Fossil pockmark-related carbonate deposition reveals late Miocene fluid migration in the Majella petroleum system (Central Italy)

Pockmarks are geomorphological depressions associated with fluid migration in marine environments; however, their occurrence in the geological record remain poorly constrained. Here we report evidence for fossil pockmark-related carbonate deposition within the Majella Mountain, one of the most important petroleum systems of Italy. The Colle del Lettuccio carbonates (CLC) crop out in the North-Western part of the Majella Mountain and lies between the base of Upper Miocene evaporites and the oligohaline upper Messinian Lago-Mare clays. The CLC are characterized by breccias containing lithoclasts from the underlying succession, microbial boundstones, and ooidal grainstones, indicating localized and short-lived depositional processes driven by focused fluid flow, related to a pockmark field. Moreover, carbon isotope analyses reveal negative δ¹³C values, consistent with a thermogenic methane source and supporting a genetic link with deep-seated fluid migration within the petroleum system. Stratigraphic relationships constrain the formation of these deposits to a narrow time interval between 5.59 and 5.33 Ma, suggesting that fluid migration occurred over less than 260 kyr. These results indicate that the CLC record a previously unrecognized fossil pockmark system in a carbonate platform setting, providing new constraints on the timing, processes, and surface expression of hydrocarbon migration in foreland basin systems.