The Permian–Triassic transition and the onset of Mesozoic sedimentation at the northwestern peri-Tethyan domain scale: Palaeogeographic maps and geodynamic implications

The main aim of this paper is to review Middle Permian through Middle Triassic continental successions in European. Secondly, areas of Middle–Late Permian sedimentation, the Permian–Triassic Boundary (PTB) and the onset of Triassic sedimentation at the scale of the westernmost peri-Tethyan domain are defined in order to construct palaeogeographic maps of the area and to discuss the impact of tectonics, climate and sediment supply on the preservation of continental sediment.At the scale of the western European peri-Tethyan basins, the Upper Permian is characterised by a general progradational pattern from playa-lake or floodplain to fluvial environments. In the northern Variscan Belt domain, areas of sedimentation were either isolated or connected to the large basin, which was occupied by the Zechstein Sea. In the southern Variscan Belt, during the Late Permian, either isolated endoreic basins occurred, with palaeocurrent directions indicating local sources, or basins underwent erosion and/or there was no deposition. These basins were not connected with the Tethys Ocean, which could be explained by a high border formed by Corsica–Sardinia palaeorelief and even parts of the Kabilia microplate. The palaeoflora and sedimentary environments suggest warm and semi-arid climatic conditions.At the scale of the whole study area, an unconformity (more or less angular) is observed almost everywhere between deposits of the Upper Permian and Triassic, except in the central part of the Germanic Basin. The sedimentation gap is more developed in the southern area where, in some basins, Upper Permian sediment does not occur. The large sedimentary supply, erosion and/or lack of deposition during the Late Permian, as well as the variable palaeocurrent direction pattern between the Middle–Late Permian and the Early Triassic indicate a period of relief rejuvenation during the Late Permian. During the Induan, all the intra-belt basins were under erosion and sediment was only preserved in the extra-belt domains (the northern and extreme southern domains). In the northern domain (the central part of the Germanic Basin), sediment was preserved under the same climatic conditions as during the latest Permian, whereas in the extreme southern domain, it was probably preserved in the Tethys Ocean, implying a large amount of detrital components entering the marine waters. Mesozoic sedimentation began in the early Olenekian; the ephemeral fluvial systems indicate arid climatic conditions during this period. Three distinct areas of sedimentation occur: a northern and southern domain, separated by an intra-belt domain. The latter accumulated sediments during the Early–Middle Permian and experienced erosion and/or no-deposition conditions between the Middle–Late Permian and the beginning of Mesozoic sedimentation, dated as Anisian to Hettangian. At the top of the Lower Triassic, another tectonically induced, more or less angular unconformity is observed: the Hardegsen unconformity, which is dated as intra-Spathian and is especially found in the North European basins. This tectonic activity created new source areas and a new fluvial style, with marine influences at the distal part of the systems. During the Anisian and Ladinian, continental sedimentation was characterised by a retrogradational trend. In other words, the fluvial system evolved into fluvio-marine environments, attesting to a direct influence of the Tethys Ocean in the southern and northern domains. Both at the end of the Olenekian (Spathian) and during the Anisian, the presence of palaeosols, micro- and macrofloras indicate less arid conditions throughout this domain.     

Early Triassic vertebrate burrows from the Katberg Formation of the south‐western Karoo Basin,South Africa

Bordy, E.M., Sztanó, O., Rubidge, B.S. & Bumby, A. 2010: Early Triassic vertebrate burrows from the Katberg Formation of the south‐western Karoo Basin, South Africa. Lethaia, Vol. 44, pp. 33–45. Very large (～30–35 cm), uniform diameter cylindrical burrows were found at two localities, ～100–110 m above Permo‐Triassic boundary in the fluvial Katberg Formation (main Karoo Basin, South Africa). Analysis of their morphology and stratigraphical distribution allows us to improve both the understanding of the ethology of burrowing, and also the reconstruction of the earliest Triassic ecosystems. These burrows have a single opening that leads, via a large, uniform diameter, semi‐horizontal tunnel, to a rounded terminus. These 3‐m‐long structures descend at angles of ～30° to a maximum of 1.5 m depth. They are devoid of chambers, branching, cross‐cutting, coiling or spiralling. Filled with coarse sediments, some have a <5‐mm clay lining, and most have subtle indentations and various scratch marks. These burrows were possibly excavated as resting, hiding or aestivating shelters, and are tentatively attributed to dicynodonts (i.e. Lystrosaurus murrayi and L. declivis). Data suggest that burrowing was widespread after the P/Tr boundary event, when in this part of Gondwana, dryland fluvial systems had large fluctuations in flow with extended low‐flow periods or drought punctuated by high‐discharge periods. We hypothesize that these constructed refuges played a role in the biodiversity recovery and maintenance in the Early Triassic (Induan) ecosystem. □Early Triassic, Karoo Basin, Katberg Formation, South Africa, Tetrapod Burrows.     

