Diagenetic Evolution and Distribution of Dolomite Bodies in a Partially Dolomitised Sequence - The Calcari Grigi Group

摘要

Amultidisciplinary study conducted over the carbonate platform deposits of the liassic Calcari Grigi Group (SouthernAlps), 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.