Sedimentology and structure of a Holocene slump deposit on the continental slope off Baja California, Mexico

Abstract

A marine sediment core located off the southernmost part of the Baja California Peninsula, NE Pacific, is analyzed to investigate a submarine mass failure. We examine the lithofacies and sedimentary structures, the total organic (TOC) and inorganic (TIC) carbon, the grain size composition, and the degree of fragmentation in foraminifera tests. The core BB03 consists of five lithostratigraphic units, from bottom to top, U1 to U5. Radiocarbon dating (AMS 14C) indicates that this sequence is inverted, where the deepest strata U1–U2 date at\u2009~\u20094,162 cal yr BP, U3–U4 at\u2009~\u200914,406 cal yr BP, and the shallower strata U5 at\u2009~\u200918,759–19,445 cal yr BP. Analysis of core and multibeam bathymetric data evidenced a submarine mass failure of the slump type, characterized by abruptly inverted layers with soft-sediment deformation structures. The event’s timing is constrained both with AMS 14C and the well-known stratigraphic identification of laminated or bioturbated layers in this highly productive upwelling zone. The event occurred during the Late Holocene as constrained by a maximum age of\u2009~\u20094,000 years. Although there is no explicit evidence on the cause of the submarine slump, the geomorphic characteristics and the close spatial connection with other submarine mass failures suggest a close relationship with the Tosco-Abreojos fault having acted either as a preconditioning factor or as a triggering mechanism. Finally, this study represents one of the few studies of submarine mass failures at the NE Tropical Pacific margin, aiming to identify how the transported sediments interact with the regional morphology and the formation of modern seafloor structures.