For this study, >40 samples from Hole 1138A, lithologic Units IV to VI, were processed, screened, and studied, some in detail. Unit IV, a cyclic alternation of light gray chalk to dark gray/black nannofossil claystone, has carbonate contents of ~95 wt% at the top of the unit. The dark gray to black nannofossil claystone is more prominent at the base of the unit in Cores 183-1138A-68R and 69R. There, the organic carbon content reaches 2.25 wt% (see above). Unit V is represented in our study only by two samples (183-1138A-69R-5, 124-126 cm, and 69R-6, 50-52 cm) and consists of glauconite-bearing to glauconitic calcareous sandstone and claystone. Throughout Core 183-1138A-72R, small and sometimes large shell fragments of pectinid bivalves and serpulid tubes are common.
Unit VI consists predominantly of dark brown silty claystone to sandstone. The carbonate content is uniformly low (1-14 wt%). The upper part (interval 183-1138A-71R-2, 38 cm, to 73R-1, 13 cm) is mostly dark brown silty claystone with very fine grained sandstone layers that contain some glauconite grains. The underlying brown sandy claystone and sandy clayey siltstone contain, in part, pebbles, shell fragments, and small wood fragments. The lowermost portion of Unit VI (interval 183-1138A-73R-3, 126 cm, through 73R-CC) is silty claystone of various colors that overlies brecciated, weathered? basaltic basement.
All samples from Hole 1138A were processed using standard paleobotanical and palynological processing methods. To concentrate the organic material, samples were first treated with 10% HCl to dissolve carbonates. After several washings and centrifugation, high-strength HF was added to dissolve silicates. The samples were sieved with a 20-µm sieve onboard ship. Samples sieved later onshore were treated with a 12-µm sieve, and several were treated with a 6-µm sieve.
Preparation for analyzing (macro-)plant fossils included four-fraction wet sieving with 750-, 250-, 125-, and 45-µm sieves. Some of the samples were difficult to dissolve, so the material was frozen and thawed several times to loosen it and was sieved with 500- and 200-µm sieves. The pieces range in size from <1 mm to 3 cm, most commonly ~1-3 mm. The material consists of partly charcoalified material (fusinite) and partly vitrinite.
The residual objects—pieces of wood and parts of fern fronds, as well as leaves and resin—were picked under a binocular microscope. Most of the palynological slides (up to 12 per sample) were prepared with glycerine jelly and surrounded by wax. In many samples finely shredded organic debris masked the taxonomic features of dinocysts, which necessitated the preparation of single-grain slides. Photographs were taken with a Zeiss light microscope. A few wood fragments and other charcoalified plant debris were studied with a scanning electron microscope (SEM).
An overview table was created while screening through most of the existing slides. For (semi)quantitative counts, an average of a half-dozen slides per sample were used and 50 to 150 sporomorphs per sample were counted. The following abundance categories, of total palynomorphs per analyzed slide, were used: