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Abstract: Late Paleozoic glacial diamictites occur in many localities in western Argentina, indicating that the region was strongly affected by glaciation during the mid-Carboniferous (late Serpukhovian–early Bashkirian). In most instances these diamictites are found in steeply walled paleovalley settings in the Andean Precordillera. This study presents new data from a locality north of the Precordillera that suggests an additional, distinct, volume of ice existed in the region during the Carboniferous. The glacigenic diamictites in the Rio Blanco Basin were ultimately emplaced as gravity flows, precluding inferences of paleo-ice volume. Fold nose orientation and soft-sediment groove orientations within the diamictites indicate that the deposits were emplaced from north to south, suggesting that glacial ice was most likely not sourced from the proto-Precordillera at this locality, requiring the need for another ice center to the north of the basin. Diamictite facies indicates that the sediment was initially supplied to the study area by a warm-based glacier. [Copyright &y& Elsevier]

Abstract: Glacimarine grounding-line fans are subaqueous depositional features that form due to the expulsion of sediment-laden subglacial waters at the grounding-lines of temperate tidewater glaciers. Few studies of ancient grounding-line fans exist. This study describes and interprets several ancient glacimarine grounding-line fans and their physical characteristics using the Lower Permian Pagoda Formation along Tillite Glacier in the central Transantarctic Mountains, Antarctica as a deep-time example. Wedge-shaped sandstone bodies are used to identify major depositional processes and products that occurred during fan formation. The depositing processes on these fans operated in tandem; as tractive freshwater discharge from beneath the glacier(s) was progressively replaced down the fans, in the direction of flow, by buoyant upwelling and the development of overflow plumes. Tractive flow deposits are characterized by trough and climbing cross-stratification, while deposits resulting from settling from meltwater plumes consist of horizontal laminations and abundant soft-sediment deformational structures (load, flame, and diapiric structures). Secondary features, such as thrust and normal faults, resulted from advance and retreat dynamics of the ice front; whereas, mass flow deposits (convolute bedding, recumbent and S-shaped folds, slumps and slides) resulted from resedimentation. Because glacimarine grounding-line fans require specific depositional conditions to develop, their identification is useful in constraining environmental conditions in the rock record. For the Pagoda Formation, the occurrence of grounding-line fan deposits is significant, as these strata were originally interpreted as deposits of a large terrestrial ice sheet centered over the location of the present Transantarctic Mountains that extended outward and covered much of Gondwana for up to 90millionyears. However, this study demonstrates that these rocks were deposited in a glacimarine setting. Results, combined with other recent studies, suggest that multiple small temperate ice sheets occurred in South Polar Antarctica during the late Paleozoic ice age rather than a single massive ice sheet. [Copyright &y& Elsevier]

Abstract: A high-resolution oxygen isotope record based on 356 measurements of conodont apatite from several low latitudinal sections in South China, USA and Iran was composed in order to unravel Permian palaeotemperature and ice volume history. The conodont apatite δ18O record is compared to published brachiopod calcite δ18O records. Brachiopods and conodonts from different palaeocontinents show significantly different δ18O values, suggesting differences in local climatic conditions (e.g., evaporation/precipitation ratio). As a consequence, secular changes in palaeotemperature and oxygen isotope composition of Permian sea water cannot be reconstructed from records combined from different areas, but have to be based on records from a specific area. Oxygen isotope analyses of different conodont taxa suggest that Streptognathodus and Hindeodus lived in near-surface seawater and recorded surface water temperature, whereas the habitat of gondolellid genera was variable depending on sea level, with both near-surface and deeper waters as potential life habitat. The oxygen isotope record measured on conodonts from South China exhibits relative high values between 22 and 23‰ VSMOW during the glaciated Early Permian, translating into warm seawater temperature between 26 and 30°C, assuming that the Late Palaeozoic ice volumes were comparable to the Pleistocene glacial maxima. In contrast to the earlier view that the Late Palaeozoic Ice Age (LPIA) terminated in the late Sakmarian, the South China conodont apatite oxygen isotope record suggests waning of the ice sheets in the Kungurian. Ice melting is indicated by a pronounced decrease in δ18O of 2‰ VSMOW, which is interpreted as reflecting the combined effect of climatic warming and glacial ice melting. Significant temperature fluctuations (4°C warming succeeded by 6 to 8°C cooling) are observed during the Guadalupian–Lopingian transition, interpreted as combined climate changes induced by Emeishan volcanism and changes in habitat depth of gondolellid conodonts. Oxygen isotope values increase to 22‰ VSMOW in the Changhsingian, which suggests climate cooling and Clarkina moving to deeper waters because of the Changhsingian sea level rise. Across the Permian–Triassic boundary, δ18O values decrease from 22 to 19‰ VSMOW, parallel to the significant negative carbon isotope excursion and the eruption of the Siberian Traps. The latter is pointing to a cause–effect relationship as a consequence of the massive release of volcanic greenhouse gases derived from the Siberian volcanism and related processes. [Copyright &y& Elsevier]

Abstract: The late Paleozoic ice age (LPIA) consists of multiple glaciations that waxed and waned across Gondwana during the Carboniferous and Permian. Three key intervals are evaluated using the concept of the equilibrium-line altitude (ELA) as a control on glaciation to provide insight into two intervals of paradoxical ice distribution during and following glaciation. The LPIA began in the mid-latitudes during the Viséan in western Argentina with the growth of glaciers in the Protoprecordillera. Glaciation was initiated by uplift of the range above the ELA. In the Bashkirian, deglaciation occurred there while glaciation was beginning at the same latitude in uplands associated with the Paraná Basin in Brazil. Analysis suggests that deglaciation of the Protoprecordillera occurred due to extensional collapse of the range below the ELA during a westward shift in the location of plate subduction. During Late Pennsylvanian–Early Permian peak glaciation for the LPIA, extensive glacimarine deposits indicate that glaciers reached sea level, which corresponds to a major lowering of the ELA due to global cooling. Finally, during the Early to early Late transition out of the LPIA, polar Gondwana was unglaciated. However, three glacial intervals occurred at mid- to high-latitudes in eastern Australia from the Sakmarian to the Capitanian/earliest Wuchiapingian. The magnitude of global cooling during these events is debatable as evidence indicates ice-free conditions and an elevated ELA at the South Pole in Antarctica. This suggests that severe global cooling was not the cause of the final three Australian glaciations, but rather that ELA-related conditions specific to eastern Australia drove these late-phase events. Possible causes for the Australian glaciations include: 1) anomalous cold conditions produced by coastal upwelling, 2) the presence of uplands allowing nucleation of glaciers, 3) fluctuations in pCO2 levels, and 4) increased precipitation due to the location of the area in the subpolar low pressure belt. [Copyright &y& Elsevier]