Newark Rift Basin Research Articles

The “Passive” Margin of Eastern North America: Rifting and the Influence of Prerift Orogenic Activity on Postrift Development

AbstractWe have analyzed and synthesized geologic and geophysical data from the onshore Newark rift basin and adjacent onshore and offshore basins to better understand the Mesozoic development of the eastern North American rift system and passive margin. Our work indicates that rifting had three phases: (1) an initial, prolonged phase of extension and subsidence; (2) a short-lived phase with higher rates of extension and subsidence, intrabasin faulting, and intense magmatism; and (3) a final phase with limited subsidence and deposition. Additionally, our work shows that anomalous uplift and erosion, associated with crustal-scale arching/warping subparallel to the prerift and syn-rift crustal fabric not the continent-ocean boundary, affected a region landward of the basement hinge zone. Uplift and erosion began during the final rifting phase and continued into early drifting with erosion locally exceeding 6 km. Subsequent subsidence was minimal. We propose that denudation unloading related to relic, prerift orogenic crustal thickness and elevated topography triggered the anomalous uplift and erosion. After the Paleozoic orogenies, postorogenic denudation unloading (cyclic erosion and isostatic rebound/uplift) significantly thinned the thickened crust and reduced topographic elevation. During rifting, extension stretched and tectonically thinned the crust, promoting widespread subsidence and deposition that dampened the postorogenic cycle of erosion and isostatic rebound/uplift. During the rift-drift transition, with extension focused near the breakup site, denudation unloading resumed landward of the basement hinge zone, producing significant erosion and uplift (related to isostatic rebound), crustal thinning, and topographic decay that left behind only eroded remnants of the once massive rift basins.

Reservoir and sealing properties of the Newark rift basin formations: Implications for carbon sequestration

The Newark Basin is one of the major Mesozoic rift basins along the U.S. Atlantic coast evaluated for carbon dioxide (CO2) storage potential. Its geologic setting offers an opportunity to assess both the traditional reservoir targets, e.g., fluvial sandstones, and less traditional options for CO2 storage, e.g., mafic intrusions and lavas. Select samples from the basal, predominantly fluvial, Stockton Formation are characterized by relatively high porosity (8%–18%) and air permeability (0.1–50 mD), but borehole hydraulic tests suggest negligible transmissivity even in the high-porosity intervals, emphasizing the importance of scale in evaluating reservoir properties of heterogeneous formations. A stratigraphic hole drilled by TriCarb Consortium for Carbon Sequestration in the northern basin also intersected numerous sandstone layers in the predominantly lacustrine Passaic Formation, characterized by core porosity and permeability up to 18% and 2000 mD. However, those layers are shallow (predominantly above 1 km in this part of the basin) and lack prominent caprock layers above. The mudstones in all three of the major sedimentary formations (Stockton, Lockatong, and Passaic) are characterized by a high CO2 sealing capacity — evaluated critical CO2 column heights exceed several kilometers. The igneous options are represented by basalt lavas, with porous flow tops and massive flow interiors, and a crystalline but often densely fractured Palisade Sill. The Newark Basin basalts may be too shallow for sequestration over most of the basin's area, but many other basalt flows exist in similar rift basins. Abundant fractures in sedimentary and igneous rocks are predominantly closed and/or sealed by mineralization, but stress indicators suggest high horizontal compressional stresses and strong potential for reactivation. Overall, the basin potential for CO2 storage appears low, but select formation properties are promising and could be investigated in the Newark Basin or other Mesozoic rift basins with similar fill but a different structural architecture.

