Definition of unconformities based on radiometric tool

The concentrations of U-238, Th-232, and K-40 measured with a portable gamma-ray spectrometer in cutting samples of two exploratory wells allowed the radiometric characterization of Cretaceous Rancheria sub-basin rocks and the definition of twelve (12) zones according to paleo-redox facies. The Th/U...

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Bibliographic Details
Published in:Applied radiation and isotopes 2023-09, Vol.199, p.110872-110872, Article 110872
Main Authors: Salazar, S., Castillo, L.A., Montes, L.
Format: Article
Language:English
Subjects:
Anoxic
Paleo-redox
Radiometry
Uranium
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Summary:The concentrations of U-238, Th-232, and K-40 measured with a portable gamma-ray spectrometer in cutting samples of two exploratory wells allowed the radiometric characterization of Cretaceous Rancheria sub-basin rocks and the definition of twelve (12) zones according to paleo-redox facies. The Th/Ua (authigenic uranium) and Th/U ratio greater than 7 (seven) indicates paleo-redox conditions related to oxygenation changes and detrital material input during deposition and terrestrial freshwater environment. However, the Lagunitas, Aguas Blancas, La Luna, and Molino formations characterize by facies from sub-oxic (dioxic) to anoxic redox. In the Aguas Blancas and Molino Formations, pyrite and the high uranium measurements determine an anoxic and euxinic environment. The high values of both + uranium and authigenic uranium in the La Luna and Molino formations relate to the conservation of organic matter, which is an essential factor in the generation of hydrocarbons. The abrupt changes of both K/U and Th/U identify potential sequential or genetic limit surfaces (e.g., maximum flooding surfaces), limiting such zones. Based on radiometric behavior, this research permitted identifying eight Cretaceous to Miocene unconformities in the area, three of them reported here for the first time. •From data were identified three new unconformities corroborated in seismic sections.•The radioelements data were used to define redox facies.•The key surfaces described from radioelements were corroborated in the seismic data.
ISSN:0969-8043
1872-9800
DOI:10.1016/j.apradiso.2023.110872