Stratigraphy and Geological Correlation, Vol. 6, No. 1, 1998, pp. 34-46. Translated from Stratigrafiya. Geologicheskaya Korrelyatsiya, Vol. 6, No. 1, 1998, pp. 36-48. Original Russian Text Copyright © 1998 by Kuznetsova. English Translation Copyright © 1998 by MAHK HayKa/lnterperiodica Publishing (Russia).

Differentiation of Foraminiferal Assemblages and Dynamics of Their Taxonomic Diversification in the K. I. Kuznetsova Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 109017 Russia Received March 27, 1996; in final form, August 26, 1996

A bstract— Data on Jurassic foraminifers from key localities in continents and oceans is analyzed. Their distri­ bution range spans the stratigraphic interval from the Aalenian to the Tithonian equal to 32 million years. Among 23 localities (including 7 Jurassic sections recovered by deep sea drilling), data for 9 are originally obtained. Information on other localities is presented on the basis of published data. The assemblages studied comprise three types of foraminiferal fauna corresponding to those distinguished by V.A. Basov for different climatic zones: Arctic (cold), Boreal (moderately cold), and Tethyan (warm tropical to subtropical). It is estab­ lished that faunas different not only in dominant components but also in taxonomic composition of a high rank were characteristic of the Tethyan and Peritethyan regions in the Jurassic. Assemblages of different types are present in adjacent sections and even in the same section. Neither climatic fluctuations nor penetration of cold or warm water masses, as well as fauna migration and invasion, can explain this phenomenon. The mosaic dis­ tribution of faunal assemblages and alternation of different fauna types are the result of bathymetric differenti­ ation and related environmental factors such as temperature, type of bottom substrate, hydrodynamics, and dis­ tance to the shore line.

Key words: foraminifers, assemblages, differentiation, paleobiogeography, endemic forms, cosmopolitan forms, bathymetric zonation.

Any stratigraphic and paleobiogeographic study at Analysis of the composition and data on strati­ the stage of generalization implies systematization of graphic and paleobiogeographic ranges of the Jurassic data on regularities in the evolution and distribution of foraminifers (Table 1) shows the following. the fauna and on factors influencing these subjects. The foraminiferal assemblages of the studied strati­ graphic interval (the Aalenian-Tithonian) are repre­ The Jurassic is of great interest in this aspect because sented exclusively by benthic forms. Planktonic fora­ of major reorganizations in the geologic history of conti­ m inifers (Eoglobigerina, Globuligerina, and Conoglo- nents and oceans that happened at that time. bigerina genera) are rare and represented by 11 species The Jurassic represents the middle part of the Meso­ only. These are known from the early Bajocian to the zoic; therefore, its fauna retains the peculiar Early Tithonian inclusive and are confined to the Tethyan, Mesozoic () features and, accordingly, genetic Peritethyan, and Subboreal zones. Planktonic foramin­ relations of many groups of organisms with those of ifers were not found in the Arctic regions (Arctic Can­ preceding epochs. At the same time, it was an epoch of ada, northern Siberia, and Arctic islands). In some formation of new groups, whose evolution and further localities (Turkey, the Russian platform, and Crimea), development were related to the . All the populations of planktonic foraminifers are as abundant factors left their imprints on foraminifers, benthic as thousands of shells per 50 g of rock. Usually, they are assemblages of which inhabited areas from the Arctic sporadic and represented by single specimens. The for­ regions to the southern hemisphere and were unique in aminiferal assemblages studied comprise 177 genera, abundance and diversity during the Mesozoic. which belong to 16 orders. The number of genera in each order is different. More abundant are genera of the Important information on the Jurassic foraminifers Lituolida, Ataxophragmiida, Lagenida, and Rotaliida of continents and oceans has been acquired to date. orders. The dynamics of generic diversification in the Deep sea drilling supplied us with material that Lagenida and Rotaliida orders during the Jurassic is enhanced our understanding of this fauna. Even a gen­ shown in Fig. 2. The comparison of stratigraphic and eral study of the published data shows the marked paleobiogeographic ranges of genera showed that cos­ diversity of the Jurassic foraminiferal assemblages, the mopolitan forms existed longer, as compared to variability of their taxonomic composition and struc­ endemic (both Tethyan and Boreal) genera demonstrat­ ture, and mosaic patterns of their distribution in the ing narrow stratigraphic intervals rarely exceeding a Jurassic sedimentary basins (Fig. 1). stage (geologic age). Arctic Canada

