Lake Bonneville: Geology of Southern Utah Valley Utah
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Lake Bonneville: Geology of Southern Utah Valley Utah GEOLOGICAL SURVEY PROFESSIONAL PAPER 257-B Lake Bonneville: Geology of Southern Utah Valley Utah By HAROLD J. BISSELL GEOLOGICAL SURVEY PROFESSIONAL PAPER 257-B Stratigraphy, origin, and engineering properties of the unconsolidated deposits of Pleistocene Lake Bonneville 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..._ _ _ _____________ _ ___________________ 101 Stratigraphy—Continued Introduction.______________________________________ 101 Quaternary deposits in southern Utah Valley—Con. Field methods_______ ______ _________________ 101 Younger deposits_-____---_-----_-_--------- 121 Previous studies__ — _ — — _______________________ 102 Post-Provo eolian sand and silt-__________ 121 Acknowledgments_____________________________ 103 Late and post-Provo, pre-Utah Lake fan Physical geography.-_______________________________ 103 gravel.______-____--___-____---_-____ 121 Chemical quality of water in Utah Lake _______________ 104 Deposits of Utah Lake________________ 122 Climate ___________________________________________ 105 Alluvium of Utah Lake age______--__-___ 123 Culture and accessibility_____________________________ 105 Comparison of fauna of Utah Lake and Stratigraphy,______________________________________ 106 Lake Bonneville ages___--_--__-------- 123 Pre-Quaternary rocks.__________________________ 106 Ancient soils_-_--_-----------_-----_--------------- 123 Quaternary deposits in the mountains adjoining Lake history. _______ — _._ — —_ — __ — -_- —— -_ — _- — 124 southern Utah Valley. _ __-_____-______-_-_-___ 107 Structural geology.--------------------------------- 125 Quaternary deposits in southern Utah Valley_______ 107 Engineering geology_______________________________ 126 Pre-Lake Bonneville fan gravel,______________ 107 Gravel---------------------------------------- 126 Lake Bonneville group._____________________ 107 Sand— ——— ———— ———— ——— —— —— ——— ——— 127 Alpine formation. ______________________ 108 Clay--------------------------------------- 127 Bonneville formation____________________ 111 Other materials____ — _ —_ — ___ — _ — _ — -_ — -_— 127 Provo formation._______________________ 113 References cited__ — ____ —__ — _ — —_ — — — _ — _ — — — 127 Fan gravel of Lake Bonneville age ____________ 121 Index._________-_---_---_------------------------- 129 ILLUSTRATIONS PLATE 5. Geologic map of southern Utah Valley. — __ — ______-__ — _________ — _ — _---__-- — - — — - — — _-- — - ——In pocket FIGURE 23. Index map of Lake Bonneville______________________________________________________________________ 102 24. Aerial view of Wasatch Mountains south of Salem showing pre-Lake Bonneville alluvial fan_________________ 104 25. Bedding in silt member of the Alpine formation-. —_ — ___ — ___ —— _____ —— -_- — — __ — —— — — _ — — — -— 110 26. Varvelike silt and clay in the Alpine formation.________________________-______-_-----_--_--_-_--------- 110 27. Disconformity between the Bonneville and Alpine formation.__________ _ _ — _ — __ — __ — ______- — — ___ — — 112 28. Bar graphs of mechanical analyses of gravel from the Bonneville formation _______-_____ — — - — — — - — - — — 112 29. Disconformity between the Alpine and Bonneville formations.________ _— — ____— — ___-_- — — — — — — — - 112 30. Diagrammatic sketch of disconformity between the Alpine and Bonneville formations __________ — — ___ — _ — - 113 31. Sorting in gravel of the Provo formation..- —_ — __ — ___ —_ — ____ —— _ — _ — -- — — — — - — — - — — — — - — — 114 32. Post-Provo, pre-Utah Lake soil, developed on deltaic gravel of the Provo formation.________________________ 114 33. Delta deposit of the Provo formation.--. —__ — ,— — _ —_____ _— ___ — _ —— .__ — —— — --- — . — — - — — — — 114 34. Bar graphs of mechanical analyses of the gravel member of the Provo formation..-_________________________ 115 35. Deltaic silt and fine sand in the silt member of the Provo formation---.-_________ _ ___ — _ — __ — - — — — - — - 118 36. Gravel member of the Provo formation overlain by the diatomaceous unit of the silt member._____ _— ____— 119 37. Tufa in Utah Lake deposits. — .