glaciation (~635 Ma). The glacio�genic beds of the Inishowen�Loch na Cille beds arepresumably correlated with the Gaskiers Glaciation(~580 Ma) (McCay et al., 2006).

Sections of the Port Askaig Formation in the Islay–Garvellachs type area contain 40–50% diamictites(Fig. 6) (Panahi and Young, 1997), as well as sand�stones, siltstones, conglomerates, dolomitic sand�

stones, and dolostones. In the lower part of the forma�tion, the diamictite clasts are mainly represented bydolostones (erosion products of the underlying IslayFormation) (Anderton, 1985), whereas clasts in theupper part of the formation are mainly represented bygranites and their schistose varieties. There are differ�ent opinions concerning the origin of diamictites ofthe Port Askaig Formation. In particular, someresearchers suggest that they represent deposits of thecontinental glacial blanket, while rocks alternatingwith them are aquagene products. In contrast, somegeologists assume that diamictites of the Port AskaigFormation are products of floating ice thawing(Panahi and Young, 1997).

According to the data reported in (Panahi andYoung, 1997), the CIA values in the diamictite matrixof the Port Askaig vary from 60 to 80 (median 70 ± 5).It is noteworthy that the highest CIA values were notedin the lower part of the Port Askaig Formation,whereas diamictites from its middle and upper parts

5 km

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Arg

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Leny limestones(Cambrian)

Inishowen�Loch na Cille Beds

Ash tuffs (601 Ma)

Tayvallich limestones

Cranford Limestones Stralinchy Formation

Bonahaven Dolomites

Port Askaig tillites

Islay limestones

1

2

3

4

Fig. 5. Schematic sections of the Dalradian Supergroup,after (McCay et al., 2006). Rocks: (1) volcanic and alumi�nosiliciclastic; (2) carbonate; (3, 4) aluminosiliciclastic:(3) fine�grained, (4) coarse�grained; (5) diamictites.

Low

er p

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Mid

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Unexposed

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Upp

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2 31 4

5 6 7 8

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Fig. 6. Section across the Port Askaig Formation, simpli�fied after (Panahi and Young, 1997). (1) Conglomerates;(2) light cross�bedded sandstones; (3) brown�red sand�stones; (4) siltstones; (5) varvelike siltstones with drop�stones; (6) beds with disturbed structures; (7) dolostones;(8) diamictites.

384


MASLOV

are characterized by almost normal CIA values. Thehigh CIA values in the diamictites from the lower partof the Port Askaig Formation may be explained by asignificant amount of recycled aluminosilicate mate�rial from the underlying rocks (Panahi and Young,1997).

The median contents of major rock�forming oxidesin diamictites of the Port Askaig Formation calculatedusing data (Panahi and Young, 1997) are listed in Table 1.As compared to PAAS, the diamictites are depleted inTiO2, Al2O3 and often Fe2O3tot (Fig. 2d). Most of thediamictite samples are also depleted in Na2O relativeto PAAS. The CaOsample/CaOPAAS ratio varies from1.12 to 12.70.

In North America, the Neoproterozoic glaciogenicdeposits occur in the Mineral Fork Formation, whichunconformably rests on rocks of the Big CottonwoodFormation southeast of the Great Salt Lake (Ojakan�gas and Matsch, 1980; Young, 2002). The lower part ofthe Mineral Fork Formation is mainly composed ofthick massive diamictites: dark gray rocks with theclayey and sandy matrix containing mainly sedimen�tary clasts of variable size. The diamictites are interca�lated with mudstones, sandstones, and conglomerates(tills and aqueous–glacial deposits) (Fig. 7). Theupper part of the formation contains abundant hori�zontally laminated mudstones (glaciomarine rocksformed under the influence of ice rafting or thawingout from a floating shelf glacier).

The most prominent lithochemical peculiarity ofrocks from the summary Mineral Fork section is asfollows: upward increase of CaO, MgO, Fe2О3, andP2О5 accompanied by decrease of SiO2. The diamic�tites are somewhat enriched in SiO2 as compared tomudstones (~72.8 ± 7.6 against ~60.7 ± 7.0, Table 1)(Young, 2002). Many diamictite samples from theMineral Fork Formation have the value CIA of ~70,which is comparable with values of this index in theaverage shales (PAAS or NASC). However, some ofthem have extremely low CIA values (<50).

In general, diamictites and mudstones from theupper unit of the Mineral Fork Formation have lowerCIA values than counterparts from the lower subunit.The highest CIA values were found in the basal diam�ictites, which suggests that their clastic materialunderwent a significant chemical weathering. Mud�stones from the underlying Big Cottonwood Forma�tion also have high CIA values (77–81). Thus, the“mature” composition of basal diamictites from theMineral Fork Formation presumably marks the pres�ence of a significant amount of local material. This isalso suggested by the analysis of percentage propor�tions of different clasts (Christie�Blick, 1983).

In the A–CN–K diagram, the data points of diam�ictites of the Mineral Fork Formation are locatedabove those of the Paleoproterozoic Gowganda For�mation, indicating a stronger weathering of its constit�uents (Young, 2002). In the CaO–Na2O–K2O dia�gram, the data points of the Paleoproterozoic and

40 m

Lo

we

r

su

bu

ni

t

Unexposed

Up

pe

r s

ub

un

it

1 2 3 4 5

Low

er

Unexposed

subu

nit

Fig. 7. Schematic section of the Mineral Fork Formation,simplified after (Young, 2002). (1) Diamictites; (2) gravel�stones; (3) sandstones; (4) alternation of shales (mud�stones), siltstones, and sandstones; (5) shales (mudstones).



Neoproterozoic glacial deposits also occupy differentpositions. Most of the data points of glacial deposits ofthe Mineral Fork Formation are restricted to the K2Оcorner because of the presence of K�rich sedimentaryrocks in their composition. In contrast, diamictites ofthe Gowganda Formation are depleted in Ca andenriched in Na.

As compared to PAAS, diamictites of the MineralFork Formation are somewhat depleted in TiO2,Al2O3, and K2O (Fig. 2e). The contents of Fe2O3tot,MgO, Na2O, and, especially, CaO in them show widevariations. In particular, the median CaOsample/CaOPAASratio is 1.13, varying from 0.02 to 2.18. For Fe2O3tot,these parameters are 0.73, 0.24, and 1.61, respectively.Mudstones of the Mineral Fork Formation are com�parable with PAAS in terms of SiO2, TiO2, Al2O3,Fe2O3tot, MgO, K2O, and P2O5 contents (Fig. 2f),whereas a significant part of these rocks is appreciablydepleted in CaO and Na2O. Median CaOsample/CaO�PAAS ratio for mudstones from the Mineral Fork For�mation is 0.28, varying from 0.06 to 3.05. The PAAS�normalized median Na2O value is 0.50 (variation from0.07 to 1.84).

Glaciogenic deposits reach significant thickness inthe McKenzie Mountains (Windermere Supergroup)in northwestern Canada (Eisbacher, 1985; Aitken,1991; Eyles, 1993; Eyles and Januszcak, 2004) and inEast Greenland (Moncrieff and Hambrey, 1990).However, lithochemical data on these rocks are scantyand, therefore, they are not considered here. TheNeoproterozoic glaciogenic deposits were also foundin northern and southern Oman (Braiser et al., 2000;Allen et al., 2004; Kellerhals and Matter, 2003; Rieuet al., 2006, 2007a).

In particular, in northern Oman, the Neoprotero�zoic Huqf Supergroup (~725–540 Ma (Allen, 2007) inthe vicinity of Jabal Akhdar comprises the AbuMahara, Nafun, and Ara groups. The sequence of theAbu Mahara Group (~725–645 Ma) includes twointervals of glaciogenic deposits (Ghubrah and Fiqformations) separated by a thick marine sequence.The lower part of the Nafun Formation is made up ofpostglacial carbonates overlain by carbonate and terrig�enous shallow� and coastal�marine deposits. The AraGroup (547–540 Ma) consists of carbonate rocks,evaporites, and organic�rich clay shales with interbedsof volcanic ashes formed on a spacious shallow�waterplatform. The most studied rocks in this section are1500�m thick glaciogenic deposits and marine sedi�mentary rocks of the Fiq Formation, which are over�lain by the 8�m�thick cap carbonates (Hadash Forma�tion) (Leather et al., 2002; Allen et al., 2004). Upsec�tion, the carbonates are gradually replaced by marineshales and sandstones of the Masirah Bay Formation(Fig. 8) (Allen and Leather, 2006). Based on the detri�tal zircon age data (Rieu et al., 2007a), some part ofthe glaciogenic rocks of the Fiq Formation is presum�ably younger than 645 Ma. According to paleomag�netic data, rocks of the Huqf Supergroup were formed

in the lower latitudes (Kempf et al., 2000; Kilner et al.,2005).

Rocks of the Masirah Bay and Fiq formations showwide variations in chemical (Table 2) and mineralcompositions (Rieu et al., 2007a). Normalization toPAAS showed that diamictites of the Fiq Formationfrom the vicinity of the Wadi Sahtan are enriched inNa2O, depleted in CaO, and marked by significantscatter in MgO and P2O5 contents (Fig. 2e). In general,mudstones of the same level are compositionally close toPAAS, but significantly depleted in CaO (Fig. 2h). In theWadi Mistal area, diamictites of the Fiq Formation aredepleted in Fe2O3tot, MgO, and CaO relative to PAAS,but enriched in Na2O (Fig. 2i). Mudstones of theMasirah Bay Formation are also significantly depletedin CaO. The Na2O content in them varies from 0.43 to0.78 × PAAS.

In the A–CN–K and quartz (Qtz)–plagioclase(Pl)–K�feldspar (Kfs) diagrams, data points of thediamictites and associated mudstones define clustersoriented approximately parallel to A–CN and plagio�clase–quartz sides, indicating relation of the mineral�ogical composition of rocks with the intensity ofchemical weathering in the source areas (Fedo et al.,1995; Nesbitt et al., 1996).

