External controls on internal organization and vertical stacking pattern of Pleistocene shallow-marine and fluvial depositional sequences

The complex interaction of regional uplift, glacio-eustasy, local tectonics, and sediment supply has a significant impact on the internal architecture and vertical arrangement of shallow-marine and fluvial depositional sequences and can be documented in well-exposed successions of Pleistocene strata cropping out along the uplifted margins of Ecuador, northern Chile, and eastern central Italy. The results stemming from these sediments have important implications for sequence stratigraphic models in tectonically active areas and lead to the following general conclusions: (i) given that rates of syndepositional regional tectonic uplift were substantially less than rates of contemporaneous eustatic changes in sea level in all of the study areas, glacio-eustasy appears to have played the main control on development of high-frequency sequences; (ii) stratal geometries, sedimentary facies, and genetic complexity of sequence bounding unconformities of these cyclic successions indicate that the internal organization of individual depositional sequences is directly controlled by the rates of sediment supply and by the occurrence of intrabasinal, short-term normal faults striking obliquely with respect to paleo-shoreline trends; (iii) the effects of the regional tectonic uplift on these eustatic sequences is on longer term, at sequence set scale, and is responsible for their distinctive stacking pattern; owing to the progressive, tectonically driven reduction of accommodation space, high-frequency sequences are nested within a forced regressive sequence set, where each successively younger sequence is displaced basinward and downward respect to the last.