Paul E. Olsen1, Christian Koeberl2, Heinz Huber2, and Alessandro Montanari3


1Lamont-Doherty Earth Observatory of Columbia University, Rt. 9W, Palisades, NY 10964, USA (
2Institute of Geochemistry, University of Vienna, Althanstrasse 14, A-1090 Vienna, AUSTRIA (
3Osservatorio Geologico do Coldigioco, I-62020 Frontale di Apiro, Italy

* Presented as a poster session at the LPI conference - "Catastrophic Events and Mass Extinctions: Impacts and Beyond" at the Geozentrum University of Vienna, Austria, July 9-12, 2000.  This web version has been reformatted to fit the www format. Abstract available at:


The Triassic-Jurassic (Tr-J) boundary marks one of the "big five" mass extinctions in the last half billion years. The Triassic-Jurassic boundary has been identified in Eastern North America in lacustrine rift basin strata of the Newark Supergroup (Fig. 1) by palynological and vertebrate biostratigraphic comparisons with Europe and elsewhere (Cornet, 1977; Cornet and Olsen, 1985; Fowell, 1994; Fowell and Olsen, 1993; Fowell et. al., 1994; Fowell and Traverse, 1995; Olsen, 1977; Olsen and Galton, 1977; Olsen and Sues, 1986; Olsen et al., 1990, 1991).

These lacustrine deposits, including the boundary sections, are profoundly cyclical with the cyclicity being attributed to astronomical (Milankovitch) forcing of climate (Olsen, 1986; Olsen et al., 1996a; Olsen and Kent, 1999). Overlying a relatively thin interval of Jurassic age lacustrine deposits is a basaltic lava flow sequence with more interbedded and overlying cyclical lacustrine sequences. The lava flows, and more specifically, their feeder systems, yield 40Ar/39Ar and U-Pb dates of about 201.5+2 my (Hodych & Dunning 1992, Sutter 1988, Ratcliffe 1988), an age, geologically indistinguishable from U-Pb dates from marine, ammonite-bearing, strata (199.6±0.3 Ma; Palfy, 2000). The Milankovitch cyclostratigraphy of the surrounding sedimentary formations in the Deerfield, Hartford, Newark, and Culpeper basins is the basis for the suggests that the entire extrusion sequence lasted no longer than about 600,000 (Olsen et al 1996b). The duration of the this igneous episode is thus similar to that of other flood basalt provinces such as the Deccan and Siberian traps (Jaeger et al 1989, Renne and Basu 1991). Thus, far the boundary has been palynologically identified at a high level of resolution (< 20 ky) in the Newark and Fundy basins. The Milankovitch cyclostratigraphy of the surrounding lacustrine sediments suggests that the boundary occurs less than 40 ky prior to the oldest basalts in these respective basins, probably about 20 ky.

Figure 1 (right): A, Pangea during the Late Triassic showing the position of the rift zone (gray), the Newark Supergroup basins (black), and the Newark basin (1). B, Major basins of the Newark Supergroup. Modified from Olsen et al., 1996.

In the Newark basin (Fig. 2, below), the boundary has been studied lithologically and paleontologically at several sites along a 1 km strike traverse in the Jacksonwald syncline (including the sections described here at Exeter), the Martinsville no. 1 core of the Newark Basin Coring Project, and outcrops near Patterson, and Clifton, New Jersey.

Figure 2 (right): Map of the Newark Basin showing the distribution of various lithological units and position of the Exeter section within the Jacksonwald syncline. Modified from Olsen et al., 1996a.

Figure 3 (above): Triassic-Jurassic boundary in the Jacksonwald syncline  (section I). Boundary (dark line) is at inset, shown in detail on right. Rocks shown are red and gray mudstones on right and gray mudstones and sandstones on left. Hill is capped by Orange Mt. Basalt.
Figure 4 (above): Detail of Triassic-Jurassic boundary at Section I. Abbreviations are: J, Jurassic strata; fs, "fern spike"; Tr, Triassic strata.
In the Jacksonwald syncline, close to the border fault system on the Newark rift basin, the boundary section occurs about 8 to 10 m below the Orange Mountain Basalt, in the uppermost part of the ~ 3 km thick Passaic Formation (Fig. 3, above). The boundary sections consists of a predominately red cyclical lacustrine mudstone sequence that becomes finer grained, and grayer towards the axis of the basin. A meter-scale sequence of red, gray and black strata contain the palynological boundary has been exposed by housing construction at many sites for 2 km along strike (Fig. 4, above). Sections at four such sites formed the basis of our study. A the three sections Sections l-111) closer to the axis of the basin, these; sections consist of a basal gray siltstone and sandstone with roots and a Triassic-type palynoflora (samples 7-11. 16-19, 25). This is succeeded by a few centimeters of white to light gray smectite-rich clay and silt (Smith et. al. 1989), also with roots (samples 3-6, 14-15, 24; ), overlain by 1 to 3 cm of black carbonaceous shale or coal. The latter two beds contain very high percentages of (~60-90%) fern spores, comparable to the K-T fern spike (Tschudy et al., 1984). This is the only coal know in the ~6 km thick Newark basin section. The black shale or coal is overlain by 0.5 to 1.5 m of gray-blue sandstone and siltstone with abundant plant fragments and charcoal. To the west, closer to the boundary fault system, this sequence becomes predominantly much more red, although the same basic litho- and palynostratigraphy is recognizable (Section IV site - samples 26-36) samples). Palynological samples from beds overlying the gray to red charcoal bearing sandstone on top of the "fern spike" are of typical Jurassic composition, completely lacking Triassic taxa.

