HR: 1340h
AN: GP33A-0090    [Abstracts]
TI: A Paleomagnetic and Magnetic Anisotropy Study of the Carboniferous Shepody Formation, New Brunswick and Nova Scotia, Canada: Possible Evidence for Inclination Shallowing in Continental Red Beds.
AU: * Bilardello, D
EM: dabc@lehigh.edu
AF: Lehigh University, EES 31, Williams Dr., Bethlehem, PA 18015 United States
AU: Kodama, K P
EM: kpk0@lehigh.edu
AF: Lehigh University, EES 31, Williams Dr., Bethlehem, PA 18015 United States
AB: To check the validity of the Tan and Kodama [2002] hematite inclination correction, the Carboniferous red beds of the Shepody Formation (Hopewell Group, New Brunswick and Nova Scotia, Canada) were sampled. A detailed magnetic stratigraphy for these rocks had been previously reported by DiVenere and Opdyke [1990, 1991]. The corrected paleopoles could then be compared to inclination-corrected paleopoles from the coeval Mauch Chunk Formation and Glenshaw Formation of Pennsylvania. Stepwise thermal demagnetization and chemical demagnetization were used on standard sized cores to isolate the characteristic remanence (ChRM). The two thermally and chemically treated populations yielded identical mean directions at the 95% confidence level, with mean D= 357.5°, I= -18° and α95= 4.7°, corresponding to a paleopole position of 34.7° N, 118.5° E, A95= 3.9°. Anisotropy of magnetic susceptibility (AMS) was measured for all samples and for each chemical demagnetization step to apply an inclination correction. Samples from different sites were divided into two groups, based on their AMS foliation. The individual particle anisotropy was estimated by fitting corrected directions to theoretical correction curves [Tan and Kodama, 2003] as a function of individual particle anisotropy. The best fit suggests that individual particle anisotropies of a= 1.07 and 1.15 should be used for the Shepody Formation; however, the corrected directions (D= 178.3° I= 47.6°, α95= 13.7°) have a strongly elliptical distribution. Assuming that a circular, or azimuthally uniform, distribution would be closer to that caused by random errors in measurement and orientation, a correction using a= 1.1 and 1.4 was made because it gives both an acceptable fit to the theoretical curves and an azimuthally uniform directional distribution. The uniformity of the directional distribution was calculated by Mu [Fisher et al., 1987; Tauxe, 1993]. The mean corrected direction of D= 177.9°, I= 29.1°, α95= 8.4° yields a corrected paleopole at 27.8° N, 117.8° E, A95= 6.6°. This pole position agrees remarkably well with the inclination-corrected Carboniferous red bed paleopole of the Mauch Chunk Formation, northeastern PA (27.9° N, 110.4° E, A95= 8.7°) [Kodama, 2005], with the corrected pole of the Carboniferous magnetite-bearing rocks of the Conemaugh Group of southwestern PA (24.5° N, 116.9° E, A95= 8.7°) [Kodama, 2005], and a re-calculated Carboniferous red bed paleopole of the Maringouin Formation of New Brunswick, Canada (31.4° N, 114.3° E, A95= 7.3°) from data of Newton and Kodama [2004] and new data from this study. The mean pole position lies at 27.9° N, 114.9° E, A95= 4.6°, N= 4. Because individual particle anisotropy is difficult to determine experimentally for hematite-bearing sedimentary rocks, partial thermal remanence magnetization (pTRM) experiments were performed in order to determine remanence anisotropy and better constrain the a value. pTRM experiments show a distinctive remanence anisotropy fabric in sample core coordinates, but not in geographic and/or stratigraphic coordinates, indicating that the fabric is an artifact of the experimental set up. A different method for measuring remanence anisotropy involving high field isothermal remanence will be tested in order to constrain the a value.
DE: 1599 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005