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Estratigrafía, petrografía sedimentaria y procedencia de las formaciones Sobral y Cross Valley (Paleoceno), isla Marambio (Seymour), Antártida.

Andean Geology (Impact Factor: 0.72). 01/2012; 39(1):67-91.
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    ABSTRACT: 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.
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    ABSTRACT: By selecting a limited number of variables (westward vs. eastward subduction polarity; oceanic vs. continental origin of downgoing and overriding plates), we identify eight end-member scenarios of plate convergence and orogeny. These are characterized by five different types of composite orogenic prisms uplifted above subduction zones to become sources of terrigenous sediments (Indo-Burman-type subduction complexes, Apennine-type thin-skinned orogens, Oman-type obduction orogens, Andean-type cordilleras, and Alpine-type collision orogens). Each type of composite orogen is envisaged here as the tectonic assembly of subparallel geological domains consisting of genetically associated rock complexes. Five types of such elongated orogenic domains are identified as the primary building blocks of composite orogens: magmatic arcs, obducted or accreted ophiolites, neometamorphic axial belts, accreted paleomargin remnants, and accreted orogenic clastic wedges. Detailed provenance studies on modern convergent-margin settings from the Mediterranean Sea to the Indian Ocean show that erosion of each single orogenic domain produces peculiar detrital modes, heavy-mineral assemblages, and unroofing trends that can be predicted and modeled. Five correspond- ing primary types of sediment provenances (magmatic arc, ophiolite, axial belt, continental block, and clastic wedge provenances) are thus identified, which reproduce, redefine, or integrate provenance types and variants originally recognized by W. R. Dickinson and C. A. Suczek in 1979. These five primary provenances may be variously recombined in order to describe the full complexities of mixed detrital signatures produced by erosion of different types of composite orogenic prisms. Our provenance model represents a flexible and valuable conceptual tool to predict the evolutionary trends of detrital modes and heavy-mineral assemblages produced by uplift and progressive erosional unroofing of various types of orogenic belts and to interpret petrofacies from arc-related, foreland-basin, foredeep, and remnant-ocean clastic wedges.
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    ABSTRACT: The Eocene La Meseta Formation is the youngest exposed unit of the back-arc James Ross Basin, Antarctic Peninsula, cropping out in Seymour (Marambio) Island. The formation comprises 720 m of clastic sedimentary rocks of deltaic, estuarine and shallow marine origin. It was subdivided into six unconformity-based units (Valle de Las Focas, Acantilados, Campamento, Cucullaea I, Cucullaea II and Submeseta Allomembers) grouped into three main facies associations. Facies association I represents valley-confined deposition in a progradational/aggradational tide-dominated and wave-influenced delta front/delta plain environment. Facies association II includes tidal channels, mixed tidal flats, tidal inlets and deltas, washover and beach environments. Facies association III represents nonconfined tide- and storm-influenced nearshore environments. La Meseta Formation sandstones are quartzofeldspathic with some hybrid arenites (glauconite and carbonate bioclasts-rich). Sandstone detrital modes are subdivided into two distinctive petrofacies: the low quartz petrofacies (petrofacies I, Q12%), interpreted to retain the original provenance signal, and the high quartz petrofacies (petrofacies II, Q>55% and L
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