Portal de Periódicos da CAPES

Campanian Bolivinoides and microfacies from the La Luna Formation, western Venezuela

1995; Elsevier BV; Volume: 26; Issue: 1-4 Linguagem: Inglês

10.1016/0377-8398(96)87759-0

1872-6186

Linda M. De Romero, Francia Antonia Galea-Alvarez,

Geological and Geochemical Analysis

Abstract Tres Esquinas, the upper member of the La Luna Formation, a 1–3 m thick condensed sequence composed of glauconitic phosphorite, signals the commencement of the Late Cretaceous regression in western Venezuela. This is the last of a series of thin phosphatic beds, the others non-glauconitic, occurring in the upper La Luna Formation. In the State of Merida, the presence of Bolivinoides culverensis restricts these phosphatic beds to the late Santonian-early Campanian, with the Tres Esquinas Member assigned to the Globotruncanita elevata-Globotruncana ventricosa Zones. Bolivinoides sp. cf. B. sirticus is also commonly found in these beds. Although no Bolivinoides have been detected in the Tres Esquinas Member in the State of Tachira to the west, the non-glauconitic phosphate bed, informally named “Capa II”, as well as the 15 m thick Ftanita de Tachira Member which underlies the Tres Esquinas Member and separates it from “Capa II”, contain Bolivinoides culverensis as well as Bolivinoides cf. B. sirticus . This occurrence, combined with the assignation of the base of the overlying Colon Formation to the Globotrucana aegyptiaca Zone, suggests a late Campanian age for the member in this area, and implies that the member is diachronous. On the basis of lithology, mineralogy, foraminiferal content, and degree of bioturbation, six microfacies and one sub-microfacies are identified. The microfacies of the phosphatic limestones containing Bolivinoides spp. are notably different in the two states.