New insights into lithology and hydrogeology of the northern Newark Rift Basin

AbstractThe marginal facies of the Triassic rift basins in the eastern United States are poorly documented, particularly on the hinge or hanging wall margins. This study presents a lithological description and multiscale petrophysical analysis of basement rocks, overlying marginal facies of the early synrift strata, and the basal contact of the Palisade Sill that were drilled and cored in the northeastern part of the Newark Basin, near its terminus. The expression of the Stockton Formation differs from that in the central basin in having thinner layers, with uncertain temporal relationship to the type area. The bottom 50 m is lithologically distinct with brick‐red to dark‐purple mudstones and sandstones, abundant gypsum‐filled fractures, and a thin zone with anomalously high uranium concentration, not associated with organic‐rich mudstones as other occurrences in the basin. The crystalline basement is apparently Fordham gneiss, overlain by a thin sandstone layer and a dark‐purple hydrophilic mudstone. Despite the abundance of coarse‐grained strata and multiple sets of tectonic fractures, hydraulically transmissive zones are sparse, and do not uniquely correlate to fracture and/or matrix characteristics. Enhanced transmissivity may exist along intrusion boundaries due to enhanced thermal fracturing, but more hydraulic data are needed to verify it. Comparison of petrophysical data in two boreholes ∼210 m apart shows no direct correlation of individual lithological units and their hydraulic properties, although the overall formation characteristics are similar. The results highlight challenges for outcrop correlation at the marginal edges of the rift basins and estimating reservoir properties of these heterogeneous formations.

Microbial stimulation and succession following a test well injection simulating CO2 leakage into a shallow Newark basin aquifer.

In addition to efforts aimed at reducing anthropogenic production of greenhouse gases, geological storage of CO2 is being explored as a strategy to reduce atmospheric greenhouse gas emission and mitigate climate change. Previous studies of the deep subsurface in North America have not fully considered the potential negative effects of CO2 leakage into shallow drinking water aquifers, especially from a microbiological perspective. A test well in the Newark Rift Basin was utilized in two field experiments to investigate patterns of microbial succession following injection of CO2-saturated water into an isolated aquifer interval, simulating a CO2 leakage scenario. A decrease in pH following injection of CO2 saturated aquifer water was accompanied by mobilization of trace elements (e.g. Fe and Mn), and increased bacterial cell concentrations in the recovered water. 16S ribosomal RNA gene sequence libraries from samples collected before and after the test well injection were compared to link variability in geochemistry to changes in aquifer microbiology. Significant changes in microbial composition, compared to background conditions, were found following the test well injections, including a decrease in Proteobacteria, and an increased presence of Firmicutes, Verrucomicrobia and microbial taxa often noted to be associated with iron and sulfate reduction. The concurrence of increased microbial cell concentrations and rapid microbial community succession indicate significant changes in aquifer microbial communities immediately following the experimental CO2 leakage event. Samples collected one year post-injection were similar in cell number to the original background condition and community composition, although not identical, began to revert toward the pre-injection condition, indicating microbial resilience following a leakage disturbance. This study provides a first glimpse into the in situ successional response of microbial communities to CO2 leakage after subsurface injection in the Newark Basin and the potential microbiological impact of CO2 leakage on drinking water resources.

A 30 Myr record of Late Triassic atmosphericpCO2variation reflects a fundamental control of the carbon cycle by changes in continental weathering

We generate a detailed ~30 Myr record of pCO2 spanning most of the Late Triassic (Carnian-Norian-Rhaetian) to earliest Jurassic (Hettangian), based on stable carbon isotope ratios of soil carbonate and preserved organic matter from paleosols in the eastern North American Newark rift basin. Atmospheric pCO2 was near 4500 ppm in the late Carnian, decreasing to below ~2000 ppm by the late Rhaetian just before the earliest Jurassic eruption of the Central Atlantic Magmatic Province, which triggered measurable pulses of CO2 outgassing. These data are consistent with published modeling results using the GEOCLIM model, which predict a decrease in pCO2 over the Late Triassic as a result of the progressive increase in continental area subject to the intense weathering regime of the tropical humid belt due to Pangea’s northward motion. The fi ner-scale pCO2 changes we observe may be dependent on the lithology introduced to the tropics, such as the dip to ~2000 ppm around 212 Ma and its rebound to ~4000 ppm at 209 Ma, which can be accomplished by introducing a more weatherable subaerial basaltic terrain. These observations indicate that the consumption of CO2 by continental silicate weathering can force long-term changes in pCO2 comparable to those driven by presumed changes in mantle degassing.

