Dispersal events of Triassic-Jurassic boundary faunas, and paleoenvironment of Tibetan Himalaya

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Citation: Yin J R, Fürsich F T. Dispersal events of Triassic-Jurassic boundary faunas, and paleoenvironment of Tibetan Himalaya. Sci China Ser D-Earth Sci, 2009, 52(12): 1993-2000, doi: 10.1007/s11430-009-0162-4

Dispersal events of Triassic-Jurassic boundary faunas, and paleoenvironment of Tibetan Himalaya

YIN JiaRun1† & FÜRSICH Franz Theodor2

1 School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China; 2 Geozentrum Nordbayern, Friedrich-Alexander Universität Erlangen, Loewenichstr. 28, D-91054, Erlangen, Germany

End-Triassic ammonoid and bivalve faunas of the Germig area, Tibetan Himalaya, lived in a tropical, shallow-water environment during the Triassic-Jurassic boundary interval. High stratigraphic resolu-tion based on ammonite-biochrons allows to tracing the place of origin of several faunal elements. The bivalves Aguilerella and Ctenostreon occurred first in the Tibetan Himalaya and migrated from there to the eastern South Pacific, exhibiting a pantropic dispersal pattern. This dispersal route is supported by the distribution pattern of the ammonites Choristoceras, Discamphiceras, Pleuroacanthites, and Psi-loceras calliphyllum. A few taxa, which went extinct everywhere else by the end of the Triassic, sur-vived in the Tibetan Himalaya into early Early Jurassic times. They include the ammonites Choristo-ceras and Eopsiloceras, and the bivalves Newaagia, Terquemia, Persia, Ryderia guangdongensis, and Cultriopsis angusta. This suggests that the Tibetan Himalaya may have played a refugia role in the course of the end-Triassic mass extinction.

end-Triassic mass extinction, paleobiogeography, bivalves, ammonites

The end-Triassic mass extinction remains one of the most poorly known and least understood of the five first-order Phanerozoic extinction events[1,2], which was followed by Early Jurassic recovery and the spectacular success of the marine biota during the rest of the Meso-zoic. Because of their great abundance and often good preservation, bivalves and ammonoids have figured prominently in assessing the magnitude and mode of the end-Triassic mass extinction[3―6]. Recently it has been suggested that the end-Triassic extinction was a more prolonged and less severe crisis, beginning as early as the Middle Norian, and affecting far fewer taxa than previously thought[7,8]. Unfortunately, because of low eustatic sea levels during the Triassic-Jurassic boundary interval, there are very few sites in the world which have preserved the continuous stratigraphic successions that provide details of this event.

The Germig site in the Nyalam area of the Tibetan Himalaya is the only locality in the eastern Tethys Realm where both bivalves and ammonoid successions

has been reported across the Triassic-Jurassic boundary interval (Figure 1), and 18 ammonoid and 25 bivalve species have been described[9―10].

1 Biostratigraphy and paleoenvironment of the Germig area

There exists a detailed biostratigraphic zonation of the Triassic-Jurassic boundary strata of the Germig section based on its ammonite fauna (Figure 2). The Upper Rhaetian, the Lower and at least a part of the Middle Hettangian are documented by the Marshi, Tibeticum, Calliphyllum and Pleuronotum zones[10]. This is the first ammonite fauna spanning the Triassic-Jurassic boundary interval in the Tethyan Realm that is not condensed.

The fact that Neophyllites sp. in association with cho- Received October 20, 2008; accepted May 20, 2009 doi: 10.1007/s11430-009-0162-4 †Corresponding author (email: [email protected]) Supported by National Natural Science Foundation of China ( Grant Nos. 40572013, 40672012) and the National Bureau of Geological Survey (Grant No. 1212010818095)

1994 Yin J R et al. Sci China Ser D-Earth Sci | Dec. 2009 | vol. 52 | no. 12 | 1993-2000

Figure 1 Locality and fossil horizons of the Germig section, Tibetan Himalaya.

ristoceratid exhibits a simplest septal suture line in comparison with those of neophyllitids known in Europe may suggest Neophyllites sp. to be earliest Jurassic form. The choristoceratid specimen which occurs with Neo-phyllites sp. on a slab is a body chamber with septal su-ture line, and has been named as a new species, Choris-toceras nyalamense[10]. This form is different from most species known in Alps by possessing two ranks of stout spines on the outer flank and ventral shoulder, and its septal suture is rather distinctive in possessing both in-cised external and lateral lobes. It is intriguing that the choristoceratid sequence in section B shows a gradual increase of incised lobes from Choristoceras marshi throughout Choristoceras cf. marshi to Choristoceras nyalamense. Septal suture of Choristoceras nyalamense is in agreement with four elements particular to Choris-toceratidae with smooth external, lateral, umbicular and internal saddles. However, incised external lobe has been unknown in any European and American forms. Therefore Choristoceras nyalamense is most likely to represent a latest choristoceratid.

Of particular significance is the Tibeticum zone. The co-occurrence of Choristoceras and Neophyllites in the Gremig section and the first appearance of Psiloceras immediately above imply that this zone approximately corresponds to the Triassic-Jurassic boundary in the sec-tion. Although probably represented by endemic species in Tibet, all three genera offer a significant correlation potential with Triassic-Jurassic boundary sections else-

where in the eastern and western Tethys realms, as well as with the East Pacific coasts of North and South America. This local Tibeticum zone most likely is the equivalent of the Psiloceras spelae zone which has been recognized in Nevada, the Alps, and Peru[10]. The Huh-joch section in the Alps established by Hillebrandt has been currently voted as GSSPs of the TJBWG, and the Psiloceras spelae zone has been defined as the earliest Jurassic biochron. (Bloos, 2008, pers. commun.)

Evidence from both bivalve and ammonite faunas in-dicates that Tibetan Himalaya might have been located at a low latitude, which is indicated by the faunal affini-ties and ecological evidence[9].

Of 18 ammonite species, eight species are regarded as tropical forms as they were originally reported from the Alps or Italy, areas that at that time belonged to the Sub-Mediterranean faunal province (Table 1). The dis-tribution pattern of Choristoceras, in particular, is char-acteristic of a low latitude position[11]. Psiloceras cal-liphyllum has been originally recorded from the Alps[12], and is also known from western Canada[13], pointing to a migration route from Europe via Tibetan Himalaya to the east Pacific domain. Another distinctive lytoceratid, Pleuroacanthites, is the only genus that includes a dwarfed form. The type species, Pleuroacanthites bi-formis, was first reported from Italy[14]. Apart from Ne-vada[15], Germig is the second locality of this genus out-side Europe.

Discamphiceras pleuronotum, which has been first

Yin J R et al. Sci China Ser D-Earth Sci | Dec. 2009 | vol. 52 | no. 12 | 1993-2000 1995

Figure 2 Ammonite and bivalve horizons in the Germig section, Tibetan Himalaya.

recorded from Italy[14], is a dominant species in Middle Hettangian beds of the Germig section. In Nevada, there occurs Discamphiceras silberlingi[15], whereas Discam-phiceras tongdzuyi is an endemic Sinemurian species from Vietnam[16].

Environmental conditions around the Triassic-Jurassic boundary interval may be reconstructed based on a taxonomic and paleoecological analysis of the bivalve fauna. The occurrences of all bivalve species can be well

defined within four ammonite zones (Figure 1). From the Marshi zone of the Upper Rhaetian to the Tibeticum zone of the Hettangian bivalves richness climbs dra-matically from 7 to 19 species. Subsequently, there is a sharp decline in richness from the Tibeticum to the Cal-liphyllum zone. Although many of the bivalves identi-fied also are known from, and in some cases common in, the Mediterranean and Northwest European faunal provinces, endemic taxa make up a significant propor-


Table 1 Endemic and tropical ammonite taxa from the Germig section Endemic taxa (4 of 18) Tropical taxa (8 of 18)

Choristoceras nyalamense Psiloceras tibeticum

Eopsiloceras germigense

Euphyllites cf. struckmanni Discamphiceras pleuronotum

Kammerkarites frigga Neophyllites sp. Psiloceras calliphyllum

Nevadaphyllites cf. psilomorphus Pleuroacanthites aff. biformis Choristoceras marshi Choristoceras cf. nobile

tion of the Rhaetian-Hettangian bivalve fauna from Germig. The endemic peak in the Tibeticum zone of the basal Jurassic is associated with a higher number of taxa that appear to be, at least at the generic level, quite similar to the forms from the taxonomically rich fauna from central Iran[17].

