Sedimentary Studies in the Middle River Drainage Basin of the Shenandoah Valley of Virginia GEOLOGICAL SURVEY PROFESSIONAL PAPER 314-F Sedimentary Studies in the Middle River Drainage Basin of the Shenandoah Valley of Virginia By DOROTHY CARROLL SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 314-F The significance of mineralogy and grain-size distribution of materials in a drainage basin UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1959 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U. S. Geological Survey Library has cataloged this publication as follows: Carroll, Dorothy, 1907- Sedimentary studies in the Middle Kiver drainage basin of the Shenandoah Valley of Virginia. Washington, U.S. Govt. Print. Off., 1959. iii, 125-154 p. maps (2 fold, in pocket) diagrs., tables. 30 cm. (U.S. Geological Survey. Professional paper 314-F. Shorter con­ tribution to general geology) "The significance of mineralogy and grain-size distribution of ma­ terials in a drainage basin." Bibliography: p. 154. 1. Mineralogy Virginia. 2. Sedimentation analysis. i. Title, u. Title: Middle River drainage basin of the Shenandoah Valley of Virginia. (Series: U.S. Geological Survey. Professional paper 314-F. Series: U.S. Geological Survey. Shorter contributions to general geology) 551.3 For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 70 cents (paper cover) CONTENTS Page Page Abstract_______________________________ 125 Rocks Continued Introduction--____________________-__.___ 126 Insoluble residues Continued Purpose of investigation.---.-.__________________ 126 Composition Continued Location____________________________________ 126 Summary____________________________ 135 Fieldwork_________________________________ 126 Significance.____________________________. 136 Laboratory procedure ___________________________ 126 Soils_ _______________________________ 136 Acknowledgments__ __________________________ 128 Distribution__________________________________ 136 Rocks_____________---___________________ 128 Residual soils________________________________ 136 Distribution_____________________________ 128 Alluvial soils.______________________. 139 Insoluble residues___.___________________________ 128 Terrace and high flood-plain soils.________________ 145 Quantity. _____________________________ 128 River-bed material____________________________ 148 Composition _______________________________ 129 Discussion of results______________________________ 150 Light fraction-_---_-_---___-_---__--_-_ 129 Summary________________________________________ 154 Heavy fraction..-._________________ 132 Literature cited___________________________________ 154 Clay__________-___-_-____--_-___ 135 ILLUSTRATIONS [Plates in pocket] Page PLATE 14. Generalized geologic map of the drainage basins of the Calfpasture, Middle, and North Rivers, Augusta and Rockingham Counties, Va. 15. Geologic map of the Middle River drainage basin. FIGURE 28. Index map of the southern part of the Shenandoah Vailey______________________________________________ 127 29. Variation in quantity of insoluble residue in selected bulk rock samples--______---_-----_-__--_---_-----._- 128 30. Cumulative frequency curves showing grain-size distribution in samples of residual soil._____________________ 138 31. Triangular diagrams showing the quantity of sand, silt, and clay in residual, alluvial, and terrace and high flood- plain soils______________________________________________________________________________________ 139 32. Variation in quantity of heavy fraction in the very fine sand of residual, alluvial, and terrace and high flood-plain soils and of river-bed material_____________________________________________________ ______ 142 33. Cumulative frequency curves showing grain-size distribution in samples of alluvial soil_____________________ 144 34. Cumulative frequency curves showing grain-size distribution in samples of terrace and high flood-plain soils____ 147 35^ Variation in mineralogic composition of heavy fractions of residual, alluvial, and terrace and high flood-plain soils and of river-bed material-_____-_____-_________________________________--__-_-_______-_------.