Leopold Krystyn

Rapid marine recovery after the end-Permian mass-extinction event in the absence of marine anoxia

A new Early Triassic marine fauna is described from the Central Oman Mountains. The fauna is Griesbachian in age, on the basis of abundant conodonts and ammonoids, and was deposited in an oxygenated seamount setting off the Arabian platform margin. It is the first Griesbachian assemblage from a well-oxygenated marine setting and thus provides a test for the hypothesis that widespread anoxia prevented rapid recovery. The earliest Griesbachian (parvus zone) contains a low-diversity benthic fauna dominated by the bivalves Promyalina and Claraia. A similar level of recovery characterizes the immediate postextinction interval worldwide. However, the middle upper Griesbachian sedimentary rocks (isarcica and carinata zones) contain an incredibly diverse benthic fauna of bivalves, gastropods, articulate brachiopods, a new undescribed crinoid, echinoids, and ostracods. This fauna is more diverse and ecologically complex than the typical middle to late Griesbachian faunas described from oxygen-restricted settings worldwide. The level of postextinction recovery observed in the Oman fauna is not recorded elsewhere until the Spathian. These data support the hypothesis that the apparent delay in recovery after the end-Permian extinction event was due to widespread and prolonged benthic oxygen restriction: in the absence of anoxia, marine recovery is much faster.

CONODONTS OF THE LOWERMOST TRIASSIC OF SPITI, AND NEW ZONATION BASED ON NEOGONDOLELLA SUCCESSIONS

Conodonts from the lowermost Triassic Otoceras woodwardi beds and adjacent strata of Spiti are described and compared with Permian-Triassic (P-T) boundary bed faunas from elsewhere. A new pelagic zonation based on Neogondolella is introduced: the interval characterized by N. carinata-N. taylorae is subdivided into three parts based on successive first appearances of N. meishanensis , N. krystyni Orchard n. sp. and N. discreta Orchard and Krystyn n. sp., the nominal species of three successive zones. The development of these Griesbachian species involves a progressive morphological change in the configuration of the axial part (blade-carina-cusp) of the pectiniform elements. The pelagic conodont zonation is intercalibrated with the parallel zonation based on species of Hindeodus and Isarcicella , and with ammonoid faunas from Spiti, other Himalayan localities, and the Arctic. The meishanensis Zone embraces the parvus Zone and part of the overlying staeschei Zone. Strata containing O. woodwardi in Spiti carry the indices to the staeschei and krystyni zones. The Neogondolella conodont fauna associated with Otoceras differs from that of the latest Permian Changshing Limestone of China, but resembles that from the P-T boundary transition beds at Meishan, where a meishanensis Zone of restricted scope occurs beneath the parvus datum. The faunal change which introduces the characteristic Neogondolella species of the N. carinata-N. taylorae fauna occurs at the base of the P-T boundary transition beds at Meishan, the proposed boundary stratotype. Slightly above this level, the disappearance of most Neogondolella species and the introduction of new Hindeodus species coincides with a change in conodont biofacies rather than an extinction event. In the Spiti sections, the N. carinata-N. taylorae fauna, associated at first with H. parvus (as in Selong, Tibet), persists through the entire Griesbachian. Indices of the three Neogondolella zones are also recognized in the Salt Range and the Canadian Arctic. Four new conodont species are described: Neogondolella discreta, N. kazi, N. krystyni , and N. nassichuki .

Magnetostratigraphy of the Late Triassic Bolücektası Tepe section (southwestern Turkey): implications for changes in magnetic reversal frequency

Abstract A magnetostratigraphic study of light-pink to white pelagic limestones from the Bolucektasi Tepe section (southwestern Turkey) provides a magnetic polarity sequence well calibrated with the conodont zonation for the Lower Carnian and uppermost Carnian-Middle Norian (Late Triassic). Thermal (between 400 and 550°C) and alternating field (30–60 mT) demagnetizations isolate the characteristic remanent components. Rock magnetic experiments suggest that magnetite is the dominant magnetic carrier, but a small hematite fraction also exists in the Lower Carnian light-pink limestones. A major sedimentary gap (Middle-Upper Carnian) divides the section in two submembers which reveal two statistically different mean directions, differing in declination by about 30°. A sequence of 39 polarity intervals is obtained, 18 in the Carnian (ten in the Lower Carnian and eight in the uppermost Carnian) and 21 in the Lower-Middle Norian. The magnetic reversal frequencies which can be derived from these results, together with the available magnetostratigraphic data for the Middle-Early Jurassic, Triassic and Late Permian, show a pattern which is in rough agreement with the suggested 150–200 million year time constant in the reversal process since the Kiaman superchron. However, significant short-period fluctuations in reversal frequency cannot be excluded.

