Phase Of Glaciation Research Articles

Seafloor geomorphology of the Wrigley Gulf shelf, Amundsen Sea, West Antarctica, reveals two different phases of glaciation

AbstractKnowledge of the behaviour of marine‐based ice sheets during times of climatic warming, such as the last deglaciation, provides important information to understand how ice sheets respond to external forcing. We analysed swath bathymetric and acoustic sub‐bottom profiler data from Wrigley Gulf on the western Amundsen Sea shelf, West Antarctica, to identify glacial features and reconstruct past changes in the extent of the West Antarctic Ice Sheet (WAIS) and ice flow directions. Glacial bedforms mapped within a bathymetric cross‐shelf trough include features showing cross‐cutting and overprinting relationship and indicate changes in ice‐flow orientation. Here, we distinguish at least two phases of different ice‐flow patterns on the Wrigley Gulf shelf. During the earlier phase, seaward ice stream flow on the inner shelf was deflected towards the east due to the existence of an ice dome on the middle‐outer continental shelf. Retreat of grounded ice towards the centre of this dome is indicated by the asymmetric cross profile of recessional moraines mapped on the middle shelf. The later glaciation phase was characterized by fast, NNW‐directed ice flow across the shelf along a broad front and subsequent stepwise landward retreat, which is evident from the common occurrence and orientation of mega‐scale glaciation lineations and grounding zone wedges on the middle‐inner shelf. It is uncertain whether the two phases of glaciation recorded on the seafloor occurred during the last and penultimate glacial periods or at different times of the last glaciation. Reliable chronological constraints from sediment cores and additional geomorphological information are needed to understand the cause of the changes in WAIS dynamics reflected by the two ice‐flow phases.

Upper Visean (Mississippian) coral biostromes during onset of the late Palaeozoic Ice Age: A record from the equatorial eastern Palaeotethys

The late Visean-Serpukhovian is a critical time in reef evolution and climate history, characterized by the gradual collapse of coral reef systems during the onset of the main glaciation phase of the late Palaeozoic Ice Age (LPIA). However, detailed palaeoecological variations of coral reefs during the collapse phase are not well understood. In this study, about one-meter thick coral biostromes are reported from the upper Visean Shangsi Formation in the Yashui section, central Guizhou Province, South China. Coral colonies are primarily in growth position resulting in the classification of autobiostrome and autoparabiostrome. Dominant colonial rugose coral species are Stylostrotion petalaxoidea and Siphonodendron pauciradiale, respectively. The biostromal framework is simple and primarily constructed by bafflestones with slightly positive relief. Diversified dwellers are found between coral skeletons, including abundant foraminifers, crinoids, calcareous algae and brachiopods with less bryozoans, tabulate and solitary rugose corals, gastropods and ostracods. Relative sea-level fluctuations control the growth and demise of the Yashui biostromes, evidenced from changes in both microfacies and biotic assemblages from their underlying to overlying strata. The petalaxoidea biostrome developed in relative deeper water depth than that of the pauciradiale biostrome, between storm wave-base and fair-weather wave-base on a shallow photic open-marine shelf. The pauciradiale biostrome in South China (eastern Palaeotethys) has similar biotic composition, colony preservation and depositional environments to coeval coral biostromes in Ireland (western Palaeotethys). The Yashui coral biostromes formed shortly after the LPIA onset, evidenced in small-scaled eustatic fluctuations and a positive shift in brachiopod oxygen isotopic signatures.

