LIBRARY COPY Bedrock Geology of the Kassler Quadrangle Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 421-B Bedrock Geology of the Kassler Quadrangle Colorado By GLENN R. SCOTT GEOLOGY OF THE KASSLER QUA.DRANGLE, JEFFERSON AND DOUGLAS COUNTIES, COLORADO GEOLOGICAL SURVEY PROFESSIONAL PAPER 421-B A survey of the east flank of the Colorado Front Range with emphasis on Cretaceous rocks and on structural geology 0 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963 , UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. CONTENTS Page Page Abstract------------------------------------------- 71 General geology-Continued Introduction_______________________________________ 71 Mesozoic and Cenozoic sedimentary rocks-Con. Niobrara formation _________________________ _ Acknowledgments_______________________________ 73 97 Geographic setting______________________________ 73 Fort Hays limestone ~ember ____________ _ 97 General geology_ _ _ __ _ _ __ _ _ __ _ _ _ _ _ _ _ __ __ _ _ __ _ _ _ __ _ _ _ 73 Smoky Hill shale member _______________ _ 98 Pierre shale _____________________ :... __________ _ 99 Precambrian metamorphic and igneous rocks_______ 7 4 Fox Hills sandstone ________________________ _ 104 Metasedimentary rocks______________________ 74 Laramie formation _________________________ _ 104 Quartzite ______________________________ · 7 4 ])awson arkose ____________________________ _ 106 Sillimanitic biotite-quartz gneiss__________ 7 4 Intrusive dike rocks ____________________________ _ 106 Biotite-quartz gneiss_ _ _ _ _ _ _ _ _ _ __ _ __ _ _ _ __ 75 Andesite ________________________ ----------- 106 Amphibolite _________________________ .___ 75 Rhyolite_--·----- __________________ --- _____ _ 107 Structure _________________ :_ _______________________ _ Lime silicate gneiss_____________________ 77 107 Precambrian structure __________________________ _ Granitized metasedimentary rocks_____________ 78 107 Granite gneiss and migmatite_ _ _ _ _ _ _ _ _ __ _ 78 Faults ______________ .___________ ------- ____ _ 108 Sillimanite granite gneiss_________________ 80 Folds ___ -·- ______________________ ----·------_ 108 Hornblende granite gneiss _______________ -. 80 Pennsylvanian structure ________________________ _ 108 Laramide structure ____________________________ _ 109 Intrusive rocks------------------------------ 81 109 Gneissic granite________________________ 81 Faults-------------------------------------Folds_. ___________________________________ _ Quartz diorite and hornblendite _ _ _ _ _ _ _ __ _ 81 110 History of Laramide structure _______________ _ 111 Biotite-muscovite granite________________ 82 Post-Laramide structure ________________________ _ Pikes Peak granite______________________ 83 112 Geologic history ___________________________________ _ 113 Granite pegmatite in Pikes Peak granite_ 84 Economic geology __________________________________ _ Granite pegmatite_______________________ 84 114 Nonmetallic deposits _________________ ---_______ _ 114. Paleozoic sedimentary rocks______________________ 85 Sandstone dikes_ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ __ _ _ _ _ 85 Mica-------------------------------------­ 114 114 Source of the sand_______________________ 86 ClayFeldspar----------------------------------- _____ .;, _______________________________ _ 114 Process of emplacement__________________ 87 . Coal.:. ____________________________________ _ 114 Fountain formation__________________________ 88 Limestone ______ - _____ ..; ____ ------------ -·~ -- 115 Lyons sandstone ________ : ______ -·-___________ 89 Structural stone-------------------------~-- 115 Lykins formation____________________________ 90 Sand-------------------------------------- 115 Mesozoic and Cenozoic sedimentary rocks__________ 91 Road metal _______________________________ _ 115 Rals~on Creek formation_____________________ 91 Metallic deposits _______________________________ _ 115 Iron ______________________________________ _ Morrison formation__________________________ 92 116 Lytle and South Platte formations____________ 94 Copper ___________________________________ _ 116 Uranium __________________________________ _ Graneros shale, Greenhorn limestone, and Car- 116 lile shale __________________________ .:. _ _ _ __ _ 94 Engineering problems _______________________________ _ 117 Graneros shale__________________________ 94 Fossil localities _______________________ -- __ - ___ - ____ _ 118 Greenhorn limestone_____________________ 95 References cited ____________________ ---------------- 120 Carlile shale____________________________ 95 lndex---------------------------------------------- 123 m IV CONTENTS