Late Cretaceous transtensional faulting of the Apulian Platform, Italy

Abstract

This work focuses on the structural setting of a small area of the Murge Plateau, southern Italy, exposing Turonian bauxites and encompassing Upper Cretaceous carbonates of the Apulian Platform. By combining field geological and structural mapping with mineralogical and petrographic investigations of representative rock samples, we document the control exerted by Late Cretaceous, syn-sedimentary, high-angle faults and dilational fissures striking ca. N105E, N135E, N170E, and N45E. Altogether, these structural elements formed a few km-long, transtensional fault system along which karst-related shafts, dissolution caves, and sinkholes developed. Karst processes first affected the topmost limestone beds of the Valanginian-Cenomanian Bari Fm. Then, during Turonian, in a continental setting, cycles of terrigenous sediment deposition and weathering localized in the karst-related cavities, dilational fissures, and at the top of down-dropped fault blocks. Weathering of the Al–Si rich sediments formed bauxites made up of kaolinite, boehmite, goethite, hematite, and anatase mineral phases. The relative enrichment in kaolinite with respect to boehmite documented for the breccia and conglomerate matrix topping the bauxites is interpreted as due to lower degrees of weathering. Differently, the individual bauxite beds do not show any internal significant variation in terms of their mineral assemblages, but form angular unconformities due to syn-sedimentary faulting. The subsequent marine transgression also occurred under the influence of active tectonics, as displayed by growth folds at the bottom of the Conacian-Early Campanian Altamura Fm. The overall results of this study are in agreement with those previously reported for nearby areas of the Murge Plateau exposing Santonian limestone rocks of the Altamura Fm. Accordingly, we infer that Late Cretaceous transtensional faulting of the Apulian Platform was due to a far field stress state, likely associated to the orogenic processes that involved the northern edge of the Adriatic micro-plate.