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The Relation of Dolomite Associated with Faults to the Stratigraphy and Structure of Central Kentucky

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The Relation of Dolomite Associated with Faults to the Stratigraphy and Structure of Central Kentucky The Relation of Dolomite Associated with Faults to the Stratigraphy and Structure of Central Kentucky G ;S O L d G I G A L SURVEY t R O P B S S I O fi A L PAPER 'lit 1 * A Prepared in cooperation with the Kentucky Geological Survey The Relation of Dolomite Associated with Faults to the Stratigraphy and Structure of Central Kentucky By DOUGLAS F. B. BLACK, WILLIAM C. MAcQUOWN, JR., and RONALD J. DEHAAS CONTRIBUTIONS TO THE GEOLOGY OF KENTUCKY GEOLOGICAL SURVEY PROFESSIONAL PAPER 1151-A Prepared in cooperation with the Kentucky Geological Survey A discussion of field and laboratory studies of newly discovered fault-associated dolomite bodies found as a result detailed geologic mapping UNITED STATES GOVERNMENT PRINTING OFFICE, W ASH I N GT O N : 1981 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Doyle G. Frederick, Acting Director Library of Congress Cataloging in Publication Data Black, Douglas F B The relation of dolomite associated with faults to the stratigraphy and structure of central Kentucky. (Contributions to the geology of Kentucky) (Geological Survey professional paper ; 1151-A) Bibliography: p. Supt. of Docs. no. : I 19.16:1151-A 1. Dolomites Kentucky. 2. Faults (Geology) Kentucky. 3. Geology Kentucky. I. MacQuown, William Charles, Jr. 1915- joint author. II. -DeHaas, Ronald J., joint author. III. Kentucky. University. Geological Survey. IV. Title. V. Series. VI. Series: United States. Geological Survey. Professional paper ; Library of Congress Cataloging in Publication Data 1151-A. QE471.15.D6B55 552'.5 79-607049 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Abstract _____________________________ Al Fault-related dolomite occurrences _______________ A9 Introduction ____________________________ 1 Representative examples of fault-related dolomite _______ 9 Dolomite classification and features used in field identification 2 Laboratory investigations ____________________ 16 Regional stratigraphy ______________________ 2 Lithologic description of dolomite types _____________ 3 Summary and conclusions ____________________ 17 Regional geologic structure and relation to dolomite _____ 3 References cited _________________________ 18 ILLUSTRATIONS Page FIGURE 1. Index map showing regional structural features in relation to study area ____________________________ A2 2. Schematic cross section, south-central to northern Kentucky showing stratigraphic relations and nomenclature of near-surface formations and schematic plot of fault-associated dolomite occurrences ___________________ 4 3. Map showing fault-associated dolomite localities in relation to geologic structural fabric in the study area ___________ 6 4. Total-intensity aeromagnetic map of the study area shown in relation to dolomite occurrences and surface faults _______ 8 5. Geologic map of part of the Winchester quadrangle that includes dolomite localities 8 and 11 _________________ 12 6. View west at sample array BW-1 to BW-9 ____________________________________________ 13 7. T-dolomite body at locality 8b ______________________________________________________ 14 TABLES Page TABLE 1. Structurally related dolomite occurrences A10 2. Chemical analyses of samples __________ 17 in CONTRIBUTIONS TO THE GEOLOGY OF KENTUCKY THE RELATION OF DOLOMITE ASSOCIATED WITH FAULTS TO THE STRATIGRAPHY AND STRUCTURE OF CENTRAL KENTUCKY By DOUGLAS F. B. BLACK, WILLIAM C. MACQUOWN, Jr.1 , and RONALD J. DEHAAS2 ABSTRACT before uplift of the horst block, and that these structures are thereiore more likely to be of cryptovolcanic rather than of meteorite-impact origin. Two modes of origin have been determined for fault-related dolomite We further suggest that the structural lineaments defined by de­ in limestone formations of central Kentucky. Dolomite bodies have tailed geologic mapping may be loci for mineral deposits and (or) been emplaced as grabens downfaulted from regionally dolomitized petroleum entrapments at depth, especially in areas where thick im­ formations much higher in the stratigraphic section. Offset on these pervious shale formations cover the brittle solution-susceptible car­ faults is as much as 800 feet, much greater than displacements of other bonate rock formations that are exposed and locally dolomitized in the faults in the area. Other dolomite bodies associated with faults resulted central part of the Jessamine Dome. Minor amounts of oil were found from inplace alteration of limestone country rock by solutions con­ in two zones in a shallow drill core and as vug fillings seen in the ducted along the faults. These bodies are elongate in plan view and are dolomite outcrop