RESEARCH· ·1970·

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GE,OLOGICAL SURVEY RESEARCH 1970 ALLOCHTHONOUS PALEOZOIC BLOCKS IN THE TERTIARY SAN LUIS-UPPER ARKANSAS GRABEN, COLORADO By RALPH E. VAN ALSTINE, Washington, D.C. Work done in cooperation with the Colorado State 1lfining Industrial Development Board A.bstra.ot.-Allochthonous breccia blocks of Paleozoic rocks, localized within or near a late Tertiary trough between the Sawatch and Sangre de Cristo Ranges of south-central Colorado, evidently were the result of gravitational sliding several miles enstward from the Sawntch Range. Seventeen detached Paleozoic blocl{S within the Dry Union Formation of Miocene and Pliocene nge nrc exposed in areas of as much as 400 by 800 feet nnd for heights of nbout 150 feet. To the west, six remnants of Paleozoic carbonate rocl{s, some in areas underlain by Precambrian gneiss and others in areas underlain by unconsolidnted fill, also mny be detached blocl\:s. Similar detached blocks bn ve been reported along the margins of other basins in the Western United States. 39" Aspen 0 Geologic investigations, made in cooperation with the Colorado State l\1ining Industrial Development Board,: sou!th west of Salida in the Southern Rocky 1\{ountains of south-central Colorado (fig. 1), revealed 1nore than 20 detached Paleozoic blocks within and adjacent to a late Tertiary trough (Van Alstine, 1968). This 11arrow tl'ough between the Sawatch and Sangre de Cr.isto Ranges is part of the San Luis-Upper Arkansas graben (Tweto, 1968, p. 566, 582) and is the northward continmttioi1 of the Rio Grande depression (Bryan and l\1cCann, · 1938, p. 2-3 ; I\:elley, 1956), a fault structure typical of the Basin and ;Range province. The detached blocks (fig. 2), composed mainly of brecciated ca_rbonate rocks, are too large to have been transported by water. They were emplaced at several stratigraphic le-\re]s in the Dry Union Formation of l\1ioce.ne ,'ai1rd Plio~ene age that fills the trough, evidently by gravitational sliding eastward frmn a structural high, the Sa watch Range (fig. 3). The trough deposits were 'derived largely from the same source area that shed the detached blocks. The Paleo- 38" oCreede SAN JUAN VOLCANIC FIELD 0 10 20 30 MILES FIGURE 1.-Index map of south-central Colorado. zoic blocks are now being exposed as the· adjacent basin fill is removed by erosion. Other interpretations have been given to several of the Paleozoic remnants. For example, from the presence of some of the brecciated Paleozoic masses, Russell ( 1950, pl. 1 and p. 17-18) inferred two steep fault zones and concluded that Paleozoic sedimentary rocks underlie the trough. fill here. DRY UNION FORMATION The Dry Union Formation, named and defined by Tweto ( 1961) in the Lead ville area about 45 miles U.S. GEOL. SURVEY PROF. RAPER 700-8, PAGES 843-851 B43 372-490 0 - 70 - 4
td :t 106'20' r--- 10' 106'00' 38'35' "' ~ L:__:_j Quaternary alluvium t :r&;i~¥1 Miocene and Pliocene Dry Union Formation Locallv capped by Pleistocene deposits. ps, lllide blocks of Paleozoic rocks, queried where slide oriQin is undetermined EXPLANATION - Oligocene volcanic rocks Paleozoic sedimentary rocks Chiefl11 Ordovician thr ough Missi8- aippia:n carbonate rocks EJ .. Precambrian metamorphic and igneous rocks Contact, approximately located u D Major fault, approximately located Dotted where concealed. U , upthrown ride; D, downth.rown side 25\ Strike and dip of beds 0750., U.S. Geological Survey vertebrate fossil locality 1 0 1 2 3 MILES CONTOUR INTERVAL BOO FEET DATUM IS MEAN SEA LEVEL • • • • • • • • • 38'25' Geology by R. E. Van Alstine , 1965-68. Paleozoic (Ordov1cian through Mississippian) rocks m Sawatch Range from Dings and Robinson (1957, pl. l).and s1x Paleozoic remnants near Maysville modified from Crawford (1913, pl. 1) ~ ~ q 8 ~ ~ 0 t;:j 0 t:"' 0 ~ FIGURE 2.-Generalized geologic map of area between the Sa watch and Sangre de Oristo Ranges, Chaffee County, Colo.
