Spatial distribution of heavy minerals in the superficial sediments of the Western Ceará Continental Shelf, Northeast of Brazil

Abstract

The continental shelf sediments of the west coast of Ceará were investigated about their texture, calcium carbonate and heavy minerals with the generation of digital bottom model of this shelf. Multivariate statistics analyses were applied for mineralogical data to aid interpretation of heavy mineral provenance. Despite the predominance of carbonate sedimentation, the western Ceará continental shelf presents significant concentrations of heavy mineral (4.54 %), resulting in placer deposits in litoclastic and litobioclastic sands located further east of the study area (Fortaleza Chart). It was possible identify irregularities in the submarine bottom, which indicate paleochannels and ancient shoreline and support heavy minerals concentration. The mineral assemblage (ilmenite, tourmaline, epidote, hornblende, monazite, staurolite, sillimanite, rutile, magnetite, zircon, andalusite, kyanite, garnet, leucoxene, diopside, apatite, spinel and cassiterite) suggests regional contributions of the reworking of sediments Barreiras Formation and local contribuition of metamorphic rocks of Ceará Complex. Crystalline basement outcrops on the continental shelf near Pecém Port (São Gonçalo do Amarante) contribute directly to sediment supply of terrigenous, hence the heavy minerals are concentrated in these places. Multivariate statistics distinguish two types of sources which were described above, however it should take attention to other contributions as coastal black sands, present fluvial supply (continental), past fluvial supply (drowned river valleys) and marine sediments from longshore drift.