Extremely distal fluvial sandstone within the playa system of Arnstadt Formation (Norian,Late Triassic), Central Germany

The Wachsenburg Sandstone of Thuringia (Central Germany) occurs within playa deposits of the Arnstadt Formation (Late Triassic, Norian) and furnishes an example of ephemeral river metamorphosis under dryland conditions. Characterized by high flow regime features, the sand-dominated lithofacies constitution exhibits sedimentation by channel processes under the influence of recurring flash floods. Bearing signatures of subaerial exposures, the fining-upward lithofacies cycles are bound by low-angle lateral accretion elements suggesting deposition in a meandering stream. Channel migration in response to point bar expansion and active bank erosion, led to the development of four laterally shifting point bar events. Unimodal palaeocurrent patterns with low variance and azimuthal dispersion support the point bar origin of the Wachsenburg Sandstone. With reduced water budget under largely semi-arid climate, the river progressively became smaller, highly sinuous and ultimately abandoned. The resulting point bar succession was finally covered with sheet flow deposits of over bank origin. The sandstone was deposited during a period of low base-level when the playa system temporarily fell dry.     

Formation Conditions and Sedimentary Characteristics of a Triassic Shallow Water Braided Delta in the Yanchang Formation,Southwest Ordos Basin,China

A large, shallow braided river delta sedimentary system developed in the Yanchang Formation during the Triassic in the southwest of the Ordos basin. In this braided delta system, abundant oil and gas resources have been observed, and the area is a hotspot for oil and gas resource exploration. Through extensive field work on outcrops and cores and analyses of geophysical data, it was determined that developments in the Late Triassic produced favorable geological conditions for the development of shallow water braided river deltas. Such conditions included a large basin, flat terrain, and wide and shallow water areas; wet and dry cyclical climate changes; ancient water turbulence; dramatic depth cycle changes; ancient uplift development; strong weathering of parent rock; and abundant supply. The shallow water braided river delta showed grain sediment granularity, plastic debris, and sediment with mature composition and structure that reflected the strong hydrodynamic environment of large tabular cross-bedding, wedge cross-bedding, and multiple positive rhythms superimposed to form a thick sand body layer. The branch river bifurcation developed underwater, and the thickness of the sand body increased further, indicating that the slope was slow and located in shallow water. The seismic responses of the braided river delta reflected strong shallow water performance, indicated by a progradation seismic reflection phase axis that was relatively flat; in addition, the seismic reflection amplitude was strong and continuous with a low angle and extended over considerable distances (up to 50 km). The sedimentary center was close to the provenance, the width of the river was large, and a shallow sedimentary structure and a sedimentary rhythm were developed. The development of the delta was primarily controlled by tectonic activity and changes in the lake level; as a result, the river delta sedimentary system eventually presented a “small plain, big front” character.     

Mesozoic and Paleogene megabreccias in Southern Sicily: New data on the Triassic Paleomargin of the Siculo-Tunisian platform

Summary Mesozoic and Paleogene clastic carbonates in deep-water successions outcropping in the Sicani mountains (central southern Sicily) represent debris-flow and turbidite deposits accumulated in slope/base-of-slope sectors of the Sicanian Basin, a Permian to Miocene deep-water sedimentary domain of Sicily. Reef-derived carbonates of late Triassic age are frequently found among the clastic elements of these deposits, in association with other shallow and deep-water Mesozoic carbonates. The provide us with new data on the stratigraphic setting of a platform paleomargin now buried beneath the Sicilian thrust and fold belt. This paleomargin bounded the wide middle and upper Triassic carbonate platform which is now known in the subsurface of the Southern Sicilian thrust and fold belt. This paleomargin bounded the wide middle and upper Triassic carbonate platform which is now known in the subsurface of the Southern Sicilian mainland and offshore in the Pelagian Platform, from the Malta escarpment to the Sciacca and Trapani areas through the Hyblean Plateau. The hinge zones between this platform domain and the Sicanian basin were particularly affected by the paleostresses related to the Mesozoic and Paleogene evolution of the Southwestern Tethys. The sedimentary successions of these areas recorded repeated episodes of progradation, aggradation, backstepping, uplift and erosion of the platform-basin system, under eustatic and tectonic forcing.     

