Structural diagenesis of shallow platform carbonates: Role of early embrittlement on fracture setting and distribution, case study of Monte Alpi (Southern Apennines, Italy).

Bed-perpendicular, opening-mode diffuse fractures are common features in carbonate rocks because they become brittle during the first stages of diagenesis. Early-fractures could be independent of tectonics and form a background structural network from sub-millimeter to 10’s of centimetres scale. This study focuses on the outcrop-tomicro scales structural, stratigraphic, and petrographic characterization of Lower Cretaceous, shallow-water, tight limestones of the Inner Apulian Platform exposed along the axial sector of the southern Apennines foldand- thrust belt, Italy. This work aims at understanding the formation of early diagenetic fractures during the first stages of sediment lithification, and on their impact on subsequent deformation mechanisms associated to polyphase tectonics. The results of field structural surveys, of petrographic and cathodoluminescence analyses of representative samples unravel the main structural-diagenetic processes in shallow-water carbonates. We document that early brittle fractures were intrinsically related to the host rock pore type and cementation processes, and summarize the overall time-dependant evolution of the structural assemblages in a conceptual model. This model includes all abutting and crosscutting relationships among the various structural elements from field to thin-section observation, and form the now days fracture network.