— — -_---___ — -_-- — _______- —— — _______-________________________ 123 TABLES TABLE 1. Chemical analyses of water in Utah Lake, 1883 to 1933__ — — ______ —__ — _-_ —— - — -__ — - — -- — — — — — 104 2. Chemical analyses of water in Utah Lake, 1933-____ — — __ — — __ — — — __ — — _ — _ — — ---_--- — — - — — - — - 104 3. Chemical analyses of water from thermal springs in or near Utah Lake._____ — _____- — -___ — _----_--_- — -_ 104 4. Chemical analyses of water of surface streams emptying into Utah Lake________ _ _ — — — __ — — — — — — - — - 105 5. Annual precipitation at various weather stations in southern Utah Valley. _________ — — ___ — — - — — — _- — -- 105 6. Monthly and annual mean temperatures in southern Utah Valley._________________________-_-_--_-_----_- 106 7. Highest temperature, lowest temperature, and prevailing wind direction in southern Utah Valley_-______-__-_ 106 8. Mechanical analyses of six samples of the gravel member of the Alpine formation_-__________-_--_____---_-- 109 9. Mechanical analyses of eight samples of the silt member of the Alpine formation._ — ________ — --- — — — _--- 111 10. Mechanical analyses of the gravel member of the Provo formation-_______________ _ ______ _ -------------- 116 11. Mechanical analyses of the sand member of the Provo formation.___________ ____ — — —_ — — — _ — — — — -- 117 12. Mechanical analyses of the silt member of the Provo formation. — __ — — — _ — __ — — __ — _ — _ — — — -- — -- — - 119 in LAKE BONNEVILLE: GEOLOGY OF SOUTHERN UTAH VALLEY, UTAH By HAROLD J. BJSSELL ABSTRACT A submature soil, as much as 2 feet thick, has formed on the up Southern Utah Valley is an area of about 400 square miles at permost beds of the Provo formation, but not on younger the east edge of Pleistocene Lake Bonneville. deposits. The valley floor consists mostly of sediments of Lake Bonne Fan gravel of late- and post-Provo age overlies the Provo ville and younger lakes. The sediments of Lake Bonneville formation; the gravel was deposited as streams incised the deltas overlap upon huge alluvial fans of pre-Lake Bonneville age and during the final recession of Lake Bonneville, in late Provo time. spread into the valley from the adjoining mountains. The fan Other post-Provo deposits include those of Utah Lake, which are 50 feet in maximum thickness and are subdivided into gravel, gravel bears a very mature (strongly developed) ancient soil, commonly 10 feet or more thick, which also is of pre-Lake sand, silt, clay, and tufa units; eolian sand; and alluvium of Utah Bonneville age. Lake age, deposited on the youngest fans and modern stream The sediments of Lake Bonneville, the Lake Bonneville group, flood plains. The lacustrine mollusks of different ages show slight differ consist of three formations: the Alpine (oldest), Bonneville, and the Provo (youngest). ences. A few species found in the deposits of Utah Lake have The Alpine formation, as much as 335 feet in exposed thickness, not been found in the Lake Bonneville group, and a few species is divided into gravel, sand, silt, and clay members, depending found in the Provo formation have not been found in the Alpine. Also, the coiling of the gastropods seems to be wholly dextral on the dominant texture. Silt and clay predominate. This formation records the first deep-water cycle of Lake Bonneville in the Alpine formation and partly sinistral in the Provo. and extends to an altitude of about 5,100 feet, the maximum of Utah Valley is a structural valley bounded by faults, but this lake cycle. folding has contributed to the deformation. Deformation has occurred repeatedly—at least twice in the Precambrian and A disconformity, representing subaerial erosion, a submature again midway in Cretaceous, Late Cretaceous, Early Tertiary, soil, and loess and alluvium locally separate the Alpine and Bonneville formations. These subaerial features occur at alti Late Tertiary, and in Quaternary time—and is still continuing. tudes as low as about 4,840 feet in southern Utah Valley and The pre-Lake Bonneville fan gravel is faulted as much as 150 indicate lake recession was at least this low between the Alpine feet, and the Lake Bonneville group is displaced as much as 50 and Bonneville lake cycles. feet by later fault movements. The Bonneville formation is much thinner, generally less than The gravel, sand, and clay in the valley are used extensively 35 feet thick, and is the smallest in volume of the Lake Bonneville as construction materials. group. It occurs mainly as a discontinuous selvage of gravel INTRODUCTION along the highest shoreline of Lake Bonneville, the Bonneville Utah Valley, in the northern part of central Utah, is shoreline of Gilbert, at an altitude of about 5,135 feet; it also an intermontane basin at the eastern margin of the occurs locally as small spits and bars at lower altitudes. It records the second deep-lake cycle of Lake Bonneville. A Basin and Range province (Fenneman, 1928). Bound maturely developed soil, generally 3 to 4 feet thick, occurs on the ed on the east by the Wasatch Mountains and on the Alpine and Bonneville formations above the Provo shoreline, west by the East Tintic and the Lake