Use of gamma-ray log for locating Cretaceous-Tertiary unconformity, Pinedale area, northern Green river basin, Wyoming

Conference · Sun Jul 01 04:00:00 EDT 1984 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:5536392

Prensky, S E

Computer-generated crossplots of the gamma-ray log versus depth in the Pinedale area, northern Green River basin, Wyoming, exhibit an abrupt shift in API gamma units over the structurally influenced depth range of 7100-8500 ft (2100-2600 m). Higher API units are recorded for all lower Tertiary rocks than for underlying Upper Cretaceous rocks. The shift, which is not obvious from viewing analog prints, coincides with the Cretaceous-Tertiary boundary as located in this area by previous workers using different methods. Evaluation of gamma-ray spectral logs from five wells, combined with petrographic and x-ray diffraction analysis of core samples from the Pinedale area, shows that this shift is caused by a higher potassium content in Tertiary rocks than in Cretaceous rocks, due to the presence of arkosic sandstones. Within the lowermost 600 ft (180 m) of the Tertiary, the potassium feldspar content of the sandstones gradually decreases with depth down to the Tertiary unconformity and then abruptly declines, essentially to zero, in the Cretaceous.

• Research Organization: Geological Survey, Denver, CO
• OSTI ID: 5536392
• Report Number(s): CONF-8408161-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 68:7
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
CENOZOIC ERA
CRETACEOUS PERIOD
FEDERAL REGION VIII
GAMMA LOGGING
GEOLOGIC AGES
MESOZOIC ERA
NORTH AMERICA
RADIOACTIVITY LOGGING
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
TERTIARY PERIOD
USA
WELL LOGGING
WYOMING