Simulation of a fully coupled 3D glacial isostatic adjustment – ice sheet model for the Antarctic ice sheet over a glacial cycle

Abstract. Glacial isostatic adjustment (GIA) has a stabilizing effect on the evolution of the Antarctic ice sheet by reducing the grounding line migration following ice melt. The timescale and strength of this feedback depends on the spatially varying viscosity of the Earth's mantle. Most studies assume a relatively long and laterally homogenous response time of the bedrock. However, the mantle viscosity is spatially variable, with a high mantle viscosity beneath East Antarctica and a low mantle viscosity beneath West Antarctica. For this study, we have developed a new method to couple a 3D GIA model and an ice sheet model to study the interaction between the solid Earth and the Antarctic ice sheet during the last glacial cycle. With this method, the ice sheet model and GIA model exchange ice thickness and bedrock elevation during a fully coupled transient experiment. The feedback effect is taken into account with a high temporal resolution, where the coupling time steps between the ice sheet and GIA model are 5000 years over the glaciation phase and vary between 500 and 1000 years over the deglaciation phase of the last glacial cycle. During each coupling time step, the bedrock elevation is adjusted at every ice sheet model time step, and the deformation is computed for a linearly changing ice load. We applied the method using the ice sheet model ANICE and a 3D GIA finite element model. We used results from a regional seismic model for Antarctica embedded in the global seismic model SMEAN2 to determine the patterns in the mantle viscosity. The results of simulations over the last glacial cycle show that differences in mantle viscosity of an order of magnitude can lead to differences in the grounding line position up to 700 km and to differences in ice thickness of the order of 2 km for the present day near the Ross Embayment. These results underline and quantify the importance of including local GIA feedback effects in ice sheet models when simulating the Antarctic ice sheet evolution over the last glacial cycle.

Glacial sedimentation in Northern Gondwana: insights from the Talchir formation, Manendragarh, India

AbstractAmong the vast swathes of Gondwanan sedimentary rocks in India, exposures of the Lower Permian Talchir Formation at Manendragarh in India are exceptional for their cold marine faunal assemblage and muddy conglomerates of possible glacial origin. They may represent a record of the late Palaeozoic glaciation that affected Gondwana in the Permo-Carboniferous. Although the fossil record is relatively well documented, the sedimentology of this area is not well understood. This paper intends to fill the gap in knowledge regarding palaeogeography and the palaeoenvironmental changes within the basin through space and time. We distinguish conglomerates that are formed by glacial and mass flow processes. The lateral variation in facies associations along a NNE-SSW transect in the study area identifies the depositional basin as an interior sea that formed when the sea spilled over a steep basement ridge during a transgression. The benthic organisms remained confined to the seaward basin margin where they only flourished in the initial stage of basin filling. Locally derived, bioclastic storm beds are limited to the seaward flank of the basin. Alternating phases of glaciation and interglaciation resulted in an interbedded succession of grey shales and interglacial density flow deposits. The channels that fed these density flows are preserved closest to the landward margin of the basin. Co-existence of glacial diamictites and interglacial density flow deposits highlights the climatic changes in this part of Gondwana during the Late Palaeozoic.

Colonial coral resilience by decreasing size: reaction to increased detrital influx during onset of the late Palaeozoic Ice Age.

Modern coral reefs and associated biodiversity are severely threatened by increasing terrestrial runoff. Similar scenarios could be suspected for geological times, but reef coral resilience is still an enigma. In late Visean-Serpukhovian (Mississippian foraminiferal zones/MFZ 14-16) times, a major glaciation phase of the late Palaeozoic Ice Age (LPIA) associated with enhanced terrestrial weathering and runoff coincides with a biodiversity crisis and coral reef decline. In this study, the impact of enhanced terrestrial runoff is tested on size variations of colonial corals Aulina rotiformis and Lithostrotion decipiens along a gradient of contemporaneous (Serpukhovian) open marine carbonate to near-shore siliciclastic facies in South China. Along this gradient, their sizes decrease from carbonate, through intermediate carbonate-siliciclastic, to siliciclastic facies. This is consistent with increasing abundance of terrestrial materials of high silicon, aluminium and phosphorus values. On a larger million-year-long interval (MFZ14-16) and for several palaeocontinents, size data of Lithostrotion decipiens and Siphonodendron pauciradiale show a distinct decline in late Visean, when enhanced terrestrial weathering occurred commonly with palaeosols developed during regression. This suggests that terrestrial sediment and nutrient input may have mainly controlled phenotypic plasticity in Mississippian reef corals, with a decrease in size as a component of resilience across the LPIA onset.

