Diagenesis of the Cambro-Ordovician sedimentary rocks of west-central Wisconsin
- Univ. of Wisconsin, Eau Claire, WI (United States). Dept. of Geology
Shales and siltstones of the Cambro-Ordovician sedimentary rocks of west-central Wisconsin record a complex history of diagenesis. This study examined clays and other minerals within clay-rich layers from fresh surface outcrops of the Cambro-Ordovician sedimentary rocks using XRD and SEM/EDX. Feldspar authigenesis in the base of the Mt. Simon Fm. represents the earliest recorded period of authigenesis. These early formed feldspars ([approximately] 60[mu]M in size) have been completely pseudomorphed by kaolinite. These feldspathization and kaolinization events are limited to the lower 80 feet of the Mt. Simon Fm. Later periods of authigenesis resulted in corrosion of the kaolinite, feldspar authigenesis and illitization with production of I/S ([approximately] 90%I) and minor neoformed filamentous illite throughout the section from the base of the Mt Simon Fm. to at least the Glenwood Fm. In rare instances the filamentous illites have been replaced by kaolinite during a second period of kaolinization. Some of the shales contain abundant authigenic pyrite and at least two generations of authigenic gypsum. Complete dissolution of K-feldspars within some of the samples is evidenced by the presence of small euhedral pits in phosphatic brachiopod shells and suggests that organic acids may have played a role in the diagenesis. The complexity of the authigenic relationships identified in these rocks indicates that they have been subjected to multiple periods of diagenesis with fluids of divergent compositions. This is most readily explained if the rocks behaved as an open system with periodic flushing of K-rich and K-poor fluids.
- OSTI ID:
- 6975446
- Report Number(s):
- CONF-9404217-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 26:5; Conference: 27. annual conference of the North-Central Section of the Geological Society of America (GSA), Kalamazoo, MI (United States), 28-29 Apr 1994; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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