Título: Sedimentary Structures of Venezuelan Upper Cretaceous marine source-rock formations La Luna, Navay and Querecual

Autor: Macsotay, O.; Erlich, R. N.; Peraza, T.

Fuente: SEPM Research Conference: Paleogeography and Hydrocarbon Potential of The La Luna Fomation and Related Cretaceous Anoxic Systems

Lugar y fecha del Evento: 7^th - 9^th September, Caracas

Editor: SEPM

País de publicación: Venezuela

Tipo de Documento: Memorias CD-ROM

Resumen:

The high organic carbon containing carbonatic/pelitic alternations of Late Albian to Santonian age, are named La Luna Formation in Western Venezuela and Querecual in the Eastern side. In intracratonic position is found Navay Formation's La Morita member of Coniacian-Santonian age in the South Andean flank. Eighteen (18) different sedimentary structures observed in surface and subsurface within these three units are: Hydrodynamic: Shale clast (Rare), Parallel lamination (Abundant), Low-Angle cross-lamination (Scarce), Graded bedding (R), Debris flows (R). Rheotropic: Slurry-slump structure (R), Carbonatic pseudoconcretions, (Frequent), Load casts (F), Injectites (R), cone-in-cone (locally F). Biogenic: Feeding burrows:Paratisoa, Chondrites, Zoophycos, etc. Diagenetic: Stylolites (locally F), Carbonate concretion (locally A), Carbonate nodules (A), Listric faults (R) cracking of carbonate pseudonodules (R) . These units were sedimented mostly on extensive shelfal environments according to foraminiferal, geochemical, sedimentological and ammonite-morphotypic studies, under the influence of red-tide-type planktonic "blooms", and restricted water circulation. The sedimentary structures reflect these exceptional conditions: A) The bottom was deep enough to accumulate sediment beyond the storms (deeper than 40 m), B) The low rate of sedimentation in La Luna Formation, facilitated the endurance of the hydroplastic state of the muddy sediment, C) Locally, tectonic fault scarps and some tilted surface developed listric fault systems and small-scale delapsional structures. D) The dysoxic bottom condition preserved most of the sedimentary structures and, E) rapid dewatering related to tectonics originated the compactional features.