Document type
Journal articles
Document subtype
Full paper
Title
Paleoweathering features in the Sergi Formation (Jurassic-Cretaceous), northeastern Brazil, and implications for hydrocarbon exploration
Participants in the publication
Cristina Pierini (Author)
Ana Misuzaki (Author)
Nuno Pimentel (Author)
IDL
Scherer, C. (Author)
Summary
Paleoweathering in the Sergi Formation has been classified and analyzed to ascertain its origin and relationship with stratigraphic evolution. The Sergi Formation belongs to the pre-rift sequence of the Recôncavo Basin (northeastern Brazil) and comprises a complex association of eolian and fluvial sandstones and lacustrine mudstones. This formation can be subdivided into three depositional sequences bounded by regional unconformities. Four paleoweathering types, each one related to a distinct origin, have been described in the Sergi Formation: (1) textural mottling, which is distinguished by alternating rock colors as a result of the iron oxide mobilization within mineral phases that evolved under alternating oxidation (yellowish, brownish and reddish shades) and reduction (grayish or greenish hues) conditions; (2) non-textural mottling, which displays a discoloration pattern that is independent of the original rock texture; (3) carbonate concentrations, usually related to carbonate nodule formation, which display a massive internal structure that reveals their origin through continuous growth or crystallization; and (4) banded carbonates (silicified), associated with the beginning of regular surface formation due to the chemical precipitation of carbonates within lacustrine environments. Both mottling color motifs and carbonate accumulation usually represent groundwater oscillation rather than pedogenesis. Only carbonate intraclasts and banded carbonate (silicified) have their origin ascribed to pedogenesis sensu stricto, although the carbonate intraclasts do not represent soil deposits in situ, but calcretes eroded from areas close to channels, and the banded carbonates (silicified) have strong diagenetic modifications. Therefore, it is reasonable to assume that fluvial and meteoric water have controlled paleoweathering evolution as well as deposition, yet both aspects are ruled by the same mechanisms (relief, sedimentation rate and, above all, climate).
Where published
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
Publication Identifiers
ISSN - 0895-9811
Publisher
ELSEVIER
Number of pages
15
Starting page
412
Last page
426
Rankings
SCOPUS Q1 (2011) - 1.163 - Earth-Surface Processes
SCIMAGO Q1 (2016) - 0.914 - Earth-Surface Processes
SCIMAGO Q1 (2010) - 0.934 - Earth Surface Processes