John H. Puffer

Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province

Life Versus the Volcanoes Correlating a specific triggering event, such as an asteroid impact or massive volcanism, to mass extinction events is clouded by the difficulty in precisely timing their occurrence in the geologic record. Based on rock samples collected in North America and Morocco, Blackburn et al. (p. 941, published online 21 March) acquired accurate ages for events surrounding the mass extinction that occurred ∼201 million years ago, between the Triassic and Jurassic Periods. The timing of the disappearance of marine and land fossils and geochemical evidence of the sequential eruption of the Central Atlantic Magmatic Province imply a strong causal relationship. Climate change triggered by massive volcanism set the stage for the era of dinosaurs. The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here, we present new zircon uranium-lead (U-Pb) geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over about 600,000 years, indicating expansive volcanism even as the biologic recovery was under way.

Separation of Morocco and eastern North America: A Triassic-Liassic stratigraphic record

New primary data from northwest Africa show that the lower Mesozoic rocks of Morocco rest with profound unconformity on Hercynian metamorphic and/or Autunian sedimentary rocks and occur in three distinct, partially synchronous volcanic-sedimentologic provinces: the Oran Meseta, the High Atlas, and the Moroccan Meseta. The Oran Meseta of northwestern Morocco contains a Middle to Late Triassic andesite and carbonate-evaporite facies related genetically to the Tethys basin. The High Atlas province of southwestern Morocco consists of Late Triassic to Early Jurassic red beds and evaporites interbedded with tholeiite lavas. These tholeiites are underlain by the Minutosaccus - Patinasporites Concurrent Range Zone of middle Carnian age and yield an average isotopic age of about 196 m.y. They are time- and rock-stratigraphic correlatives of the First and Second Watchung-York Haven suite and the Quarryville basalts of Pennsylvania and New Jersey. The Moroccan Meseta of western and central Morocco consists of Lower Jurassic (Liassic) evaporites intercalated with low-alkali quartz tholeiites, yielding an isotopic mean age of 186 ± 8 m.y. This tholeiite is a rock- and time-stratigraphic correlative of the Rossville basalt of Pennsylvania. The tectonic model best explaining the chemical and stratigraphic distribution of lower Mesozoic rock now on the margins of the North Atlantic includes the following sequence: (1) Permian to Late Triassic uplift and crustal thinning along the axis of the future Atlantic Ocean; (2) Middle to Late Triassic strike-slip faulting and andesitic volcanism along east-trending fracture zones, followed by a westward advance of the Tethys Sea across northern Morocco; (3) Late Triassic rifting along the axis of the proto-Atlantic Ocean and shearing along east-west fracture zones, which had the combined effect of decoupling segments of the African and North American plates and providing a pathway for the marine transgression of the Tethys Sea across northern Morocco and south along the axis of rifting; and (4) Late Triassic to Early Jurassic crustal extension and extrusion of olivine and quartz tholeiites, followed by extrusion of subalkalic quartz tholeiites and collapse of the continental margins with the concomitant deposition of marine carbonates.

Cyclo-, Magneto-, and Bio-Stratigraphic Constraints on the Duration of the CAMP Event and its Relationship to the Triassic-Jurassic Boundary

Early Mesozoic tholeiitic flood basalts of the Central Atlantic Magmatic Province (CAMP) are interbedded throughout much of their extent with cyclical lacustrine strata, allowing Milankovitch calibration of the duration of the extrusive episode. This cyclostratigraphy extends from the Newark basin of the northeastern US, where it was first worked out, to Nova Scotia and Morocco and constrains the outcropping extrusive event to less than 600 ky in duration, beginning roughly 20 ky after the Triassic-Jurassic boundary, and to within one pollen and spore zone and one vertebrate biochron. Based principally on the well-known Newark astronomically calibrated magnetic polarity time scale with new additions from the Hartford basin, the rather large scatter in recent radiometric dates from across CAMP (>10 m.y. ), centering on about ∼200 m.y., is not likely to be real. Rather, the existing paleomagnetic data from both intrusive and extrusive rocks suggest emplacement of nearly all the CAMP within less than 3 m.y. of nearly entirely normal polarity. The very few examples of reversed magnetizations suggest that some CAMP activity probably occurred just prior to the Triassic-Jurassic boundary. Published paleomagnetic and 40 Ar/ 39 Ar data from the Clubhouse Crossroads Basalt are reviewed and with new paleomagnetic data suggest that alteration and possible core misorientation could be responsible for the apparent differences with the CAMP. The Clubhouse Crossroads Basalt at the base of the Coastal Plain of South Carolina and Georgia provides a link to the volumetrically massive volcanic wedge of seaward dipping reflectors present in the subsurface off the southeastern US that may be part of the same igneous event, suggesting that the CAMP marks the formation of the oldest Atlantic oceanic crust.