In situ stress analysis in the northern Newark Basin: Implications for induced seismicity from CO2 injection

AbstractWe present detailed stress analysis in a deep well drilled in the northern Newark Rift Basin and evaluate the risk of induced seismicity for underground fluid injection at the locality. In situ stress orientation and magnitudes were estimated using quantitative analysis and modeling of borehole breakouts identified in high‐resolution wellbore images. The distribution of breakouts and natural fractures in the well suggests significant variability in orientation of the principal horizontal stresses in the depth range of 450–1450 m. Evidence from surface seismic reflection imaging indicates potential presence of faults at about 800 m and 1200 m that bound zones of distinctly different stress orientation at this locality. Stability of natural fractures and faults under injection conditions was evaluated for a range of potential stress magnitudes and the observed stress variability with depth. Shallow crust above ~800 m appears to be critically stressed under ambient conditions, and further pore pressure increase would put it at risk of frictional failure on favorably oriented fractures and faults. Deeper reservoirs, however, may allow over 10 MPa increase in pore pressure without fault reactivation due to a more relaxed state of stress. Additional in situ test data are needed to more accurately constrain the magnitude of the minimum horizontal stress in the basin and to enable a more complete assessment of the induced seismic risk from potential CO2 injection in the region.

Rift-basin development: lessons from the Triassic–Jurassic Newark Basin of eastern North America

Abstract We use seismic, field, core, borehole and vitrinite-reflectance data to constrain the development of the Newark Rift Basin, one of the largest and most thoroughly studied basins of the eastern North American rift system that formed during the break-up of Pangaea. These data provide critical information about the geometry of the preserved synrift section and the magnitude of post-rift erosion. We incorporate this information into a new structural restoration of the basin. Our work shows that the Newark Basin was initially narrow (<25 km) and markedly asymmetric; synrift strata show significant thickening towards the basin-bounding faults. Subsequently, the basin became wider (perhaps >100 km wide), deeper (up to 10 km) and less asymmetric; synrift strata exhibit subtle thickening towards the basin-bounding fault system. Several intrabasin faults dissected the Newark Basin after synrift deposition, and the basin fill was tilted ( c. 10°NW) and folded. Erosion (up to 6 km) accompanied the intrabasin faulting, NW tilting and folding, significantly reducing the basin size. Our work suggests that the eastern North American rift system is characterized by a very broad zone of upper-crustal extension in which a few, wide, deep, long-lived, fault-bounded basins (like the Newark Basin) accommodated much of the extension.

Rapid emplacement of the Central Atlantic Magmatic Province as a net sink for CO2

Recent evidence from the ~201.5Ma Central Atlantic Magmatic Province (CAMP) in the Newark rift basin demonstrates that this Large Igneous Province produced a transient doubling of atmospheric pCO2, followed by a falloff to pre-eruptive concentrations over ~300kyr. This paper confirms the short-term findings from the Newark basin, and tests the million-year effects of the CAMP volcanism on Early Jurassic pCO2 from strata in the corollary Hartford basin of Eastern North America (ENA) also using the pedogenic carbonate paleobarometer. We find pCO2 levels for pre-CAMP background of 2000±700ppm (at S(z)=3000±1000ppm), increasing to ~5000±1700ppm immediately above the first lava flow unit, consistent with observations from the Newark. The longer post-extrusive Portland Formation of the Hartford basin records a fourth pulse of pCO2 to ~4500±1200ppm, about 240kyr after the last lava recorded in the ENA section. We interpret this fourth increase as due to a major episode of volcanism, and revise the main CAMP duration to 840±60kyr. The Portland also records a post-eruptive decrease in pCO2 reaching pre-eruptive background concentrations of ~2000ppm in only ~300kyr, and continuing to levels below pre-CAMP background over the subsequent 1.5Myr following the final episode of eruptions. Geochemical modeling (using modified COPSE code) demonstrates that the rapidity of the pCO2 decreases, and fall to concentrations below background can be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the CAMP basalts themselves. These results demonstrate that a continental flood basalt capable of producing a short-term perturbation of the carbon system may actually have an overall net-cooling effect on global climates due to a long-term net-decrease in pCO2 to below pre-eruptive levels, as previous models have suggested followed the emplacement of the Deccan Traps.

