Late Paleozoic glaciation

Soreghan et al. (2022) conducted field research to find evidence of ancient upland
glaciation “in the absence or near-absence of icecontact indicators”, and as an example they
presented a case study mainly from the Late Paleozoic palaeoequatorial Cutler Formation
(Colorado, United States). This is a good aim, because upland areas are subject to much
higher rates of erosion than lowland or marine environments, the latter which more often
exhibit deposition. Even today there are glaciers close to or even at the equator, on e.g.,
Mount Kenya (Mahaney, 1990).
As Soreghan et al. (2022) describe, the problems of identifying ancient upland glaciation
are substantial. A large part of the paper is used to try to explain how fluvial deposits can be
interpreted as glaciofluvial. The work is diligent, but there is no definite answer to the origin
based on the appearance of the deposits themselves.

The Gondwana Late Palaeozoic Ice Age is probably best represented by the Dwyka Group in South Africa. Striated and grooved surfaces or pavements are commonly considered to have formed subglacially, as are diamictites which have been interpreted as in-situ or reworked tillites. These interpretations were tested by investigation of outcrops in formerly well-studied areas, throughout South Africa. Detailed analyses have focused on striated surfaces/pavements and surface microtextures on quartz sand grains in diamictites. The sedimentological context of four pavements, interpreted to be glaciogenic, display features commonly associated with sediment gravity flows, rather than glaciation. A total of 4,271 quartz sand grains were subsampled from outcrops that are considered mainly to be tillites formed by continental glaciation. These grains, analysed by SEM, do not demonstrate the characteristic surface microtexture combinations of fracturing and irregular abrasion associated with Quaternary glacial deposits, but mainly a mix of surface microtextures associated with multicyclical grains. The Dwyka Group diamictites warrant reinterpretation as non-glacial sediment gravity flow deposits.

For more than 150 years, geologic characteristics claimed to be evidence for pre-Pleistocene glaciations have been debated. Advancements in recent decades, in understanding features generated by mainly glacial and mass flow processes, are here reviewed. Detailed studies of data offered in support of pre-Pleistocene glaciations have led to revisions that involve environments of mass movements. Similarities and differences between Quaternary glaciogenic and mass movement features are examined, to provide a more systematic methodology for analysing the origins of more ancient deposits. Analyses and evaluation of data are from a) Quaternary glaciogenic sediments, b) formations which have been assigned to pre-Pleistocene glaciations, and c) formations with comparable features associated with mass movements (and occasionally tectonics). Multiple proxies are assembled to develop correct interpretations of ancient strata. The aim is not per se to reinterpret specific formations and past climate changes, but to enable data to be evaluated using a broader and more inclusive conceptual framework. Regularly occurring pre-Pleistocene features interpreted to be glaciogenic, have often been shown to have few or no Quaternary glaciogenic equivalents. These same features commonly form by sediment gravity flows or other non-glacial processes, which may have led to misinterpretations of ancient deposits. These features include, for example, environmental affinity of fossils, grading, bedding, fabrics, size and appearance of erratics, polished and striated clasts and surfaces ("pavements"), dropstones, and surface microtextures. Recent decades of progress in research relating to glacial and sediment gravity flow processes have resulted in proposals by geologists, based on more detailed field data, more often of an origin by mass movements and tectonism than glaciation. The most coherent data of this review, i.e., appearances of features produced by glaciation, sediment gravity flows and a few other geological processes, are summarized in a Diamict Origin Table.

Enhanced geochronologic and biostratigraphic subdivision of Australian Cisuralian (lower Permian) strata is being achieved by chronometrically calibrating strata and their embracing biostratigraphic (largely palynostratigraphic) units to the Geologic Time Scale (GTS). Our approach employs the highly-advanced methodology of CAIDTIMS (chemical abrasion-isotope dilution thermal ionisation mass spectrometry) U–Pb dating of zircons derived from tuffaceous layers in sedimentary basins; intercalated sedimentary rocks have provided associated palynological control. Tuffaceous deposits have wide lateral distribution, and, as such, assist correlation and assessments of depositional rates. This isotopic procedure, in the absence of components inherited from the magma chamber, generally provides accurate plateau ages for zircon crystallisation. It has been estimated that such determinations have a 95% confidence interval below 0.1% (Crowley et al., 2007) and generally provide highly accurate ag...

Permian carbon isotopic and clay mineralogical records were recovered from the carbonates in the Xikou section, a complete and uninterrupted Upper Carboniferous to Lower Triassic carbonate-dominated succession exposed in Zhen'an, Shaanxi Province, central China, which were used to document carbon isotopic signatures and climatic changes affecting the easternmost Paleo-Tethys region during the Permian. Both carbon isotope and clay mineralogical

The timing of the final collision and particularly the disappearance of the gateway between the Rheic and Tethyan oceans is quite controversial and poorly established. The accurate timing on the gateway closure is vitally important for the understanding of global sea-level fluctuations, ocean circulation, regional and global environments, salinity and reorganization of the thermohaline circulation, enhanced deep water organic carbon production in the western Tethys and the overall decline of atmospheric CO 2 concentrations. Here we present a new approach by applying warm-water benthic foraminifera (WWBF) data to precisely constraint the Rheic-Tethys gateway (RTG) closure, utilizing taxonomic and statistical methods. The link between the RTG closure with the profound biotic transformations in the oceans, sea-level, and expansion of the Gondwana ice sheet is discussed herein. The records of the WWBF in the studied regions precisely constraint the exact moment of the RTG cutoff and much stronger support a linkage of the cutoff and the onset of Bashkirian glaciation.

The sub-meridional seaway that connected Paleo-Arctic and Paleo-Tethys basins was one of the most important geographical attributes of the Late Paleozoic Pangea landscape, paleogeography and paleoclimate. Existing models about the timing of the disconnection of the Paleo-Arctic and the Paleo-Tethyan oceans is very controversial and poorly documented. Warm-water benthic foraminifera (WWBF) were utilized to establish the precise timing of the closure of the Urals-Precaspian-Paleo-Tethys Seaway (UPTS) during Cisuralian time. The WWBF of Paleo-Tethys and those of the Ural-Precaspian Basins during the Gzhelian-Asselian, display a considerably high level of similarity. Beginning from the Sakmarian, the faunas of these two regions became dissimilar, suggesting a break in the connection between the Paleo-Tethys and Ural-Precaspian Basins. The sedimentological evidence (olistostromes and seismites) of the final collision of the Eastern Ural, Kazakhstania, Scythian-Turan plates with the southeastern part of the Russian Platform during Late Paleozoic also support the emergence of the Precaspian Isthmus at the Asselian-Sakmarian transition. The oceanic currents in the Precaspian and the Southern Ural Basins before the Sakmarian were directed northward and later changed to the south. These biotic and physical changes are consistent with the proposed timing of the cutoff of the UPTS. The biotic and sedimentologic features clearly suggest the UPTS closure and the origination of Precaspian Isthmus during the Asselian-Sakmarian transition. The abrupt changes in the oceanic circulation triggered changes in atmospheric CO 2 , atmospheric circulation and, possibly, albedo feedback. The emergence of the Precaspian Isthmus induced an increase in the poleward salt and heat transport towards mid-to lower latitude Gondwana and Cathasia margins. The warm water currents and moisture along the margins of Gondwana caused a rapid increase in the precipitation necessary to build significant ice sheets during the early-middle Sakmarian.

