Structural analysis and tectonic evolution of the El Bolon and Bateig secondary minibasins in the Eastern External Betics (Betic fold-and-thrust belt—Iberian Peninsula)

The Eastern External Betics correspond to the external part of the Betic fold-and-thrust belt that crops out in the Valencia and Alicante provinces. It mainly consists of a system of ENE-trending cover folds and thrust sheets detached in the Triassic salt along with a significant amount of diapirs and allochthonous sheets made by this salt. Most primary diapirs formed during the extensional evolution of the southern Iberian passive margin during Jurassic to early Santonian time. These diapirs were later shortened and squeezed forming syn-contractional salt sheets and secondary minibasins during the Africa/Eurasia convergence that, beginning at late Santonian times, led to the formation of the Pyrenean and Betic orogens.

Based on detailed stratigraphic analysis, structural field mapping, fracture analysis, and by comparison with other salt-bearing fold-and-thrust belts we revisit one of the major allochthonous salt sheets of the area, the Elda salt sheet, to reinterpret its structural evolution. The Elda salt sheet includes fragments of the feeding diapir roof as well as secondary minibasins made by late Santonian to middle Miocene syn-contractional sediments and it is covered by upper Miocene to Pliocene post-contractional deposits.

This presentation will focus on the evolution of the El Bolon and Bateig secondary minibasins. El Bolon minibasin is characterized by a basal section comprising Late Cretaceous (Senonian) marls that correspond to the carapace above a diapir. The Senonian sequence is conformably overlain by Paleocene-Eocene siliciclastics that are characterized by a series of syn-sedimentary normal faults that sole into the salt with significant variations in thickness throughout the minibasin. In Oligocene times, coeval with the onset of the Betic Orogeny, renewed diapirism resulted in the extrusion of allochthonous salt and dismembered the diapiric roof. Diapir derived detritus (Jacintos de Compostella) in the Oligocene-Miocene sequence indicate that allochthonous salt was exposed at the surface while El Bolon minibasin continued to passively grow. Throughout the Early to Middle Miocene El Bolon minibasin developed hook halokinetic sequences and episodic unconformities with onlaps recording the progressive rotation of the minibasin. By the end of the Middle Miocene the whole minibasin was completely encased in salt. Coeval to or shortly after the encasement of the El Bolón minibasin the Bateig minibasin, comprising Miocene calcarenites and siliciclastics, began to subside into the allochthonous sheet. Continued shortening due to the Betic Orogeny further rotated the El Bolón minibasin around a horizontal axis to its present position (vertical to overturned) contemporaneous with the southward tilting and partial encasement of the Bateig minibasin.