Serravallian-Tortonian buried stratigraphy of Crotone basin: sedimentary and compositional evolution

The starting phase of the Crotone Basin infill is recorded by a siliciclastic Serravallian–Tortonian cycle, reliable both on outcrop and in the subsurface. In this study, a total of 16 well logs, located both onshore and offshore, were analysed to evaluate the stratigraphical and sedimentological variations along transects of 60 km (N-S) and 27 km (W-E), which entirely cover the area of Crotone Basin with more than 3.700 m in depth. The studied Serravallian-Tortonian cycle starts with the San Nicola dell’Alto Fm., dominantly composed of arenites and conglomerates, testifying an alluvional to coastal depositional environment. In the studied wells, the San Nicola dell’Alto Fm. is commonly found at depth spanning from 897 m to 2.976 m, in the diverse wells, and shows a constant thickness of ca. 300 m in average, with a maximum of 468 m in the southernmost portion of the basin and a minimum of 32 m in its central part. The San Nicola dell’Alto Fm. passes upward to the Ponda Fm. (detectable between 780-2.570 m in the diverse wells), dominantly characterized by claystones, marly mudstones and secondly by sandstone levels, indicating a deep marine pelagic depositional environment interested by frequent turbiditic sedimentation. The Ponda Fm. shows extreme variation in thickness, with a maximum of ca. 1.147 m in the northernmost part of the Crotone Basin and a minimum of 37 m in its southernmost part. The allochthonous Cariati Nappe, that cut the upper part of this sedimentary cycle, is not fully intersected by the studied well logs unless its siliciclastic turbiditic portions. The sandstone levels both found in the recovered cores were analysed through a sandstone modal analysis in order to evaluate their composition and to correlate them with their outcrop counterparts. The base of the basin shares a quartzolithic input that becomes quartzofelspathic upward (Cariati Nappe). Sandstone addressable to San Nicola dell’Alto and Ponda formations reveal quartzofeldspathic suites. In particular quartzolithic sandstone (Q52 F5 L42) has abundance of extrabasinal carbonate grains, argillite and low metamorphic fragments. While moving to quartzofeldspathic sandstone (Q50 F40 L10), lithic variability types are still kept, but lower than feldspar and quartz input that increase rapidly upward. Diagenetic features of San Nicola dell’Alto and Ponda formations do not share a deep compaction and cementation, unless some samples that show early carbonate cementation, and rarely replacement and dissolution. Samples were all stained and coloured to well appreciate porosity that suffer a reduction with depth. These data are processed with a digital method for a next implementation in GIS environment to create a 3D model of compositional and diagenetic variation along the basin.