Paleosols in Permo-Triassic Continental Sediments from Prydz Bay, East Antarctica
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ABSTRACT ODP Leg 119 drilled a sequence of ?Permo-Triassic continental red beds 58 m thick containing paleosols in Prydz Bay, East Antarctica. The paleosols, mainly in overbank siltstones and mudstones, are characterized by extensive destruction of sedimentary structures and the presence of mottles, rootlets, and rare chalky caliche. Because of the shallow depth of burial and limited compaction and diagenesis, the paleosols have retained most of their original microstructure and fabric. Micromorphological analysis of the paleosols reveals the presence of phreatic monopodial root systems, nodules, and a variety of soil structures and fabrics as well as a micritic root structure with alveolar texture. Most of the paleosols are weakly developed, with small, incomplete ped structures and lack of illuviation. They resemble weakly developed alluvial soils with A-C and B(C) profiles, and are similar to modern base-deficient inceptisols. The nature of the paleosols suggests relatively high permeabilities and water circulation during soil formation and a relatively mobile water table, with little reduction of iron except locally on the less well drained parts of the alluvial plain. Extensive pedogenic carbonate formation was precluded by the soil-moisture regime and relatively wet climate. During Late Permian and Early Triassic times Prydz Bay, which lay some 30° south of the Equator, experienced climatic conditions broadly similar to parts of the contemporary tropics, dominated by a ubtropical high-pressure system, easterly winds, and seasonal rainfall.Keywords:
Paleosol
Continental Margin
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Bay mud
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Mobile Bay is a shallow, micro-tidal estuary in the northern Gulf of Mexico. The Bay receives the 4 th largest river discharge in the continental United States of America. The large river discharge results in strong water column stratification not only inside the Bay but on the inner shelf adjoining the Bay. This paper presents two cases that highlight the importance of stratification in the tidal Mobile Bay system on: (1) vertical mixing in the shallow inner portion of the Bay and (2) salt exchange with the Gulf through the Bay mouth.
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The data presented in this report are the results of granulometric analyses, conducted in the Department of Oceanography, University of Washington, of the marine sediment samples from the continental shelf, and the upper part of the continental slope, off the Washington coast. In addition, the report contains data from the Columbia River Estuary, Willapa Bay, and Grays Harbor.
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