Contact zone permeability at intrusion boundaries: new results from hydraulic testing and geophysical logging in the Newark Rift Basin, New York, USA

Hydraulic tests and geophysical logging performed in the Palisades sill and the underlying sedimentary rocks in the NE part of the Newark Rift Basin, New York, USA, confirm that the particular transmissive zones are localized within the dolerite-sedimentary rock contact zone and within a narrow interval below this contact zone that is characterized by the occurrence of small layers of chilled dolerite. Transmissivity values determined from fluid injection, aquifer testing, and flowmeter measurements generally fall in the range of 8.1E-08 to 9.95E-06 m2/s and correspond to various scales of investigation. The analysis of acoustic and optical BHTV images reveals two primary fracture sets within the dolerite and the sedimentary rocks—subhorizontal fractures, intersected by subvertical ones. Despite being highly fractured either with subhorizontal, subvertical or both fracture populations, the dolerite above and the sedimentary rocks below the contact zone and the zone with the layers of chilled dolerite are significantly less conductive. The distribution of the particular conductive intervals is not a function of the two dominant fracture populations or their density but rather of the intrusion path of the sill. The intrusion caused thermal fracturing and cracking of both formations, resulting in higher permeability along the contact zone.

Astronomically tuned geomagnetic polarity timescale for the Late Triassic

Cycle stratigraphic and magnetostratigraphic analyses of a ∼5000‐m‐thick composite section obtained by scientific coring in the Newark rift basin of eastern North America provide a high‐resolution astronomically calibrated geomagnetic polarity timescale (GPTS) spanning over 30 m.y. of the Late Triassic and earliest Jurassic. Only normal polarity is found in ∼1000 m of interbedded volcanics and continental sediments of earliest Jurassic age but a total of 59 normal and reverse polarity magnetozones are delineated in the underlying 4000+ m of Late Triassic continental sediments. Lithologic facies response to climatically induced lake level variation provides a full spectrum of Milankovitch cyclicity; the prominent 404 kyr orbital eccentricity climate cycle has a mean thickness of about 60 m and is the basis for scaling most of the stratigraphic section in time. When indexed to available radioisotopic dating, the resulting astronomically calibrated GPTS spans from the 202 Ma Triassic/Jurassic boundary to 233 Ma. Results of detailed sampling profiles across 42 magnetozone boundaries representing 35 different polarity reversals indicate transition durations that average 7.9 kyr, comparable to the estimated duration of recent polarity reversals. The polarity intervals have a mean duration of 0.53 m.y. with a corresponding reversal rate of 1.88 m.y.−1 and no significant polarity bias and are closely approximated by an exponential distribution with a gamma index k indistinguishable from 1. The longest polarity interval is about 2 m.y., and the shortest is about 0.02 m.y. The overall statistical properties indicate that the behavior of the geomagnetic field in the Late Triassic was not very different from that in the Cenozoic. This geomagnetic polarity record of the Late Triassic provides a well‐dated chronostratigraphic framework suitable for detailed global correlation.

Diagenesis of the Newark Rift Basin, Eastern North America

Late Triassic nonmarine strata in the Newark Rift Basin, eastern North America, accumulated in a subsiding half‐graben prior to opening of the Atlantic Ocean. These strata consist, in ascending order, of the Stockton, Lockatong, and Passaic formations. Although different in specific lithology, these formations all exhibit diagenetic fabrics dominated by authigenic albite and analcime. These same minerals have a similar presence in Late Triassic (Newark Supergroup) strata of other rift‐related basins to the north, suggesting that related authigenesis is not simply a result of local diagenetic factors.The basal deposit, the Stockton Formation, is composed of fluvial sandstones and overbank mudstones, with nodular pedogenic calcite (calcrete). During burial, original micrite was first recrystallized into sparry calcite and then later subjected to partial replacement by authigenic albite, which is also present as overgrowths and void fillings in overbank mudstones. The Lockatong Formation contains organic‐rich shales, carbonates, and evaporative mudstones deposited under cyclic conditions in laterally extensive lacustrine environments. Analcime comprises up to 40% of these strata by volume, occurring within the matrix, as a replacement of original carbonates and evaporites, and as fillings in macrovoids. The overlying Passaic Formation is made up of massive red mudstones, evaporites, and local calcareous lacustrine sequences. Evaporites are replaced by coarse‐grained anhydrite together with some authigenic albite.A central question concerns the source for the Na, Si, and Al required for albite and analcime authigenesis. It is suggested that, in addition to alteration of primary siliciclastic material, sodium in particular was supplied in two ways: (1) from high concentrations in original evaporative brines and groundwaters (Lockatong and Passaic formations); and (2) from dissolution of associated sodium‐bearing evaporites (Lockatong and Passaic Formation) during diagenesis. It is proposed here that basin‐sourced, Na‐enriched brines circulated through the section over time. As albite is more stable at elevated temperatures relative to analcime, it developed in the lowermost strata of the basin (Stockton Formation). Analcime is more prevalent in the overlying Lockatong Formation.

