2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 210-76
Presentation Time: 9:00 AM-6:30 PM


ROBINSON, Caroline, MCKINLEY, Kelsea and ST. JOHN, Kristen, Department of Geology and Environmental Science, James Madison University, Harrisonburg, VA 22807, robin5cm@dukes.jmu.edu

The Ontong Java Plateau hosts an excellent record of Cenozoic ocean history and carbonate deposition in the western equatorial Pacific. Color bands were characteristic of the Pleistocene ODP Leg 130 carbonate record. They were interpreted as diagenetically-altered horizons of volcanic ash based on microprobe geochemical analyses which showed finely disseminated iron sulfide in purple bands and finely disseminated Fe- and Al-bearing silicates (probably clays) in green bands. IODP expedition 320T revisited this location and noted similar color bands at site U1330, although ICP analysis of whole rock samples showed no correlation between geochemistry and color banding. The purpose of our study was to use smear slides and x-ray florescence (XRF) analysis to further characterize the composition of the U1330 color bands, as well as other color changes in the Holocene-Pleistocene sediments. Based on core photos, Core 1 did not contain any color bands but included several gradual color changes from brown to white. In contrast, Core 2 showed groupings of color bands every ~2 m, with a varied distribution of individual bands (spacing of 0.2 to 0.98 m) within each group. 29 samples were taken from color band and non-color band horizons. Smear slides were made for each sample, and a Bruker handheld XRF was used to scan for major and minor elements. One sample from each section of core was scanned repeatedly 5 times to evaluate reproducibility; the average standard deviation of the mean is <0.04. Ca was the most abundant of the elements detected, reflecting the carbonate ooze lithology. The gradual color changes from brown to white in Core 1 correlated with elemental data; the elements Fe, K, Si, Cu, and Ti were all more abundant in intervals of browner calcareous ooze suggesting greater influx of fine terrigenous sediment by eolian processes. Increased Si also corresponds with trace siliceous microfossils found in smear slides for Core 1. In Core 2, the purple bands are higher in Br, Cu, and K, whereas the green color bands are higher in Si, Fe, and Ca. No ash or siliceous microfossils were identified in smear slides of the color bands. We are experimenting with different ways to increase the elemental count signal to better detect additional minor elements.