Organic geochemical constraints on tectonic evolution of the North American Midcontinent rift

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

OSTI ID:5719671

Hieshima, G B ^[1]; Pratt, L M ^[2]

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1. Exxon Production Research Co., Houston, TX (United States)
2. Indiana Univ., Bloomington, IN (United States). Dept. of Geological Sciences

The approximately 1.1 Ga Nonesuch Formation, northern Wisconsin and Michigan, represents marine sedimentation in a failed continental rift that is part of the North American Midcontinent rift system. Indicators of thermal maturity based on solvent-extractable (bitumen) and insoluble (kerogen) organic matter suggest marginal to moderate levels of maturity with respect to zones of petroleum generation and preservation. Values of sterane 20S/(20S + 20R) ratio, hopane 22S/(22S + 22R) ratio, methylphenanthrene index, and temperature of maximum pyrolytic yield from Rock-Eval (Tmax) indicate maximum burial temperatures of around 80 C. Geologic constraints indicate maximum burial conditions for the Nonesuch of around 4 km for approximately 50 million years. Overlying sandstones buried the Nonesuch quickly. Assuming a surface temperature of around 20 C yields a geothermal gradient of 15 C/km, significantly lower than predicted based on heat flow in modern rifts. Unless burial histories are grossly inaccurate, geothermal gradients were depressed as a result of thermal insulation by non-radiogenic basalts and/or hydrologic circulation in underlying coarse-grained strata generated an anomalously low geothermal gradient. Hydrothermal circulation was a significant component of mineralization in the structurally complex White Pine deposit, lending credence to the hypothesis that hydrologic circulation caused regionally depressed geothermal gradients. In addition, regional heat flow may have been low as a result of the insulating effect of a thick accumulation of rift basalts represented by the Portage Lake Volcanics. Organic geochemical indicators of thermal alteration provide a framework for interpreting tectonic development of the North American Midcontinent rift system.

• OSTI ID: 5719671
• 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

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
BITUMENS
BITUMINOUS MATERIALS
CARBONACEOUS MATERIALS
CHEMISTRY
DEVELOPED COUNTRIES
GEOCHEMISTRY
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOTHERMAL GRADIENTS
HYDROTHERMAL ALTERATION
KEROGEN
MATERIALS
MATTER
MATURATION
MICHIGAN
MINERAL RESOURCES
NORTH AMERICA
OIL YIELDS
ORGANIC COMPOUNDS
ORGANIC MATTER
OTHER ORGANIC COMPOUNDS
PETROLEUM DEPOSITS
RESOURCES
RIFT ZONES
SOURCE ROCKS
TAR
TECTONICS
TEMPERATURE GRADIENTS
USA
WISCONSIN
YIELDS