Tectonic Controls on Coarse-Grained Delta Depositional Systems in Rift Basins
- Albina Colella3,
- David B. Prior4
Published Online: 2 APR 2009
Copyright © 1990 The International Association of Sedimentologists
How to Cite
Gawthorpe, R. L. and Colella, A. (2009) Tectonic Controls on Coarse-Grained Delta Depositional Systems in Rift Basins, in Coarse-Grained Deltas (eds A. Colella and D. B. Prior), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303858.ch6
Universita della Calabria, Italy
Atlantic Geoscience Center, Nova Scotia, Canada
- Published Online: 2 APR 2009
- Published Print: 19 OCT 1990
Print ISBN: 9780632028948
Online ISBN: 9781444303858
- tectonic controls on coarse-grained delta;
- rift basins;
- Gulf of Suez;
- consequent drainage basins;
- footwall-derived coarse-grained deltas;
- basin-fill architecture
Rift basins (extensional and transtensional) commonly have an asymmetric, half-graben form that results from the throw on one border fault zone being much greater than on the other basin margin. This structural geometry, the detailed linkages between fault segments and the episodic nature of fault activity have a pronounced effect on coarse-grained delta depositional systems. A clear tectonic control can be observed on the location, form and basin-fill architecture and on the internal geometry of individual coarse-grained delta sequences in both modern and ancient rift basins. Delta location is related to structurally controlled topography and bathymetry; lateral (footwall- and hanging-wall-derived) and axial coarse-grained deltas may develop. However, the lower gradients of the hanging wall, and particularly the axial slopes, tend to promote the development of finer-grained deltaic systems. Transfer zones linking major fault segments act as loci for drainage entering the rift basin and hence are commonly the sites of coarse-grained delta deposits.
Due to the steep basin margin and large bathymetric differential across the border fault zone, footwall-derived coarse-grained deltas are generally of Gilbert-type and form isolated fan- to wedge-shaped bodies, occupying an area of < 10 km2. In contrast, the lower gradient of the hanging wall promotes the development of coarse-grained deltas with a wedge- to sheet-like form which have a low-gradient delta-front. These deltas commonly coalesce and occupy a much larger area than footwall-derived systems. Axial fan deltas are expected to show vertical stacking patterns adjacent to the border fault zone. When deformation involves a significant strike-slip component, the architecture of the basin-fill becomes complex due to lateral offset of feeder channels and depocentres. This effect is most pronounced adjacent to oblique-slip border faults and in strike-slip transfer zones, where asymmetric, off-lapping coarse-grained deltas may develop.
Near-surface coseismic deformation may trigger major failure of the delta front, leading to a complex internal structure of stacked foreset units separated by slide planes. However, where near-surface deformation is less intense, a simpler delta foreset unit may develop, consisting of alternating sigmoidal and oblique clinoforms which reflect episodes of slip and no slip respectively. Coarse-grained deltas deposited during tectonic activity should also display evidence for tilting associated with fault displacements; in the simplest case, the degree of tilt should increase in progressively older deltas. Tectonic effects on the internal structure of fan deltas and evidence for syndepositional tilting are most apparent in systems deposited adjacent to the border fault zone.