József Pálfy

Synchrony between Early Jurassic extinction, oceanic anoxic event, and the Karoo-Ferrar flood basalt volcanism

A well-known second-order mass extinction took place during the Pliensbachian and Toarcian Stages of the Early Jurassic. First recognized as a minor Pliensbachian peak in the global extinction rate, it has alternatively been interpreted as a regional response to the early Toarcian oceanic anoxic event. Detailed studies established it as a global long-term event spanning five successive ammonoid zones. Here we present a revised time scale based on highprecision U-Pb ages resolved to the zone level, which suggests that elevated extinction rates were sustained for about 4 m.y. and peak extinction occurred at 183 Ma. Recent isotopic dating of flood basalts from the southern Gondwanan Karoo and Ferrar provinces documents a culmination in volcanic activity ca. 183 Ma. The onset of volcanism is recorded as an inflection and start of a rapid rise of the seawater 87 Sr/ 86 Sr curve. The synchrony of voluminous flood basalt eruptions and biotic crises, as already noted for three of the major mass extinctions, permits a causal relationship, which in this case may be mediated by widespread oceanic anoxia.

The Triassic timescale: new constraints and a review of geochronological data

Abstract A review of geochronological data underlying the geological timescale for the Triassic yields a significantly different timescale calibration than that published in the most recent compilation (Geologic TimeScale 2004). This is partly due to the availability of new radio–isotopic data, but mostly because strict selection criteria are applied and complications arising from biases (both systematic and random) are accounted for in this contribution. The ages for the base and the top of the Triassic are constrained by U–Pb ages to 252.3 and 201.5 Ma, respectively. These dates also constrain the ages of major extinction events at the Permian–Triassic and Triassic–Jurassic boundaries, and are statistically indistinguishable from ages obtained for the Siberian Traps and volcanic products from the Central Atlantic Magmatic Province, respectively, suggesting a causal link. Ages for these continental volcanics, however, are mostly from the K–Ar (40Ar/39Ar) system, which requires accounting and correcting for a systematic bias of c. 1% between U–Pb and 40Ar/39Ar isotopic ages (the 40Ar/39Ar ages being younger). Robust age constraints also exist for the Induan–Olenekian boundary (251.2 Ma) and the Early–Middle Triassic (Olenekian–Anisian) boundary (247.2 Ma), resulting in a surprisingly short duration of the Early Triassic, which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time. Furthermore, the Anisian–Ladinian boundary is constrained to 242.0 Ma by new U–Pb and 40Ar/39Ar ages. Radio–isotopic ages for the Late Triassic are scarce, and the only reliable and biostratigraphically-controlled age is from an upper Carnian tuff dated to 230.9 Ma, yielding a duration of more than 35 Ma for the Late Triassic. All of these ages are from U–Pb analyses applied to zircons with uncertainties at the permil level or better. The resulting compilation can only serve as a guideline and must be considered a snapshot, resolving some of the issues mainly associated with inaccurate and misinterpreted data in previous publications. However, further advances will require revision of some of the data presented here.

Timing the end-Triassic mass extinction: First on land, then in the sea?

The end-Triassic marks one of the five biggest mass extinctions, but current geologic time scales are inadequate for understanding its dynamics. A tuff layer in marine sedimentary rocks encompassing the Triassic-Jurassic transition yielded a U-Pb zircon age of 199.6 ± 0.3 Ma. The dated level is immediately below a prominent change in radiolarian faunas and the last occurrence of conodonts. Additional recently obtained U-Pb ages integrated with ammonoid biochronology confirm that the Triassic Period ended ca. 200 Ma, several million years later than suggested by previous time scales. Published dating of continental sections suggests that the extinction peak of terrestrial plants and vertebrates occurred before 200.6 Ma. The end-Triassic biotic crisis on land therefore appears to have preceded that in the sea by at least several hundred thousand years.

Volcanism of the Central Atlantic Magmatic Province as a Potential Driving Force in the End‐Triassic Mass Extinction

Radiometric dating suggests that eruptions in the Central Atlantic magmatic province (CAMP) are synchronous with the ∼200 Ma end-Triassic mass extinction. Although stratigraphic evidence for major flows prior to the extinction horizon is still lacking, the vast extent of the province allows the assumption of cause-and-effect relationship between volcanism and extinction, mediated by drastic environmental change. A recently recognized negative carbon isotope anomaly at the Triassic-Jurassic boundary is interpreted to reflect combined effects of volcanically derived CO 2 input, methane release through dissociation of gas hydrates in a global warming episode, and a possible marine productivity crisis. Maximum duration of the Rhaetian stage is estimated as only 2 m.y., and the isotope event appears short, lasting for less than 100 k.y. A variety of marine and terrestrial fossil groups (e.g., radiolarians, corals, bivalves, and plants) experienced correlated and sudden extinction at the end of Triassic, although some groups (e.g., ammonoids and conodonts) underwent a prolonged period of declining diversity. Post-extinction faunas and floras are cosmopolitan. Biotic recovery was delayed and the earliest Hettangian is a lag phase characterized by low diversity, possibly due to sustained environmental stress. The hypothesis of CAMP as the principal driving force in the end-Triassic extinction appears more consistent with paleontological and isotopic observations than alternative models. The temporally adjacent large igneous provinces, the Siberian Traps at the Permian-Triassic boundary and the Early Jurassic Karoo-Ferrar province, are also linked to extinction events, albeit of differing magnitude.

Dating the end-Triassic and Early Jurassic mass extinctions, correlative large igneous provinces, and isotopic events