----_- 152 TABLES Page 1. Rock samples collected from formations in Augusta County, Va____________________-_-_----_-------_----------_ 129 2. Quantity of insoluble residue of rocks in the Middle River drainage basin_________________-_____-_-___-_-_--_----_ 129 3. Mineralogic composition of insoluble residue of rocks and of the very fine sand fraction of residual, alluvial, and ter­ race and high flood-plain soils and of river-bed material_____________--____-_-___-_-_-_----__--_----_---------- 130 4. Types of zircon in insoluble residues of rocks and in the very fine sand fraction of residual, alluvial, and terrace and high flood-plain soils and of river-bed material___-_____-____-______-____--_-_----_---------__-_- __________ 133 5. Summary of principal minerals present in rock types of the Middle River drainage basin_ _______________ ____________ 135 6. Residual-soil samples collected in Augusta County___________-_______-_____-____--_-_-----_-----------_-_---- 137 7. Description and chemical and physical characteristics of residual, alluvial, and terrace and high flood-plain soils from Augusta County.______-___-___-_-_-_-_-.____________________________,_____--______-__---__------------ 140 8. Alluvial-soil samples collected in Augusta County--_------___---___---__--__---__-_--------__------------------ 143 9. Samples of terrace and high flood-plain soils collected along the Middle River__-_-_________-_--_-----~_-----------_ 146 10. Samples of river-bed material collected from the Middle River and its tributaries.- .__________________.___--_--_-_-- 149 11. Derived data from mechanical analyses of residual, alluvial, and terrace and high flood-plain soils_--______----_-----_ 151 12. Variation in heavy fraction and contents of opaque grains and zircon in residual and terrace and high flood-plain soils and in river-bed material in three groups of samples from adjacent sampling sites__________________-_-_-_----_-_- 153 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY SEDIMENTARY STUDIES IN THE MIDDLE RIVER DRAINAGE BASIN OF THE SHENANDOAH VALLEY OF VIRGINIA By DOROTHY CARROLL ABSTRACT the heavy fractions (>sp gr 2.9) in each sample was deter­ The Middle River in Augusta County, Va., drains an area of mined, and the percentage of individual minerals in each heavy about 370 square miles in the southern part of the ghenandoah fraction was obtained by grain counts. The insoluble residues Valley of Virginia. The country rocks of this area are of sev­ of the country rocks contain varying amounts of heavy minerals eral lithologic types sandstone, shale, limestone, and dolomite ranging from 10,630 pounds per acre-inch of sandstone of the and range in age from Cambrian to Ordovician. The head­ Chemung formation to about 1% ounces in the Elbrook dolo­ waters of the Middle River are in Cambrian rocks but impor­ mite. The minerals found are quartz, chert, orthoclase and tant tributaries cut sandstone of Devonian age; the largest plagioclase feldspars, microcline, shaly particles, and mica in tributary, Christians Creek, flows across shale of Ordovician the light fraction, and opaque grains (magnetite, ilmenite, and age for its entire length. indefinite iron oxides), zircon, tourmaline, rutile, garnet, pyrite, The Middle River drainage basin has residual, alluvial, and kyanite, sphene, chloritpid, staurolite, anatase, zoisite, epidote, terrace and flood-plain soils. Residual soils are largely eon- and amphibole in the heavy fractions. Apart from the opaque trolled by the underlying rocks and have developed profiles grains, zircon and tourmaline are the only minerals that are under podzolizing conditions in which acid leaching is the most abundant. Both the sandy b§ds of the Oonococheague limestone important factor. The soils are silty with most of the material and the sandstone of the Chemung formation contain distinc­ between 0.05 and 0.002 mm in grain diameter. The average tive zircon and tourmaline varieties. median grain diameter is 0.011 mm. The minerals in the residual soils are essentially those which The alluvial soils have a grain-size distribution similar to that were identified in the insoluble residues of the rocks except that of the residual soils, but the alluvium coming directly from the authigenic anatase is more abundant. The quantity of the Devonian sandstone areas is coarser, with a median grain heavy fraction is generally less than 1 percent by weight of the diameter of 0.19 mm. fine-sand fraction. Most of the alluvial soils contain a smaller Soils of the terraces and high flood plains along the Middle percentage of heavy fraction than the residual soils, but there River are now high enough above the river so that they are is considerable variation. Thus, the Middle River alluvium rarely flooded. These soils contain a greater amount of sand contains a larger percentage of heavy minerals than the allu­ than do the residual or alluvial soils. The average median vium of the Folly Mills Creek system and Christians Creek; the grain diamater is 6.04 mm. material carried from the sandstone of Devonian age may Data derived from the figures for mechanical analyses show account for the larger quantities in the Middle River alluvium. that all the soils are poorly sorted. None of the alluvial