Large�scale variations of CIA across the Fiq For�mation section in the Wadi Sahtan area correlate withvariations in the mineralogical index of alteration(Mineralogical Index of Alteration), MIA =quartz/(quartz + K�feldspar + plagioclase) (Nesbittet al., 1996, 1997; Nesbitt and Markovics, 1997) (Fig. 9).This is presumably caused by the enrichment of rocksof the Fiq Formation in clay minerals due to feldsparalteration. Contents and proportions of the major andtrace elements in the considered rocks, as well as theresults of microscopic study, testify that paleodrainageareas were mainly composed of rocks of the granodior�ite composition (Rieu et al., 2007). This is confirmedby the predominance of felsic clasts in diamictites(Allen et al., 2004), while the absence of correlationbetween CIA and geochemical indicators in the sourceareas (for instance, Th/Sc, Al/Ti, and Zr/Ti) suggeststhat CIA variations observed in the Fiq Sequence werenot controlled by rock composition of the paleodrain�age area. There are no data on correlation of CIA vari�ations with facies composition of the rocks.

One more peculiarity of the rocks of the Fiq andMasirah Bay formations is the relatively low Zr/Scratio, which suggests their formation from material ofthe first sedimentation cycle (McLennan et al., 1993).However, the significant amount of sedimentary clasts(on the average, up to 40%) suggests the presence ofredeposited detrital material in their composition.This explains to some extent fairly high CIA values(median ~73), atypical of sediments exclusivelyrelated to physical/mechanical erosion, in glacialrocks of the Fiq Formation.

In general, three levels of rocks with low CIA andMIA values were identified in the Fiq Formation sec�

386


MASLOV

tion. They are interpreted as rocks formed during asignificant weakening of weathering on paleodrainageareas. This is well consistent with the presence ofdiamictites and thinly laminated silty�clayey rockswith dropstones at the levels indicated above. Therocks with relatively high CIA and MIA values lackevidence of glacial sedimentation and are regarded asinterglacial rocks (Rieu et al., 2007). The end of theglacial epoch is marked by the sharp increase of CIA(>80) and MIA (up to 100) in rocks from the lower partof the Masirah Bay. According to (Leather et al., 2002;Allen et al., 2004; Allen and Leather, 2006), thegrowth of CIA in the Fiq and Masirah Bay sectionscoincides with the maximums of transgressions, whiletheir decrease correlates with the appearance ofupward coarsening cycles grading into glacial deposits,i.e., shoaling of the basin. Calculation of the accumu�lation time of the Fiq Formation with the allowancefor sedimentation rate in rift basins suggests that theFiq glacial epoch lasted for ~10 Ma or somewhatlonger (Rieu et al., 2007a, 2007b).

In southern Oman, diamictites of the Ghubrah For�mation, which compose the base of the Huqf Super�group, correlate with the Mirbat Group. The latter issubdivided into two glacial sequences separated bymarine terrigenous rocks about 1 km thick (Fig. 7)(Kellerhals and Matter, 2003; Rieu et al., 2006,2007a). Based on paleomagnetic data, these rocks, likethe rocks of the Huqf Supergroup, were accumulatedin the relatively low (tropical) paleolatitudes (Kempfet al., 2000; Kilner et al., 2005).

Total thickness of the Mirbat Group is 1500 m. Itconsists of the Ayn, Arkahawl, Marsham, and Shareefformations. Rocks of the Ayn Formation were pre�sumably accumulated in the Early Cryogenian withthe detrital zircon age of <722 ± 12 Ma (Rieu et al.,2007). The younger glaciogenic level is represented bythe Shareef Formation, which possibly corresponds todiamictites of the Fiq Formation in northern Oman.

The Ayn Formation is represented by the approxi�mately 400�m�thick sequence of coastal�basin sedi�ments accumulated under the influence of glacial set�

500 m

Jabal Akhdar area Huqf Area

Huq

f Sup

ergr

oup

Abu

Mah

ara

Gro

upN

afun

Gro

upA

ra Fara Fm.

Buah Fm.

Shuram Fm.

MasirahBay Fm.

Hadash Fm.

Fiq

For

mat

ion

Saqlah Fm.

Ghubrah Fm.

Precambrian/Cambrian boundary

(542 ± 0.3Ma

Cap carbonate(~635 Ma)

unconformity712 ± 1.6 Ma

Buah Formation

Shuram Formation

Khufai Formation

Masirah Bay FormationHadash Formation Halfayn Formation;(~802 Ma)

Mirbat area Shareef Formation

Marsham Formation

Arkahawl Formation

Cap carbonate

Ayn Formation

726 ± 0.4 Ma

Mir

bat

Gro

up

1 2 3 4

5 6 7

Khufai Fm.

Fig. 8. Stratigraphic columns of the Neoproterozoic rocks of the Huqf Supergroup and Mirbat Group in the northern and south�ern Oman, after (Rieu et al., 2007a). (1) Dolomites, (2) limestones; (3) shales and siltstones; (4) sandstones; (5) diamictites;(6) extrusive volcanic rocks; (7) basement rocks.



tings indicated by the presence of massive and strati�fied diamictites, thinly laminated silty mudstones withdropstones, faceted and flatiron�shaped clasts withstriation, and so on. Its section demonstrates an alter�nation of intervals of glaciomarine, turbidite, fluvial,and deltaic deposits (Kellerhals and Matter, 2003;Rieu et al., 2006).

