Recognition of upper Triassic temperate foraminiferal assemblages: Insights from the Khodz Group (NW Caucasus, Russia)

https://doi.org/10.1016/j.gloplacha.2020.103152Get rights and content

Highlights

  • Upper Triassic Khodz Group (Great Caucasus) contains diverse Trocholinidae

  • Depositional setting is shallow part of temperate carbonate ramp

  • Foraminiferal assemblage belongs to western Eastern Laurasia bioprovince

  • Trocholinidae retained their diversity during the end-Triassic biotic crisis

  • Refugia for survivors might be sought at high palaeolatitudes or in deeper sea

Abstract

A more than 300 m thick succession of thick-bedded pink to grey limestone of the NorianRhaetian Khodz Group in the NW Caucasus serves to document the development of a temperate carbonate ramp during the final stages of the Cimmerian orogeny. Limestone samples were collected on the west side of Mt. Kolokolnia. The lower part of the Khodz Group contains bioclastic packstone microfacies composed largely of heterotrophic organisms: bryozoans, brachiopods, echinoderms, bivalves, small benthic foraminifers, juvenile ammonoids, agglutinated worm tubes, gastropods, ostracods and sponges. The upper part is comprised of layers of wackestone with frequent evidences of short episodes of emersion. Sponge spicules locally predominate; very few coral fragments also occur. Foraminiferal assemblages of the Khodz Group contain a high proportion of involutinids, including Licispirella violae (Blau), L. iranica (Senowbari-Daryan, Rashidi & Torabi), Coronaserra deminuta (Blau), Coronipora sp., ?Kristantollmanna bicarinata (Blau), Frentzenella perforata Rigaud, Blau, Martini & Rettori, ?Involutina turgida Kristan, ?Trocholina turris Frentzen, and T. ex gr. intermedia/umbo Frentzen, together with porcelaneous foraminifers such as Galeanella tollmanni (Kristan), and Decapoalina schaeferae (Zaninetti, Altiner, Dager & Ducret), which are typical reef dwellers in tropical platforms. Such faunal and foraminiferal association points to a shallow (photic zone) marine depositional environment. Trocholinids are among the most successful survivors of the end-Triassic crisis. The rich occurrence of diversified trocholinids in temperate Triassic seas at high latitudes within the western Eastern Laurasia palaeobiogeographic province suggests that: 1) temperate areas may have played an important role as refugia for marine life during this major biotic event, and 2) the importance of ocean acidification in the selective extinction of marine organisms is overestimated.

Introduction

The “reef-rush” has considerably impacted the study of Triassic carbonate platforms, leaving a grey area outside the tropical belt (palaeolatitudes higher than 35°). Most studies have focused on the Tethyan Realm, particularly the warm, tropical Peri-Tethys area. The study of Triassic foraminiferal assemblages is also clearly unbalanced. Panthalassan and non‑carbonate occurrences of Triassic foraminiferal assemblages were only poorly known until recently (e.g., Apthorpe, 2003; Chablais et al., 2010a, Chablais et al., 2010b, Chablais et al., 2011; Haig and McCartain, 2010; Rigaud et al., 2012, Rigaud et al., 2013a, Rigaud et al., 2013b; Rigaud et al., 2015a, Rigaud et al., 2015b, Rigaud et al., 2016; Rigaud and Martini, 2016), and foraminifers from temperate regions were found (e.g. Efimova, 1975; He, 1980, He, 1982; He and Norling, 1991; Vuks, 2000; Korchagin et al., 2003; Senowbari-Daryan et al., 2010), but never studied as such. The palaeogeographic potential of Triassic foraminifers has, as a result, remained tremendously undeveloped.

