Milankovitch Forcing of Cambrian Cyclic Shallow Marine Carbonates of Malyi Karatau Range, Kazakhstan Republic: Preliminary Results of Advanced Time Series Analysis

Dmitry A. Bazykin and Linda A. Hinnov

A new advanced time series technique that uses frequency modulation (FM) analysis (Hinnov, 1994) has been applied to a thick succession of Middle to Upper Cambrian cyclic shallow marine carbonates in the Malyi Karatau region of Kazakhstan to search for spectral peaks characteristic of Milankovitch forcing. Three sections located on the Lower PaIeozoic Aisha-Bibi seamount (Cook et al., 1991, and others) were analyzed. The sections are composed of stacks of tens to over one hundred uninterrupted meter-scale shallowing upwards cycles (SUCs). Individual cycles shallow up from subtidal cross-stratified grainstones to supratidal mudcracked laminites. FM analysis of the time series reconstucted from SUC successions reveals FM spectra displaying characteristic peaks matching thos of Cambrian theoretical climatic precession FM spectra. Cambrian precession was calculated using Berger's solution modified by the predicted Gambrian faster length-of-day and general precession rate (Berger, 1978; Berger et al., 1988, 1992). This is the first time FM analysis has been applied to Cambrian tidal flat cycles and the results are encouraging enough that other techniques, including ^ggr-analysis to reconstruct incremental time scales for the sections, and computer modeling of cyclic carbonate platform deposition are being applied to gain a better understanding of the origin of the cycles.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California