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Fig-1 . Taxonomic composition of Jurassic foraminiferal assemblages (by orders, %): Madagascar after Espitalig and Sigal (1963) and Kuznetsova (1976); Syria after Kuznetsova etal., (1996); Israel after Mayne (1966) and Picard and Hirsch (1987); Egypt, Sinai, after Said and Barakat (1958); Morocco, Central Atlas, after Sossipatrova and Rahhali (1974); Riegraf et ai (1984); India, Kutch Bay, after Bhalla and Abbas (1978); Indian Ocean, Argo Abyssal Plain, DSDP Leg 27, Site 261, after Kuznetsova (1974); Crimea after Kuznetsova and Gorbachik (1985); Sardinia after Azema etal. (1977); Poland after Bielecka (I960), Bielecka and Styk (1968, 1981), and Bielecka and Kuznetsova (1969); England after Cordey (1963) and Kuznetsova (1979); Russian platform after Kuznets­ ova (1979), Grigyalis (1985), and Azbel’ (1989); Arctic Canada after Souaya (1976) and Hedinger (1995); northwestern Atlantic, the Bahamas, DSDP sites 100, 101, 534 after Luterbacher (1972), Gradstein (1978, 1983), and Gradstein and Sheridan (1983). Orders of foraminifers: (1) Astrorhizida, (2) Ammodiscida, (3) Lituolida, (4) Rzehakinida, (5) Trochamminida, (6) Textulariida, (7) Atax- ophragmiida, (8) Orbitolinida, (9) Involudnida, (10) Comuspirida, (11) Spirillinida, (12) Miliolida, (13) Lagenida, (14) Polymor- phinida, (15) Rotaliida, (16) Globigerinida; (I) Tethyan endemics; (II) Tethyan and Subtethyan forms; (III) Boreal and cosmopolitan forms; (IV) Boreal endemics. Table 1. Stratigraphic and paleogeographic ranges of the Jurassic foraminifers

Order, genus J2a J2bj J2bt J2cl J3OX J3km J3t(v) Order Astrorhizida Rhizammina ------— ------—------— Saccammina Hyperammina Bathysiphon Lagenammina Rhabdammina Order Ammodiscida Ammodiscus Ammodiscoides Hemidiscus A renoturrispirillina Lituotuba - Satumella Tolypammina Glomospira Glomospirella Amovertella Turritellella Order Lituollda Reophax ------~ ------— — —------— Haplophragmoides ------~ ----- — Ammobaculites ------— ------Bulbobaculites Ammomarginulina Ammoscalaria Kutsevella — ~------Evolutinella Flabellammina Flabellamminopsis — — Triplasia — ------Frankeina Nautiloculina Phenacophragma ~ ~ ~ ~ ~ ~ ~ ~ ~ Stomatostoecha Placopsilina ------Acruliammina Recurvoides — ------Plectorecurvoides Cribrostomoides Haplophragmium — ------<------Charentia ---~-—------Melathrokerion Labyrinthina Feurtillia ------Order, genus Alveo septa Bramkampella Pseudocyclammina Choffatella Torinosuella Dhrumella Everticyclammina Amijiella A nch is pi rocyclina Pseudospirocyclina Haurania Timidonella Alzonella Limognella Flabellocyclolina Order Trochamminida Eggerella Trochammina Conotrochammina O rder Textulariida Textularia Spirotextularia Spiroplectammina Eomarssonella Marssonella Orientalia Dorothia Riyadhella Redmondoides Riyadhoides Pseudomarssonella Bigenerina Pseudobolivina Order Ataxophragmiida Paleopfenderiuna Pfenderella Sanderella Satorina Steinekella Praekumubia Kumubia Arenovirgulina Gaudryina Vemeuilina Vemeuilinoides Order, genus J2a J2bj J2bt J2cl J 3ox J 3km J3t(v) Belorussiella Paleogaudryina ~~~~~~~~ Gaudryinella Plectina Morulaplecta Karreriella Tritaxia O rder Orbitolinida Kilinanina Meyendorffina — Paracoskinolina — O rder Involutinida Involutina Protopeneroplis Trocholina Order Cornuspirida Comuspira

