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3.3. Tectonics of Rifting and Drifting: Pangea
Breakup
3.3.2. Extracting Tectonic Information from Cores in Rift Basins
Roy W. Schlische
Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854-8066 U.S.A.
Rift basins are tectonic features. Thus, a goal of any large-scale study
involving rift basins should be a better understanding of the tectonic
processes controlling basin formation and infilling. The NSF-funded
Newark Basin Coring Project (NBCP) demonstrated that it is possible to
extract tectonic information from cores in rift basins. This section
reviews the successes of NBCP in terms of tectonics and basin evolution
and briefly highlights some of the unanswered questions.
Figure 3.3.3.1. Schematic cross
section of the Newark basin
showing offset coring technique;
marker unit at the base of one core
correlates with same marker unit at
top of adjacent core. From
Schlische (2000).
NBCP used an offset drilling technique (e.g., Olsen et al., 1996a) to take
advantage of the eroded half-graben geology of the Newark basin. Core
sites were positioned so that the bottom of one hole overlapped with the
top of an adjacent hole in a distinctive stratigraphic interval (Figure
3.3.2.1). Correlations are based on cyclostratigraphy and
magnetostratigraphy (Olsen et al., 1996a; Kent et al., 1995). The
overlap sections allowed construction of a composite stratigraphic
section (Olsen et al., 1996a; section 3.2.2). In addition, the overlap
sections by themselves provide useful tectonic information. For
example, the overlap section between the Rutgers and Somerset cores
shows that stratigraphic units thicken by ~12% across the 10 km
between these holes (Figure 3.3.2.2). In addition, lake facies are
deeper in Somerset than Rutgers. All overlap sections thicken from the
lateral edge of the basin toward the basin center (e.g.,
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Rutgers-Titusville) and from the hinged margin toward the intrabasinal
faults and/or border fault system (e.g., Nursery-Titusville) (Figure
3.3.2.3). The simplest interpretation of these variations in thickness and
facies is variations in basin subsidence caused by syndepositional
faulting (see Figure 3.3.2.1).
Figure 3.3.3.2. Overlap section of the Rutgers and Somerset cores,
showing pronounced increase in thickness and proportion of deeper-water
mudstones (gray and black units) from Rutgers to Somerset. Based on data
in Olsen et al. (1996a).
Click on the image at left to view a larger version.
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Figure 3.3.3.3. Geologic
map of the north-central part
of the Newark basin showing
the locations of the seven
NBCP drill sites. Arrows
indicate the amount of
thickening between overlap
sections of stratigraphically
adjacent cores based on
correlations in Olsen et al.
(1996a). Abbreviations for
drill holes are: M,
Martinsville; N, Nursery; P,
Princeton; R, Rutgers; S,
Somerset; T, Titusville; W,
Weston. From Schlische
(2000).
Correlations of the NBCP cored sections to outcrop sections is also
extremely useful (e.g., Silvestri, 1994, 1997; Olsen et al., 1996a;
Schlische, 1999). The Perkasie Member of the Passaic Formation extends
across 125 km of the Newark basin (Figure 3.3.2.4). Variations in
thickness of the Perkasie Member indicate that the Newark basin is a
large longitudinal syncline, consistent with border-fault displacement
being highest near its center and declining towards its lateral ends (e.g.,
Schlische, 1992) (also see Figure 3.3.2.1). Additional core-to-outcrop
correlations, coupled with seismic-reflection profiles, indicate that a
hierarchy of fault-related folds along the border fault system and
intrabasinal faults formed, at least in part, syndepositionally (Jones,
1994; Schlische, 1992, 1995; Reynolds, 1994; Olsen et al., 1996).
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Figure 3.3.3.4. Basinwide correlation of
the Perkasie Member of the Passaic
Formation showing variations in thickness
and facies. Inset sketch map of Newark
basin shows locations of sections. Modified
from Olsen et al. (1996a).
Click on the image at left for a larger
version.
The large-scale basin geometry outlined above, the large-scale
stratigraphic architecture present in the NBCP composite section (see
Figures 2.4 and 3.3.1.5), and onlap relationships revealed by seismic
data can be reproduced in quantitative basin-filling models (see Figure
3.3.1.3). Although these basin-filling models successfully explain many
aspects of the stratigraphy of the Newark basin and many other
non-marine rift basins (e.g., Lambiase, 1990; Schlische and Olsen,
1990; Olsen, 1997), this simply indicates that the models are viable. The
models are bolstered because they also make quantitative predictions
about accumulation rates. In the Newark basin, accumulation rates are
derived from Milankovitch lacustrine cycles in the NBCP composite
section (Figure 3.3.2.5a; Contreras et al., 1997; Olsen and Kent, 1999).
The most sophisticated numerical basin filling models (which incorporate
self-similar faulting, flexure, isostasy, and sediment diffusion; Contreras
et al., 1997) broadly account for observed trends in accumulation rates
in the NBCP data (Figure 3.3.2.5b). In addition, the basin-filling models
place constraints on the boundary conditions of the rifting process
(constant strain-rate conditions are favored over constant
fault-lengthening rate), the rheology of the crust and lithosphere, and
the nature of fault growth (Schlische, 1991; Schlische and Anders, 1996;
Contreras et al., 1997).
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Figure 3.3.3.5. Accumulation rate data derived
from NBCP cyclostratigraphy (a) and constant
strain-rate basin-filling model (b). The two
accumulation rate data sets were normalized by
the maximum accumulation rate in each data set
to facilitate comparisons. The numbered curves in
(b) were derived from vertical drill holes through
the model rift basin shown in map view on right.
