Stratigraphy of Kenai Group, Cook Inlet, Alaska, and application of ecological shift plot

Conference · Fri May 01 04:00:00 EDT 1987 · AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)

OSTI ID:5784607

Wiggins, V D; Hill, J M

Regional well-to-well correlations within the five nonmarine formations of the Kenai Group in Cook Inlet, Alaska, are poor at best. The erratic nature of these fluvial deposits, indistinct heavy mineral zonations, and long-ranging palynomorphs have made correlations difficult. Correlations are even more difficult along the basin margin where increased paleotectonic uplift and subsidence have affected deposition. These changes in depositional environments strongly affect electric log character, enough to give the impression that they are correlating like depostional cycles instead of time-stratigraphic units. This leads to incorrect paleodepositional and paleotectonic reconstructions. A new statistical technique called an Ecological Shift Plot was used to help solve these correlation problems. Standard palynological slides are prepared from composite ditch samples every 90 ft. The slides are examined, and spores and pollen characteristic of warm and cold climatic extremes within the total flora are identified and counted. A ratio of specific warm and cool spore-pollen taxa is calculated, and the value for each 90-ft interval is plotted on semilog paper. On a completed profile for the Kenai Group, the two upper formations, the Sterling and Beluga, shift rapidly between warm and cool cycles. However, below the unconformity at the base of the Beluga, a strong, distinct shift to warm climatic conditions occurred during deposition of the upper Tyonek Formation. A strong, distinct cool shift then occurs within the lower Tyonek Formation and persists down through the Hemlock Formation. This cool shift occurs below a local unconformity which is informally called the Middle Ground Shoal unconformity. Below the base of the Hemlock, the flora again shift to a warm cycle within the West Foreland Formation.

• Research Organization: Chevron USA Inc., Ventura, CA
• OSTI ID: 5784607
• Report Number(s): CONF-870606-
• Conference Information: Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States) Journal Volume: 71:5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
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ALASKA
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MINERAL RESOURCES
NORTH AMERICA
PETROLEUM DEPOSITS
RESERVOIR ROCK
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SEDIMENTARY BASINS
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USA