Lacustrine deltas in a Mesozoic alluvial sequence from Camp Hill, Antarctica

first_imgSedimentary rocks of late Mesozoic age exposed at Camp Hill, northern Antarctic Peninsula, are associated with calc‐alkaline volcanic rocks. They represent deposition on a fault‐controlled floodplain, with marginal alluvial fans, on a volcanic arc. Finely laminated mudstone and occasional graded laminae were deposited from suspension and by density underflow currents, respectively, in small shallow lakes. Thickening‐ and coarsening‐upward sandstone bodies overlying the lake deposits are interpreted as lacustrine deltas of which two types are preserved: (1) Gilbert‐type with steep foresets and (2) mouth‐bar type which lack steep foresets. Sections through the latter type reveal the presence of sub‐environments characteristic of fluvial‐dominated marine deltas, i.e. prodelta, distributary mouth‐bar and distributary channel. Abandoned mouth‐bars resulting from avulsion are recognized. It is suggested that the processes which operated during formation of the mouth‐bar deltas resulted from hyperpycnal flow. By contrast, the Gilbert‐type delta is thought to be the consequence of a reduced inflow of suspended sediment causing homopycnal flow, and thorough mixing of the river and lake waters.last_img read more