Triassic Basin Research Articles

Geology of the Late Carboniferous, Permian and Early Triassic basins of the Eastern Pyrenees

ABSTRACT We present a detailed geological map of the Upper Carboniferous, Permian and Triassic rocks of the southern border of the Axial Zone in the Eastern Pyrenees. These units were deposited in three intra-mountain, terrestrial basins, characterized by the emplacement/deposition of volcanic, sub-volcanic and volcaniclastic units (ca. 1000 m thick) together with continental red beds. The map is based on unpublished drafts, sketches and structural data. This previous information was complemented with new structural, petrologic and stratigraphic data. The geological map is presented together with three cross-sections, a detailed lithological description, and a stratigraphic correlation panel to help understand the stratigraphy, volcanism and structure and, ultimately, the geometry and origin of the highly subsident areas of this segment of the chain in post-Variscan times. The geological map gives new clues for reconstructing the geometry of these basins and the distribution of the volcanic episodes during the Late Carboniferous and Permian.

Closing of the east Palaeo‐Tethys Ocean: Source–sink records from Middle Triassic sediments, Hainan Island, China

During the Late Palaeozoic to Early Mesozoic, the eastern segment of the Palaeo–Tethys Ocean closed, resulting in the collision and amalgamation of the South and North Hainan Islands. However, the exact location of the collision and amalgamation remains controversial. The main collision locations are the Baisha, Jiusuo–Lingshui and Changjiang–Qionghai faults. The U–Pb age of detrital zircons was used to determine the main source area of the Middle Triassic basin in the eastern part of Hainan Island and the closed position of the eastern section of the Palaeo‐Tethys Ocean. The U–Pb dating of detrital zircons revealed that the Middle Triassic Lingwen Formation contains four age groups: 235–258, 335–446, 766–986 and >1000 Ma. Notably, rock masses aged 248–252 Ma that were formed in a post‐orogenic tension setting have been identified in the western region of Hainan Island, whereas no igneous rocks from this period have been discovered in the eastern region. The detrital zircon samples from the Lingwen Formation revealed a peak at 249 ± 2 Ma U–Pb age, which is important evidence indicating that the Changjiang–Qionghai Fault is the product of collision between the southern and northern Hainan terranes. Affected by the bipolar subduction of the eastern segment of the Palaeo‐Tethys Ocean, the collision and amalgamation of the South and North Hainan terranes occurred, and experienced a post‐collision (extensional) process at ca. 249 ± 2 Ma.

The role of structural inheritance in the tectonic configuration of the Moroccan Meseta Coastal Block: Insights from morpho-structural and aeromagnetic data

The Coastal Block (CB) of the Western Meseta (Morocco) is located between the Atlantic passive margin and the Middle and High Atlas Mountains. In this contribution, a morpho-structural analysis using topographic data and an aeromagnetic data interpretation have been integrated to map tectonically related structures and to unravel the surface-subsurface faults interaction and their geodynamic implications in the CB. The morpho-structural analysis allowed the structural lineaments mapping through the processing of the topographic and hydrographic data. The application of derivatives operators on the magnetic anomaly map reduced to the pole allowed the assessment of the tectonic framework. The visual integrated analysis of surface and subsurface structures allowed to establish a synthetic structural map of the CB. Several N–S to NNE-SSW, NW-SE and NE-SW oriented fault systems were identified, some of which were confirmed and others were newly outlined. Four geometrically horst and graben type blocks were well distinguished, including the Triassic Basins of Berrechid to the north and of Doukkala to the south separated by the Casablanca Paleozoic block. Meanwhile, the Sahel represents an uplifted zone separating the Doukkala Basin from the continental shelf to the west. Rooted faults bounding these blocks, which are heavily inherited from the pre-Mesozoic tectonic events, record variable reactivation indicators related to the Neogene-Quaternary Atlasic shortening.