The end-Triassic marks one of the five biggest mass extinctions, and was followed by a well-known second-order extinction event in the Early Jurassic. Previously published geological time scales were inadequate for correlation of extinctions with other global events and to unravel their dynamics. Here we present a revised time scale based on high-precision U-Pb ages integrated with ammonoid biochronology resolved to the zone level. This compilation suggests that the end of the Triassic Period (ca. 200 Ma) coincided with peak volcanism in the Central Atlantic magmatic province and that terrestrial floral and faunal extinctions may have slightly preceded the marine biotic crisis. The Sr/Sr and dC stratigraphic records are compatible with volcanically induced global environmental change that could be the proximal cause of extinction. The revised Early Jurassic time scale suggests that peak extinction in the early Toarcian occurred at 183 Ma. Recent isotopic dating of flood basalts from the southern Gondwanan Karoo and Ferrar provinces documents a synchronous culmination in volcanic activity at 183 2 Ma. The onset of volcanism is correlative with the start of a rapid rise in seawater Sr/Sr ratios. A recently recognized negative dC anomaly, tentatively ascribed to a massive release of methane hydrate, and the subsequent widespread oceanic anoxia suggest that the environmental perturbations thought to trigger the extinction also seriously disrupted the global carbon cycle. The interval between these two extinctions is 18 m.y., significantly shorter than the hypothetical 26 m.y. periodicity of extinctions. Palfy, J., Smith, P.L., and Mortensen, J.K., 2002, Dating the end-Triassic and Early Jurassic mass extinctions, correlative large igneous provinces, and isotopic events, in Koeberl, C., and MacLeod, K.G., eds., Catastrophic Events and Mass Extinctions: Impacts and Beyond: Boulder, Colorado, Geological Society of America Special Paper 356, p. 523–532. *E-mail: palfy@paleo.nhmus.hu INTRODUCTION The Mesozoic era is framed by the two most studied mass extinctions, the end-Permian and Cretaceous-Tertiary events. Much less research effort has been devoted to two other events that occurred in the first half of the Mesozoic, i.e., at the close of Triassic and in the Early Jurassic. The end-Triassic mass extinction is the least studied and most poorly understood event among the five major mass extinctions (Hallam, 1996a). A subsequent extinction in the Early Jurassic, a second-order event J. Palfy, P.L. Smith, and J.K. Mortensen 524 close to the Pliensbachian-Toarcian boundary, is one of the better known minor events (Harries and Little, 1999). However, a common impediment to the reconstruction of these crises and identification of their causes is the inadequate knowledge of their timing, due to the poor calibration of the latest Triassic and Early Jurassic time scale. Extraterrestrial impacts, climate changes, sea-level changes, oceanic anoxia, and flood basalt volcanism are among the most frequently cited agents that could lead to elevated extinction rates or ecosystem collapse. In each case, testing of competing hypotheses requires precise timing and correlation of events. A recent revision of the Jurassic numerical time scale employed high-precision U-Pb zircon or Ar/Ar geochronology of volcanic-ash layers embedded in fossiliferous sedimentary rocks (Palfy et al., 2000b). Herein we review the new timing limitations of early Mesozoic extinctions in order to gain new insights into their potential causes. The ramifications of the refined time frame have been discussed elsewhere for the end-Triassic (Palfy et al., 2000a) and early Toarcian events (Palfy and Smith, 2000). In this chapter we compare the two events and cite evidence for the synchronicity of extinctions and pulses of flood basalt volcanism. Temporal relationships between biotic crises and flood basalt volcanism in the Central Atlantic magmatic province and the Karoo-Ferrar igneous province are analyzed using a summary of recently published isotopic dates for the two large igneous provinces. Synchrony suggests possible causal relationships, as proposed earlier (e.g., Rampino and Stothers, 1988; Courtillot, 1994). If volcanically triggered environmental perturbations were the driving force of these extinctions, then distinctive isotopic signatures are expected in the stratigraphic record and can be used to test hypotheses. Therefore we also assess the compatibility of such scenarios with recent isotopic data. RADIOMETRIC DATING OF EARLY MESOZOIC EXTINCTIONS The accuracy of numerical time scales commonly used in the 1990s (e.g., Harland et al., 1990; Gradstein et al., 1994; Fig. 1) is compromised by several problems: (1) they are based on a small number of isotopic ages, (2) many of the isotopic ages were produced by K-Ar and Rb-Sr dating methods, which are considered less reliable than U-Pb and Ar/Ar ages, and (3) the unjustified assumption of equal duration of biochronologic units is used for interpolation and the estimation of boundary ages. Recent integrated dating around the critical extinction intervals, primarily using U-Pb geochronology and ammonite biochronology from the western North American Cordillera, is summarized here. This work led to the first interpolation-free, independent stage and zonal boundary and duration estimates (Palfy et al. 2000b; Fig. 1). The biochronological underpinning of the time scale is a North American regional ammonoid zonal scheme correlated with the primary standard chronostratigraphy of northwestern Europe (Smith et al., 1988, 1994; Jakobs et al., 1994). Age of the end-Triassic event It is generally accepted that a mass extinction corresponds to the Triassic-Jurassic (Tr-J) system boundary, even though detailed documentation is hindered by a dearth of fossiliferous and continuous sections worldwide (Hallam, 1990). One of the four proposed sections for the basal Jurassic Global Stratotype Section and Point is located on Kunga Island (Queen Charlotte Islands, British Columbia). At this locality, a tuff layer in the marine sedimentary section that contains the Tr-J boundary yielded a U-Pb zircon age of 199.6 0.4 Ma (Palfy et al., 2000a). This age provides a direct estimate for the age of the Tr-J boundary because the sampled layer is immediately below the system boundary as defined by integrated radiolarian, ammonoid, and conodont biochronology. Ages quoted by published time scales are invariably older by several million years (Fig. 1). The two most widely used estimates are 208.0 7.5 Ma (Harland et al., 1990) and 205.7 4.0 Ma (Gradstein et al., 1994). Other time scales list 208 Ma (Palmer, 1983), 210 Ma (Haq et al., 1988), and 203 Ma (Odin, 1994) as the best boundary estimates. Several additional biostratigraphically defined U-Pb dates were recently obtained from marine island arc terranes of the North American Cordillera (Table 1). These dates were not considered in previous time scales, but they convincingly support the conclusion that the true age of the Tr-J boundary is close to 200 Ma (Palfy et al., 2000a). The age of the end-Triassic extinction can also be estimated from terrestrial sections in eastern North America, where precise U-Pb dates are available from volcanic units within the continental Newark Supergroup (Dunning and Hodych, 1990; Hodych and Dunning, 1992). The North Mountain Basalt was dated as 201.7 1.4/ 1.1 Ma, whereas the Palisades and Gettysburg sills yielded ages of 200.9 1.0 Ma and 201.3 1.0 Ma, respectively. On the basis of geochemical and field evidence, the Palisades sill appears to have fed the lowermost flows of the Orange Mountain Basalt (Ratcliffe, 1988). The extrusive volcanic rocks postdate the palynologically defined Tr-J boundary (Fowell and Olsen, 1993) by only 20–40 k.y., on the basis of cyclostratigraphic evidence (Olsen et al., 1996). Vertebrate extinction, as deduced from tetrapod remains (Olsen et al., 1987) and their trace fossil record (Silvestri and Szajna, 1993), is coincident with the peak in floral turnover. The three overlapping isotopic ages and their respective errors suggest that the terrestrial extinction occurred no later than 200.6 Ma. The marine event, best represented by a sharp turnover in radiolarian taxa and delimited by the U-Pb age from Kunga Island, did not occur before 200.0 Ma. Taking these dates at face value suggests that the crisis of terrestrial biota preceded that of the marine realm by at least 600 k.y. (Palfy et al., 2000a). This is the first indication of such temporal dichotomy within a major mass extinction. Dating the end-Triassic and Early Jurassic mass extinctions, correlative large igneous provinces, and isotopic events 525 Figure 1. Comparison of Early Jurassic and latest Triassic (shaded) numerical time scales. Note different estimates for age of Triassic-Jurassic and Pliensbachian-Toarcian boundaries in previously widely used time scales vs. revised scale of Palfy et al. (2000b). Small numbers at stage boundaries indicate stated uncertainty of estimates. Stage abbreviations: NOR, Norian; RHA, Rhaetian; HET, Hettangian; SIN, Sinemurian; PLB, Pliensbachian; TOA, Toarcian. Time-scale abbreviations: DNAG, Decade of North American Geology; GTS, geological time scale; MTS, Mesozoic time scale. Note that Rhaetian stage is not recognized by DNAG scale, whereas Odin (1994) did not estimate age of Norian-Rhaetian boundary. TABLE 1. LIST OF RECENTLY PUBLISHED U-Pb ZIRCON DATES RELEVANT TO THE AGE OF THE TRIASSIC-JURASSIC BOUNDARY