Ophthalmidium ------~------Dolosella Nubeculinella Nodobacularia O rder Spirillinida Spirillina ------Turrispirillina Conicospirillina Patellina Paalzowella Miliospirella Trochospirillina O rder Miliolida Sigmoilina Quinqueloculina Paleomiliolina Labalina Orthella Comuloculina Miliolinella Order Lagenida Lagena Ichtyolaria Geinitzinita Lingulina Nodosaria Dentalina Vaginulina ■ “ Order, genus J2a J2bj J2bt J2cl J3OX J3kiTi J3t(v) Vaginulinopsis Pseudonodosaria Lenticulina ------~~------Astacolus — ------~ — ----~------Frondicularia Saracenaria Planularia ■ Citharina — — — ~ ------Citharinella Marginulina Marginulinita Ma rg inulinopsis Berthelinella — Dainitella Bojarkaella Neoflabellina ™ “ Falsopalmula Lingulonodosaria Spirofrondicularia Grigelis Order Polvmorphinida Globulina Guttulina — — ------—- Eoguttulina Glandulopleurostomella Glandulina Enantiomorphina Ramulina Ramulinella Paradentalina Bullopora Pyrulinq Order Rotaliida Conorboides Ceratolamarckina Cancrisiella Paulina Praelamarckina Pseudo lamarckina Lamarckella — ~ ------Reincholdella Ceratocancris Mironovella Epistomina ------Epistominita Rectoepistominoides Kaptarenkoella Discorbis — Ceratobulimina Order Globigerinida Eoglobigerina — Globuligerina — ~ ~ ~ ~ ~ Conoglobigerina - Distribution ranges of foraminifers in the Boreal and Arctic areas. - Same in the Peritethys. ------Same in the Tethys. Order Lagenida Order Rotaliida, suborder Robertinina Tithonian y m m m m m r r Tithonian Kimmeridgian Kimmeridgian Oxfordian Oxfordian Callovian Callovian Bathonian Bathonian Bajocian i Bajocian Aalenian Aalenian i i i i S l Toarcian Pliensbachian Pliensbachian MM Sinemurian Sinemurian Hettangian y//////////////y Hettangian MM i i 'm m ...... - 5 10 15 20 25 30 35 Number of genera Number of genera

Fig. 2. Number of Jurassic genera in orders Lagenida and Rotaliida (suborder Robertinina), after Tappan and Loeblich, (1988).