During the late Paleozoic and early Mesozoic Timor lay in the northern part of the north-south East Gondwana rift system along which the western margin of Australia later developed. Discovery of a latest Gzhelian bioherm in the central highlands of Timor Leste has implications for latest Carboniferousearliest Permian climate history and deglaciation in basins further south in the rift system. Limestone outcrop of the Maubisse Formation near the village of Kulau is recognized as a bioherm with a massive lower unit, including reef framework at the base, and a bedded grainstone upper unit. The bioherm developed on a basalt substrate in warm shallowwater, as indicated by photozoan assemblages in the massive lower unit. Foraminifera belonging to 17 genera are recorded from the bioherm. These include representatives of the families Biseriamminidae, Biwaellidae, Bradyinidae, Cornuspiridae, Lasiodiscidae, Palaeotextulariidae, Pseudotaxidae, Ozawainellidae, Schubertellidae, Schwagerinidae, Staffellidae and Textrataxidae. Twenty-one species have been referred to known types and 12 species are left in open nomenclature. The assemblage probably belongs within the uppermost Gzhelian Schwagerina robusta-Ultradaixina bosbytauensis Zone although a possible lowest Asselian correlation cannot be excluded. The bioherm is the oldest carbonate unit so far recorded from the Maubisse Formation, and the oldest sedimentary unit biostratigraphically dated in Timor. The dominantly heterozoan composition of the skeletal component of the limestone (except for the basal photozoan assemblage) and the taxonomic diversity of the larger foraminifera suggest a subtropical environment consistent with a palaeolatitude of about 40° S. The late Pennsylvanian was a time of glaciation that in Australia is represented by a significant stratigraphic hiatus in basins to the south of Timor in the East Gondwana rift system. The development of the Kulau bioherm during the latest Gzhelian may have coincided with a global warming spike that led to rapid melting of continental ice sheets and a substantial influx of glacigene sediment (alternating diamictite and mudstone) in the southern basins.

The sub-meridional seaway that connected Paleo-Arctic and Paleo-Tethys basins was one of the most important geographical attributes of the Late Paleozoic Pangean landscape, paleogeography and paleoclimate. Existing models about the timing of the disconnection of the Paleo-Arctic and the Paleo-Tethyan oceans is controversial and poorly documented. Warm-water benthic foraminifera (WWBF) were utilized to establish the precise timing of the closure of the Urals-Precaspian-Paleo-Tethys Seaway (UPTS) during Cisuralian time. The WWBF of Paleo-Tethys and those of the Ural-Precaspian Basins during the Gzhelian-Asselian, display a considerably high level of similarity. Beginning from the Sakmarian, the faunas of these two regions became dissimilar, suggesting a break in the connection between the Paleo-Tethys and Ural-Precaspian Basins. Sedimentological evidence (olistostromes and seismites) of the final collision of the Eastern Ural, Kazakhstania, Scythian-Turan plates with the southeastern part of the Russian Platform during Late Paleozoic also supports the emergence of the Precaspian Isthmus at the Asselian-Sakmarian transition. Oceanic currents in the Precaspian and the Southern Ural Basins before the Sakmarian were directed northward and later changed to the south. The biotic and sedimentologic features clearly suggest the UPTS closure and the origination of Precaspian Isthmus during the Asselian-Sakmarian transition. The abrupt changes in the oceanic circulation triggered changes in atmospheric CO 2 , atmospheric circulation and, possibly, albedo feedback. The emergence of the Precaspian Isthmus induced an increase in the poleward salt and heat transport towards mid-to lower latitude Gondwana and Cathasia margins. The warm water currents and moisture along the margins of Gondwana caused a rapid increase in the precipitation necessary to build significant ice sheets during the early-middle Sakmarian.

The timing of the final collision and particularly the disappearance of the gateway between the Rheic and Tethyan oceans is quite controversial and poorly established. The accurate timing on the gateway closure is vitally important for the understanding of global sea-level fluctuations, ocean circulation, regional and global environments, salinity and reorganization of the thermohaline circulation, enhanced deep water organic carbon production in the western Tethys and the overall decline of atmospheric CO 2 concentrations. Here we present a new approach by applying warm-water benthic foraminifera (WWBF) data to precisely constraint the Rheic-Tethys gateway (RTG) closure, utilizing taxonomic and statistical methods. The link between the RTG closure with the profound biotic transformations in the oceans, sea-level, and expansion of the Gondwana ice sheet is discussed herein. The records of the WWBF in the studied regions precisely constraint the exact moment of the RTG cutoff and much stronger support a linkage of the cutoff and the onset of Bashkirian glaciation.

