n Alas - Alaska Division of Geological & Geophysical Surveys - State ...

More documents

Recommendations

Info

0 25 KILOMETERS u EXPLANATION 0s . ' Surtlcfal dsposlis (Ouatemary) Contact-A~or~mately Iocalsd ks~.Ciinlwell Fonnatlon swllmenlary rocks, undlvldad (Tertlay) A 1 1 I vdcale rocks. In pan conmpmnem with the bnlwbll ionnation (Tertiay) k.':;:l Kof - Granitic rocks (ablefeous~ - - A 2 Fault MCmnorphlt i~rad-Appo)rlrmlely located: dashed where concealed Bi, Blbflla Gar, Carnec 7-r Appmimatu extent a! arnphlballb Iacles m0larncqhlsrn-Dashed where concealed: Bahs toward amphlboll(e facles Locality descrbad In 10x1 Egwe~ 46.-Generalized geologlc map showing Cretaceous plutonic rocks and the McKinley fault In the Wealy quadrangle, southern Alsska. Geology in part after Capps (19331, Wolfe and Wahrheftig (1970), Beikrnan and others (19771, and Csejtey and others (1982).
The cantwell(?) Pormation south of the McKin- ley lault composes a flat-lying or gently dipping sequence of conglomerate with intercalated sandstone and siltstone. This sequence rests with angular uncon- formity on Lntensely deformed Lower Cretaceous flysah deposits and is exposed in a narrow band of erosional remnants along ridgetops near the head- waters of the West Fork of the Chulitna River, in the southwestern part of the Healy quadrangle (Pig. 49). Although the top of the sequence is nowhere exposed, a maximum thickness of about 100 to 150 m still re- mains. At locality 1 (fig. 49) the conglomerate is whitish gray and poorly to moderately well cemented, with a chalky sand and clay matrix. The clasts are clay coated, subangular to well rounded, and commonly between 1 and 3 cm in diameter, dthough some are as much as 10 cm across. Most clasls consist of white quartz and gay and black chert, but some are of gray quartzite, pink fine-grained sandstone, ligh t-green and medium-brown chert, nnd fineqained chert conglorn- erate. The conglomerate of the sequence forms massive apparently lenticular layers, e few to several tens of meters thick. The intercalated sandstone and siltstone occur in beds as much as a few meters thick, me gray and brown, and contain carbonized plant fragments, some of which have been identified by J. A. Wolfe (oral commun., 1982) es Metasequoia occidentalis (Newberry) Chancy. This spacies, which indicates m early Tertiary age, is part or the flora of the Cantwen Pormation north of the McKinley fault (Wolfe and Wahrhaftig, 2970; Wolfe and Tanai, 1980). North of the Mcliinley fault, the main body of the Cantwall Formation forms a broad east-west- trending belt. According to Wolfe and Wahrhaftig (1970), the focmcltion herc consists predominantly of interbedded congloniernte, sandstone, argillite, shale end a few coalbeds. Lacally, it contains some flows md related tuff of maPic to intermediate composl- tion. The formation L also intruded by numerous dikes and sills ranging in composition from dlabase to rhyo- lite. Bedding is generally massive. The maximum preserved thickness of the formation north of the McKin- ley fault is about 3,000 m. Everywhere north of the McKinley fault, the generally gently deformed Cant- well Formation rests with pronounced angular uncon- formity on intensely deformed older rocks of Precam- brian(?) to Early Cretaceous age. At locality 2, the Cantwell Pormation conslsts of fine- to medium-grained arkose. The finegrained variety ir gray to black end is extremely indurated, breaking with great difficulty. The medlum-gcained arkose is well sorted and contains grains of gray quartz, feldspar weathering to chalky-white chy, and dark-olored chert, and (or) quartz. A grayish-brown moderately well indurated mas sive conglomerate wlth a "salt and peppern coarse-sand matrix is present at locality 3. The subangular to weUrounded pebbles, as much as 3 cm in diameter, are composed of groy-green sandstone, dsrk gray and bLack chert, white