Neogene fjordal sedimentation on the western margin of the Lambert Graben, East Antarctica

Abstract

The Lambert Graben is occupied by the world’s largest fjord system, through which flows the Lambert Glacier, the Amery Ice Shelf and their tributaries. Along the western margin of the graben, in the northern Prince Charles Mountains, remnants of uplifted Miocene and Pliocene strata of the glacigenic fjordal Pagodroma Group total more than 800 m in thickness. These sediments provide evidence for a dynamic East Antarctic ice sheet during the Neogene Period. Each of the four Pagodroma Group formations defined from this region rests unconformably on either Proterozoic or Permo‐Triassic rocks. The unconformity surfaces represent parts of the walls and floors of Neogene fjords. For these surfaces to have been eroded, the ice must have been grounded out as far as the continental shelf in Prydz Bay. The Pagodroma Group was deposited by wet‐based glaciers discharging into a fjordal setting and includes lithofacies that are quite different from those produced by modern Antarctic ice masses. The principal lithofacies are massive diamicts and soulder gravels, deposited both close to a calving, grounded glacier terminus and from icebergs. The few stratified diamicts are the product of more distal iceberg sedimentation. An ice‐transported gravel lithofacies includes rockfall debris derived from palaeofjord walls and mixed with subglacially derived diamicts. Some lithofacies contain evidence of subaquatic slumping and gravity flowage. Volumetrically minor lithofacies include laminites, with some exposures exhibiting large ice‐rafted clasts. The laminites represent less proximal, mainly ice‐free fjordal sediments, resulting either from tidal‐current sorting of suspended sediment originating from subaquatic glaciofluvial discharge, or from turbidity currents derived from unstable subaquatically deposited glacigenic sediment. The Pagodroma Group provides a record of multiple glaciation by dynamic, sliding glaciers carrying large amounts of both basal and supraglacial debris. The closest modern analogues, in terms of the thermal and dynamic characteristics of the Neogene Lambert Glacier, appear to be the fast‐flowing tidewater glaciers of East Greenland. These glaciers originate from the interior ice sheet and discharge large volumes of icebergs; the resulting lithofacies are predominantly diamicts.

Neoproterozoic Glaciated Basins: A Critical Review of the Snowball Earth Hypothesis by Comparison with Phanerozoic Glaciations

“…Glacial and non-glacially influenced strata deposited over the past 800,000 years on the southwestern part of the Barents Sea Shelf are known to approach 150 m in thickness (Rafaelsen et al, 2002), Miocene to Quaternary strata in the Polar North Atlantic exceed 1 km in thickness (Thiede et al, 1998), Miocene and Pliocene deposits of the Pagodroma Group in Antarctica are ~300 m thick (Hambrey & McKelvey, 2000) and Miocene to Pleistocene deposits of the Yakataga Formation along the southern continental margin of Alaska arẽ 7 km thick (Zellers & Lagoe, 1992). In the lower part, the Yakataga Formation consists primarily of debrites and turbidites, passing up into glacimarine diamictites, sandstones and mudstones (Eyles & Lagoe, 1990;Zellers & Lagoe, 1992), and in this respect bears similarity to many Neoproterozoic glacially influenced facies associations.…”

Fossil weevils (Coleoptera: Curculionidae) from latitude 85°S Antarctica

“…From di¡erent sides of the continent, an extinct species of scallop from the Antarctic Peninsula (Jonkers and Kelley, 1998) and species of whales and dolphins from the Vestfold Hills con¢rm that the coastal waters of Antarctica were warmer during the Pliocene (Quilty, 1993;Harwood et al, 2000;Quilty et al, 2000). On land, discontinuities within the glacial sequences of the Miocene and Pliocene-aged Pagodroma Group indicate that during warm episodes the Lambert Glacier retreated 250 km inland from the Amery Ice Shelf where it is positioned today (Hambrey and McKelvey, 2000;Whitehead and McKelvey, 2001). Finally, ¢eld-based evidence for Pliocene warmth in Antarctica has been consistently supported by the results of di¡erent general circulation model (GCM) experiments (Chandler et al, 1994;Sloan et al, 1996;Haywood et al, 2000).…”

A Pleistocene warming event at 1 Ma in Prydz Bay, East Antarctica: Evidence from ODP Site 1165

“…On the other hand, other evidence (e.g. Hambrey and McKelvey, 2000) suggests that the EAIS was subject to major fluctuations up to Pliocene time implying considerable climate variation extending from the late Miocene through the Pliocene-Pleistocene (Escutia et al, 2003).…”