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The AAPG/Datapages Combined Publications Database

CSPG Special Publications


Fluvial Sedimentology — Memoir 5, 1977
Pages 669-702
Fluvial Facies Models

Alluvial Fan Sequence and Megasequence Models: With Examples From Westphalian D — Stephanian B Coalfields, Northern Spain

Alan P. Heward


Sequences, megasequences and basin-fill sequences of progressively changing character appear common to many alluvial fan accumulations. Their study can provide evidence of depositional processes (sequences), short term fan behaviour (sequences), longer term fan behaviour (megasequences) and the depositional basin setting (basin-fill sequences). The occurrence and identification of these sequences appear dependent on down-fan trends in sediment character and depositional process, the localisation, switching and migration of the region of active fan sedimentation, a regularity of depositional event magnitude, and an absence of reworking by subsequent floods.

“The prime requisite of fan formation is the setting of highland and lowland side by side”, Denny (1967). Where alluvial fans are dependent solely on initial fault scarp or erosional topography, geographically limited, relatively thin accumulations of decreasing grain size result. Fan sediments of greater geographical extent and thickness, repeated vertical stacking of sequences and megasequences, and the occurrence of alluvial fan basin-fill sequences result from continued movement along fault lines.

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