(Table 1) Pigments isolated from DSDP Leg 56 Holes

A relatively well documented record of intermediate and late chlorophyll diagenesis in marine sediments now exists. Intermediate diagenetic stages include conversion of chlorins to DPEP-series porphyrins and subsequent chelation with nickel, vanadyl, and, in special cases, copper. Increasing thermal stress leads to etio-series generation and transalkylation (Baker, 1969; Baker and Smith, 1975; Baker et al., 1977; Palmer and Baker, in press). In contrast, the early transformations of clorophyll are still largely unknown. Very early diagenetic reactions must certainly include loss of magnesium, deesterification, decarboxylation, reduction of ring-conjugating groups, and finally, oxidative-aromatization of carbons 7 and 8 in ring IV to yield free-base porphyrins (Baker and Smith, 1973; Smith and Baker, 1974). Chlorins (7,8-dihydroporphyrins) are very difficult to isolate and identify, because of hydrocarbon impurities which absorb in the blue to violet region of the electromagnetic spectrum and which co-chromatograph with the pigments. Further complications possibly can arise from artifact formation during isolation. In the present study, twelve DSDP Leg 56 core samples, ranging in sub-bottom depth from 4 to 420 meters and in age from Pleistocene to middle Miocene, were analyzed for tetrapyrrole pigments. Chlorins, in concentrations ranging from about 4 to less than 0.002 µg/g sediment, wet weight, were the only tetrapyrroles found. A carotenoid (tetraterpene) was isolated from Section 434-1-3.

(Table 1) Lithology, mineralogy, and physical properties of Cretaceous cherts and porcellanites at DSDP Hole 56-436

Cretaceous chert and porcellanite recovered at Site 436, east of northern Honshu, Japan, are texturally and mineralogically similar to siliceous rocks of comparable age at Sites 303, 304, and 307 in the northwest Pacific. These rocks probably were formed by impregnation of the associated pelagic clay with locally derived silica from biogenic and perhaps some volcanic debris. Fine horizontal laminations are the only primary sedimentary structures, suggesting minimal reworking and transport. Collapse breccias and incipient chert nodules are diagenetic features related to silicification and compaction of the original sediment. Disordered opal-CT (d[101] = 4.09 Å) and microgranular quartz (crystallinity index < 1.0) are the two common silica minerals present. Some samples show quartz replacing this poorly ordered opal- CT, supporting the notion that opal-CT does not become completely ordered (i.e., d[101] = 4.04 Å) in some cases before being converted to quartz. The present temperature calculated for the depth of the shallowest chert and porcellanite at this site is 30 °C; this may represent the temperature of conversion of opal-CT to quartz. High reflection coefficients (0.29-0.65) calculated for the boundary between chert-porcellanite and clay-claystone support the common observation that chert is a strong seismic reflector in deep-sea sedimentary sections.