Global cooling initiated the Middle-Late Mississippian biodiversity crisis

During the Mississippian period, metazoan reefs and other marine faunas gradually recovered from the Late Devonian mass extinctions and reached a peak in the late Visean (~334–332 Ma). Faunal diversity started to decline from the latest Visean (~332–330 Ma) through Serpukhovian (~330–323 Ma), with significant genera/species losses and ecosystem reconstruction. This Middle-Late Mississippian biodiversity crisis (M-LMBC) was thought to have been caused by global cooling associated with the late Paleozoic Ice Age (LPIA), but existing sedimentological and temperature proxy data suggest that the global cooling event—that marks the onset of the main glaciation phase of LPIA—happened either ~4 Myr before or ~ 1–5 Myr after the initial biodiversity decline at ~332 Ma. Here, we report oxygen isotope data of diagenetically screened, well-preserved brachiopod calcite (δ18Ocalcite) from late Visean-Serpukhovian (or Middle-Late Mississippian; ~334–323 Ma) strata in South China where biodiversity data are well documented. The δ18Ocalcite data reveal a ~ 2.0‰ positive shift from −4.6 ± 0.2‰ to −2.7 ± 0.5‰ with an estimated ~4.7–5.5 °C drop in sea surface temperature (SST) during ~332.5–331.5 Ma in the late Visean. This cooling event coincides with fast decline of metazoan reef abundance, followed by decrease of benthic faunal diversity. The δ18Ocalcite data, in combination with calibrated sedimentological and biodiversity data, demonstrate the coupling between late Visean (~332 Ma) onset of the main glaciation phase of the LPIA and initiation of the M-LMBC.

Glaciations on ophiolite terrain in the North Pindus Mountains, Greece: New geomorphological insights and preliminary 36Cl exposure dating

A glacial geomorphological analysis of three valleys on Mt. Mavrovouni (North Pindus Mountains, Greece) is presented alongside a pilot study using cosmogenic 36Cl to obtain surface exposure ages from iron-rich ophiolite glacial and periglacial boulders. At least three distinct morphostratigraphic units of glacial (moraines) and periglacial (relict pronival ramparts) origin have been identified. Four 36Cl surface exposure ages were obtained from the stratigraphically youngest glacial and periglacial deposits. Although this limited dataset with relatively large uncertainties cannot support a robust geochronology, the ages are consistent with the 36Cl-based chronologies of limestone-derived moraines on Mt. Tymphi (NW Greece) and Mt. Chelmos (S Greece), confirming that the last glaciers on this massif formed during the Last Glacial Maximum as also indicated by other studies in the Pindus mountains. At the same time it provides confidence in the suitability of 36Cl dating for iron-rich samples, such as ophiolites, using an updated 36Cl model that incorporates improved production rates for iron spallation. The presented preliminary chronology of moraines and pronival ramparts is based on those ages as well as on local and regional morphostratigraphic correlations. The stabilisation of the most extensive Late Pleistocene glaciers took place during the Last Glacial Maximum, at 27.0 ± 6.5 ka whereas the presence of pronival ramparts dated at 20.2 ± 4.8 ka suggests persisting cold and arid conditions. Older, still undated glacial deposits exist lower in the valleys which can be attributed to the Middle Pleistocene major glaciation phases (MIS 12/MIS 6), based on their relative morphostratigraphic position within the glacial sedimentary sequence.

Krol Sandstone-black shale association of the Lesser Himalayan Neoproterozoic succession, Himachal Pradesh, India: An unexplored record of the hothouse aftermath

