Resumen de Identificación de Tractos Sedimentarios en sedimentos pelágicos mediante métodos geoquímicos. Formación La Luna, Occidente de Venezuela
G. Soto, V. Kertznus, E. Zapata
An integrated study of the geochemistry, sedimentology and biostratigraphy of two outcrop sections of the La Luna Formation in Western Venezuela was carried out to determine the eustatic changes that influenced the deposition and preservation of anoxic sediments in the Late Cretaceous. Five (5) depositional sequences within the La Luna Formation were identified in the studied outcrop sections (Las Hernández and San Miguel) by shifts in 13C stable isotopes, as well as in CaCO3, Si, and Ti elemental content (normalized to Al).
Transgressive system tracts (TST) are characterized by heavier values in 13C isotopes, lower CaCO3, and higher content of TOC. During these periods the values of Si/Al and Ti/Al show an increasing trend and reach their highest peaks at the maximum flooding surfaces (MFS). Highstand system tracts (HST) are characterized by high contents of CaCO3, and a shift towards lighter values of 13C isotopes. The sequence boundaries (SB) are evidenced by a rapid shift in the 13C isotopes (from lighter to heavier values) and by the geochemical contrast between the HST and the TST.
The identified systems tracts (Turonian-Campanian), clearly correspond with the Haq et al (1988) global sea-level change curve.
