DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY

145°48'

145°30°

145°00°

69°40 —
=

OPEN FILE REPORT
89-123

144°30°
69°40"

69°35’

145°48'

.
 DALASKA'

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AREA OF MAP
CORRELATION OF MAP UNITS
Qa Ql \ QUATERNARY CENOZOIC
Jo JURASSIC
MESOZOIC
TRIASSIC
RPs AND.
PERMIAN
PENNSYLVANIAN PALEOZOIC
PM AND
MISSISSIPPIAN
Op€ku
Op€k | p€km
pé€ki PRECAMBRIAN
pé€ub
p€u
EXPLANATION

~~~ CONTACT--Dashed where approximately located, dotted where
concealed

—————~  FAULT--Dashed where approximately located, dotted where concealed

a4444.. THRUST FAULT--Dashed where approximately located, dotted where
concealed, queried where probable. Sawteeth on upper plate,
solid where thrusting has emplaced older rocks on younger rocks,
open where detachment is uncertain and parallel to bedding

MAJOR FOLD

[Se — Anticline

—_}—_ Syncline

30
= STRIKE AND DIP OF INCLINED BEDS
1 CHEMICAL ANALYSIS SAMPLE LOCALITY--See table 1 for

chemical analysis

145°30'

2

Jg

‘RPs

Op€k
Op€ku

SCALE 1:63 360

2

3 4 5 MILES

2 3

4 5 6 7 KILOMETERS

5
cece

DESCRIPTION OF MAP UNITS

Alluvium (Quaternary)--Sand, silt, and gravel in lower parts of valleys and
along streams and rivers. Includes some coalluvium and fan deposits

Landslide deposits (Quarternary)-- Dislocated mass of Lisburne Group at
northern edge of the area about 2.5 km west of Itkilyariak Creek

Gabbro (Jurassic)--Dark-gray, reddish-brown-weathering, fine- to medium-
grained rock intruded into unnamed Proterozoic shale, siltstone, and
quartzite. Consists of approximately equal amounts of labradorite and
augite and accessory amounts of opaque crystals and apatite. Labradorite
crystals are subhedral to anhedral and commonly 0.6-1.0 mm long.
Augite occurs between labradorite grains as separate anhedral crystals or,
more commonly, as clusters of mutually interfering crystals 0.5-0.8 mm
across. Augite crystals have abundant exsolution laminae and have been
partly converted to chlorite. The chemical composition is given in table 1.
The age of the rock, as determined by K-Ar methods on plagioclase, is
161+5 Ma (Reiser and others, 1970). Thickness is several tens of meters

Sadlerochit Group (Triassic and Permian)--Consists of the Lower Triassic
Ivishak Formation and the Upper Permian Echooka Formation. The
Ivishak is composed mostly of silty shale and siltstone and subordinate
clean, massive quartzite. The Echooka is dark orthoquartzite, sandstone,
and siltstone together with calcareous siltstone and lime mudstone. Rocks
of the Sadlerochit Group are exposed in steep slopes and ridges along the
southern part of the map area. Thickness is at least 200 m

Lisburne Group (Pennsylvanian and Mississippian)--Consists of the
Wahoo Limestone of Early and Middle Pennsylvanian age and the Alapah
Limestone of Late Mississippian age. The Wahoo is mainly a sequence of
shoaling -upward cycles of shallow marine, bryozoan-echinoderm
calcareous algae packstones to ooid-foraminiféral grainstones that grade
upward into supratidal dolomite. The underlying Alapah consists of lime
mudstone and bryozoan-echinoderm- brachiopod wackestones and
packstones, and it contains thin dolomite beds. The Alapah was deposited
in a shallow marine environment to possibly subtidal and intertidal
environments. Thickness ranges from 450 m in the western part of the
range, where the Alapah makes up 350 m of the section, to 520 m in the
eastern part, where the two formations are of about equal thickness

Nanook Limestone (Ordovician) and Katakturuk Dolomite
(Proterozoic) undivided --Locally divided into:

Upper member (Ordovician and Proterozoic)--As mapped includes light-
to medium-gray limestone and dolomite of the upper part of the Nanook
Limestone. Ordovician trilobites similar to those reported from the
Nanook in the Shublik Mountains have been found in the Mt. Michelson
C-2 quadrangle in NE1/4, SW1/4 sec. 19, T. 3 N., R. 30 E. (James
Clough, oral commun., Feb. 8, 1989). Thickness of the Nanook may be
as much as 100 m.

The Katakturk Dolomite is light- to dark-gray and pale brownish-
gray, fine- to coarse-grained dolomite. Bedding commonly indistinct.
Common sedimentary structures are birds-eyes, zebra beds with late,
void-filling baroque dolospar, planar cryptoalgal laminites, intralaminar
shrinkage cracks, contorted structures composed of algae laminae, rip-up
clasts, small scale cut and fill structures, and cross beds. Some beds are
formed of dolomicrite with crystals in the 2-6 jum size range and excellent
