The Paleomagnetism of Clastic and Precipitate Deposits in Limestone and Dolomite Caves
LATHAM, ALFRED G., Liverpool University, Liverpool, U.K., and DEREK C. FORD,* McMaster University, Hamilton, Ontario, Canada
Clastic sediments and calcite precipitates (stalagmites, flowstones, etc.) are abundant in modern limestone caves and normally are the dominant infillings in buried (paleokarst) caves. Clastic sediment fillings are chiefly of fluviatile or local breakdown origin, but lacustrine, colluvial, eolian, and glacial deposits are known. Paleomagnetism has been studied in the fluviatile and lacustrine types: (1) reversal stratigraphy aids dating of geomorphic and paleoclimatic events in the late Pliocene/Pleistocene; (2) fine magnetostratigraphy has yielded estimates of the westward drift. Calcite precipitates (speleothems) may display natural remanent magnetism of either depositional (DRM) or chemical (CRM) origin. NRMs of modern speleothems are primary, not diagenetic; CRMs are invariably as ociated with the degradation of surface organic matter. (1) Coarse reversal stratigraphy dates geomorphic, etc., events and erosion rates. (2) Fine stratigraphy combined with (230)Th:(234)U dating gives high precision estimates of secular variation, westward drift, and rate of change of geomagnetic anomalies in upper Pleistocene and Holocene deposits. Magnetostratigraphy of paleokarst speleothem fillings associated with hydrocarbons in Ordovician limestones suggest a Permian age for the karstification. Potential applications of magnetostratigraphy to paleokarst deposits of many different scales are considerable.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)