Remnants of the “Grande Savane?” Insights from Soil Organic Matter at Two Sites in the Deep River Triassic Basin of North Carolina

Narrative accounts and floristics suggest a broader historical distribution of Piedmont upland savannas and woodlands with a prairie-affinity flora than today, although dates of emergence, spatiotemporal extent, and historical dynamics remain unclear. To help address the question whether remnant prairie-affinity patches in the state represent at least historical, if not ancient, grasslands, we analyzed stable carbon isotopes from soil organic matter from two well-known localities hosting prairie-affinity heliophytes, both within the boundaries of historically mapped “Grande Savane”. Soil cores for δ13Corg analysis and radiocarbon dating were collected from five sites, hosting different present-day plant communities and spanning three soil orders. Recovered δ13Corg values suggest historical grasslands, likely savanna-type with some fluctuations in cover, were present at both localities essentially continuously over the past 2000 years until the more recent canopy closure over the past century. These findings are consistent with historical narrative accounts, although significant additional sampling is needed to determine its spatiotemporal extent. While the general trend at our localities transitions from open to closed systems, pronounced fluctuations are apparent in all profiles, particularly between 1254–1468 CE. Precipitation does not appear predominantly responsible, but available climatic reconstructions are from an adjacent basin. The timing of the pronounced vegetation class fluctuations is intriguingly coincidental to the timing of Siouan occupancy and intertribal movements, suggesting a need for more vigorous interdisciplinary investigations.

Facies sedimentology, high-resolution sequence stratigraphy, and depositional environment in the Imini Triassic basin (southern High Atlas of Marrakech, Morocco)

Facies sedimentology, high-resolution sequence stratigraphy, and depositional environment in the Imini Triassic basin (southern High Atlas of Marrakech, Morocco)

Late Triassic basin inversion of the Qiangtang Basin in northern Tibet: Implications for the closure of the Paleo-Tethys and expansion of the Neo-Tethys

Sedimentologic and tectonic records in the Qiangtang Basin, northern Tibet, indicate a negative basin inversion during the Late Triassic, which reveals Paleo-Tethys closure and Neo-Tethys expansion. In the Triassic sedimentary succession, there is a clear sedimentary facies shift. The Middle Triassic to Carnian (Late Triassic) sequence displays typically shallowing-upward changes related to regional uplift and terrestrial erosion. On the other hand, the Norian (Late Triassic) to Middle Jurassic sequence has typically deepening-upward changes due to the tectonic subsidence and transgression. The negative basin inversion underwent a transition from previous marine environment to terrestrial erosion in the North Qiangtang depression but a terrestrial erosion to marine environment transition in the South Qiangtang depression during the Late Triassic. Elemental data show bimodal volcanic rocks for the Nadi Kangri Formation with intracontinental rift setting. The initial negative inversion started with the Nadi Kangri bimodal volcanic eruption and alluvial/fluvial basal conglomerate that overlapped angular unconformably, disconformably, or conformably on the underlying formations. The U-Pb ages of volcanic samples from the Nadi Kangri Formation range from ∼220 to 201 Ma, and its initial eruption age (∼220 Ma) represents the onset time of negative basin inversion. Our data reveal that the exhumation of northern Qiangtang foreland basin during the early Late Triassic recorded the closure of the Paleo-Tethys Ocean and its branches along the Hoh Xil–Jinshajiang and the Longmu Co–Shuanghu, respectively. The initiation of Qiangtang rifting during the late Late Triassic could be related with the rapid expansion of the Neo-Tethys Ocean along the Bangong–Nujiang.

Middle Triassic sedimentary evolution in the Upper Yangtze region with implications for the collision between the South and North China Blocks