The Regional Stratigraphic Scale (RSS) of the Permian deposits in northeastern Russia represents the only complete stratigraphic succession of Permian marine deposits distinguished in Russia, which serves as a standard at the correlation of Permian deposits of all regions of the eastern part of the Boreal Biogeographic Superrealm. However, a high level of faunistic endemism makes it extremely difficult to correlate directly stratons of the RSS with stages of the International Stratigraphic Scale (ISS) of the Permian deposits. The first U-Pb SIMS age datings of zircons from felsic tuffs of the Omchak Formation of the Ayan-Yuryakh Anticlinorium (the lower part of the Permian Khivachian Horizon of the RSS of northeastern Russia) allowed us to obtain the important reference level for the Upper Permian subdivision of the Permian RSS. The zircon age of 257.1 ± 3.0 Ma is in good agreement with the stratigraphic position of the studied sample, which makes it possible to correlate the surrounding deposits with the Wuchiapingian Stage of the Permian deposits in the International Stratigraphic Scale.

Enhanced geochronologic and biostratigraphic subdivision of Australian Cisuralian (lower Permian) strata is being achieved by chronometrically calibrating strata and their embracing biostratigraphic (largely palynostratigraphic) units to the Geologic Time Scale (GTS). Our approach employs the highly-advanced methodology of CAIDTIMS (chemical abrasion-isotope dilution thermal ionisation mass spectrometry) U–Pb dating of zircons derived from tuffaceous layers in sedimentary basins; intercalated sedimentary rocks have provided associated palynological control. Tuffaceous deposits have wide lateral distribution, and, as such, assist correlation and assessments of depositional rates. This isotopic procedure, in the absence of components inherited from the magma chamber, generally provides accurate plateau ages for zircon crystallisation. It has been estimated that such determinations have a 95% confidence interval below 0.1% (Crowley et al., 2007) and generally provide highly accurate ag...

Uranium-Lead dating of Zircon using the Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS) technique has largely overcome the problem of radiogenic lead loss, and has greatly improved the precision of the dating. That improvement in precision and the plethora of tuffs throughout the Permian and Triassic successions in eastern Australian basins (Tasmania, Sydney, Gunnedah, Bowen and Galilee) permits the recalibration of the Australian spore and pollen palynostratigraphic scheme directly to the numerical timescale, obviating the need for a multi-step process of correlation. The Permian recalibration has, for example, shown the base of the Dulhuntyispora parvithola (APP5) Zone to be about 6 million years younger than previously calibrated, and in the Triassic, the base of the Polycingulatisporites crenulatus (APT5) Zone could be about as much as 10 million years younger than previously calibrated.

Here we establish a magnetostratigraphy susceptibility zonation for the three Middle Permian Global boundary Stratotype Sections and Points (GSSPs) that have recently been defined, located in Guadalupe Mountains National Park, West Texas, USA. These GSSPs, all within the Middle Permian Guadalupian Series, define (1) the base of the Roadian Stage (base of the Guadalupian Series), (2) the base of the Wordian Stage and (3) the base of the Capitanian Stage. Data from two additional stratigraphic successions in the region, equivalent in age to the Kungurian-Roadian and Wordian-Capitanian boundary intervals, are also reported. Based on low-field, mass specific magnetic susceptibility (x) measurements of 706 closely spaced samples from these stratigraphic sections and time-series analysis of one of these sections, we (1) define the magnetostratigraphy susceptibility zonation for the three Guadalupian Series Global boundary Stratotype Sections and Points; (2) demonstrate that x datasets provide a proxy for climate cyclicity; (3) give quantitative estimates of the time it took for some of these sediments to accumulate; (4) give the rates at which sediments were accumulated; (5) allow more precise correlation to equivalent sections in the region; (6) identify anomalous stratigraphic horizons; and (7) give estimates for timing and duration of geological events within sections. B. B. ELLWOOD ET AL.

distinctly less abundant than at Mount Broughton, but the same post-magmatic hydrothermal processes were operative. The restricted occurrence of mineralisation at Mount Broughton and the lack of discoveries at other alkaline intrusions, however, discount the Southern Highlands of New South Wales as a significant gold province deserving comprehensive exploration.

