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

Sedimentary 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

Late Mesozoic sedimentation in the northern Antarctic Peninsula and its relationship to the southern Andes

Two distinct phases of island-are evolution are recognized in late Mesozoic sedimentary rocks of the northern Antarctic Peninsula. During late Jurassic (Kimmeridgian-Tithonian) times, alternating radiolaria-rich mudstones and ash-fall tuffs were deposited under shallow marine euxinic conditions in association with restricted volcanic centres. The name Nordenskjöld Formation is proposed for this lithostratigraphic unit. Subsequently, during the early Cretaceous, a major episode of volcanism and uplift led to the construction of an emergent are-terrane. Simultaneous development of a retro-arc basin resulted in the accumulation of coarse volcaniclastic detritus along the eastern side of the arc. Retro-are sedimentation and intermittent volcanism continued into the late Cretaceous and early Tertiary. Although the pattern of sedimentation in the northern Antarctic Peninsula is broadly comparable to that of the southern Andes, an active marginal basin has not been recognized in the former area. Interbedded mudstones and tuffs, identical to those of the Nordenskjöld Formation, were deposited in the southern Andes and South Georgia during the late Jurassic - early Cretaceous

Sedimentation associated with the late mesozoic volcanic arc of the Northern Antarctic peninsula

SIGLELD:D48805/84 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Submarine glide blocks from the Lower Cretaceous of the Antarctic Peninsula

Isolated exotic blocks of late Jurassic age occur within an undeformed succession of marine Lower Cretaceous back‐arc basin deposits on the west coast of James Ross Island, Antarctica. These flat, tabular slabs range up to 200 × 800 m in cross‐section and lie concordant with the enclosing Cretaceous strata. Although mainly undeformed, one block displays a range of emplacement‐related deformation structures, comparable in many respects to tectonic fabrics produced by simple shear. Emplacement by submarine block gliding is proposed, possibly as the final phase in the evolution of a composite mass transport event. Derivation of such gigantic slabs requires the existence of a steep, highly unstable basin margin during the early Cretaceous. In more complex terranes, differentiation between gravity slides and thrust slices can be difficult. Clearly, internal and marginal disruption of an allochthonous unit is not diagnostic since structures developed within a lithified block during submarine gliding may closely mimic tectonic fabrics. Where contact relationships are ambiguous, emplacement by gravity sliding is suggested by the increasing intensity of internal disruption towards the basal margin and by the style of deformation, reflecting simple shear under low overburden