The Upper Triassic (Norian – Rhaetian) Khodz Group of the Northern Caucasus was deposited in a marine basin at approximate 40–50° northern palaeolatitude (Stampfli and Kozur, 2006). There, a succession of pinkish and light grey thick-bedded limestone more than 300 m thick contains a rich and diverse assemblage of brachiopods (Dagys, 1963, Dagys, 1974), ammonoids (Shevyrev, 1995), corals and sphinctozoan sponges (Boiko et al., 1991; Belyaeva and Punina, 1994), echinoids, thin-shelled bivalves, sponge spicules, and bryozoans. Previous determinations of foraminifers were performed by Efimova, 1975, Efimova, 1991 and Vuks, 1996, Vuks, 2000, Vuks, 2004. Gaetani et al. (2005) provided new stratigraphic data for the Upper Permian to Jurassic sequences of the Northern Caucasus and identified a rich assemblage of foraminifers in the Mt. Tkhach – Sakhray – Kamennomostsky area, but did not describe the assemblage in detail.

This study provides a thorough account of temperate foraminifers from the Khodz Group and adds important data for the palaeobiogeographic and palaeolatitudinal distribution of Late Triassic foraminifers that support the existence of the Eastern Laurasia palaeobioprovince of Chablais et al. (2011). Compared to tropical-belt shallow marine foraminiferal assemblages, the recorded assemblage contains a relatively high number of diverse trochospiral involutinids, which are known to have remarkably survived the end-Triassic extinction event and characterize more open marine settings in the Early Jurassic (e.g. Gušić, 1975; Blau, 1987a, Blau, 1987b; Blau and Haas, 1991; Ebli, 1993; Blau and Grün, 1997). Their prevalence in high-latitude Triassic shallow seas adds important information in determining the driving factors behind the end-Triassic biotic crisis.

Section snippets

Regional setting

The wide collisional belt of the Caucasus is the result of a long-term convergence between the Eurasian continental margin, Gondwana-derived terranes of Palaeozoic and Mesozoic age (Cimmerian continents), and also the Arabian plate (Nikishin et al., 2001; Golonka, 2004, Golonka, 2007; Adamia et al., 2011). Today, the Caucasus consists of numerous tectonic units (Fig. 1), which comprise, from north to south: (i) the Scythian (pre-Caucasus) platform; (ii) the fold-thrust mountain belt of the

Stratigraphic succession

The Permian – Triassic stratigraphic succession of the Fore Range overlies the Variscan basement that was uplifted and partly dissected during the Late Palaeozoic to form a horst and graben topography. In most areas, Permian clastic sediments filled the grabens, but in the studied Mt. Tkhach – Sakhray – Kamennomostsky area, the metamorphic basement is unconformably overlain by Lower Triassic carbonates of the Tkhach Group (Fig. 4).

An unconformity on the top of the Tkhach Group marks a second

Previous studies of foraminifers in the northern Caucasus

Norian – Rhaetian assemblages of the Khodz Group were previously investigated by Efimova, 1975, Efimova, 1991, Vuks, 1996, Vuks, 2000, Vuks, 2004, and Gaetani et al. (2005). Efimova (1991) and Vuks, 1996, Vuks, 2000, Vuks, 2004 distinguished two local foraminiferal zones for the Triassic of the Caucasian Fore Range. The “Aulotortus friedli” (now Parvalamella friedli) zone in the lower part of the Khodz Group indicates the late Norian, as suggested by the concomitant presence of the bivalve

Material and methods

Rocks belonging to the Khodz Group mainly crop out at the upper reaches of the Tkhach River, forming the highest part of the Bol'shoy Tkhach and of Mt. Kolokolnia, and at Mt. Yatyrgvarta (see Gaetani et al., 2005). Five samples from four levels were collected from a section exposed on the west side of Mt. Kolokolnia (Fig. 4). A total of 27 thin sections of sizes 47 mm × 28 mm, and one thin section of size 15 cm × 10 cm were made. No obvious change in foraminiferal assemblage was detected among

Lithology of the Khodz Group

The Khodz Group consists of thick-bedded pinkish to light grey limestone. The entire group is more than 300 m thick. The Kolokolnia section (Fig. 4) spans only about one-third of the group. Pink bioclastic limestone predominates in the lower part of the section and pink muddy limestone (calcilutite) characterizes the upper part. The limestone displays “dissolution/precipitation and hematite enrichment”, interpreted by Gaetani et al. (2005) as episodes of emersion. Bioclastic limestone and

