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CONSTRAINING THE EFFECTS OF AUTOCYCLICITY, TECTONICS AND CLIMATE ON ALLUVIAL FAN ARCHITECTURE, SE EBRO BASIN, SPAIN

Elizabeth Baresch

University of South Carolina, Department of Geological Sciences

Columbia, South Carolina

[email protected]

Due to their sensitivity to changes in sediment supply, discharge and slope, alluvial fans provide a laboratory to investigate the influence of tectonics, climate and autocyclicity on sedimentary processes and stratigraphic architecture. This study focuses on the wedge-top and proximal foredeep depozones of the southeastern Ebro basin in attempts to tie the architecture and composition of the alluvial fan conglomerates of the Montsant Formation to autocyclicity, tectonic activity in the adjacent Catalán Coastal Ranges, well-known Paleogene climate changes, or a combination of these influences. Data collected from these Paleogene strata include measured-section, lithofacies-assemblage, conglomerate-composition, sandstone-petrography and paleocurrent measurements. This unit’s lithofacies are commonly conglomerates with subordinate interbedded sandstones, mudstones and fresh-water carbonates due to deposition of channel, lobe and sheetflood strata and minor lacustrine sediment accumulation. Conglomerate clast composition data and sandstone petrography indicate sediment derivation from Mesozoic sedimentary cover and Hercynian basement source strata. The progressive evolution and uplift of the source area suggest a normal unroofing sequence and rare occurrences of recycled clasts suggest reworking of previously deposited source area gravel. Paleocurrent measurements from conglomerate clast imbrications reveal a predominant paleoflow direction of ~N45W° whereas basal furrows have a tightly clustered, northward orientation. The data suggests that the Montsant Formation of the central Catalán Coastal Ranges is typical of non-marine alluvial fan deposits and autocyclicity and tectonism were dominant in controlling the architecture. Evidence for known Paleogene paleoclimatic changes were not conclusively identified and suggest that climate was not a dominant factor in controlling the architecture and sedimentation.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid