Paleosols in Permo-Triassic Continental Sediments from Prydz Bay, East Antarctica

Abstract

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.