Pierini,C., Mizusaki,A.M., Pimentel,N., Faccini,U.F. and Scherer,C.M.S.(2010): Paleoweathering features in the Sergi Formation (Jurassic-Cretaceous), northeastern Brazil, and implications for hydrocarbon exploration. Journal of South American Earth Sciences, 29, 412-426.

『ブラジル北東部のセルギ層群（ジュラ紀−白亜紀）における古風化の特徴および炭化水素開発との関係』

『Abstract
　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 Reconcavo（最初のoの頭に＾） 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).

Keywords: Paleoweathering; Stratigraphy; Jurassic-Cretaceous』

Resumo
１. Introduction
2. Paleoweathering
3. Geological setting
4. Methodology
5. Paleoweathering: description and origin
　5.1. Macroscopic features
　　5.1.1. Textural mottling
　　5.1.2. Non-textural mottling
　　5.1.3. Carbonate concentration
　　5.1.4. Banded carbonate (silicified)
　5.2. Microscopic features
　　5.2.1. Textural mottling
　　5.2.2. Non-textural mottling
　　5.2.3. Carbonate concentration
　　5.2.4. Banded carbonate (silicified)
6. Chemical and isotopic analyses
7. Depositional setting and its significance
　7.1. Paleoweathering and relationships to the stratigraphic succession
　7.2. Paleogeography, paleoclimate and the role of paleoweathering on the development of the heterogeneities in the Sergi Formation
8. Conclusions
Acknowledgements
References

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