Depositional environment

The foraminiferal assemblage from the Kolokolnia section corresponds to the Rhaetian (according to great thickness, also late Norian?) Involutina liassica local zone (Efimova, 1991; Vuks, 2000), and its taxonomic composition is remarkably similar to the assemblage described from the Nayband Formation near Esfahan in Central Iran (Senowbari-Daryan et al., 2010). The Norian to Lower Jurassic Nayband Formation is a succession of clastic sediments and, to a minor extent, carbonates, which filled a

Conclusions

The Rhaetian foraminiferal assemblage from the Khodz Group differs from most Late Triassic assemblages from the western Tethys and Panthalassa domains in the abundance of trochospirally-coiled involutinids (Trocholinidae) as well as the paucity and limited diversity of porcelaneous “reef-dwellers”. In view of existing palaeolatitudinal data (40–50° northern palaeolatitude: Stampfli and Kozur, 2006), the heterozoan nature of the carbonate platform and the absence of ooids, we interpret the

Data availability

Any data used in this study and not presented is available on request to the corresponding author.

Declaration of Competing Interest

None.

Acknowledgements

The material investigated in this research was gathered by the late Maurizio Gaetani in the scope of the Peri-Tethys Programme and the Italian MURST–Cofin 1999 programme. The research is financially supported by the Slovenian Research Agency (Programme No. P1-0011 by L.G.). We thank Galina Nestell, one anonymous reviewer, and the editor for their constructive remarks and the time they invested in reading the manuscript.

References (107)

  • S. Adamia et al.

    Geology of the Caucasus: a review

    Turk. J. Earth Sci.

    (2011)
  • A. Aghanabati

    Geology of Iran

    (2004)
  • M. Apthorpe

    Early to lowermost Middle Triassic Foraminifera from the Locker Shale of Hampton-1 well, Western Australia

    J. Micropalaeontol.

    (2003)
  • F. Barattolo et al.

    Shallow carbonate platform bioevents during the Upper Triassic-lower Jurassic: an evolutive interpretation

    Boll. Soc. Geol. It.

    (2005)
  • A. Bartolini et al.

    Disentangling the Hettangian carbon isotope record: implications for the aftermath of the end-Triassic mass extinction

    Geochem. Geophys. Geosyst.

    (2012)
  • G.V. Belyaeva et al.

    Late Triassic corals and sphinctozoa of the northwestern Caucasus

    Albertiana

    (1994)
  • F. Berra et al.

    The evolution of the Tethys region throughout the Phanerozoic: a brief tectonic reconstruction

  • J. Blau

    Neue Foraminiferen aus dem Lias der Lienzer Dolomiten. – Teil I: Die foraminiferenfauna einer roten Spaltenfüllung in Oberrhatkälken

    (1987)
  • J. Blau

    Neue Foraminiferen aus dem Lias der Lienzer Dolomiten. Teil II (Schluss): Foraminiferen (Involutinina, Spirillinina) aus der Lavanter Breccie (Lienzer Dolomiten) und den Nördlichen Kalkalpen

    (1987)
  • J. Blau et al.

    Neue Involutinen (Foraminifera) aus dem marmorea-Hartgrund (Hettangium/Sinemurium, Lias) von Adnet (Österreich)

    N. Jb. Geol. Paläont. (Abh.)

    (1997)
  • J. Blau et al.

    Lower Liassic involutinids (foraminifera) from the Transdanubian Central Range

    Hungary. Paläont. Z.

    (1991)
  • E.V. Boiko et al.

    Phanerozoic Sphinctozoa of the USSR Territory

    (1991)
  • M.K. BouDagher-Fadel

    Evolution and geological significance of larger benthic foraminifera

  • P. Brönnimann et al.

    Lithostratigraphy and foraminifera of the Upper Triassic Naiband Formation

    Iran. Rev. Micropal.

    (1971)
  • J. Chablais et al.

    Microfacies and depositional setting of the Upper Triassic mid-oceanic atoll-type carbonates of the Sambosan Accretionary complex (southern Kyushu, Japan)

    Facies

    (2010)
  • J. Chablais et al.

