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Scientific drilling 20, 1-12 (2015). doi:10.5194/sd-20-1-2015, Published by IODP, Sapporo

Mapping the Middle to Upper Pleistocene Rhine-Meuse sequence in the southern North Sea based on new core and seismic data has allowed a detailed palaeoenvironmental re-assessment. An integrated seismo-lithostratigraphic and malacological biostratigraphic framework is correlated with the optically stimulated luminescence-dated Rhine-Meuse sequence onshore. The data point to a dynamic interplay of fluvial and marine systems in the southern part of the North Sea driven by longer-term (>100 ka) tectonic and epeirogenic processes and shorter-term (100 ka) uplift of the Wealden-Artois synclinorium and compaction-driven subsidence of Tertiary shales within the Voorne Trough. The dominant erosive sedimentary signatures within the Rhine-Meuse sequence resulted through shorter-term (

Warm intervals within the Pliocene epoch (5.33–2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century1 and atmospheric CO2 concentrations similar to today2, 3, 4. Estimates for global sea level highstands during these times5 imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.

During the middle and late Eocene (∼ 48-34 Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarctica induced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rose despite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an ice-sheet grounding line.

The Integrated Ocean Drilling Program Expedition 318 to the Wilkes Land margin of Antarctica recovered a sedimentary succession ranging in age from lower Eocene to the Holocene. Excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals. Drill sites recovered the lower and middle Eocene, nearly the entire Oligocene, the Miocene from about 17 Ma, the entire Pliocene and much of the Pleistocene. The paleomagnetic properties are generally suitable for magnetostratigraphic interpretation, with well-behaved demagnetization diagrams, uniform distribution of declinations, and a clear separation into two inclination modes. Although the sequences were discontinuously recovered with many gaps due to coring, and there are hiatuses from sedimentary and tectonic processes, the magnetostratigraphic patterns are in general readily interpretable. Our interpretations are integrated with the diatom, radiolarian, calcareous nannofossils and dinoflagellate cyst (dinocyst) biostratigraphy. The magnetostratigraphy significantly improves the resolution of the chronostratigraphy, particularly in intervals with poor biostratigraphic control. However, Southern Ocean records with reliable magnetostratigraphies are notably scarce, and the data reported here provide an opportunity for improved calibration of the biostratigraphic records. In particular, we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the Paleogene and a substantially improved diatom calibration for the Pliocene. This paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the Wilkes Land margin cores. It further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region.

In 2007, the Antarctic Geological Drilling Program (ANDRILL) drilled 1138.54 m of strata ~10 km off the East Antarctic coast, includ ing an expanded early to middle Miocene succession not previously recovered from the Antarctic continental shelf. Here, we pre sent a facies model, distribution, and paleoclimatic interpretation for the AND-2A drill hole, which enable us, for the fi rst time, to reconstruct periods of early and middle Miocene glacial advance and retreat and paleo environmental changes at an ice-proximal site. Three types of facies associations can be recognized that imply signifi cantly different paleoclimatic interpretations. (1) A diamictite-dominated facies association represents glacially dominated depositional environments, including subglacial environments, with only brief intervals where ice-free coasts existed, and periods when the ice sheet was periodically larger than the modern ice sheet. (2) A stratifi ed diamictite and mudstone facies association includes facies characteristic of open-marine to iceberg-infl uenced depositional environments and is more consistent with a very dynamic ice sheet, with a grounding line south of the modern position. (3) A mudstone-dominated facies association generally lacks diamictites and was produced in a glacially infl uenced hemipelagic depositional environment. Based on the distribution of these facies associations, we can conclude that the Antarctic ice sheets were dynamic, with grounding lines south of the modern location at ca. 20.1‐19.6 Ma and ca. 19.3‐18.7 Ma and during the Miocene climatic optimum, ca. 17.6‐15.4 Ma, with ice-sheet and sea-ice minima at ca. 16.5‐16.3 Ma and ca. 15.7‐15.6 Ma. While glacial minima at ca. 20.1‐19.6 Ma and ca. 19.3‐18.7 Ma were characterized by temperate margins, an increased abundance of gravelly facies and diatomaceous siltstone and a lack of meltwater plume deposits suggest a cooler and drier climate with polythermal conditions for the Miocene climatic optimum (ca. 17.6‐15.4 Ma). Several periods of major ice growth with a grounding line traversing the drill site are recognized between ca. 20.2 and 17.6 Ma, and after ca. 15.4 Ma, with evidence of cold polar glaciers with ice shelves. The AND-2A core provides proximal evidence that during the middle Miocene climate transition, an ice sheet larger than the modern ice sheet was already present by ca. 14.7 Ma, ~1 m.y. earlier than generally inferred from deep-sea oxygen isotope records. These fi ndings highlight the importance of high-latitude ice-proximal records for the interpretation of far-fi eld proxies across major climate transitions.