A review of geochronological data underlying the geological timescale for the Triassic yields a significantly different timescale calibration than that published in the most recent compilation (Geologic Time Scale 2004). This is partly due to the availability of new radio-isotopic data, but mostly because strict selection criteria are applied and complications arising from biases (both systematic and random) are accounted for in this contribution. The ages for the base and the top of the Triassic are constrained by U-Pb ages to 252.3 and 201.5 Ma, respectively. These dates also constrain the ages of major extinction events at the Permian-Triassic and Triassic-Jurassic boundaries, and are statistically indistinguishable from ages obtained for the Siberian Traps and volcanic products from the Central Atlantic Magmatic Province, respectively, suggesting a causal link. Ages for these continental volcanics, however, are mostly from the K-Ar (40 Ar/ 39 Ar) system, which requires accounting and correcting for a systematic bias of c. 1% between U-Pb and 40 Ar/ 39 Ar isotopic ages (the 40 Ar/ 39 Ar ages being younger). Robust age constraints also exist for the Induan-Olenekian boundary (251.2 Ma) and the Early-Middle Triassic (Olenekian-Anisian) boundary (247.2 Ma), resulting in a surprisingly short duration of the Early Triassic, which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time. Furthermore, the Anisian-Ladinian boundary is constrained to 242.0 Ma by new U-Pb and 40 Ar/ 39 Ar ages. Radio-isotopic ages for the Late Triassic are scarce, and the only reliable and biostratigraphically-controlled age is from an upper Carnian tuff dated to 230.9 Ma, yielding a duration of more than 35 Ma for the Late Triassic. All of these ages are from U-Pb analyses applied to zircons with uncertainties at the permil level or better. The resulting compilation can only serve as a guideline and must be considered a snapshot, resolving some of the issues mainly associated with inaccurate and misinterpreted data in previous publications. However, further advances will require revision of some of the data presented here.

Here we establish a magnetostratigraphy susceptibility zonation for the three Middle Permian Global boundary Stratotype Sections and Points (GSSPs) that have recently been defined, located in Guadalupe Mountains National Park, West Texas, USA. These GSSPs, all within the Middle Permian Guadalupian Series, define (1) the base of the Roadian Stage (base of the Guadalupian Series), (2) the base of the Wordian Stage and (3) the base of the Capitanian Stage. Data from two additional stratigraphic successions in the region, equivalent in age to the Kungurian-Roadian and Wordian-Capitanian boundary intervals, are also reported. Based on low-field, mass specific magnetic susceptibility (x) measurements of 706 closely spaced samples from these stratigraphic sections and time-series analysis of one of these sections, we (1) define the magnetostratigraphy susceptibility zonation for the three Guadalupian Series Global boundary Stratotype Sections and Points; (2) demonstrate that x datasets provide a proxy for climate cyclicity; (3) give quantitative estimates of the time it took for some of these sediments to accumulate; (4) give the rates at which sediments were accumulated; (5) allow more precise correlation to equivalent sections in the region; (6) identify anomalous stratigraphic horizons; and (7) give estimates for timing and duration of geological events within sections. B. B. ELLWOOD ET AL.

High-resolution geochronology with an age resolution at the permil level is instrumental in testing proposed causal links between continental-scale, short-term volcanic events and environmental crises that affect life globally. Synchroneity with large-scale volcanic events has been shown for three of the five most severe extinctions, namely the end-Permian extinction coinciding with Siberian Trapp volcanism, the end-Triassic extinction with Central Atlantic Magmatic Province) volcanism and the end-Cretaceous with Deccan Trapp volcanism. Recent studies also show that the magnitude of the extinction is not solely a function of the size (volume) of the volcanic event but more importantly of the eruption rate and also the nature of the host rock that is intruded, and the resulting reactions and release of gases that can affect climate.

The age of the Emeishan lavas in SW China remains poorly constrained because the extrusive rocks are (1) thermally overprinted and so represent an open system unsuitable for 40 Ar/ 39 Ar geochronology and (2) in most cases devoid of zircon so that it is impossible for the application of U-Pb geochronology. Existing radiometric age constraints of Emeishan large igneous province are mainly from the application of SIMS and LA-ICP-MS U-Pb techniques to zircons from mafic and felsic intrusions, which represent indirect constraints for the lavas. In an attempt to directly determine the age of the Emeishan lava succession, high-resolution chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) zircon U-Pb techniques have been used on the felsic ignimbrite at the uppermost part of the Emeishan lava succession. These techniques have yielded a weighted mean 206 Pb/ 238 U age of 259.1 ± 0.5 Ma (n = 6; MSWD = 0.7). We interpret this age as the termination age of the Emeishan flood basalts. The age of the Guadalupian-Lopingian boundary is still unconstrained by high-resolution geochronology but is likely to be close to our new age for this felsic ignimbrite.