Gordon (1970) was first in systematization of avail­ the Callovian and Oxfordian assemblages from the able data and distinguished two types of foraminiferal Maritime Range of western Syria (Kuznetsova et al., assemblages: shelf communities subdivided into three 1996); the Bajocian and Bathonian assemblages of subtypes, and Tethyan assemblages, which include two Morocco (Hottinger, 1967; Sossipatrova and Rohhali, groups. Gordon’s subtypes of the shelf assemblages are 1977); the Callovian, Oxfordian, and Kimmeridgian as follows: (1) the nodosariid and mixed nodosariid assemblages of Israel and Egypt (Maync, 1966; Said subtype, (2) the subtype dominated by primitive agglu­ and Barakat, 1958); the Tithonian assemblages from tinated forms, and (3) the subtype of secretory benthic the mountains and eastern area of Crimea (Gorbachik foraminifers different from nodosariids of the first sub- and Kuznetsova, 1994), and also from Portugal (Stam, type. The Tethyan foraminifers were subdivided by 1986; Exton and Gradstein, 1984) and Spain (Fourcade Gordon into assemblages with dominant agglutinated et al., 1977). Moreover, I observed in many sections and planktonic forms. that the Tethyan endemic assemblages of the cycla­ minid-pfenderinid type confined to carbonate rocks V.A. Basov (1974) suggested the typification of for­ alternate with assemblages of the nodosariid-episto­ aminiferal faunas on the basis of the areal-genetic prin­ minid type occurring in terrigenous and terrigenous- ciple. He distinguished three types of fauna corre­ carbonate interlayers. It is notable that this alternation sponding to various climatic zones: (1) the nodosariid- may have taken place within one stage or sometimes ammodiscid found in the Arctic zone; (2) the nodosa- within one foraminiferal zone. riid-epistominid found in the Boreal and Subboreal moderately warm zones; and (3) the cyclaminid- The examples cited above show that Basov’s typifi­ pavonitinid (later renamed as cyclaminid-pfenderinid) cation (1974), quite adequate as a whole, ignored an fauna of tropical and subequatorial basins characteris­ important additional factor that influenced the evolu­ tic of the Tethys. The typification clarified our under­ tion and distribution of benthic faunas in the Jurassic standing of the diversity of foraminifer assemblages seas. I believe that the bathymetric zoning of basins, and elucidated their paleobiogeographic features. Nev­ important for the distribution of benthic organisms, ertheless, the subsequent accumulation of data and could be such a factor. Later, Basov also demonstrated especially the detailed study on foraminifers from the its importance for the distribution of Jurassic and Cre­ Jurassic sections of the Tethys (northern Africa, south­ taceous foraminiferal assemblages, and, when analyz­ western Europe, and countries of the Eastern Mediter­ ing their changes in various facies of the Mesozoic oce­ ranean region) showed that this typification was not anic sediments, he showed that the composition of consistently successful as was expected. It was found assemblages was dependent on the depth of their dwell­ that at least the cyclaminid-pfendirinid (Tethyan) and ing (Basov and Vasilenko, 1986; Basov, 1991). nodosariid-epistominid (Boreal) faunas inhabited the My analysis of materials on the problem shows that same climatic zone of the subequatorial Tethys in the the available data characterize Jurassic foraminifers Jurassic time. Geographic ranges of these dissimilar from all bathymetric zones from the abyssal to littoral assemblages were contiguous, and changes in the com­ settings of past basins. These data are supplemented position of the assemblages occurred quickly in the lat­ with information on the facies confinement of benthic eral direction, since it was established in sections organisms and on their taxonomic composition in all spaced only a few dozens of kilometres apart. Such climatic zones of the Jurassic time. It should be pointed abrupt changes in the composition of bottom assem­ out that the climatic zones can be easily recognized by blages are exemplified by the Bathonian assemblages the geographic ranges of the faunas studied, whereas from the Anti-Lebanon and Maritime Ranges of Syria; their bathymetric confinement is detectable on the basis Table 2. Data on Jurassic deposits penetrated by deep sea drilling holes