Citation of the inferred glacial diamictite-cap carbonate association, as the unequivocal evidence of the Snowball Earth hypothesis, fails to explain the absence of the sedimentary record of the intermediate period between the onset of thawing and the restoration of the optimum temperature for carbonate deposition. The Krol Sandstone-black shale association of the Lesser Himalayan Neoproterozoic succession, represents the initial phase of that hothouse aftermath. The black shale is the product of oceanic anoxia developed during the initial thawing phase of late Cryogenian glaciation. As the melting process continued, remobilization of some pre-existing aeolian sand sheet deposit, lying on the melting ice sheet in the upper shelf region, led to the accumulation of deeper shelf fans, the Krol Sandstone, over this black shale. The petrographic composition, detrital zircon age, and the palaeoflow directions, in conjunction with the available reconstructed paleogeography, suggest that the constituent sand particles of Krol Sandstone were possibly derived from a Late Neoproterozoic aeolian sand sheet of South Australia formed during the coldest phase of the late Cryogenian Elatina glaciation. These findings not only document the sedimentary record of the initial phase of the hothouse aftermath, but also open up a new line of evidence for paleogeographic reconstruction.

Evidence of a South Asian Proto‐Monsoon During the Oligocene‐Miocene Transition

AbstractThe geological history of the South Asian monsoon (SAM) before the Pleistocene is not well‐constrained, primarily due to a lack of available continuous sediment archives. Previous studies have noted an intensification of SAM precipitation and atmospheric circulation during the middle Miocene (∼14 Ma), but no records are available to test how the monsoon changed prior to this. In order to improve our understanding of monsoonal evolution, geochemical and sedimentological data were generated for the Oligocene‐early Miocene (30–20 Ma) from Indian National Gas Hydrate Expedition 01 Site NGHP‐01‐01A in the eastern Arabian Sea, at 2,674 m water depth. We find the initial glaciation phase (23.7–23.0 Ma) of the Oligocene‐Miocene transition (OMT) to be associated with an increase in water column ventilation and water mass mixing, suggesting an increase in winter monsoon type atmospheric circulation, possibly driven by a relative southward shift of the intertropical convergence zone. During the latter part of the OMT, or “deglaciation” phase (23.0–22.7 Ma), a long‐term decrease in Mn (suggestive of deoxygenation), increase in Ti/Ca and dissolution of the biogenic carbonate fraction suggest an intensification of a proto‐summer SAM system, characterized by the formation of an oxygen minimum zone in the eastern Arabian Sea and a relative increase of terrigenous material delivered by runoff to the site. With no evidence at this site for an active SAM prior to the OMT we suggest that changes in orbital parameters, as well as possibly changing Tethyan/Himalayan tectonics, caused this step change in the proto‐monsoon system at this intermediate‐depth site.

Last-glacial-cycle glacier erosion potential in the Alps

Abstract. The glacial landscape of the Alps has fascinated generations of explorers, artists, mountaineers, and scientists with its diversity, including erosional features of all scales from high-mountain cirques to steep glacial valleys and large overdeepened basins. Using previous glacier modelling results and empirical inferences of bedrock erosion under modern glaciers, we compute a distribution of potential glacier erosion in the Alps over the last glacial cycle from 120 000 years ago to the present. Despite large uncertainties pertaining to the climate history of the Alps and unconstrained glacier erosion processes, the resulting modelled patterns of glacier erosion include persistent features. The cumulative imprint of the last glacial cycle shows a very strong localization of erosion potential with local maxima at the mouths of major Alpine valleys and some other upstream sections where glaciers are modelled to have flowed with the highest velocity. The potential erosion rates vary significantly through the glacial cycle but show paradoxically little relation to the total glacier volume. Phases of glacier advance and maximum extension see a localization of rapid potential erosion rates at low elevation, while glacier erosion at higher elevation is modelled to date from phases of less extensive glaciation. The modelled erosion rates peak during deglaciation phases, when frontal retreat results in steeper glacier surface slopes, implying that climatic conditions that result in rapid glacier erosion might be quite transient and specific. Our results depict the Alpine glacier erosion landscape as a time-transgressive patchwork, with different parts of the range corresponding to different glaciation stages and time periods.

