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Data Series 280

U.S. GEOLOGICAL SURVEY
Data Series 280

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Table 1. Ages and seawater strontium isotopic composition (87Sr/86Sr) of stratigraphic units present in the Nevada Test Site region, southern Nevada.

[Stratigraphic units and epochs are from the U.S. Geological Survey Geologic Names Lexicon (GEOLEX) database (http://ngmdb.usgs.gov/Geolex/geolex_home.html). Age assignments are based on the time scale of Young and Laurie (1996), which McArthur and others (2001) used to construct the Paleozoic seawater curve (fig. 3). Maximum, minimum, and mean Sr isotopic compositions are determined from values shown in figure 3 averaged over the time period given. Age ranges are given in millions of years before present (m.y.)]

Symbol Stratigraphic unit Epoch Age range (m.y.) Minimum 87Sr/86Sr Maximum 87Sr/86Sr Mean 87Sr/86Sr
PPt Tippipah Limestone Pennsylvanian and Early Permian 270–325 0.7073 0.7084 0.7080
PMb Bird Spring Formation–undivided Late Mississippian and Early Permian 270–340 .7073 .7084 .7079
PMbl Bird Spring Formation–lower member Late Mississippian and Early Permian 270–340 .7073 .7084 .7080
Mm Monte Cristo group Early and Late Mississippian 325–354 .7077 .7084 .7079
Mc Chainman Shale Early and Late Mississippian 325–354 .7077 .7082 .7079
Mj Joana Limestone Early Mississippian 340–354 .7077 .7082 .7080
MDe Eleana Formation Late Devonian and Mississippian 325–369 .7077 .7083 .7080
MDg Gap Wash Formation Late Devonian and Mississippian 325–369 .7077 .7083 .7080
Dg Guilmette Formation Middle and Late Devonian 354–384 .7078 .7083 .7080
Df Fluorspar Canyon Formation Middle Devonian 369–384 .7078 .7079 .7079
Dsi Simonson Dolomite Middle Devonian 369–384 .7078 .7079 .7079
Dtc Rocks of Tarantula Canyon Devonian 354–410 .7078 .7088 .7082
Dsv Sevy Dolomite Early and Middle Devonian 369–410 .7078 .7088 .7082
Du Undifferentiated rocks of Devonian in age Devonian 354–410 .7078 .7088 .7082
DSlm Lone Mountain Dolomite Late Silurian and Early Devonian 384–420 .7079 .7088 .7085
DSu Undifferentiated rocks of Devonian or Silurian age Devonian or Silurian 354–434 .7078 .7088 .7083
Sr Roberts Mountains Formation Silurian 410–434 .7080 .7088 .7084
Sl Laketown Dolomite Silurian 410–434 .7080 .7088 .7084
Oes Ely Springs Dolomite Late Ordovician 434–459 .7079 .7085 .7081
Op Pogonip Group Late Cambrian and MiddleOrdovician 459–498 .7084 .7091 .7089
Op-av Antelope Valley Limestone of Pogonip Group Early and Middle Ordovician 459–490 .7084 .7091 .7089
Op-g Goodwin Limstone of Pogonip Group Early Ordovician and LateCambrian 470–498 .7089 .7091 .7090
Ou Undifferentiated rocks of Ordovician age Ordovician 434–490 .7079 .7091 .7085
OCu Undifferentiated rocks of Ordovician or Cambrian age Ordovician or Cambrian 434–509 .7079 .7091 .7086
Cn Nopah Formation Late Cambrian 490–498 .7091 .7092 .7091
Cn-s Smoky Member of Nopah Formation Late Cambrian 490–498 .7091 .7092 .7091
Cn-h Halfpint Member of Nopah Formation Late Cambrian 490–498 .7091 .7092 .7091
Cn-d Dunderberg Shale Member of Nopah Formation Late Cambrian 490–498 .7091 .7092 .7091
Cb Bonanza King Formation Middle and Late Cambrian 490–509 .7088 .7092 .7091
Cb-b Banded Mountain Member of Bonanza King Formation Late Cambrian 490–498 .7091 .7092 .7091
Cb-p Papoose Lake Member of Bonanza King Formation Middle Cambrian 498–509 .7090 .7092 .7090
Cu Undifferentiated rocks of Cambrian Age Cambrian 490–542 .7085 .7091 .7088
Cc Carrara Formation Early and Middle Cambrian 498–542 .7085 .7092 .7087
Cc-m Carrara Formation-Middle Part Early and Middle Cambrian 498–542 .7085 .7092 .7087
CZw Wood Canyon Formation Neoproterozoic and EarlyCambrian 509–600 .7079 .7088 .7084
CZw-u Wood Cyn Formation-Upper Member Early Cambrian 509–542 0.7085 0.7088 0.7086
CZw-l Wood Cyn Formation-Lower Member Neoproterozoic 542–600 .7085 .7079 .7084
Zs Stirling Quartzite Neoproterozoic 542–1,000 .7055 .7085 Undefined
Zs-c Stirling Quartzite-C Member Neoproterozoic 542–1,000 .7055 .7085 Undefined
Zs-d Stirling Quartzite-D Member Neoproterozoic 542–1,000 .7055 .7085 Undefined
Zj Johnnie Formation Neoproterozoic 542–1,000 .7055 .7085 Undefined
Zn Noonday Dolomite Neoproterozoic 542–1,000 .7055 .7085 Undefined
ZYb Beck Spring Dolomite Neoproterozoic and Mesoproterozoic 542–1,600 .7055 .7085 Undefined
ZYc Crystal Spring Formation of Pahrump Group Neoproterozoic and Mesoproterozoic 542–1,600 .7055 .7085 Undefined

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