Channel-levee complexes of the Fossil Bluff Group, Alexander Island, Antarctica

A4000-m (13,120-ft)-thick Mesozoic sedimentary succession outcrops in a belt 250 km (155 mi) long by 30 km (18 mi) wide on the eastern coast of Alexander Island, Antarctica. The sequence represents the fill of a fore-arc basin, unconformably overlying and faulted against an accretionary complex. The basin originated as a terrestrial to shallow-marine fore-arc terrace during the Middle Jurassic. Rifting in Late Jurassic (Kimmeridgian) time formed a deep-marine basin. The fill of this basin was initially hemipelagic muds, overlain in places by a large-scale (tens of km [<20 mi]) slope mass-transport complex and succeeded by deep-marine channel-levee complexes of the Upper Jurassic to Lower Cretaceous Himalia Ridge Formation, which are the subject of this paper.

Ten facies are recognized from the Himalia Ridge Formation channel-levee complexes that were deposited from a wide spectrum of sediment gravity flows. These facies form three main associations, interpreted as conglomeratic, inner-fan channel complexes; overbank levees and crevasse splays; and mud-rich, interchannel slope deposits. There are three distinct pulses of coarse-grained sediment input to the basin that reflect a strong allocyclic tectonic control at the source. Channel-levee complexes are characterized by a complex facies relationship because of the lateral juxtaposition and vertical stacking of channels and levees as a result of an autocyclic control on channel avulsion.

The introduction of coarse-grained sediment into the basin and its confinement into discrete, fan-channel-levee complexes localized adjacent to the basin margin was probably the result of a combination of factors. These include arc-related controls on the development of alluvial cones, a variable, narrow shelf, and the development of canyon systems at the shelf edge. The documented pulses of channel-levee complexes at Ganymede Heights and Planet Heights correlate with a well-documented episode of arc volcanism and extension, reflecting the active tectonic control on the position of the basin margin, and the arc unroofing history determined from provenance studies.