Color (lightness), organic carbon content, total nitrogen content, carbonate content, and bulk and clay mineralogy were determined for most of the sapropelic sediments recovered by Leg 42A and for some of their adjacent normal sediments.Maximum values of organic carbon and nitrogen reach 16.7% and 1%, respectively. Carbon/nitrogen ratios generally increase with greater organic carbon content and with increasing age. Very high ratios of some sapropel material suggest a considerable supply of terrigenous organic material.The color of the sediment becomes darker with increasing organic carbon content. This is interpreted as the result of monosulfide formation which is controlled by the original content of finely dispersed organic matter. In contrast, the formation of pyrite in sapropels seems to depend upon the presence or absence of lumps of organic matter.Total carbonate content ranges between almost zero and 78% in the sapropels. In comparison to normal sediments, no major carbonate dissolution could be observed. Calcite is the dominant carbonate mineral, while the content of detrital dolomite reaches a maximum of 16%. Occasionally, appearances of calcite and aragonite are attributed to turbiditic supply of shallow water carbonates. In the Messinian evaporitic sequence of Site 374, primary or early diagenetic dolomite is the only carbonate mineral.Calcite, mainly derived from the tests of foraminifers and coccolithophorids; has no relation to the content of organic carbon. This, together with the abundance of plant debris, suggests that the main part of the organic material in sapropels does not originate from plankton.Gypsum is a common component of sapropels, while anhydrite is restricted to the evaporitic sediments of Messinian age. For these strata, contemporaneous formation of sulfides (pyrite) and sulfates (gypsum, anhydrite) is assumed.The clay mineralogy of the sapropel shows considerable differences from that of the normal host sediments: greater contents of organic matter result in increased mineral alteration. The alteration leads to a degradation of the minerals towards mixed-layer types or chlorite, or to their complete destruction. The process increases in the series: kaolinite, illite, chlorite, smectite, attapulgite. The degree of alteration is greatest at the bases of sapropels. It appears to occur when a rich supply of detrital fragile materials has been available to sites in the center of the sapropelic area in the deeper parts of the basin. It is clear that the mechanisms of sapropel formation operate at the sediment/seawater interface and do not depend on depth of burial.

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Twenty-three samples of Site 374 (Ionian Sea) Miocene to Quaternary carbonates were analyzed to determine their stable oxygen and carbon isotopes and mineralogical contents. In addition, the isotopic ratios of organic carbon were determined in eight samples of sapropel. Different depositional environments provided different mechanisms of carbonate formation and deposition as suggested by characteristic isotopic and mineralogical compositions. The extremely low δC 13 values of organic carbon in sapropels may be attributed to fractionation processes which are not completely understood at present.

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Samples were dried at 40°C, ground and mixed to a homogeneous powder. Subsequently, samples were divided in several parts for different determinations. One part was analyzed for its total carbon content. A second one was treated with hydrochloric acid and analyzed for residual "organic" carbon. The difference between total and organic carbon, called here "inorganic" carbon, was used for carbonate calculation (Müller, this volume). Carbon determinations were made using a LECO Carbon Analyzer. Procedure and precision of this method is described in detail by Boyce and Bode (1972). Relative error of own measurements is calculated to about ± 1%. Nitrogen was determined by the standard micro-Kjeldahl method. Mostly sapropel(ic) sediments were analyzed (Sigl et al., this volume). Due to the small amounts of sample material available, the values reported here have a precision of ±3% only. In sediments with low nitrogen content (<0.1%), the relative analytical error may increase to ±6%. By the Kjeldahl method, the content of total nitrogen is measured. This includes organic nitrogen and so-called fixed and ex-changeable ammonia nitrogen (Bremner, 1965). Data are presented in Table 1. ACKNOWLEDGMENT This study is a part of the sedimentological survey of Leg 42A samples financed by the Deutsche Forschungsgemeinschaft. I am indebted to C. Lutz, A. Schneider, and W. Schuster for laboratory work and performance of analyses.