The Cretaceous Austin Chalk contains large numbers of fractures and normal faults whose orientations have been attributed to either regional stresses (e.g., the Balcones fault trend) or, by analogy with the mudrocks, to polygonal faulting resulting from compaction. In this study, we present geomorphic data, field study, and stable isotope data to support that the majority of these faults in North Texas are polygonal. Field-measured fault orientations suggest randomly distributed fault strikes, indicating a polygonal fault structure. Using geomorphologic data (topographic and DEM data) on stream orientations suggests that the polygonal fault patterns are best reflected in the headwater (1st or 2nd order) streams. The higher-order streams tend to reflect the down-dip direction of the chalk. Furthermore, to simulate the formation of polygonal faults, desiccation of ooze-like muds to produce mud cracks generates polygonal patterns with cracks having orthogonal, Y, non-orthogonal, and crossing intersections. Preliminary results suggest a compositional dependence for the distribution of intersection types and a relationship between thickness and polygonal area. Fault asperity, striated calcite veins, and host-rock chalk samples have δ18O values of -9.5 < δ18OPDB 18O Inoceramid -2.6 < δ18O

Degree Date

Summer 2023

Document Type


Degree Name



Earth Sciences


Robert Gregory



Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License