A new plant assemblage (microfossil and megafossil) from the Lower Old Red Sandstone of the Anglo-Welsh Basin: its implications for the palaeoecology of early terrestrial ecosystems

Lower Old Red Sandstone deposits penetrated by a series of cored boreholes near Newport (South Wales) have been sedimentologically logged, and recovered plant assemblages (microfossil and megafossil) investigated. Sedimentological logging indicates that the deposits are typical of the extensive terrestrial-fluviatile floodplain deposits of the Anglo-Welsh Basin. Palynomorph assemblages have been recovered from a number of horizons and comprise entirely terrestrial forms (spores and phytodebris). They essentially represent a single assemblage, belonging to the middle subzone of the micrornatus-newportensis sporomorph assemblage biozone, and indicate an Early Devonian (mid-Lochkovian) age. The new biostratigraphical data enables correlation with other Lower Old Red Sandstone deposits of the Anglo-Welsh Basin, and the deposits are assigned to the lower part of the St. Maughan's Group. A plant megafossil/mesofossil assemblage recovered from one of the spore-bearing horizons includes a zosterophyll assigned to Zosterophyllum cf. fertile. This is the earliest reported zosterophyll from the Anglo-Welsh Basin. The new palynological/palaeobotanical data provide important information on the palaeoecology and palaeobiogeography of the vegetation of the southeastern margin of the Old Red Sandstone continent during Lochkovian times. Palaeogeographical variation in the distribution of plant microfossils and megafossils is interpreted as reflecting differences between the flora of the lowland floodplain and inland intermontaine basins, although this is to a certain extent overprinted by variation due to localized differences in environmental conditions.     

Trace fossils in fluvial deposits of the uppermost Stockton Formation (Late Triassic), Newark Basin,New Jersey

Abstract

Fluvial deposits of the uppermost Stockton Formation (Late Triassic), Newark Basin, west-central New Jersey have yielded an assemblage of trace fossils. Dominated by burrows, specimens include Cochlichnus anguineus, Helminthoidichnites tenuis, Planolites beverleyensis, Scoyenia gracilis, Spongeliomorpha carlsbergi, Treptichnus bifurcus, Treptichnus pollardi, plant remains, and an undetermined vertebrate trace fossil. The assemblage belongs to the Scoyenia ichnofacies. On the basis of stratification and primary sedimentary structures, the beds are interpreted as deposits in a meandering stream environment. Larval insects, wormlike forms, and arthropods are probably responsible for most of the animal traces in wet or moist channel, floodplain, and point bar sediments subject to subaerial exposure.     

Pangea Megasequences of Tethyan Gondwana-margin reflect global changes of climate and tectonism in Late Palaeozoic and Early Triassic times—A review

The maximum concentration of continental crust at the Pangea stage is characterized by a specific depositional sequence generally referred to as the Pangea Megasequence. Extending in time from the Late Carboniferous to the middle of the Triassic, the succession exhibits similar trends across the whole of Gondwana. Invariably, the sequence was initiated by Late Carboniferous to Early Permian glacial and periglacial deposits. Deglaciation occurred in Early Sakmarian time, evidenced by a typical, commonly transgressive facies. The succeeding formations comprise, in ascending order, coal measures, redbeds, some more coal measures and again redbeds with an intercalation of fluviatile sands in the Early Triassic.After deglaciation the basic depositional theme was modified, depending on postglacial adjustments of climate and on the type of regional tectonic regimes. Extension of the tropical climatic belt after deglaciation was one factor that governed the resulting sediment facies. Coal deposition that prevailed in central Gondwana in the Early Permian gave way to dominance of redbeds in the Middle and Late Permian and, in more distal positions, evaporitic deposits were laid down, following deglaciation. Within marine realms, coralline limestones were formed.Within Gondwana the depositional period of the Pangea Megasequence was governed by three distinctive tectonic regimes: collision dominated the Panthalassa margin, transpressional sag controlled the interior basins, and extension and rifting was experienced along the entire Tethyan margin. In the Early Permian, large and complex graben structures commenced to develop between Africa and India (Malagasy Trough) and between India and Australia (West Australian Trough), giving access to Tethyan waters during deglaciation, commencing in the late Early Sakmarian.Rifting along the Tethyan margin commenced in the Early Permian and was associated with active volcanism between Cashmere and Yunnan and in north-western Australia. Spreading of Neo-Tethys and the formation of oceanic crust, leading to the separation of the Cimmerian Blocks from Gondwana, commenced in the late Early Permian and continued into the Triassic. Thus two facies realms developed, an intracratonic rift facies comprising the Cashmere, Lhasa and Baoshan blocks and a facies controlled by detachment, comprising more distal blocks, such as Tengchong, Malay and Sumatra. The present distribution of individual blocks was governed by fold movements of the Himalayan Orogeny, complicated by transpression along the eastern Himalayan Syntaxis.     

