Tectónica de depositación y bioestratigrafía de las areniscas del grupo Azúcar en el sector Santa Rosa de la Península de Santa Elena

Abstract:

The Azúcar Group (Late Paleocene) consists of sandstones, shales and conglomerates; overlaps the Santa Elena Formation (Late Cretaceous-Early Paleocene) and underlies the Ancón Group (Middle Eocene). The Azúcar sandstones and conglomerates have produced hydrocarbons for 106 years. The objective of the study is to define the composition, sedimentary environment, biostratigraphy and tectonics of deposition of the sandstones of the Azúcar Group in Santa Rosa, Santa Elena Province. In Santa Rosa, twelve outcrops, thirteen thin sections, eleven biostratigraphic samples were analyzed and tectonic provenance diagrams were used (Dickinson et al., 1983; Dickinson and Suczek, 1979). The Azúcar Group in Santa Rosa are massive sandstones with minor claystones nd limolites; are turbidite because they evidence Bouma sequences: truncated (a and a, b), incomplete (e and d, e) and incomplete truncated (d). Outcrops 1 to 10 are turbidite stacked channels. The lower part of outcrops 8 to 11 correspond to interchannel facies. The Azúcar Group in Santa Rosa are massive sandstones with minor claystones and limolites; are turbidite because they evidence Bouma sequences: truncated (a and a, b), incomplete (e and d, e) and incomplete truncated (d). Outcrops 1 to 10 are turbidite stacked channels. The lower part of outcrops 8 to 11 correspond to interchannel facies. Agglutinated benthic foraminifera (Bathysiphon gerochi and Bathysiphon eocenica) of Paleocene age and deep marine paleoenvironment of 3000 meters were identified (outcrops 2 to 10). The Santa Rosa sandstones are mainly sublitharenite and litharenite with 74,92% quartz, 20,01% lithic fragments and 5,07% feldspars. The monocrystalline components are: monocrystalline quartz 60,33%, total lithic 34,60% and feldspar 5,07%. The polycrystalline components are: polycrystalline quartz 41,15%, volcanic lithic 40,77% and lithic sedimentary 18,08%. The polycrystalline quartz of the sandstones decreased from 41,15% in the Santa Rosa sector to 19,60% in Santa Paula, 24,99% in Ancón, 27,30% in Zapotal hill and 28,40% in Playas cliffs. Volcanic stones increase from 40,77% to 66,75% in Santa Paula; And decrease to 25,83% in Ancón and 29,80% in Playas cliffs. Sedimentary lithics decrease from 18,08% to 13,66% in Santa Paula; and increased to 48,17% in Ancón, 26,92% in Zapotal hill and 41,80% in Playas cliffs The tectonic provenance diagrams indicate recycled orogeny (arc orogen and tendency to subduction complex) for the Santa Rosa sandstones. In the trench-arc system of the Circum-Pacific orogenic belt, typically lithicfeldspar or feldsparlithic sandstones derived from the magmatic arc are deposited (Dickinson, 1982). The Azúcar sandstones of the Santa Rosa sector show that other tectonic factors influenced their deposition in the southwest of Ecuador. It has been suggested that Azúcar was deposited (Late Paleocene) in a forearc or slope basin by colliding the remaining Cayo island arc with the Andean continental margin (Jaillard et al., 1995). This interpretation agrees with the results of the present study. Consequently, the monocrystalline quartz would come from the Andean continental margin; the polycrystalline quartz from the Santa Elena and Guayaquil formations (Maastrichtian - Paleocene); volcanic lithic from the Cayo remnant island arc; and sedimentary lithic from the Chongón Colonche mountain range. The Santa Elena geological map indicates that the Cayo Formation (Late Cretaceous) outcrop in Santa Rosa; however, the biostratigraphic, depositional and petrographic data of this study confirm these outcrops as Azúcar Group. The knowledge of the depositional tectonics and composition of the Azúcar sandstone will expand the hydrocarbon exploration of Ecuador.

Año de publicación:

2017

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Fuente:

rraae