Ecologically, the bivalve fauna is dominated by epi-faunal suspension-feeding pteriods, pectinoids, limoids, and ostreoids. Of these epifaunal groups, the majority is cemented to firm substrates (e.g. plicatulids, pro-spondilids). Epibyssate suspension-feeders (e.g., bakev-elliids and limids) also contribute significantly to the fauna. The diverse epifauna, in combination with its common association with crinoids and the high degree of encrustation and bioerosion of the shells, suggests a shallow, warm, marine environment of normal salinity and low turbidity；the few mobile infaunal bivalves, either suspension-feeders (e.g., veneroids) or detritus feeders (e.g., nuculoids), suggest low rates of sedimen-tation.

Of 25 bivalve species, eight are tropical taxa ranging from the upper Rhaetian to the basal Hettangian, which preferred to live in the tropical or subtropical zone (Ta-ble 2).

Furthermore, by the late Early Jurassic shallow-water carbonate platform environments had become widely established in the Himalayan zone. They have a huge thickness and tropical biostrome-forming bivalves, the lithiotids are widespread.

2 Faunal dispersal patterns

The latest Triassic extinction is one of the most impor-tant episodes of mass extinction in the Phanerozoic. It affected mainly ammonites, brachiopods, and conodonts, but can be confirmed at the generic and subgeneric level also by bivalves. There are very few localities in the world that exhibit a more or less continuous marine sedimentary succession across the Triassic-Jurassic boundary. Recent work on ammonites and bivalves in the Germig section helps to understand the nature of the end-Triassic extinction in Tibetan Himalaya.

The extinction event is drastically expressed by am-monites. In the section, four suborders, the Ceratitina, Ammonitina, Phylloceratina, and Lytoceratina, are rep-resented by 13 genera and 18 species which exhibit a close affinity to Sub-Mediterranean faunas (Figure 3). Traditionally, the Ceratitina went extinct shortly before the Triassic-Jurassic boundary, and Choristoceras has been regarded as an index genus of the Rhaetian stage[18,19]. It is interesting that an endemic species, Choristoceras nyalamense occurs associated with Neo-phyllites sp.[10], although Neophyllites is thought to be the earliest Jurassic psiloceratid[20]. In addition, Eopsi-loceras was once thought to be restricted to the No-rian[21]. Wiedmann[22] showed that it also occurs in the Rhaetian. Rhacophyllites frequently occurs in the Upper Triassic. However, both taxa, Eoplisoceras germigense and Rhacophyllites sp., seem to cross the boundary in the Germig section, ranging from the Marshi to the Ti-beticum zone (Figure 3).

Hallam[3] estimated that nearly half the existing bi-valve genera and nearly all the species failed to survive the end-Triassic extinction event. However, the bivalve fauna of the Germig section, which is biostratigraphi-cally controlled, does not correspond to support this statement. The Upper Rhaetian assemblage (Marshi zone) consists of eight species i.e., Ryderia guandon-

Table 2 Endemic and tropical bivalve taxa from the Germig section

Endemic taxa Tropical taxa Taxa appearing first Taxa disappearing last Ryderia guangdongensis Ryderia guangdongensis Aguilerella Ryderia guangdongensis

Ctenostreon newelli Newaagia lanonglaensis Ctenostreon Cultriopsis angusta Persia hallami Aguilerella sp. Terquemia cf. difformis

Liostrea tibetica Catella cf. laticlava Catella cf. laticlava Newaagia lanonglaensis Cultriopsis angusta Persia

Aguilerella sp. Krumbeckiella timorensis Newaagia Palaeocardita trapezoidalis Terquemia cf. difformis

6 of 25 8 of 25 2 of 25 6 of 25


Figure 3 Ranges of ammonoids of the Triassic and Jurassic boundary interval from the Germig section, Tibetan Himalaya.

