n Alas - Alaska Division of Geological & Geophysical Surveys - State ...
n Alas - Alaska Division of Geological & Geophysical Surveys - State ... n Alas - Alaska Division of Geological & Geophysical Surveys - State ...
(Tanam and Llve- quadran@es; area 10, ffg. 23) in the Rampart district ara poorly fwsilifero~ and resulted in collections of radiolarim chert from structurally complex, little is presently known con- several dliferent terranes (flg. 24. Because the mks g the stratigraphic relations or ages of the Pigum 23.-Areas artd localltles In t iCral.4Laska &used in this volume. A listing of authorship, applicable figures and tables, and atticle paginetion (in parentheses) relating to the numbered arm follows. I, Aleinikoff, DM-Bacon, and Foster, figure 27, tables 8 and 5 (p. 45-48); 2, Aleinikoff, Foster, and others, figures 25 and 26, table 7 (p. 43-45)] 3, Bweck and others, figure 32, table 12 (p. 54-57); 4, Carter and Gdloway, figure 41 (p. 66-68); 5, Cllshing and Poster, 500 KILOMETERS I figures 39 and 45); 6, Wel-Bacon and Bacon, figures 28 end ZY ~p. 46-50); 7, Dusel-Bacon, figures 30 and 31, tables 10 and 11 tp. 50-54); 8, Poster, CusNng, and others, figure 38 (p. 62-64); 9, Poster, Weber, md Dutro, figures 36 and 37 ( . 6062); 10, Jones and others, figure 21, tabla 6 yp. 39-43); 11, Laird mcl others, figures 33 through 35, table 13 (p. 57-60); 12, I Weber and Ager, fipes 42 end 43 (p. 68-70); 13, Yeend (p. 65-66).
various Utholagic units present Thus, ages derived from dating of radlolarian chert provide important new information neeesary for correlating these rocks with nearby, better dated sections. RAMPART GROUP Acdirtg to Mertie (19371, the Rampart Group consists of basaltlc to andeaitic flows; basaltic, ende- sitic, and rfiyolltic tW and breocfa; and lesser amounts of interbedded chert, shale, argilli te, and Umestone. No type section has been established and the stcatlgrephio and structural relations of these heterogeneous rock types remain unclear. Certainly, some rocks, suah as the rhyolite tuff and breccia ex- posed southwest of Rampart, should b excluded from the group because they appear to be Cenozoic and to overlie unconformablg the more complexly deformed older rocks. Only two fmil Localtles, both near Point NO Polnt on the Yrikon River, wete known previdy from the Rampart Gmp. ?he fossils consist mainly of brgozoans occurring ms cI8st.s in overtuned prisrnatlc limestone. Aocording to Bm& and others (1969), these bryozaans are probably Permian, and the pelecy- pod prisms may belong to the Permian bivalve genus Atomodesma. These I& have served to assign a p~obable Permfan ege to the entire Rampart Group. Mafic intrusive rocks that cut the Umestone-bearing bedded sedimentary and volcanic sequence derlbed by Br-6 and others (1969) yield a Late Triassic or earliest Jurassic (2108 m.y .) potassium- age. Expsmes of the Rampart Group both north and south of the Yukon Wver and west of Point No Point consist mainly of thln septa of red chert and argllllte, maroon and green tuff, and minor volcmfc graywacke, intruded by enormous volumes of mafic intrusive rocks, primmity diebase and gabbro but also Inchding EXPLANATION SEDIMENTARY DEPOSITS (QUATERNARY CHERT ARGILLITE, AND GABBRO AND TERTIARY) I " 1 PALE~ZOIC~~ I GRANITIC ROCKS fh4BS0201C+M+inly Cmtaceaus in age FLYSCH DEPOSITS AND QUARTZITE (MESOZOIC) FLYSCH DEPOSITS (PERMIAN) I GfR2 I&MRZARF;,~A$-J?~ SLATE IC*MBR 1.4 N cottun RAMPART GROUP, MAFlC lNTRUSIVL ROCKS. ,, ~ ~ ~ l t AND BASALT TTRIASSIC? AND PALEOZOIC) SEDIMENTARY AND MINOR VOLCANIC Thw fault-Snwtcclh on upper plate ROCKS (DEVONIAN TO ORDOVICIAN) . 3 Radiolarlsn cben mmple locality and numkr METASEDIM ENTARY ROCKS (LOWER? (sac Table 6) PALEOZOICkMay ~nclude some Precambrian 'pb Pillow bnsrlt motascdimmtary rocb F@se 24.--Qeologlc map of the Rampart district east+entr&l Alaska, ahowing locations of dated radiolarian- chert samples. Modified from Eberleh rind others (1977).
