Calcium carbonate stratigraphy of ODP Site 177-1090

A total of 776 sediment samples were measured for percent CaCO3 using a coulometer. These data are compared with percent blue reflectance (450-550 nm) measured with the Oregon State University split-core analysis track. In previous studies percent blue reflectance has been an excellent proxy for percent CaCO3 and in this study shows many of the main depositional trends (i.e., a 100-k.y. cycle, with a 55% reflectance range is evident in the upper 900 k.y., underlain by sediments exhibiting a 40-k.y. cycle with only a 30% reflectance range). Between ~21 and 5 Ma the average percent reflectance decreases from ~35% to ~8%. A similar decrease is also recorded between ~24 and 22 Ma. Percent CaCO3 trends closely match those of the percent blue spectral reflectance. This is especially well shown in the 100-k.y. cyclicity and in the interval between 24.5 and 21.5 Ma. In both intervals CaCO3 analyses are abundant. An exception occurs in the interval between 2 and 5 meters composite depth (~193 and 240 k.y.). There, percent CaCO3 and percent reflectance are out of phase. The lack of agreement is not likely to be due to a very wet core, in which water would dominate the spectral reflectance instead of sediment, or to problems with the composite depth slice. The discrepancy remains unexplained and provides clear evidence that when noninvasive measurements are used as proxies for chemical measurements they must be substantiated by the actual chemical or physical measurements.

Orbital control on carbonate-lignite cycles on sediment core KAP-107 in the Ptolemais Basin, northern Greece

Time control is essential for the reconstruction of geological processes. We use a combination of relative and absolute methods to establish the chronology and related paleoclimatic processes for Late Neogene lacustrine sediment from the Ptolemais Basin, northern Greece. We determined changes in magnetic polarity and correlated them to the global magnetic polarity time scale, which again is calibrated by radiometric methods, to provide a low-resolution age model for the Upper Miocene to Lower Pliocene (7 - 3 Ma). Sedimentary successions show rhythmic alterations of lignites, clays, and marls. Using photospetrometry we measured this variability at 1-cm resolution, and correlated the pattern to known changes in earth's orbital parameters, namely to eccentricity and precession. For 230-m long borehole KAP-107 from the Amynteon Sub-Basin we obtained a high-resolution age model that spans 2 myr from 5.1 to 3.1 Ma, with age control points at insolation maxima (20-kyr resolution). We recommend using photospectrometry as reliable tool to establish orbital-based chronologies and to reconstruct paleoclimate variability at high resolution.