Chemical remagnetization caused by burial diagenesis: Testing the hypothesis in the Pennsylvanian Belden Formation, Colorado.

摘要

Lower Pennsylvanian Belden Formation carbonates from Central Colorado were subjected to paleomagnetic, rock magnetic and geochemical studies to test for a connection between a chemical remanent magnetization (CRM) in authigenic magnetite and burial diagenesis. Thermal demagnetization shows that Belden lithologies carry up to two components of natural remanent magnetization (NRM) beside a modern, viscous magnetization. An intermediate unblocking temperature (250-400;Based on previous studies and petrographic evidence, the CRM interpreted to reside in authigenic magnetite formed by replacement of pyrite. Although elevated ;The TVRM present in Belden carbonates is pervasive whereas the CRM is widespread but site specific, thus providing an opportunity to magnetically characterize the two components. Specimens with the CRM have higher saturation remanence and acquire an anhysteretic magnetization over a broader coercivity range than the TVRM. The CRM has higher coercivity and saturation remanence/saturation magnetization values indicating that it is carried by finer grains of magnetite than the TVRM. Coercivity and saturation magnetization ratios are consistent with other carbonates interpreted to be remagnetized by chemical processes. The TVRM is interpreted to be carried by coarser authigenic or detrital grains of magnetite than the CRM.