Middle Triassic marine carbonate successions deposited on the northwestern Yangtze passive continental margin preserve information about the initial collision between the South China Block (SCB) and the North China Block (NCB). We extracted data from 51 boreholes and 23 outcrops of the Middle Triassic Leikoupo Formation to interpret the spatio-temporal stratigraphic framework, depositional transition, and contractional deformation in the Upper Yangtze region. The sedimentological analysis indicates that the Leikoupo Formation may be divided into nine successions, which were overall deposited in restricted-evaporative marine platform and lagoon environments during the Anisian. From the thickness distributions of each sequence, the Upper Yangtze region is shown to have experienced northwest-southeast horizontal compression and vertical uplift, which drove northwestward migration of the coeval depocenters and marine regression. We propose that the marine deposits of the Leikoupo Formation and the contemporary paleo-uplifts can be considered products of the forebulge and backbulge depozones of a peripheral foreland basin. The Early Triassic passive continental margin in the Upper Yangtze region had thus transformed into a peripheral foreland basin in response to the collision between the SCB and NCB by the Anisian. The northwestward retreat of seawater with synchronous growth of the forebulge further supports the oblique suturing between the two rotating blocks. In response to continuous basin-ward thrusting of the Micangshan-Daba Shan and Longmen Shan belts, new transpressional flexural subsidence developed, leading to the formation of terrestrial deposits in the Late Triassic basin.

Provenance of upper Permian–Triassic sediments in the south of North China: Implications for the Qinling orogeny and basin evolution

The Triassic Qinling Orogenic Belt was formed during the closure of the Paleo-Tethys Ocean, and its evolution can be traced by provenance analysis of sediments in the south of North China. We present detrital zircon ages, sandstone petrographic observations, paleocurrent data, and paleogeographic reconstructions that allow the evolution of this basin–mountain system to be reconstructed. Detrital zircons from upper Permian sedimentary rocks yield two major age peaks at 1876 and 259 Ma, and two minor age peaks at 2526 and 363 Ma. These zircons were likely sourced from recycled sediments in the Southern North China Block. Detrital zircons from Lower Triassic sedimentary rocks have multiple age peaks at ca. 2500, 1850, 950, 745, 450–430, and 310–250 Ma, reflecting a mixed provenance from the Qinling Orogenic Belt and Southern North China Block. Zircons from a Middle Triassic sandstone have a concentrated age peak at ca. 250 Ma and two subordinate age peaks at ca. 1800 and 2500 Ma. Hafnium isotope data for the late Paleozoic detrital zircons are characterized by negative εHf(t) values of −23.11 to −0.11, and only two grains have positive εHf(t) values of +1.45 and +2.10. We infer that these zircons were derived from recycled sediments in the Southern North China Block. The provenance data show that the North Qinling Belt and Southern North China Block had been uplifted prior to the Early Triassic. The uplift was mainly related to the continental collision between the South China and North China blocks. These and previously published data indicate the Southern North China Block experienced exhumation during the Middle−Late Triassic, firstly involving Permian cover rocks, followed by Cambrian and Neoproterozoic strata, and finally Mesoproterozoic basement rocks. The fold-and-thrust belt in the Southern North China Block probably formed during the Middle Triassic. Uplift and denudation of the Qinling Orogenic Belt controlled Triassic basin evolution in the south of North China.

Geochemistry and paleogeographic implications of Permo-Triassic metasedimentary cover from the Tauern Window (Eastern Alps)