Cap carbonates (<4 m) overlain by marine shales(Fig. 10) were found at the base of the Arkahawl For�mation overlying the Ayn Formation (Rieu et al.,2006). Upsection, they grade into the coarse�grainedproximal turbidites alternating with the fine�graineddistal sediments of turbidite fans or deltaic deposits.The upper part of the Arkahawl Formation is repre�sented by the hemipelagic distal siltstones and mud�stones, which are replaced by shallow marine and flu�vial sandstones, siltstones, and mudstones of the Mar�sham Formation. They are overlain by the relativelypoorly exposed diamictites of the Shareef Formation(Rieu et al., 2007a).

In the A–CN–K and Qtz–Pl–Kfs diagrams, datapoints of rocks of the Mirbat Group are plotted paral�lel to the A–CN and Qtz–Pl sides, while glacial rocksof the Ayn Formation in the Qtz–Pl–Kfs diagram arelocalized near the Kfs corner, being compositionallyclose to the unweathered granodiorite (Rieu et al.,2007a). Hence, rock composition in the source areaswas slightly modified by chemical weathering duringthe accumulation of the Ayn rocks.

The median CIA value in the fine�grained matrixof diamictites of the Ayn Formation is 54 ± 2 (Rieuet al., 2007), indicating almost complete absence ofchemical weathering on paleodrainage areas duringtheir formation (cold and dry settings). According to(Nesbitt and Young, 1982), similar low CIA valueswere noted in tills (~52) and glacial clays (~60–65) ofthe Pleistocene. Mudstones of the Arkahawl Forma�tion (interglacial deposits) have median CIA of 76 ± 5,which is comparable with the average values of thisparameter in standard Post�Archean shales (PAAS,NASC, and others).

Rocks from the upper part of the Arkahawl Forma�tion have somewhat lower average CIA and MIA val�ues (60 and 36, respectively). This fact suggests aweakening of chemical weathering during their accu�mulation and gradual transition to cold and arid cli�matic conditions inherent to timing of the overlyingShareef Formation (Fig. 10) (Rieu et al., 2007a).Deposits of the preglacial Ayn and Marsham andinterglacial Arkahawl formations are characterized bysomewhat elevated Al2O3 contents. Hence, these rockscontain material subjected to chemical weathering.

Median contents of the major oxides in rocks of theAyn, Arkahawl, and Marsham formations calculatedaccording to (Rieu et al., 2007a) are presented in Table 3.In terms of the major element composition, the fine�grained matrix of diamictites of the Ayn Formation isvery close to PAAS, but distinguished by much higherNa2O contents (Fig. 2j). This statement is also valid for

Table 2. Median contents (%) of major rock�forming oxides and CIA values in the glaciogenic and related deposits of the Fiqand Masirah Bay formations (in the vicinity of the Wadi Sahtan and Wadi Mistal areas)

Components

Fiq Formation, mud�stones (Wadi Sahtan)

Fiq Formation, diamictites

(Wadi Sahtan)

Masirah BayFormation, mud�

stones (Wadi Sahtan)

Fiq Formation, diamictites

(Wadi Mistal)

Masirah BayFormation, mud�

stones (Wadi Mistal)

Md SD Md SD Md SD Md SD Md SD

SiO2 60.19 4.42 62.53 4.22 63.84 7.56 66.95 5.98 61.32 2.91

TiO2 1.02 0.20 0.97 0.26 0.99 0.25 0.87 0.19 1.02 0.05Al2O3 17.62 2.50 16.53 1.85 16.6 4.15 16.79 3.08 21.46 2.04Fe2O3tot 6.47 1.72 5.90 2.01 4.02 3.55 3.175 1.67 4.03 2.88

MnO 0.07 0.03 0.05 0.02 0.02 0.02 0.02 0.01 0.02 0.02MgO 2.43 0.69 2.36 0.83 1.33 0.83 1.07 0.46 1.40 0.86

CaO 0.44 0.15 0.45 0.23 0.22 0.08 0.49 0.27 0.11 0.02Na2O 1.59 0.67 1.43 0.65 0.65 0.15 2.26 0.48 0.71 0.15K2O 3.66 0.94 4.28 1.06 2.99 0.92 3.74 1.02 4.23 0.49

P2O5 0.24 0.07 0.24 0.16 0.06 0.04 0.24 0.06 0.07 0.01L.O.I. 4.41 0.82 4.34 0.74 4.87 0.64 3.78 1.63 5.45 0.66

Total 100.10 0.54 99.8 0.46 99.35 0.41 100.28 0.33 100.04 0.23CIA 69 5 68 3 77 3 66 2 80 2

76 6 74 5 83 1 71 3 86 1

n 39 17 4 10 6

Note: (*) CIA corrected for the maximal possible value of alterations due to K�metasomatism.

