In the southern Blythe Basin, the stratigraphically highest and youngest unit of the Bouse Formation is an enigmatic combination of siliciclastic and bioclastic deposits. This upper bioclastic unit (Tbz) has a wide range of composition, grain size and clastic texture, and exhibits several intermixed lithofacies generally separated into a calcarenite or bioclastic lithofacies, a quartz arenite lithofacies, and gravel-dominated lithofacies. Vertical and lateral distribution of lithofacies is complex, but where relatively thick sections of these deposits are preserved they generally coarsen upwards. Below ~110 m above sea level (asl) unit Tbz unconformably overlies non-deformed to strongly deformed Bouse siliciclastic deposits (unit Tbs). Between ~110 m and 160 m asl unit Tbz is considered conformable with the underlying Bouse siliciclastic interbedded sand and mud. This is the zone where relatively thick Tbz deposits coarsen upward and grade semi-conformably into overlying siliciclastic post-Bouse fanglomerate. Between ~160 m to ~205 m asl (the highest unambiguous Tbz outcrop), Tbz overlies basal Bouse carbonate deposits over an obvious erosional unconformity. From these relationships, we infer that the upper bioclastic deposits represent an off-lap sequence of tributary-sourced alluvial fan and margin sediments rich in reworked basal Bouse carbonate deposits. Locally, these deposits record a near-shore environment on the margin of a standing body of water. Thus, these deposits were partially derived from and deposited across a piedmont covered with Bouse carbonate deposits that were re-exposed as the base level of a standing body of water declined.
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