Bird and Mammal Footprints From the Tertiary of Navarre (Western Pyrenees)

A rich variety of vertebrate footprints is known from a number of Upper Eocene to Lower Miocene localities of Navarre (western Pyrenees). The sediments were deposited in a wide range of depositional environments, from marginal marine to diversified terrestrial. Abundant bird tracks have been found in the coastal deposits of the Upper Eocene Liedena Sandstone of the Yesa and Itzagaondoa areas. Ciconiiformes-like (Leptoptilostipus pyrenaicus) and Charadriiformes-like (Charadriipeda ichnospp.) footprints have been recognized. Mammal ichnites have been discovered in the Oligocene and Lower Miocene deposits of Navarre. Equoid perissodactyl ichnites similar to those of Plagiolophustipus occur in the Oligocene fluviatile rocks of the Mués Sandstone of Olexoa and the Rocaforte Sandstone near Oibar and Sada. Trackways of entelodontids (Entelodontipus) are known in fluviatile-palustrine beds of the Oligocene Mués Sandstone of Olkotz. Additionally, bird (Charadriiformes-like) tracks are known in fluviatile-palustrine floodplain deposits of the Lower Miocene Ujué Formation of Los Arcos. In the same area, the Desoio and Los Arcos outcrops have also yielded perissodactyl trackways of possible Equoidea. Trackways of rhinocerotids (?) and artiodactyls (possibly Pecoripeda) are described from the Lower Miocene (Ramblian) palustrine limestones marginal to the Lerín Formation of Kaparroso and from alluvial fan deposits of the Uncastillo-Perdón Formation of Altzorritz, respectively.     

Reinvestigation of conchostracans (Crustacea: Branchiopoda) from the Permian–Triassic transition in Southwest China

Sedimentary deposits of the Permian–Triassic transition are well-exposed in numerous outcrops of South China. Depending on the palaeogeographic positions of the sections, their lithofacies vary from fully marine, shallow marine, lagoonal, lacustrine, and fluvial to alluvial. In the present study, conchostracans (Crustacea: Branchiopoda) were newly collected from the continental deposits of the Kayitou and Jialingjiang formations around the Kangdian Highland elevated by the Emeishan Basalt in the southern Sichuan, western Guizhou, and northeastern Yunnan provinces. The conchostracan fauna of the Kayitou Formation is composed of Pseudestheria chatangensis, Euestheria fuyuanensis, and Euestheria sp. aff. E. gutta. These species occur in varying lithofacies types of different sections. In particular, the late Permian Pseudestheria chatangensis occurs in grey siltstones interbedded with pebbly sandstones, which are interpreted as lacustrine deposits. Euestheria fuyuanensis and Euestheria sp. aff. E. gutta were obtained from yellowish to greenish–grey clay- and siltstones, interpreted as coastal plain deposits. In comparison to other regions, occurrences of Euestheria gutta are indicative of an early Induan to Olenekian (Early Triassic) age. The fossil record of Euestheria fuyuanensis is so far restricted to a few occurrences in the Kayitou Formation of Southwest China and, therefore, using this species for long-distance biostratigraphic correlation requires further investigation. The distribution of late Permian pseudestheriid and Early Triassic euestheriid species in the respective sections possibly depends on the local lithofacies and, therefore, a diachronous age of the Kayitou Formation within the study area can be assumed. Additionally, Magniestheria sp. aff. M. mangaliensis and Magniestheria sp. aff. M. subcircularis were recorded in the Jialingjiang Formation, which represents a lithostratigraphic unit considered as late Early Triassic (Olenekian). Further investigations of both taxonomy and the real stratigraphic ranges of the conchostracan species as well as cross-correlations with other age data are recommended, in order to better constrain the position of the Permian–Triassic boundary and the specific timing of the terrestrial end-Permian mass extinction in continental deposits of Southwest China.     

