Vertical sequences in turbidite successions : fact or fiction?

Forster, Christopher Mark (1995) Vertical sequences in turbidite successions : fact or fiction? University of Southampton, Doctoral Thesis.

Abstract

The Angola Basin, cored during DSDP (Deep Sea Drilling Project) Leg 75, reveals datasets from two distinctly different turbidite systems - the Cretaceous gren fan and the Upper Miocene to Recent brown fan. More quantitative techniques with a higher resolution data-set enable the detection of more intricate smaller-scale sequence trends and also enables an assessment of previously documented broader sequences. The general interpretation of fan development is subsequently modified to account for the increased sequence definition. The results of vertical sequence analysis upon two Upper Miocene to Pliocene cores from ODP (Ocean Drilling Program) Leg 116 in the distal Bengal Fan illustrate the interplay between turbidite deposition and tectonics. This study shows how periodic times of active faulting and associated local uplift, affect the production of differential sequence architecture between terminal lobe successions. The study also elucidates the role of topography and flow restricting barriers upon turbidite thickness. Another area of study, in the Late Oligocene Izu Bonin forearc basin, included the sequence analysis of volcaniclastic turbidites and debrites cored from three laterally equivalent sites. These were selected because active forearc basin settings are not widely documented and therefore poorly understood. The results of the study of sequences in the basin show quantitative proof of seismic controls upon gravity flow propagation.

Despite the increasing knowledge of the planform geometries and processes acting in modern-day deep-water systems, most sequence types are always related to old models based upon field studies. Two investigations were included in the thesis to document the types of sequences found in two well studied field areas and to offer support to the studies on the extensive vertical cores. Firstly, the validity of compensation cycles, which have been identified and commonly referred to in studies of lobe and lobe-fringe settings, was assessed through the study of successions from the Hecho Basin, south-central Pyrenees. The present study found no evidence that documented cyclic thickening-upwards sequences exist in such settings. This is thought to be a function of the greater complexity which exists as a result of a number of intrabasinal controls upon lobe deposition. (DX191317)

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