at Georgia State University
Diagenesis and Fluid Movement in Basins: The concept of large scale movement of fluids and energy through foreland basins is not new. What is new and different is that this movement is believed to be the result or prompted by convergent tectonism (Oliver’s Fluid Expulsion Hypothesis or later variants proposing fluid movement from tectonically formed highland by Grant Garven and students). There is a clay mineral connection. The diagentic illite (illite-smectite) is thought also to record the movement of fluids through the Appalachian Foreland basin in response to the Alleghanian Orogeny. The ages of diagenetic illites are “Alleghanian” in age with ages increasing from SE to NW (Elliott and Aronson, 1987, Geology; Elliott and Aronson, 1993 Basin Research, and Elliott and Haynes, 2003, Am. Mineralogist). The K/Rb ratios of the diagenetic illite are significantly higher relative to crustal average showing the illite formed from a potassic fluid migrating through these rocks during the Alleghanian Orogeny.
The studies above are dated but still referred to in the literature. I have enjoyed renewing this interest with Doug Elmore and colleagues and students. Another potential Alleghanian signal is paleomagnetic remagnization ( a chemical remnant magnetization) of sediments. Elmore and colleagues believe some of this remagnetization is a function of the smectite to illite transition. We studied this transition in the Disturbed Belt in NW Montana. In Stephen Osborn’s MS thesis at GSU, where he measured a series of K-Ar dates from illites collected from bentonite and potassium bentonites to compare to the chemical remnant magnetization resulting from thrusting. If the CRM is early syntilting, the results are consistent with a connection between thrust loading and illitization. This work was funded by the US Department of Energy in separate awards to Elliott and Elmore. Further work will address and test this connection between CRM and formation of diagenetic illite. Our group has also studied the illlitzation in the Phosphoria Formation with the help of Dick Grauch from the USGS to understand processes leading to the thermal maturation of these source rocks (funded by USGS).