Depositional environment of sirius group sediments, table mountain, dry valleys area, antarctica

Abstract

Outcrops and cores of the Sirius Group sediments were studied at Table Mountain, Dry Valleys area, Antarctica. These sediments form a surficial veneer at least 9.5 m thick. Three facies — a gravelly sandstone, a sandstone, and a sandy conglomerate — are mapped and described from 13 outcrops and three cores. The gravelly sandstone, constituting 13%of all cored material, is bimodal with matrix‐supported clasts comprising 5–33%of the facies. Fabric analysis indicates that it was deposited primarily by lodgment from glacial ice but with minor elements of meltout and flow. The sandstone facies, constituting 77%of all cored material, is a well‐sorted, fine‐ to medium‐grained sand, which commonly has laminated bedding. It is predominantly a glaciofluvial deposit but has some glaciolacustrine elements. The sandy conglomerate, constituting 10%of all cored material, is a minor facies. It is massive and clast‐supported. It was deposited in a high‐energy environment suggestive of subglacial meltwater channels.Sirius Group sediments at Table Mountain are the result of wet‐based ice advancing and retreating over waterlain deposits. This is consistent with an advancing ice mass in climatic conditions that were warmer than present. The majority of the sediments were deposited by alpine ice following a similar pathway to the present‐day Ferrar Glacier and as such the depositional environment is one that concurs with evidence of a stable East Antarctic Ice Sheet approach. At Table Mountain, the predominantly glaciofluvial and glaciolacustrine facies is inferred to represent a more distal part of the Sirius Group environment than that seen at other outcrops in the Dry Valleys.