The Permian-Triassic boundary is marked by paleoenvironmental,
paleoclimatic and geochemical global changes, partly attributable to catastrophic
events. The intense continentalization of supercontinent Pangaea with the
development of extensive deserts succeeded Permian coastal to platform setting.
The records of these events in the northern Brazil are found in intracratonic basins,
particularly in the Parnaíba Basin, where the Permian-Triassic boundary include the
contact zone between the siliciclastic deposits of Motuca and Sambaíba formations.
Facies, stratigraphic and geochemical study of outcrops of these units in the Loreto
region, State of Maranhão, allowed reconstructing the paleoenvironment and to infer
the possible disturbances in the geochemical cycle. The upper Motuca Formation
consists of siltstones, mudstones and fine-grained sandstones with even parallel
stratification, sigmoidal cross bedding, interpreted as lacustrine/deltaic deposits. The
basal Sambaíba Formation consists of fine to medium grained sandstones with well
rounded grains, even parallel stratification, medium- scale cross-bedding, convolute
lamination and sin-sedimentary faults, interpreted as marginal dune-field deposits.
The metastable heavy minerals like garnet, apatite and kyanite dominated
lacustrine/deltaic deposits, while zircon, tourmaline, rutile, staurolite are common in
deposits of the marginal dune-field. Provenance preliminary data suggest reworking
of the units of the basin and sourcelands of igneous and metamorphic rocks.
Geochemical anomalies in trace elements like Mn, Cr, Co, Cu and Ni in the Permian-
Triassic boundary can indicate leaching of elements or concentration related to
catastrophic event triggered by meteorite impact.
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