CIAcorrect*

388


MASLOV

the mudstones of this unit. In addition, they have sig�nificantly lower contents of Fe2O3tot, MgO, and CaOthan PAAS. The contents of TiO2, Fe2O3, MgO, andCaO in the matrix of diamictites of the Arkahawl For�mation is lower than those in PAAS, while the Na2Ocontent is about four times higher (Fig. 11a). In termsof SiO2, TiO2, Al2O3, and K2O contents, mudstones ofthe Arkahawl Formation are fairly close to PAAS. Atthe same time, they are significantly depleted in CaO;the majority of analyzed samples are enriched inNa2O; and the total iron content shows wide variations(Fig. 11a). The fine�grained sedimentary rocks of theoverlying Marsham Formation, in contrast, differfrom PAAS only in the contents of CaO (0.44–0.63 ×PAAS), Na2O (1.65–3.60 × PAAS), and K2O (0.65–0.79 × PAAS) (Fig. 11b).

Mineralogical and geochemical data (similar com�position of detrital zircons, relatively constant valuesof Th/Sc ratio, and approximately similar REE pat�

terns) indicate a relatively constant rock compositionof source areas during accumulation of the Ayn, Arka�hawl, and Marsham formations (Rieu et al., 2007a).Correlation is also absent between CIA, on the onehand, and Th/Sc, Al/Ti, and Zr/Ti ratios, on the otherhand. This gives grounds to suppose that significantCIA variations observed in the Mirbat Group are con�trolled by climatic variations rather than variations ofthe rock composition in source areas.

Like the data on petrographic studies, low (<60–63)CIA and PIA (Plagioclase Index of Alteration, PIA = 100 ×(Al2O3–K2O)/(Al2O3 + CaO + Na2O–K2O) (Fedoet al., 1995) found in diamictites of the Grand Con�glomerat and Petit Conglomerat formations, which lieat the base of the Neoproterozoic Nguba and Kunde�lungu groups, respectively, in southeastern Kongosupport the concept of their formation under cold cli�matic conditions, whereas rocks of the higher levelswere presumably accumulated in significantly warmer

1600

m

1200

800

400

060 70 80 100

СIA MIA

T6

T5

T4

T3

T2

T1

Glacialsettings

Intensification of chemical

weathering

1 2 3 4 5 6

60 80

Intensification of chemical

weathering

Glacialsettings

Glacialsettings

Cap carbonate

Fig. 9. Large�scale variations of CIA and MIA values across the section of the Fiq Formation in the vicinity of the Wadi Sahtan,simplified after (Rieu et al., 2007a). (1) Cap carbonates; (2) diamictites; (3) sandstones; (4) shales, siltstones, and fine�grainedsandstones; (5) dropstones; (6) transgression. Numbers are shown according to data in (Leather et al., 2002; Allen et al., 2004).In the CIA curve, solid line denotes corrected values; dashed line, uncorrected values. Error in the CIA determination is less than1.5%. MIA values are given at ±2σ level.



(tropical or subtropical) climatic settings (Batumikeet al., 2006).

One of the most complete sections of the EarlyVendian Lapland glacial horizon is represented in theMiddle Urals (Kvarkush–Kamennogorsk anticlino�rium). According to (Chumakov, 2004), this sectionincludes the entire Serebryanka Group with two thickglacial sequences (Tanin and Koiva formations) andthe lower (diamictite�containing) part of the Staropech�nin Formation of the Sylvitsa Group (Fig. 12). It is sug�gested that these rocks correlate with two glacialepochs of the Lapland glacial period. Each of theseepochs can be subdivided into glacial ages with corre�sponding rock complexes. Such a complex comprisesa set of diamictite units alternating with glaciomarineand/or basin deposits (Chumakov, 1978, 1996, 2004).This intricate sequence was accumulated in the alter�nation zone of distal deposits of floating glaciers on the

shelf and iceberg deposits (Chumakov and Sergeev,2004).

The Serebryanka Group of the Kvarkush–Kamen�nogorsk anticlinorium is subdivided into the Tanin,Garev, Koiva, Buton, and Kernos formations. TheTanin Formation (up to 800 m thick) is made up ofdiamictites (Figs. 13a–13d) intercalated with felds�pathic–quartz sandstones, siltstones, and silty clayeyshales. The Garev Formation (200–750 m) unitesfine�grained sandstones and thinly banded (varved–laminated?) shales. The Koiva Formation (250–300 m) is represented by thin alternation of the phyl�lite�type schists, siltstones, and varicolored lime�stones. Some sections contain packages and beds ofdiamictites (Figs. 13f, 13g). The Buton Formation(300–350 m) comprises banded dark gray low�car�bonaceous shales with rare intercalations of siltstones.The Kernos Formation (200–350 m) consists of sand�stones and phyllite�type silty�clayey rocks. In some

50 60 70 60

1 2 3 4 5 6

20 40

7

0

2

1

Ark

ahaw

l For

mat

ion

Ayn

For

mat

ion

CIA MIA

Glacial epoch II

Interglacialinterval

Венчающиекарбонаты

~722 Ma

Glacial epoch I

Decrease oftemperature;

Rapid increase ofувеличение

температуры

726 ± 0.4 Ma

Fig. 10. Distribution of CIA and MIA across the Mirbat Group section, modified after (Rieu et al., 2007b). Numbers denote for�mations: (1) Marsham, (2) Shareef. Error in the CIA determination is less than 2%. (1) Diamictites; (2) sandstones; (3) leuco�cratic granites; (4) magmatic and metamorphic basement rocks; (5) limestones; (6) shales and mudstones; (7) dropstones.