Abstract. The chemical composition of metasediments is a valuable source of paleogeographic information about the protolith's sedimentary environment. Here, we compile major- and trace-element whole-rock data, including B contents, and 10/11B-isotope ratios from the Permo-Triassic metasedimentary cover of the Pfitsch–Mörchner basin, overlying the Variscan basement in the western Tauern Window, Eastern Alps (Austria and Italy). The basement consists of orthogneiss (“Zentralgneis”, metamorphosed Variscan granitoids with intrusion ages between 305 and 280 Ma), and the roof pendant consists of granites (amphibolites, paragneiss, and minor serpentinites). The Zentralgneis is partly hydrothermally altered into pyrite quartzite with high Al–S contents, low Na–Sr–Ca–Mg contents, and very strong depletion of the light rare earth elements. Comparison with published detailed mapping of this and other time-equivalent basins in the western Tauern Window, with radiometric age data in the literature, and with unmetamorphosed basins in the South Alpine realm yields a late Permian to Early Triassic age of sedimentation. Although during Alpine metamorphism all rocks were strongly deformed, the whole-rock chemical compositions of the metasediments were not pervasively changed during deformation. We show that the sediments were deposited in a small, probably lacustrine–fluviatile, intramontane basin, under arid to semi-arid climatic conditions. The sequence starts with metaconglomerates, which can be interpreted as a mixture of the different basement rocks, based on a combination of major-element ratios Na2O / (Na2O + K2O) and MgO / (MgO + Fe2O3) with concentrations of trace elements Cr, V, and Ni. The sequence is overlain by a fining-upwards sequence of clastic sediments, in which the behavior of K, Rb, and Sr allows the reconstruction of intense diagenetic K–B metasomatism, which raised the K2O contents up to ∼ 10 wt %. The average B content of 218 µg g−1 is well above the B content of common sediments, and the B-isotope composition reaches extremely low values of down to −33 ‰ δ11B. The top of the sequence is a lazulite quartzite, interpreted as a former conglomeratic phosphatic sandstone, which marks the transition from a closed Permian basin to an open Triassic basin. Within the clastic sequence, the presence of hydrothermal tourmalinite veins documents a hydrothermal event after deposition but before the onset of Alpine metamorphism. A metamorphosed mafic dike swarm in the orthogneiss indicates a post-Variscan event of basaltic magmatism, and this event is tentatively correlated with increased heat flow in the Triassic basin and hydrothermal activity. A consistent conceptual model of this basin and its diagenetic modifications, based on a combination of geochemical data with petrographical and field information, provides the geodynamic context of the European margin at the onset of the Alpine orogeny.

Illite and chlorite cementation of siliciclastic sandstones influenced by clay grain cutans

The distribution and amount of clay rim cements are different for Permian Rotliegend and Lower Triassic Bunter sandstones in the Southern Permian and German Triassic Basins, respectively. Both are similar fluvial-aeolian deposits in hot-arid endorheic basins. In both Permian and Triassic sandstones clay grain cutans can be present, but clay rim cement is often lacking or rare in Bunter sandstones. At first sight it would appear that the presence of cutans is thus not relevant for the development of clay cementation. However, at closer inspection, it appears that authigenic clay is indeed present in both cases. In Rotliegend sandstones, the authigenic clay mainly developed as rims around the clay grain cutans, which are often thin and well microlaminated with few intra-micropores and composed of platy particles. The clay crystals in the rim decrease the pore interconnectivity and lower permeability significantly. In Bunter sandstones, most of the authigenic clay developed within the cutans. These cutans are less well microlaminated, have ample micropores, and are composed of more equant-shaped particles. The latter looser structure facilitated clay authigenesis within the cutans and their micropores. This often led to exfoliation of the cutan laminae and expansion of the entire cutan. These expanded cutans also lower pore connectivity. The presence and thickness of clay rim cement on top of cutans and grains is thus not correlated with the thickness of the cutans but with the texture of the cutans. The latter determined where authigenic clays precipitated and the thickness of cutans is partly the result of clay authigenesis within the cutans. This demonstrates that the composition and the texture of sedimentary components constrained and controlled burial diagenesis.

Revision of the Conodont Mockina slovakensis and Its Paleogeographic Implications for the Upper Triassic Intraplatform Basins of the Alps

Mockina slovakensis, thought to have evolved from Epigondolella praeslovakensis, is an important species of the Norian (Upper Triassic), generally considered as the representative of the uppermost Alaunian to upper Sevatian in the Tethys. The previous description of M. slovakensis was incomplete, thus has led to some misidentifications. We thus update the description of M. slovakensis and discuss its comparisons and occurrence based on the new conodont investigations in Dolomia di Forni and the data from previous literatures. The conodont assemblage in the succession of Dolomia di Forni is dominated by M. slovakensis, along with rare M. postera and E. praeslovakensis. We described two morphotypes of M. slovakensis (morphotypes A and B), on the basis of shape of the lateral profile. These two morphotypes can also be observed in the E. praeslovakensis. Moreover, M. slovakensis is usually documented as almost monospecific conodont association in intraplatform basins, thus its paleogeographic implications are also discussed.

