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"Bouse-Type" Deltaic System: Alluvial-Deltaic Interactions in High-Relief Basin

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Deltaic facies of the Miocene-Pliocene Bouse Formation (southeastern California-western Arizona) differ significantly from previously published deltaic facies models. Whereas in conventional deltaic models, the nature of the delta is dictated by processes operating in the receiving basin. In the "Bouse-type" system receiving basin physiography is the principal first-order control on the character of the sediment package. A "Bouse-type" system is produced when a major river progrades into a steep irregular basin where emergent topographic highs form islands. Thus, (1) the delta plain is characterized by a complex system of distributary channels that are deflected around topographic highs, (2) locally derived alluvial/fan-delta deposits flank emergent highs and interfinger asinward with fine-grained deltaic material, (3) depositional basinward dip of marginal coarse-clastic strata produces a buttressing relationship with flat deltaic beds, and (4) radial downslope and shore-perpendicular transport directions in basin margin units show complex relationships with the dominant downchannel paleocurrent direction of deltaic strata.

In general, studies of modern deltaic systems, even in steep topographically irregular settings, focus on strata of deltaic (fluvial-derived) origin, and fail to consider adjacent/interfingering alluvial units. Study of the Bouse Formation demonstrates that in some contexts, flanking alluvial strata form an integral part of the overall character of the "deltaic" sediment package. Evaluation of both modern and ancient systems in the light of the evolving "Bouse-type" model is expected to allow improved recognition and more precise understanding of a category of deltaic deposits that may remain misidentified or poorly understood under existing facies models.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.