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

westward into a narrow band that extends cross cow-
try along a nearly straight come for more than 19 km
(fig. 36). In the weatern Crazy Mountains, siinfler-
appeering Umestone occurs in several outcrops,
possibly isolated by faulting or erdon.
Most of the large outcrop (fig. 37) In the eastern
Crazy Mountalns weather gray and are of medium-
light-gray to medium-gray Umestone wlth yellowish-
brown mottling. A minor amount of darkgray lime-
stone occurs looally, and a few darkway smooth-
surfaced dolomite beds are interlnyered. The lime
stone is fine grained with incipient recrystallization; it
is generally masslve but may be thin bedded locally.
Commonly, small white calcite veins and veinlets Lace
the outcrop. The limeatone generally has a spongy-
appearing solutionpf tted surface; rillenstein and other
small solution features occur.
Figure 37.-Typical outcrop of Ernsian limestone in the
eastern Cmzy Mountains. View westward.
At two loudtias, corals Vlat were collected in
1980 suggest an Early Devonian age, These corals
were identified by W. A. Oliver, Jr., who reported
from one locality: "80A Fr 307 (USGS 10314-SD), see.
8, T. 10 N., R. 14 E.; Circle C-2 quadrangle.
closely related $ecies of ~artind~h~llum &d cl.
Spangonaria are Emsian.
Also present are indeterminate bryozoans and
the two-holed cdnoid wide Gasterocoma bicaula
Johnson and Lane. J. T. Dutro , Jr., indicated an
Emsian-early Eifelian agerange for the distinctive
crinoid ossicle; the consensus is that the most likely
age is Emsian (late Early Devonian). h Emsian age is
also supported by data from conodonts (Anita Harris,
oral commun., 1981). Fieldwork in 1981 shows that
much of the limestone in the eastern Crazy Mountains,
on trend .with locality 103144D, contalm the two-
holed crinoids and that the entire outcrop belt may
reasonably be dated by this collection as probable
Bmsian.
Another collection, BOA Wr 312 (UWS 10315-
SD), to the west b the Circle M quadr-e, westm
Crazy Mountains (fig. 961, contains, according to
Oliver: Amphlpora, StrIatopora, Syringopora, cf.
Pseudoplasmopora, and cf. Spinolasrna. Tnis collection
h also kly Devonian but may be slightly Older Lhan
collection 10314-SD. Conodonts also indicate a slight-
ly older age for this limestone (Anita Hawis, oral
Corn mun., 1981).
The stratigraphic and structural relations of the
rocks adjoidng the Umestone are unclear. In the
eastern Crazy Mountah, the Ilmestone, on the south,
has a covered contact with a thick coarse chert-pebble
congumerate of unknown age and attitude. To the
north, the Urnatone lles in apparently unconformable
(covered) contact with a sequence of rocks including a
thlck very dark gray, nearly black arenaoeous Lime
stone, olive, green, maroon, and gray argillite, a lew
thin beds of chert, and a thick section of quartzite and
stltstone. OUve argillite has yielded the Early Cam-
brian trace fossil Oldhamla (Chuckin and Brabb,
1965). The nature of both the north and south contacts
of this limestone b uncertain, and neither wmnforrn-
ities nor fault contacts completely satisfy the mapped
geologic relstiona.
Faunal evidence for post-Devonian cocks in the
main part of the mazy Mountains is absent, except lor
the occurrence of late Paleozoic and early Mesozoic
radiolarims (D. L. Jones and others, written cornmun.,
1981) in chert associated with mafic igneous rocks that
crop out in the northern part of the study area and are
included in the Circle Volcanics (Mertie, 1937).
A different sequence of Limestone and clastic
rocks crops out on the south bank of the North Pork of
Preacher Creek, just south of the western Crazy
Mountalns. In exposures along the high bluff, about
300 m of massive-appearing bedded limestone contalns
plsotites, spongellke bodies, and possible wchaeo-
cyathlds. This Limestone weathers medium gray and is
cream cobred on some vertical surfaces; it k general-
ly medium gray on fresh surfaces and is fine grained
but mostly recrystallized. The limestone beds are 2.5
to 30 cm thiak. Medium-gray very fine grained limy
mudstone, some of which is finely laminated with
millimeter-thiok tan-colored siliceous layers, is locally
interbedded. Thin bands of black chert nodules or
lenses also occur, but they rue rare. Stylolites are
present in some of the very fine grained lImy
mudstone.
This Umestone, on the west side, is in probable
fault contact with red and green argillite, darkgray to
black limestone, dolomite, and basalt, inchding pilow
basalt. Its lithology and pwlble faunal content
suggest a correlation with the Lower Cambrian Funnel
Creek limestone of the Tatonduk fiver area (Brabb,
1967). The adjacent rocks have Uthologies suggestive
of part of the Tindir Group (Proterozoic). Although
these rocks include maroon and green argillite, they
are unlike any other lithologic sequence seen in the
Yukon-Tanana Upland. The block containing this un-
usual group of rocks appears to be exotic: it might
have moved in from the southeast, possibly caught up
between two fault strands of the Tintins Eault system
(fig. 36).