Computer modelling of the influence of tectonics on sequence architecture of coarse-grained fan deltas

Abstract

Fan delta deposition and extensional faulting are combined in a computer model using a general tectonosedimentary forward modelling equation. Fan delta forms and architectures resulting from tectonic activity are investigated using this model. Fan deltas formed during periods of tectonic quiescence are shown to have a sheet-like form and grow mainly as a result of progradation. Topset development is limited, resulting in the development of oblique to sigmoidal clinoforms. Fan deltas formed during periods of tectonic activity have a more wedge-shaped form and are restricted to a region adjacent to the controlling fault. These fan deltas grow as a result of both progradation and aggradation, resulting in the development of sigmoidal clinoforms. Under conditions of constant tectonic subsidence and sediment supply, fan deltas are shown to undergo a brief period of progradation followed by aggradation and a long period of retrogradation. This is a consequence of an increasing amount of sediment being deposited as topset material as the delta progrades and the position of the offlap break being displaced basinward during hangingwall subsidence. Other controls on fan delta architecture, such as variations in sediment supply and sea/lake level, are also considered. Pleistocene-Recent, Gilbert-type fan deltas from the southern margin of the Gulf of Corinth rift, Greece contain many of the features described above and modelling is used to investigate whether it is possible to identify the controls on their sequence architectures.