Remanence in authigenic magnetite: Testing the hydrocarbon-magnetite hypothesis
- Univ. of Oklahoma, Norman (United States)
Paleomagnetic, rock magnetic, petrographic, and geochemical studies of hydrocarbon-saturated speleothems in southern Oklahoma indicate there is a relation between hydrocarbons and a chemical magnetization that resides in magnetite. The speleothems, which are composed of light and dark calcite bands, occur in caves of karst origin in the Ordovician Kindblade Formation. Vertebrate fossils interbedded with the deposits indicate they are Permian in age. The dark bands contain primary hydrocarbon-filled fluid inclusions. The dark calcites possess over an order of magnitude stronger natural remanent magnetization than the lighter bands which do not yield stable decay during demagnetization. Alternating field (AF) and thermal demagnetization of specimens of the dark bands reveal a Permian direction of magnetization (declination = 160, inclination = 3, k = 17, {alpha}95 = 5, n = 56). The results of rock magnetic experiments, and the fact that most maximum unblocking temperatures are below 580 C, suggest that the dominant component resides in magnetite. In some specimens stable decay to 640 C suggests the presence of a weak component residing in hematite. The presence of authigenic magnetite spheres in magnetic extracts of the dark calcites supports a chemical origin for the magnetization. Shallow burial depths probably eliminate the possibility of a thermoviscous magnetization. The occurrence of primary hydrocarbons seeped into the caves during precipitation of the speleothems and were trapped in the calcite crystals. The relationship between intensity of magnetization and hydrocarbon abundance leads the authors to propose that chemical conditions created by the hydrocarbons caused precipitation of authigenic magnetite and acquisition of the associated chemical remanence.
- OSTI ID:
- 5119107
- Journal Information:
- Journal of Geophysical Research; (United States), Vol. 95:B4; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
MAGNETITE
MAGNETIZATION
OKLAHOMA
PETROLEUM DEPOSITS
GEOLOGIC MODELS
CALCITE
CORRELATIONS
DEMAGNETIZATION
EXPLORATION
GEOCHEMISTRY
GEOLOGIC HISTORY
GEOLOGY
HYDROCARBONS
MAGNETIC PROPERTIES
PALEOMAGNETISM
PERMIAN PERIOD
PETROGRAPHY
RESERVOIR ROCK
CARBONATE MINERALS
CHEMISTRY
DEVELOPED COUNTRIES
FEDERAL REGION VI
GEOLOGIC AGES
GEOLOGIC DEPOSITS
IRON ORES
MAGNETISM
MINERAL RESOURCES
MINERALS
NORTH AMERICA
ORES
ORGANIC COMPOUNDS
OXIDE MINERALS
PALEOZOIC ERA
PHYSICAL PROPERTIES
RESOURCES
USA
020200* - Petroleum- Reserves
Geology
& Exploration
580000 - Geosciences