Deglacial and postglacial sedimentary architecture in a deeply incised paleovalley-paleofjord--The Pennsylvanian (late Carboniferous) Jejenes Formation, San Juan, Argentina

摘要

Quebrada de las Lajas, near San Juan, Argentina, preserves an early Pennsylvanian deglacial-postglacial succession in a highly confined paleofjord setting. The sedimentary succession records four distinct stages in the evolution of the valley fill. Stage 1 is represented by the deposits of subglacial diamictites, ice-contact deltas, and related deep-water lacustrine environments, including several subaqueous channels. Stage 2 records a glacio-eustatic marine transgression, and a slow-down of the clastic supply into the paleofjord. Stage 3 records a sandy, confined turbidite environment. Stage 4 consists of a coarse-grained delta, which represents a significant rejuvenation of the sedimentary system in the paleofjord. The transition from stage 1 to stage 2 was abrupt and basinwide, and has proven to be a good regional correlation marker. In this paleovalley, the glacio-eustatic rise probably caused floating and consequent rapid melting of the valley glacier. This resulted in a paleovalley-wide turbidite event that is up to 5 m thick and indicates an overall waning character. The rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass-transport events at the stage 1–2 boundary.