Chemical composition and stratigraphic correlation of Mesozoic basalt units of the Newark Basin, New Jersey, and the Hartford Basin, Connecticut: Summary

New major– and trace– element analyses of the Messozoic basalts of the Hartford Basin of Connecticut (the Talcott, Holyoke, and Hampden Basalts) indicate that the basalts are chemically very similar to the Mesozoic basalts of the Newark Basin of New Jersey (the First, Second, and Third Watchung Basalts). Our geochemical data impose some constraints on any time-stratigraphic correlation of the basalts in the two basins. We suggest that the Holyoke and Second Watchung Basalts are fractionation products of a Talcott-First Watchung parent magma. We also suggest that the Hampden and Third Watchung Basalts are synchronous fractionation products of a magma unlike any of the eastern North American basalt types described in the literature, but they may instead be the fractionation products of a magma resembling a magma of the same type as that of the Mid-Atlantic Ridge. From a petrologic standpoint, the most straight-forward time-stratigraphic interpretation is a one-to-one correlation of the three flows of the Newark Basin with the three flows of the Hartford Basin. Our geochemical and petrologic evidence is particularly supportive of time-stratigraphic correlations between the First Watchung and the Talcott basalts and between the Third Watchung and the Hampden basalts. Our data, however, are not inconsistent with the possibility that the Second Watchung may be slightly older than the Holyoke Basalt.

Distribution and Origin of Magnetite Spherules in Air, Waters, and Sediments of the Greater New York City Area and the North Atlantic Ocean

ABSTRACT Perfectly spherical sand to clay size particles composed of magnetite occur in a wide variety of environments. Within the greater New York City area such spherules are found in smoke-stack filtrate, urban-air filtrate, ditritus collected from highway surfaces, lake sediments, marsh sediments, and in beach sands. The abundance of spherules in such environments diminishes away from industrial centers. The abundance of magnetite spherules in core samples of lake and marsh sediment decreases sharply near the palynologically determined stratigraphic boundary separating sediments deposited before the area was settled and industrialized from sediments deposited afterward. Their abundance in samples of deep ocean-floor sediment also drops off sharply within the upper 10 cm of core. The spheru es become rare to absent below this depth. We conclude that the great majority of magnetic spherules presently accumulating in sediments are of industrial origin, while we recognize the existence of spherules of probable extraterrestrial origin in ancient sediments. The ease of identification and recovery of magnetite spherules from sediments facilitates their use as indicators of probable post-industrial age.

Transmission of Flood Basalts through a Shallow Crustal Sill and the Correlation of Sill Layers with Extrusive Flows: The Palisades Intrusive System and the Basalts of the Newark Basin, New Jersey, U.S.A.

The Palisades Intrusive System consists of a 350-m-thick early Jurassic sill together with thinner comagmatic sills and dikes exposed within the Newark Basin of New Jersey and New York. The Palisades System is overlain by flood basalt that is interbedded with early Jurassic redbed formations. New and recently published data indicate that some of the basalt flows correlate with geochemically defined layers within a central well-exposed sill portion of the Palisades System at Fort Lee, New Jersey. Our interpretation views the sill as a progressively inflated conduit through which huge volumes of flood basalt flowed. The geochemical data are consistent with a Palisades sill fed by three compositionally distinct intrusion events. The first magma flowed through the sill and broke out near the northern end as three Orange Mountain basalt flows. Each of the three extrusive pulses is identified within the lower 150 m of the sill on the basis of distinct geochemical reversals. The end stage of each pulse was characterized by pyroxene phenocryst accumulation within the sill. Magma from a second source inflated the sill by an additional 170 m after approximately 260 k.yr. of minor intermittent igneous activity interbedded with sediments deposited above the Orange Mountain basalt. The second magma extruded as a highly fractionated 150-m-thick Preakness basalt flow and crystallized as a central layer of Palisades diabase of similar composition. Subsequent extrusions of relatively thin Preakness flows (magma 3) correlate with upper layers of the Palisades sill. We interpret the distinct layering of the Palisades sill as injections of magmas that were largely prefractionated at deeper levels and then modified to varying degrees by in situ processes.

A Reactivated Back‐Arc Source for CAMP Magma

Although several Mesozoic magma types are found within the geographic boundaries of CAMP, magmatic activity peaked during the extrusion of basalt characterized by 1 wt. % TiO 2 and a uniform composition that is found on each of the circum-Atlantic continents. Other CAMP magmas pre-date or post-date this peak CAMP event or are confined to restricted portion of the province. Evidence is presented indicating that most CAMP basalt is the product of decompression induced eutectic melting of a back-arc source that had been dormant since Paleozoic magmatism associated with the assembly of Pangea. The composition of most CAMP basalt is unlike OIB, plume, hot -spot, N-MORB, or E-MORB magma types but resembles typical arc-related basalt and back-arc basin basalt in particular. Similarities to arc and back-arc basalts include a distinct negative Nb anomaly and overlapping lines plotted on silicate earth normalized spider diagrams. The uniform composition of CAMP basalt indicates that fractionation and contamination played only minor roles and that CAMP magma was quickly generated and extruded during the break-up of Pangea. The composition of CAMP basalt also closely resembles Paleozoic volcanics that stratigraphically underlie Eastern North American CAMP flows including the Ordovician Ammonoosuc and Partridge Formations and the Silurian Newbury and Lieghton Formations that were extruded onto arcs and back-arc basins during the assembly of Pangea. The enriched mantle involved in the Paleozoic magmatism remained trapped under the Laurentian - Gondwana suture until early Jurassic extentional tectonism forced renewed melting.