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Page 3 and 4: CONTENTS GEOLOGIC STUDIES Petrology
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Page 7 and 8: B2 PETROLOGY AND PETROGRAPHY for bi
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Page 13 and 14: B8 PETROLOGY AND PETROGRAPHY TABLE
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Page 25 and 26: B20 PETROLOGY AND PETROGRAPHY Sigva
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Page 29 and 30: B24 PE~ROLOGY AND PETROGRAPHY schis
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Page 41 and 42: B36 PETROLOGY AND PETROGRAPHY Post-
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Page 51 and 52: B46 STRUCTURAL GEOLOGY FIGURE 4.-Vi
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Page 55 and 56: B50 STRUCTURAL GEOLOGY clined slide
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Page 59 and 60: B54 GEOPHYSICS (1950), Domzalski (1
Page 61 and 62: B56 GEOPHYSICS STRATIGRAPHY AND LIT
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Page 67 and 68: B62 GEOPHYSICS Hammer, Sigmund, 193
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Page 73 and 74: B68 GEOPHYSICS A' San 0 p A c I F I
Page 75 and 76: B70 GEOPHYSICS lies occur over rela
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Page 79 and 80: B74 GEOPHYSICS igneous massif is co
Page 81 and 82: B76 GEOPHYSICS A 50 Bouguer gravity
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Page 85 and 86: B80 GEOPHYSICS FIGURE 1.-Bouguell'
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Page 93 and 94: EXPLANATION Pikes Peak • batholit
Page 95 and 96: DISTRIBUTION OF URANIUM IN URANIUM-
Page 97 and 98: B92 GEOCHRONOLOGY Fleischer, R. L.,
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B94 ECONOMIC GEOLOGY 103° 35' w 1/
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'B96 ECONOMIC ·GEOLOGY 0 500 FEET
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B98 ECONOMIC GEOLOGY TABLE !.-Summa
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BlOO ECONOMIC GEOLOGY surface seems
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GE 1 0LOGICAL SURVEY RESEA·RCH 197
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B104 EJrucJh of the four samples wa
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B106 ECONOMIC GEOLOGY R. 56 E. R. 5
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B108 ECONOMIC GEOLOGY outcrop under
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BllO Brady, of the Museum of Northe
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Bll2 PALEONTOLOGY FIGURE 1.-ProtobZ
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B114 PALEONTOLOGY c .,;# I I ' ' lO
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B116 PALEONTOLOGY ments, the larges
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GErOLOGICAL SURVEY RESEA·RCH 1970
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B120 L xMH 'xE soo~~B_R~I __ T_I __
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B122 PALEONTOLOGY Tetrataxis sp. Te
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GE~OLOGICAL SURVEY RESEARCH 1970 TR
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Bl26 PALEONTOLOGY TABLE 2.-Ranges o
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B128 PALEONTOLOGY l
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BI30 PALEONTOLOGY Ocmt/rrence.-P. m
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Bl32 PALEONTOLOGY proximately 5.7 m
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Bl34 PALEONTOLOGY a b c d e f g - D
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Bl36 PALEONTOLOGY --- 1963. The ori
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B138 PALEONTOLOGY core are m1ssmg,
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B140 PALEONTOLOGY death assemblage:
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Bl42 STRATIGRAPHY EXPLANATION l:.\.
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B144 STRATIGRAPHY ver. We do not in
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B146 STRATIGRAPHY age. A stratigrap
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B148 5 10 15 20 X X Plntygonus Pla.
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GE~OLOGICAL SURVEY RESEARCH 1970 CL
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B152 STRATIGRAPHY at a depth of 58
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••••• 0 .... ••••
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B156 STRATIGRAPHY REFERENCES Brown,
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B158 STRATIGRAPHY In what follows,
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Bi60 STRATIGRAPHY TABLE !.-Stratigr
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B162 SEDIMENTATION with increasing
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llj ...... ~ TABLE 2.-Specific grav
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B166 TABLE 3.-Settling time for a 1
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Bl68 GEOMORPHOLOGY 74° 44° YERMON
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B170 GEOMORPHOLOGY have also been r
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B172 GEOMORPHOLOGY end of Long Isla
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GEOLOGICAL SURVEY RESEARCH 1970 DET
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~ooo ______________ B176 ANALYTICAL
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B178 terranes where the search for
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B180 Reproducibility Replicate anal
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B182 ANALYTICAL METHODS in the aque
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GEOLOGICAL SURVEY RESEARCH 1970 CHE
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B186 ANALYTICAL METHODS 3.31 percen
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Bl88 ANALYTICAL METHODS 3" 2%" Oute
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GEOLOGICAL SURVEY RESEA~RCH 1970 TR
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B192 GROUND-WATER RECHARGE I T I 14
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B194 GROUND-WATER RECHARGE Therefor
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GEOLOGICAL SURVEY RESEARCH 1970 PRE
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B198 GROUND-WATER RECHARGE the basi
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B200 GROUND-WATER RECHARGE t \ \)
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B202 GROUND-WATER RECHARGE Water is
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B204 GROUND-WATER CONTAMINATION rv
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B206 GROUND-WATER CONTAMINATION TAB
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B208. GROUND-WATER CONTAMINATION fa
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GEOLOGICAL SURVEY RESEARCH 1970 MEA
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B212 SURFACE WATER plotted, and the
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GEOLOGICAL SURVEY RESEA·RCH 1970 T
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B216 SURFACE WATER however, if the
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B218 SURFACE WATER TABLE 4.-Variati
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B220 RELATION· BETWEEN GROUND eral
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B222 -0.010 f -0.005 (i) RELATION B
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GEOLOGICAL SURVEY RESEARCH 1970 THE
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'B226 RELATION BETWEEN GROUND WATER
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B228 RELATION, BETWEEN GROUND WATER
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B230 RELATION BETWEEN GROUND WATER
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GEOLOGICAL SURVEY RESEARCH 1970 HYD
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B234 EROSION AND SEDIMENTATION side
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B236 EROSION AND SEDIMENTATION s·o
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B238 EROSION AND SEDIMENTATION Cont
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B240 EROSION AND SEDIMENTATION 2 3
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GEOLOGICAL SURVEY RESEARCH 1970 SPE
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B244 GEOCHEMISTRY OF WATER REFERENC
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B246 HYDROLOGIC TECHNIQUES The upla
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B248 HYDROLOGIC TECHNIQUES type in
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GEOLOGICAL SURVEY RESEARCH 1970 ,,.
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B252 formula may also be useful in
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GEO'LOGICAL SURVEY RESEARCH 1970 CO
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B256 randomly fluctuating component
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B258 HYDROLOGIC TECHNIQUES 1.0 ~ Qj
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~ B260 HYDROLOGIC TECHNIQUES 1-3, f
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I B262 HYDROLOGIC TECHNIQUES REFERE
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,' B264 Page Gravitational sliding,
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., / )
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RESEARCH· ·1970·

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