AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
A Preliminary Diagenetic and Paleomagnetic Study of the Fayetteville Shale, Arkansas
(1) ConocoPhillips School of Geology and Geophysics, The University of Oklahoma, Norman, OK.
We are undertaking an integrated diagenetic and paleomagnetic study of outcrops of the Fayetteville Shale in Arkansas to determine the timing of diagenetic events and assess how diagenesis has affected the lithological variability in the unit. Preliminary petrographic analysis indicates that the carbonate beds sampled in the upper Fayetteville Shale range from micrite to microspar (25-40 μm). The microspar could be neomorphically altered micrite and/or detrital in origin. Minor euhedral dolomite, calcite with dolomite rims, thin veins, pyrite, and dark organic matter are present. Preliminary paleomagnetic analysis indicates that carbonate beds contain a characteristic remanence magnetization (ChRM) with southeasterly declinations and shallow down inclinations. The ChRM is interpreted to reside in magnetite based on the demagnetization characteristics and rock magnetic studies. Tilt test results indicate that the ChRM was acquired prior to localized tilting. The ChRM is interpreted to be chemical remanence magnetization (CRM) based on maximum unblocking temperatures of 480°C and low burial temperatures (~100°C). The paleopole for the CRM plots near the Early Permian part of the apparent polar wander path. The modeled timing that the Fayetteville entered the oil window (~300MA) is just prior to the timing of CRM acquisition which suggests that the CRM could be related to a burial diagenetic process such as maturation or organic matter or perhaps the smectite to illite transformation. We are conducting tests of this hypothesis as well as testing if the rocks have been altered by externally-derived fluids which could have caused acquisition of the CRM.