Sedimentology and architecture of upper Eocene deep-water deposits, Talara Basin, NW Peru.

摘要

The objective of this study is to characterize and interpret the sedimentology and architecture of turbidite systems at several scales using outcrop, core, well log, and petrographic data from the upper Eocene deep-water formations of the Talara Basin. The most widely exposed deep-water formation in the basin is the Verdun Formation. Together, Verdun paleocurrent and lithofacies distributions suggest the presence of a major source area to the north-northwest. Sandstone petrography and conglomerate clast composition suggest a source area more quartz-rich than that which supplied clastic debris in the underlying formations.; Seacliff outcrops south of the village of Lobitos provide nearly continuous 3 km-wide exposure of a 200 to 280 m-thick fining-upward succession of upper Eocene amalgamated, thick-bedded, coarse-grained turbidites dominated by current-structured divisions. The abundance of traction structures, coarse grain-size, and common scoured contacts of the turbidites suggest the succession represents proximal submarine channel fill.; Large-scale cross-bedding is especially abundant throughout the deep-water units of the Talara Basin, where layers of large-scale cross-stratification commonly overlie normally graded Lowe S1 and S3/Bouma Ta turbidite divisions. Sediment texture and sedimentary structures in several such turbidites suggest two types of turbidity currents form cross-bedding: those that undergo high initial suspended-load fallout rates that decrease during deposition, and quasi-steady flows in which suspended load fallout rates do not change significantly during deposition. Dune formation likely resulted from coarse sediment available to the flows and high flow energy. The coarse grain size and the great thickness of the turbidites of study indicate the depositing flows initiated by slope failure rather than by "sustained" flows representing hyperpycnal currents from a river in flood.