Sedimentology of the Miocene Capaya Formation in the Orégano River Section, Anzoátegui State, Eastern Venezuelan Basin

Marilyn Daniela Herrera
Universidad de Los Andes (ULA), Mérida, Venezuela

The studied section of the Capaya Formation is located in the eastern Venezuelan basin, northeast of the Anzoátegui State. The geometry, orientation and phisycal quality of the sedimentary deposits were established in order to contribute with the exploration projects undertaken in this area. On the basis of lithofacies analysis, ichnofacies, fossil content and sedimentological parameters, the Capaya Formation was interpreted as deposited in a fluvial dominated deltaic environment, with an important influence of wave energy. Foraminifera and calcareous nannoplancton studies reveals a transitional to inner neritic environment (benthic foraminifera biofacies), deposited during the early to middle Miocene.

Macroscopic outcrops description in the Orégano river section allows identification of the following sedimentary lithofacies: 1.- Seven fair to poor bioturbated sandy lithofacies (A2/A3X/A1H/A2M/A1L/ A3GL/B) and its bioturbated counterpart (A1B); 2.- One heterolithic lithofacies (H) and its bioturbated counterpart (HB); 3.- One shaly lithofacies (L) and 4.- One coal to coaly shale lithofacies (C). This sedimentary facies are grouped in four sedimentary facies associations: fluvial distributary channel, mouth bar/delta front, interdistributary bay and prodelta.

Petrographycal analysis of 57 thin sections, complemented with XRD analysis, permitted to classify the sandy facies mainly as quartzarenite and, in less proportion, as subarkoses, litharenites, arkoses and sublitharenites. The studied section is a type II sequence. Six system tracts were recognized: three high stand system tracts (HST) and three transgressive system tracts (TST).