Fossil manganese deposits buried within DSDP/ODP cores, Legs 1-126

Probable in-situ manganese deposits larger than 1 cm in diameter buried in ODP/DSDP cores were selected for study after examining previous descriptions of the manganese deposits in site reports and the ODP data base. Most of the selected samples from 11 cores occur at or just above sedimentary hiatuses or in slowly deposited sediments and are overlain by rapidly deposited sediments of biogenic, terrigenous or volcanogenic origin. The changes in sedimentation recorded in the lithostratigraphic sections around these deposits are closely related to changes in tectonic evolution, deep water circulation or biological productivity at the sites. The similarity in composition and structure of the buried deposits to those of the modern manganese nodules and crusts with no evidence of post-depositional change suggest that buried manganese deposits may be used as indicators of past sedimentary conditions during which they formed. Their major components are hydrogenetic and earlydiagenetic manganese minerals as well as detrital minerals. The characteristics of these manganese deposits suggests that similar processes of deposition have taken place since the Paleogene or older.

(Table 2) Chemical composition of skeletons of scleractinian non-zooxanthelate corals

The first data on chemical composition of nonreef-building non-zooxanthellate deep-sea corals presented in this publication allow us to identify following tendencies manifested in the biomineralization process. Comparison of concentration levels of some chemical elements in scleractinian corals and ambient ocean waters suggests that corals do not accumulate K in the process of biomineralization and weakly accumulate Mg, whereas Ca, Sr, Si, Al, Ti, Mn, Zn, Cu, Cd, Pb, and Fe are concentrated in skeletons of corals with enrichment coefficients of 10**3 to 10**7. Correlations between components contained in the skeletons of scleractinian corals suggest that the source of Al, Si, Fe, and Ti in them is the clayey constituent of bottom sediments and zooplankton, while trace elements are likely accumulated via bioassimilation from seawater. Such elements as Mn, Sr, Pb, and Cd can structurally substitute Ca in calcite and aragonite. Variations in concentrations of the elements in coral skeletons depending on their habitat depths are fairly significant. As could be expected Ca and Mg concentrations are prone to decrease with depth (R = -0.55 and -0.51, respectively), which can possibly be caused by partial dissolution of carbonate skeletons with increasing depth, whereas the Sr/Ca ratio does not depend on depth.