Overburden and physical properties in the Marathon fold and thrust belt, West Texas, using conodont thermal maturity and vitrinite reflectance

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5689430

Merrifield, Jr, G T ^[1]

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1. Texas A and M Univ., College Station, TX (United States). Center for Tectonophysics and Ocean Drilling Program

Distribution of Ordovician conodonts used in this study covers the southern two-thirds of the 2,400 km[sup 2] in the exposed thrust belt. Conodont color alteration indices (CAI) vary from 1.5 in the northwest to 3.0 eastward and 4.0--4.5 in the extreme southeast. These variations correlate with the 3 km increase in stratigraphic overburden from west to east in the accretionary rocks (Mississippian to Mid Pennsylvanian). In the western exposures, CAI increase southward to 2.0--2.5 within the Dagger Flat structural culmination and decrease to 1.0--1.5 further southward. Increased overburden due to structural thickening explains the CAI increase within the culmination. In the northern one-third of the exposed thrust belt, CAI from the Dimple formation (Mid Pennsylvanian) decrease northward from 2.5 to 1.0--1.5. Neither restored stratigraphic overburden nor local intrusions explain the elevated CAI value of 2.5. Extrapolation of the vitrinite reflectance gradient to the 0.2% value in a well less than 10 km east of this location indicate that between 2.5 and 4.3 km of overburden has been eroded. Structural thickening accounts for at least some of the elevated thermal maturity in this area. Vitrinite reflectance gradients are greater in the accretionary prism strata than in the older basinal facies (Upper Cambrian to Lower Mississippian). Since both facies are shale-rich, lithology alone plays little role in thermal conductivity and maturity variations. Instead, the age of compaction (and possibly undercompaction) relative to the times of thrusting subaerial exposure and erosion, and preservation of maximum thermal maturity are a more important factor. There is a slight discontinuous increase in the thermal maturity across the basal thrust, which is not explained by lithologic variations. Above and below the basal thrust, vitrinite gradients increase and is best explained by induced fracture permeability and flow of hot fluids.

• OSTI ID: 5689430
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
COLOR
DEVELOPED COUNTRIES
FLUIDS
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
GEOLOGY
GEOPHYSICAL SURVEYS
GEOTHERMAL FLUIDS
LITHOLOGY
MACERALS
MATURATION
NORTH AMERICA
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
OVERBURDEN
PERMEABILITY
PETROLOGY
PHYSICAL PROPERTIES
REFLECTIVITY
SEDIMENTARY BASINS
STRATIGRAPHY
SURFACE PROPERTIES
SURVEYS
TEXAS
USA
VITRINITE