Foreword

Introduction

Acknowledgments

Overview

Water Use

Topography of the County

Geology of the County

Groundwater Availability

Exploration for Groundwater

Karst

Water Quality

Maps and Data

Additional Reading

References Cited

Definitions of Geologic Terms

Rock Descriptions

In Clark County, water is obtained from consolidated sedimentary rocks from Ordovician, Silurian, and Devonian ages, and from unconsolidated sediments of Quaternary age. The oldest rocks exposed on the surface in Clark County were deposited in shallow seas 490 million years ago during the Ordovician. Lying on top of the Ordovician rocks are rocks of the Devonian, which includes the New Albany shale. The New Albany shale, also called the black shale, is 400 million years old and was formed when the deep sea floor became covered with an organic black muck. The muck is now hard black shale (an oil shale) which is one of the most distinctive of all geologic formations in Kentucky. Over the last million years, unconsolidated Quaternary sediments have been deposited along the larger streams and rivers.

Geologic Formations in the County
Limestones
UPPER PART OF LEXINGTON LIMESTONE (Tanglewood Limestone, Millersburg, Strodes Creek, Devils Hollow, Sulfur Well, Brannon and Perryville Members) (Ol)
LOWER PART OF LEXINGTON LIMESTONE (Grier, Logana and Curdsville Members) (Ol)
HIGH BRIDGE GROUP ( Tyrone Limestone, Oregon Formation, Camp Nelson Limestone) (Ohb)

Dolomitic limestones
KNOX GROUP (Okx)

Interbedded clay shales, siltstones, and sandstones
GARRARD SILTSTONE (Okc)

Fractured shales
NEW ALBANY SHALE (MDnb)

Clay shales
CRAB ORCHARD FORMATION AND BRASSFIELD DOLOMITE (Scb)

Interbedded limestones and shales
DRAKES FORMATION (Od)
ASHLOCK FORMATION and CALLOWAY CREEK LIMESTONE (Oaf)
CLAYS FERRY FORMATION (Okc)

Interbedded shales and limestones
KOPE FORMATION (Okc)

For more information, see the definitions of geologic terms and rock descriptions, a geologic map of the county, a summary of the geology of Kentucky, and a discussion of fossils and prehistoric life in Kentucky.

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