English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The distribution of lipids and the stable carbon isotopes of humic substances were examined in a core from the Blake-Bahama Basin (Leg 44, Site 391) to recognize terrestrial as opposed to marine origins for these fractions. The lipids in all core sections are mainly of autochthonous marine origin with some having an allochthonous terrestrial contribution. The humic acids in the Quaternary and Miocene sediments are also mainly marine but those of Albian to Tithonian age are predominantly terrestrial. Preferential degradation of lipids compared to humic acids during transport and sedimentation of terrestrial organic matter may have occurred. The lipids examined from dark Albian sediments show similar distributions to other Cretaceous black shales, although lipid yields are much lower. INTRODUCTION Probably the oldest sediments existing in any oceanic basin today are present in the Blake-Bahama Basin. We have analyzed eight representative samples from this site down to a depth of 1392 meters (in the Tithonian) for lipids and humic substances in relation to depth of burial. The relative contributions of autochthonous marine and allochthonous terrigenous lipids were evaluated from the distribution data of the n-alkanes and «-fatty acids and the origin of the humic substances were differentiated using the ratios of the stable carbon isotopes. The relative amounts of humic acids versus total organic carbon were correlated to test whether the diagenetic transformation of humic substances to kerogen occurred in this core. We also analyzed the organic matter in the dark-colored Albian claystone as we were particularly interested in whether its origin was similar to the Cretaceous black shales from the southern and eastern Atlantic Ocean. EXPERIMENTAL PROCEDURES The samples examined were collected on board D/V Glomar Challenger, placed in glass jars, and maintained in a frozen condition until they were analyzed. All samples were from Site 391 located in the center of the Blake-Bahama Basin (28°13.17'N; 75°36.88'W) at a water depth of 4963 meters (Site 391 Report, this volume). The sample descriptions are given in Table 1. The frozen core samples were lyophilized, pulverized, and then extracted for 72 hours in a Soxhlet apparatus with toluene:methanol (1:1). The extracts were concentrated to near dryness and then saponified by reflux in 0.5 N KOH in 95 per cent methanol, 5 per cent 'Contribution No. 1662: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California. water for 2 hours. The non-saponifiable lipids were recovered by liquid-liquid extraction of the diluted (H2O) and acidified mixture with dichloromethane. These lipid extracts were then methylated with 14 percent BF3 in methanol and subjected to silica gel thinlayer chromatography (TLC) using dichloromethane as eluent. After development in iodine vapor, the bands corresponding to hydrocarbons, esters and ketones were scraped off the TLC plate and eluted with CH2CI2. These fractions were analyzed by gas chromatography. The gas chromatography analyses were carried out on a Hewlet t -Packard Model 5830A gas chromatograph with a 16 m×0.75 mm stainless steel SCOT column coated with OV-101, programmed from 110 to 280°C at 4°C/min and using He carrier gas (3 m^/min). Humic acids were extracted from the sediment following the extraction of lipids described above. The dried sediment was acidified to remove carbonates and extracted in batches by shaking with 0.1 N NaOH under nitrogen until the extracts were colorless. The basic extracts were centrifuged (17,000 G; 45 min) to remove suspended sediment and then acidified with HC1 to pH 1 to precipitate humic acid. The humic acid was washed with 0.01 N HC1 to remove salt and lyophilized to yield the dry humic acid in the protonated form. Stable carbon isotope analyses were carried out according to methods described previously (Kaplan et al., 1970) and values are reported in the standard δ notation relative to the Chicago Pee Dee Belemnite standard. RESULTS AND DISCUSSION Lipids The sample descriptions, carbon analyses, lipid yields, and data for the humic substances are given in

Varying Sources for the Lipids and Humic Substances at Site 391, Blake-Bahama Basin, DSDP Leg 44