Twenty-eight new high-precision Chemical Abrasion Isotope Dilution Thermal Ionisation Mass Spectrometry
U-Pb zircon dates for tuffs in the Sydney and Bowen Basins are reported. Based on these new dates, the
Guadalupian-Lopingian/Capitanian-Wuchiapingian boundary is tentatively placed at the level of the Thirroul
Sandstone in the lower part of the Illawarra Coal Measures in the Sydney Basin. The Wuchiapingian-
Changhsingian boundary is at or close to the Kembla Sandstone horizon in the Illawarra CoalMeasures, southern
Sydney Basin, in themiddle part of the Newcastle CoalMeasures in the northern Sydney Basin, and in the middle
of the Black Alley Shale in the southern Bowen Basin. The end-Permian mass extinction is recognised at
the base of the Coal Cliff Sandstone in the southern Sydney Basin, at the top of the Newcastle Coal Measures in
the northern Sydney Basin, and close to the base of the Rewan Group in the Bowen Basin and is dated at
c. 252.2 Ma. The end-Permian mass extinction is interpreted to be synchronous globally in both marine and
terrestrial environments, and in high and low latitudes (resolution b0.5 my). The GSSP-defined Permian-
Triassic boundary is interpreted to be approximately at the level of the Scarborough Sandstone in the lower
Narrabeen Group, Sydney Basin, and in the lower Rewan Group, Bowen Basin. Newdates presented here suggest
that the P3 and P4 glacial episodes in the Permian of eastern Australia are early Roadian to early Capitanian, and
late Capitanian to midWuchiapingian in age respectively. The greenhouse crisis in the uppermost Pebbly Beach
and Rowan Formations of the Sydney Basin is interpreted as early mid Roadian, a mid-Capitanian age for the crisis
at the base of the Illawarra/Whittingham Coal Measures is confirmed. Greenhouse crises in the upper Illawarra/
Newcastle Coal Measures and lower Narrabeen Group of the Sydney Basin are dated as upper Changhsingian-
Induan, and in the upper Narrabeen Group/lower Hawksbury Sandstone as upper Olenekian.

As wildfires are today important sources of disturbance in many terrestrial ecosystems, it is of great interest to understand how different environmental parameters and fire-activity interacted during past periods of the Earth history. Fossil charcoal, inertinites, and pyrogenic polycyclic aromatic hydrocarbons (PAHs) represent the only direct evidence for the occurrence of such palaeo-wildfires. In the present study, a review of published data, together with new data on the occurrence of fossil charcoal for the Permian and the Triassic is presented. For a long time, it has been speculated, that an assumed lack of evidence for palaeo-wildfires during the Triassic should be explained by a large drop in atmospheric oxygen concentration following or during the end-Permian mass extinction event, preventing the occurrence of wildfires. However, evidence for palaeo-wildfires is relatively common in many middle and late Triassic strata, whereas such evidence is almost totally lacking from early Triassic sediments. The interpretation of this "charcoal gap" or depression is difficult, as many factors (e.g. atmospheric oxygen concentration, taphonomical biases, lack of sediments suitable for the preservation of macroscopic charcoal, lack of fuel, and "ignorance" of scientists) may have influenced not only the production, but also the preservation and recovery of evidence for palaeo-wildfires during this period. Thus, it is not clear whether this Early Triassic "charcoal gap" can also be seen as evidence for an assumed "wildfire gap" or not. Without any doubt further investigations on the early Triassic record of charcoal and other evidence for palaeo-wildfires will be necessary before this problem can be solved. In fact, it can be expected that the number of published records of (early) Triassic evidence for palaeo-wildfires will increase in the future as more and more scientist working on sediments of this age may become aware of the interest in fires from this time. This will certainly make it possible to give a much better picture of the temporal and regional distribution of wildfires during this period in the future.