Curve 2 fits the Newark basin data reasonably
well, but fails to reproduce the marked increase in
accumulation rates at ~27.5 M.yr. since the onset
of extension (Early Jurassic extrusive interval).
Modified from Olsen (1997), Contreras et al.
(1997), and Schlische (2000).
Deviations from the predictions of the models are also important. The
most notable deviation in the Newark basin concerns the markedly
higher accumulation rates (Figure 3.3.2.5) and deeper lake facies
present in the Early Jurassic strata (tectonostratigraphic (TS) package
IV; see Figure 3.3.1.5) compared with those in TS-III (Olsen et al.,
1996a, b). Strata belonging to TS-IV are interbedded with a series of
lava flows (CAMP flows) that were emplaced in as little as 650 kyr
(Olsen et al., 1996b). Schlische and Olsen (1990) postulated that
accelerated faulting and tilting would markedly increase basin
asymmetry. This would cause sediments and water to shift toward the
basin depocenter, increasing accumulation rates and average lake
depths. This anomaly is not just limited to the Newark basin: a plot of
cumulative stratigraphic thickness versus age (Figure 3.3.2.6) shows
marked increases in accumulation rates for all of the eastern North
American rifts containing Early Jurassic strata (Schlische and Anders,
1996). Thus, tectonics is likely responsible for this "anomaly", although
the relationship of CAMP volcanism to this tectonic anomaly is not clear.
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Figure 3.3.3.6. Cumulative stratigraphic thickness versus
geologic age for various exposed rift basins in eastern
North America. The Culpeper (C), Deerfield (D), Fundy
(F), Hartford (H), and Newark (N) basins all show
pronounced increases in stratal thickness in earliest
Jurassic time (extrusive interval). Other abbreviations are
DR, Deep River; DV, Danville; and R, Richmond basins.
Modified from Schlische and Anders (1996).
References:
Contreras, J., Scholz, C.H., King, G.C.P., 1997, A general model of rift basin evolution:
constraints of first order stratigraphic observations: Journal of Geophysical Research, v. 102, p.
7673-7690.
Jones, B.D., 1994, Structure and stratigraphy of the Hopewell fault block, New Jersey and
Pennsylvania: M.S. Thesis, New Bruswick, NJ, Rutgers University.
Kent, D.V., Olsen, P.E., and Witte, W.K., 1995, Late Triassic-earliest Jurassic polarity sequence
and paleolatitudes from drill cores in the Newark rift basin, eastern North America: Journal of
Geophysical Research, v. 100, p. 14,965-14,998.
Lambiase, J.J., 1990, A model for tectonic control of lacustrine stratigraphic sequences in
continental rift basins, in Katz, B.J., ed., Lacustrine Exploration: Case Studies and Modern
Analogues: AAPG Memoir 50, p. 265-276.
Olsen, P.E., 1997, Stratigraphic record of the early Mesozoic breakup of Pangea in the
Laurasia-Gondwana rift system: Annual Reviews of Earth and Planetary Science, v. 25, p.
337-401.
Olsen, P.E. and D.V. Kent, 1999, Long-period Milankovitch cycles from the Late Triassic and
Early Jurassic of eastern North America and their implications for the calibration of the early
Mesozoic time scale and the long-term behavior of the planets: Transactions of the Royal
Society of London, series A, in press.
Olsen, P.E., Kent, D.V., Cornet, B., Witte, W.K., and Schlische, R.W., 1996a, High-resolution
stratigraphy of the Newark rift basin (early Mesozoic, eastern North America): Geological
Society of America Bulletin, v. 108, p. 40-77.
Olsen, P.E., Schlische, R.W., and Fedosh, M.S., 1996b, 580 kyr duration of the Early Jurassic
flood basalt event in eastern North America estimated using Milankovitch cyclostratigraphy, in
Morales, M., ed., The Continental Jurassic: Museum of Northern Arizona Bulletin 60, p. 11-22.
Reynolds, D.J., 1994, Sedimentary basin evolution: tectonic and climatic interaction: Ph.D.
thesis, New York, Columbia University.
Schlische, R.W., 1991, Half-graben filling models: new constraints on continental extensional
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basin development: Basin Research, v. 3, p. 123-141.
Schlische, R.W., 1992, Structural and stratigraphic development of the Newark extensional
basin, eastern North America; Implications for the growth of the basin and its bounding
structures: Geological Society of America Bulletin, v. 104, p. 1246-1263.
Schlische, R.W., 1995, Geometry and origin of fault-related folds in extensional settings: AAPG
Bulletin, v. 79, p. 1661-1678.
Schlische, R.W., 1999, Progress in understanding the structural geology, basin evolution, and
tectonic history of the eastern North American rift system, in LeTourneau, P.M., and Olsen, P.E.,
eds., Aspects of Triassic-Jurassic Rift Basin Geoscience: New York, Columbia University Press,
in press.
Schlische, R.W., and Anders, M.H., 1996, Stratigraphic effects and tectonic implications of the
growth of normal faults and extensional basins, in Beratan, K.K., ed., Reconstructing the
Structural History of Basin and Range Extension Using Sedimentology and Stratigraphy: GSA
Special Paper 303, p. 183-203.
Schlische, R.W., and Olsen, P.E., 1990, Quantitative filling model for continental extensional
basins with applications to early Mesozoic rifts of eastern North America: Journal of Geology, v.
98, p. 135-155.
Silvestri, S.M., 1994, Facies analysis of Newark basin cores and outcrops: Geological Society of
America Abstracts with Programs, v. 26, p. A-402.
Silvestri, S.M., 1997, Cycle correlation, thickening trends, and facies changes of individual
paleolake highstands across the Newark basin, New Jersey and Pennsylvania: Geological Society
of America Abstracts with Programs, v. 29, p. 80.
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