Sequence stratigraphy and organic geochemistry: An integrated approach to understand the anoxic events and paleoenvironmental evolution of the Ceará basin, Brazilian Equatorial margin

An organic geochemical investigation combined with sequence stratigraphy was performed in the Ceará Basin, an offshore basin located Northeastern Brazil. The information available from 30 well logs (gamma-ray, resistivity, density), besides (TOC, and pyrolysis indexes) isotopic (?13C) data, aided preparation of a dataset for this study. application sequence-stratigraphic methods helped classify correlate seismic facies. Four key petroleum source-rock units were identified, oldest to youngest: (1) Mundaú Formation – top Rift Sequence (Berriasian-Aptian); (2) Paracuru Breakup (Aptian-Albian); (3) Itapajé Member Ubarana Continental Drift (Albian-Turonian), (4) Uruburetama (Turonian-Maastrichtian). characteristics (high total carbon (TOC), hydrogen index (HI), relative hydrocarbon potential (RHP = (S1 + S2)/TOC)) point typical transgressive sequence. Six transgressive-regressive (T-R) cycles recognized entire Formation. best marker is related This stratigraphic unit can be correlated major anoxic event source rock basin. Evaporitic facies found section, maximum RHP values (anoxic conditions), flooding surfaces events characterize interval. Moreover, wide spatial cover organic-rich rocks, recognition favorable anoxia other basins Equatorial Margin are suggestive Aptian-Albian Oceanic Anoxic Event (OAE-1b) occurring Basin. represented by yields least promising rocks. However, high TOC suggest occurrence late Cenomanian–early Turonian (OAE-2), when strata started deposit deep-water regions. predominance regressive interval points oxic or sub-oxic conditions. Additionally, correlations between Brazilian its African counterpart, characterization allied definition depositional systems these regions proved useful oil exploration.