High-Resolution Sequence Stratigraphy from Outcrop Study, with the Integration of Log and Seismic Data

The detailed sequence stratigraphic analysis of the siliciclastic-dominated Late Cretaceous sediments (Aren Sandstone and Garumnian red beds, south central Pyrenees, Spain) reveals the repeating disposition of critical elements and controlling mechanisms of cycles and sequences. Our approach integrates (a) hierarchy of unconformity-bounded units, (b) physical expression of boundaries traceable from the continent to the basin, (c) featuring facies and depositional systems, (d) well log and seismic expression, and (e) driving basing-filling mechanisms. A comparison to other active basins is suggested in order to prove the validity beyond the regional scale. Four basin-wide transgressive facies cycles were identified and interpreted as third-order units. The transgressive phase of each cycle is represented by mixed shelf deposits, while regressive periods consists of complex delta systems. The cycles are composed within their regressive phase of fourth-order depositional sequences, trapped in structural lows, which are controlled by synsedimentary compressive tectonics. Both cycles and sequences are set up by similar building blocks. Our example, cycle two, localized in the Tremp area, displays seven sequences: lowstand systems tracts are channelized turbidites; transgressive systems tracts are lagoon-barrier systems and/or storm-dominated shoreface deposits; and fluvial, coastal plain, and delta deposits build highstand systems tracts. The physical continuity of themore » sequences (and cycles) is frequently disrupted by erosion due to lowstand or transgressive processes and active faulting. Synsedimentary ramp anticlines, which control the entire basin, and third-order unconformities have been recognized in seismic lines. Their interpretation has led to the identification and correlation of cycles and sequences in the well logs of the region.« less