Hindeodus Research Articles

Some aspects of the Permian–Triassic boundary (PTB) and of the possible causes for the biotic crisis around this boundary

The first appearance datum (FAD) of Hindeodus parvus is an excellent datum very close to the base of the Otoceras woodwardi Zone (priority base of the Triassic). For the first time, it allows an exact correlation of the PTB in all marine facies and faunal realms. The following features of the extinction and recovery patterns near the PTB are most important for the search for causes of the PTB biotic crisis: (1) most strongly affected were the (siliceous) plankton (radiolarians) and the warm-water benthos and nekton; (2) most of the cold-water faunas were not significantly affected; (3) the recovery of the warm-water benthos and siliceous plankton occurred only after an unusually long time (during the late Olenekian and Middle Triassic); (4) the productivity of the terrestrial plants dropped strongly and the recovery was mainly in the upper Olenekian and in the Middle Triassic; (5) several terrestrial extinction events occurred at different levels within the Upper Permian, considerable before the marine PTB; at or close to the FAD of Lystrosaurus no extinction event in the terrestrial faunas can be observed; (6) terrestrial faunal elements that survived the Dzhulfian–Dorashamian extinctions were able to survive some months of extreme climatic conditions by hibernation-like life stages (vertebrates), or by dry- and freezing-resistant eggs (conchostracans); (7) about 50% of the genera that disappeared at the PTB re-appeared in the Olenekian–Middle Triassic interval (Lazarus taxa), or in this time interval genera appeared that had undoubtedly evolved from genera that had disappeared at the PTB; and (8) the PTB is preceded by mass occurrences of marine (and continental?) fungi, and the fungal spike ends abruptly a little before the PTB. A scenario for the PTB biotic crisis is elaborated that takes into consideration: the real (not interpolated) diversity patterns of different marine and continental fossil groups, the exact correlation of bioevents in different faunal realms and facies, the strong biotic crisis in the Tethyan warm-water faunas in contrast to the much weaker biotic event in cold-water faunas, the severe Dzhulfian–Dorashamian climate in many parts of the world caused by the continent–ocean configuration and by Siberian Trap volcanism, the cooling of the Boreal area by the northward drift of Pangaea that interrupted the exchange of warm-water benthos between the Tethys and western North America during the Guadalupian, the extinction event at the Guadalupian–Lopingian boundary that restricted most of the affected warm-water faunas to the Tethys, the importance of lower Scythian anoxia that reached an unusually shallow level, and above all the effects of the contemporaneous huge volcanic events about 250 m.y. ago on the Siberian Platform and in the eastern Tethys that caused a 3–6-months-lasting volcanic winter with strong cooling in low latitudes, followed by a strong global warming.

Permo-Triassic boundary and Lower to Middle Triassic in South Tibet

The abundance of conodonts increases sharply across the Permian/Triassic boundary in South Tibet, and as a consequence Griesbachian assemblages are much better defined than Changxingian ones. The “ Otoceras latilobatum bed”, representing the base of the Triassic at Selong, is a condensed biocalcirudite including abundant macrofossils (crinoids, corals, bryozoans, brachiopods) of Permian aspect associated with a varied conodont assemblage (including Hindeodus parvus) of early Griesbachian age. Condensation and reworking at the P/T boundary is interpreted as related to starvation and subaqueous erosion/redeposition during rapid transgression at the base of the Triassic rather than to subaerial exposure during a first-order sea-level drop. All of the Lower Triassic is strongly condensed, particularly in the west (Gyirong and Selong) where total thickness is 6.5 m at most, to 8.5 m; thickness is more comparable with other Himalayan localities at Tulong, where the Dienerian to Spathian section reaches 20 m. As in central Nepal, carbonate intervals dated as early Griesbachian to Dienerian, early to mid-Smithian and latest Smithian to earliest Aegean are separated by two mudrock intervals (locally reduced to millimetric interbeds) dated as late Dienerian or earliest Smithian and late Smithian. Condensed wackestone/packstone intervals were deposited during transgressive stages on the outermost shelf to continental slope. During highstand stages, mudrock intervals slowly accumulated on the outer shelf, whereas only a thin veneer of mud was deposited close to the shelf-break. Oceanic currents, intruding onto the outermost shelf during peak transgressions, are inferred to be the main causes of winnowing and resuspension of mud during the Spathian, when oxidized packstones in “Ammonitico Rosso” facies were deposited at Tulong. Grey limestones locally with bacterial mats or containing agglutinated foraminifers and intercalated black mudrocks indicate instead dysoxic conditions, which were widespread from Griesbachian to Smithian times. The Middle Triassic is mostly represented by marls and marly wackestones with crinoids, pelagic bivalves and benthic foraminifers. A notable increase in silty to sandy quartzo-feldspathic detritus is recorded at mid-Aegean times, and very fine-grained subarkoses characterize the mid-Anisian section at Tulong. Terrigenous supply was renewed probably in the Early Carnian, but accumulation rates sharply increased only in the latest Carnian and Norian.

The Conodonts Hindeodus, Isarcicella and Sweetohindeodus in the Uppermost Permian and Lowermost Triassic

Illindeodus REXROAD & FURNISH, 1964 and Isarcicella KOZUR, 1975 belong to the stratigraphically most important fossils near the Permian-Triassic boundary. The first appearance of H. parvus (KOZUR & PJATAKOVA) in the phylomorphogenetic lineage H. typicalis - H. latidentatus praeparvus - H. parvus is the best marker for the P/T boundary. Some representatives of Hindeodus and Isarcicella are insufficiently known. Consequently, all known lHindeodus and Isarcicella species from near the P/T boundary, are redescribed or discussed. Hindeodus parvus erectus n.subsp.., H. julfensis wardlawi n.subsp., H. latidentatus praeparvus n.subsp. and H. sosioensis n.sp., and the new genus Sweetihindeodus n.gen. with two species, Sweetohindeodus bidentatus n.gen. n.sp. and S. tridentatus are proposed.

The importance of Hindeodus parvus (Conodonta) for the definition of the Permian-Triassic boundary and evaluation of the proposed sections for a global stratotype section and point (GSSP) for the base of the Triassic

The biostratigraphic Permian/Triassic (P/T) boundary is defined by the first appearance of H. parvus. The first appearance of H. parvus within the cline H. latidentatus-H. parvus is a globally recognizable event in the conodont evolution. The first appearance of H. parvus is not facies related and can be observed both in ammonoid-free shallow-water deposits and in ammonoid-bearing pelagic deposits. H. parvus is a common, easily determinable species known so far from the entire Tethys, Japan, western North America, Boreal realm (Greenland) and the Tethyan margin of Gondwana. H. parvus is the first species with world-wide distribution to appear after the absolute minimum in the faunal diversity indicated by the minimum in δ13C. The Meishan section (South China) contains a continuous, pelagic sedimentary record across the P/T boundary without stratigraphic gaps. It is nearly unaltered thermally (CAI = 1-1.5). Its fossil content (ammonoids, conodonts, foraminifers, bivalves, brachiopods, sporomorphs etc.) and event succession have been thoroughly studied. Absolute age and magnetostratigraphy have also been subjected to intensive studies. The section is readily accessible and under protection of the government. This section is best suitable as a global stratotype section and point (GSSP) for the base of the Triassic. No other section in the world is known to be qualified for defining the P/T boundary in a GSSP. H. parvus made its earliest appearence in the middle part of Boundary Bed 2 (Bed 27) at Meishan. It evolved within Bed 27 from H. latidentatus within a phylomorphogenetic continuum in a continuous and monofacial stratum. The biostratigraphic P/T boundary lies very close to the event boundary (15cm above the event boundary at the base of Boundary Bed 1 = Bed 25, and a few centimetres above the minimum in δ13C in the lower Boundary Bed 2).

Guadalupian (Middle Permian) Conodonts of Sponge-Bearing Limestones from the Margins of the Delaware Basin, West Texas

The Guadalupian Series (with Roadian, Wordian and Capitanian stages in ascending order) is very suitable for world-wide application as the Middle Permian standard. The conodont faunas of the Delaware Basin and its slope are dominated by pelagic forms represented by ribbed Mesogondolella restricted to the Middle Permian of intraplatform basins and to near-shore slopes of tropical open seas. The first appearance of the serrated Mesogondolella nankingensis (CHING) is important for the definition of the base of the Middle Permian (base of the Guadalupian Series = base of the Roadian Stage). Mesogondolella nankingensis evolved in a phylomorphogenetic cline from the unserrated M. idahoensis (YOUNGQUIST, HAWLEY & MILLER) through transition forms closely related to M. phosphoriensis (YOUNGQUIST, HAWLEY & MILLER). The appearance of serrated Mesogondolella is a very characteristic event in Permian conodont evolution, which can be traced in southwestern and western North America, Arctic Canada and in China. This event is very suitable for the world-wide correlation of the base of the Middle Permian Guadalupian Series. At the upper boundary of the Guadalupian, the serrated Mesogondolella shannoni WARDLAW changed in a phylomorphogenetic cline into the smooth Clarkina altudaensis KOZUR. This cline was also found in intraplatform basins of the eastern Tethys (China). For this reason, the top of the Guadalupian can be well correlated with the Tethyan scale, in which the Late Permian Lopingian Series is defined. The first appearance of Clarkina crofti KOZUR & LUCAS in the uppermost Lamar Limestone and in the uppermost Altuda Formation is very important as it is penecontemporaneously with the first appearance of C. altudaensis. This species is restricted to greater water depths. Two new conodont species, Hindeodus gulloides n. sp., and H. altudaensis n.sp. are described. Additionally, Clarkina crofti KOZUR & LUCAS n.sp. is described to avoid the use of nomina nuda, because the paper of KOZUR & LUCAS (in press) has not yet been printed.

Biostratigraphy and correlation of several Permian-Triassic boundary sections in southwestern China

Detailed investigations of five complete Permian-Triassic boundary sections in southwestern China demonstrate the transitional nature of the Permian-Triassic boundary and the presence of a white clay at the boundary in the working area. The uppermost Permian is represented by the Neochonetes substrophomenoides-Notothyris crassa-Waagenites pigmaea brachiopod assemblage or the Clarkina changxingensis-C. deflecta conodont zone. The transitional beds of basal Triassic are represented by the Lingula fuyuanensis-Crurithyris flabelliformis brachiopod assemblage, or the Pteria ussurica variabilis-Towapteria scythicum-Eumorphotis multiformis bivalve assemblage, which is overlain everywhere by the Pseudoclaraia wangi bivalve zone. Faunal correlations show that the stratigraphy and faunal composition of the Permian-Triassic boundary sections in southwestern China do not differ substantially from the other two Global Stratotype Section Point candidates in south China and the transitional beds approximately correspond to the Otoceras woodwardi ammonoid zone, but the Hindeodus parvus conodont zone only corresponds to the upper part of transitional beds.

Hindeodus parvus ‐ proposed index fossil for the Permian‐Triassic boundary

<i>Hindeodus parvus ‐</i> proposed index fossil for the Permian‐Triassic boundary