gensis, Cassianella sp., Krumbeckiella timorensis, An-tiquilima sp., Astarte sp., Palaeocardita trapezoidalis, Schafhaeutlia sp., and Unionites griesbachi. Two spe-cies, Ryderia guandongensis and Astarte sp., occur in both the Rhaetian and in the Tibeticum zone, thereby crossing the Triassic-Jurassic boundary. Terquemia dif-formis and Cultriopsis angusta are essentially Late Tri-assic forms. The earliest record of Terquemia difformis is from Middle Triassic strata of Germany[23], and this spe-cies is also known from Rhaetian beds of England[24]. However, no species of Terquemia has been recorded from Jurassic strata before. Cultriopsis angusta is a common species, but restricted to Norian strata of Ger-many, North America, and south China[9]. Chlamys va-loniensis is a cosmopolitan species, ranging from Rhaetian to Hettangian beds of England, New Zealand, and Chile[9]. The first record of Catella cf. laticlava is from the Rhaetian of Burma[25] but its age has not been confirmed by ammonites so far. At the generic level, Newaagia and Persia are normally restricted to Middle and Upper Triassic strata[26], their latest records have been known so far being the Norian-Rhaetian of central Iran [17]. However, Newaagia lanonglaensis and Persia hallami from the Germig section must be the youngest record of these genera, as they occur conspicuously in the Tibeticum zone.

Given the distribution of the taxa outlined above, it seems to be without doubt that faunas frequently mi-grated from Sub-Mediterranean areas to Tibetan Hima-

laya. This means that Jurassic paleobiogeographic pro-vincialism became established as early as around the Triassic-Jurassic boundary interval. At that time, Tibetan Himalaya most likely was located at a low latitude, as the most of the taxa exhibit ecological favor living in tropical or subtropic zones. The fact that a few Triassic taxa, including Choristoceras, Newaagia, Terquemia, and Persia, escaped from the end-Triassic mass extinc-tion, surviving in earliest Jurassic time, most likely in-dicates that Tibetan Himalaya served as a refugium dur-ing the extinction event.

Not only do the Triassic forms that survived into the Jurassic time characterize the Germig bivalve fauna, but also the Jurassic taxa Aguilerella and Ctenostreon, which have their earliest record in the area because both occur associated with Psiloceras tibeticum, an index species of the Tibeticum zone in the Germig section[9,10].

As is well known, Aguilerella and Ctenostreon appear in Chile and Argentina earlier than in Europe. Aguil-erella neuquensis is known from the Plienbachian of Argentina[27], and from the Sinemurain of Chile[28]. Ctenostreon wrighti is known from the Sinemurian of North Chile[28] , but occurs in Pliensbachian and Toar-cian strata in Europe[26, 29, 30]. Thus, there is an eastward dispersal route: fauna migrated first from the Himalayas to eastern South America, then did not migrate from the eastern Pacific to the western Tethys until to the Spanish seaway became available in the Toarcian times (Figure 4).


Figure 4 Possible dispersal routes of bivalves and ammonoids during the Triassic and Jurassic boundary interval, as well as in the Toarcian times. Ir, Iran; In, Southeast Asia; Y, South China; NC, North China.

With respect to a long distance migration between the

eastern and southwestern (or Indo-West) Pacific, New-ton[31] suggested a pantropic dispersal pattern. Subse-quently, Damborenea[32] suggested that such migration would have to occur “step by step”. Indeed, migration of Aguilerella and Ctenostreon is reasonably explained this way. Moreover, the data from Tibet confirm that the Hispanic seaway was available for faunal migration be-tween the western Tethys and the eastern Pacific, at least as early as in Pliensbachian time, as suggested before by Damborenea[32] and Nauss and Smith[33].

The distribution of ammonites seems to be similar to that of the bivalves. It has long been known that Cho-ristoceras had a wide tropical distribution. At the ge-

neric level, Psiloceras has a cosmopolitan distribution, but Psiloceras calliphyllum has a tropical to subtropical distribution, being known from the Alps, Tibetan Hima-laya, and western North America[13]. Such a faunal dis-persal pattern might have lasted until the middle Hettan-gian, as Pleuroacanthites and Discamphiceras had mi-grated westward to Nevada by the late Early Hettangian and Middle Hettangian as did early Early Hettangian ammonites (Figure 4).

