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The West Antarctic Peninsula (WAP) margin is dominated by glaciomarine fjords and has experienced rapid climate warming in recent de cades. Glacial calving along the peninsula delivers ice-rafted debris (e.g. dropstones) to heavily sedimented fjord basins and the open continental shelf. Dropstones provide hard substrate, increase habitat heterogeneity, and may function as island habitats surrounded by mud. We used seafloor photographic transects to evaluate the distribution and community structure of Antarctic hard-substrate megafauna and the role of dropstones as island habitats in 3 WAP fjords and at 3 nearby shelf stations. Several lines of evidence indicate that dropstones function as island habitats; their communities adhere to principles of island biogeography theory with (1) a positive correlation between dropstone size and species richness, (2) an increase in the proportion of colonized dropstones with increasing dropstone size, and (3) a species−area scaling exponent consistent with island habitats measured globally. Previous work on the soft-sediment megafauna of this region found strong differences in community composition between fjord and shelf sites, whereas we found that dropstone communities differed within sites at small scales (1 km and smaller). We identified 73 megafaunal morphotypes associated with dropstones, 29 of which were not previously documented in the soft-sediment mega - fauna. While dropstones constituted >1% of the total seafloor area surveyed, they contributed 20% of the overall species richness of WAP megabenthos at depths of 437–724 m. WAP dropstone communities adhere to key principles of island biogeography theory, contribute environmental heterogeneity, and increase biodiversity in the WAP region.

During more than a century since its original identification, the Gowganda Formation in Ontario (Canada) has gradually been reinterpreted from representing mainly subglacial tillites to secondary gravity flow and glaciomarine deposits. The main pieces of geological evidence advanced in favour of glaciation in recent articles are outsized clasts that have been interpreted as dropstones and patches of diamictites in a single small-sized area at Cobalt which is still interpreted as displaying subglacial basal tillites. The present research considers field evidence in the Gowganda Formation in the light of more recent work on gravity flows linked to tectonics. Detailed studies have demonstrated that the clasts which are interpreted to be dropstones rarely penetrate laminae and are commonly draped by sediments the appearance of which is similar to lonestones in gravity flows. The “subglacial area” at Cobalt displays evidence of tectonics and gravity flows, which can be traced from the underlying bedrock, and then further in the overlying sequence of diamictites and rhythmites. The sum of geological features displays appearances at odds with a primary glaciogenic origin, and there is no unequivocal evidence present of glaciation. The data indicate deposition by non-glaciogenic gravity flows, including cohesive debris flows for the more compact units, probably triggered by tectonic displacements.

The seafloor beneath floating ice shelves accounts roughly a third of the Antarctic’s 5 million km 2 of continental shelf. Prior to this study, our knowledge of these habitats and the life they support was restricted to what has been observed from eight boreholes drilled for geological and glaciological studies. The established theory of sub-ice shelf biogeography is that both functional and taxonomic diversities decrease along a nutrient gradient with distance from the ice shelf front, resulting in a depauperate fauna, dominated by mobile scavengers and predators toward the grounding line. Mobile macro-benthic life and mega-benthic life have been observed as far as 700 km under an ice shelf. New observations from two boreholes in the Filchner-Ronne Ice Shelf challenge the idea that sessile organisms reduce in prevalence the further under the ice you go. The discovery of an established community consisting of only sessile, probably filter feeding, organisms (sponges and other taxa) on a boulder 260 km from the ice front raises significant questions, especially when the local currents suggest that this community is somewhere between 625 km and 1500 km in the direction of water flow from the nearest region of photosynthesis. This new evidence requires us to rethink our ideas with regard to the diversity of community types found under ice shelves, the key factors which control their distribution and their vulnerability to environmental change and ice shelf collapse.

