John E. Zumberge

Prediction of source rock characteristics based on terpane biomarkers in crude oils: A multivariate statistical approach

Abstract The distributions of eight tricyclic and eight pentacyclic terpanes were determined for 216 crude oils located worldwide with subsequent simultaneous RQ-mode factor analysis and stepwise discriminate analysis for the purpose of predicting source rock features or depositional environments. Five categories of source rocks are evident: nearshore marine (i.e., paralic/deltaic); deeper-water marine; lacustrine; phosphaticrich source beds; and Ordovician age source rocks. The first two factors of the RQ-mode factor analysis describe 45 percent of the variation in the data set; the tricyclic terpanes appear to be twice as significant as pentacyclic terpanes in determining the variation among samples. Lacustrine oils are characterized by greater relative abundances of C21 diterpane and gammacerane; nearshore marine sources by C19 and C20 diterpanes and oleanane; deeper-water marine facies by C24 and C25 tricyclic and C31 plus C32 extended hopanes; and Ordovician age oils by C27 and C29 pentacyclic terpanes. Although thermal maturity trends can be observed in factor space, the trends do not necessarily obscure the source rock interpretations. Also, since bacterial degradation of crude oils rarely affects tricyclic terpanes, biodegraded oils can be used in predicting source rock features. The precision to which source rock depositional environments are determined might be increased with the addition of other biomarker (e.g., steranes) and stable isotope data using multivariate statistical techniques.

Organic solids produced by electrical discharge in reducing atmospheres: Tholin molecular analysis

The complex brown polymer produced on passage of an electrical discharge through a mixture of methane, ammonia, and water, is analyzed by pyrolytic GC/MS. Pyrolyzates include a wide range of alkanes, alkenes, aromatic hydrocarbons, aliphatic and aromatic nitriles, pyrroles, and pyridine. Similar pyrolyzates are obtained from polypeptides and polynucleotides with hydrocarbon moieties. This polymer is remarkably stable up to 950 C; its degradation products are candidate constituents of planetary aerosols in the outer solar system and the grains and gas in the interstellar medium.

The origin, distribution and hydrocarbon generation potential of organic-rich facies in the Nonesuch formation, central North American Rift System: A regional study

Abstract Precambrian, unmetamorphosed, organic-rich clastic rocks, whilst uncommon in the geologic record, are of interest with respect to their potential for hydrocarbon generation. The ∼ 1.1 billion year old Nonesuch Formation is primarily a lacustrine deposit which is part of a thick sequence of volcanic and clastic sedimentary rocks that filled an aborted rift in central North America. Previous organic geochemical investigations of the Nonesuch Formation have been limited to isolated samples from the basal portion of the Nonesuch Formation at a copper mine (White Pine) in northern Michigan. In the present study, 183 outcrop and core samples of the Nonesuch Formation from northern Wisconsin and Michigan (Upper Peninsula) were collected for sedimentologic and organic geochemical analyses. Total organic carbon (TOC) values for the samples ranged from 0.0 to 2.5% and showed a strong correlation between organic richness and depositional environment. Detailed petrographic analysis using incident white light and reflected blue light fluorescence revealed two major organic petrographies (1 and 2) which could be further distinguished using combined pyrolysis-gas chromatography/mass spectrometry (PY/GC/MS). Whereas the composition of Organic Petrography 1 kerogens is primarily aliphatic, the composition of Organic Petrography 2 kerogens is dominated by aromatic and/or phenolic constituents. The geographic and stratigraphic distribution of rocks bearing the two organic petrographies indicate that variable source-input or preservation, superimposed over maturity differences, is responsible for both organic petrographic and kerogen pyrolysate compositions.

Effects of paleolatitude on the stable carbon isotope composition of crude oils

Attempts to determine the geologic ages of crude oils based on their stable carbon isotope compositions have been unsuccessful. This is a consequence of the large range of δ 13 C values for crude oils from any specific time interval. These ranges have generally been attributed to differences in the relative contributions of biomass inputs of varying isotopic compositions and, to a lesser extent, isotopic fractionations associated with crude oil formation. However, a potentially important parameter that appears to have been largely overlooked is the effect of paleolatitude on δ 13 C of the marine biomass. In this study, Upper Jurassic–sourced oils representing most major and minor petroleum basins were investigated to assess the effects of paleogeography on their δ 13 C values. From high to low paleolatitudes, the oils become increasingly enriched in 13 C. Thus, for this specific geologic time interval (and likely others), the δ 13 C values of oils from the major marine basins reflect that of the primary marine biomass, which varied as a function of spatial paleoenvironmental parameters, in particular sea-surface paleotemperature.