- 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: 1912 sample (a mediumwey pumice blo
- 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 and 88: Thin lenses of cabonate packtone to
- Page 89 and 90: The cantwell(?) Pormation south of
- 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
various Utholagic units present Thus, ages derived<br />
from dating <strong>of</strong> radlolarian chert provide important new<br />
information neeesary for correlating these rocks with<br />
nearby, better dated sections.<br />
RAMPART GROUP<br />
Acdirtg to Mertie (19371, the Rampart Group<br />
consists <strong>of</strong> basaltlc to andeaitic flows; basaltic, ende-<br />
sitic, and rfiyolltic tW and breocfa; and lesser<br />
amounts <strong>of</strong> interbedded chert, shale, argilli te, and<br />
Umestone. No type section has been established and<br />
the stcatlgrephio and structural relations <strong>of</strong> these<br />
heterogeneous rock types remain unclear. Certainly,<br />
some rocks, suah as the rhyolite tuff and breccia ex-<br />
posed southwest <strong>of</strong> Rampart, should b excluded from<br />
the group because they appear to be Cenozoic and to<br />
overlie unconformablg the more complexly deformed<br />
older rocks.<br />
Only two fmil Localtles, both near Point NO<br />
Polnt on the Yrikon River, wete known previdy from<br />
the Rampart Gmp. ?he fossils consist mainly <strong>of</strong><br />
brgozoans occurring ms cI8st.s in overtuned prisrnatlc<br />
limestone. Aocording to Bm& and others (1969),<br />
these bryozaans are probably Permian, and the pelecy-<br />
pod prisms may belong to the Permian bivalve genus<br />
Atomodesma. These I& have served to assign a<br />
p~obable Permfan ege to the entire Rampart Group.<br />
Mafic intrusive rocks that cut the Umestone-bearing<br />
bedded sedimentary and volcanic sequence derlbed<br />
by Br-6 and others (1969) yield a Late Triassic or<br />
earliest Jurassic (2108 m.y .) potassium- age.<br />
Expsmes <strong>of</strong> the Rampart Group both north and<br />
south <strong>of</strong> the Yukon Wver and west <strong>of</strong> Point No Point<br />
consist mainly <strong>of</strong> thln septa <strong>of</strong> red chert and argllllte,<br />
maroon and green tuff, and minor volcmfc graywacke,<br />
intruded by enormous volumes <strong>of</strong> mafic intrusive<br />
rocks, primmity diebase and gabbro but also Inchding<br />
EXPLANATION<br />
SEDIMENTARY DEPOSITS (QUATERNARY CHERT ARGILLITE, AND GABBRO<br />
AND TERTIARY) I " 1 PALE~ZOIC~~<br />
I GRANITIC ROCKS fh4BS0201C+M+inly<br />
Cmtaceaus in age<br />
FLYSCH DEPOSITS AND QUARTZITE<br />
(MESOZOIC)<br />
FLYSCH DEPOSITS (PERMIAN)<br />
I GfR2 I&MRZARF;,~A$-J?~ SLATE IC*MBR 1.4 N<br />
cottun<br />
RAMPART GROUP, MAFlC lNTRUSIVL ROCKS. ,, ~ ~ ~ l t<br />
AND BASALT TTRIASSIC? AND PALEOZOIC)<br />
SEDIMENTARY AND MINOR VOLCANIC<br />
Thw fault-Snwtcclh on upper plate<br />
ROCKS (DEVONIAN TO ORDOVICIAN) . 3 Radiolarlsn cben mmple locality and numkr<br />
METASEDIM ENTARY ROCKS (LOWER?<br />
(sac Table 6)<br />
PALEOZOICkMay ~nclude some Precambrian 'pb Pillow bnsrlt<br />
motascdimmtary rocb<br />
F@se 24.--Qeologlc map <strong>of</strong> the Rampart district east+entr&l <strong>Alas</strong>ka, ahowing locations <strong>of</strong> dated radiolarian-<br />
chert samples. Modified from Eberleh rind others (1977).
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