Petroleum-generating potential of sediments at DSDP Leg 64 Holes

Sediments from the Gulf of California contain sufficient amounts of thermally reactive organic matter to be considered fair-to-good potential petroleum source rocks. While sediments deposited within the present oxygen-minimum zone have the greatest amounts of organic matter, those deposited below the oxygen-minimum contain sufficient organic matter to be considered potential source rocks. The organic matter in the sediment is almost exclusively marine, Type II kerogen. Different techniques of determining kerogen composition produce generally compatible answers, although pyrolysis gives somewhat misleading results. Elemental analysis of the kerogen and vitrinite reflectance measurements indicate that the organic matter is not buried to sufficiently great depth for significant petroleum generation, despite the high temperature gradients.

C1-C8 hydrocarbons in DSDP Leg 64 Holes sediments

Sediments from the Baja California Continental Margin Transect - Sites 474 and 476 - showed small amounts of C2-C8 hydrocarbons and functionalized compounds (alkenes) typical of organic-rich, Recent, cold (<30°C) marine sediments. In contrast, some samples from Sites 477, 478, 479, and Hole 481A in the Guaymas Basin, an active spreading center, showed the characteristics of thermally generated hydrocarbons. These include an increase (sometimes exponential) in amount and diversity of C2-C8 hydrocarbons and a decrease in alkenes in more thermally mature sediments. The results indicate that the injection of basaltic sills has minimal effect on C2-C8 hydrocarbon generation except in the immediate vicinity of the sill. The absence of light hydrocarbons close to the hottest sills suggests that the compounds distill away as they are formed in these areas of very active hydrothermal circulation. A sample of young sediment exposed to very high temperatures (>300°C) from deeper thermal sources at the hottest site, 477, showed a very limited hydrocarbon distribution, including primarily ethane, benzene, and toluene, together with smaller amounts of propane and butane.

Pollen and spore counts, influx rates and concentrations at DSDP Hole 64-480

Preliminary analyses of 56 samples from the upper 49 meters of Hole 480 (Cores 1-11) show marked changes in pollen frequencies and concentrations. The largely varved cores (1, 2, 3, 10, and 11) are characterized by low concentrations and pollen types such as Gramineae, Low-spine Compositae and Cheno/Ams. The largely homogeneous section (Cores 3 through 10) contains higher pollen concentrations and is dominated by TCT (probably Juniperus) and Artemisia. Picea pollen is also present in this section. The record as a whole is thought to represent most of the last glacial cycle.

Subdivisions of the sediment column, carbon and calcium carbonate at DSDP Hole 64-480

We analyzed 580 integrated scrape-samples from HPC Site 480 for organic and carbonate carbon. Once precise dating is available, these will provide a high-resolution framework for understanding late Quaternary Oceanographic and climatic fluctuations in this region. Organic carbon ranges mostly within a narrow band of 1.8 to 3.5% C. Calcium carbonate varies from undetectable to over 20%, with an average of only about 5%. Source of carbonate are mostly benthic and planktonic foraminifers, although some sections are dominated by diagenetic carbonate, shelly hash, or nannofossils. Detrital sources are low in carbonate. We divided the sequence into 17 calcium carbonate (CC) zones to separate pulses, low and median values. The CC-Zones show various second-order patterns of cyclicity, asymmetry, and events. Laminated zones have lowest uniform values, but a perfect correlation between carbonate content and homogeneous or laminated facies was not found. Maximum values tend to be located near the transition of these two sediment types, showing that accumulation of carbonate is favored during times of breakdown of stable Oceanographic conditions.