The sedimentary geology, palaeoenvironments andichnocoenoses of the Lower Devonian Horlick Formation, OhioRange, Antarctica

[摘要] Six ichnocoenoses in the clastic Devonian Horlick Formation (max. 56 m) confirm the nearshoremarine character of eight of the nine lithofacies present. Abasal sand sheet overlies a weathered granitic landsurface (Kukri Erosion Surface) on Cambro–Ordovician granitoids. The level nature of this surface and theway it cuts across weathering profiles, suggests that the surface had been modified by marine processes priorto deposition. The basal sand sheet (Cross-bedded Sand sheet Lithofacies) contains tidal bundles, and at itstop, abundant Monocraterion (Monocraterion Ichnocoenosis). The second sand sheet (PleurothyrellaLithofacies) is heavily burrowed and shows alternating periods of sedimentation, burrowing, and erosionbelow wave base as the sea deepened (Catenarichnus Ichnocoenosis). With increasing transgression, finersediments were deposited (Laminated Mudstone and Feldspathic lithofacies) in an unstable pattern of coarsesandbars and finer troughs (Cruziana-Rusophycus and Arenicolites ichnocoenoses) crossed by activelongshore marine channels (Poorly-sorted Lithofacies, Spirophyton Ichnoocoenosis). Short-lived butpowerful storms produced thin shelly tempestites (Shell-bed Lithofacies), whereas sporadic, very thinphosphate rich beds (Phosphatic Lithofacies) may have resulted from marine transgressions across the basin.The deepest water is probably represented by sediments of the Spirifer Lithofacies (Rosselia Ichnocoenosis).The Schulthess Lithofacies is regarded as fluvial, deposited in the lower reaches of a river draining a landarea that lay towards Marie Byrd Land. Channels in the basal sand sheet indicate movement to the southwest,but orientation became more variable higher in the sequence. Four new measured sections are figured.The relationship of the Ohio Range to the rest of Antarctica during the Devonian is suggested.

[学科分类] 自然科学（综合）