Supercontinental inheritance and its influence on supercontinental breakup: The Central Atlantic Magmatic Province and the breakup of Pangea

The Central Atlantic Magmatic Province (CAMP) is the large igneous province (LIP) that coincides with the breakup of the supercontinent Pangea. Major and trace element data, Sr-Nd-Pb radiogenic isotopes, and high-precision olivine chemistry were collected on primitive CAMP dikes from Virginia (VA). These new samples were used in conjunction with a global CAMP data set to elucidate different mechanisms for supercontinent breakup and LIP formation. On the Eastern North American Margin, CAMP flows are found primarily in rift basins that can be divided into northern or southern groups based on differences in tectonic evolution, rifting history, and supercontinental inheritance. Geochemical signatures of CAMP suggest an upper mantle source modified by subduction processes. We propose that the greater number of accretionary events, or metasomatism by sediment melts as opposed to fluids on the northern versus the southern Laurentian margin during the formation of Pangea led to different subduction-related signatures in the mantle source of the northern versus southern CAMP lavas. CAMP samples have elevated Ni and low Ca in olivine phenocrysts indicating a significant pyroxenite component in the source, interpreted here as a result of subduction metasomatism. Different collisional styles during the Alleghanian orogeny in the North and South may have led to the diachroneity of the rifting of Pangea. Furthermore, due to a low angle of subduction, the Rheic Plate may have underplated the lithosphere then delaminated, triggering both the breakup of Pangea and the formation of CAMP.

Pegmatoid and Gabbroid Layers in Jurassic Preakness and Hook Mountain Basalts, Newark Basin, New Jersey

Coarse‐grained segregations are found in several subaerial flows of Jurassic flood basalts in the Watchung Mountains, New Jersey. They are particularly common within a 140–180‐m‐thick quartz‐tholeiitic Preakness flow, the thickest of the Watchung flows. The segregations are enriched in iron and depleted in aluminum compared with the enclosing basaltic rock and are composed of pyroxene, plagioclase, and magnetite in a dark fine‐grained interstice. Most of the segregations are characterized by a 0.1–0.6‐cm (gabbroid) crystal size range, but a few lenses are characterized by a 0.4–2‐cm (pegmatoid) size range. Three types of coarse‐grained segregations are found within the thickest Preakness flow: type 1, vesicular horizontal sheets (<2 m, typically 5–20 cm thick) within the upper 40 m of the flow; type 2, a thick (10–30 m) mappable but discontinuous nonvesicular layer located at the contact of the colonnade with the overlying entablature; and type 3, very thick (up to 96 m) lens‐shaped accumulations within thickened portions of the flow. No single mechanism is capable of generating all three types. Our evidence indicates that most type 1 segregations were transported from the top of the lower crystallization front to the base of the upper crystallization front as vesiculated diapirs of residual melt, and type 2 segregations were filter pressed out of thickened lower colonnade during the collapse of crystal networks. At two locations, some type 2 residual melt drained into depressions caused by local subsidence, resulting in type 3 accumulations.

Distribution of asbestos in the bedrock of the northern New Jersey area

Asbestos has been identified at fifty-five locations in the bedrock of the northern New Jersey area. Most occurrences are confined to (1) The Precambrian rocks of the New Jersey Highlands, particularly the marbles; (2) the Paleozoic serpentinites of Staten Island, New York, and Hoboken, New Jersey; and (3) the Mesozoic basaltic rocks of the Newark Basin. Chrysotile and tremolite asbestos are present in local concentrations in the marbles. In the most extensive exposure of the marble, the Franklin band, traces of tremolite-actinolite asbestos are commonly present. Crocidolite asbestos occurs in localized areas associated with fracture systems in Precambrian pegmatites and associated rocks. The Paleozoic serpentinites contain chrysotile asbestos as a major component in deformed zones. Megascopic chrysotile and anthophyllite asbestos veins occur locally in the serpentinites. Actinolite asbestos occurs in the Mesozoic basaltic rocks of the Newark Basin.Potential environmental problems associated with asbestosbearing bedrock include production and use of rock products containing asbestos, introduction of asbestos into environments surrounding excavations, and asbestos contamination of soils and water supplies.