Geotechnical Resistances of Drilled Shafts in Triassic Basin Sedimentary Rocks

Load tests on drilled shaft foundations with rock sockets in sedimentary formations associated with various Triassic Basins in the Mid-Atlantic region show that some generalizations are possible for estimating geotechnical resistances. Axial load tests on drilled shafts in locations several hundred miles apart produce surprisingly similar results. The common feature is the geology: all of the load-tested rock sockets considered were constructed in sedimentary rock associated with one of the rift basins that developed in response to breaking apart of the supercontinent Pangaea that began during the late Triassic Period (about 220 million years ago) and coincided with opening of the Atlantic Ocean. More specifically, all of the tested rock sockets were in the ‘red bed’ facies of the rift basin sediments consisting of reddish-brown siltstone, sandstone, and shale. Each of the projects described herein and the associated load tests are described and used to illustrate fundamental principles of rock socket design and how load testing can be used as a design tool. The important role of quality construction, in combination with quality assurance through inspection and testing, is emphasized, especially as it relates to the evaluation of base resistance for rock socket design.

Middle Triassic carbonates of Eastern Iberia (Western Tethyan Realm): A shallow platform model

Much of the eastern sector of the Mesozoic Iberian basin belongs to the ‘Mediterranean type’ Triassic. This type is characterized by a Middle Triassic stratigraphic record comprised of two carbonate Muschelkalk units (lower and upper) separated by a detrital-evaporite middle Muschelkalk unit. In the present study areas, the two first marine flooding episodes of the Middle Triassic led to the deposition of extensive shallow-water carbonates on a block-controlled epicontinental platform in the lower and upper Muschelkalk units. These carbonates were part of third-order transgressive–regressive sequences. The two carbonate sequences display similar vertical facies and stratigraphic sub-unit arrangements. The base of the two sequences is marked by a (lower) carbonate-marl alternation, which was deposited in mixed tidal flat-to-lagoon settings. In the middle of the sequences, the carbonate character is predominant and facies associations mainly suggest shallow waters and high environmental variability. The change from a transgressive to regressive trend occurs in the middle of the sequences, although the position of the maximum flooding zone can vary from one to another stratigraphic section. The tops of the sequences show two different lithological assemblages, which are coeval and grade laterally to each other. One assemblage is a ‘carbonate terminal complex’ formed by tidal flat and sabkha deposits, which is predominant in the lower Muschelkalk unit. The other assemblage is a lagoon-peritidal (upper) carbonate-marl alternation, predominant in the upper unit. Together, the two sequences suggest a complex platform morphology with a mosaic facies distribution, which evolved from a not very high energy ramp-like profile (transgressive phases, TST) to a lower energy rimmed shelf, ending with tidal/lagoon environments (regressive phases, HST). Facies associations, however, suggest somewhat deeper depositional settings for the upper than lower Muschelkalk unit. Here we compare the two carbonate units in the study areas with those described in the literature from other Triassic basins of Eastern Iberia and the SW Germanic Basin, all forming part of the Peri-Tethys area of the Tethyan Realm.

Generation and structural modification of the giant Kengdenongshe VMS-type Au-Ag-Pb-Zn polymetallic deposit in the East Kunlun Orogen, East Tethys: Constraints from geology, fluid inclusions, noble gas and stable isotopes