390


MASLOV

sections (for instance, near the Serebryanka settle�ment), it contains members and units of diamictites(Ablizin et al., 1982).

The Sylvitsa Group is subdivided into theStaropechny, Perevalok, Chernokamen, and Ust’�Sylvitsa formations. The lower part of the StaropechnyFormation (up to 500 m) consists of diamictites (Figs.13g–13i), whereas the upper part is represented by thedark colored sandstones, siltstones, and shales. Rocksof the Staropechny Formation rest on the underlyingrocks with hiatus and fill a set of incised valleys(Ablizin et al., 1982; Grazhdankin et al., 2005). ThePerevalok Formation (~300 m) combines dark graymudstones, sandstones, and gravelstones. Upward,these rocks grade into a thick (up to 1300 m) sequenceof substantially greenish gray fine�grained sandstones,siltstones, and mudstones united into the Chernoka�men Formation. The section of the Sylvitsa Group iscrowned with the polymictic and feldspar–quartzsandstones with thin intercalations of siltstones andmudstones of the Ust’�Sylvitsa Formation (500–600m). Rocks of the three upper formations of the SylvitsaGroup lack any signs of glaciogenic settings.

Table 4 lists median contents of the major rock�forming oxides in the fine�grained rocks and diamic�tite matrix from some levels of the SerebryankaGroup, as well as Staropechny and Chernokamen for�

mations of the Sylvitsa Group1. The fine�grained

matrix of diamictites of the Tanin Formation is char�acterized by fairly high CIA values (median 67 ± 5,

minimum 58, and maximum 69). Approximately thesame values were found in the shales of this level (69 ±3, minimum 62, and maximum 77). The median CIAvalue in shales and silty mudstones of the Koiva For�mation is 71 ± 6. At the same time, the lowest CIAvalue (55) found in our sampling corresponds to valuestypical of the fine alumosiliciclastics weakly trans�formed by chemical weathering, whereas the highestvalue (77) is typical of deposits formed in humid con�ditions. The fine�grained rocks of the Kernos Forma�tion in terms of CIA show no principal differencesfrom rocks of the underlying levels of the SerebryankaGroup (CIAmedian 69 ± 3, minimum 59, maximum 71).The same is true of shales of the Staropechnin Forma�tion of the Sylvitsa Group (CIAmedian 69 ± 6, minimum49, maximum 73), although the minimum CIA valuein these rocks is 10 units lower than that in shales of theKernos Formation. It is noteworthy that the fine�grained alumosiliciclastic rocks of the ChernokamenFormation have the same median CIA value (69 ± 2)as silty mudstones of the Staropechny Formation,although their minimum and maximum CIA values(63 and 73) show significantly lower differences.

Shales of the Tanin Formation are characterized byan extremely weak positive correlation of CIA withTh/Sc (0.32) and La/V (0.19). The same correlationsare observed in silty mudstones and shales of the Ker�

1 In this work, the Chernokamen Formation exemplifies depositsformed in the semiarid/semihumid climate (Maslov and Krupe�nin, 2007).

Table 3. Median contents (%) of major rock�forming oxides and CIA values in the glaciogenic and associated deposits of theAyn, Arkahawl, and Marsham formations

Components

Ayn Formation,matrix of diamictites

Arkahawl Formation,matrix of diamictites

Arkahawl Formation, mudstones

Marsham Formation, mudstones

Md SD Md SD Md SD Md SD

SiO2 60.21 3.61 65.59 0.23 59.09 4.79 64.32 6.29

TiO2 0.77 0.30 0.63 0.01 0.89 0.19 0.96 0.13

Al2O3 16.61 0.63 16.64 0.29 21.36 2.24 15.77 1.26

Fe2O3tot 6.47 1.58 3.30 0.21 4.29 4.50 6.14 0.80

MnO 0.075 0.04 0.02 0.002 0.02 0.06 0.07 0.02

MgO 2.78 1.22 1.54 0.05 1.01 0.43 2.12 0.62

CaO 2.04 0.79 0.76 0.04 0.45 0.11 0.70 0.09

Na2O 4.83 0.36 5.14 0.27 1.615 0.57 3.57 0.87

K2O 2.85 0.40 3.41 0.01 3.36 0.69 2.57 0.21

P2O5 0.22 0.11 0.14 0.01 0.095 0.06 0.20 0.05

L.O.I. 2.81 0.75 2.74 0.08 6.63 1.57 3.71 0.93

Total 99.34 0.43 99.89 0.49 99.90 0.49 100.21 0.56

CIA 54 2 56 1 76 5 62 6

n 4 2 12 8



nos level (rCIA–Th/Sc = 0.04; rCIA–La/V = 0.19). The fine�grained rocks of the Koiva Formation show negativecorrelation of CIA with Th/Sc and La/V (–0.57 and⎯0.22, respectively). Silty mudstones of the Cher�nokamen Formation also lack positive correlationbetween these components (rCIA–Th/Sc = –0.20; rCIA–

La/V = 0.06). All these facts indicate that CIA valuescalculated for the fine�grained rocks of the Serebry�anka and Sylvitsa groups (Kvarkush–Kamennogorskanticlinorium) are controlled by climatic conditionsrather than provenance rock composition.

