EXAMINATION OF LATE PALEOZOIC GROUNDING-LINE FAN DEPOSITS AT TILLITE GLACIER, CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA

The Pagoda Formation near the head of Tillite Glacier in the Central Transantarctic Mountains (CTM), Antarctica, was recently reassessed using modern facies analysis to identify the depositional environment and glacial thermal conditions that contributed to the accumulation of these glacigenic deposits. These rocks were formerly interpreted and documented as terrestrial glacial deposits; however recent studies demonstrate, at this location, the rocks were actually of glaciomarine origin: deposited from a wet-based, temperate tidewater, glacier ending in a marine embayment. Importantly, grounding-line fans were recently recognized utilizing modern day studies and described in detail to understand ancient glacier depositional characteristics and processes. Here, the wedge-shaped grounding-line fan deposits are examined in detail and categorized into two major sedimentological processes: 1) bed-contact sedimentation regions of the thicker portions of the wedge, consisting of tractive signatures (i.e. cross-beds/cross-laminations, climbing cross-stratification), overall coarser-grained, with plastic deformation, which grade into, in the direction of flow, 2) rain-out, buoyant sedimentation conditions of the thinner portions of the wedges, consisting of “traction failed” sedimentation (i.e. coarse-grained “pods” loaded into fine-grained sandstone, failed ripples, convolute laminations), overall finer-grained with abundant soft sediment deformation. Glide planes and slump structures occur within the thicker wedge-shaped fan regions, which likely resulted from ice-contact and/or gravitational deformation. Understanding these deposits and processes improves understandings of glacier conditions. These particular fan characteristics display how effluent flow turned buoyant just beyond the grounding line, which aids in the corroboration of classifying these deposits as entering into a marine rather than into a lacustrine basin. Recent rock reevaluations have revealed that the previous perspective of the LPIA, originally portrayed and characterized by a large, massive, single ice sheet covering large terrestrial regions of Gondwana, is inaccurate. This study reinforces modern research that previous interpretations of the LPIA glaciations in Antarctica are inaccurate.