at the Stoner Branch locality. adjacent to the conduit faults, commonly on the downthrown sides. The fault-related dolomite bodies are in the central Kentucky mineral district located on the highly faulted central part of the' INTRODUCTION Jessamine Dome of the Cincinnati Arch where barite has been mined Anomalous local bodies of dolomite were found in the past from veins that also contain minor amounts of fluorspar, lead, and zinc. The veins occur in limestone and have a northerly associated with many faults in the predominantly strike. The dolomite is found chiefly along faults that strike northwest limestone terrane of central Kentucky (fig. 1) during the and contains only trace amounts of vug-fill barite locally. detailed geological mapping program conducted Some of the dolomite lies along the major fault systems of the area cooperatively by the Kentucky Geological Survey and that are known to displace Proterozoic basement rocks and to have the U.S. Geological Survey (USGS). Fossils found in been active intermittently during their history. The remaining dolomite bodies, including those found at each of two cryptoexplosive some of these dolomite bodies during the early work led structures in the study area, lie along lineaments defined by geological­ the geologists to think that all these bodies were ly mapped structural features, such as swarms of faults, grabens, small downfaulted blocks derived from overlying Upper Or- steep-walled structural basins, and linear folds. We suggest that these dovician and younger dolomite formations. Black (1974) structurally expressed lineaments, though defined by relatively minor determined that in some places the dolomitization was disruption of the surface rocks, also reflect basement faults along which displacement has taken place periodically. due to inplace alteration of limestone by solutions mov­ Circular cryptoexplosive structures, such as the Jeptha Knob and ing along faults and fractures. This interpretation was Versailles structures in this area, have been attributed to meteorite made first at the Stoner Branch locality in the Win­ impacts by some geologists and to subterranean explosions by others chester Quadrangle where a body of dolomite is bounded who call the resulting structures cryptovolcanic. At the center of the on only one side by a fault. The dolomite is underlain by Jeptha Knob disturbance, a horst was discovered that consists of dolomitized limestone, uplifted about 450 feet from its normal a quartz siltstone, the Garrard Formation, which, stratigraphic position. The horst is in direct fault contact with un- though its interstitial calcite cement has been locally dolomitized carbonate rock. The dolomitic rock is derived from a unit dolomitized, was traceable along four stream valleys that is nowhere else known to be dolomitized. In the absence of con­ beneath the dolomitized limestone of the overlying for­ tradicting evidence, this fact, coupled with the apparent coincidence of mation. Thus, the possibility that the dolomite body had both the Jeptha Knob and Versailles features and structural lineaments presumed to reflect deep-seated faults, suggests that the been downfaulted from higher dolomitic formations was dolomitization is related to the structure, that it took place at depth ruled out. Syndepositional dolomitization was also con­ sidered, but this hypothesis was discarded later when an 1 University of Kentucky, Lexington, Ky. 40506 excavation revealed the nature of lateral gradation from 2 University of Michigan, Ann Arbor, Mich. 48109 dolomite to limestone. Al A2 CONTRIBUTIONS TO THE GEOLOGY OF KENTUCKY EXPLANATION Cryptoexplosive structure Fault Ordovician and Sflurian outcrop area 100 MILES FIGURE 1. Index map showing regional structural features in relation to study area. Central Kentucky faults sketched from recent geologic maps; others from Jillson (1929); Grenville Front in Ohio and southern Kentucky from Bayley and Muehlberger (1968). Map also shows location of dolomite localiaty T24. Two means of emplacement are now recognized for area of the Jessamine Dome are very similar to the Up­ the bodies of dolomite associated with faults in the per Ordovician to Middle Devonian S-dolomites in outly­ region: grabens faulted down from younger dolomite ing areas. This, coupled with a Silurian- or Devonian-age formations and inplace dolomitization of limestone. We determination based on fossils at one of the Nicholasville must distinguish between the two origins of dolomite to localities, caused us to map all these bodies as grabens understand the geology of the area. This study deals derived from the younger rocks. Subsequently, other chiefly with field relations and observations pertaining bodies were found, and they, too, were all mapped as to the dolomites. It also briefly summarizes laboratory grabens until the discovery
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