Late Cretaceous and Eocene phreatomagmatic volcanism and magma-sediment interaction in the Big Bend area of west Texas

This project examines two separate aspects of the volcanic evolution of the Big Bend area. Detailed mapping of phreatomagmatic, basaltic air-fall and base-surge deposits at Pena Mountain shows that they represent the erosional remnants of at least two maars. The deposits intertongue with the Campanian upper shale member of the Aguja Formation, increasing the known extent of Cretaceous volcanism in the Big Bend region. Zircon grains extracted from basalt bombs in the pyroclastic deposits yield a U-Pb SHRIMP-RG age of 76.6 +/- 1.3 Ma.; On the Pitcock Ranch and adjacent parts of the park, Eocene basaltic dikes and phreatomagmatic diatreme root zones show various styles of magma-sediment interaction with the Javelina, Black Peaks, and Hannold Hill Formations. Billowed dike margins, intrusive pillows, and different types of peperite developed in strata as old as the Late Cretaceous, which must have remained unconsolidated and rich in pore water into the Eocene.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat.