Abstract A glaciated margin is a continental margin that has been occupied by a large ice mass, such that glacial processes and slope processes conspire to produce a thick sedimentary record. Ice masses take an active role in sculpting, redistributing and reorganizing the sediment that they erode on the continental shelf, and act as a supply route to large fan systems (e.g. trough mouth fans, submarine fans) on the continental slope and continental rise. To many researchers, the term ‘glaciated margin’ is synonymous with modern day areas fringing Antarctica and the Arctic shelf systems, yet the geological record contains ancient examples ranging in age from Precambrian to Cenozoic. In the pre-Pleistocene record, there is a tendency for the configuration of the tectonic plates to become increasingly obscure with age. For instance, in the Neoproterozoic record, not everyone agrees on the location of rift margins and some fundamental continental boundaries remain unclear. Given these issues, this introductory paper has two simple aims: (1) to provide a brief commentary of relevant Geological Society publications on glaciated margins, with the landmark papers highlighted and (2) to explain the contents of this volume.

Abstract The Chuos Formation of Namibia is the sedimentary product of the Neoproterozoic Sturtian ( c. 720–660 Ma) glaciation and contains massive diamictites intercalated with finely laminated iron formation. Similar Sturtian glacially associated iron formations are found globally. The iron formations are laminated and generally very pure. The diamictites are massive, contain abundant clasts and can be highly ferruginous. These two lithofacies are repeatedly interbedded with no facies transition. The iron formations preserve the rare earth element geochemistry of their contemporaneous seawater and contain rare Ce and Eu anomalies. The geochemistry does not implicate a hydrothermal influence. The Chuos iron formation is interpreted to have been deposited in an ice-proximal glacio-marine setting in a sub-ice shelf environment. Oxygenated fluids, such as sea ice brines and glacial meltwater, are invoked as a mechanism to precipitate iron oxides due to mixing with ferruginous seawater. The iron formation accumulates under an ice shelf with little clastic input. Episodic movement of the grounding line reworks the sediments into ferruginous diamict. Glaciogenic debris flows are intercalated with the iron formations. Palaeobathymetric depressions and accompanying brine pools increased the preservation potential of these iron formations. This model explains the relationship between glaciation and iron formation in the Neoproterozoic. Supplementary material: The full set of geochemical data is available at https://doi.org/10.6084/m9.figshare.c.4031125.v1

Abstract The Death Valley area of California, USA, exposes an outstanding record of a Neoproterozoic (Cryogenian) glaciated margin: the Kingston Peak Formation. Despite the quality of the exposure, however, the outcrops of glaciogenic strata are fragmentary, forming isolated, laterally offset outcrop belts at the western extremity of the Basin and Range province. Excellent evidence for glacially modulated sedimentation includes (1) ice-rafted dropstones in most ranges, (2) thick diamictites bearing a variety of exotic (extrabasinal) clasts, (3) striated clasts and (4) local occurrences of glacitectonic deformation structures at the basin margins. In tandem with this, there is a distinct signature of slope collapse processes in many ranges, including (1) up to kilometre-scale olistoliths, (2) extensional growth fault arrays, (3) dramatic proximal-distal thickness changes and (4) basalt occurrences. New sedimentological observations reinforce long-held views of rifting superimposed on glaciation (or vice versa), with both processes contributing to a complex record whereby rift and glacial processes vie for stratigraphic supremacy. We consider that a mechanism of diamictite accumulation in a series of rift-shoulder minibasins produced greatly contrasting successions across the Death Valley area, under the incontrovertible influence of hinterland ice sheets.