Models (paradigms) and former interpretations have often been presupposed when conducting field research. In the 19 century diamictites were for the first time interpreted to have originated from ancient glaciations. These interpretations have to a large part prevailed in the geological community, although there has been much progress in the areas of sedimentology, glaciology and physical geography. The present work is an effort to find criteria which most clearly discriminate between geological features produced by different processes, mainly glaciation and mass flow, the latter predominantly sediment gravity flows. Geological features which have been interpreted to have formed by glaciation throughout pre-Pleistocene Earth history are compared to similar-appearing geological features formed by mass flow and tectonics, so as to uncover variations in the appearance between features resulting from these different processes. The starting point for this comparison is documentation of the appearance of Quaternary products of erosion and deposition, in order to discern the origin of older formations. It is shown that the appearance and origin of pavements, dropstones, valleys, small-scale landforms, surface microtextures and most other geological features may in some cases be equivocal, but in others the details are indicative of the process which generated the feature. Detailed geological field data which have been compiled by geologists from outcrops of pre-Pleistocene strata, more often than is considered in most papers, commonly point to a mass flow origin, mainly a sediment gravity flow origin, rather than a glaciogenic origin. A process of multiple working hypotheses or interpretations is therefore advocated, based mainly on a comparison of the appearance of features formed by different geological processes documented from different research disciplines. Instead of starting with current interpretations or models, this multiple working hypothesis or methodology helps to avoid confirmation bias and jumping to conclusions.

We present geomorphic, stratigraphic, and chronological data acquired along the General Carrera–Buenos Aires (GCBA) glacial lake located along a major morphological incision across the Andes. Complementing relevant available data, relative chronology of morphoclimatic records together with 18 10Be cosmic ray exposure ages allow constraining the timing of the Patagonian ice sheet fluctuations since the last glacial maximum. It improves the knowledge of Patagonia climate evolution in the 46°–48°S area and allows documenting the uplift rates (glacial rebound) for the past ∼7–9 ka. The first major ice lobe retreat occurred after 17.3 ± 0.6 ka and has likely continued during the Antarctic cold reversal from ∼12.9 to 14.5 ka. Between ∼12.9 and ∼10.9 ± 1.3 ka, the General Carrera Lake evolved as an endorheic basin. Terraces T4–T1 (top to bottom) have recorded abrupt lake regressions likely controlled by rainfall deficit. They have accumulated in the time interval ∼17.3–12.3 ka (maximum limits). Two glacial re-advances at ∼10.9 ± 1.3 and ∼7.9 ± 1.1 ka marked a major climate change that led the lake to be ice dammed again. A major transgression occurred that subsequently flooded the previously accumulated terraces. Since then, a pervasive regression has steered the GCBA Lake to the situation at present. The highest shoreline of the transgression is used as a passive marker in order to quantify the magnitude and character of the regional deformation. At long 72°30′W, the GCBA Lake area uplifted (glacial rebound) at a rate between 15 and 33.5 mm yr−1 during the past ∼7.9 ± 1.1 ka. We infer that the high uplift rate mainly originates from the North Patagonian icefield ice loss.

This study developed a novel, detailed sedimentological analysis for the complex interactions between rainout, iceberg rafting, tractional underflows, and settling of fines along a glacially influenced basin margin. The glaciomarine interval of the El Imperial Formation (Pennsylvanian, Serpukhovian–Bashkirian) in the San Rafael basin comprises massive to stratified diamictites, interpreted as rainout tills, thinly bedded diamictites, associated with cohesive debris flows, and mudstones containing ice-rafted debris (IRD), all capped by postglacial, transgressive, fine-grained sediments. The rhythmic intercalation of IRD-bearing (dropstone mudstones) and IRD-free (mudstones) intervals likely indicates variations in debris content within the ice margins, the on-and-off switching of ice streams, or dynamic oscillations of the ice terminus. The glaciomarine deposits exhibit soft sediment deformation on both large (metric to decametric) and small (centimetric) scales. This contribution refines previous interpretations of the soft sediment deformation, discerning between loading and slope triggered deformation. Large-scale deformation is characterized by coherent slump folds with low dispersion in the orientations of fold axial plane vergence and fold b -axes. Downslope-verging folds indicate a northward paleoslope, consistent with paleoflow indicators from flute casts found in sandstone turbidite beds. The diamictites affected by the large-scale soft sediment deformation are interpreted as rainout tills with a variable degree of gravity remobilization. Their association with thinly bedded diamictites and laminated mudstones with dropstones suggests that ice rafting played a significant role in the deposition of this succession. Graphical abstract

The late Paleozoic archives a prolonged icehouse, long recognized by means of Gondwanan continental glaciation. In contrast, the paleotropics have long been considered warm. Here we present the hypothesis of upland glaciation in the Ancestral Rocky Mountains (ARM) of western equatorial Pangaea, a region located within 11° of the paleoequator. The data to support this hypothesis include (a) a Permo-Pennsylvanian valley with glacial attributes and diamictite exhibiting rare striated clasts; (b) coarse-grained lacustrine strata onlapping the valley and preserving lonestones in Gilbert-type deltaic deposits proximally, along with (c) coarse-grained fluvial siliciclastic strata with microstriae and evidence for widespread flood deposition; (d) polygonally cracked paleosurfaces inferred to reflect frozen ground; and (e) voluminous paleoloess. Tropical glaciation occurs today at altitudes >4500 m and descended to 2100-3000 m at the last glacial maximum (LGM). However, ARM depositional systems terminating at sea level and emanating from inferred ice-contact facies indicate that ice-terminus elevations were lower (<1200-1600 m) than those of the LGM. If valid, tropical temperatures were -15°C cooler than today during intervals recording hypothesized tropical glacial conditions. This implies at least episodic cold within western tropical Pangaea, which conflicts with inferences from oxygen isotope paleothermometry. Furthermore, climate models for the late Paleozoic cannot reproduce tropical upland glaciation except under prohibitively low PCO2, implying the need to consider other forcings, such as cloud and aerosol behavior. Upland glaciation in the Permo-Pennsylvanian tropics was potentially widespread, given the global orogenesis accompanying Pangaean assembly. However, testing this hypothesis requires identification of pro- and periglacial indicators, owing to widespread erosion of upland (glaciated) regions. Midlatitude glaciation in both hemispheres also was likely, challenging climate models and paleogeographic consensus for this period.

The ∼2700 Ma Talya Conglomerate is comprised of 15 diamictites (i.e. matrix-supported conglomerates) interbedded with mudstone and sandstone units, and is interpreted as a glaciomarine deposit. The entire thickness of this conglomeratic member within the Vanivilas Formation, the lowest formation of the Chitradurga Group of the Neoarchean Dharwar Supergroup, is exposed in a 543 m-thick measured section. It is in a sub-vertical attitude, is highly sheared, and has undergone greenschist facies metamorphism. The diamictites had an original matrix of laminated mud/silt and fine sand. While including diamictites throughout, the Talya is a fining-upward sequence with intercalated sandstones dominant in its lower portion and mudstones dominant in its upper portion. We interpret that the Talya Conglomerate was deposited in a marine environment, with diamictites composed of ice-rafted detritus (IRD) deposited from icebergs calved from tidewater glacier tongues and/or possibly from ice shelves. In these 'rainout diamictites', the larger clasts were dropped into finegrained bottom sediment deposited by sediment plumes and currents. The source ice sheet was located to the west and southwest on a land mass that included the older than 2720 Ma Bababudan Group of quartzites and mafic volcanics and older than 3000 Ma basement of granitic/gneissic rocks. Application of Walther's law indicates that the mudstone-bearing portion of the Talya was deposited upon the sandstone-bearing portion as the sea further inundated the land mass due to glacial retreat and a decrease in glacial mass, thereby resulting in the fining-upward nature of the Talya Conglomerate. We also interpret the lower portion of the Kaldurga Conglomerate, located 50–75 km to the southwest of the Talya, to be equivalent with the Talya. The Kaldurga contains mostly granitic basement detritus, perhaps exposed due to basement uplift related to isostatic rebound caused by glacial melting or due to tectonism related to westward subduction.

