From salt carapace to secondary minibasin encasement—The Bolon Secondary Minibasin, Eastern External Betics, SE Iberia

Abstract

The Bolon Secondary Minibasin (BSM) evolved on the now eroded Elda Salt Sheet, which contains fragments of the diapiric roof and syn-contractional sediments. Our detailed analysis of the BSM reveals how diapir rejuvenation and salt sheet evolution can affect the structural and stratigraphic architecture of secondary minibasins. We present a comprehensive analysis of the BSM integrating detailed cartography with stratigraphic, paleontological, and structural data. The field data show that the BSM contains a carapace of latest Cretaceous marlstones overlain by an up to 800 m thick roof of terrigenous and outer platform deposits. These suprasalt deposits are characterized by tabular beds without diapir derived detritus and are cut by a series of extensional growth faults that sole into the salt. In the Oligocene, diapir rejuvenation due to contractional deformation resulted in the breaching and dismemberment of this diapiric roof and extrusion of allochthonous salt. Roof dismemberment is recorded as an unconformity truncating the roof strata and diapir derived detritus in the Oligocene-lower Miocene units. Throughout the middle Miocene composite halokinetic sequences, rapidly shifting depocenters, episodic unconformities, and stratigraphic onlaps record the rapid sinking and progressive northward rotation of the BSM. Debrite wedges, diapir derived detritus, and ramp-flat geometries along the upper salt-sediment contact show that in the middle Miocene the BSM was fully encased in allochthonous salt. Continued shortening and further extrusion of allochthonous salt rotated the BSM an additional 60° to the NW before its eventual grounding on subsalt strata.