Abstract The late Ordovician glaciation in the Kingdom of Saudi Arabia is spectacularly represented in the rocks of the Sarah Formation, although relatively little has been published about this formation. This paper describes and discusses the Zarqa megafacies of the Sarah Formation, which crops out across a distance of 720 km in the NW of the Kingdom as a heavily deformed diamicton, representing an example of widespread subglacial deformation. At outcrop, this Zarqa megafacies consists of two major subfacies. Subfacies (M) consists of a deformed, pebble-bearing substrate of interstratified, argillaceous, very fine- to fine-grained sandstones and siltstones. It displays a glacio-tectonically derived internal stratigraphy consisting of two units. Unit (i) is a pebbly diamictite displaying recumbent folding and thrusting indicative of progressive simple shear and manifest in a number of glacio-tectonically stacked detachment sheets. Unit (i) is abruptly overlain by Unit (ii). This consists of a lower Unit (iia), which displays soft sediment folding, including common sheath folds, as well as dewatering phenomena, passing up gradationally into almost completely homogenized sandy siltstone of Unit (iib) with rare detached masses of contorted sandstone. Subfacies (M) represents subglacial deforming bed conditions that reflect variable, but overall upwardly increasing, pore fluid overpressure in the pre-glacial substrate as it was overridden by the advancing Hirnantian ice sheet. It has been identified in subsurface core material, displaying asymmetrical strain profiles that also indicate subglacial deforming bed conditions. Subfacies (N) is a heavily deformed, boulder-bearing subglacial tillite commonly expressed in a distinctive mounded landscape of irregular piles of debris up to 8 m high. Extremely poorly sorted, it contains outsize boulders of glaciogenically deformed Lower Paleozoic sediments and striated Precambrian crystalline rocks. This subfacies represents a subglacially uprooted substrate that was transported considerable distances by the overriding ice sheet. Aspects of the Zarqa megafacies have parallels in coeval glaciogenic rocks identified from across northern Gondwana and beyond. This megafacies is therefore considered to have considerable sequence stratigraphic significance, representing deformed lowstand substrate and subglacial deposits associated with the accumulation and advance(s) of the late Ordovician ice sheets.

Abstract Late Ordovician glacial deposits are of great importance in North Africa and the Middle East as a result of their significance as reservoirs for hydrocarbons and groundwater. The sedimentary record of this glaciation in NW Saudi Arabia (the Sarah Formation) is generally preserved in meridionally oriented palaeovalleys cut beneath northward-flowing ice sheets. In the Tabuk region of NW Saudi Arabia, an apparently intersecting complex of north–south- and east–west-oriented palaeovalleys occurs in the Alwizam area. Field relationships show two generations of palaeovalley incision, suggesting that the north–south-oriented palaeovalley was cut subglacially, filled, subsequently deformed and then cross-cut by the east–west-oriented palaeovalley. Abundant facetted and striated quartzite clasts occur at the base of each palaeovalley, testifying to a subglacial origin. Detailed examination of the north–south-oriented palaeovalley shows it to be well-defined with symmetrical sides. Its fill is composed of nine lithofacies grouped into four facies associations. About 80% of the fill consists of three sandstone facies: a parallel-bedded massive sandstone, a stacked scoured sandstone and a massive sandstone. Centimetre-scale extensional faults developed in soft sediments are commonly found throughout the stratigraphy, along with a glacially striated surface seen mid-way through the succession. These features provide evidence for direct ice contact, synglacial fill, and consequent reworking, cannibalization and deformation by the fluctuating ice margin.

Abstract Latest Ordovician glacial sediments crop out in southern Jordan and adjacent areas of Saudi Arabia, where they consist of mainly coarse clastics. These sediments were in part deposited within steep-sided tunnel valleys with palaeotransport towards the north to NE. In NE Jordan, the distal equivalents of some of these valley-confined clastics are encountered in the subsurface, where they form the reservoir units within the Risha gas field. Here, the succession consists of stacked sandstone units ranging from a few metres to >20 m thick alternating with thinner mudstone horizons. Some of the sandstone intervals show cleaning-upwards profiles and they can be correlated over tens of kilometres between the wells. Their lateral extents are much greater than the tunnel valleys and they are interpreted as stacked proglacial outwash sheets deposited subaqueously in front of the ice sheet. The reservoir quality of the sandstones has been compromised by extensive quartz cementation, although better porosities and permeabilities are preserved in the upper parts of some of the cleaning-upwards profiles, resulting in correlatable intervals from which gas is produced without stimulation.

