Stratigraphy and Petrology of the Tascotal Mesa Quadrangle, Texas

RI0018. Stratigraphy and Petrology of the Tascotal Mesa Quadrangle, Texas, by R. L. Erickson. 34 p., 4 figs., 1 map, 4 pls. Reprinted from Geological Society of America Bulletin, v. 64, no. 12, 1953. RI0018.


To purchase a copy of the geologic map only (scale 1:62,500, 1953), please order MM0031.

Excerpted from the Introduction
The Tascotal Mesa quadrangle is in southeastern Presidio and southwestern Brewster counties, Trans Pecos Texas. Bandera Mesa and Tascotal Mesa are reached most easily from Marfa, 50 miles north, by the Marfa-Lajitas road which traverses the quadrangle from north to south. Green Valley in the northeastern part of the area is most easily reached from Marfa by the 02 Ranch road in Paradise Valley; an alternate route is from Alpine by the Terlingua highway and the 02 Ranch road.

This investigation is primarily concerned with a thick succession of volcanic tuff and and related sediments with intercalated lava flows which Goldich and Elms (1949, p. 1143) named the Buck Hill volcanic series. Six months was spent in the field during the summer of 1949 and the spring of 1950. Mapping was done on aerial photographs and later transferred to the U.S. Geological Survey topographic quadrangle map (ed., 1944; surveyed in co-operation with the War Department).



Keywords: Brewster County, Presidio County, Texas, Tascotal Mesa quadrangle, Marfa area, Alpine area, tuff, lava, Buck Hill, maps


CONTENTS
Introduction

Location

Scope of work

Acknowledgments

Climate and vegetation

Topographic development

Pediments

Cretaceous system

General statement

Glen Rose limestone

Devils River limestone

Grayson clay

Buda limestone

Boquillas formation

Tertiary system

Buck Hill volcanic series

Pruett formation

Duff formation

Pruett-Duff beds

Mitchell Mesa tuff flow

Tascotal formation

Description

Lower tuff member

Basalt intercalation

Stratigraphic relations

Rawls basalt

Description

Basalt

Volcanic breccia

Trachyandesite porphyry

Tuff and breccia beds

Stratigraphic relations

Age and correlation

Quaternary system

Intrusive igneous rocks

Rhyolitic intrusives

Basaltic intrusives

Syenitic intrusives

Gabbro of La Mota dome

Chemistry and petrology

Extrusive rhyolitic rocks

Intrusive rhyolitic rocks

Extrusive basaltic rocks

Intrusive basaltic rocks

Intrusive syenitic rocks

Welded luff and breccia

Variation diagram

Structural geology

Regional setting

Northern part of quadrangle

Southern part of quadrangle

Summary geologic history

References cited

Figures

1. Index map of part of Trans-Pecos Texas

2. Diagrammatic cross section

3. Variation diagram of igneous rocks from the Tascotal Mesa quadrangle and adjacent areas

4. Structure of southern Trans-Pecos Texas

Plates

1. Geologic map and structure sections of the Tascotal Mesa quadrangle, Texas

2. Cretaceous formations

3. Boquillas formation

4. Duff formation

5. Tascotal formation and Rawls basalt

Tables

1. Geologic formations in the Tascotal Mesa quadrangle

2. Chemical analyses of rhyolitic rocks

3. Chemical analyses of Rawls flows

4. Chemical analyses of syenogabbro, microsyenite, and plagioclase syenite

5. Chemical analyses of indurated and partially fused tuff-breccia bed between flows of Rawls basalt

6. Chemical analyses of Tascotal Mesa rocks and norms of igneous rock



Citation
Erickson, R. L., 1953, Stratigraphy and Petrology of the Tascotal Mesa Quadrangle, Texas: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 18, 34 p.