Scarce ctenacanthiform sharks from the Mississippian of Austria with an analysis of Carboniferous elasmobranch diversity in response to climatic and environmental changes

ABSTRACT The Carboniferous is characterized by drastic climatic and environmental fluctuations, which include multiple phases of glaciation resulting in an icehouse climate. Additionally, dynamic continental reconfigurations forced the contraction of the Rheic Ocean resulting in the closure of the Rheic–Tethyan Gateway, which precluded further faunal exchanges between the North American and Eurasian marine realms. Interestingly, cartilaginous fishes seem to be relatively immune to these drastic climatic and environmental changes. The Eurasian fossil record of Paleozoic sharks is strongly biased towards intensively sampled localities from England, Ireland, Scotland, and the Russian Platform. Here we present rare dental material from the Serpukhovian (early Carboniferous) of Austria, adding new information to the paleogeographic distribution of ctenacanthiform sharks. The new material revealed the first record of the genus Saivodus in Central Europe and allowed us to recognize a new species, Cladodus gailensis sp. nov., and a remnant of fossilized cartilage. In an attempt to identify possible linkages between climatic or environmental fluctuations on shark diversity throughout the Carboniferous, we provide a synopsis of the distribution and diversity of elasmobranchs based on primary literature. This preliminary assessment at genus level indicates two pronounced events of extinction, with the first one occurring during the latest Mississippian and the second one towards the end of the Pennsylvanian. The first extinction event distinctly correlates with the known diversity decline of other marine inhabitants and the second occurred during an unstable period of multiple phases of glaciation.

A Pleistocene deposit preserved in deep karst at Coolough, County Galway, western Ireland

Buried karst features result from a complex interplay between carbonate bedrock and structural geology. The enhancement of carbonate aquifers through this interplay creates hydrogeologically complex subsurface drainage networks and highly variable surface topographies. This article reports on the sediment fill and fossil pollen record from a large enclosed negative karst landform at Coolough, near Galway City in the west of Ireland. The landform was discovered during the preliminary site investigation for the proposed N6 Galway City Ring Road. Major joint sets developed in the Carboniferous (Mississippian) Limestone bedrock govern the local hydrogeology and structural evidence suggests that a local fault has controlled the east–west propagation of the deep enclosed depression. Fluvial and lacustrine palaeoenvironments are interpreted from the sediments infilling the enclosed depression, within which three discrete diamicts are identified, potentially representing distinct phases of glaciation. Pollen assemblages, which reflect palaeoenvironments of open woods and grasslands, have been correlated with other deposits in Ireland and Europe and suggest a minimum date of the Early Pleistocene for the oldest of the diamicts, and thus an upper age limit on the development of the karst depression. Fluvial disturbance to the deposit is evident and is likely to be responsible for the chronological discrepancy between the Early Pleistocene and Middle Pleistocene sediments both recorded from the deposit infill. The findings of this multidisciplinary study contribute to an understanding of Quaternary landscape evolution in western Ireland.

Geology and Aquifer Sensitivity of Quaternary Glacial Deposits Overlying a Portion of the Mahomet Buried Bedrock Valley Aquifer System

To characterize the distribution of Holocene and Late Quaternary deposits and to assess the contamination potential of the Mahomet Aquifer, surficial geologic and aquifer sensitivity maps of the Gibson City East 7.5-Minute Quadrangle were created. Geologic data, extent, and thickness of the geologic materials were coupled with LiDAR topographic data and analyzed using ESRI’s ArcGIS 10.6.1. Aquifer sensitivity to contamination was calculated based on the depth to the first aquifer unit, aquifer thickness, and the lithology of the aquifer materials. The surficial geologic mapping identified five lithostratigraphic units: the Cahokia Formation, the Equality Formation, the Henry Formation, and the Yorkville and Batestown Members of the Lemont Formation. The southeast to northwest trending Illiana Morainic System is the most prominent feature in the study area and delineates the maximum extent of the glaciers during the Livingston Phase of glaciation. Postglacial deposits of the Cahokia Formation, alluvium, interfinger, and overlie with glacial outwash of the Henry Formation along channels and drainage ways downslope of the moraine. The areas of least sensitivity are located over the Illiana Morainic System, whereas the greatest potential to contamination occurs where the thickest deposits of the Henry Formation and Cahokia Formation lie at or just below the land surface.

