Geology of the Paleocene Sepultura Formation, Mesa de La Sepultura, Baja California

Abstract

At its Mesa de La Sepultura type area, the upper-lower to upper Paleocene Sepultura Formation lies with apparent disconformity on the lower Maastrichtian, marine upper slope and shelf deposits of the Rosario Formation. In places the uppermost Rosario Formation is marked by a kaolinite-rich paleosol. The Sepultura Formation is a deepening-upward sequence divided into a lower glauconitic-clastic member and an upper limestone member. The lower member has a basal plutonic-volcanic conglomerate overlain by sandstone containing abundant Turritella peninsularis of late-early to early-late Paleocene age. The dominant lithology is calcite-cemented, glauconitic, fossiliferous arkose or lithic arkose of apparent Peninsular Ranges provenance. The beds contain abundant red algal nodules, storm deposits, and iron-stained corrosion surfaces. Terrigenous sediment influx was diverted so that the upper member is virtually pure limestone dominated by branching red algae fragments and forams but devoid of micrite. The Sepultura Formation at Mesa de La Sepultura is a carbonate sediment-dominated record of late-early to late Paleocene deepening that progressed from shallowest marine at the base to 200 m deep shelf waters at the top. During this time, terrigenous coarse sediment deposition was blocked here even though it dominated in areas to the north and South.