Diagenetic evolution and distribution of dolomite bodies in a partially dolomitised sequence - The Calcari Grigi Group

A multidisciplinary study conducted over the carbonate platform deposits of the liassic Calcari Grigi Group (Southern Alps), highlighted how the use of a 3D field analogues can contribute to better define the distribution of dolomitic bodies related to fault networks, to characterise the petrophysical properties of the dolomitic sequence and to unravel a complex diagenetic history. Pervasive unimodal and patchy polymodal dolomites characterize a thick portion of the Group, and are topped by a smoothly curved - not stratigraphic front. This latter tend to uprise near to the major faults and fracture swarms, with massive chaotic dolomite. Associated to these zones there is the development of stacked high-porosity and permeability bedding-parallel bodies that show excellent petrophysical properties. Thin section, Cathodoluminescence, isotopic and fluid inclusions analyses were used to constrain the paragenetic evolution of the sequence. The result is a complex paragenetic evolution, in which good porosity developed but in later stages porosity was reduced by the deposition of calcite and dolomite cements. Fluid inclusions results relate the evolution to a complex interplay between fluid evolution, tectonics, burial and hydrological processes, while isotopic analysis suggests a Miocene age as a timing for the late diagenetic stages.