Joseph A. Curiale

Leg 67: The Deep Sea Drilling Project Mid-America Trench transect off Guatemala

Drill cores from a transect of the Mid-America Trench off Guatemala were obtained at three sites on the oceanic Cocos plate, and at four sites on the continental Caribbean plate. An ocean sub-bottom seismometer was successfully emplaced in the deepest hole in the trench landward slope where it was left to record data after departure of the drill ship. Drilling on the Cocos plate recovered a basal chalk sequence deposited during early and mid-Miocene time, a short interval of abyssal red clay, and an upper sequence of late Miocene and younger sediment deposited within an area influenced by a terrigenous source. In the trench, a mud and sand fill less than 400,000 yr old overlies the oceanic sequence. The entire section shows no evidence of compressive deformation even at holes drilled against the trench9s landward slope. In contrast, the section cored on the trench9s landward slope 3 km from the trench axis is affected by tectonism. The section contains a Cretaceous to Pliocene claystone sequence, broken by hiatuses but in a normal stratigraphic succession that is capped by Pliocene to Quaternary hemipelagic slope deposits. Seismic records show that the section overlies probable igneous oceanic crust from which it is separated by a few hundred metres. That thickness of undrilled section is insufficient to accommodate the potential offscraped volume of oceanic sediment carried into the trench during Neogene plate convergence. At the estimated 10 cm/yr rate of convergence, much of the oceanic sediment must have been subducted rather than tectonically accreted to the Guatemalan margin. Current models for convergent margin tectonics do not satisfactorily explain the surprising occurrence of Cretaceous to Miocene mudstone at the base of this trench slope. The recovery of gas hydrates prevented drilling to some landward-dipping reflections presumed to be imbricate thrust slices at two sites near the middle of the trench landward slope.

Petroleum-Related Origin for Uraniferous Organic-Rich Nodules of Southwestern Oklahoma

Geologic field relations and geochemical analyses imply a petroleum-related origin for the organic matter of uraniferous nodules in the Permian Hennessey Group red beds in Kiowa County, Oklahoma. The local presence of crude oil in the shallow subsurface and the absence of local occurrences of plant debris suggest a hydrocarbon-related origin for these nodules. Several oil seeps in the general vicinity of the study area indicate that major steep reverse faults near the nodule site may have provided vertical conduits for petroleum migration from deeper zones. Geochemical analyses of the uraniferous nodules, including infrared spectroscopy and elemental analysis, reveal characteristics of both coal and petroleum. Carbon isotopic analyses favor a petroleum-related origin. A model incorporating field and geochemical evidence is suggested whereby crude oil, migrating from depth, is initially altered near the surface to a more viscous material. Concurrently migrating uranium-bearing ground water is then stripped of its uranium by the degraded petroleum. Therefore, presence of such nodules in the shallow subsurface may suggest buried petroleum deposits. Confirmation of this model must await further study of the effects of radiation damage on organic matter.

Molecular Thermal Maturity Indicators in Oil and Gas Source Rocks

Many detailed chemical parameters have been proposed as indicators of thermal maturity in oil and gas source rocks. Certain classical maturity parameters involving carbon preference indices and compound class ratios, such as hydrocarbons/extract yield and extract yield/total organic carbon, are less commonly used today, having been complemented with detailed molecular parameters. Among these parameters, the molecular distributions of metalloporphyrins, cyclic hydrocarbons, low-molecular-weight hydrocarbons, and gases are most commonly used. Recent instrumental advances have allowed the routine measurement of molecular ratios in geochemical organic matter, stimulating the development and use of biological markers, such as steranes, hopanes, and metallated tetrapyrroles, as thermal maturity indicators. Increased chromatographic resolution of source rock hydrocarbons has also led to the use of low-molecular-weight hydrocarbons, methylphenanthrenes, and aromatized steranes as maturity indicators. In this paper, we discuss these developments, emphasizing the applications and the pitfalls of using molecular maturity indicators.