Comparison with PAAS shows that the diamictitematrix of the Tanin Formation is sufficiently close tothe average PAAS composition (Fig. 11c), whereasshales of this level are characterized by a significant

depletion in CaO (median CaOsample/CaOPAAS = 0.25)and enrichment in Na2O (medianNa2Osample/Na2OPAAS = 1.18). The lowered CaO con�tents are also retained in shales of the Koiva Forma�tion, whereas contents of other rock�forming oxides,with rare exception, are comparable with their con�tents in PAAS (Fig. 11d). The same trend is observedin shales and silty mudstones of the Kernos andStaropechny formations (Figs. 11e, 11f), although theKernos Formation shows some enrichment in Na2Orelative to PAAS. Distribution of the rock�formingoxides in shales and silty mudstones of the Chernoka�men Formation is more “ordered,” but generally lacksany difference from their distribution in the underly�ing rocks (Fig. 11f).

(f)10

1

0.1

(e)

SiO2 TiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O P2O5 SiO2 TiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O P2O5

(d)10

1

0.1

(c)

(b)10

1

0.1

(а)

Fig. 11. PAAS�normalized major�element distribution patterns for glaciogenic and associated rocks. The Neoproterozoic Mirbatgroup, southern Oman: (a) mudstones and fine�grained diamictite matrix of the Arkahawl Formation; (b) mudstones of the Mar�sham Formation; (c–f) Vendian Serebryanka and Sylvitsa groups of the Middle Urals: (c) silty mudstones and fine�grained diam�ictite matrix of the Tanin Formation, (d) silty mudstones of the Koiva Formation, (e) silty mudstones of the Kernos Formation;(f) silty mudstones of the Staropechnin and Chernokamen formations (the latter is distinguished by gray field).

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CONCLUSIONS

Precambrian glaciogenic and related deposits con�sidered in this communication are characterized byfairly wide range of CIA index and diverse chemicalcomposition. In particular, the CIA values in thediamictites and their fine�grained matrix vary from54 ± 2 (Ayn Formation) and 56 ± 1 (Arkahawl Forma�tion) to 70 ± 5 (Port Askaig Formation) and 74 ± 5 (FiqFormation). Among rocks considered in our work, thehighest median CIA value was found in diamictites ofthe Upper Archean Coronation Formation (83 ± 18).However, these rocks contain a negligible amount ofcrystalline clasts. Therefore, such a high CIA valuecan be related to the presence of redeposited sedimen�tary material in their composition. As compared to

PAAS, diamictites of the Coronation Formation aresignificantly depleted in CaO, Na2O, and K2O.

Diamictites of the Neoproterozoic Ayn and Arka�hawl formations with the minimum CIA values aresignificantly enriched in Na2O as compared to PAAS,whereas the CaO content is slightly higher relative toPAAS only in the Ayn Formation. In terms of the K2Ocontent, no significant differences relative to PAASare observed in both cases.

Diamictites of the Mineral Fork Formation(CIAmedian = 60 ± 8) are characterized by relativelyinsignificant depletion in Na2O as compared to PAAS,whereas the CaO content in them can be both higheror lower than in PAAS.

Diamictites of the Port Askaig and formations (themedian CIA value is 70–75) show different trends rel�ative to the average PAAS. The Port Askaig diamictitesare enriched in CaO and depleted in Na2O, while theFiq diamictites are depleted in CaO. The medianNa2Osample/Na2OPAAS ratio varies from ~1.2 near theWadi Sahtan area to ~1.9 in Wadi Mistal.

The fine�grained matrix of diamictites of the LowerVendian Tanin Formation from the western slope ofthe Middle Urals has a median CIA value of 67 ± 5 andshows no significant depletion in CaO, Na, and K rel�ative to PAAS.

The fine�grained terrigenous rocks associated withdiamictites show significant CIA variations: from 60–62 in the Mineral Fork and Marsham sections to 69–76 in the Lower Vendian Tanin, Koiva, Kernos, andStaropechnin sections of the Middle Urals, as well asthe Fiq and Arkahawl sections. As compared to PAAS,mudstones and shales of the majority of the aforemen�tioned lithostratigraphic units are significantlydepleted in CaO (this is a characteristic feature ofmany fine�grained clastic rocks formed not only inglacial settings) and enriched in Na2O to a variableextent (from 1.18 to 1.57 × PAAS). Only mudstonesfrom the Serpent and Marsham formations areenriched in Na2O (approximately two and three times,respectively) relative to PAAS. In the fine�grainedrocks of the Serpent Formation, the K2Omedian is also~1.6 times higher than that in PAAS. However, thisenrichment is attributed to K�metasomatism (Fedoet al., 1997). As compared to PAAS, banded�lami�nated mudstones (with dropstones) of the Paleoprot�erozoic Gowganda Formation are slightly depleted inCaO and K2O (~0.69 and 0.88 × PAAS, respectively),whereas the average Na2O content is approximately2.5 times higher than that in the average Post�ArcheanShale. According to data presented in (Young, 2001),this is also typical of the Pleistocene varves that overliethe Huronian and Archean rocks in the Superior Prov�ince (Canada).However, as compared to PAAS, theyare significantly enriched in CaO (3.3 and 5.9 times,respectively) and somewhat depleted in CaO.

