Masters Theses

Date of Award

3-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Otto C. Kopp

Committee Members

R. Arnseth, D. Byerly, S. Driese

Abstract

Seat rocks below the Middle Pennsylvanian Hazard coal of the Breathitt Formation were investigated in the field and laboratory. Field observations of the study site, which is located on the Daniel Boone Parkway in eastern Kentucky, suggest that the thin coal is part of a channel-fill sequence and that a diastem exists at the coal-underclay contact. Evidence for the diastem includes underlying truncated beds, root traces, a clay horizon on the banks, and the preferential accumulation of peat. In the channel, the coal is up to 48 cm thick, whereas it is only as a few centimeters thick on the northwestern bank. The diastem, in effect, defines a paleotopographic surface. Measurement of the paleotopography indicates that the northwest bank stood 6 m above the base of the channel, whereas the northeast bank was 3-4 m above the base of the channel.

The paleotopography undoubtably influenced groundwater circulation and the presence of standing water, and thus peat deposition. Organic matter in turn affected Eh/pH conditions. Two separate and distinct environments were produced by the irregular paleotopography and subsequent accumulation of organic matter. Because the study site has a limited lateral (200 m) and vertical extent (25 m), variation due to macroenvironmental influences on the rocks at the time of deposition such as climate, sediment source, chemistry of depositional basin waters, etc., was minimized. Chemical and mineralogical changes in the seat rocks below the diastem may be related to micro-environmental factors such as Eh and pH conditions, groundwater circulation, presence of standing water, etc., which were primarily controlled by the paleotopgraphy.

Fifty-eight seat rock samples were collected from 14 vertical profiles and analyzed by XRD and XRF methods. Bulk mineralogy determined by XRD includes quartz, kaolinite, illite-mixed layer material, chlorite, microcline feldspar, 2m muscovite, and pyrite. Several mineralogical trends indicate that the banks and the channel were separate environments. Seat rock samples were analyzed for Na2O, MgO, AI2O3, SiO2, P2O5, S, K2O, CaO, TiO2, Cr, Mn, Fe, Rb, Sr, Zr, and Ba. The analyses reveal distinct chemical trends for the banks and channel.

On the banks, Fe, MgO, and MnO show marked decreases upward towards the coal. Minor reductions upward in P2O5/ CaO, and Ba are noted. S values in the bank seat rocks are uniformly low. Zr increases upward, especially on the northwest bank. Chlorite is absent in the upper portions of some vertical profiles, most notably on the northwest bank. Kaolinite/Illite ratios were somewhat higher at the paleotopographically highest sample profiles, whereas 3.24A/4.26A (microcline feldspar:quartz) ratios and sharpness ratios of 10A material are typically lower at these sites. Such trends are consistent with leaching of the paleotopographically higher areas.

The channel area, where the seat rocks directly below the coal consist of dark, carbonaceous shales, was a zone of concentration for several elements. High values of S (12%), Fe (9%), MgO (2.6%), Na20 (2.2%), Ba (0.25%), and P2O5 (1.4%) exist in the 0-3 cm zone of the channel seat rocks. Pyrite is present in substantial amounts in the channel samples, indicating reducing conditions existed. The clays and organic matter of the 0-3 cm zone in the channel apparently collected ions which may have been mobilized from the paleotopographically higher, leached areas as circulating groundwater moved downward. An additional source of ions may have been the initial presence of standing brackish water that remained after the channel-incising event. High values of Na2O, S, and Mg may have originated in this manner. Chlorite, which probably holds the Mg, may be detrital in origin, having withstood acidic conditions on the channel bottom, or may be chlorite regenerated by the later addition of Mg to degraded chloritic structures or mixed-layer clays.

Chemical and maceral analyses of selected coal samples reveal similar patterns. Coals from the paleotopographically higher northwest bank have greater percentages of detrital material, which may have originated because of drying conditions. Inertinite macerals are also abundant, which confirms that oxidizing conditions existed during peat deposition. Coals in the channel are banded, and exhibit high percentages of vitrinite macerals, which indicates constant wet conditions existed in the channel during peat deposition.

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