Where the salt sheet ends - submarine allochthonous salt advance and hindrance, The Elda Salt Sheet, Eastern Prebetics (Southern Iberia)

Abstract

The Eastern Prebetics are part of the External Zone of the Betic Fold-and-Thrust Belt in SE Iberia where a significant amount of salt structures crops out including: diapirs, allochthonous sheets, welds, primary and secondary minibasins, and rafts. Our study focuses on the subsalt, syn-contractional, early to middle Miocene (Aquitanian-Langhian) stratigraphy of the Elda Salt Sheet, aiming to document the sub seismic scale deformation and salt-sediment interactions during allochthonous salt advance. Stratigraphic sections, halokinetic fold analysis, geologic field mapping and foraminiferal dating are used to characterize the subsalt sediments exposed in contact with the northwestern edge of the outcropping Elda Salt Sheet. Based on the subsalt sedimentary and structural relationships we show that the Elda Salt Sheet advanced at least 8 km towards the north during the syn-orogenic Aquitanian – Langhian times before being buried during the latest Langhian - Serravallian times. This overall northward advance can be defined by six main phases. All the phases occur in submarine conditions in a carbonate ramp with water depths ranging from 10's to 100's of meters and are: (1) the extrusion of a salt sheet in an inner – outer carbonate ramp environment coeval to the onset of regional Oligocene-Miocene shortening corroborated by an Aquitanian aged flat and stranded intrasalt stringers along the subsalt flat; (2) Burdigalian-early Langhian burial of the salt sheet toe in an outer shelf – basinal environment where pinned inflation, and subsequent breakout of a confined salt sheet is evidenced by a hectometric halokinetic fold ramp and rafts of Burdigalian stratigraphy above the salt sheet. (3) early-middle Langhian rapid lateral advance of the salt sheet along a base salt flat which occurred in a deepwater basinal environment; (4) middle-late Langhian hindrance of the salt advance, development of subsalt decametric thick and decametric spaced halokinetic fold ramps in a basinal – outer shelf environment; (5) late Langhian salt sheet burial by shallow water carbonates and deepwater basinal marlstones; and (6) subsidence of secondary minibasins. These stages reflect a detailed history of a salt sheet lineage. This field-based study documents for the first time the structural and stratigraphic architecture of a subaqueous salt sheet lineage in a contractional setting.