Correlation of Oil and Asphaltite in Ouachita Mountain Region of Oklahoma: GEOLOGIC NOTES

Several chemical characteristics of oils and asphaltites in the frontal and central Ouachita Mountains have been examined. Results indicate that the three oils and six asphaltites examined from Atoka, Pittsburg, and Pushmataha counties in southeastern Oklahoma originated from a common source. Carbon isotope ratios for oil and asphaltite suggest that the asphaltite is neither a protopetroleum nor a thermally degraded crude oil. Results of metallic and elemental analyses are consistent with an oil alteration origin for Ouachita solid bitumens. It is proposed that low-temperature, near-surface alteration phenomena, such as biodegradation and water washing, have degraded crude oil to produce asphaltite in the frontal and central areas. These results suggest that previous assu ptions of a high temperature history are unwarranted.

Regional Source Rock Potential of Lacustrine Oligocene Kishenehn Formation, Northwestern Montana

Intermontane basins of the northern United States Overthrust belt have received only minor attention from petroleum geologists and geochemists in the modern literature, despite the common occurrence of oil shales and thick sediment columns in such basins. The present study investigates the petroleum source rock potential of the freshwater lacustrine sediments, including mudstones, oil shales, and lignites, of the Kishenehn basin of northwestern Montana and southeast British Columbia. Outcrop samples of the Tertiary Kishenehn Formation include excellent, albeit immature, petroleum source rocks. Average total organic carbon contents and hydrogen indices exceed 6% and 500 mg/g, respectively, and numerous samples contain type I kerogen. All samples studied are thermally immat re to marginally mature, having vitrinite reflectance values of 0.28 to 0.51% Ro. Organic geochemical and petrographic analyses of the Kishenehn sediments allow estimates of detailed depositional setting and specific biological input to the sediment column. The southernmost sediments in the basin contain the least land-plant organic matter input and possess the richest petroleum source potential. Although vitrinite reflectance values are not particularly sensitive to maturity differences in this sample set, molecular geochemical data were found to be useful in evaluating fine maturity distinctions and are used here to establish the order of Kishenehn outcrops on the basis of maturity. This use of molecular markers as maturation and depositional setting indicators for freshwater lacustrine environments has widespread application in thrust belts. The results of this tudy will be useful in exploration of over two dozen intermontane basins throughout the northern extent of the United States Overthrust belt.

A summary of Deep Sea Drilling Project Leg 67 shipboard results from the Mid-America Trench transect off Guatemala

Summary The Middle America Trench off Guatemala was transected by 24-channel seismic reflection surveys, seismic-refraction surveys, and drilling with the Glomar Challenger. The drilling was done at three sites on the oceanic Cocos plate and four sites on the Caribbean plate. These plates converge at about 10 cm yr−1. At all drill sites sediment of upper Miocene to Quaternary age is almost entirely hemipelagic mud with interbedded thin volcanic ash, except in the trench where mud and fine sand turbidites less than 400 000 yr old are ponded. However, the underlying rocks are very different. On the oceanic Cocos plate a basal chalk sequence of lower and middle Miocene age is overlain by a thin section of abyssal clay. At a site only 3 km landward of the trench axis where drilling penetrated the slope deposits we recovered a Cretaceous to lower Miocene claystone sequence resting on a section containing igneous rock of continental affinity. A large net subduction of sediment along with ocean crust has occurred during the present (Miocene-Quaternary) episode of subduction and perhaps parts of the continental framework have been subducted as well. However, no current model satisfactorily explains the surprising occurrence of Cretaceous-Miocene claystone at the foot of the trench slope.

Molecular Thermal Maturity Indicators in Oil and Gas Source Rocks: ABSTRACT

Detailed chemical parameters have been proposed as indicators of thermal maturity in oil and gas source rocks. Certain classical maturity parameters involving carbon preference indices and compound class ratios such as HC/EOM and EOM/TOC are infrequently used today, having been largely replaced by detailed molecular parameters. Among these parameters, the molecular distributions of metalloporphyrins, cyclic hydrocarbons, low molecular weight hydrocarbons, and gases are most commonly used. Recent instrumental advances have allowed the measurement of detailed molecular ratios in geochemical organic matter, stimulating the development of biologic markers, such as steranes, hopanes, and metallated tetrapyrroles, as thermal maturity indicators. Increased chromatographic resolu ion of source rock hydrocarbons has also promoted the use of low molecular weight hydrocarbons, methylphenanthrenes, and aromatized steranes as maturity indicators. The future use of molecular thermal maturity indicators in source rocks is expected to increase significantly. In addition to further advances in understanding the significance of biologic marker hydrocarbons, metalloporphyrins, and thermally generated light hydrocarbons, the use of other nonhydrocarbons as maturity determinants will probably develop. End_of_Article - Last_Page 247------------

