Late Permian age of ammonium-bearing illite in Pennsylvania anthracites: Temporal constraints on coalification in the central Appalachians
- Chevron Petroleum Technology Co., La Habra, CA (United States)
K/Ar dating of authigenic NH4-bearing illite in coal from the Anthracite region of eastern Pennsylvania yields apparent ages of 253-236 Ma ([+-]8 m.y.). The oldest K/Ar date of 253 Ma ([+-]8 m.y.) is a minimum age for the thermal event associated with anthracite formation and illite authigenesis. This date is probably within [approx]10 m.y. of the time at which coal-bearing rocks experienced peak temperatures, which suggests an age range of 265-255 Ma for this event. Age dates for authigenic NH[sub 4]-bearing illite reflect the approximate age of late-stage coalification (formation of anthracite-rank coal) because this mineral formed only during late-stage coalification (T=200-275[degrees]C) from a kaolinite (potassium-free) precursor, and the K/Ar data suggest that NH[sub 4] does not significantly influence the closure temperature of illite. K/Ar dates, in conjunction with paleomagnetic and vitrinite reflectance data, constrain the thermal pulse and deformation associated with the Alleghanian orogenic episode to a time period of 25-35 m.y., beginning in Early Permian time ([approx]285 Ma) after coal deposition, and concluding by Late Permian time ([approx]260-250 Ma). Syn- and post-folding secondary chemical remanent magnetizations constrain Alleghanian folding in the Central Appalachians to Late Permian time, which coincides with the postulated time range of 265-255 Ma for NH[sub 4]-bearing illite authigenesis and anthracite formation derived from the K/Ar data. The similar time range for anthracite formation and Alleghanian folding is consistent with vitrinite reflectance data that suggests anthracite formation was a syn-folding thermal event.
- OSTI ID:
- 6597358
- Report Number(s):
- CONF-960527-; CODEN: AABUD2
- Journal Information:
- AAPG Bulletin, Vol. 5; Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANTHRACITE
AGE ESTIMATION
COALIFICATION
PENNSYLVANIA
COAL DEPOSITS
BLACK COAL
CARBONACEOUS MATERIALS
COAL
DEVELOPED COUNTRIES
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOLOGIC DEPOSITS
MATERIALS
MINERAL RESOURCES
NORTH AMERICA
RESOURCES
USA
011000* - Coal
Lignite
& Peat- Reserves
Geology
& Exploration