Internal architecture of mass-transport deposits in basinal carbonates: A case study from southern Italy

Submarine mass-transport deposits represent important stratigraphic heterogeneities within slope and basinal sedimentary successions. A poor understanding of how their distribution and internal architecture affects the fluid flow migration pathway, may lead to unexpected compartmentalization issues in reservoir analysis. Studies of modern carbonate mass-transport deposits 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 scale and mesoscale (metres to several tens of metres) carbonate mass-transport deposits 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 mass-transport deposits developed in near-slope basinal carbonates, a structural and sedimentological analysis of sub-seismic-scale mass-transport deposits has been undertaken on the eastern margin of the Apulian Carbonate Platform in the Gargano Promontory, south-east Italy. These mass-transport deposits, that locally comprise a large proportion (50 to 60%) of the base of slope to basinal sediments of the Cretaceous Maiolica Formation, 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 mass-transport deposits. This study helps elucidate the emplacement processes, frequency and character of sub-seismic-scale mass-transport deposits within the basinal carbonate environment, and thereby reduces the uncertainties in the characterization of sub-surface carbonate geofluid reservoirs.