Abstract

The major-element and trace-element geochemistry of 57 diamicts and muds of the Sirius Group is evaluated to determine the provenance and stratigraphic relations of geographically widespread outcrops in the Transantarctic Mountains. The origin and age of the Sirius Group are heavily debated because of the presence of marine diatoms inferred to indicate a reduced East Antarctic ice sheet as recent as the Pliocene. A key question is whether glaciers transported sediments and the enclosed diatoms from the East Antarctic interior to the Transantarctic Mountains. Major-element and trace-element ratios indicate that the greater part of the Sirius Group sediments have an East Antarctic provenance and that a few high-elevation deposits are locally derived. The degree of chemical weathering of the materials in the Sirius Group, expressed as the chemical index of alteration (CIA), has a wide range (41-70). On the basis of geochemical provenance, weathering intensity, and morphostratigraphic position, the Sirius Group can be subdivided into three subgroups, which probably represent multiple glacial phases: (1) sediments with a local provenance from high-elevation outcrops on spurs and mountain summits, > 2000 m, which contain abundant weathered materials; (2) sediments in high-elevated outcrops, > 2000 m, with intermediate CIAs, originating from an East Antarctic Ice Sheet, which was overriding parts of the Transantarctic Mountains and; (3) sediments recovered within, or on the margins of, the present glacial troughs at 1500-1800 m, with low CIAs and an East Antarctic provenance. Comparison with the weathering history inferred from drilling records in the nearby Victoria Land Basin reveals that glaciation in the Transantarctic Mountains probably commenced with small ice caps and alpine glaciers prior to the Eocene-Oligocene transition, and from the Oligocene onward continued with multiple phases of continental glaciation. These results and interpretations contribute considerably to the understanding of the landscape evolution of the Transantarctic Mountains, the Sirius Group debate, and the history of East Antarctic glaciation.

You do not currently have access to this article.