preservation of original microfabric. The allochems are ooids, pisoids,
peloids, mud pellets and coated grains, fragments of algal mats,
cryptoalgal particles, stromatolites, and small grains with micritic
envelopes. Many dolomite beds are composed of 200-500 um anhedral
crystals of dolomite in which the original microfacies are obliterated.
Solution breccias several tens of meters thick composed of rounded to
angular dolomite clasts from sand to blocks 1 m across near the top of the
member in the central part of the area. Stromatolites as much as 51 cm
high occur near the base at several localities. Dolomicrite packstones and
grainstones have some intraparticle and interparticle porosity. Most of the
member consists of shoaling-upward sequences deposited under subtidal-
intertidal to supratidal environments. Thickness at least 1,200 m

CONTOUR INTERVAL 50 FEET

pékm

péki

Middle member (Proterozoic)--Medium- to very dark-gray dolomite that
from a distance commonly crops out in prominent, well defined beds,
many of which weather black. Biscuit stromatolites present locally at the
upper contact, and pisoid packstone beds totalling about 2 m thick
commonly occur a few meters below the upper contact. The member is
formed of shoaling-upward sequences deposited in subtidal to supratidal
environments. Each cycle is of varying thickness and complexity and
consists of massive dolomite. The sedimentary structures are algal-
laminated sediments, rip-up clasts, mud cracks, birdseye structures,
stromatolites, pseudomorphs of anhydrite diapirs, pseudomorphs of
nodular anhydrite, and pseudomorphs of "chicken-wire" texture anhydrite
to zebra beds (the voids of the pseudomorphs are filled with baroque
dolomite and to a lesser extent with quartz). Some beds are dolomicrite
packstones formed of cryptoalgal particles with rip-up clasts and flat
pebble conglomerate. Cross-beds in sets 5-50 cm thick are present in
dolomite beds in the middle of the member. The upper part of the lower
quarter of the middle member has a prominent zone 2 m thick of ooid to
pisoid packstone with some vuggy porosity. Well developed zebra beds
with acicular and columnar dolomite cement, dolospar, and baroque
dolomite together with sparse black chert nodules in dark-gray dolomite
occur below the ooid-pisoid packstone beds. Some dolomitrites are
formed of dolomite crystals in the 2-6 jim size range with excellent
preservation of the original microfabric. The allochems are ooids,
pisoids, peloids, mud pellets and coated grains, cryptogalgal particles,
fragments of algal mats, stromatolites, and small grains with micritic
envelopes. The pisoids and oncolite packstone beds are interpreted as
having formed on very low energy evaporitic tidal flats. Cryptoalgal
sedimentary structures in the form of oncolites, laminites, and
stromatolites are common in the subtidal to supratidal carbonate rocks.
These dolomites with 2-6 jum rhombs and well preserved sedimentary
details result from the dolomitization of allochems and cements of the
calcium carbonate precursor (Zempolich and others, 1988). The dolomite
is thought to have replaced directly the primary aragonite and high
magnesium calcite. Early and late baroque dolospar cements record
dolomite cementation during continued open-space filling. Many dolomite
beds are composed of 100- 500 j1m anhedral crystals of dolomite with the
destruction of the original microfacies and microfabric. In many of the
dolomites, intercrystal pore space is in the micron to millimeter size range
and has been filled with quartz. The resulting dolomite appears to be
arenaceous. Thickness about 600 m

Lower member (Proterozoic)--Mostly light- to medium-gray, fine- to
medium-grained dolomite capped with a unit a few tens of meters thick of
black shale, black calcareous sandstone, and tan-weathering platy
dolomite. Dolomite below the upper unit appears to be a replacement of

pelotoidal packstone. Well developed zebra beds with baroque dolospar
are prominent 20 m below the top of the unit. These beds are a few
centimeters thick and contain abundant chert. The chert is interpreted as
vug-filling pseudomorphs of anhydrite. This part of the section has well
developed stromatolites of the laterally linked hemispheroid type.
Associated with the stromatolites are dolomicrites and partly silicified
oolid to pisoid packstones. Some beds have abundant zebra structures
formed by baroque dolospar pseudomorphs filling voids after nodular and
"chicken wire" anhydrite. Associated with these shoaling-upward cycles
are algal mats, stromatolites, peloids, mudcracks, chips, and