Abstract The deglaciation of southern Gondwana during the Early Permian was preceded by waxing and waning of the south polar ice sheet. The fluctuations in ice extent are recorded in the sedimentary record by strata separating thick deposits of glacial diamictite from post-glacial mudrock. These deposits span across all of the major Gondwana fragments, now recognized as South Africa, South America, India, Antarctica and Australia, and also occur on the Falklands and Ellsworth Mountains microplates created during break-up of the supercontinent in the Mesozoic. We present sedimentary evidence for the progression of deglaciation from the Falkland Islands microplate using a series of borehole core runs acquired during onshore mineral exploration. Glacial advance and retreat phases are inferred from the Hells Kitchen Member of the Port Sussex Formation; the rock succession that conformably overlies the main body of glacial diamictite known locally as the Fitzroy Tillite Formation. The pulsated nature of the transition to fully post-glacial conditions was accompanied by an intricate interplay of sedimentary processes, including soft sediment deformation, meltwater pulses and turbidity currents. The Falkland Islands core data lend insight into the evolving Early Permian environment and offer an unusually complete view of continental margin deglaciation preserved in the ancient sedimentary record. Supplementary material: Borehole core photographs from the Fitzroy Tillite Formation, Hells Kitchen Member and Black Rock Member for cores DD029 and DD090 are available at https://doi.org/10.6084/m9.figshare.c.4031119.v1

Abstract Deglacial sedimentary sequences recording the decay and final demise of ice sheets result from intricate interactions between the pattern of ice margin retreat, inherited basin physiography and relative sea-level (RSL) changes. A specific emphasis is here given to the glacio-isostatic adjustment (GIA), which may force postglacial local RSL fall in spite of concomitant glacio-eustatic rise. In this contribution, we characterize a Quaternary deglacial succession emplaced in such a setting, subsequently used as an analogue to interpret an end-Ordovician deglacial record. The Quaternary deglacial succession, tens of metres thick, formed under condition of RSL fall forced by the GIA in c. 10 000 years in the aftermath of the deglaciation. This sedimentary succession consists of a lower, fining-upward sequence representing the backstepping of ice-contact depocentres following the retreat of the ice margin, and an upper, coarsening-upward sequence that relates to the subsequent progradation of a glaciofluvial delta system. A very similar stratigraphic stacking pattern characterizes the Ordovician analogue, suggesting a comparable deglacial sequence. By analogy with the Quaternary succession, this ancient deglacial record would have hence been emplaced under conditions of RSL fall forced by the GIA. Moreover, it must only represent a very short time interval that could be viewed as virtually instantaneous regarding the Late Ordovician glaciation. Such a vision is at odds with commonly accepted interpretations for such successions.

Abstract The impact of high-latitude physical processes on the sedimentary geology of a passive continental margin is addressed using a sediment record from the Wilkes Land margin of Antarctica. We present sequence stratigraphic models based on analytical data and genetic interpretations of sedimentary facies assemblages observed in drill cores collected by the Integrated Ocean Drilling Program. The examination of drill cores within a previously published seismostratigraphic context enhances the resolution of the sequence stratigraphic interpretations. Weaker tidal forcing, a stronger Coriolis effect and more pronounced seasonality are some of the physical processes that affect erosion and sedimentation at high latitudes, even if ice sheets are absent. In addition, the presence of an ice sheet affects erosion rates, crustal motion, and atmospheric and ocean circulation, with major implications for the development of depositional systems. As a result, high-latitude, ice-covered, passive margins show distinct sedimentary facies associations and their interpretation requires the application of a different suite of sequence stratigraphic models from those applied to low-latitude continental margins. Supplementary material: A supplementary data file is available at http://doi.org/10.6084/m9.figshare.c.4031218.v1

Abstract Trough mouth fans (TMFs) are sediment depocentres that form along high-latitude continental margins at the mouths of some cross-shelf troughs. They reflect the dynamics of past ice sheets over multiple glacial cycles and processes operating on (formerly) glaciated continental shelves and slopes, such as erosion, reworking, transport and deposition. The similarities and differences in TMF morphology and formation processes in the Arctic and Antarctic regions remain poorly constrained. We analyse the dimensions and geometries of 15 TMFs from Arctic and Antarctic margins and the grain size distribution of 82 sediment cores centred on them. We compare the grain size composition of sub- and proglacial diamictons deposited on the shelves and glacigenic debris flows deposited on the adjacent TMFs and find a significant difference between Arctic and Antarctic margins. Antarctic margins show a coarser grain size composition for both glacigenic debris flows and shelf diamictons. This significant difference provides insight into high-latitude sediment input, transportation and glacial–interglacial regimes. We suggest that surface runoff and river discharge are responsible for enhanced fine-grained sediment input in the Arctic compared with the Antarctic.

