The ODP color digital imaging system: Color logs of quaternary sediments from the Santa Barbara basin,site 893     

Russell B. Merrill  John W. Beck 《Marine Georesources & Geotechnology》2013,31(4):381-408

Digital color logs of cores from leg 146, holes 893A and 893B, have been taken from images captured during January 1993, within days after the cores were split and described. The images were captured and color analyses performed on the Ocean Drilling Program (ODP) color digital imaging system, which was assembled from relatively inexpensive, off‐the‐shelf components. The images were used to calculate sedimentation rates by fitting chronological data from hole 893A to void‐corrected depths determined by eliminating all voids mapped from the images as >1 cm in length measured downcore. Color measurements were made at intervals between 0.22 and 1.0 mm in length, and then Commission Internationale de l'Eclairage (CIE) 1931 chromaticity values were computed. Results plotted within CIE chro‐maticity space lie in close proximity to the Munsell 5Y hue plane, confirming that the instrumental color analysis technique has produced results consistent with those of the human observers who described colors visually. Significant periodicities occurring at 12, 17, 31, and 90 years correlate with sunspot activity cycles, suggesting that color variations may reflect global climatic forcing functions. Linear correlation between color data sets from holes 893A and 893B suggests that as much as 1.2 m of material present at or near the top of hole 893B may not have been recovered from hole 893A, and that there is a 70‐cm depth discrepancy in the opposite direction at 51.5 m below seafloor (mbsf). The article recommends that the 1931 CIE chromaticity system be used routinely for describing colors of geological materials because it readily accommodates the mathematical manipulations required for statistical and time‐series analyses and avoids the subjectivity and other weaknesses inherent in the Munsell Color System.  相似文献   

Phosphorus and iron cycling in deep saprolite,Luquillo Mountains,Puerto Rico     

Heather L. Buss  Ryan Mathur  Arthur F. White  Susan L. Brantley 《Chemical Geology》2010,269(1-2):52-61

Rapid weathering and erosion rates in mountainous tropical watersheds lead to highly variable soil and saprolite thicknesses which in turn impact nutrient fluxes and biological populations. In the Luquillo Mountains of Puerto Rico, a 5-m thick saprolite contains high microorganism densities at the surface and at depth overlying bedrock. We test the hypotheses that the organisms at depth are limited by the availability of two nutrients, P and Fe. Many tropical soils are P-limited, rather than N-limited, and dissolution of apatite is the dominant source of P. We document patterns of apatite weathering and of bioavailable Fe derived from the weathering of primary minerals hornblende and biotite in cores augered to 7.5 m on a ridgetop as compared to spheroidally weathering bedrock sampled in a nearby roadcut.Iron isotopic compositions of 0.5 N HCl extracts of soil and saprolite range from about δ⁵⁶Fe = 0 to ? 0.1‰ throughout the saprolite except at the surface and at 5 m depth where δ⁵⁶Fe = ? 0.26 to ? 0.64‰. The enrichment of light isotopes in HCl-extractable Fe in the soil and at the saprolite–bedrock interface is consistent with active Fe cycling and consistent with the locations of high cell densities and Fe(II)-oxidizing bacteria, identified previously. To evaluate the potential P-limitation of Fe-cycling bacteria in the profile, solid-state concentrations of P were measured as a function of depth in the soil, saprolite, and weathering bedrock. Weathering apatite crystals were examined in thin sections and an apatite dissolution rate of 6.8 × 10^? 14 mol m^? 2 s^? 1 was calculated. While surface communities depend on recycled nutrients and atmospheric inputs, deep communities survive primarily on nutrients released by the weathering bedrock and thus are tightly coupled to processes related to saprolite formation including mineral weathering. While low available P may limit microbial activity within the middle saprolite, fluxes of P from apatite weathering should be sufficient to support robust growth of microorganisms in the deep saprolite.  相似文献   

The use of passive treatment alternatives for the mitigation of acidic drainage at the Williams Brother mine,California: Bench-scale study     

Erin J. Clyde  Pascale Champagne  Heather E. Jamieson 《Applied Geochemistry》2010

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