Towards accurate numerical calibration of the Late Triassic: High- precision U-Pb geochronology constraints on the duration of the Rhaetian

Numerical calibration of the Late Triassic stages is arguably the most controversial issue in Mesozoic stratigraphy, despite its importance for assessing mechanisms of environmental perturbations and associated biologic consequences preceding the end-Triassic mass extinction. Here we report new chemical abrasion–isotope dilution– thermal ionization mass spectrometry zircon U-Pb dates for volcanic ash beds within the Aramachay Formation of the Pucara Group in northern Peru that place precise constraints on the age of the Norian- Rhaetian boundary (NRB) and the duration of the Rhaetian. The sampled ash bed–bearing interval is located just above the last occurrence of the bivalve Monotis subcircularis, placing this stratigraphic sequence in the uppermost Norian, perhaps ranging into the earliest Rhaetian. Zircon U-Pb dates of ash beds constrain the deposition age of this interval to be between 205.70 ± 0.15 Ma and 205.30 ± 0.14 Ma, providing precise constraints on the age of the NRB. Combined with previously published zircon U-Pb dates for ash beds bracketing the Triassic-Jurassic boundary, we estimate a duration of 4.14 ± 0.39 m.y. for the Rhaetian. This ends a prolonged controversy about the duration of this stage and has fundamental implications for the rates of paleoenvironmental deterioration that culminated in the end-Triassic mass extinction.

Integrated Upper Carnian to Lower Norian biochronology and implications for the Upper Triassic magnetic polarity time scale

Abstract We summarize the ammonoid, conodont and halobiid biochronology of the Upper Carnian to Lower Norian, based on a discussion of data in the Alps, Sicily, Balkans, Turkey, Himalayas and Timor. With this integrated biostratigraphic scale, the Pizzo Mondello section (Sicily) can be recalibrated and the Carnian–Norian boundary more precisely located there. As a result, the magnetostratigraphy of this section is now in good agreement with previous results from Turkey, although the latter series are more condensed. Cross-correlation of available magnetostratigraphic data from marine Tethyan sections allow us to construct a composite Upper Carnian to Upper Norian geomagnetic polarity time scale (GPTS). This GPTS leads us to question previously proposed magnetobiostratigraphic and chronostratigraphic correlations within the Upper Triassic Newark non-marine sedimentary sequence.

Magnetostratigraphy of the Mayerling section (Austria) and Erenkolu Mezarlik (Turkey) section: Improvement of the Carnian (late Triassic) magnetic polarity time scale

Abstract We present a magnetostratigraphic study of two Carnian (late Triassic) pelagic limestone sections from the Northern Calcareous Alps (Mayerling section) and southwestern Turkey (Erenkolu Mezarlik section). Biostratigraphic control is based on conodont zonation for the Mayerling section, and both on conodonts and ammonoids for the Erenkolu Mezarlik section. In both sections, the characteristic magnetization is essentially carried by a mineral of the magnetite family. Eight magnetic intervals are obtained from the Mayerling section and fourteen from Erenkolu Mezarlik. When these results are compared to the Carnian magnetostratigraphic sequence obtained from the Bolucektasi Tepe section, satisfactory correlations are observed and a composite Carnian magnetic polarity time scale containing 24 intervals can be proposed by combining all these results. The lower part of the upper Carnian is however missing (Tuvalian 1 zone and lower part of the Tuvalian 2 zone). No clear correlation is observed between our composite sequence and the other published magnetostratigraphic data of Carnian age. The satisfactory correlation observed between the Mayerling and the Bolucektasi Tepe sections indicates that both sections were deposited in the northern hemisphere, thus providing constraints on the origin of the Antalya nappes.

Upper Anisian to Lower Carnian magnetostratigraphy from the Northern Calcareous Alps (Austria)

We present a magnetostratigraphic study of three pelagic limestone sections (Gamsstein, Mendlingbach and Mayerling) from the eastern part of the Northern Calcareous Alps. Together these sections, which contain a rich conodont fauna, yield a sedimentary record encompassing the uppermost Anisian, the Ladinian and the Lower Carnian. Thermal demagnetization and isothermal remanent magnetization experiments indicate that the magnetization is essentially carried by a mineral of the magnetite family. The high unblocking temperature components isolated from the three sections provide clear magnetic polarity zonations. Correlations between these results, based on the biostratigraphic data and tephrochronology, allow the construction of a composite magnetic polarity sequence from the Illyrian substage (Upper Anisian) to the Julian 2 zone (Lower Carnian). This sequence contains 17 well-defined polarity reversals, and eight more poorly defined intervals. Correlations can be suggested between the new data and other magnetostratigraphic results previously obtained from marine sections. We estimate that the magnetic reversal frequency was 2.5 to 3.6 reversals per million years during the Ladinian.