[1] This paper aims to investigate the distribution and stability of large-scale bed forms in response to storm and fair-weather conditions in a shallow marine environment. Multibeam and side-scan sonar data off the Dutch coast (median grain size 0.25-0.35 mm) were collected to monitor sand waves (λ = 100-800 m) and superimposed megaripples (λ = 1-40 m) through multiple storm and fair-weather events. Box cores were used to observe the vertical bed structure and grain size. In the Dutch coastal area, two-dimensional (2-D) megaripples (X = 1-15 m) are the dominant bed forms in current-dominated (>0.4 m/s) tidal flow regimes with oscillatory flows 0.4 m/s, undulating bed topography of mound-like 3-D bed forms (λ = 20-40 m) is observed. Immediately after storms, these bed forms are covered by smaller 3-D megaripples, which are related to sets of low-angle converging laminae in box cores, interpreted as hummocky cross stratification (HCS). The sand waves form compound bed forms of sets of 2-D and 3-D megaripples. The morphology of the sand waves is a function of the general wind-wave climate of the marine environmental setting, with flat-topped 3-D sand waves occurring in shallow wave-dominated settings and 2-D sand waves occurring in the tide-dominated environment farther offshore. Copyright 2005 by the American Geophysical Union.

Separate regions within the Transantarctic Mountains, the uplifted flank of the West Antarctic rift system, appear to have distinct Neogene histories of glaciation and valley downcutting. Incision of deep glacial outlet valleys occurred at different times throughout central and northern Victoria Land. This is corroborated by measurements of cosmogenic nuclides 21Ne, robe and 26Al of glacial erosion surfaces and high-elevated moraines. 21Ne ages of two summit plateaus, at elevations of 1650 m in central Victoria Land and ~ 2800 m in northern Victoria Land, range from 3.84 to 11.2 Ma, respectively. The latter date indicates that these glacial erosion surfaces are the oldest known exposure dated surfaces on Earth. Glacial erosion terraces, remnants of early phases of valley downcutting, have 21Ne ages of 1.27 and 6.45 Ma for central and northern Victoria Land, respectively. Therefore, deglaciation of summit plateaus, valley downcutting and topographic uplift occurred during the Mid-Miocene in northern Victoria Land and not earlier than the Mid-Pliocene in central Victoria Land. In northern Victoria Land, ice flow directions changed markedly from the time a regional ice sheet occupied the level of the highest summits to the present condition with summits rising up to 800 above the valley glaciers. In central Victoria Land, the oldest documented ice flow direction occupying the summit erosion surface prior to incision was SW-NE, draining the East Antarctic Ice Sheet along an outlet glacier at least 10 times as wide as the present E-W-flowing David Glacier. This great variation in denudation histories probably results from differential tectonic uplift of various regions within the presently active rift flank. Three tectonic processes contribute to Late Neogene uplift: (1) ongoing extension in adjacent Ross Sea rift basins; (2) regional dextral transtension following SE-trending Precambrian and Palaeozoic structural trends which offsets the ~ N-S-trending grain of the rift and reactivates earlier faults; and (3) isostatic response to valley downcutting and related denudation. (C) 1999 Elsevier Science B.V.