This study presents the first analysis of benthic megafauna and habitats from the Sabrina Coast shelf, encompassing a proposed Marine Protected Area. Sea bed imagery indicated an abundant benthic fauna compared to other parts of the Antarctic shelf, dominated by brittle stars, polychaete tubeworms, and a range of other sessile and mobile taxa. The distribution of taxa was related (ρ=0.592, P<0.001) to variations in water depth, latitude, substrate type and phytodetritus. High phytodetritus cover was associated with muddy/sandy sediments and abundant holothurians and amphipods, while harder substrates hosted abundant brachiopods, hard bryozoans, polychaete tubeworms, massive and encrusting sponges, and sea whips. Brittle stars, irregular urchins and anemones were ubiquitous. Variations in substrate largely reflected the distribution of dropstones, creating fine-scale habitat heterogeneity. Several taxa were found only on hard substrates, and their broad regional distribution indicated that the density of dropstones was sufficient for most sessile invertebrates to disperse across the region. The hexactinellid sponge Anoxycalyx joubini and branching hydrocorals exhibited a more restricted distribution, probably related to water depth and limited dispersal capability, respectively. Dropstones were associated with significant increases in taxa diversity, abundance and biological cover, enhancing the overall diversity and biomass of this ecosystem.

We examined encrusting organisms on seven polymetallic nodules from the eastern Clarion Clipperton Fracture Zone (CCFZ, ∼4070 m water depth, eastern equatorial Pacific). Apart from occasional sponges and a single bryozoan, all the organisms were foraminifera or foraminifera-like protists. A total of 75 morphotypes (presumed to be morphospecies) was recognised, with between 9 and 19 being present on individual nodules. Additional species were observed during shipboard examination of the nodules, bringing the total number of species to 86. The assemblage was dominated by a variety of mat-like formations, clusters of patches, isolated domes, broad trails, anastomosing networks and branched or unbranched tubular structures that either lay flat against the nodule surface or projected away from the surface. These forms were interpreted as monothalamous foraminifera (monothalamids). Most have mainly agglutinated walls but a few are predominately organic. Some can be assigned to the Komokiacea (notably the genus Chondrodapis ) or families such as the Hemisphaeramminidae ('domes'), while others (e.g. many of the mats and patch-like forms) are difficult to place into existing monothalamid groupings. Some of the branching and anastomosing tubes resemble the genus Rhizammina . The most easily recognisable morphotypes include Telammina , in which tiny chambers are linked by extremely thin tubes to form a network, and sinuous orange tubes that incorporate sponge spicules and can be assigned to the genus Saccorhiza based on the occasional presence of a proloculus. Polythalamous foraminifera are also fairly common. They include various calcareous species (mainly Cibicides spp.), as well as agglutinated forms such as Hormosina , ? Placopsilina and trochamminaceans. Similar assemblages, including some morphospecies that are clearly identical to ours, have been described previously from somewhat deeper sites (4500–5000 m) in the CCFZ. In order to explore distributions at a global scale, we compared our Pacific nodule assemblages to foraminifera attached to ice-rafted dropstones from several deep seamounts in the abyssal northeast Atlantic Ocean, mainly on the Porcupine Abyssal Plain (4630–4680 m depth) with additional material from the BIOTRANS area (3796–4351 m). These hosted superficially similar assemblages of mats, tubular forms, komokiaceans and polythalamous calcareous and agglutinated foraminifera. However, apart from the sometimes extensive development of Telammina networks, there were no morphospecies in common between the Pacific and Atlantic assemblages. These preliminary observations, based on limited material, suggest that most of the foraminiferal morphospecies encrusting hard substrates are widely distributed at regional scales in the abyssal Pacific but not necessarily at global scales. The study of abyssal encrusting assemblages poses considerable challenges. Priorities for the future include the development of reliable methods for distinguishing living and dead individuals, and molecular approaches to clarifying the taxonomic affinities of novel morphotypes.