Geochemistry of labile organic matter in sediments and interstitial waters of ODP Sites 107-651 and 107-653

Sediment and interstitial water from Sites 651 and 653 (ODP Leg 107) were investigated by organic geochemical methods to characterize labile organic compound classes (amino compounds and carbohydrates) and to evaluate their progressive diagenetic and thermal degradation in deep-sea sediments. Downhole distribution of dissolved organic carbon (DOC) appears related to redox zones associated with bacterial activity and of diagenetic recrystallization of biogenic tests and not so much to organic matter concentrations in ambient sediments. DOC ranges from 250 to 8300 µmol/L (3-100.1 ppm). Amino acids contribute 10%-0.3% of DOC; carbohydrates range from 78 to 5 µmol/L. Rate of degradation of amino acids by thermal effects and/or bacterial activity at both sites (significantly different in sedimentation rates: average 41 cm/1000 yr in the top 300 m at Site 651, average 3.9 cm/1000 yr in the Pliocene/Quaternary sequence at Site 653 to 220 mbsf) is more dependent on exposure time rather than on the depth within the sediment column. Variability in neutral, acidic, and basic amino acid fractions of total amino acids (with a range of 1.1-0.02 µmol/g sediment; up to 2.5% of organic carbon) varies with carbonate content and by differences in thermal stability of amino acids. Distribution patterns of monosaccharides are interpreted to result from differences in organic matter sources, sedimentation rates, and the degree of organic matter decomposition prior to and subsequent to burial. Total particulate carbohydrates range from 1.82 to 0.21 µmol/g sediment and contribute about 8% to the sedimentary organic matter. Investigation of trace metals in the interstitial waters did not show any correlation of either DOC, amino compounds, or carbohydrates.

Biostratigraphic events close to the Tortonian-Messinian boundary at ODP Hole 107-654A (Table 1)

Correlations of biostratigraphic datums to the geomagnetic reversal time scale (GRTS) at Leg 107 sites provide a means of correlating these datums to sections outside the Mediterranean. Unfortunately, poor recovery and core deformation due to rotary drilling at Sites 651, 652, and 654 severely hampered efforts to acquire detailed magnetostratigraphies and biostratigraphies. However, many biostratigraphic markers could be correlated to the GRTS, including those close to the Miocene/Pliocene and Tortonian/Messinian boundaries. These boundaries are interpreted to occur in Chrons 3r and 3B, respectively (chron nomenclature after Cox, 1982). Comparison of the correlation of Plio-Pleistocene calcareous plankton biostratigraphic events to the GRTS in the Mediterranean and in the open oceans indicates that many events are broadly synchronous between the two environments. The outstanding exception is the first occurrence of Globorotalia margaritae which is delayed in the Mediterranean by about 1 m.y.

Calcareous nannofossils of ODP Leg 107 holes

This paper summarizes the nannoplankton biostratigraphy and the paleoenvironmental interpretations obtained from Leg 107 in the Tyrrhenian Sea. Marine sediments are ranging in age from late Tortonian to Recent. The Mediterranean as a semiclosed adjacent sea of the Atlantic is strongly controlled by paleoceanographic changes in the Atlantic which are related to the global climatic evolution. This influence of the Atlantic is more pronounced in the western than in the eastern Mediterranean. The occurrence of sapropels and sapropelic layers also in the western Mediterranean was shown for the first time.