Quimioestratigrafia de fósforo do testemunho de sondagem 1-labio-pe3 (furo iate): investigação sobre o registro de evento de anoxia oceânica na bacia Pernambuco

Abstract

Theoccurrence of a gas-smelling black shale, with total organic Carbonand Sulfurcon-centrations of about 1%, interleaved with lithologies typical of transitional sedimentary environment, found on the 1-LABIO-PE3 stratigraphic borehole core, located in Recife, Northern region of the Pernambuco Basin, raised suspicion that a major environmental turnover had occurred during its deposition. The present paper showsthe resultsof aninvestigation about oceanic anoxic event on Upper Cretaceous sedimentary rocks (CenomanianTuronian) of the Pernambuco Basin, NE-Brazil. The study was based on Phosphorus chemostratigraphy, done by using 34 core samples spanning from 80.50 to 54.00 meters depths. The phosphorus concentrations were measured by ultraviolet-visible spectrophotometryand subdivided into two distinct phases: organic (P-Organic) e inorganic (P-Inorganic). The results obtained suggest that the black shale bed ofthe Estiva formation had been deposited during the oceanic anoxic event II (or the Bonarelli Event). High paleotemperatures and sea levels during the Cretaceous period would have favored the input of nutrients into the oceanic basin. The bacteriological degradation of organic matteron the bottom of the ocean would have consumed the water free oxygen, making areduced environment. Under these conditions, the storage of Phosphorus on the sediments, as authigenic mineralization, would be prevented, recyclingit as nutrient into trophiczone.