Thus, the data presented above suggest the follow�ing point: it is impossible to distinguish any specific

Low

er V

endi

anU

pper

Ven

dian

Ser

ebry

anka

Gro

upS

ylvi

tsa

Gro

up

Tan

in F

orm

atio

nC

her

nok

amen

For

mat

ion

500 m

1

2

3

4

5

6

1

2

3

4

5

6

7

Fig. 12. Schematic section of the Vendian rocks of theMiddle Urals. (1) Diamictites; (2) sandstones; (3) silt�stones; (4) shales and mudstones; (5) limestones; (6) vol�canogenic rocks. Numbers in the column show the forma�tions: (1) Garev, (2) Koiva; (3) Buton, (4) Kernos;(5) Staropechnin; (6) Perevalok, (7) Ust’�Sylvitsa. Aster�isk denotes volcanic ashes with the U–Pb zircon age of557 ± 13 Ma (Ronkin et al., 2006).



lithochemical parameters typical of only glacial sedi�mentary rocks of the Upper Archean, Lower Protero�zoic (Paleoproterozoic), and Upper Riphean–Ven�dian (Neoproterozoic). At the same time, most of theobjects analyzed in this work are undoubtedly glacio�genic deposits in terms of structures and textures. Onlyin some Neoproterozoic (Oman) and Upper Paleo�zoic (South Africa) sections, the CIA variation trends

in general are consistent with the geological and pale�oclimatic data.

ACKNOWLEDGMENTS

The author is grateful to N.S. Glushkova for thepreparation of figures, as well as to D.V. Grazhdankin

(а) (b) (c)

(d) (e) (f)

(g) (h) (i)

Fig. 13. Diamictites in sections of the Vendian Tanin (a–d), Koiva (e–f), and Staropechnin (g–i) formations of the Kvarkush–Kamennogorsk anticlinorium (western slope of the Middle Urals). Scale bar is 5 cm.

394


MASLOV

and V.N. Podkovyrov for help in collecting therequired literature.

The works were supported by the Russian Founda�tion for Basic Research (project nos. 09�05�00279 and07�05�00455) and the Presidium of the Russian Acad�emy of Sciences (program no. 15).

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Table 4. Median contents (%) of major rock�forming oxides and CIA values in the Vendian glaciogenic and related deposits ofthe Kvarkush��Kamennogorsk anticlinorium (Middle Urals)

Components

Tanin Forma�tion, silty mud�

stones

Tanin Forma�tion, matrix of

diamictite

Koiva Forma�tion, silty mud�

stones

Kernos Forma�tion, silty mud�

stones

Staropechnin Formation, silty

mudstones

Chernokamen Formation, silty

mudstones

Md SD Md SD Md SD Md SD Md SD Md SD

SiO2 60.98 4.66 71.44 1.02 61.59 3.81 63.17 3.86 60.65 4.17 61.26 1.98

TiO2 0.79 0.16 0.54 0.06 0.72 0.14 0.71 0.14 0.76 0.17 0.88 0.06

Al2O3 17.95 2.21 12.51 0.46 17.94 3.18 16.99 1.75 18.73 2.52 16.65 1.20

Fe2O3tot 7.02 1.90 4.82 0.18 7.29 1.77 6.14 2.27 7.41 1.49 7.35 0.76

MnO 0.04 0.02 0.06 0.02 0.05 0.02 0.06 0.05 0.06 0.04 0.09 0.05

MgO 2.23 0.72 1.61 0.33 2.09 0.36 1.99 0.43 2.18 0.34 2.50 0.16

CaO 0.32 0.31 1.06 0.48 0.30 0.49 0.31 0.40 0.21 0.84 0.53 0.19

Na2O 1.42 1.14 1.30 0.61 1.26 0.57 1.89 0.74 1.08 0.74 1.40 0.49

K2O 3.78 1.35 2.47 0.33 4.09 1.50 3.86 0.96 4.94 1.33 4.01 0.47

P2O5 0.18 0.17 0.17 0.04 0.14 0.11 0.14 0.16 0.16 0.17 0.17 0.03

L.O.I. 3.62 0.55 2.95 0.39 3.70 0.57 3.50 0.72 4.13 0.43 4.50 0.54

Total 99.32 0.56 99.22 0.44 99.40 0.51 99.50 0.48 100.22 0.70 99.37 0.75

CIA 69 3 67 5 71 6 69 3 69 6 69 2

n 22 4 35 24 17 75



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Glaciogenic and related sedimentary rocks: Main lithochemical features. Communication 1. Late...

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