Origin of fibrous gypsum in the Newark rift basin, eastern North America

ABSTRACT Cores from the red beds constituting the Upper Triassic Passaic Formation, a syn-rift sequence in the Newark Basin, display subhorizontal fractures (veins) filled with satin spar gypsum. Such veins are apparent in the shallow subsurface, 100-300 m below present ground level, but are not observed in outcrops or in quarries because of groundwater dissolution. These fractures are roughly parallel to the present ground surface in the basin, suggesting topographic influence on their formation. Fractures observed in cores are seen to crosscut stratigraphic boundaries, indicating that the veins formed after stratal tilting and faulting and thereby post-date the early Late Jurassic. The gypsum crystals making up the vein fill grew perpendicular to the fracture walls, suggesting that opening and filling of the fractures was contemporaneous and that the fractures are extensional. That gypsum crystallizes from meteoric and connate waters and is derived by dissolution of associated evaporites is reflected in the D, 18O, 34S, and 87Sr/86Sr isotopic compositions of the sulfate. Fractures are interpreted to be a result of unloading and exhumation. Fractures were initiated after major depositional and tectonic events took place and post-date the Late Jurassic. Satin spar precipitated in those fractures, carried in by gypsum-saturated brines derived either by dissolution of the near-surface sulfate evaporites or rehydration of more deeply buried anhydrite. Such satin spar veins are not evaporites, but are composed of chemically remobilized sulfate

Origin of Fibrous Gypsum in the Newark Rift Basin, Eastern North America

Origin of Fibrous Gypsum in the Newark Rift Basin, Eastern North America

Evolution of late Triassic rift basin evaporites (Passaic Formation): Newark Basin, Eastern North America

ABSTRACTThe Passaic Formation of the late Triassic Newark Supergroup is 2700 m thick and was deposited in series of wide, deep to shallow lacustrine environments in the Newark rift basin (eastern North America). The Passaic Formation can be divided into lower, middle, and upper sections based on depositional structures, composition and the distribution and morphology of its evaporites. Evaporites formed as a result of syndiagenetic cementation and/or displacive processes. Evaporitive minerals now include gypsum and anhydrite, although other mineral species, such as glauberite, may have originally existed. Most of the evaporites of the Passaic Formation occur within massive red mudstone and siltstone lithologies in the form of diffuse cements, void‐fillings, euhedral crystals, crystal clusters and nodules. These evaporites grew displacively within the fine siliciclastic matrix as a result of changes in the hydrochemical regimes of the rift basin.A well‐developed upward increase in the amount of evaporite material is present in the Passaic Formation. This resulted from: (1) long‐term, progressive increase in aridity, and (2) significant increase in evaporation surface area of the basin during its tectonic evolution. A nonmarine source for the evaporites is evident from the isotopic data. Sulphate δ34S ranges from 11%. to 3.3%. CDT, while δ18O ranges from + 15.1%. to + 20.9%. SMOW, indicating derivation from early diagenetic oxidation of organic sulphur and pyrite within the organic‐rich, lacustrine deposits. The 87Sr/86Sr ratios in sulphate are radiogenic (average 0.71211), showing the interaction of basin waters with detrital components and that the Newark Basin was isolated from the world ocean.Most of the original evaporites show evidence of diagenetic change to polycrystalline and polymineralic pseudomorphs now filled with recrystallized coarse‐grained anhydrite (1–3 mm size) and low‐temperature albite. Homogenization temperatures of fluid inclusions within the coarse‐grained anhydrite indicate crystallization temperatures for anhydrite in the range of 150° to 280°C. Such elevated temperatures resulted from circulation of hot water in the basin. Later exhumation of these rocks caused partial to total replacement of anhydrite by gypsum in the upper part of the section. The resulting increase in volume due to hydration of anhydrite at shallow depths also emplaced non‐evaporative satin‐spar veins (fibrous gypsum) along bedding planes and in fractures.While the local geology of the Newark rift basin controlled the distribution of facies, the sedimentological development of the Passaic Formation evaporites resulted from the world‐wide climatic aridity that prevailed during the late Triassic. because the Newark Basin sequence was only covered with about 3 km of sedimentary overburden that correspond to about 100°C and hence suggests that evaporites have experienced alteration by hot fluids.5 As the Triassic marks the greatest evaporite formation world‐wide and profound sense of parched continentality throughout the world existed before the final break‐up of the Pangea, the Passaic Formation evaporites are an example of the influence of these palaeoclimatic conditions at the eastern margin of North America.