ILLUSTRATIONS J:>age PLATE 2. Bedrock geologic map of the Kassler quadrangle_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ In pocket 3. Correlation of rocks in the Kassler quadrangle with a reference sequence for the western interior of conterminous 1Jnited States--------------------------------------------------------------------------------- In pocket FIGURE 28. IndexmaP----------------------------------------------------------------------------------------- 72 29. Granite gneiss and migmatite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 79 30. Pikes Peak granite in nearly fresh outc~OP-------·------------------------------------------------------ 83 31. Distribution of sandstone. dikes ______ ---______________________________________________________________ 85 32. Thinning of the Fountain formation to the south by faulting_______________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 89 33. Contour diagram of ·lineations___________________________________________________________ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 08 34. Jarre Creek fault an~ general view of south end of quadrangle____________________________________________ 110 35. Cross section of Front Range showing tilting of mountain front___________________________________________ 111 TABLES Page TABLE 1. Spectrographic analyses of sandstone dikes and Sawatch quartzite________________________________________ 87 2. Stratigraphic distribution by ammonite zones of fossils of the Pierre shale__________________________________ 100 3. Lithology and faunal zones of the Pierre shale------------------------------.---~------------------------ 103 GEOLOGY OF THE KASSLER QUADRANGLE, JEFFERSON AND DOUGLAS COUNTIES, COLORADO BEDROCK GEOLOGY OF THE KASSLER QUADRANGLE, COLORADO By GLENN R. ScOTr ABSTRACT jasper, and locally gypsum. At the base of the Morrison for­ The Kassler quadrangle lies along the South Platte River mation is a lenticular sandstone unit. The upper part of the on the east flnnk of the Colorado Front Range a few miles Morrison formation is also of continental origin and consists south of Denver. of fresh-water limestone, variegated siltstone, and thin sand­ Precambrian metamorphic and igneous rocks constitute the· stone beds. bedrock of the mountains. The oldest rocks are metasedimen­ Most of the Cretaceous beds in the urea are of marine origin. tnry quartzite, amphibolite, lime silicnte gneiss, biotite-quartz The Lytle and South Platte formations are predominantly beach gneiss, nnd sillimnnitic biotite-quartz gneiss. These older rocks sand, but contain a thin bed of marine shale near the middle. were invaded by granitic solutions that generally produced The Graneros shale, Greenhorn limestone, and Carlile shale con­ large bodies of grnnite gneiss, but that locally were so inti­ sist of black marine shale including (a) a thin siliceous silt­ mately interbedded with the metasedimentary rocks that mig­ stone (Mowry equivalent) in the lower part; (b) calcareous mntite wns formed. Gneissic granite (probably equivalent shale, brown calcarenite and gray dense limestone in the middle, to the Boulder Creek granite) and quartz diorite and asso­ and (c) chalky shale, silty and sandy shale, and calcarenite in. cinted hornblemHte also inyaded the older rocks and were given the upper part. The Niobrara formation consists of the Fort n metnmorphic structure by the last stage of regional meta­ Hays limestone member at the base and the Smoky Hill shale morphism to affect the crystalline rocl\:S of the Front Range. member. The Pierre shale is predominantly dark marine shale, The biotite-muscovite granite, the Pikes Peak granite, and but contains the friable marine Hygiene sandstone member grnnite pegmatite were intruded into all earlier rocks in later near the middle and another soft sandstone near the top. Faunal Precambrian time. zones were defined in the Pierre shale on the basis of n remark­ In Inte Precambrian time a r:mg-e of low mountains ap­ able fauna of ammonites. The Fox Hills sandstone, a brackish­ parently wns uplifted in the present position of the Colorado water marine sandstone, overlies the Pierre shale. The sea Front Runge, nnd fnults, such as the Jarre Creek fault and withdrew from the area for the last time after the Fox Hills other northwest- and northeast-trending faults that cross the sandstone was deposited. The Laramie formation, which over­ l1'rout Rnnge, were formed. These faults are the framework lies the Fox Hills, was deposited in the streams and swamps ; it of the ll'ront Rnnge fault system, and major movements have contains the only minable deposits of coal in the area.