to gay quartz, gay quartzite(?), and gray to black argillite. The matrix is a coarse sand of chert, quartz, quartzite(?) and (or) mgUte(?), and weathered feldspar. Iron-oxide coatings ere present on some of the grains. Also at locality 3 is a medium-grained "salt-and-pepper" arkose contahing a few pebbles and granules. The sand gains are of gray, graygreen, or black chert, gray to whlte quartz, feldspar weathering to white clay minerals, quartzite(?), and argillite(?). Gray to black arglllite containing carbonized f ragrnents of Metasequoia(?) sp. completes the Cantwell sequence at locality 3. A masslve mottled-gray-white-brown moderately well-Indurated to well-indurated conglomerate occurs at locality 4. The subangular to welk-rounded pebbles conslst of whlte quartz and gray and brown phyllite and quartzite. Most of the pebbles are 1 to 2 cm in diameter, but some we as large as 7 cm in diameter. Generally very little matrtx is present. Some of the rock samples from this locality appear to have been sheared by postdepositional deformation. The correlation of the CantweU Formation across the McKinley fault, based on stratigraphic and lithologic similarities, should be regarded as probable and not as certain. Nevertheless, the proposed correlation, Ln conjunction with the continuity of a Creta- ceous metamorphic belt across the McKinley fault and the occurrence of the same geologic formations on both sides of this fault, tends to support the interpre- tation of limited Cenozoic dextral offset dong the Denali fault system (Csejtey and others, 1982). The disparity in the volumes of the Cantweil Pormation exposed on apposite sides of the McKinley fault can be explained by southside-up vertical separation along the fault during post-Cantwell time. REFERENCES ClTED Beikman, A. M., Holloway, C. D., and MacKevett, E. M., Jr., 1977, Generalized geologic map of the eestern part of southern Abka: U.S. Geological Survey Open-File Report 77-169-8, scale 1:1,000,000. Capps, S. R., 1933, The eastern portion of Mount McKinley National Park, & Mineral resources of Alaska: Report on progress of investigations in 1930: U.S. Geological Survey Bulletin 836, p. 219-345. 2940, Geology of the Alaska Railroad region: U.S. Geological Survey Bulletin 907, 201 p. Csejtey, BQla, Jr., Cox, D. P., Evarts, R. C., Stricker, Q. D., and Poster, H. L., 1982, The Cenozoic Denali fault system and the Cretaceous accre- tionary development of southern Alaska: Journal of Geophysical Research, v. 07, no. 85, p. 3741- 3754. Forbes, R. B., Smith, T. B., and Turner, D. L., 1974, Comparative petrology md structure of the Mac laren, Ruby Range, and Coast Range belts: Im- plications for offset along the Denali fault system [abs.]: Geological Society of America Abstracts wlth Programs, v. 6, no. 3, p. 177. Crantz, Arthur, 1966, Strikeslip faults in Alaska: U.S. Geological Survey open-file report, 82 p. Wolfe, J. A., and Tanai, Toshimaaa, 1980, The Miocene Seldovia Point flora from the Kenai Group, Alaska: U.S. Geological Survey Professional Paper 1105, 52 p. Wolfe, J. A., and Wehrhaftig, Clyde, 1970, The Cant- well Formation of the central Alaska Range, & Cohee, G. V., Bates, R. G., and Wright, W. B., Changes in stratigraphic nomenclature by the U.S. Geological Survey, 1968: U.S. Geological Survey Bulletin 1294-A, p. A41-A46.
Page 1 and 2:
n Alas Accompli: ' I.S. GE OLOGI CA
Page 3 and 4:
I CONTENTS Page A bst raet ........
Page 5 and 6:
-- --A I ALASEU i nued rral expluru
Page 7 and 8:
........ igure .JB. ;5~ercn map ox
Page 9 and 10:
. , ".,k a. ,.e ,\a 1 y U11 IIIUUII
Page 11:
THE UNITED STATES GEOLOGICAL SURVEY
Page 15 and 16:
~ t I r n t S i m ~ ~ Alarr a ~ man
Page 17 and 18:
I -1977, RelImlnary documentat!on l
Page 19 and 20:
I I MaCenn, W. R., Perez, 0. J., an
Page 21 and 22:
were deslgned to impMve the accurac
Page 23 and 24:
Noatak Sandstom and is overlaln con
Page 25 and 26:
I (Nilsen and others, 1981a); (2) f
Page 27 and 28:
I that contains the Upper Devonian
Page 29 and 30:
who found Westeqaardodina sp., posb
Page 31 and 32:
Table 2 lists the means rtnd for th
Page 33 and 34:
' Noatak Vdley (fig. 129. This ice
Page 35 and 36:
3 EUMN OF MAP UNITS WAmWARY OUAERNA
Page 37 and 38: -om displacement of the cc tween th
Page 39 and 40: I US I Surlicial dcnrrua,ts [~dater
Page 41 and 42: I Plafker, George, Hudson, Travis,
Page 43 and 44: !omlensed iring vapors generated by
Page 45 and 46: and the thinning. -upward cycles .,
Page 47 and 48: Kellum, L. B., Devless, S. N., and
Page 49 and 50: 1912 sample (a mediumwey pumice blo
Page 51 and 52: various Utholagic units present Thu
Page 53 and 54: fault, and Its depositional basemen
Page 55 and 56: suggested by coplanar foUaticm and
Page 57 and 58: 1 slgnlficarrtly more umnlum (73&1,
Page 59 and 60: ecrSigtallized catadastic matrix of
Page 61 and 62: analyzed to determine whether Immob
Page 63 and 64: are tgplcd of both ocean-floor basa
Page 65 and 66: & Fclsic in~rutirt rucks 0 Eio~ite
Page 67 and 68: are Lrdlcated by coexisting @&ite+q
Page 69 and 70: (Mg3.09 pe2+ 0.69 pe 0.~1~0.01~~0.9
Page 71 and 72: westward into a narrow band that ex
Page 73 and 74: EXF'lANATIOW 66600' Contan-Apprnimn
Page 75 and 76: ! few fold closures are preserved.
Page 77 and 78: even thickness and conform to irreg
Page 79 and 80: (Alnus ap.), heaths (Ericaceae, + E
Page 81 and 82: terrane extends at least 300 krn to
Page 83 and 84: Table 19.--6tneral petrography of M
Page 85 and 86: were measured on 8 12-in. mass spec
Page 87: Thin lenses of cabonate packtone to
Page 91 and 92: in the 18 lava flows b thermoremane
Page 93 and 94: Upper Cretaceous shale in contact w
Page 95 and 96: Gran tz, Arthur, 1960, Generalized
Page 97 and 98: at 15 to 20 percent. Primary Inolus
Page 99 and 100: addition, this factor generally def
Page 101 and 102: Joreskog, K. G., Klovan, J. E., and
Page 103 and 104: Mineral qItWation end r ~ k t k W e
Page 105 and 106: 1 "~_liO-/ 200 1000 B roo C E % A B
Page 107 and 108: Smaller placer mines ere active on
Page 109 and 110: Figme 62.-Plant fassils from the co
Page 111 and 112: Hallam, Anthony, 1975, Alfred Wegen
Page 113 and 114: u ALASKA Figure 65.--Sketch map of
Page 115 and 116: F ' i a?.-Intertidal bluffs compose
Page 117 and 118: C-s - - Figure 70.-Products of eros
Page 119 and 120: curve is based indicates that 6.1 c
Page 121 and 122: sampled is related to widespread ma
Page 123 and 124: marble is alsa locally present In t
Page 125 and 126: Bedding in the conglomerate ranges
Page 127 and 128: 1 purpose of this study wes to dete
Page 129 and 130: The secona k~~-~ri?tation mmes that
Page 131 and 132: epizonb'l granitic Miss, mixed with
Page 133 and 134: 40 40 Forbes, R. B., and Engels, J.
Page 135 and 136: foliated and inequigranular end con
Page 137 and 138: I I thy euheclra. Sphene anhedra an
Page 139 and 140:
Quartz Alkali feldspar Plagioclase
Page 141 and 142:
F'@m 85.--Sketch map of Juneau area
Page 143 and 144:
HoUister, L. 8, 1966, Garnet zoning
Page 145 and 146:
! ~ bI8oO, (IN PERMIL) ~lqp~e 87.-8
Page 147 and 148:
Figure 90.-Offshore ereas discussed
Page 149 and 150:
Preliminerg analpsis of miemfauna f
Page 151 and 152:
Survey tn Alaekai AccompUshments hh
Page 153 and 154:
Gecllogical Survey Open-File Report
Page 155 and 156:
I provenance, and tectonia sIgnific
Page 157 and 158:
Keith, T. E. C, Barnes, Ivan, afrd
Page 159 and 160:
Open-Flle Report 8P811C, 19 p. + 2
Page 161 and 162:
United States Qeological Survey in
Page 163 and 164:
, ,. nldslra poblisbe!d by Prior, D
Page 165 and 166:
60, Alaska: Offshore Technology Con
Page 167:
Author Index [Page number underscor
Page 170 and 171:
Parks. Bruce ......................
show all

n Alas - Alaska Division of Geological & Geophysical Surveys - State ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?