The Kengdenongshe giant Au-Ag-Pb-Zn polymetallic deposit is located in the East Kunlun Orogen (EKO). It contains about 42.2 t of Au, 608.6 t of Ag and 1.05 Mt of Pb and Zn with an average grade of Au 2.31 g/t, Ag 19.29 g/t and Pb + Zn 3.49 wt% (Pb: 1.23 wt%, Zn: 2.26 wt%). The NWW-trending ore bodies are predominantly hosted in Late Permian to Triassic rhyolitic tuff, which formed during Late Permian back-arc extension to Triassic arc-continental collision. The ore bodies are subdivided into Pb-Zn rich ore bodies on the top with high grades of Pb and Zn and low grades of Au and Ag, and Au-Ag rich ore bodies below with high grades of Au and Ag and low grades of Pb and Zn. The Pb-Zn rich ore bodies occur as vein, stockwork, and in breccia, and comprise quartz, pyrite, galena, sphalerite, and small amounts of chalcopyrite. The Au-Ag rich ore bodies consist of auriferous barite-sulfide-oxide veins and contain barite, pyrite (early strawberry and oolitic pyrite and later eu- to subhedral pyrite), galena, sphalerite, chalcopyrite, tetrahedrite and covellite. Gold is present as electrum, kustelite and native gold and silver is present as polybasite, pearceite, kongsbergite, and as minor native silver in microfractures in sulfides. The hydrothermal alteration minerals include, from bottom to top, quartz + barite + calcite around the Au-Ag rich orebodies, quartz + chlorite + epidote around the Pb-Zn rich orebodies, and quartz + K-feldspar within the tuff. Fluid inclusions from both the Pb-Zn rich and the Au-Ag rich orebodies consist of two phases (V–L-type) fluid inclusions of which the vapor phase has a size of 10–40 vol%. Fluid inclusions microthermometry reveal homogenization temperatures of fluid inclusions in Pb-Zn rich and Au-Ag rich ore bodies of 128–230 °C and 110–320 °C, with corresponding salinities of 0.7–9.9 and 0.2–18.3 wt% NaCl equivalent, respectively. H-O-S-Pb stable isotope and He-Ar noble gas isotope data indicate a mixed magmatic water-seawater source for both the Pb-Zn and Au-Ag rich ore bodies, and an additional meteoric water component for the Au-Ag rich ore bodies. The Pb-Zn and Au-Ag rich ore bodies share the same sulfur and lead sources, i.e. sulfur is derived from crustal magma and seawater/marine sulfate, and the lead originated from a mixed magmatic-ancient crustal sedimentary source. Collectively, the regional geology, mineralogy, alteration, and geochemistry indicate that the Kengdenongshe Au-Ag-Pb-Zn polymetallic deposit can be characterized as a VMS-type (volcanic-associated massive sulfide) deposit. Formation of the ore-hosting rhyolite tuff and mineralization are associated with Late Permian to Triassic marine volcanic exhalation. Middle to Late Triassic basin closure and arc-continent collision modified the deposit and resulted in the location inversion of the Pb-Zn and Au-Ag rich orebodies.

Triassic-Jurassic thermal evolution and exhumation of the western Gondwana foreland: Thermochronology and basalt thermobarometry from the Argentine Sierras Pampeanas

The geological record of the eastern Sierras Pampeanas province, in the modern Andean broken foreland of Argentina can be divided into four main events: (1) Proterozoic to early Paleozoic collisional tectonics, (2) middle-late Paleozoic anorogenic magmatism, relief generation and glacial paleovalley formation followed by (3) a classical foreland filling in the Permian and two proximal alluvial sedimentation associated with (3) Cretaceous rifting and (4) Neogene intermontane foreland accumulation. The region lacks Silurian, Triassic and Jurassic records, commonly associated with unknown deformation and/or no-sedimentation stages (bypass zone?). In this work, we analyzed the Mesozoic (Triassic-Jurassic) Pampean unconformity, using low-temperature thermochronological modelling. After a rapid Carboniferous cooling track, a Triassic reheating followed by a slow Jurassic to Cretaceous cooling. Considering that (1) no Triassic basins have been described to date in the eastern Sierras Pampeanas (i.e., reheating cannot be related to burial), (2) coeval surface heat flows are anomalously high in western Sierras Pampeanas, in the Ischigualasto basin, and (3) our petrogenetic modelling on Triassic basalts evidence mantle potential temperatures of ~1350–1400 °C (i.e., the heat source cannot be related with an anomalously high basal heat flows and/or mantle plumes); we interpreted the formation of the Mesozoic unconformity as a result of ridge collision and slab window formation, followed by slab rollback. Both processes might have affected not only the surface heat flow but also triggered a lithospheric thickness reduction, which drove isostatic rebound. In this context, the Jurassic history of the unconformity could be associated with cooling by erosion and exhumation until the Cretaceous, when the region was under extension. Our model agrees with other observations like the formation of back-arc hydrocarbon-productive Triassic-Jurassic depocenters to the west (Cuyo and Ischigualasto basins) and the magmatic evolution, from 28° to 34° SL, described along the Chilean margin.

