Linking benthic fauna and seismic facies to improve stratigraphic reconstructions: The case of the mid-adriatic deep since the late glacial period (central adriatic sea)

Direct observations from the geologic record are commonly used in conjunction with indirect seismic inferences to detail environmental settings and stratal architecture of sedimentary successions. However, examples of integration between seismic and macrobenthic insights are scarce and limited to the use of such a group as an auxiliary to other proxies. We investigated mollusc and ostracod assemblages along an onshore-offshore transect that intersects the C2 clinothem (15.6 - 14.4 ka BP) and the overlying transgressive deposits that recorded the last phase of progradation and abandonment of the Po River Lowstand Wedge (PRLW). We applied multivariate analyses to benthic data to assess the extent to which mollusc and ostracod assemblages can improve both the resolution of seismic-derived depositional environments and the sequence stratigraphic architecture of targeted sedimentary succession. Along the onshore-offshore transect, seismic reflection geometries correspond with three broad sedimentary environments: High Amplitude Continuous reflections (HAC) are interpreted as delta plain/subaqueous shelves, High Amplitude Continuous Wavy Dipping reflections (HACWDip) as prodeltas and Low Amplitude Continuous reflections (LAC) are associated to distal basin settings. The integration of quantitative palaeoecologic trends with seismic-derived depositional environments allowed us to subdivide the HAC facies into a proximal (core LSD-26) and distal (cores LSD-27 and -28) area. The proximal HAC facies, in particular, encompasses lower delta plain semi-barred settings with vegetated substrates that upcore pass to nearshore settings. The distal HAC facies is distinguished by clusters that suggest ecological mixing due to strong bioturbation and wave-aided hyperpycnal flows in offshore transition/inner shelf settings. The paucity of benthic fauna for the geophysical units HACWDip (core LSD-05) and LAC (core LSD-04) hampered a complete reconstruction of the palaeoenvironmental dynamics. However, both benthic groups support a seismically derived interpretation of shelf and basinal settings, respectively, and both were subjected to high sedimentation rates. Moreover, integration of mollusc and ostracod multivariate-derived trends with grain-size data across the onshore-offshore transect reveals distinctive stratal stacking patterns that are useful in constraining the position of the Maximum Regressive Surface that marks the abandonment of the PRLW in the Central Adriatic Sea.