3 Conclusions Based on facies analysis there is little environmental change from the upper Rhaetian to the Hettangian in the Germig section[34], which may be one of the reasons


why there are unexpected temporal faunal patterns such as the “latest disappearance” or the “first appearance” of some taxa. It would be interesting to further document, with more data, whether Tibetan Himalaya could have acted as a refugium from drastic environmental changes affecting Pangea during the end-Triassic event.

Ammonites and bivalves from the Triassic-Jurassic boundary in the Germig section document that Tibetan Himalaya might have occupied a position in the tropical or subtropical zone. As a result, trans-Pacific faunal migration took place by the pantropic dispersal mode.

Several Tethyan forms first occurred in the Indo-west Pacific at the Triassic-Jurassic boundary interval, then appeared in the eastern Pacific domain during the Sine-murian and Toarcian, and finally migrated to western Europe during the Toarcian, thus confirming that the central Atlantic seaway had become established by the Toarcian. This paper was primarily written during a two-months’ stay (July－August 2007) of Yin J R at the Institute of Geology and Palaeontology of Würz-burg University, Germany, financially supported by the AvH Foundation, which is sincerely appreciated. We thank Dr. Miao Desui and two anony-mous referees for their comments.

1 Sepkoski J J Jr. Phanerozoic overview of mass extinctions, In: Raup D M, Sepkoski J J Jr. eds. Patterns and Processes in the History of Life. Berlin: Springer, 1986. 277―296

2 Hallam A, Wignall B P. Mass extinctions and their aftermath. Lon-don: Oxford University Press, 1997. 1―320

3 Hallam A. The end-Triassic bivalve extinction event. Palaeogeogr Palaeoclimat Palaeoecol, 1981, 35: 1―44

4 McRoberts C A, Newton C R. Selective extinction among end- Triassic European bivalves. Geology, 1995, 23(2): 102―104

5 Page K N. Mesozoic ammonoids in space and Time. In: Landman N H, Tanabe K, Davis R A, eds. Ammonoid Paleobiology. New York and London: Plenum Press, 1996. 756―813

6 Wiedmann J, Kullmann J. Crises in ammonoid evolution. In: Land-man N H, Tanabe K, Davis R A, eds. Ammonoid Paleobiology. New York-London: Plenum Press, 1996. 795―843

7 Hallam A. How catastrophic was the end-Triassic mass extinction. Lethaia, 2002, 35: 147―157

8 Tanner L H, Lucas S G, Chapman M G. Assessing the record and causes of late Triassic extinctions. Earth-Sci Rev, 2004, 65: 103―139

9 Yin J R, McRoberts C. Latest Triassic-Earliest Jurassic bivalves of the Germig Formation from Lanongla (Tibet, China). J Paleontol, 2006, 80(1): 104―120

10 Yin J R, Smith P L, Pálfy J, et al. Ammonoids and the Trias-sic/Jurassic boundary in the Himalayas of southern Tibet. Paleon-tology, 2007, 49: 711―737

11 Wiedmann J. Upper Triassic heteromorph ammonites. In: Hallam A, ed. Atlas of palaeobiogeography. Amsterdam: Elsevier, 1973. 235―249

12 Wähner F. Beiträge zur Kenntnis der tieferen Zonen des Unteren Lias in den nordöstlichen Alpen. Beiträge zur Paläontologie Österreich-Ungarns und des Orients, 2 (1882): 73―85; 3 (1884): 105―124; 4 (1886): 135―226; 9 (1894): 1―54; 11 (1898): 154―178

13 Tozer E T. Latest Triassic (Upper Norian) and earliest Jurassic (Hettangian) rocks and ammonoid fauna, Halfway and Pine Pass

map areas, British Columbia. Current Research, Part A. Geol Surv Canada Paper, 1982, 82-1A: 385―391