Sinemurian (Lower Jurassic)ammonoid biostratigraphy of the Queen Charlotte Islands, Western Canada

Abstract The Sinemurian ammonoid succession of the Queen Charlotte Islands is subdivided into, in assending order, the Canadensis Zone, the “Coroniceras”, Arnouldi, Varians, Harbledownense, and Tetraspidoceras assemblages. The Hettangian-Sinemurian boundar is drawn within the Canadensis Zone, at the first appearance of Badouxia columbiae and Metophioceras div. sp. The Sinemurian-Pliensbachian boundary has not yet been satisfactorily defined as the Tetraspidoceras Assemblage contains elements with both Sinemurian and Pliensbachian affinities. Correlation with the northwest European Standard Zonation as well as with the Mediterranean Province and South America is possible but often ambiguous. The present scheme contributes to the development of a Standard ammonite Zonation for North America.

THE OLDEST TRIASSIC PLATFORM MARGIN REEF FROM THE ALPINE - CARPATHIAN REGION (AGGTELEK, NE HUNGARY): PLATFORM EVOLUTION, REEFAL BIOTA AND BIOSTRATIGRAPHIC FRAMEWORK

The 1:10,000 scale mapping of the southern part of the Aggtelek Plateau (Western Carpathians, Silica Nappe, NE Hungary) and the study of five sections revealed two Middle Triassic reef bodies. In the late Pelsonian the uniform Steinalm Platform was drowned and dissected due to the Reifling Event. A connection with the open sea was established, indicated by the appearance of gladigondolellid conodonts from the early Illyrian. Basins and highs were formed. In the NW part of the studied area lower - middle? Illyrian basinal carbonates were followed by a platform margin reef (early?-middle Illyrian; reef stage 1) developed on a morphological high. This is the oldest known Triassic platform margin reef within the Alpine-Carpathian region. The reef association is dominated by sphinctozoans and microproblematics. The fossils are characteristic of the Wetterstein-type reef communities. Differently from this in the SE part of the studied region a basin existed from the late Pelsonian until the early Ladinian. During the late Illyrian- early Ladinian, the reef prograded to the SE, and reef stage 2 was established. Meanwhile, on the NW part of the platform a lagoon was formed behind the reef. Based on our palaeontological study the stratigraphic range of Colospongia catenulata, Follicatena cautica, Solenolmia manon manon, Vesicocaulis oenipontanus must be extended down to the middle Illyrian. Synsedimentary tectonics were detected in the 1. Binodosus Subzone, 2. Trinodosus Zone - the most part of the Reitzi Zone, 3. Avisianum Subzone.