Magnetostratigraphy of the Kavur Tepe section (southwestern Turkey): A magnetic polarity time scale for the Norian

We present the magnetostratigraphy of the late Triassic pelagic Kavur Tepe section from the Taurides (southwestern Turkey). The section investigated is about 30 m thick and consists of fine-grained whitish limestones. The biostratigraphy, based on the conodont zonation, gives an age from the Lacian 2 zone (lower Norian) to the Sevatian 2 zone (upper Norian). The paleomagnetic analyses indicate very favourable behaviour, with two magnetic components which can be isolated both by thermal and AF demagnetization. The magnetization is carried by magnetite and goethite, which are clearly evident in IRM experiments. The first component of normal magnetic polarity has roughly the direction of the present-day field. The high unblocking temperature component shows directions of both polarities. In total, fifteen magnetic polarity intervals are observed within the Kavur Tepe section. The characteristic calculated Fisherian mean direction is particularly tightly grouped: D = 220.2° and I = 32.1°, with K = 40.9, α95 = 1.7° and Nsamp = 179 (after bedding correction). Polarity correlations with two other sections in Turkey and in Austria (Northern Calcareous Alps) show that the Kavur Tepe sediments were deposited in the southern hemisphere. By combining the magnetostratigraphic results from the Bolucektasi Tepe [1] and the Kavur Tepe sections, an almost complete Norian magnetic polarity sequence is established, showing 30 magnetic intervals that are well calibrated with the conodont and ammonoid zonations. A magnetic reversal frequency close to about 2.7 reversals/Myr is derived for the Norian. This medium frequency is in agreement with the hypothesis of a long time constant (150–200 Myr) in the changes of the magnetic reversal frequency since the Kiaman reversed superchron.

Triassic pelagic deposits of Timor: palaeogeographic and sea-level implications

Abstract In West Timor, Triassic deposits are found in the Parautochthonous Complex, as well as in the Allochthonous series of Sonnebait. A detailed biostratigraphic investigation, integrating field observations and facies analysis, allowed the reconstruction of a synthetic lithostratigraphic succession for the Upper Triassic; a stratigraphic transition from Carnian shales to Upper Norian–Rhaetian limestones is also shown by this study. The fossil content predominantly originates from an open marine environment; lithostratigraphic Units A–E are dated on the basis of radiolaria and palynomorphs, and Unit H, on ammonites and conodonts. The presence of pelagic bioclasts, together with normal grading, horizontal laminations, and current ripples, is indicative of a distal slope to basin environment. The ammonite rich condensed limestone of Unit H was deposited on a ‘pelagic carbonate plateau’ exposed to storms and currents. The organic facies have been used as criteria for biostratigraphy, palaeoenvironmental interpretation, and sequence stratigraphy. The palaeontological analysis of the Triassic succession of West Timor is based on the investigation of radiolaria and palynomorphs, in the marls and limestones of Units A–E, and also on ammonites and conodonts in the condensed limestone of Unit H. Units A and B are Carnian (Cordevolian) in age, based on the occurrence of the palynomorph Camerosporites secatus , associated with ‘ Lueckisporites ’ cf. singhii , Vallasporites ignacii , Patinosporites densus and Partitisporites novimundanus . Unit C is considered as Norian, on the basis of a relatively high percentage of Gliscopollis meyeriana and Granuloperculatipollis rudis. Unit D contains significant palynomorphs and radiolaria; the organic facies, characterized by marine elements, is dominated by the Norian dinocysts Heibergella salebrosacea and Heibergella aculeata ; the radiolaria confirm the Norian age. They range from the lowermost Norian to the lower Upper Norian. Unit E also contains radiolaria, associated in the upper part with the well-known marker of the Upper Norian, Monotis salinaria . For Unit E, the radiolaria attest to a Lower to Upper Norian age based on the occurrence of Capnodoce and abundant Capnuchosphaera ; the upper part is Upper Norian to Rhaetian based on the presence of Livarella valida . Finally, the blocks of condensed limestone with ammonites and conodonts of Unit H allowed the reconstruction of a synthetic stratigraphic succession of Upper Carnian to Upper Norian age. Our stratigraphic data lead to the suggestion that the Allochthonous complex, classically interpreted as a tectonic melange of the accretionary prism of the Island Arc of Banda, is a tectonically dismembered part of a Triassic lithostratigraphic succession.

New constraints on the Upper Permian and Lower Triassic geomagnetic polarity timescale from the Abadeh section (central Iran)

We present the magnetostratigraphy of the Abadeh section (central Iran). Thermal demagnetization shows two magnetic components: one at low unblocking temperatures, which corresponds to a present day-field direction, and another at high temperatures. This second component, which contains both polarities, is interpreted as a primary magnetization acquired during sediment deposition at a paleolatitude of about 7.7°S. A sequence of 14 magnetic polarity zones is obtained in the intervals during the Upper Dzhulfian-Lower Changhsingian (Upper Permian) and during the Griesbachian (Lower Triassic). Combining data from south China, Canada, Pakistan, and Iran, we propose a composite (but still uncomplete) Upper Permian and Lower Triassic geomagnetic polarity timescale.