Latest Pleistocene glacial and climate history of the Wasatch Range, Utah

The geologic record of mountain glaciation is one of the most sensitive archives of terrestrial climate change during the late Quaternary Period. Pleistocene glacial deposits are exceptionally well preserved in the Great Basin of North America where they are found in close proximity to shoreline deposits of coeval paleo-lakes, representing a unique opportunity to investigate paleoclimate change using both hydrologic systems. Mountain glaciers advanced across much of the Wasatch Range, Utah during the same general time interval when Lake Bonneville expanded in the adjacent Bonneville Basin. Here we present a range-wide Latest Pleistocene glacial history for the Wasatch Range based on 22 new and 41 recalculated cosmogenic 10Be surface exposure ages, and reconstruct glaciers and climate for the Last Glacial Maximum (LGM) and Lateglacial periods. Our results indicate three distinct, range-wide phases of glaciation in the Wasatch including the Pinedale 1 (ca. 21–20 ka), Pinedale 2 (ca. 17.5 ka) and Pinedale 3 (ca. 15 ka). Our modeling results indicate that the Pinedale 1 advance, near the end of the global LGM, was primarily driven by decreased annual temperatures with little to no change in precipitation as compared to modern. Wasatch glaciers appear to have reoccupied near maximum positions after the end of the LGM during the Pinedale 2, responding to increased precipitation in concert with rising lake levels across Western North America, and then retreated from ice-distal positions near ca. 17.5 ka. Wasatch glaciers occupied recessional positions at approximately half their maximum lengths during Pinedale 3 until ca. 15 ka, followed by rapid (i.e. several millennia) deglaciation. Our glacial chronologies establish that Wasatch glaciers responded synchronously across the range to global and regional climate forcings during the Latest Pleistocene. The new Wasatch glacial chronology, combined with global glacial chronologies and paleoclimate proxies from Western North America, suggest glacier change was driven by a combination of long-term global temperature forcing as well as regional to local modifications in precipitation.

Timing of the Late Palaeozoic glaciation in western Gondwana: New ages and correlations from Paganzo and Paraná basins

During the Late Palaeozoic, the Gondwana supercontinent formed an extensive Southern Hemisphere landmass that was affected by multiple glacial episodes, known collectively as the Late Palaeozoic Ice Age (LPIA). This resulted in the deposition of glacial, periglacial and deglacial sediments over much of the supercontinent. The Mississippian to early Pennsylvanian phase of glaciation is widely represented along the western margin of Gondwana. This constitutes one of the largest glaciations of the Phanerozoic in terms of its recorded extent and the widespread erosional hiatus it produced in the stratigraphic record. It was this mid Carboniferous glaciation, recorded in the Paganzo Basin of NW Argentina, that carved most of the paleovalleys and paleofjords present there. We report new U-Pb zircon ages from a single glacial succession (Guandacol Formation) of 326 ± 3 Ma and 320 ± 5 Ma, that in comparison with neighbouring dated sequences allow for the first time a reliable estimate of the timing and duration of glacial cycles. Palynological studies of these glacial-deglacial events yielded palynoassemblages of the MQ (Late Visean) and DMa (Sepukhovian-Bashkirian) Palynozones. The Carboniferous glacially-related strata and glacial cycles of the Paganzo Basin are compared here with equivalent units of the Paraná Basin of SE Brazil, suggesting a similar climate record for most of western Gondwana. We propose a new correlation between these two basins. The new U-Pb zircon ages reported here indicate that a regional glacial peak occurred almost coincident with the Mississippian-Pennsylvanian boundary, suggesting that the ensuing postglacial transgression is the best regional marker to differentiate the Mississippian and Pennsylvanian as it forms an identifiable interbasinal horizon. The biostratigraphic and chronostratigraphic comparison with other LPIA successions from South America reinforces that the First Appearance Datum of monosaccate pollen grains occurs in the late Serpukhovian. Their correlation confirms that similar climate conditions prevailed across most of western Gondwana during this phase of the LPIA.

