MRCSP Phase I Geologic Characterization Report - Midwest ...

APPENDIX A: LOWER CRETACEOUS WASTE GATE FORMATION
137
Figure A17-3.—Diagram showing the Fall Zone, the Salisbury Embayment
and other tectonic features of the middle Atlantic area (from Hansen, 1978).
Wi-Cg 37) at a depth interval of 4,745 to 5,360 feet. The well was
drilled in Maryland about 22 miles west of the Atlantic coast, about
8.5 miles south of the Delaware state line, and slightly west of a
place referred to as “Waste Gate”. Waste Gate appears to be an
informal name for an area around the intersection of Waste Gate
Road and Route 350 that is in the vicinity of Waste Gate Creek. The
well was drilled in 1944; core descriptions and electric logs were
published by Anderson and others (1948).
NATURE OF LOWER AND UPPER CONTACTS
Hansen (1982) defined the Waste Gate Formation on the basis
of significant differences in age, lithology and petrophysics from
the overlying Patuxent Formation and Arundel Formations. In the
type well, the top of the Waste Gate occurs at a depth of 4,745 feet.
At this depth, the electric log shows a general increase in resistance
associated with sandier intervals (Anderson, 1948, figs. 10 and 20),
and an increase in garnet content (Anderson, 1948, fig. 3). Anderson
(1948, p. 71) noted “the sands below the 4,750 foot level are all
soft, partially consolidated, and poorly sorted and doubtless possess
a relatively high permeability.” However, Anderson (1948) did not
recognize the Waste Gate as a separate unit, instead including these
sediments in the Patuxent Formation.
The Waste Gate is characterized as an overlapped subsurface sequence
of interbedded sandstones and shales; however, the nature
of the upper contact of the Waste Gate Formation is not clearly
defined. Various diagrams in Hansen (1984) seem to emphasize
the undetermined nature of the contact by showing it as a questionable
unconformity or possibly a conformable contact. Due largely
to the paucity of data, it is not clear if significant time is missing at
the contact or how the nature of the contact may vary at different
locations.
Hansen (1982, 1984) reported that palynology data indicate the
sediments from the Waste Gate Formation are “pre-palynozone I of
Brenner (1963),” largely, if not wholly, Berriasian to Hauterivian()
in age, and thus older than the overlying Patuxent Formation (Berrimanian
and younger). However, Hansen did note that, in one well,
an angiosperm type common in the Palynozone I, associated with
the younger (overlying) Patuxent-Arundel Formations (undivided),
was reported in the upper part of an interval assigned to the Waste
Gate, thus leaving open the possibility of upper beds of the Waste
Gate possibly being as young as early Barremian. Therefore, it is
possible that little or no time separates the Waste Gate from the
overlying Patuxent Formation.
In Maryland, the Waste Gate has been penetrated in only four
wells (referred to as Hammond No. 1, Bethards No. 1, DOE Crisfield,
and Esso No. 1), and even fewer penetrate into the underlying
basement rocks. In general, in the vicinity of the Hammond No.
1 well, and to the east of this well, Cretaceous units are underlain
by rocks of Jurassic() or Triassic() age (Anderson and others,
1948; Hansen, 1982). To the west, the Waste Gate Formation is
presumably underlain by older, pre-Mesozoic basement metamorphic
rocks. In the Hammond No. 1 well, there are approximately
135 feet of what are referred to as Triassic() rocks by Anderson
and others (1948) and Jurassic() by Hansen (1982). The top of
the sequence is a hard, indurated quartz conglomerate containing
some white feldspars and lime cement. Below the conglomerate
are hard, reddish-brown and apple-green shales, sandy shales, and
sandstones. In the Bethards No. 1 well, there are approximately 585
feet of Triassic()/Jurassic() rocks (assigned to the Newark series)
characterized by sandstones, sandy shales, and shales with a basal
conglomerate (Anderson and others, 1948).
Anderson and others (1948) indicate that, at the Hammond No. 1
well, the top of the pre-Mesozoic basement contact is characterized
by “rotten schistose rock containing mica, chlorite, and feldspar and
cut by small veins of pegmatite in which the feldspars are almost
entirely decomposed.” This weathered zone was estimated to be
approximately 31 feet thick and underlain by either a biotite-rich
quartzite or a mica gneiss and cut by veins of pegmatite. At the
Bethards No. 1 well, pre-Mesozoic basement rock appears to be
characterized by dark greenish-black gabbros containing joints occasionally
filled with carbonate).
LITHOLOGY
Hansen (1984) described the Waste Gate lithology as follows:
The Waste Gate Formation consists largely of an unconsolidated
to moderately lithified sequence of interbedded light gray to white
arkosic to feldspathic sandstones and drab to occasionally mottled,
silty shales (or clays), often fi nely laminated with carbonaceous
material. Anderson (1948, p. 14) reports that the sandstones
(sands) are relatively poorly sorted, ranging from fi ne to very
coarse-grained with an occasional pebbly bed. The feldspars are
often strongly kaolinized, resulting in a pervasive, clayey matrix
suffi ciently binding to form friable sandstones in place. The more
indurated sandstones are associated with occasional occurrences
of calcareous cement. Core descriptions provided by Anderson and
others (1948, p. 408-412) indicate that about 27 percent of the arenaceous
footage is suffi ciently lithified to be called “sandstone,”