Origin for Uraniferous Organic Nodules, Hennessey Group (Permian), Oklahoma: ABSTRACT

End_Page 560------------------------------Geologic field relations may be used to infer a coal- or petroleum-related origin for uraniferous organic nodules of the Hennessey Group (Permian), in Kiowa County, Oklahoma. The local presence of crude oil in the shallow subsurface and the local absence of commercial coal deposits suggest a petroleum-related origin for these nodules. This conclusion is compatible with the subsurface structure near the nodule site, which is dominated by several major near-vertical reverse faults, below the Permian unconformity. These faults may provide vertical conduits for petroleum sources below. Geochemical analyses of the uraniferous nodules, including infrared spectra and elemental analyses, reveal characteristics of both coal and petroleum. However, carbon isotopic analyses favor a petroleum-related origin. A model can be proposed whereby petroleum, migrating from depth, is initially altered near the surface to a more viscous material. Concurrently migrating, uranium-rich ground water is then stripped of its uranium by the degraded petroleum. Subsequent radiation damage in the uranium-rich nodules has resulted in unusual chemical characteristics. Such a model suggests that associated petroleums may geochemically correlate to the organic matter of the nodules. This is confirmed by carbon isotope ratios, which are very similar for both the petroleum and the uraniferous nodul s. End_of_Article - Last_Page 561------------

Hydrocarbon Occurrences in Frontal and Central Ouachita Mountains, Oklahoma: ABSTRACT

Hydrocarbons in the frontal and central Ouachitas are in three distinct forms: crude oil, asphaltite, and as organic matter disseminated in potential source rocks. Each of these types has been examined geochemically, in an attempt to correlate oil to asphaltite and oil to source rock. In addition, the general source rock potential of the central Ouachitas has been evaluated. Results show that the crude oil produced to date is chemically mature and largely undergraded, although production is as shallow as 148 ft (45 m) in one field. The asphaltite is predominantly grahamite throughout the Ouachitas, and correlates geochemically to the crude oil, as indicated by similar stable carbon isotope ratios. An examination of the Ouachita section for source potential indicates that everal formations are high enough in organic carbon to have produced oil, although some may be ruled out on the basis of the type of organic matter present. Association of oil and asphaltite along the strike of the Windingstair fault indicates that this listric reverse fault may have served as a migration conduit. Geochemical similarities between analyses of asphaltite from the Upper Ordovician Bigfork and that from the Mississippian Stanley group further indicate the possibility of vertical migration. Finally, migration along a listric fault, with subsequent near-surface degradation of the oil, would provide a concise explanation for the close association of near-surface solid asphaltite with sightly deeper liquid oil. End_of_Article - Last_Page 1497------------

Origin and Geochemical Correlation of Near-Surface Oil and Asphaltite Deposits of Southeastern Oklahoma: ABSTRACT

End_Page 915------------------------------Three Oklahoma oils and six associated asphaltites were studied and found to have a common source, based on geologic and geochemical criteria. Bulk analyses reveal the following: (1) vanadium and nickel are enriched in the asphaltite relative to the oil by an average factor of 41, although the V/Ni ratio only ranges from 0.5 to 3.5 in most of these samples; (2) the average H/C atomic ratio decreases and the average O/C, N/C, and S/C atomic ratios increase significantly from oil to asphaltite; and (3) stable carbon isotope ratio values show that the ratio of 13C to 12C in the asphaltites is essentially the same as that in the oils, being approximately -29.8 ppt (relative to PDB) in almost all cases. These bulk analyses and analysis of isolated chemical fractions o these materials indicate that the asphaltites and oils are of common origin and have a similar temperature history. These data further indicate that asphaltite is a secondary product after oil and that biodegradation, accompanied by other near-surface effects, is the causal mechanism for asphaltite formation. This conclusion is supported by the geology of the region, insomuch as local listric faults could have served as conduits of migration, bringing deeper oil into the zone of near-surface alteration. End_of_Article - Last_Page 916------------