Genesis of the pleistocene hummocky moraines in the Moracke Planine Mountains (Montenegro)

The Moracke Planine Mountains, situated in the central part of Montenegro, were the center of intensive Pleistocene glaciation. Specific type of moraines - hummocky ones, which have not been recorded in the southeastern Dinarides up to now, were recently identified and investigated in western part of the Moracke Planine Mts. Moraine material accumulated on limestone basement, where several tens of irregularly distributed hummocks and similar number of bowl-shaped dolines have been carved already. The hummocky moraines formed in the glaciokarst landscape where the well-developed karst morphology has been shaped before glaciation. Pre-glacial karst morphology determined the direction of glacier movement as well as its main morphological characteristics (thickness and width). During the most intensive glaciation phase (?IS 12) the Lukavicko-lukovski Glacier, spread out from the central part of mountain towards west, reaching a length of 16.5 km. Due to uneven glacier thickness, the deglaciation process led to its breaking and separation of the lower and shorter part from the rest of the icy mass. Stagnant state of the icy mass led to specific accumulation of moraine material in a form of numerous hummocks, whose melting produced a bowl-shaped dolinas in-between. The paleogeographic significance of hummocky moraines lies in the possibilities of more detailed studies of the Pleistocene glaciers specifics that arise from their evolution in glacio-karst conditions.

Deep ocean 14C ventilation age reconstructions from the Arctic Mediterranean reassessed

The present-day ocean ventilation in the Arctic Mediterranean (Nordic Seas and Arctic Ocean), via transformation of northward inflowing warm Atlantic surface water into cold deep water, affects regional climate, atmospheric circulation and carbon storage in the deep ocean. Here we study the glacial evolution of the Arctic Mediterranean circulation and its influence on glacial climate using radiocarbon reservoir-age reconstructions on deep-sea cores from the Fram Strait that cover the late glacial period (33,000–20,000 yr ago; 33–20 ka). Our results show high Benthic-Planktic 14C age differences of ∼1500 14C years 33–26.5 ka suggesting significant water column stratification between ∼100–2600 m water depth, and reduction and/or shoaling of deep-water formation. This phase was followed by break-up of the stratification during the Last Glacial Maximum (LGM; 26–20 ka), with Benthic-Planktic 14C age differences of ∼250 14C years, likely due to enhanced upwelling. These ocean circulation changes potentially contributed to the final intensification phase of glaciation via positive cryosphere-atmosphere-ocean circulation-carbon cycle feedbacks. Our data also do not support ‘extreme aging’ of >6000 14C years in the deep Arctic Mediterranean, and appear to rule out the proposed outflow of very old Arctic Ocean water to the Nordic Seas during the LGM and to the subpolar North Atlantic Ocean during the deglacial period.

Pleistocene glacial history of the New Zealand subantarctic islands

Abstract. The New Zealand subantarctic islands of Auckland and Campbell, situated between the subtropical front and the Antarctic Convergence in the Pacific sector of the Southern Ocean, provide valuable terrestrial records from a globally important climatic region. Whilst the islands show clear evidence of past glaciation, the timing and mechanisms behind Pleistocene environmental and climate changes remain uncertain. Here we present a multidisciplinary study of the islands – including marine and terrestrial geomorphological surveys, extensive analyses of sedimentary sequences, a comprehensive dating programme, and glacier flow line modelling – to investigate multiple phases of glaciation across the islands. We find evidence that the Auckland Islands hosted a small ice cap 384 000 ± 26 000 years ago (384±26 ka), most likely during Marine Isotope Stage 10, a period when the subtropical front was reportedly north of its present-day latitude by several degrees, and consistent with hemispheric-wide glacial expansion. Flow line modelling constrained by field evidence suggests a more restricted glacial period prior to the LGM that formed substantial valley glaciers on the Campbell and Auckland Islands around 72–62 ka. Despite previous interpretations that suggest the maximum glacial extent occurred in the form of valley glaciation at the Last Glacial Maximum (LGM; ∼21 ka), our combined approach suggests minimal LGM glaciation across the New Zealand subantarctic islands and that no glaciers were present during the Antarctic Cold Reversal (ACR; ∼15–13 ka). Instead, modelling implies that despite a regional mean annual air temperature depression of ∼5 ∘C during the LGM, a combination of high seasonality and low precipitation left the islands incapable of sustaining significant glaciation. We suggest that northwards expansion of winter sea ice during the LGM and subsequent ACR led to precipitation starvation across the middle to high latitudes of the Southern Ocean, resulting in restricted glaciation of the subantarctic islands.

