Cretaceous and Tertiary Stratigraphy of the Elk Neck Area, Northeastern Maryland: Elk Neck State Park, Maryland, July 12, 1989

31 Pages·2.188 MB·English

by  James P. Owens, John D. Glaser(auth.)

Cretaceous and Tertiary Stratigraphy
of the Bk Neck Area,
Northeastern Maryland
Elk Neck State Park, Maryland
July t 2, t989
Field Trip Guidebook T2t t
Leader: James P. Owens
Associate Leader: John D. Glaser
American Geophysical Union, Washington, D.C.
Copyright 1989 American Geophysical Union
2000 Florida Ave., N.W., Washington, D.C. 20009
ISBN: 0-81590-580-3
Printed in the United States of America
COVER View of Elk Neck bluff.
Leader:
James P. Owens
U.S. Geological Survey
Mail Stop 926
12201 Sunrise Valley Drive
Reston, VA 22092
Associate Leader:
John D. Glaser
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218
IGC FIELD TRIP T21!:
CRETACEOUS AND TERTIARY STRATIGRAPHY OF THE ELK NECK AREA,
NORTHEASTERN MARYLAND
James P. Owens
U.S. Geological Survey, Reston, Virginia
John D. Glaser
Maryland Geological Survey, Baltimore, Maryland
INTRODUCTION Delmarva Peninsula to the east. The central
bedding styles and particularly the
Elk Neck is a small peninsula which lies compositional differences between the
at the northern end of the Chesapeake Bay. Potomac and Pensauken formations will be
This peninsula is an erosional remnant of a discussed.
once more widespread Coastal Plain. The
peninsu1a is re1ative1y sma11, approxirnately Geologic Setting and Geologic History of the
13 miles long and 5.5 miles wide at its Elk Neck Peninsula
widest point. Elevations within the
peninsula range from sea level to just over The formations examined on this field
300 feet above sea level. The west side of trip lie within a large continental margin
the peninsula is characterized locally by basin named the Salisbury embayment (fig.
steep bluffs and numerous landslides. 1). Sediments in the emerged part of this
Because of the continued sluffing in the basin are as much as 8000 feet in
land slide areas, the exposures continually thickness. In some areas, rocks of Lower
are alternately covered or uncovered, and Cretaceous or older age range up to 60
the sections shown in this report may not be percent of the basin thickness (fig. 2).
the same when the field trip is run. The Lower Cretaceous rocks crop out along the
east side of the peninsula is less inner margin of the Coastal Plain from
precipitous than the west side. Here the Virginia to New Jersey (fig. 3). In that
land surface descends more gradually to the region these sediments have been assigned to
Elk River. The field trip will concentrate the Potomac Formation or Potomac Group of
for the most part on the exposures along the some. The Salisbury embayment is the only
west side of the peninsula in the vicinity place in the entire Gulf and Atlantic
of Mauldin Mountain near Elk Neck State Coastal Plains except for Texas where beds
Park. Of particular interest here will be of this age crop out. The Potomac
the exposures of the Potomac Formation of Formation is thick and well exposed at Elk
late Early to early Late Cretaceous age. As Neck. This formation is overlain by a thin
much as 135 feet of the Potomac Formation sequence of marine to marginal marine Late
are intermittently exposed at this locality Cretaceous formations (late Santonian to
which is an unusually thick exposure of the late Campanian in age). The upper part of
Potomac Formation. The Potomac Formation is this marine sequence is truncated by a
overlain by a thin series of deeply highly dissected coarse gravelly unit called
weathered marine and marginal marine the Upland Gravels. The age of these coarse
units. If access is available to the top of clasts is poorly known but most
the bluff, these formations will also be investigators consider this unit to be
examined briefly in order to illustrate the Tertiary(?) in age. Following the
differences in bedding style between the deposition of these gravels the Coastal
non-marine beds of the Potomac Formation and Plain was uplifted and dissected. Another
the marine-influenced younger Cretaceous gravelly unit (Pensauken Formation - middle
formations. The field trip will also visit Miocene age) was then emplaced along the
the southernmost part of the peninsula at eastern and southern part of the
Turkey Point. Here a channel of the middle peninsula. This gravelly unit is widespread
Miocene Pensauken Formation has eroded to the east in the Delmarva Peninsula where
deeply into the underlying Potomac it is the major surficial unit. During the
Formation. The Pensauken like the Potomac Pleistocene the modern form of the peninsula
Formation is a fluvial unit. The Pensauken was developed. The west side of the
deposits on Elk Neck Peninsula mark the peninsula is bordered by Chesapeake Bay, a
western boundary of a highly eroded gravel drowned estuary formed in 1ate Wisconsin
sheet which caps the northern part of the time. The east side is bordered by the Elk
T211 :
GeorgesBanktrough
I-------\~ ~-
NEW YORK • CONN ............"...".... -) ),
_-----~ ,\ . /',/~/{~~\\)1/~///~~~~~~fQ
, _------ '..r-.. ~' ///' tt..»·' /~~~~,rr>
L----- /~~ S'\)
t'N··J / ~G--~ ~
N \ //~~s~~~
• PENNSYLVANIA Raritan//
'\ . ' I. embayment /~ ~'b
, South New Jerseyhigh , l I' . /(~~~~
I A ' ) ~ ~" I/~~~~
~\ ---- 1> ~ ,~
:~l.- _/.-.-..-.--;:r::M-ne(- 8 'I
J' ----\ ,---' , iIj' ,1'1II..I,1..-ItI6altimoreCanyon
./ · / J I / I / trough
J WEST , \i .. I I / I
j-
VIRGINIA"r-Salisbury \ : lEI I
,.' jembayment 1,:~5' I
" Fort II
\, ,IVIRGINIA .f: Monroe \1\
,/.._--."" f hi~~-=:::: \:
I' --------;:- --- ( \'
/::--------r-- \,
~~
.- /_.r"" NORTH (,0 CAROLINA \ Albemarleembayment
, ~--
./1'-/ /------~; ... .. capel
_----.-1----( 'lJ~
"-" .., .... Fear J
\ \:h.i-gh--./
· 'e' SOUTH /
\ GEORGIA ~<::-(:'..CAROLINA
~ "'.. I Generalized outlineof
\. \, ! basinsand highs
,X
o 200 KILOMETE~S
I
FIGURE 1 Diagram showing the major basins and highs of the western
Atlantic continental margin (from Owens and others, 1968). The
Salisbury embayment, the largest of these hasins, is the site of
the field trip.
A A'
I CHESAPEAKE BAY DELAWARE BAY I
U.S.G.S. J&JEnterprises-
NorfolkTW-l E.G.TaylorI-G SoconyVacuum AnchorGas U.S.G.S.
Bethards1 Dickinson1 IslandBeachPark1
o 25 50 KILOMETRES
I I VerticalexaggerationapproximatelyX42
FIGURE 2 Coast parallel cross-section showing the distribution of the Potomac Formation in
the Salisbury embayment. As shown the Potomac Formation is thickest beneath the Delmarva
Peninsula where it comprises over 60 percent of the entire Coastal Plain section (Minard
and others, 1976).
T211: 2
of Elk Neck. J.A. Wolfe, who analyzed the
River which apparently has the same late pollen, suggested that the pollen in these
Pleistocene origin as the Chesapeake Bay. beds was younger than pollen zone lIB and
older than the Raritan Formation pollen of
Stratigraphy. The formations occurring New Jersey and, therefore, was probably
on the Elk Neck peninsula region are shown earliest Cenomanian in age. He'referred to
in tab1e 1. In all, 7 formations are this pollen zone as the"El k Neck beds."
present. The bay fill of Holocene to Later, Doyle (1969) and Doyle and Robbins
Wisconsinan age is not exposed but is known (1977) dr ppedthename Raritan for the
0 II II
to be present from bottom studies of "Elk Neck beds" and included these beds in
Chesapeake Bay. All the other units crop the Patapsco Formation. In these
out on the peninsula. As can be seen in the publications the "Elk Neck beds" or youngest
age part of table 1, there are typically Patapsco were designated pollens zones IIC
large time gaps between many of the units, a and III. Doyle (1982) and Hansen (1982)
situation one might expect along the basin reexamined the pollen in the deepest parts
margin. Because of time constraints the of wells in the lower Delmarva Peninsula.
major focus of this field trip will be only Doyle found a pollen assemblage in the
on the Potomac and Pensauken Formations. lowest beds which pre-dated pollen zone I
found in the base of the up-dip wells. He
POTOMAC FORMATION called this lower palynozone pre-zone I and
assigned a Berriasian age to this zone.
The oldest formation exposed on the Elk Hansen named the pre zone I beds the Waste
Neck peninsula is the Potomac Formation. Gate Formation. In summary, according to
This unit was originally named by McGee the classification favoring a group status,
(1886) for the basal sediments exposed in the Potomac includes the Waste Gate
the District of Columbia and nearby areas. (oldest), Patuxent, Arundel and Patapsco
Later, Clark and Bibbins (1897) subdivided (youngest). The Potomac Group or Formation
the Potomac Formation in the same general as presently defined, therefore, has
region into the Patuxent, Arundel, Patapsco sediments which range from Berriasian to
and Raritan formations and raised the earliest Cenomanian. The relationship of
Potomac to group status. The Raritan of New these zones to the European and Gulf Coast
Jersey subsequently was found to be younger stages' isshown in tab1e 2. As shown, the
than the Potomac Group and was dropped from Potomac Group sediments were deposited
the group. The stratigraphic definition intermittently over a period of about 35-38
prevai1eduntil 1966 when the "Raritan" 0f million years. Jordan (1983) evaluated the
Maryland was reexamined by Owens (published Potomac Group vs. Potomac Formation
1969). The results of this study will be nomenclature regionally. He noted that even
detailed later. though locally a tripartite subdivision is
Because of the non-marine character of possible, in a regional sense the three
the Potomac Group the dating of these formations subdivision was not possible. We
sedi~ents depended for the most part on follow this designation in the remainder of
widely scattered leaf deposits. It was from our report.