云南墨江上三叠统歪古村组燧石质砾石中的晚古生代放射虫化石及其地质意义

云南哀牢山缝合带由于长期未找到晚石炭世至二叠纪深海环境的化石及沉积地层记录,对哀牢山古特提斯盆地演化历史存在着不同认识。文中报道了采自云南墨江坝留地区上三叠统歪古村组底砾岩中的早石炭世和中二叠世放射虫化石,所有放射虫化石发现于4件燧石质砾石中,共计11属9种和7未定种及1属种未定放射虫。其中,3件砾石含有Albaillella deflandrei Gourmelon,Albaillella sinuosa Won and Seo等早石炭世放射虫化石组合,另1件砾石含有Pseudoalbaillella spp.,Quadricaulis scalae Caridroit and De Wever,Cauletella sp.和Ishigaum sp.等中二叠世放射虫化石组合。由此表明,哀牢山缝合带存在着早石炭世和中二叠世深海盆地沉积地层记录,哀牢山深海盆地应该在中二叠世之后封闭。该成果为探讨哀牢山古特提斯盆地演化提供了放射虫古生物学证据,进而说明哀牢山缝合带与金沙江缝合带一样,也存在石炭纪和二叠纪深水洋盆沉积地层记录,指示其演化历史是相同的。     

Large tetrapod burrows from the Middle Triassic of Argentina: a behavioural adaptation to seasonal semi‐arid climate?

Krapovickas, V., Mancuso, A.C., Marsicano, C.A., Domnanovich, N.S. & Schultz, C.L. 2013: Large tetrapod burrows from the Middle Triassic of Argentina: a behavioural adaptation to seasonal semi‐arid climate? Lethaia, Vol. 46, pp. 154–169. We report the discovery of large burrow casts in the early Middle Triassic Tarjados Formation, at Talampaya National Park, north‐western Argentina. Facies analysis indicates the burrows are preserved in sandbars deposited by an ephemeral river under semi‐arid and seasonal climatic conditions. The structures are mostly preserved in longitudinal cross‐section and consist of an opening, an inclined tunnel (ramp), and a terminal chamber. The ramp is 8–14 cm in height, up to 130 cm in length and penetrates 49–63 cm bellow the palaeosurface with an inclination of 22°–30°. We studied burrow cast dimensions, overall architectural morphology, surficial marks, and compared them with other large burrows of both invertebrate and vertebrate origin. A tetrapod origin of the burrow casts was established based on: distinctive architecture, and size, which is more than twice the most common size range for large terrestrial invertebrate burrows. Comparison with other Upper Permian and Triassic tetrapod burrows allows us to identify three general morphological groups: (1) simple inclined burrows; (2) helical burrows; and (3) burrow network complexes, representing different behaviours. A study of tetrapod body fossils preserved within other Upper Permian and Triassic burrows shows that the Tarjados structures were most likely produced by non‐mammalian cynodonts. The environmental and climatic context suggests that aridity and seasonality played a fundamental role selecting burrowing behaviour in therapsids and that by the Early–Middle Triassic their burrowing behaviour attained a complexity comparable to modern mammals. □Argentina, behaviour, palaeoclimate, Permo‐Triassic, Tarjados Formation, Tetrapod burrows.     

Trophic network models explain instability of Early Triassic terrestrial communities

Studies of the end-Permian mass extinction have emphasized potential abiotic causes and their direct biotic effects. Less attention has been devoted to secondary extinctions resulting from ecological crises and the effect of community structure on such extinctions. Here we use a trophic network model that combines topological and dynamic approaches to simulate disruptions of primary productivity in palaeocommunities. We apply the model to Permian and Triassic communities of the Karoo Basin, South Africa, and show that while Permian communities bear no evidence of being especially susceptible to extinction, Early Triassic communities appear to have been inherently less stable. Much of the instability results from the faster post-extinction diversification of amphibian guilds relative to amniotes. The resulting communities differed fundamentally in structure from their Permian predecessors. Additionally, our results imply that changing community structures over time may explain long-term trends like declining rates of Phanerozoic background extinction.     

