are inferred from deposits at recognizably differ-
il
Deposits of the lower intertidal zone--In
ent, somewhat terrace-like levels; however, no
some places include driftwood and gravel
in a shoreward-most part of deposit where
shorelines have been recognized definitively. The
they form discontinuous storm beach.
land/water interface probably fluctuated repeat-
Reworked twice daily when covered by wa-
edly as glacier fronts withdrew and then read-
ter at high tides; exposed a low tides.
vanced and as world-wide sea level fluctuated,
Deposits extend into area mapped as water
and also as the land surface responded to regional
where they are exposed at low tides. Upper
glacioisostatic and tectonic effects. Inlet water
boundary may be a few meters above mean
was at least partly in contact with glacier ice, as
high water.
reflected in both the volume and the variety of
iu
material types, especially in their relative coarse-
Deposits of the upper intertidal zone--
Locally more sandy and gravelly than
ness and poor sorting. These deposits consist of
lower-zone deposits, especially in upper-
varying combinations of interbedded diamicton,
most parts of zone, which are covered by
stony silt, fine sand, silt, clayey silt, and silty clay,
water only at times of exceptionally high
with coarser sand and gravel present locally.
tides coupled with major storms. Contain
Contacts are generally well defined; contacts
some driftwood and fine gravel as well as
between adjacent glacioestuarine deposits are
finer organic and windblown material. Sur-
located only approximately, but deposits are
face marked by standing water in some ar-
probably not in gradational contact. Topography
eas where drainage is very poor.
is commonly smooth but marked locally by small
Beach deposits--Chiefly sand with some
ib
subdued hills or minor surface irregularities;
gravel, well bedded and sorted; locally
slopes are very gentle to moderate
driftwood laden near base of bluffs. Encom-
pass the lower and upper intertidal zones
Bootlegger Cove Formation--(Bootlegger
bc
along base of bluffs in northern part of map
bcu
Cove Clay of Miller and Dobrovolny
area; elsewhere not shown separately from
[1959]; redesignated as Formation in
map unit s but shown on Figure A3. Near
Updike et al. [1982]). Silty clay and clayey
shoreward end of Eagle River Flats, form
silt with minor interbedded silt, fine sand,
belt between upper and lower intertidal
fine to medium sand, and thin beds of
zones.
diamicton, and with scattered pebbles and
cobbles in widely varying concentrations.
Older estuarine deposits (Holocene). These are
Brackish-marine microfossils are present
only rarely flooded by present day high tides.
throughout much of the formation
They are more firm than modern estuarine depos-
(Schmidt 1963, Smith 1964); mollusk shells
its. Contacts are well defined, except indefinite in
in one horizon have an uncalibrated radio-
the part adjacent to younger deposits. Topography
carbon age of about 14,000 years (Schmoll
is smooth, locally incised by channels of small
et al. 1972). Thickness as much as 35 m
streams; slopes are nearly flat.
(Updike et al. 1988), quite variable because
of irregular lower and upper contacts
io
Intertidal deposits--Chiefly silt, fine sandy
(Trainer and Waller 1965). Principal
silt, and fine sand, well bedded and sorted;
deposit of ancestral Cook Inlet during and
may include some thin beds of peat, drift-
immediately following withdrawal of gla-
wood, and other organic material, and
cier ice. Occurs widely in subsurface
windblown material. Thickness commonly
underlying deposits mapped at the sur-
several meters to possibly a few tens of
face from north of the Elmendorf Moraine
south to bluffs near Turnagain Arm. Sensi-
meters. Occur extensively in Eagle River
tive zones within formation responsible
Flats and locally near mouth of Fire Creek.
for catastrophic landsliding along bluffs
ibo
Beach deposits--Chiefly sand with some
west of map area during large-magnitude
gravel. Thickness probably a few meters.
earthquakes such as that of 1964 (Hansen
Occur locally marginal to south side of
1965). Present knowledge of distribution
Eagle River Flats.
and age of formation well summarized by
Glacioestuarine deposits (late Pleistocene). These
Reger et al. (1995). Shown mainly within
accumulated in a variety of environments in
map unit s (Fig. 4). bcu is a concealed
ancestral Cook Inlet. Several different water levels
occurrence at Glenn HighwayBoniface
62
to contents
Previous Page