these leaf deposits that the Early Owens and Gohn (1985) in an evaluation of
Cretaceous age for the Potomac Group was the Cretaceous of the emerged Atlantic
established. Because the leaf localities Coastal Plain noted the importance of
were so sparse and widely scattered, deltaic sedimentation within these beds. In
however, large areas of the Potomac Group particular they reexamined the Potomac
could not be dated by this technique. Formation and subdivided this unit into a
Pollen which is much more abundant and variety of deltaic controlled lithofacies.
widespread were then analyzed to refine the Overall they considered the Potomac
biostratigraphy and age of the Potomac Formation to be dominated by non-marine
Group. In 1963, Brenner reported the deltaic facies although marine influenced
results of a pollen study from two cores at delta front deposits occur in the deep
Bowie, Md., just northeast of Washington, subsurface near the coast. In addition they
D.C., which penetrated much of the Potomac noted that the pollen zonation indicated
Group. At this site, Brenner used the that the deltas within the Potomac Formation
tripartite stratigraphic nomenclature for migrated northward through time. Arevised
the Potomac Group and assigned a roman version of their diagram is shown in figure
numeral designation to the three formations; 4. This migration of delta lobes suggests
Patuxent and Arundel~I and Patapsco-IIA and that the delta movement followed tectonic
lIB. In 1969, Owens reported the results of movements during their deposition. Of
a .po11enstudy from c1aysin the "Raritan" interest to the field trip is that Elk Neck
T211: 3
76
-+ +
Elk
-+ 39
+ + 38
approximate outcrop b'elt
of Potomac Formation
+
+ +37
. miles
o
100
FIGURE 3 Generalized diagram showing the outcrop pattern of the
Potomac Formation The Potomac Formation crops out along the
o
innermost part of the Coastal Plain from New Jersey to Virginia.
T211: 4
ZONEI
m
ZONE ZONE :Dr
approximate distribution of Potomac Formation
palynozones in Salisbury Embayment
FIGURE 4 Distribution of the palyzones in the Potomac Formation
(Zone I-III). Zone IV represents the late Cenomanian-early
Turonian(?) palynozone (Raritan Formation). The movements of
the delta lobes associated with Zones I-III clearly indicate a
northward movement through time. Zone IV represents a mixed
marginal marine-delta with the marine facies dominant.
T211: 5
TABLE 1 Stratigraphic column showing the formations and their
ages which are pre~ent~ithinthe Elk Neck Peninsula or nearby.
AGE YEARS UNIT
CD
c:
CD
.0.
0 late Wisconsinan 18x103 bay and river fill
-CD
-CD
0-
Unconformit.y
late 'Miocene ·g,x106 Pensauken
~
--eLu- unconformity
L-
.C-D
-Tertiary· 25x106 Upland Gravels
(?J
unconformit~
74x106 M!)unt Laurel
6
75x10 Marshalltown
Campania·n unconformity
6
82x10 Englishtown
Santonian 86x106 MerchantviIIe
un·c0 nformity
a
Cenomanian 97x10 6
tJ) <D
~ c:
0 0
CD N
-(j
co
0CLD.. Albian 100x10 6 ~c<D: Potomac ForrPation
0
N
H
Aptian-Barremian 110Xl06 CD I
c:
0
N
peninsula is one of the few places 10 the shaped units are ..p... resent, with trough type
Salisbury Embayment where parts of zones I,
being the most common. Thin clay strata are
II, and III crop out within a relatively
commonly interbedded with the sands, mostly
short distance.
where the sands grade into clays (fig.
Llthology and petrology. At Elk Neck,
7A). Rip-clay clasts or clay conglomeratic
the Potomac Formation is 1argely an
strata are also present within some of the
interbedded sand and clay sequence with the
cross-bedded sandy units (fig. 78). In a
sandy strata more abundant (fig. 5). In
few places clay clast conglomerates occur in
general the sandy and clayey strata are
small channels mixed with fine (0.5 inches
lensing and thus lithofacies changes between
maximum diameter) quartz gravel. Gravel for
outcrops are rapid.
the most part, however, is rare in the
The sandy strata are cross-bedded (fig.
Potomac Formation of the Elk Neck peninsula.
6). The scale of cross-bedding is small
The sands are locally cemented by iron
with the cosets typically less than 12
oxides. Large masses of ironstone are
inches in thickness. Both planar and trough
common within the sands locally (fig. 8A).
T211: 6