Geology topics

Tamara Frank

Publications and source records attributed to Tamara Frank.

3 recordsLinked to original sources

USGS1990

Hydrocarbon gases in Tertiary and Quaternary sediments offshore Peru; results and comparisons

Hydrocarbon gases (methane, ethane, propane, isobutane, «-butane, ethene, and propene) are present in Tertiary and Quaternary shelf, upper-slope, and lower-slope deposits of the Peruvian continental margin. Methane dominates the composition of the hydrocarbon gas at all 10 sites examined during Ocean Drilling Program (ODP) Leg 112. Generation of methane is regulated by the amount of sulfate in pore water. Wherever sulfate concentrations approach or equal zero, methane concentrations increase rapidly, reaching values near 100,000 /tL/L of wet sediment at eight of the 10 sites. Methane at all 10 sites results from methanogenesis, which is inhibited where sulfate is present and microbial reduction of sulfate occurs. Hydrocarbon gases heavier than methane also are present, but at much lower concentrations than methane. These hydrocarbons are thought to result from early thermal and microbial diagenesis, based on relative gas compositions and trends of concentrations with depth. With few exceptions, the results obtained in the shipboard and shore-based laboratories are comparable for methane and ethane in sediments of Leg 112. Reanalyses of canned sediments from ODP Leg 104 and from Deep Sea Drilling Project (DSDP) Legs 76 and 84 show that gas samples can be stored for as long as 8 yr, but the amounts of individual hydrocarbon gases retained vary. Nevertheless, the trends of the data sets with depth are similar for fresh and stored samples.

ODP Leg 112↗

USGS1990

Hydrocarbons in sediment of the Weddell Sea, Antarctica

Heavy hydrocarbons (about C15+) are ubiquitous but minor components in sediment from three sites (692, 693, and 694) drilled during Ocean Drilling Program (ODP) Leg 113. This preliminary report is the first to describe the distribution of some of these hydrocarbons in sediment of the Weddell Sea. Samples from Sites 692 and 693, located on a mid-slope bench along the margin of Queen Maud Land, span a time interval from Early Cretaceous to Pleistocene. In samples from the Tertiary portion of the record, having an average organic-carbon content of about 0.2%, n-alkanes are common and are characterized by populations that indicate both marine and terrigenous sources. In contrast, samples from the Cretaceous portion of the record, having an average organic carbon content of about 4%, contain mixtures of hydrocarbons in which n-alkanes are secondary in abundance to the isoprenoid hydrocarbons, pristane and phytane. Diasterenes, sterenes, and hopenes are present in anomalously high concentrations and indicate immaturity. The Cretaceous hydrocarbons appear to be mainly primary, whereas the Tertiary hydrocarbons contain compounds which indicate that the sediment, along with its organic content, has been recycled. Samples from Site 694, located in the Weddell Sea on the abyssal plain, range in age from late Miocene to early Pliocene.

Proceedings of the Ocean Drilling Program: Scienti↗

USGS1988

Aliphatic hydrocarbons in sediments from Prydz Bay, Antarctica

High molecular weight aliphatic hydrocarbons were extracted from sediments at two sites (741 and 742) drilled during ODP Leg 119 in Prydz Bay. The distributions of n-alkanes and triterpenoid and steroid hydrocarbons suggest that the n- alkanes and steranes are mainly of terrestrial origin and that the hydrocarbons are immature to slightly mature in the Lower Cretaceous sediments and immature to mature in the Tertiary sediments. At Site 741, the Lower Cretaceous depositional sequence, which is generally characterized by immature hydrocarbons, is interrupted by sediment having more mature components, suggesting a change of source during part of Early Cretaceous time. At Site 742, the mature geochemical parameters of a Pliocene sample correlate with results reported elsewhere for Site 739. In all but one of the other Tertiary samples, the geochemical parameters indicate intermediate maturity. The Lower Cretaceous and Pliocene sediments average about 1.9% organic carbon, a value of interest from the point of view of potential sources of petroleum offshore of Antarctica.

Proceedings of the Ocean Drilling Program: Scienti↗