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Detailed Mapping in the NE Glass Mountains Reveals Angular Unconformities which Constrain Timing of Deformation Events

Paul Gully¹ and Joseph I. Satterfield¹

¹Angelo State Texas Tech University, Department of Physics and Geosciences, San Angelo, TX


Project objectives were to produce a 1:12,000-scale geologic map of a 42 km² field area in the NE Glass Mountains, 27 km NE of Marathon, Texas, and to supplement outcrop descriptions of four Pennsylvanian – Permian formations with thin-section petrography. The mapping documented two angular unconformities and constrained timings of five Permian – Cenozoic deformation events. Published maps of this area are less detailed: King (1930, 1980; 1:62,500), King (1937; 1:125,000). The map area contains the upper plate of the frontal thrust of the Marathon thrust belt, the Southern shelf of the Permian basin, the NE flank of the Marathon uplift, and the easternmost Basin and Range province (McBride, 1988). The Pennsylvanian Gaptank Formation, Wolfcampian Lenox Hills Formation, Leonardian Hess Limestone and Cathedral Mountain Formation crop out in the map area. An angular unconformity separates the Lenox Hills Formation and Gaptank Formation. A second angular unconformity separates Cretaceous limestone and Hess Limestone. Gaptank Formation dips average 22 NW, while overlying Lennox Hills and Hess dips average 9 – 14 NW. Cretaceous rocks are subhorizontal. A NW-striking high-angle fault cross-cuts Permian rocks in the NW corner of the map area. Our new mapping leads to this sequence of deformations: 1) Pre-Lenox Hills tight folding and thrust faulting (Marathon-Ouachita orogeny), 2) Subsidence and deposition of shallow-marine Hess and Cathedral Mountain carbonates (Marathon-Ouachita orogeny), 3) Pre-Cretaceous gentle NW tilting of Cathedral Mountain Formation and older units (Marathon Ouachita orogeny), 4) Post-Cretaceous broad warping (Marathon uplift, Laramide orogeny), 5) Late Cenozoic high-angle faults cross-cut Cretaceous rocks.


AAPG Datapages/Search and Discovery Article #90190©AAPG Southwest Section Annual Convention, Midland, Texas, May 11-14, 2014