Continental systems tracts of the Brazilian Cretaceous Bauru Basin and their relationship with the tectonic and climatic evolution of South America

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• 作者：Alessandro Batezelli
• 刊名：Basin Research
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：29
• 期：S1
• 页码：1-25
• 全文大小：22020K
• ISSN：1365-2117

文摘

The application of sequence stratigraphy concepts to continental deposits lacking the referece provided sea level has been a challenge, mainly because the temporal relationships between stratigraphic surfaces and systems tracts depend on the tectonic and climatic evolution of the area. Using the concept of accommodation space (A) and sediment supply (S), we identify specific stacking patterns of aeolian, lacustrine, fluvial and alluvial systems that correspond to the particular tectonic and climatic evolution of the southeastern portion of South America. With the end of the Early Cretaceous volcanism (133 Ma), the southeastern portion of South America underwent tectonic restructuring, which generated basins that encompassed continental sedimentary sequences. The tectonic events responsible for the accumulation of these sequences occurred during two primary phases. The first phase is related to Early Cretaceous thermal subsidence, which was more pronounced in the regions where the thickest Serra Geral Formation basaltic successions are found, resulting in the formation of Bauru Basin. The second phase was related to the Late Cretaceous uplift in southeastern Brazil as a result of magmatic/volcanic activity associated with the Trindade Mantle Plume. Stratigraphic analysis based on well-logs and outcrops and aided by petrographic studies identified three sequences that are bounded by regional unconformities that record important changes in the Bauru Basin's tectonic and paleoenvironmental conditions. The unconformity K-0 is related to the origin of the Bauru Basin in the Early Cretaceous. The Early Cretaceous Sequence 1 (Caiuá Group) is interpreted as a second- order sequence, formed by aeolian and fluvial deposits and constituting a Fluvial-Aeolian Systems Tract. Unconformity K-1 that was generated in the Late Cretaceous (Cenomanian – Campanian?) is related to the tectonic evolution of the basin and source area. Overlying Unconformity K-1, lacustrine, fluvial and alluvial deposits display progradational characteristics of the two-third- order sequences: Sequences 2A and 2B, constituted by the Fluvial-Lacustrine and Alluvial Systems Tracts, respectively, and separated by the Unconformity K-1A. Sedimentological characteristics, paleosols and stratigraphic architecture, suggest that A/S ratio was neutral in the late stage of the Sequence 1, whereas in the Sequence 2 there was an increase (Sequence 2A) followed by a decrease in the A/S ratio (Sequence 2B). Aeolian facies and paleosol P1 (Sequence 1), fluvial-lacustrine facies and hydromorphic soils (Sequence 2A), and alluvial facies and Paleosol P2 (Sequence 2B), indicate climatic changes in the South American during the Cretaceous. The stratigraphic framework, subaerial unconformities and paleosols provide key elements for subdividing of the Brazilian continental sequence into third-order sequences and systems tracts, for identification of allocyclic and autocyclic patterns in time and space.