The quest for refined calibration of the Jurassic time-scale

The Jurassic time-scale assigns numerical ages to boundaries of chronostratigraphic units. A well-established ammonite biochronology forms the basis of stage definitions that are being formalized by Global Stratotype Sections and Points. Two major updates of the Jurassic time-scale (referred to as JTS2000 and GTS2004) were published recently. JTS2000 relies heavily on U-Pb and 40 Ar/ 39 Ar dates, whereas GTS2004 emphasizes complementary scaling methods using strontium (Sr) isotope stratigraphy, cyclostratigraphy and magnetostratigraphy. U-Pb and 40 Ar/ 39 Ar dates remain the backbone of the time-scale; relevant new developments are reviewed briefly. Fourteen recently published ages are added to the database of calibration points. Floating cyclostratigraphies already cover a significant portion of the Jurassic, allowing measurements of durations that need to be anchored and linked to chronostratigraphy. Where tie-points are sparse, reliance on scaling methods remains necessary. Sr isotope stratigraphy and magnetostratigraphy are increasingly sophisticated and useful for both correlation and scaling. Further refinements of calibration are expected from more accurate and densely spaced radioisotopic age tie-points, especially in the Late Jurassic, and from an extended coverage of Jurassic astrochronology. In the computer era, time-scales increasingly are being delivered digitally, updated continuously and accessed interactively by their users.

Did the Puchezh-Katunki Impact Trigger an Extinction?

The 80 km diameter Puchezh-Katunki impact crater is the only one of the six largest known Phanerozoic craters that has not been previously considered as a factor in a biotic extinction event. The age of impact is currently regarded as Bajocian (Middle Jurassic), on the basis of palynostratigraphy of crater lake sediments, but there is no significant extinction in the Bajocian. Earlier K-Ar age determinations of impactites compared with a current Jurassic time scale permit that either the end-Triassic or the Early Jurassic (Pliensbachian-Toarcian) extinction was coeval with the Puchezh-Katunki crater. The stratigraphical and paleontological record contains clues that suggest that an impact may have occurred at these horizons. The age of the Puchezh-Katunki crater needs reevaluation through 40Ar/39Ar dating of impact rocks and/or revision of the palynology of the oldest crater fill. A definitive age determination will help constrain the impact-kill curve.

Small-scale moisture availability increase during the 8.2-ka climatic event inferred from biotic proxy records in the South Carpathians (SE Romania)

In this paper, we present high-resolution early Holocene pollen, plant macrofossil, charcoal, diatom, biogenic silica, and loss-on-ignition records from a mountain lake in the South Carpathians in order to reveal ecosystem response to the 8.2-ka climatic oscillation. We found significant changes both in terrestrial vegetation and lake diatom assemblages in the northern slope of the Retezat Mts between c. 8300 and 8000 cal. yr BP. Rapid changes in relative frequencies and pollen accumulation rates of the major deciduous pollen types associated with peaks in microcharcoal accumulation rates suggested that vegetation disturbance mainly took place in the mixed-deciduous forest zone, where woodland fires partially destroyed the populations of Fraxinus excelsior, Quercus, and Corylus avellana and facilitated the establishment of Carpinus betulus in the forest openings. The diatom record furthermore showed the spread of a planktonic diatom species, Aulacoseira valida, at 8150 cal. yr BP, coincidently with a short-lived expansion of C. betulus. Since diatom blooms mainly occur in spring in the Retezat Mts, increased spring water depth and increased water turbulence were inferred from these data. The expansion of C. betulus against F. excelsior and C. avellana at the same time suggested a modest increase in available moisture during the growing season. Taken together, these data imply that during the 8.2-ka event, winter and spring season available moisture increased, while summers were characterized by alternating moist/cool and dry/warm conditions.