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

the basins and also corresponding with thicker, nonmagnetic sed-
imentary rocks in basins. Negative radiometric anomalies are
associated with diabase, basalt, and greenstone conglomerates.
Electrical resistivity anomalies discriminate between basement
rocks and the conductive sedimentary fill of the Durham-Sanford
basin, as is the case in most early Mesosoic basins.
Gravity, magnetic, radiometric, and electrical methods are
very useful for a regional overview, especially when used in con-
junction. Reflection seismology offers the highest resolution of
any geophysical technique. Such data can provide specific and
precise information about the geometry of border and internal
faults and about velocity, and can define unconformities within
the rocks in the basins or determine the number and thickness of
diabase sills or basalt flows at depth.
STRATIGRAPHY, FACIES,
DEPOSITIONAL ENVIRONMENTS,
AND PALEONTOLOGY OF
THE NEWARK SUPERGROUP
Paul E. Olsen
INTRODUCTION
The stratigraphy and facies of the wedge-shaped lithosomes
that fill the exposed Newark Supergroup half graben fall into two
broad, geographically separated categories: northern- and south-
era-type sequences. The more northern Newark Supergroup
basins (Fundy, Deerfield, Hartford, Pomperaug, Newark, Gettys-
burg, and Culpeper) (Plate 5A; Fig. 4) are divided into three
parts: (1) a lower, dominantly fluvial and lacustrine sequence of
mostly Late Triassic age; (2) a middle, relatively thin zone of
tholeiitic basalt flows interbedded with fluvial and lacustrine
strata of earliest Jurassic age; and (3) an upper, fluvial and lacus-
trine sequence of Early Jurassic age that in the Hartford and
possibly Fundy basins may be as thick as the lower sequence but
is usually thinner, possibly reduced by erosion in other basins
(Fig. 4).
The more southern exposed basins (Danville-Dan River,
Deep River, Richmond, Taylorsville, and Farmville and asso-
dated basins) (Plate 5A) lack interbedded basalt flows or Jurassic
sediments. Sedimentation in these basins may have ceased prior
to the time of extrusion. Some onshore southern basins buried
beneath the Atlantic Coastal Plain, such as the northern part of
the Riddelsville basin, are capped by basalt flows. Although these
flows are geochemically similar to other Newark flows and intru-
sions, they are more or less conformable to the overlying coastal
plain (Daniels and others, 1983; Gottfried and others, 1983).
Each major structural basin of the Newark Supergroup has,
for the most part, a separate series of lithologically defined forma-
tions (Fig. 4) that either have no formal inclusive name or that are
joined into one or more groups (Froelich and Olsen, 1984). All
told, the Newark Supergroup consists of six such groups, 57
formations, and scores of named members (McLaughlin, 1946;
Van Houten, 1980; Froelich and Olsen, 1984; Lee, 1977, 1980;
Post-Paleozoic activity 343
Lehmann, 1957) (Plate 5A; Fig. 4). Ten large and five small
basins and their contained formations are not united into groups.
This does not include the intrusive units or the very large number
of duplicate names for various formations and groups.
Almost all Newark basins are cut by intrusive tholeiites, in
the form of thick sheets, irregular plutons, and thin dikes of
diabase (see McHone and Puffer, this chapter), many of which
have been named. Some of these intrusions, mainly dikes, also cut
the surrounding pre-Newark rocks. The nomenclatural status of
the majority of these is unclear, even extending to whether some
should be included within the supergroup.
AGE AND CORRELATION
The Triassic versus Jurassic age of the Newark Supergroup
has been a continuous matter of controversy (Maclure, 1822;
Marcou, 1849; Rogers, 1843; Bunbury, 1847; Redfield, 1856;
Lyell, 1857; Emmons, 1857; Cope, 1887; Russell, 1892; Marsh,
1896; Reeside and others, 1957; McKee and others, 1959; Olsen
and Sues, 1986). The major problem is a basic lack of compara-
ble age-correlative data from the early Mesozoic type sections of
Europe and from eastern North America. The European sections
lack radiometric dates from igneous rocks and the American
sections are wholly continental, whereas the European Early Ju-
rassic is marine, limiting the kinds of organisms that are shared.
Nonetheless, some classes of data are shared directly be-
tween parts of the European type areas and the Newark Super-
group. These include pollen and spore assemblages, tetrapod
skeletal remains, and terrestrial vertebrate footprints. Comet and
others (Cornet and others, 1973; Cornet and Traverse, 1975;
Cornet and Olsen, 1985) have proposed seven sporomorph zones
within the Newark deposits (Fig. 4). The older four zones corre-
late with the European late Middle Triassic and Late Triassic
(Ladinian through Late Norian [Rhaetic of older works]), and the
younger three zones correlate with the European Early Jurassic
(Hettangian through Toarcian). This correlation involves over
200 species of pollen and spores collected from several hundred
localities, with most basins being fairly well represented.
Middle and Late Triassic pollen and spore zones are marked
by relatively highdiversity assemblages that include hundreds of
unnamed species. The Triassic-Jurassic boundary is fairly well
defined and is characterized by the dramatic rise to dominance of
the conifer pollen genus Corollina, which remains dominant
through the upper Newark Supergroup. Primarily on this basis, as
well as on the basis of the presence of certain typical Early
Jurassic taxa, the Triassic-Jurassic boundary is placed just below
the oldest Newark basalt flows (Cornet and Olsen, 1985).
The vertebrate assemblages of the Newark are divided into
five biostratigraphic zones (Comet and Olsen, 1985). The oldest
zone is apparently early Middle Triassic (Anisian) in age (Olsen,
1988b) but is represented only in the Fundy basin (Fig. 4). The
next three zones span the Late Triassic, and the youngest zone
covers most of the Early Jurassic.
Radiometric dates from the flows, diabase intrusions, and