Abstract

The Late Cretaceous seas of Venezuela were characterized by deposition of organic carbon-rich limestones, cherts, and shales in the Maracaibo and Barinas/Apure Basins of western Venezuela (La Luna and Navay Formations) and in the Maturín and Guarico Sub-basins of eastern Venezuela (Querecual, Tigre, and San Antonio Formations). Deposition of these units typically occurred under low-energy, low-oxygen conditions that were punctuated by the episodic activity of bottom currents, debris flows, turbidites, syndepositional faulting, and by intermittent oxygenation. These events produced a characteristic set of sedimentary structures that can be used to provide more detailed interpretations of each depositional system. Four main types of sedimentary structures noted in this study are: (1) hydrodynamic—primarily produced through the actions of currents; (2) rheotropic—structures produced during loading and dewatering of unconsolidated sediments; (3) biogenic—formed through the actions of living organisms, such as trace fossils; and (4) diagenetic—structures and textures formed through near surface and burial diagenetic processes.

Identification of these structures can provide new insights on the hydrodynamic and biologic settings of Venezuelan Cretaceous strata. Utilizing observations made in this study along with previously published works, bottom-water conditions in the La Luna depositional system are interpreted to have been maintained consistently in a state of anoxia or very low dissolved oxygen content. This contrasts with bottom waters in the Querecual depositional system, during which strong periods of anoxia or low dissolved oxygen content were punctuated by periods of intermittent oxygenation.

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