Middle–Late Triassic evolution of the Jameson Land Basin, East Greenland

AbstractThe Jameson Land Basin lies within the Greenland–Norway rift, to the south of Triassic basins on the Halten Bank and East Greenland shelf, and can therefore offer insights into the development of these less-well-documented offshore basins and the wider North Atlantic. This study focuses on the stratigraphic development of the Jameson Land Basin. Broad-scale stratigraphic logging is augmented with heavy mineral analysis that constrains the dominant source catchments during this period. A thickness of over 1.5 km of Middle–Late Triassic strata fill the Jameson Land Basin, predominantly comprising continental deposits laid down during arid to semi-arid climatic conditions. The basal Pingo Dal Group thickens westwards into the Stauning Alper Fault, forming a typical syn-rift succession. Thickness variations have also highlighted the presence of an intrabasinal high and an associated unconformity between the Pingo Dal Group and the overlying Gipsdalen Group, which provides the first direct evidence for Middle–Late Triassic rifting in East Greenland. Thickness variations in the overlying Gipsdalen Group are more subdued, and the Fleming Fjord Group, and its formations, display remarkably tabular geometries, with little evidence for significant lateral facies variance; this is suggestive of reduced topography and a more regional thermal subsidence signature. Provenance data indicate sediment sourcing from both the western and eastern basin margins during the deposition of the Pingo Dal Group, above which the western source area becomes dominant, alongside some axial input from the south.

Non-mammaliaform cynodonts from western Gondwana and the significance of Argentinean forms in enhancing understanding of the group

Terrestrial Triassic assemblages are an important component of the heritage of Argentina, particularly because of their diverse record of fossil vertebrates. Triassic basins from western Argentina have a good representation of therapsids, a lineage that includes a series of stem extinct groups plus crown Mammalia. Because of their diversity and abundance, non-mammaliaform cynodonts are the most conspicuous therapsids in the Argentinean Triassic. Cynodonts have been intensively researched in Argentina since the 1960s and continue to provide key advances in the understanding of the evolution and biology of the lineage. Here we offer a summary of Triassic Argentinean non-mammaliaform cynodonts, presenting a historical context of research on this group, and highlighting seminal contributions of Triassic Argentinean cynodonts to the global knowledge of the group. To provide a Gondwanan context we review the cynodont record in the two other places where the lineage is best represented: Brazil and southern Africa (including Madagascar), highlighting commonalities in the Argentinean record with these places. Considering the important role of non-mammaliaform cynodonts in the interpretation of the origin of mammals, we provide a historical account on the contribution of Argentinean, and Gondwanan, cynodonts to the understanding of this topic. This is supplemented with a summary of the progression of phylogenetic ideas and hypotheses for all non-mammaliaform cynodonts and for the most prolific subgroups represented in western Gondwana.

Macroecological patterns of the terrestrial vegetation history during the end-Triassic biotic crisis in the central European Basin: A palynological study of the Bonenburg section (NW-Germany) and its supra-regional implications

Abstract The end-Triassic mass extinction is often linked to environmental and climate change triggered by the activity of the Central Atlantic Magmatic Province ca. 201 Mya. In the German Triassic Basin, the transition from pre-extinction to the so-called extinction interval is documented from the fossil-rich Contorta Beds to the mostly barren Triletes Beds. However, despite the lack of macrofossils, plant microfossils are present and studying palynomorph diversity and assemblages still give us a detailed insight into the impact of environmental changes on the flora. Here, we present data from 64 samples taken from the new Triassic-Jurassic section ‘Bonenburgʼ, which originates from a brick quarry in North Rhine-Westphalia (Germany), and encompasses the Triassic–Jurassic transition in the Germanic Basin. Using palynofacies analysis, we document changes in the depositional environment. Based on terrestrial and marine palynological analysis, we also document quantitative changes in four assemblage zones for correlation with other European sections. Further, we discuss the vegetation history with special focus on the transition from the pre-extinction to extinction interval (Contorta to Triletes Beds). Additionally, we investigate palynofloral diversity patterns especially prior to the Triassic-Jurassic transition, to evaluate the ecological impact of environmental upheaval on the flora. Furthermore, we document intraspecific palynomorph variability, indicating a variety of aberrant spore, pollen, and tetrad formation, in the middle Rhaetian, the lowermost upper Rhaetian, and the lowest Hettangian. Our study supports existing paleogeographical reconstructions for the region and reveals, that vegetation underwent gradual changes with intermediate successional stages rather than dramatic extinction or drastic turnover as documented for animals. Diversity patterns coinciding with aberrant palynomorph occurrences, potentially associated with episodes of increased environmental stress, suggest three disturbances pulses of probably increasing severity. Although environmental stress in the context of diversity patterns seems a likely explanation for the occurrence of aberrant palynomorphs, further investigations are needed to better understand the underlying mechanisms and their evolutionary significance and temporal connection with biotic crises.