14 Canavari M. Beiträge zur Fauna des unteren Lias von Spezia. Pa-laeontographica, 1882, 29: 122―192

15 Guex J. Ammonites hettangiennes de la Gabbs Valley Range (Ne-vada, USA). Mémoires de Géologie (Lausanne), 1995, 27: 1―131

16 Meister C, Khuc V, Huyen D T. Les ammonites du Jurassic inférieur des provinces de Dak Lak et de Hô Chi Minh Ville, Viêt Nam du Sud. Revue de Paléobiologie, Genève, 2002, 21: 439―483

17 Hautmann M. Die Muschelfauna der Nayband Formation (Obertrias, Nor-Rhät) des ostlichen Zentraliran. Beringeria, 2001, 29: 1―182

18 Tozer E T. Canadian Triassic ammonoid faunas. Geol Surv Canada Bull, 1994, 467: 1―348

19 Dagys A S, Dagys A A. Global correlation of the terminal Triassic. Mémoires de Géologie (Lausanne), 1994, 2: 25―34

20 Bloos G. Neophyllites (Ammonoidea, Psiloceratidae) in the earliest Jurassic of South Germany. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 1999, 211: 7―29

21 Arkell W J. Mesozoic Ammonoidea. In: Moore R C, ed. Treatise on Invertebrate Paleontology Part L, Mollusca 4. Kansas: University Kansas Press, 1957. 80―465

22 Wiedmann J. Über den Ursprung der Neoammonoideen-as Problem einer Typogenese. Eclogae Geologicae Helvetiae, 1970, 63: 923―1020

23 Schmidt M. Die Lebewelt unserer Trias. Hohenlohe'sche 4 Buchhandlung Ferdinand Rau, Oehringen. 1928. 1―61

24 Ivimey-Cook H C, Hodges P, Swift A, et al. Bivalves. In: Swift A, Martill D, eds. Fossils of the Rhaetian Penarth Group. Palaeon-tological Association Field Guides to Fossils, 1999, 9: 83―127

25 Healey M. The fauna of the Napeng beds or the Rhaetic beds of Upper Burma. Palaeontol Indica, 1908, 2(4): 1―88

26 Cox L R. Bivalvia. In: Moore R C. ed. Treatise on Invertebrate Pa-leontology, Mollusca 6, Part N. Lawrence: Universith of Kansas Press, 1969. N1―N1224

27 Damborenea S E. Early Jurassic Bivalvia of Argentina, Part 2: Su-perfamilies Pteriacea, Buchiacea and part of Pectinacea. Palaeonto-


graphica (A), 1987, 199(4-6): 113―216 28 Aberhan M. Early Jurassic Bivalvia of northern Chile. Part 1. Sub-

classes Paleontaxodonta, Pteriomorphia, and Isofilibranchia. Ber-ingeria, 1994, 13: 1―115

29 Muster H. Taxonomie und Paläobiologie der Bakevelliidae (Bivalvia). Beringeria, 1995, 15: 1―161

30 Liu C L. Jurassic bivalve paleobiogeography of the proto-Atlantic and the application of multivariate analysis methods to paleo-geography. Beringeria, 1995, 16: 3―123

31 Newton C R. Significance of “Tethyan” fossils in the American Cordillera. Science, 1988, 242: 385―391

32 Damborenea S E. Hispanic Corridor: Its evolution and the biogeog-raphy of bivalve molluscs, In: Hall R L, Smith P L, eds. Advances in Jurassic Research 2000, Proceedings of the Fifth International Symposium on the Jurassic System. Geol Res Forum, Trans Tech Publishers, Zürich, 2000, 6: 369―380

33 Nauss A L, Smith P L. Lithiotis (Bivalvia) bioherms in the Lower Jurassic of east central Oregon, U.S.A. Palaeogeogr Palaeoclimat Palaeoecol, 1988, 65: 253―268

34 Hallam A, Wignall P B, Yin J R, et al. An investigation into possible facies changes across the Triassic-Jurassic boundary in southern Ti-bet. Sediment Geol, 2000, 137: 101―106

Dispersal events of Triassic-Jurassic boundary faunas, and paleoenvironment of Tibetan Himalaya

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