Depositional framework of Permian coal-bearing strata, southern Victoria Land, Antarctica

Abstract

Abstract The Permian Weller Coal Measures of Antarctica are exposed in a narrow belt that extends along the edge of the Polar Plateau from the Mawson Glacier to the Mulock Glacier in southern Victoria Land. These rocks record a rapid change from glacial to postglacial conditions, with the establishment of polar peat forming conditions, during the late Paleozoic in Antarctica. The 222 m thick Weller consists of interstratified fine- to coarse-grained quartzo-feldspathic sandstone, laminated siltstone, mudstone and coal. Regional lithofacies patterns and paleocurrent orientations define a narrow elongate basin. In the lower Weller, coarse-grained sandstone sheets occur along both eastern and western basin margins. These deposits are similar to those of modern sandy braided streams. Toward the axis of the basin, this lithofacies grades into coarse-grained tabular sandstone. Lateral-accretion beds suggest that deposition of this lithofacies occurred within meandering streams. Coarse-grained basin-margin deposits interfinger with fine-grained basin-axis lithofacies of interstratified laminated siltstone and graded sandstone beds deposited from suspension and underflow currents within a lacustrine environment. In the upper Weller, braided stream deposits dominate much of the basin, grading downstream into meandering streams. Establishment of vegetation in southern Victoria Land occurred immediately following late Paleozoic deglaciation. Upward in the Weller, the distribution of plant fossils and coal seams is lithofacies dependent. Thick coals and abundant plant fossils occur in meandering stream lithofacies, while they are scarce within the lacustrine and braided stream deposits. Abrasion during transport probably contributed to the destruction of vegetable material in the braided stream environments, and to material introduced into the axial lake. Depositional patterns within the Weller Coal Measures are similar to those in the Takrouna Formation in northern Victoria Land. Similarities suggest deposition in either the same or a similar basin. Comparison of the Weller Coal Measures with Permian strata in the central Transantarctic Mountains suggest deposition in two separate basins, which are now juxtaposed across the Byrd Glacier, the sight of a possible Cenozoic strike-slip fault. Causes for the formation of the depositional basin containing the Weller Coal Measures are unknown; however, the geometry of the basin and the regional distribution of lithofacies are similar to those of rift basins and to basins excavated by glacial erosion. The ultimate cause of basin subsidence however, may be related to long-distance stress produced during late Paleozoic orogenic activity along the paleo-Pacific margin of Antarctica.