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Channels in Carbonate Environments: 3-D-Seismic Characteristics Extracted From the Sedimentary Record

Abstract

Submarine channels can form important hydrocarbon reservoirs, and modern and ancient siliciclastic channels have been therefore intensively studied in the past. Significantly less is known of channels in carbonate environments. Particularly in non-tropical carbonate settings, information on channel geometries, morphology, architecture and channel-forming processes is limited. This study presents 3D seismic-reflection data of kilometre-scale submarine channels in non-tropical carbonates from different stratigraphic intervals of the European North Sea and the NW Australian Shelf. Though all systems studied developed under non-tropical deepwater conditions, they show distinctly different geometries interpreted to reflect differences in input variables including sediment flux and size, but also differences in the tectonic environment. 3D-seismic analysis of a kilometre-scale channel in the Upper Cretaceous part of the Chalk Group of the North Sea Central Graben documents a rather isolated, sinuous, leveed system that displays many of the architectural elements known from siliciclastic deepwater turbidites. This channel is interpreted to have formed an important conduit for recurrent turbulent flows transporting failed chalk material into the deeper basin depocentres in response to inversion tectonics. Nearby and at the same stratigraphic level, there are other, less extensive, highly asymmetric channels. These systems lack levees and are interpreted to have been eroded by bottom currents and filled laterally by chalk drifts. The channels preserved in the Paleogene section of the Browse Basin, NW-Australian Shelf, in contrast, are much narrower than the North Sea examples and occur in arrays as vertically and laterally-offset stacked multi-storey systems. The repetitive character and restriction to clinoform fronts suggests their development in response to sedimentation-driven clinoform oversteepening and failure under rather stable tectonic conditions. The significant variability in geometry, morphology and architecture of the deep-water carbonate channels presented documents that generalized predictions of deposit type and the associated reservoir properties are difficult. Controlling factors for this variability include active tectonics, differences in sediment type and size, the type of mass-transport system and the superimposed current regime. An understanding of these parameters will be essential for a successful exploration in deepwater carbonates.