--> ABSTRACT: Proximal, Supply-Controlled Sequences Versus Distal, Base Level-Controlled Sequences in Alluvial-Fan and Fan-Delta Complexes (Eocene, South Pyrenean Foreland Basin, NE Spain), by M. Marzo, M. Lopez-Blanco, J. Pina; #91020 (1995).

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Proximal, Supply-Controlled Sequences Versus Distal, Base Level-Controlled Sequences in Alluvial-Fan and Fan-Delta Complexes (Eocene, South Pyrenean Foreland Basin, NE Spain)

M. Marzo, M. Lopez-Blanco, J. Pina

The physical relationships observed between laterally connected alluvial-fan and fan-delta facies along a 20 km long and 850 m thick dip-oriented cross-section show:

1) There is not a systematic correlation between surfaces marking abrupt lithological changes (i.e. from monogenic to poligenic conglomerates) in the proximal alluvial-fan and the internal or bounding surfaces observable in the lower-frequency, transgressive-regressive composite sequences identified in the coastal areas.

2) The passage from proximal to distal alluvial facies shows a series of poorly defined retrograding-prograding cycles, which, in some cases, coincide (although slightly out of phase) with the coastal, transgressive-regressive composite sequences.

3) The laterally persistent beds of monogenic conglomerates identified in the proximal alluvial segments do not correlate with any specific stratigraphic horizon or interval of the retrograding-prograding cycles observed either in the distal alluvial zone or in the coastal areas. These monogenic units occur randomly in the succession.

4) The higher-frequency, coastal transgressive-regressive, fundamental sequences are hardly traceable and recognizable in the distal alluvial zone, although some maximum flooding surfaces could be correlated with some some fine-grained alluvial intervals.

We conclude that sequential arrangement in most of the alluvial area was not governed by the relative sea-level changes which controlled cyclicity in the coastal zone. Sediment supply variations in response to tectonically-triggered geomorphological processes operating in the alluvial catchament area seem to be the most efficient factor.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995