Depositional Environment and Petrography of Preglacial Continental Sediments from Hole 740A, Prydz Bay, Antarctica

Abstract

ODP Hole 740A is located on the inner part of the East Antarctic continental shelf in Prydz Bay, at the seaward end of a major onshore rift structure known as the Lambert Graben. Drilling at this site led to the recovery of some 65 m of continental sediments (Prydz Bay red beds) that form part of a much thicker (2-3 km) pre-continental breakup sequence, the development of which may be related to the initiation and rifting of the Lambert Graben. Palynological and paleomagnetic studies have not been able to determine the age of the sediments; they may be equivalent to the onshore late Permian Amery Group or younger. The succession consists predominantly of sandstone, siltstone, and claystone arranged in erosively based, pedogenically influenced fining-upward sequences up to 5 m thick. These were deposited by shallow, braided streams draining an extensively vegetated alluvial plain, with sufficient topographic relief to trap finegrained sediment and inhibit rapid channel shifting. Pedogenic processes were initiated on the alluvial plain, but climatic conditions were generally unsuitable for extensive pedogenic carbonate formation and the development of mature soil profiles. The sediments were probably derived from a rapidly uplifted fault block terrain composed of upper Proterozoic and Archaean gneisses lying to the southeast of the depositional site. Uplift may have taken place along the tectonically active seaward extension of the eastern faulted margin of the Lambert Graben, which passes immediately southeast of Hole 740A. Differences in mineralogical composition between the Amery Group and the Prydz Bay red beds probably reflect differences in rock composition in the source area. The age of the Prydz Bay red beds has still to be resolved.

Early Triassic (early Olenekian) life in the interior of East Gondwana: mixed marine–terrestrial biota from the Kockatea Shale, Western Australia

“…1B). Further southwest within this system, sedimentation along the AntarcticIndian margin was primarily non-marine (Turner, 1991(Turner, , 1993Veevers and Tewari, 1995;. Marine mudstone is a major component of the Lower Triassic succession in most of the Western Australian basins, and regularly includes estuarine-like facies.…”

Fluvial sedimentology and revised stratigraphy of the Triassic Flagstone Bench Formation, northern Prince Charles Mountains, East Antarctica

“…The Jetty Member is exposed only in the cliffs of McKelvey Ledge facing Beaver Lake. However, similar red-bed successions have been identified in the subsurface during ODP drilling operations in Prydz Bay (Turner, 1991(Turner, , 1993. The Jetty Member's total thickness has not been determined because the base of the unit is not exposed.…”

“…Although Amery Group exposures are restricted to the Beaver Lake area, sedimentary rocks found in moraine at Mount Rymill (250 km to the south) contain characteristic Permian Glossopteris and Vertebraria fossils (White, 1962) suggesting that Amery Group sediments may be extensively distributed beneath ice and Cenozoic cover throughout much of the graben. Around 169 m of continental red-beds were recorded beneath a thin Cenozoic glacial and glacio-marine sequence in Prydz Bay (Turner, 1991). Although no biostratigraphic data is available, these beds are lithologically similar to, and probably correlative with, part of the Flagstone Bench Formation exposed at Beaver Lake.…”

Denudation and uplift of the Mawson Escarpment (eastern Lambert Graben, Antarctica) as indicated by apatite fission track data and geomorphological observation

“…Both the continental Amery Group and the Paleozoic red bed sediments of Prydz Bay were deposited in an actively subsiding basin where rapid uplift, erosion, and deposition preserved their immature composition (e.g., Turner, 1991;Webb & Fielding, 1993). A similarly thick upper Cretaceous sedimentary sequence is reported from Prydz Bay (Turner & Padley, 1991) and can be envisaged in the Lambert Graben from the geophysical record (e.g., Fedorov et al, 1982).…”