INTERNAL ARCHITECTURE OF MASS-TRANSPORT DEPOSITS IN BASINAL CARBONATES: A CASE STUDY FROM SOUTHERN ITALY

Submarine mass-transport deposits (MTDs) represent important stratigraphic heterogeneities within slope and basinal sedimentary successions. A poor understanding of their distribution and internal architecture that affect the fluid flow migration pathway, may lead to unexpected compartmentalization issues in reservoir analysis. Studies of modern carbonate MTDs mainly focus on large seismic-scale slope failures however the near-platform basinal depositional environment often hosts mass-transport deposits of various dimensions. The small- and meso- scale (metres to several tens of meters) carbonate MTDs play a considerable role in distribution of sediment and therefore have an impact on the heterogeneity of the succession.

In order to further constrain the geometry and internal architecture of MTDs developed in near-slope basinal carbonates, we have undertaken a structural and sedimentological analysis of subseismic-scale MTDs degrading the eastern margin of the Apulian Carbonate Platform in the Gargano Promontory, southeast Italy. These MTDs, that locally comprise a large proportion (50 - 60%) of the base-of-slope to basinal sediments of the Cretaceous Maiolica Formation. Here, the MTDs typically display a vertically bipartite character, including debrites and slump deposits of varying volume ratios. A range of brittle and ductile deformation styles developed within distinct bed packages, together with the presence of both chert clasts, folded chert layers and spherical chert nodules, suggests that sediments were at different stages of lithification prior to downslope movement associated with MTDs.

This study helps elucidate the emplacement processes, frequency, and character of sub-seismic-scale MTDs within the basinal carbonate environment, and thereby reduces the uncertainties in the characterisation of sub-surface carbonate geofluid reservoirs.