江苏丹徒大力山二叠—三叠系界线层的牙形刺

本文简要报道了江苏丹徒大力山二叠－三叠系界线层剖面中所产的丰富的牙形刺（计７属１３种及３个未定种）、腕足类、鱼鳞及鱼牙化石,讨论了二叠－三叠系生物地层界线的划分,并对牙形刺的３个未定种进行了描述,对江苏二叠－三叠系生物地层界线的划分具有重要意义。     

End-Permian stratigraphic timeline applied to the timing of marine and non-marine extinctions

A latest Permian timeline (251.9 Ma) can be constructed from the perspectives of: a global nickel spike attributed to emissions from the coeval Siberian flood-basalt eruptions, the correlative end-Permian marine mass extinction (EPME), a transition from reversed to normal paleomagnetism, and a negative anomaly in δ¹³C_carb and δ¹³C_org. In a number of marine and non-marine localities, this timeline is also correlated (to within ≤30 ky) with palynological evidence for the latest Permian destruction of terrestrial vegetation and the accompanying short-lived global fungal (Reduviasporonites) event. This correlation suggests that devastation in marine and non-marine environments was essentially coeval at a time marked by hyperthermal conditions and anoxic oceans.We utilized this proposed timeline to estimate the relative timing of the extinction of latest Permian vertebrates in the Karoo Basin of South Africa. In several sections in the Karoo, the LAD of the therapsid Dicynodon, is correlated with the proposed timeline. In the Carlton Heights section in the Karoo we estimate that the palynological changes and the fungal event occurred within ≤30 ky of the LAD of Dicynodon. Further sampling in the Karoo and other Permian–Triassic non-marine basins would help to clarify the relative timing of the global marine extinctions, plant devastation and the disappearance of non-marine vertebrates.     

KATBERGIA GEN. NOV., A NEW TRACE FOSSIL FROM UPPER PERMIAN AND LOWER TRIASSIC ROCKS OF THE KAROO BASIN: IMPLICATIONS FOR PALAEOENVIRONMENTAL CONDITIONS AT THE P/TR EXTINCTION EVENT

Abstract:  A new ichnogenus and ichnospecies of burrow, Katbergia carltonichnus , are described from Upper Permian and Lower Triassic rocks of the Karoo Basin, South Africa, where they are preserved in pedogenically modified overbank deposits that are interpreted as inceptisols subsequently gleysol overprinted. Sigmoidal burrows consist of a long (≥0.5 m) cylindrical tube, ranging from 1–2 cm in diameter, terminating in a slightly larger living chamber. The burrows are unlined and passively filled, preserving a hierarchy of scratch patterns on the burrow walls. Scratch patterns include longitudinal, transverse, and crescent-shaped markings found around the circumference of the burrow, but which are less densely concentrated on the burrow floor. Calcareous concretions are associated with burrowed siltstone intervals, generally restricted to the lowermost decimetre, with nodules nucleating around burrows. Stable δ¹³C and δ¹⁸O isotope data on calcite cement in the burrow fill, entombing siltstone, and associated calcareous nodules all cluster together when plotted, indicating that nodule formation occurred following burrow horizon abandonment and a rise in regional water table. Isotopic data reflect calcite precipitation under a semi-closed system in saturated conditions. A model for burrow emplacement, abandonment and infill, and subsequent cementation by calcite is presented demonstrating that previous interpretations of Late Permian and Early Triassic palaeosol types associated with the P/Tr extinction event must be re-evaluated.     

Lystrosaurus species composition across the Permo–Triassic boundary in the Karoo Basin of South Africa

Lystrosaurus is one of the few therapsid genera that survived the end-Permian mass extinction, and the only genus to have done so in abundance. This study identifies which species of Lystrosaurus have been recovered from Permian and Triassic strata to determine changes in the species composition across the Permo–Triassic (P–T) boundary in the Karoo Basin of South Africa. Data generated from museum collections and recent fieldwork were used to stratigraphically arrange a total of 189 Lystrosaurus specimens to determine which species survived the extinction event. Results reveal that L. curvatus and L. maccaigi lived together on the Karoo floodplains immediately before the extinction event. L. maccaigi did not survive into the Triassic in South Africa. L. curvatus survived, but did not flourish and soon became extinct. Two new species of Lystrosaurus , L. murrayi and L. declivis , appeared in the Early Triassic. It is possible that L. murrayi and L. declivis occupied different niches to L. maccaigi and L. curvatus , and had special adaptations that were advantageous in an Early Triassic environment. We suggest that L. maccaigi may be used as a biostratigraphic marker to indicate latest Permian strata in South Africa and that, in support of previous proposals, the genus Lystrosaurus should not be used as a sole indicator of Triassic-aged strata. Our field data also show that L. curvatus may be regarded as a biostratigraphic indicator of the P–T boundary interval.     