Abstract A robust collection of seismic and geomorphic data is used to examine the evolution of the Antarctic Ice Sheet within the Ross Sea Embayment. We use geomorphic data to reconstruct Last Glacial Maximum and post-Last Glacial Maximum ice sheet drainage and demonstrate retreat behaviours for the East Antarctic and West Antarctic sectors of the ice sheet. Using this framework, we then use seismic data and chronostratigraphic information from drill cores to reconstruct the long-term evolution of the ice sheet. Early ice sheet evolution during the Late Oligocene was characterized by isolated ice caps on bathymetric highs, followed by an interval of sediment infilling of rift basins and the development of more subdued relief in the eastern Ross Sea than in the western Ross Sea. Both ice sheets have experienced multiple episodes of expansion across the continental shelf since the Middle Miocene, with the frequency increasing during the Plio-Pleistocene. We conclude that seafloor bathymetry has been the principal control on ice sheet palaeodrainage and retreat behaviour since at least the middle Miocene, demonstrated by broad West Antarctic ice streams loosely guided by south to north cross-shelf troughs, whereas East Antarctic ice streams were funnelled through troughs that merge and converge around banks.

Abstract Swath bathymetry data and seismic profiles collected in the NW Gulf of St Lawrence reveal a series of wedge-shaped depositional systems interpreted as grounding zone wedges (GZWs). Some segments of the GZWs change locally to form frontal moraines, or morainal banks, and subaqueous ice-contact fans, reflecting changes in either the nature of the ice margin or the rate of sediment input. These grounding zones (GZ) of the ice margin extend laterally along three isobaths at depths of 180 (GZ1), 120 (GZ2) and 80 (GZ3) m (±20 m) along the Québec North Shore shelf, the 120 m-deep GZ2 system being traceable over a distance of >300 km. Associated GZWs can occur in three geometries along a same isobath system: curvilinear, lobate and shelf-break. GZ systems were built during three distinct stages of stabilization of the marine-based southeastern margin of the Laurentide Ice Sheet following its rapid retreat across the deeper waters of the Laurentian Channel in the Gulf of St Lawrence after 14.8 cal ka BP. The occurrence of GZ along distinct isobaths indicates that bathymetry exerted a strong control on ice stabilization during deglaciation by reducing the relative water depth at the ice margin and thereby the buoyancy and rate of iceberg calving. However, fluctuations and re-advances of the ice margin are also recorded by the overprinting of a portion of the GZ2 system by the younger GZ3 system, potentially suggesting an additional response to climate-driven forcing.

Abstract Major glaciations or ‘ice ages’ are known to have affected the Earth’s surface over the past three billion years. The best preserved records of these glaciations are often found in high-latitude continental margin settings where sediment has been delivered to, and then accumulated at, the edge of the ice sheet in thick glacier-influenced marine sequences. The composition and geometry of these deposits and the related assemblages of glacial landforms provide a wealth of information about the environmental setting during successive cycles of glaciation and deglaciation, including ice-dynamic and oceanographic processes. Here, we discuss modern (present day), Quaternary (last 2.6 myr) and ancient (last 1 gyr) high-latitude continental margin settings, and then contrast the methodologies used and glacier-influenced deposits and landforms most often identified for each time period. We use examples from the literature to identify synergies, as well as to note differences, between studies of glacier-influenced sediments from ancient to modern environments.

Understanding the sedimentary and geophysical archive of glaciated margins is a complex task that requires integration and analysis of disparate sedimentological and geophysical data. Their analysis is vital for understanding the dynamics of past ice sheets and how they interact with their neighbouring marine basins, on timescales that cannot be captured by observations of the cryosphere today. As resources, sediments deposited on the inner margins of glaciated shelves also exhibit resource potential where more sand-dominated systems occur, acting as reservoirs for both hydrocarbons and water. This book surveys the full gamut of glaciated margins, from deep time (Neoproterozoic, Ordovician and Carboniferous–Permian) to modern high-latitude margins in Canada and Antarctica. This collection of papers is the first attempt to deliberately do this, allowing not only the similarities and differences between modern and ancient glaciated margins to be explored, but also the wide spectrum of their mechanisms of investigation to be probed. Together, these papers offer a high-resolution, spatially and temporally diverse blueprint of the depositional processes, ice sheet dynamics, and basin architectures of the world’s former glaciated margins; a vital resource in advancing understanding of our present and future marine-terminating ice sheet margins.