R egion Age of deposits (by foraminifers) R eferences D epth (m) at present Basin depth in the Jurassic (km) D SD P sites Thickness of deposits (m) North Atlantic 99 Oxfordian-Kimmeridgian 4914 Less than 3 Luterbacher, 1972 North Atlantic 100 Oxfordian-Kimmeridgian-Tithonian 5325 3 Luterbacher, 1972 North Atlantic 105 Oxfordian-Kimmeridgian-Tithonian 5251 630 3 Luterbacher, 1972 North Atlantic 391C T ithonian 4963 1412 3 -3 .5 Gradstein, 1978 North Atlantic 534A Middle Callovian-Tithonian 4974 1636 3 -3 .5 Gradstein, 1983 North Atlantic 367 Oxfordian-Kimmeridgian-Tithonian 4758 3 Kuznetsova and Seibold, 1978 North Atlantic 416 T ithonian 3 -3 .5 Sliter, 1980 Indian Ocean 216 Oxfordian-Kimmeridgian 5125 542 3 Kuznetsova, 1974; Bartenstein, 1974 of some features often missed by investigators, because remarkable that Luterbacher (1972) and Gradstein it is difficult to recognize them in sections. As a result, (1983) reported about planktonic foraminifers of the we observe similar assemblages from shallow-water Globuligerina genus in the Jurassic deposits of the shelf areas of the Arctic and Boreal regions, on the one abyssal bathymetric zone. The available data shows hand, and from deeper zones of tropical seas, on the that deposits directly overlying the basaltic basement other. are the Late Jurassic (Oxfordian, Kimmeridgian, and Naturally, other factors, such as the near-bottom Tithonian) in age. The only exception is Site 534A, temperature, the composition and character of sedi­ where the recovered deposits are referred to the interval ments (the substrate for living organisms), the distance to from the Callovian to the Tithonian (Gradstein, 1983). the shoreline and related hydrodynamic regime, the chem- It should be pointed out that abyssal assemblages of istry and salinity of the water, the content of calcium car­ foraminifers are present only in oceanic sediments pen­ bonate in it, and the trophic and other conditions, are etrated by deep sea drilling. Jurassic deposits of this directly related to the bathymetric zoning of a basin. bathymetric zone have not been found in continents. Deposits of the bathyal zone more widespread in Juras­ It is difficult to present a detailed analysis of all sic sea basins are known in a section of the northwest­ biotic and abiotic factors in a short paper; therefore, ern Atlantic Ocean (the Bahamas region), western I shall try to summarize briefly only data on principal Europe (Holzer, 1969; Feninger and Holzer, 1970), and reasons including the depth and bathymetric zones of a Arctric Canada (Hedinger, 1993). basin, as well as the facies type of deposits, since they Along with primitive agglutinated forms from the all control the taxonomic composition of foraminiferal Astrorhizida order, the bathyal foraminiferal assem­ assemblages, their structure, and geographic ranges. blages comprise ammodiscids, lituolids, and trocham- minids. Foraminifers with a secretory shell (lagenids BATHYMETRIC ZONING AND COMPOSITION and epistominids) are less abundant. Planktonic fora­ OF FORAMINIFERAL ASSEMBLAGES minifers have not been found. Hedinger (1993) reported on the characteristic composition of foramin­ Abyssal assemblages are established in many sec­ iferal assemblages from the Upper Jurassic deposits tions of the Jurassic deposits penetrated by deep sea (the Oxfordian-Volgian) studied in the Richardson drilling (Fig. 1) in the northwestern (Sites 100, 101, Mountains (the Aklavik Range of Arctic Canada). The 105, 534) and eastern Atlantic Ocean (Sites 370, 367, assemblage from clay and shale beds of the Husky For­ 416), and also in the Indian Ocean (Sites 216, 261). mation includes here 95 species of agglutinated foramin­ Data on the Jurassic foraminifers are presented below ifers belonging to 29 genera, as well as 46 secretory spe­ in Table 2 modified after Gradstein (1983). cies of 20 genera. The density of these populations is as The abyssal assemblages, studied in the cited works, high as more than 100 shells per g of the rock sample. comprise representatives of 13 orders and about The foraminiferal assemblages from the Middle 60 genera, including forms with secretory calcite shells Jurassic sections of the Central Atlas (Morocco) pre­ from the Nodosariidae, Lenticulinidae, Ceratobu- sumably characterized the bathyal and partly epibathyal liminidae, and Spirillinidae families. They indicate that deposits (Sossipatrova and Rohhali, 1977) (Fig. 1). sediments and coeval foraminifers were formed above Lagenids comprising the diverse and abundant Citha- the carbonate compensation depth (CCD). It is also rina, Lenticulina, Astacolus, and Planularia species are the dominant group. Similar but more diverse assem­ bear a peculiar foraminiferal assemblage exclusively blages, which include lituolids, trochamminids, and consisting of nodosariids, mainly of Marginulina spe­ ataxophragmiids, are described from the Middle Juras­ cies (Kuznetsova, 1979, Fig. 22). sic (Aalenian-Callovian) deposits of France (Wemli, Foraminiferal assemblages quite different in taxo­ 1971), the Middle and Upper Jurassic deposits of Ger­ nomic composition inhabited shallow-water marine many (Lutze, 1960), and from the eastern Atlantic sediments of the Tethys. Cyclaminid-pfenderinid Ocean (Riegraf e ta l.y 1984; Sliter, 1980). assemblages populated shallow and warm zones of sea The transition to the epibathyal