Milankovitch climate forcing in the tropics of Pangaea during the Late Triassic

During the Late Triassic, the Newark rift basin of Eastern North America was in the interior of tropical (2.5–9.5°N) Pangaea. Strikingly cyclical lacustrine rocks comprise most of the 6770 m of continuous core recovered from this basin by the Newark Basin Coring Project. Six of the seven drill cores (each from 800 to 1300 m long) from this project are used to construct a composite lake-level curve that provides a much needed record of long term variations in continental tropical climate. The correlations on which the composite section is based show complete agreement between lake level cycles and independent magnetic polarity boundary isochrons. The main proxy of lake level and hence climate used to construct this lake level curve is a classification of water-depth related sedimentary structures and fabrics called depth ranks. We then use Fourier frequency analysis (both FFT and multitaper methods) and joint time-frequency approaches to resolve the periodic properties of the cyclicity and the secular drift in those properties. A consistent hierarchy in frequencies of the lake level cycles is present throughout the Late Triassic (and earliest Jurassic) portions of the cores, an interval of about 22 m.y.. Calibration of the sediment accumulation rate by a variety of methods shows that these thickness periodicities are consistent with an origin in changes in precipitation governed by celestial mechanics. The full range of precession-related periods of lake level change are present, including the two peaks of the ∼20,000 year cycle of climatic precession, the two peaks of the ∼100,000 year eccentricity cycle, the single peak of the 412,900 year eccentricity cycle, and the ∼2,000,000 year eccentricity cycle. There is also good correspondence in the details of the joint-time frequency properties of lake level cycles and astronomical predictions as well. Even in an ice-free world, the tropical climate of Pangaea responded strongly to astronomical forcing, suggesting that precession-dominated climatic forcing probably always has been a prominent feature of tropical climate.

High-resolution stratigraphy of the Newark rift basin (early Mesozoic, eastern North America)

VirtuallytheentireLateTriassicandear- liest Jurassic age section of the early Meso- zoic Newark continental rift basin has been recoveredinover6770mofcontinuouscore as part of the Newark Basin Coring Project (NBCP). Core was collected using an offset drilling method at seven sites in the central partofthebasin.Thecoresspanmostofthe fluvial Stockton Formation, all of the lacustrine Lockatong and Passaic forma- tions, the Orange Mountain Basalt, and nearly all of the lacustrine Feltville Forma- tion. The cores allow for the first time the full Triassic-age part of the Newark basin stratigraphic sequence to be described in detail. This includes the gray, purple, and red, mostly fluvial Stockton Formation as well as the 53 members that make up the lacustrine Lockatong (mostly gray and black)andPassaic(mostlyred)formations. The nearly 25% overlap zones between each of the stratigraphically adjacent cores are used to test lateral correlations in detail, scalethecorestooneanother,andcombine them in a 4660-m-thick composite section. This composite shows that the entire post- Stockton sedimentary section consists of a hierarchy of sedimentary cycles, thought to be of Milankovitch climate cycle ori- gin. Lithostratigraphic and magnetostrati- graphic correlations between core overlap zonesandoutcropsdemonstratethatthein- dividual sedimentary cycles can be traced essentially basinwide. The agreement be- tween the cyclostratigraphy and magne- tostratigraphy shows both the cycles and the polarity boundaries to be isochronous horizons. Detailed analysis of the Newark basin shows that high-resolution cyclos- tratigraphy is possible in lacustrine, pri- marily red-bed rift sequences and provides a fine-scale framework for global correla- tions and an understanding of continental tropical climate change.

Late Triassic‐earliest Jurassic geomagnetic polarity sequence and paleolatitudes from drill cores in the Newark rift basin, eastern North America

Paleomagnetic study of about 2400 samples from nearly 7 km of core recovered at seven drill sites in the Newark continental rift basin of eastern North America provides a detailed history of geomagnetic reversals and paleolatitudinal motion for about 30 m.y. of the Late Triassic and earliest Jurassic (Carnian to Hettangian). Northward drift of only about 7° is recorded in the continental sediments and minor interbedded basaltic lavas in the basin, from 2.5° to 6.5° north paleolatitude in the Carnian and from 6.5° to 9.5° north paleolatitude over the Norian‐“Rhaetian” and the early Hettangian. A total of 59 polarity intervals, ranging from about 4 m to over 300 m in thickness, have been delineated in a composite stratigraphic section of 4660 m. The lateral continuity and consistent relationship of lithological lake level cycles and magnetozones in the stratigraphically overlapping sections of the drill cores demonstrate their validity as time markers. A geomagnetic polarity timescale was constructed by scaling the composite section assuming that lithostratigraphic members in the predominant lacustrine facies represent the 413‐kyr orbital periodicity of Milankovitch climate change and by extrapolating a sedimentation rate for the fluvial facies in the lower part of the section; a 202 Ma age for the palynological Triassic/Jurassic boundary was used to anchor the chronology based on published concordant radiometric dates linked to the earliest Jurassic igneous extrusive zone. Geomagnetic polarity intervals range from about 0.03 to 2 m.y., have a mean duration of about 0.5 m.y., and show no significant polarity bias. The cyclostratigraphically calibrated record provides a reference section for the history of Late Triassic‐earliest Jurassic geomagnetic reversals. Correlations are attempted with available magnetostratigraphies from nonmarine sediments from the Chinle Group of the southwestern United States and marine limestones from Turkey.

Well Logging Results from the Newark Rift Basin Coring Project

Wireline logs were acquired at seven sites in the Newark Rift basin using dipmeter, gamma ray, resistivity, velocity, porosity, density, magnetic susceptibility, temperature, and acoustic televiewer tools. The logs indicate that the formations are clay rich and dip on average 9°N-NW. Densities are relatively constant (2.60-2.80 glee) and compressional velocities vary from 4.2-5.5 km/s. Thin uranium-rich layers and basalt flows are clearly delineated. The boreholes are mostly in-gauge, but deviated, and borehole temperature gradients vary between 15 to 26°C/km. These data are potentially useful as indicators of fluid flow and regional stress, lithologic cycles, and for core orientation in the Newark Rift basin.

Sedimentation and Diagenesis of Lacustrine Sequences (Upper Triassic) Lockatong Formation, Newark Rift Basin, Eastern USA: ABSTRACT

Sedimentation and Diagenesis of Lacustrine Sequences (Upper Triassic) Lockatong Formation, Newark Rift Basin, Eastern USA: ABSTRACT

Pattern of hydrothermal circulation within the Newark basin from fission-track analysis

Fission-track (FT) data from the Late Triassic-Early Jurassic Newark rift basin indicate long-lived convective downwelling along the border fault. Zircons and apatites from the basin and the surrounding basement yield FT ages averaging ∼180 Ma and ∼140-150 Ma, respectively (i.e., younger than the age of the host rocks). However, along the border fault of the basin, zircon ages exceed 300 Ma and apatite ages are as high as 214 Ma (i.e., older than the depositional ages). The proximity of samples heated to >220 ±40 °C, which reset zircons, and those never heated above 120 ±20 °C across a zone 5-10 km wide indicates an anomalous zone of low temperatures that resulted from the downwelling of water at the border faults. The FT results and other indicators of Hydrothermal flow attest to the circulation of relatively high temperature (100-250 °C) fluids in a pervasive Jurassic hydrothermal convection system. The fluid-convection downwelling along the border fault of the basin may be the consequence of the high topography that bordered the Newark basin in Triassic and Jurassic time. Hydrothermal flow ended by the time coastal-plain sediments covered the basin. Hydrothermal fluids circulating in extensional environments are potentially very important in modifying the temperature structure of the basins and crust.