Definition of unconformities based on radiometric tool

Area of Science:

• Geochemistry
• Sedimentology
• Stratigraphy

Background:

• Understanding paleo-redox conditions is crucial for characterizing sedimentary basins and assessing hydrocarbon potential.
• Radiometric dating provides insights into depositional environments and geological history.

Purpose of the Study:

• To radiometrically characterize Cretaceous rocks in the Rancheria sub-basin using U-238, Th-232, and K-40 concentrations.
• To define paleo-redox facies and identify depositional environments.
• To detect unconformities within the Cretaceous to Miocene sequences.

Main Methods:

• Utilized a portable gamma-ray spectrometer to measure U-238, Th-232, and K-40 in cutting samples from two exploratory wells.
• Analyzed Th/Ua (authigenic uranium) and Th/U ratios to infer paleo-redox conditions.
• Interpreted abrupt changes in K/U and Th/U ratios to identify sequence boundaries.

Main Results:

• Defined twelve zones based on paleo-redox facies, indicating shifts from terrestrial freshwater to sub-oxic and anoxic conditions.
• Identified anoxic and euxinic environments in the Aguas Blancas and Molino Formations, evidenced by pyrite and high uranium.
• Recognized high uranium and authigenic uranium in La Luna and Molino formations, suggesting organic matter preservation favorable for hydrocarbon generation.
• Identified eight Cretaceous to Miocene unconformities, including three previously unreported.

Conclusions:

• Radiometric data effectively characterize paleo-redox conditions and depositional environments in the Rancheria sub-basin.
• The study successfully identified key facies, including those conducive to hydrocarbon generation.
• This research established a framework for identifying unconformities, crucial for stratigraphic correlation and basin analysis.