There have been two previous and unsuccessful attempts to find shocked quartz in the boundary sections in eastern North America. The oldest was that by Mark Anders (Columbia University) cited in Olsen et al. (1987) in the Fundy basin of Nova Scotia, Canada. The process was repeated again by Mossman et al. (1998) in the Fundy basin, and also in the Newark basin, including a suite of samples from near Section I of this study. Neither sampled the palynologically identified boundary with precision, however.


Iridium contents were measured by iridium coincidence spectrometry (ICS). This sensitive method is tailored to the determination of iridium at very low abundance levels (sub-ppb range) with a detection limit of less or equal than about 20 ng/g (ppt) in carbonate rocks. The ICS does not require dissolution or any other chemical treatment of the samples, which is an advantage compared to radiochemical neutron activation analysis (RNM) or ICP-MS, as it avoids possible contamination.

Principles of coincidence counting

The main purpose of a coincidence setting is the reduction of background and the removal of spectral interferences by counting of coincident events from two g-rays from the decay cascade of 1921r. The coincidence system (Koeberl and Huber, 1999) is composed of low energy planar HpGe-detectors, two (pre-) amplifiers, two analog-to-digital-converters (ADCs) and a multiparameter analyzer small bus box (Fast Com Tec MPA-SBB). Only signals occurring within a certain time from both detectors are accepted by the MPA and plotted in a 1024*1024 matrix. Then the regions of the iridium peaks (316.5 keV and 468.1 keV) are extracted and fitted (Fig. 5). The resulting peak volumes are corrected (live time correction, decay time correction, flux correction, background subtraction) and compared with the standards.

Figure 5 (left)

The samples show variations in Ir content from 19 to 285 ppt. Section I shows no systematic collection between Ir content and stratigraphy, but all other Sections show a distinct Ir anomaly directly at the boundary. The elevated levels of Ir are mostly associated with higher levels of Al in a white smectitic claystone, directly adjacent to the thin coaly layer (Fig. 6). It is especially suggestive that the anomaly is directly associated with the previously identified spore spike in these sections, recalling the similar pattern at the K-T boundary in the western US. It is possible the relatively weak Ir anomaly seen thus far is a consequence of dilution by the rather coarse sampling level (ca. 3 cm / per sample) required by the very high accumulation rates (ca. 1 m / 2000 yr) in the sampled part of the Newark basin.

Ir contents measured with the iridium coincidence spectrometry (ICS)
[all values ppt]

Section I
Section II
Section III
Section IV
Ir content
Ir content
Ir content
Ir content
< 80
While tantalizing, the observed anomaly (Fig. 6) requires much additional geochemical and mineralogical analysis for its significance to be under-stood for testing hypotheses of the origin of the Tr-J boundary. Although the microstratigraphy is very similar to continental K-T boundary sections, and this lithological similarity is matched by a similar biotic pattern, we cannot rule out volcanic or even a diagenetic hypotheses for that data we have thus far.

Figure 6 (above): Concentrations of Ir and Al at Sections I - III. 

The search for shocked quartz grains was not successful. Only a few grains with subplanar deformation features were found (see figure), but none are characteristic for shock metamorphism.

Thus, at this time we are left with the observation that three out of four studied sections do show a distinct sidererophile element anomaly. Clearly, this requires more studies and efforts to determine if the Ir anomaly is of extraterrestrial origin or not.

Figure 7 (right): Grain showing subplaner deformation features characteristic of processes other than shock metamorphism.


The analytical work in Vienna was supported by FWF grant Y58-GEO (to C.K.) and the collection of the samples was funded by US NSF Grant EAR 98-14475 to PEO and H. D. Sues.


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