Palaeoseismic structures in Quaternary sediments of Hamburg (NW Germany), earthquake evidence during the younger Weichselian and Holocene

Investigations at a construction site in Hamburg (NW Germany) exposed palaeoseismic structures from moderate to strong earthquakes. Based on the large size of large blowout clastic dykes being up to 2.0 m wide and 2.5 m high, as well as the occurrence of infill structures, erratics/rafts of up to 9 kg in weight, seismites s.s. and decimetre-scale folds or seismoslumps, the magnitude of the earthquakes could be in the order of up to M ≥ 6. This is significantly higher than previously assumed for prehistorical seismic events in NW Germany. The structures are assigned to earthquakes possibly related to NW–SE-oriented faults that are evident in Lidar and SAR surface interpretations. Organic material from blowout-related infill bowls, assumed to be synchronously formed collapse depressions, are analysed for 14C ages. The dates reveal ages between 31,500 and 1200 14C cal a BP, indicating five prehistoric earthquakes. Accordingly, three of these earthquakes occurred before and after the main Weichselian glaciation phase (ca. 31,350, 26,850 and 18,980 14C cal a BP), and two occurred during the Subatlantic (ca. 4900 and 1200 14C cal a BP). The Weichselian events indicate seismic activity in the ice marginal zone during or following interstadials/Dansgaard–Oeschger events, as well as suggesting that advancing ice sheets foster earthquakes.

Mississippian lithofacies and foraminiferal biozonation of the Alborz Mountains, Iran: Implications for regional geology

The Mississippian rocks at 5 sections, Kalariz, Peyghambaran, Jaban, Naserabad, and Dozdehban, have been measured and sampled in a SE–NW direction across the Alborz Mountains. Foraminiferal zones recognized in those sections, as well as a revision of other foraminiferal assemblage previously published from the Alborz Mountains, allow to recognize 12 biozones: 5 in the Tournaisian: Unilocular (MFZ1–MFZ2? interval), Septabrunsiina krainica (MFZ3–MFZ5 interval), Eotextularia diversa (MFZ6), Darjella monilis (MFZ7), and primitive Eoparastaffella (MFZ8); 5 Viséan biozones: Eoparastaffella simplex (MFZ9), primitive archaediscids (MFZ10), Uralodiscus rotundus (MFZ11), Pojarkovella–Koskinotextularia (MFZ12), Neoarchaediscus (Upper Mikhailovian), Howchinia gibba–Archaediscus/Paraarchaediscus at angulatus‐tenuis stage–Neoarchaediscus akchimensis (Venevian substage); and 2 Serpukhovian biozones: Biseriella parva–Climacammina (Tarusian–Steshevian substages) and Turrispiroides multivolutus–Brenckleina–Eostaffellina protvae (Protvian substage) for the Mississippian rocks of Alborz. Analysis of foraminiferal assemblages indicates a noticeable age difference of the Mississippian rocks between the northern and southern flanks of Alborz. Accordingly, south‐eastern and east‐central Alborz (Kalariz, Peyghambaran, and Jaban sections) display complete Tournaisian deposits (MFZ1–MFZ8), whereas northern Alborz contains the strata dated from Late Tournaisian to Late Serpukhovian (MFZ8–MFZ16). The sedimentological studies also reveal sharp facies variations following the mentioned age variation. Previously, the age variations of these rocks were attributed to various events, such as the Mississippian glaciation phases. However, the age, facies, and thickness variations of lithostratigraphic units in the Alborz are not specific to the Mississippian and are reported during the entire Palaeozoic and even Mesozoic and Cenozoic. They can rather be attributed to the inherited basement and syn‐sedimentary E–W‐trending faults.