Post-Paleozoic activity - Lamont-Doherty Earth Observatory ...

348 ' W. Manspeizer and Others
Fluvial and Shoreline Depositional Fades
Deposits of Newark Supergroup fluvial systems and
marginal-lacustrine facies have received less detailed study than
the "typical" lacustrine sequences. In addition, recent work,
largely unpublished, indicates that major revisions of our
understanding of Newark fluvial systems are in the offing. Al-
though alluvial fan, debris flow, braided and meandering river,
and shoreline deposits have been recognized sporadically in the
Newark Supergroup, it is very unclear how these deposits relate
to one another within individual formations or basins.
Conglomerate beds commonly present along the margins of
most Newark basins have been traditionally referred to as "fan-
glomerates" or alluvuial fan conglomerates (Krynine, 1950;
Longwell, 1922; Randazzo and others, 1970). More recent de-
tailed studies of bedforms and fabrics show that alluvial fan de-
posits are indeed present, at least in the Newark (Arguden and
Rudolfo, 1986) and Hartford basins (Hubert and others, 1982;
LeTourneau and McDonald, 1985; and LeTourneau and Smoot,
1985). Debris flows occur within some of these units (Arguden
and Rodolfo, 1986). Red mudstone and brown sandstone,
matrix-supported basalt conglomerates have been interpreted as
talus slope and debris-flow deposits along the northern edge of
the Fundy basin by Hubert and Mertz (1984) and by Olsen and
others (1987). Some of these sequences contain extremely
abundant reptile and fish bones (Olsen and others, 1987).
Braided river deposits have been described from many por-
tions of the Newark Supergroup, including the Fundy basin (Hu-
bert and others, 1983); the Hartford, Deertield, and Pomperaug
basins (Hubert and others, 1982; Stevens and Hubert, 1980); the
Newark basin (Allen, 1979; Weddle and Hubert, 1983); the
Danville-Dan River basin (Thayer and others, 1970); and the
Deep River basin (Gore and others, 1986).
Most of the braided river deposits consist of red to brown
poorly sorted pebbly sandstone and arkose with a complex pat-
tern of plane beds and cross beds, and red coarse siltstone
showing abundant bioturbation by roots and burrows and some-
times well-developed caliche paleosol profiles. Silicified logs, rep-
tile skeletons and bones, clams, and footprints occur sporadically
in these types of sequences.
Meandering river deposits have not been commonly recog-
nized in the Newark, although this is probably an artifact of poor
exposure and problems with scale (Smoot, 1985). Smoot (1985)
has identified large-scale (4+ m) laterally accreted beds of point
bars in the Deep River basin. These lateral accretion beds consist
of 20 to 30 cm thick and 5 to 10 m wide lenses of trough
cross-bedded sandstone interbedded with intensely bioturbated
mudstone. Similar examples have been identified by Smoot
(1985) in the Culpeper and Newark basins. In small outcrops,
such sequences can easily be misidentified as interbedded shallow
braided-river and overbank deposits; some Newark Supergroup
supposed braided-river deposits may fall into this category. Rep-
tile and amphibian bones, burrows of the Scoyenia type, and
plant stems and leaves are relatively common locally within these
sequences.
Small-scale upward-fining cycles, a mean of 3 m thick, have
been described from the Passaic and Towaco formations of the
Newark basin by Olsen (1980b) and Weddle and Hubert (1983)
and are interpreted as shallow meandering river, bank, and flood
basin deposits. Pedogenic carbonate nodules are common, but
they do not make up caliche-type paleosols. Reptile footprints are
abundant in the upper parts of these cycles, but burrows are
relatively uncommon.
LeTourneau and McDonald (1985,1986), LeTourneau and
Smoot (1985), Turner-Peterson (1980), and Turner-Peterson and
Smoot (1985) have recently identified a number of different
kinds of shoreline facies within the Newark Supergroup. Silt-
stones and sandstones made up of internal "deceleration-of-flow"
sequences dominated by climbing ripple cross-lamination that
make up low-angle inclined foresets, which intertongue with la-
custrine siltstone at their toes, are present within division 1 and
division 3 of many Van Houten cycles. Some of these sequences
appear to make up small "Gilbert9'-type delta sequences within
single Van Houten cycles in at least the Stockton, Lockatong, and
Passaic Formations; these are apparent only in the largest expo-
sures. A second type of sequence consists of similar packets of
low-angle inclined foresets, but there are abundant mudstone
partings with large polygonal shrinkage cracks and soft-sediment
deformation structures. These probably represent broad, flat delta
fronts formed by the intersection of flash-flooding streams and an
expanding shallow lake. The latter two types of deposits may
contain calcareous tufas, oncolites, and lenses of calcareous con-
glomerate derived in part from tufa fragments. Unionid clams and
reptile and fish bones are common fossils in these sequences
(McDonald, 1985). A third type of shore facies consists of cobble
and pebble conglomerates with well-sorted sand or granule ma-
trix and well-sorted, medium- to coarse-grained sandstones show-
ing horizontal lamination and oscillatory ripple cross-lamination.
The latter have thus far been found only on the fault-bound side
of the basins and appear to represent wave-sorted alluvial fan-toe
deposits. In the past these types of sequences have been lumped as
fluvial deposits or even "fanglomerates."
Alluvial fan, braided river and meandering river, and deltaic
and other shoreline facies interfinger with clusters of Van Houten
cycles in some formations. However, the lateral relationships of
all of these types of deposits are still more or less unknown, as are
the relative volumetric importance of each kind.
Eolian Deposition
Until Hubert and Mertz's (1980,1984) description of wide-
spread dune sands in the Fundy basin, eolian deposits had not
been recognized in the Newark Supergroup. Dune sands occur in
all of the sedimentary formations of the Fundy basin, but they are
especially important in the Late Triassic Wolfville Formation and
near the base of the Early Jurassic McCoy Brook formations of