Low-field, mass specific magnetic susceptibility (chi) and gamma radiation spectra (GRS) field and laboratory data sets for two Upper Cretaceous marine sedimentary sequences representing the Cenomanian-Turonian (C-T) boundary in the Western Interior Seaway in central Colorado have been measured, sections including the C-T Global boundary Stratotype Section and Point (GSSP) and a similar to one kilometer distant co-eval sequence, the S Section. It has previously been established that both chi and GRS data sets are controlled by detrital/eolian fluxes into the marine environment, although the effect of weathering, if any, on these parameters when exposed in outcrop, is not well documented. In addition, these parameters are controlled by differing detrital/eolian components that may be derived from different sources, or be differentially concentrated within the marine system. Of great interest is (I) how well these data sets record climate cycles, (2) how the chi and GRS data are affected by weathering, and (3) how well the two methods support each other. Reported here are the results of a number of field and laboratory experiments designed to evaluate instruments and how chi and GRS data sets co-vary, and to test their usefulness as correlation tools in stratigraphy. Results show that both chi and K-40 data sets from laboratory measurement on samples collected in the field, where rocks are relatively fresh, are generally well correlated, respond closely to climate and the corresponding detrital/eolian flux into the marine environment, and can be used for a rough proxy for each other. However, weathering appears to affect the K-40 data by removing K-40, thus reducing correlation potential, although chi does not appear to suffer as badly in more weathered sections and good correlations between sections remain. Field GRS measurements produce a broadly smoothed data set that regionally can be very useful for correlation, although potential global correlations are not tested here. Using chi data reported here, and comparing these data to a similar to 100 kyr cyclic, eccentricity (E1) climate model for the Upper Cretaceous at similar to 93.9 Ma, shows that chi x and K-40 data, measured in the laboratory, can be used to build floating point time scales that produce essentially equivalent results as do other studies using absolute dates. (C) 2013 Elsevier B.V. All rights reserved.