Kinetics of amino acid racemization in Sequoiadendron giganteum heartwood

Abstract Activation energies and Arrhenius frequency factors were calculated for the racemization reaction of four bound amino acids (asp, glu, pro, phe) isolated from sequoia heartwood, by using elevated temperature rate constants. In addition, a first-order rate constant of 2.1 × 10−5 year−1 was calculated for the racemization of bound aspartic acid from the extent of racemization in dendrochronologically dated sequola heartwood samples. Because the racemization reaction is temperature dependent, an average temperature which the bound aspartic acid in sequoia had experienced during the past ∼2200 years was obtained. This value agrees with modern temperatures near the sample location and estimated paleotemperatures during the past ∼2000 years.

Carbon content and carbonate 13C abundances in the Early Precambrian Swaziland sediments of South Africa

Abstract Carbon content (0.02–0.68% organic), carbonate content (0–69.7%) and carbonate 13C abundances ( − 7.5−+2.3‰ ) were obtained on samples from the Swaziland sediments of South Africa, which are among the oldest known sedimentary rocks on earth (> 3·109 years old). The carbon chemistry of these sediments may serve as evidence for early life and/or for products of chemical evolution. The variation of organic and carbonate carbon concentrations in different sedimentary horizons seems to be controlled by differences in depositional and diagenetic histories. The carbonate δ 13C values did not vary significantly from the ordinary range of Phanerozoic limestone values.

Indications of a biological and biochemical evolutionary trend during the archean and early proterozoic

Abstract Micropaleontological observations and organic geochemical analyses imply, but certainly do not prove, that life may not have been present ∼3,800 Ma ago in Southwestern Greenland; however, physiologically complex prokaryotes flourished by the Early Proterozoic in other locations. It is, of course, also possible that life may have appeared earlier in locations other than Greenland. Investigations of Precambrian biological and biochemical evolutionary trends require interdisciplinary efforts, up-to-date instrumentation and methodology (such as ultramicrochemical analyses of individual microfossils/microstructures), and caution in the interpretation of experimental results.

Organic geochemical correlation of Oklahoma crude oils using R- and Q-mode factor analysis

For the past several decades, there has been a significant amount of crude oil exploration and production throughout the state of Oklahoma. Publications with respect to biological marker compound distributions and stable isotopic compositions of Oklahoma crude oils, their potential genetic relationships and possible sources have, however, been very limited. In this study, a detailed organic geochemical investigation of 46 crude oils from throughout the state of Oklahoma is presented. In addition to assessing similarities and differences of the oils with respect to reservoir ages and geologic provinces, an attempt was made to establish possible genetic relationships on the basis of combined R- and Q-mode factor analysis of source-related geochemical parameters. While the oils from throughout the state were found to be remarkably similar in chemical and stable isotopic composition, four genetic families of oils have been delineated based on this statistical approach. The possible effects of thermal alteration, migration, and multiple sources, i.e. mixing of the oil groups, are discussed.

Effect of glucose on aspartic acid racemization

Abstract The racemization of aspartic acid in aqueous solution with and without phosphate buffer was found to increase in the presence of d -glucose. This increase in racemization appears to involve the formation of an imine intermediate (Schiff base). Subsequent proton tautomerization leading to the loss of asymmetry during the early stages of melanoidin formation could account for the observed increase in racemization. The racemization reaction did not follow reversible first order kinetics when glucose was added to buffered aspartic acid solution at 80°C; in unbuffered solution reversible first order kinetics were followed up to 624 hr.

Variations in aspartic acid racemization in uniformly preserved plants about 11000 years old

Abstract Amino acid racemization forms a basis for determining the chronology and paleotemperature of old plant constituents. Disparity in the extent of aspartic acid racemization was found in different taxa of plants subjected to the same environmental history and found in close proximity within an ancient packrat midden. One taxon showed different rates of aspartic acid racemization in two different anatomical sites. Temperature, pH and time being virtually identical in this one micro-environment within the midden, the differences in racemization rates may have been ultimately derived from physiological variants among the plants. Thus, at least, aspartic acid racemization data should be used selectively.