Microfossils from Cerro Prieto geothermal wells, Baja California, Mexico

Conference · Tue Jan 01 04:00:00 EST 1980

OSTI ID:5384920

Cotton, M L; Vonder Haar, S

To aid in a paleoenvironmental and age reconstruction of the Cerro Prieto reservoir system, 59 samples of well cuttings were analyzed for microfossils. The cuttings were obtained at depths from 351 to 3495 m in 14 geothermal wells in the Cerro Prieto field, Baja California, Mexico. We found foraminifera in 6 samples, ostracodes in 19 samples, and nannoplankton as coccoliths in 24 samples. Other groups, such as molluscs, insects, fish skeletal parts, and plant material were occasionally present. Detailed interpretations are not possible at this time because of poor preservation of samples. This is primarily due to causes: dissolution by geothermal fluids that reach 350{sup 0}C, and the extensive mixing of filled Cretaceous forms (reworked from the Colorado Plateau region) with Tertiary species during drilling. Further studies of ostracodes and foraminifera from colder portions of the wells are needed. The abundant and well-preserved ostracodes indicate marine to brackish water environments that correspond, in part, to lagoonal or estuarine facies. The presence of the mid-Tertiary (15-My-old) marine foraminifera, Cassigerinela chipolensis, in wells M-11 and M-38, 350 to 500 m deep, is perplexing. These are not laboratory contaminates and, as yet, have not been found in the drilling mud. If further studies confirm their presence at Cerro Prieto, established ideas about the opening of the Gulf of California and about Pacific Coast mid-Tertiary history will need to be rewritten.

• Research Organization: University of Southern California, Los Angeles (USA). Dept. of Geological Sciences; California Univ., Berkeley (USA). Lawrence Berkeley Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5384920
• Report Number(s): LBL-10303; CONF-7910166-9
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150202* -- Geology & Hydrology of Geothermal Systems-- Non-USA-- (-1989)
ALGAE
ANIMALS
AQUATIC ORGANISMS
ARTHROPODS
CERRO PRIETO GEOTHERMAL FIELD
CRUSTACEANS
DATA ANALYSIS
DRILL CORES
FLUIDS
FORAMINIFERA
FOSSILS
GEOTHERMAL FIELDS
GEOTHERMAL FLUIDS
GEOTHERMAL WELLS
Geothermal Legacy
INVERTEBRATES
MICROORGANISMS
PLANTS
PROTOZOA
SAMPLING
WELLS