zone is marked by basins rich in calcium carbonate. Such assemblages of an enrichment and transformation of foraminiferal larger foraminifers are unknown beyond the limits of assemblages, in which epistominids and ceratobu- these bathymetric zones of the Tethys. The assem­ liminids (the Rotaliida order), coexisting with diverse blages include genera Paleopfenderinay Meyendorf- agglutinated and secretory foraminifers, play a leading finay Kilianinay Timidonellay Alzonellay Paracoskino- role (Fig. 1). The geographic range of these assem­ linaf Dhrumellay Paraurgoninaf Hauraniaf Kumubiat blages is wider than that of the bathyal assemblages. RedmondoideSy Riyadhellaf Bramkampella and others. They are known from the Middle and Upper Jurassic Representatives of nodosariids, epistominids, polymor­ (Callovian-Tithonian) deposits of Portugal (Stam, phinids, and other smaller foraminifers either are not 1986), the Oxfordian deposits of France (Bastien and present or are represented by single shells seldomly Sigal, 1962), and the Middle and Upper Jurassic encountered. Many genera and families of these assem­ (Bathonian-Tithonian) deposits of Madagascar (Espi- blages are endemic. The species diversity is very low, talie et Sigal, 1963), southern England (Cordey, 1963; whereas the density of populations for some species is Lloyd, 1959, 1962), central Poland (Bielecka, 1960; very high (up to 1000 specimens per 100 g of dry rock). Bielecka and Styk, 1981), eastern Crimea (Kuznetsova This is especially typical of genera Kurnubiaf and Gorbachik, 1985), Sinai (Said and Barakat, 1958), Pseudocyclamminay Choffatellay and Anchispirocy- and the Anti-Lebanon Ridge in Syria (Kuznetsova, clina. Assemblages of this composition are present in 1994; Kuznetsova and Dobrova, 1995; Kuznetsova the Bathonian, Callovian, Oxfordian (very locally), e ta l.t 1996). The presence of Globuligerina bathoni- Kimmeridgian, and Tithonian deposits of Syria (Kuz­ ana (Pazdro), G. oxfordiana (Grig.), and G. callovien- netsova et al.y 1996), France (Peybemes, 1976), the sis Kuzn. is characteristic of sections in Syria, Crimea, eastern Carpathians (Dragastan, 1975), Sardinia Poland, and Portugal. (Azema et al., 1977), Antalia (Bassoullet and Poisson, The further taxonomic diversification of foramin­ 1975), and Morocco (Hottinger, 1967). Incomplete iferal assemblages is observed in the transition to the assemblages consisting of Anchispirocyclinat Choffa- shallower areas of sea basins representing their sublit­ telkiy and Bramkampella forms are found in the Titho­ toral zone. The geographic differentiation of benthic nian carbonate rocks of the Crimea Mountains (Gor­ assemblages from this zone becomes more pro­ bachik and Kuznetsova, 1994) (Fig. 1). A brief review nounced. However, nodosariids (diverse ornamented of the taxonomic composition of foraminiferal assem­ and psilate Lenticulinaf Marginulinay Marginulinopisf blages and their distribution in bathymetric zones of the Citharina, and Citharinella genera) and diverse genera Jurassic sea basins shows that the Jurassic benthic and species of epistominids are still the dominant assemblages inhabited the whole series of settings from groups. Forms with agglutinated shells such as large the abyssal to the littoral zones. Geographic ranges of AmmobaculiteSy Haplophragmoidest Evolitinellat Kut- Jurassic abyssal assemblages were limited. sevella and other genera of lituolids preserve their sig­ More diverse assemblages, which include more than nificance. Abundant polymorphinids inhabited areas 60 genera of agglutinated and secretory foraminifers, remote from the shoreline, where the hydrodynamic are present in sediments from the depth of 2000-3500 m regime was less active. Benthic foraminifers of the sub­ and have wider geographic ranges (the northwestern littoral zone are clearly differentiated in accordance and central Atlantic and Indian Ocean). They are with latitudinal and climatic zones. In the Boreal areas, known only in oceanic sections, where the Upper Juras­ they are diverse and have the above-mentioned taxo­ sic sediments directly overlie the basaltic basement. nomic composition, but, despite a good preservation, they rarely occur in abundance. The sublittoral and lit­ The bathyal zone shows again the increasing taxo­ toral deposits are known on the Russian platform, nomic diversity of foraminiferal assemblages compris­ where in the lectostratotype of the Volgian Stage there ing here more than 80 genera with secretory and agglu­ is the bathymetric succession of the bathyal (?) (the tinated shells, and also planktonic foraminifers upper Kimmeridgian-lower Volgian), epibathyal (the appeared for the first time. The geographic range of middle Volgian), and sublittoral to littoral (the upper assemblages from this zone is also widened, and they Volgian) sediments. The deposits of the littoral zone are are known in northern, western, and central Europe; in represented by shallow-water sediments, namely, by the northern Russian platform; northern Siberia; Arctic quartz, glauconite, and polymictic sands and sand­ islands; northwestern Africa; Hindustan; and the east­ stones, in places coarse-grained, which show numerous ern Atlantic Ocean. The geographic differentiation of traces of erosional unconformities. These sediments their taxonomic composition is poorly pronounced. N um ber o f genera Ml ra 2 M 3

C

Fig. 3. Dynamics of species diversity in dominant genera of the Boreal and Tethyan fauna types of foraminifers: (1) Syria; (2) Crimea; (3) Russian platform and England. (A) Lenticulina and (B) Epistomina genera of the nodosariid-epistominid fauna type. (C) Kur- nubia and (D) Pseudocyclammina genera of the cyclamminid-pfenderinid fauna type.

The epibathyal and outer sublittoral zones (500-200 m Changes in the taxonomic composition of foramin­ deep) display the presence of abundant and diverse for- iferal assemblages in different bathymetric zones of the aminiferal assemblages, which inhabited wide areas in Jurassic seas show that, in addition to the long-lived the Boreal and Tethyan provinces during the Jurassic. cosmopolitan genera demonstrating a high degree of The number of genera, which belong to 16 orders, tolerance and wide geographic ranges, the assemblages increases up to 100-110. The geographic differentia­ in question also comprise endemic genera of highly tion is distinct. specialized forms with a lower degree of tolerance, more limited geographic ranges, and, as a rule, shorter The middle and inner sublittoral (200-100 m deep) existence periods. Other peculiar features of genera of and littoral zones comprise foraminiferal assemblages the two aforementioned types—endemic and cosmo­ diverse in composition and including more than politan—are interesting as well. The quantitative anal­ 100 genera. The geographic and climatic differentia­ ysis of generic and specific diversity is important, first tion is extremely high. The number of endemic genera of all for those genera that dominate in the different- and families increases in the Tethys, whereas the diver­ type assemblages, i.e., in the Boreal nodosariid-episto­ sity of endemic species grows in the Boreal zone. Geo­ minid (widespread) and Tethyan cyclaminid-pfend- graphic ranges of these assemblages are limited. erinid (endemic) faunas (Fig. 3). When the number of species of each indicated gen­ lower, and their life period was limited, not exceeding, era is compared, a clear regularity becomes obvious. as a rule, a stage, i.e., a geological age. The Lenticulina genus is present in deposits of all The analysis of taxonomic composition of foramin­ stages in territories under comparison, although the iferal assemblages from different climatic and bathy­ number of species of the genus in Syria, the Crimea, metric zones allows me to conclude that changes and the Russian platform differs greatly (Fig. 3A). For related to the bathymetric zoning are similar to those instance, the number of Lenticulina species in the that are dependent on the geographic (climatic) posi­ Bathonian deposits is 2 in Syria, 4 in the Crimea, and tion of the assemblages in the Jurassic sedimentary 11 in the Russian platform. The distinction is even basins. The only exception is the foraminiferal commu­ sharper for the Callovian and Oxfordian deposits. The nity of the tropical littoral and sublittoral zones, which Callovian deposits of the Lenticulina genus comprise 3 is unique, as compared to assemblages from other species in Syria, 19 in the Crimea, and 32 in the Rus­ bathymetric and climatic zones of the Jurassic sea sian platform. The Oxfordian deposits of Syria are basins. known to include 11 species of the Lenticulina genus, while 7 are reported from the Crimea and 31 from the Russian platform. Some decrease in the species diver­ ACKNOWLEDGMENTS sity of the Lenticulina genus is observed in the Kim- This study was supported by the Russian Founda­ meridgian, but, in the Tithonian (Volgian), the number tion for Basic Research, project no. 97-05-64884. of species of the genus increases abruptly: the deposits of this age in the Crimea and Russian platform com­ prise 18 and 30 species, respectively, and they yielded REFERENCES only 4 species in Syria. 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