Timothy Cullen

First insights into stratigraphic architecture in proximal deepwater syn-rift sediments in the hanging-wall of a rift margin border fault

Tim Cullen (VISTA Visitor from University of Leeds , PhD Student in the Syn Rift Systems Group)

Syn-rift deep-water sands represent a significant play type worldwide with recent exploration successes in the North Sea highlighting a need to further the understanding of stratigraphic architecture. Sediment dispersal patterns and the resultant stratigraphic architecture in syn-rift settings is complex and controlled by the interplay of topography, sediment supply and base-level changes, which are all highly variable spatially and temporally. Extensive outcrops surrounding the Xylokastro Horst in the Gulf of Corinth, Greece present an exceptional opportunity to investigate syn-rift deltas and a coeval deep-water clastic system deposited in the hanging wall of a rift margin border fault. The Early-to-Middle Pleistocene syn-rift stratigraphy comprises 400 m thick Evrostini/Ilias Gilbert type deltas located at fault segment boundaries along the northern flank of the Xylokastro Horst. The northern hanging-wall to the horst is filled with axially deflected gravity current deposits that are connected to the bottomsets of the deltas. The generation of a new stratigraphic scheme for the West Xylokastro Fault block from integrated fieldwork, digital outcrop modelling and core data from a research borehole will allow investigation of architectural changes in relation to key basin-evolution events such as fault activity and sea level fluctuations. Preliminary observations from the core show a variety of core expressions of outcrop stratigraphic architectures which further the application of these outcrops as reservoir analogues.

The outcrops of the Evrostini/Ilias deltas and gravity current deposits permit investigation of down-dip flow transformation in relation to seabed topography at bed-scale through to seismic- scale stacking patterns. The depositional architecture is complicated by the influence of multiple sediment sources, including what are thought to be laterally emplaced mass transport deposits. The significant facies and architectural variation are related to activity on both small and large rift structures, which have influenced the character of coarse-grained pinchouts in the distal parts of the system. An understanding of sand architecture can be gained in the context of a deforming basin-floor providing significant control on syn-rift reservoir distribution, highly analogous to current ongoing developments and exploration targets worldwide.