57-12 Timing and Temperature of Deformation of the Cutoff Formation: Evidence for Miocene Fluid Migration in the western Delaware Basin, west Texas.

Session: Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records, Part II

Presenting Author:

Nathaniel Brunello

Authors:

Brunello, Nathaniel T.¹, Möller, Andreas², Lane, Adam Eldon³, Goldstein, Robert H.⁴, Sisson, Virginia B.⁵, Copeland, Peter C.⁶

(1) Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA, (2) Geology, University of Kansas, Lawrence, KS, USA, (3) Geology, University of Kansas, Topeka, KS, USA, (4) Geology, University of Kansas, Lawrence, KS, USA, (5) Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA, (6) Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA,

Abstract:

The Cutoff Formation (Permian), part of the Guadalupian reef complex of the Delaware basin of west Texas and SE New Mexico, contains extensive networks of carbonate-filled fractures with at least three orientations. In this area, the age of brittle deformation and fluid migration associated with fracture fill are poorly understood. This study aims to fill that gap in knowledge by using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) U-Pb geochronology combined with fluid inclusion analysis to better understand the age of deformation and the composition, temperature, and pressure of fluid inclusion formation conditions. We collected samples of carbonate-filled fractures from an outcrop of the Williams Ranch Member of the Cutoff Formation along US highway 62-180, south of Guadalupe Mountains National Park. Samples were processed to produce polished thick sections for fluid inclusion analysis and LA-ICPMS analysis. Our samples of carbonate-filled fractures contain both aqueous and hydrocarbon fluid inclusions. Aqueous fluid inclusions with a melt temperature below -25°C suggest a composition with high salinity and divalent cations (Ca²⁺). Preliminary results indicate homogenization of the aqueous fluid between 75 to 130°C. Our values align with other regional temperature estimates derived from vitrinite reflectance, Raman spectroscopy, and clumped isotope thermometry data. U-Pb dating of calcite fractures yields TW isochrons with lower intercepts with two end-member ages of around 240 Ma and 10 Ma. Other results produce ages intermediate to these, which we interpret as mixtures between the end members. The various ages are distributed in all generations of fractures, suggesting multiple phases of fluid flow through the same network of cracks. We interpret the younger ages to be the consequence of fluid migration and entrapment along the western flank of the Delaware basin associated with Basin and Range extension in the late Miocene.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10375

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