Burial cements in Lower Cretaceous Pearsall Formation and lower Glen Rose Formation, south Texas
Lower Cretaceous platform carbonates and shales were buried to depths in excess of 2000 ft (610 m) by the end of Eocene time, and were locally affected by late-stage cementation. Burial diagenetic cements include ferroan baroque dolomite, ferroan and nonferroan calcite, anhydrite, kaolinite, barytocelestite, galena, and sphalerite. The lack of these minerals in outcrop and their occurrence in fractures are evidence for a subsurface origin. Carbonate cements are chemically and isotopically zoned; the FeCO/sub 3/ content in baroque dolomite cement varies by as much as 10 wt% across a single crystal. Stratigraphic and regional distribution of iron in baroque dolomite indicates that the iron is derived from local sources. Good negative correlation between delta/sup 13/C values and iron contents of baroque dolomite suggests the simultaneous reduction of iron oxides and oxidation of organic material. Some of the late subsurface carbonate cements with extremely depleted delta/sup 18/O values precipitated either from hot brine or from isotopically light water; both possibilities require the vertical movement of fluid along faults. Galena and sphalerite occur in small amounts in some cores; a single fluid inclusion homogenization temperature from sphalerite was 20/sup 0/C (68/sup 0/F) higher than the present formation temperature at that depth. Brines moving up faults after albitizing feldspars in more deeply buried formations could be the source of lead and zinc for these minerals. Strontium isotopic ratios for calcite cement in these rocks are similar to ratios for brines from the Stuart City reef trend that are believed to originate deep in the Gulf of Mexico basin.
- Research Organization:
- Univ. of Texas, Austin
- OSTI ID:
- 6001177
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 67:3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
02 PETROLEUM
03 NATURAL GAS
SEDIMENTARY ROCKS
CEMENTS
TEXAS
GEOLOGIC FORMATIONS
BRINES
CRETACEOUS PERIOD
MINERALIZATION
PRECIPITATION
REEFS
RESERVOIR ROCK
BUILDING MATERIALS
FEDERAL REGION VI
GEOLOGIC AGES
GEOLOGIC STRUCTURES
MATERIALS
MESOZOIC ERA
NORTH AMERICA
ROCKS
SEPARATION PROCESSES
USA
580100* - Geology & Hydrology- (-1989)
020200 - Petroleum- Reserves
Geology
& Exploration
030200 - Natural Gas- Reserves
Geology
& Exploration