Pedogenesis and paleoclimatic implications of the Chamberlain Pass Formation, Basal White River Group, Badlands of South Dakota

The Chamberlain Pass Formation is a new lithostratigraphic unit representing the first phase of deposition of the Paleogene White River Group in western South Dakota. Analysis of pedogenic features within the channel and overbank deposits of the Chamberlain Pass Formation allows for a refinement of Middle to Late Eocene paleoclimates of this area. Pedogenic features within distal overbank deposits of the Chamberlain Pass Formation have long been recognized and classified as the Interior Paleosol Series (Retallack, 1983). Previous interpretations held that distal overbank sediments and soils of this time were deposited and formed under humid, acidic environments. This research demonstrates that, while this interpretation is correct, soils of the Chamberlain Pass Formation were also subjected to periods of dryness. Pedogenic features preserved within the channel sandstone and proximal overbank deposits (which include root traces, peds, cutans, glaebules, Bt, Btc and Bc horizons, silcretes and altered detrial sandstone mineralogy) suggest the formation of Aqualfs, Aquults and Durixerults. Soils appear to have been acidic to slightly alkaline, oxidizing and moderately-to well-drained, depending upon the physiographic position of the soil and the prevailing climate at the time of formation. Soils formed within the channel and proximal overbank deposits represent a new soil series, herein designated as the Weta Paleosol Series. The Weta and Interior Paleosol Series have a catenary soil relationship, based on differences in parent material and soil moisture conditions.

Middle to Late Eocene paleoclimate appears to have fluctuated between humid and dry conditions. Within the Weta Paleosol Series, soils formed within one physiographic and climatic regime were successively overprinted by pedogenic features of soils formed during later periods under different physiographic and climatic regimes. This has resulted in the presence of humid climate soil pedorelicts in dry climate soils, dry climate pedorelicts within humid climate soils and the overlapping of various physiogrpahically controlled pedogenic processes as baselevels changed. Sediments of similar pedostratigraphic and lithostratigraphic arrangement can be found in Nebraska, northern South Dakota and North Dakota. The recognition of these similar sediments in different basins across the northern Great Plains may allow for an increased understanding of regional tectonic, depositional, climatic and geomorphic events during the Paleogene.     

Palynofacies analysis for interpreting paleoenvironment and hydrocarbon potential of Triassic–Jurassic strata in the Sichuan Basin,China

The Sichuan Basin is one of the largest petroliferous basins in China. The continental fluvial?lacustrine sediments of the Upper Triassic Xujiahe Formation and the Lower Jurassic Zhenzhuchong Formation yield diverse fossil organisms and host one of the most important gas reservoirs in the basin. However, paleontological implication for the paleoenvironment and hydrocarbon source is less documented. Here, we report, for the first time for this basin, results from palynofacies analyses combined with thermal alteration data in the Early Mesozoic deposit of the Qilixia section, northeastern Sichuan Basin. The results show that, organic matters in sediments are dominated by phytoclasts, with less abundant palynomorphs and a few amorphous organic matters (AOMs). Four palynofacies assemblages were identified, reflecting depositional settings in a general proximal and oxic fluvial?deltaic environment, with two distal–proximal sedimentary cycles. The prominent dominance of opaque phytoclasts within the lower Zhenzhuchong Formation may be related to frequent wildfires across the Triassic–Jurassic transition. Palynofacies data (especially the relative abundance of opaque phytoclasts) may reflect 405 kyr eccentricity cyclicity pattern. The palynofacies and thermal alteration index (TAI), combined with geochemical data indicate the presence of type III kerogen in mature to post-mature phases, suggesting gas potential of the Xujiahe and Zhenzhuchong formations in the northeastern Sichuan Basin. This study provides significant implications for better understanding the paleoenvironment variations during the Triassic–Jurassic transition and the future gas exploration in this area.