    Aulotortus friedli from the Upper Triassic gravitational flow deposits of the Kumagawa River (Kyushu, southwest Japan)

    Paleontol. Res.

    (2010)
  • J. Chablais et al.

    Upper Triassic foraminifers from Panthalassan carbonate buildups of southwestern Japan and their paleobiogeographic implications

    Micropaleontology

    (2011)
  • M.-E. Clémence et al.

    Bentho-planktonic evidence from the Austrian Alps for a decline in sea-surface carbonate production at the end of the Triassic

    Swiss J. Geosci.

    (2010)
  • A.E. Črne et al.

    Jurassic neptunian dykes at Mt Mangart (Julian Alps, NW Slovenia)

    Facies

    (2007)
  • A.E. Črne et al.

    A biocalcification crisis at the Triassic-Jurassic boundary recorded in the Budva Basin (Dinarides, Montenegro)

    Geol. Soc. Am. Bull.

    (2011)
  • A.S. Dagys

    Upper Triassic Brachiopods of the South of the USSR

    (1963)
  • A.S. Dagys

    Triassic brachiopods

    Trudyi Inst. Geol. Geof. Novosibirsk

    (1974)
  • R.J. Dunham

    Classification of carbonate rocks according to depositional texture

  • O. Ebli

    Foraminiferen aus dem Unterlias der Nördlichen Kalkalpen

    Zitteliana

    (1993)
  • N.A. Efimova

    Foraminifera from deposits of the Khodz Group of the North-West Caucasus (Tkhach River)

    Trudy VNIGNI

    (1975)
  • N.A. Efimova

    Triassic system

  • A.F. Embry et al.

    A late Devonian reef tract on northeastern Banks Island

    NWT. Bull. Can. Petrol. Geol.

    (1971)
  • L.V. Eppelbaum et al.

    Tectonical-geophysical setting of the Caucasus

  • F.T. Fürsich et al.

    The Upper Triassic Nayband and Darkuh formation of east-central Iran: stratigraphy, facies pattern and biota of extensional basins on an accreted terrane

    Beringeria

    (2005)
  • M. Gaetani et al.

    Stratigraphic evidence for Cimmerian events in NW Caucasus (Russia)

    Bull. Soc. Géol. France

    (2005)
  • L. Gale

    Rhaetian foraminiferal assemblage from the Dachstein Limestone of Mt. Begunjščica (Košuta Unit, eastern Southern Alps)

    Geologija

    (2012)
  • L. Gale et al.

    Critical review of Pseudocucurbitidae (Miliolina, Foraminifera) from the Late Triassic reef environments of the Tethyan area

    J. Micropalaeontol.

    (2012)
  • L. Gale et al.

    Integrated Rhaetian foraminiferal and conodont biostratigraphy from the Slovenian Basin, eastern Southern Alps

    Swiss J. Geosci.

    (2012)
  • I. Gušić

    Upper Triassic and Liassic Foraminiferida of Mt. Medvednica, Northern Croatia (families: Involutinidae, Nubeculariidae)

    Palaeont Jugoslavica

    (1975)
  • D.W. Haig et al.

    Triassic organic-cemented siliceous agglutinated foraminifera from Timor Leste: conservative development in shallow-marine environments

    J. Foramin. Res.

    (2010)
  • Ø. Hammer et al.

    Paleontological data analysis

    (2006)
  • Ø. Hammer et al.

    PAST: Paleontological Statistics software package for education and data analysis

    Palaeontol. Electron.

    (2001)
  • M. Hautman

    Effect of end-Triassic CO2 maximum on carbonate sedimentation and marine mass extinction

    Facies

    (2004)
  • Y. He

    Sketch of the Triassic foraminiferal biostratigraphy of Northwestern Sichuan (Szechuan)

    China. Riv. Ital. Paleont. Strat.

    (1980)
  • Y. He

    Upper Triassic foraminifera of eastern Xizang

  • Cited by (7)

    View all citing articles on Scopus

    Dr Gaetani is deceased.

    View full text