intraformational conglomerates. Generally in this member, internal
moldic voids in the halfmoon ooids, ooids, pisoids and small fenestral
cavities in the algal mats and stromatolites have been partly filled with
acicular, columnar cement, dolospar, baroque dolospar, crystal silt and
internal sediment and/or spar dolomite and/or quartz. Intercrystal voids
also have been filled with acicular cement and/or quartz. Dolomicrite
ooid-pisoid packstones and grainstone have varying amounts of
intraparticle and interparticle porosity. Vuggy porosity also occurs
between the planar cryptoalgal laminites. The underlying dolomite that
forms the bulk of this member is a monotonous sequence of dolomites
and dolomicrites that locally contains coated chips, oolites, and zebra
beds. Sedimentary structures indicate that the member was deposited in
subtidal to supratidal environments as a sequence of complex shoaling-
upward cyqles. Locally weathers to prominent spires. Shaly beds at top
are rarely exposed because of structural dislocation and cover of
solifluction debris. Maximum thickness about 750 m

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144°30'

Geology by C. T. Wrucke, A. K. Armstrong, and J. S. Kelley, 1988,
and J. S. Kelley and C. M. Molenaar, 1985. Contact at base of
unnamed basalt (p€ub), for part of the contact between the
Katakturuk Dolomite and the unnamed rocks (p€u) west of Itkilyariak
Creek, and for the gabbro (Jg) west of Itkllyariak Creek are from
Reiser and others (1970).

Unnamed Rocks (Proterozoic)--Divided into:
Basalt--Dark-gray, faintly reddish flows of porphyritic basalt occurs near the

Nularvik River. Consists of dull greenish-gray plagioclase in
glomeroporphyritic clots 2-4 mm across and phenocrysts 2 mm long in an
intergranular groundmass of plagioclase laths and fine-grained augite(?),
opaque grains, and chlorite. The plagioclase has been converted to albite
flecked with white mica. Abundant amygdules are lined with chalcedony
and filled with chlorite. Calcite fills some amydules and occurs locally in
the groundmass. The texture and chemistry (table 1) of the rock show
that it is basalt. The albite content suggests that the flows have been
subjected to greenschist facies metamorphism. Thickness possibly 250
m, top not exposed

Sedimentary rocks--Siltstone, shale, dolomite, and quartzite unconformably

beneath the Katakturuk Dolomite. Siltstone occurs as fine laminations
separated by greenish-black shale in layers commonly 0.5-5 mm thick.
Breaks into shaly chips and thin plates. Locally cut by cleavage at low
angle to bedding. The quartzite is nearly pure quartz arenite, very light-
gray, fine-grained, well sorted, and structureless. Quartz grains are
mostly subangular to subrounded, a few are rounded and have
overgrowths. Most have nonundulatatory extinction. Also present are
trace amounts of rounded tourmaline in grains about the same size as the
quartz. A few quartzite beds have hematitic cement. Some quartzite beds
are continuous, others are lenticular. Discontinuous beds probably are
lenticular because of structural dislocations. Dolomite in the unnamed
rocks west of Mount Weller is light- to medium-gray, commonly medium
bedded, and forms a section 100 m or more thick. Unnamed rocks east of
Mount Weller lack dolomite. Quartzite in that area is fine to medium
grained and well sorted. A few beds have ripple marks. Some fine-
grained quartzite in that area has black hematite between quartzite
laminations. Interbedded with the quartzite is subordinate dark-gray
siltstone in sections 3 m thick and minor black shale in sections 2-3 m
thick. Thickness 1,000-1,500 m

Table 1.--Chemical analyses of basalt and gabbro from the Sadlerochit
Mountains.
[Analyses by U.S. Geological Survey using X-ray spectrographic
techniques. Analyst, D.V. Vivit. Wet chemical techniques used for FeO,
H20*, H20-, and CO2. Analyst, S.T. Pribble.]

Map unit J Cub
Map no. r ‘ 2
Field no. S66F SS9A
ae 46.5 47.0
2 2-3 16.1
Fe203 6.23 8.86
FeO 10.57 3.18
MgO 5.8 58
CaO 10.6 10.1
Na2O 19 3.0
K20 0.32 1.0
H20+ 1.83 17)
H20- 0.30 0.41
TiO) 2.34 0.90
P205 0.12 0.08
MnO 0.22 0.14
CcO2 <0.01 1.49
SUM 99.0 2
Rock type Gabbro Basalt

GEOLOGIC MAP OF THE KATAKTURUK DOLOMITE, SADLEROCHIT MOUNTAINS, ALASKA

BY

Chester T. Wrucke, John S. Kelley, and Augustus K. Armstrong

1989

This map is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial
standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is
for descriptive purposes only and does not imply endorsement by the U.S. Government.