Stratigraphic and provenance analysis of Triassic rock units between 28-29° S, northern Chile: implications on the tectonic and paleogeographic evolution of the southwestern margin of Gondwana

Triassic rock units of northern Chile (28-29° S) record the transition, both in time and space, between two major orogenies that affected the southwestern margin of South America, the Gondwanian and Andean orogenies. The geodynamic configuration of the margin during this transition is still a matter of debate, particularly whether subduction was interrupted or continued under different parameters in between the orogenies. In order to evaluate these hypotheses by understanding the paleogeographic evolution of the margin, this work synthesizes recent stratigraphical, structural and geochronological data from northern Chile (28-29° S), along with detrital zircon analysis and detritus characterization of the two main siliciclastic Triassic basins present in the area. A detailed study of the evolution of the San Félix and the Canto del Agua basins, their source areas, and exhumation processes of the margin recognizes two stages of intra-arc/forearc basins system development separated by a Carnian unconformity. The first stage (Lopingian-uppermost Middle Triassic) develops an eastern intra-arc basin, which is represented by the volcaniclastic rocks included in the Guanaco Sonso Formation and the roots of the volcanic arc represented by Chollay Plutonic Complex, bounded to the east by a Pennsylvanian-Cisuralian basement block. The forearc basin for this stage is constituted by two graben depocenter, separated by a topographic high, of marine to transitional depositional environment and proximal sediment sources. The eastern graben is filled by conglomerates and turbiditic rocks grouped in Members M1 to M4 of the San Félix Formation, and the western graben, by sedimentary and volcanic rocks of the lower section of the Canto del Agua Formation. The second stage (Norian-Rhaetian) involves an eastern intra-arc basin, represented by the volcanic rocks of the La Totora Formation that seals the exhumed roots of the magmatic arc developed in the previous stage, and a marine to transitional forearc basin to the west, represented by the sedimentary rocks of M5 member of the San Félix Formation and the upper section of the Canto del Agua Formation. These two successions show basal fluvial conglomerates unconformably overlying Anisian prodelta deposits of the first stage, recording a major base level drop of the forearc basin.

The Atlas-East Variscan -Elbe shear system and its role in the formation of the pull-apart Late Palaeozoic basins

The Variscan orogeny occurred as a result of the Late Devonian to Late Carboniferous collision and accretion of Gondwana-derived microcontinents and continental masses with those of Laurussia. The irregular boundaries of the colliding continents caused isochronous transpressional and transtensional tectonics, accompanied by a complex pattern of intracontinental shear zones at the scale of the southern European Variscides. These shear zones and their configuration controlled the subsequent evolution of Permian to Middle Triassic paleogeography. The geographic distribution, from Morocco to the Eastern Alps, of the Late Carboniferous–Permian up to Triassic basins, most of which are considered as pull-apart basins, was related with the development of the Late Palaeozoic intracontinental shear network. Our analysis of the stratigraphic, tectonic and volcanic features of the Late Carboniferous/Permian continental basins across the Laurussia/Gondwana boundary reveals the role of the East Variscan Shear Zone during this time as a precursory lineament for the development of the Permian to Triassic rifting of Pangaea and the following opening of oceanic basins (e.g., the Neothetyan Ocean).