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PETROLEUM GEOLOGY IN THE PALEOZOIC CLASTICS OF THE MIDDLE AMAZON BASIN, BRAZIL
Author(s) -
Carozzi Albert V.
Publication year - 1979
Publication title -
journal of petroleum geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.725
H-Index - 42
eISSN - 1747-5457
pISSN - 0141-6421
DOI - 10.1111/j.1747-5457.1979.tb00692.x
Subject(s) - geology , clastic rock , paleontology , sedimentary rock , fluvial , precambrian , geomorphology , structural basin
Paleoenvironmental maps of all the stratigraphic units of the Middle Amazon Basin from Ordovician to Early Carboniferous are analysed in terms of their source‐rock and reservoir potentials. These maps were obtained by applying the following techniqes; detailed petrography of diamictites, sandstones and siltstones including measurements of index of clasticity; analysis of early and late diagenetic cementation processes; environmental interpretation of sedimentary structures; geochemistry of trace elements and lateral variations of clay mineral assemblages based on X‐ray diffraction data. Five distinct sedimentary models were recognized. Fluvio‐deltaic model consisting of fluvial, deltaic, distal deltaic and offshore subenvironments. Tidal flat model consisting of marshes, intertidal flat, shoreface and offshore subenvironments. Beach model consisting of dunes (inferred), beach, shoreforce and offshore subenvironments. Glacial model (Nhamundá time, Early Silurian), consisting of glacial (tillites), fluvial, beach, shoreface and offshore subenvironments. Glacial model (Curiri time, Late Devonian) consisting of glacial (tillites with subglacial sandstone channels and interglacial braided streams), shoreface and offshore subenvironments. From the association of these depositional models, the direction and intensity of the supply of coarse clastics was determined in a semi‐quantitative manner for each stratigraphic unit. The time andspace distribution of the detritalsupplies and of the areas of coarse clastic sedimentation indicates a continuous synsedimentary tectonic control of the depocenters by the differential subsidence of the underlying Precambrian basement in the shape of large blocks limited by a system of NW‐SE and NE‐SW lineaments. By using an index of synsedimentary tectonic activity it is possible to define three major episodes of coarse clastic sedimentation which have the best reservoir potential: Early Silurian fluvio‐glacial systems, Early Devonian progmding deltas and Late Devonian fluvio‐glacial systems. The tmps for hydrocarbons are mainly stmtigmphic but enhanced by the weak structures of the basin and result from the relationship between the coarse clastics and two intervening sequences of mature black shales.