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Donald E. Anders

Publications and source records attributed to Donald E. Anders.

4 recordsLinked to original sources
USGS1987

Possible Late Middle Ordovician organic carbon isotope excursion: Evidence from Ordovician oils and hydrocarbon source rocks, mid-continent and east-central United States

Oils generated by Middle Ordovician rocks are found throughout the Mid-Continent and east-central regions of the United States. Gas chromatographic characteristics of these oils include a relatively high abundance of n-alkanes with carbon numbers less than 20, a strong predominance of odd-numbered n-alkanes between C 10 and C 20 , and relatively small amounts of branched and cyclic alkanes. Saturated and aromatic hydrocarbon fractions of 43 Ordovician oils from the Anadarko, Ardmore, Forest City, Illinois, Michigan, Salina-Sedgwick, and Williston basins and the Iowa shelf demonstrate a wide range in carbon isotope composition (^dgr 13 C sat = -24.9 ^pmil to -33.9 ^pmil, (^dgr 13 C arom = -24.3 ^pmil to -33.7 ^pmil). Saturated and aromatic hydrocarbons extracted from late Middle Ordovician shales (17 core samples) show ranges in ^dgr 13 C similar to that of the oils. The wide ranges in ^dgr 13 C for oils and rock extracts reflect a major, positive excursion(s) (6-9 per ^pmil) in organic matter ^dgr 13 C in late Middle Ordovician rocks. This excursion has at least a regional significance in that it can be documented in sections 480 mi (770 km) apart in south-central Kansas and eastern Iowa. The distance may be as much as 930 mi (1,500 km) if the carbon isotope variations observed in Michigan basin Ordovician oils and in organic matter from late Middle Ordovician rocks in southwestern Ontario are related to the same carbon isotope excursion. Organic-matter ^dgr 13 C in core samples from south-central Kansas and eastern Iowa is not directly related to variations in quantity or quality of organic matter, or maceral compositi n. The positive excursion in organic matter ^dgr 13 C is a possible result of increased organic matter productivity and/or preservation. The parallel shifts in organic and carbonate ^dgr 13 C in core samples from 1 E. M. Greene well, Washington County, Iowa, imply changes in the isotope composition of the ocean-atmosphere carbon reservoir. Differences in the magnitude of the carbon isotope shifts between organic matter (8.8 ^pmil) and carbonate (4.2 ^pmil) in this core suggest a decrease, either locally or regionally, in available dissolved CO 2 , possibly a result of high organic-matter productivity and/or limited circulation in the late Middle Ordovician seas.

American Association of Petroleum Geologists Bulle↗
USGS1987

Marine and nonmarine gas-bearing rocks in Upper Cretaceous Blackhawk and Neslen Formations, eastern Uinta Basin, Utah: Sedimentology, diagenesis, and source rock potential

The Upper Cretaceous Blackhawk and Neslen Formations in the eastern Uinta basin contain large amounts of thermogenic gas that was generated from interbedded humic-rich source rocks. The geometry and distribution of hydrocarbon source and reservoir rocks are controlled by depositional environment. The Blackhawk, composed of laterally extensive sandstone and locally interbedded carbonaceous siltstone and minor coal, reflects deposition in nearshore marine and backshore environments. The Neslen contains organic-rich siltstone and mudstone with lesser amounts of carbonaceous shale, coal, and lenticular sandstone that formed in coastal and lower alluvial-plain depositional settings. Potential reservoir sandstones are composed dominantly of monocrystalline quartz grains and sedimentary lithic fragments. Mechanical compaction during early burial was followed by the precipitation of quartz, carbonate, and barite later in the burial history. Variations in porosity and permeability (2-10%; < 1 md) reflects the presence of authigenic clay, mineral cements, and dissolved lithic grains. Natural fractures, cemented with carbonate, barite, and kaolinite, occur locally. Active hydrocarbon generation occurred in the Neslen and Blackhawk during the Oligocene and Miocene when these units were near their maximum burial depth and temperature. The rate of hydrocarbon generation decreased from the late Miocene to the present, owing to widespread cooling that occurred in response to regional uplift and erosion associated with the development of the Colorado Plateau. Temporally equivalent rocks in other areas of the basin may have experienced similar diagenetic and hydrocarbon generation histories.

Colorado, Utah↗