- journal_title：Geological Society of America Bulletin
- Contributor：CHARLES E WEAVER ; J. M WAMPLER
- Publisher：Geological Society of America
- Date：1970-
- Format：text/html
- Language：en
- Identifier：10.1130/0016-7606(1970)81[3423:KAIB]2.0.CO;2
- journal_abbrev：Geological Society of America Bulletin
- issn：0016-7606
- volume：81
- issue：11
- firstpage：3423
K, Ar, and mineral analyses of montmorillonitic mud samples 4233 ft to 16,450 ft deep from a well in the Mississippi Delta area show that, with depth, the apparent K-Ar ages of the bulk samples decrease 100 m.y.; the >2μ fraction is relatively constant in apparent age at approximately 400 m.y.; and the apparent age of the <2μ fraction decreases 40 m.y. with depth. With increasing depth and temperature, K (0.8 percent) appears to be released from the course K-feldspar and mica and to become fixed between the montmorillonite layers. Due to the formation of chloritic layers, fewer illitic layers are formed than is commonly supposed. K-Ar data may be useful in reconstructing the thermal and burial history of shales.