Late Paleozoic Remagnetization of Shallow-Water Limestones in the Cordillera: Results of "Micro"-Fold Tests from Stylolitic Compaction around Chert Nodules
GILLETT, STEPHEN L., University of Nevada, Reno, NV, and JOHN W. GEISSMAN, University of New Mexico, Albuquerque, NM
In the Desert Range (southern Nevada), the Egan Range (central Nevada), and the southern House Range (western Utah), heterogeneous, shallow-water, miogeoclinal limestones of the Pogonip Group (Early Ordovician) locally contain abundant replacive chert that preserves relict textures from the host limestones as well as clearly detrital grains (e.g., blue-luminescing feldspars). Differential compaction on major stylolites wrapping around chert masses has caused local deformation. The stylolites are a very late diagenetic feature as (1) they cut late cements; and (2) other studies suggest a threshold load is needed to initiate stylolite formation.
All three sections yield a low-inclination, southerly characteristic magnetization, residing in magnetite, that must reflect remagnetization because directions from different samples are not dispersed by the compaction deformation. The uniform reversed polarity suggests late Paleozoic remagnetization. It is tentatively attributed to late diagenetic magnetite, such as is well-documented in the Appalachians, because (1) the cherts are almost nonmagnetic, as would be expected from their impermeability if the magnetite were precipitated from late fluids; and (2) abundant authigenic alkali feldspar also suggests late metasomatism.
These results underscore the importance of integrating paleomagnetic observations with carbonate textures; both the timing of magnetization and of diagenetic events can be constrained.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)