Micha Horacek

87Sr/86Sr stratigraphy from the Early Triassic of Zal, Iran: Linking temperature to weathering rates and the tempo of ecosystem recovery

Recovery from the Late Permian mass extinction was slowed by continued environmental perturbations during the Early Triassic. Rapid fluctuations of the Early Triassic marine carbonate carbon isotope record indicate instability in the global carbon cycle, and recent δ 18 O apatite studies link elevated temperatures to the prolonged biotic recovery. High temperatures potentially caused enhanced continental weathering that was detrimental to marine ecosystems, but linking weathering rates to temperature has proven difficult. One proxy for weathering is the 87 Sr/ 86 Sr of marine carbonate; we present here an 87 Sr/ 86 Sr record from an upper Permian–lower Triassic succession near Zal, Iran, that is coupled to a δ 13 C carbonate record. An increase in the rate of 87 Sr/ 86 Sr rise from the Dienerian to the Smithian may be linked to elevated continental weathering rates caused by warming during the Smithian.

Multiple episodes of extensive marine anoxia linked to global warming and continental weathering following the latest Permian mass extinction

Multiple episodes of extensive oceanic anoxia delayed the marine ecosystem recovery from the latest Permian mass extinction. Explaining the ~5-million-year delay in marine biotic recovery following the latest Permian mass extinction, the largest biotic crisis of the Phanerozoic, is a fundamental challenge for both geological and biological sciences. Ocean redox perturbations may have played a critical role in this delayed recovery. However, the lack of quantitative constraints on the details of Early Triassic oceanic anoxia (for example, time, duration, and extent) leaves the links between oceanic conditions and the delayed biotic recovery ambiguous. We report high-resolution U-isotope (δ238U) data from carbonates of the uppermost Permian to lowermost Middle Triassic Zal section (Iran) to characterize the timing and global extent of ocean redox variation during the Early Triassic. Our δ238U record reveals multiple negative shifts during the Early Triassic. Isotope mass-balance modeling suggests that the global area of anoxic seafloor expanded substantially in the Early Triassic, peaking during the latest Permian to mid-Griesbachian, the late Griesbachian to mid-Dienerian, the Smithian-Spathian transition, and the Early/Middle Triassic transition. Comparisons of the U-, C-, and Sr-isotope records with a modeled seawater PO43− concentration curve for the Early Triassic suggest that elevated marine productivity and enhanced oceanic stratification were likely the immediate causes of expanded oceanic anoxia. The patterns of redox variation documented by the U-isotope record show a good first-order correspondence to peaks in ammonoid extinctions during the Early Triassic. Our results indicate that multiple oscillations in oceanic anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction.

Nitrogen and Carbon Isotope Data of Olenekian to Anisian Deposits from Kamenushka/South Primorye, Far-Eastern Russia and Their Palaeoenvironmental Significance

The Kamenushka Formation, exposed in the northern part of South Primorye (Kamenushka-1 and Kamenushka-2 sections), is one of the few localities in the world with richly fossiliferous Lower–Upper Olenekian sedimentary successions. Lower to Middle Triassic ammonoid-, brachiopod- and conodont-bearing silty-clayey deposits of the Kamenushka-1 and Kamenushka-2 sections have been isotope-geochemically investigated in detail. As a result, these sections, together with the previously investigated Abrek Section, exposed in the southern part of South Primorye, provide almost complete 15Norg- and 13Corg- records for the Lower Triassic of this region. Nine N-isotope intervals and the five negative C-isotope excursions, reflecting, apparently, unstable climatic and hydrological conditions, have been distinguished in the Lower Triassic of South Primorye. On the basis of the new C-isotope data the Mesohedenstroemia bosphorensis Zone (upper part), Shimanskyites shimanskyi and Neocolumbites insignis zones of South Primorye are correlated now with the Lower Smithian part of the Yinkeng Formation, the Upper Smithian part of the Helongshan Formation and the Middle Spathian part of the Nanlinghu Formation in South China, respectively, as has been observed in the Abrek, Kamenushka-2, West Pingdingshan and Majiashan sections.

Western Tethyan Epeiric Ramp Setting in the Early Triassic: An Example from the Central Dinarides (Croatia)

In the central part of the External Dinarides in Plavno, Croatia, near Knin, a remarkably thick (927.5 m) Early Triassic depositional sequence was investigated. The Plavno sequence starts in the EarlyGriesbachian and ends with a continuous transition into the Anisian strata. A complete 13C isotope curve has been achieved and combined with conodonts, bivalves and ammonoids to establish and correlate stage and substage boundaries. The δ13C curve is consistent with former studies. It displays a general increase from the Griesbachian to a prominent maximum beyond the +8‰ amplitude around the Dienerian-Smithian boundary (DSB), followed by a steep and continuous decline to low, negative values in the Smithian. Around the Smithian-Spathian boundary (SSB) a steep rise to a second maximum occurred. It is followed by a saw-tooth shaped decline in the Spathian and a similar increase to a peak at the Spathian-Anisian boundary (SAB).Sedimentologically, the Plavno sequence is interpreted as having been deposited on an extensive epeiric ramp under long-term transgressive conditions, sharing depositional characteristics of both the epeiric platform and the carbonate ramp. The entire Plavno sequence was deposited above the storm-wave base and was storm influenced. Three informal members are differentiated: 1) the dolostone member (Early Griesbachian); 2) the siliciclastic member (red-coloured shale, siltstone, sandstone with oolitic/bioclastic grainstone intercalations), which can be further divided into lower, middle and upper intervals (Late Griesbachian, Dienerian and Smithian); and 3) the mudstone member (grey lime mudstones, marls and calcisiltites with common ammonoids and gastropods-Spathian). The Plavno sequence is compared with other western Tethyan sections. Observed differences stem from local controls on deposition in the overall shallow marine environment.

N and C Isotopic Compositions of the Lower Triassic of Southern Primorye and Reconstruction of the Habitat Conditions of Marine Organisms

N and C isotopic data are recorded and presented for the first time for the Lower Triassic claystones of Southern Primorye (Abrek Section). Five N isotope intervals and 11 more or less pronounced negative C isotope excursions, likely to reflect instability of the temperature regime and the oceanographic situation in the Early Triassic, are recognized in the section. The most favorable conditions for ammonoid recovery and other marine organisms in the Early Triassic (after the end- Permian ecological crisis) were associated with the late Induan—early Olenekian transgression and probable cooling.

Upper Permian to Lower Triassic Carbon Isotope Record in the Oman and Zagros Mountains: An Overview from the Shallow Platform to the Basin

The Oman Mountains as well as the Zagros Mountains expose a segment of Neo-Tethyan southern margin. We will review the 13C and 18O isotope curves in various sections from shallow- to deep-water facies zones for the Upper Permian–Lower Triassic carbonate sequences from Oman and show some preliminary results from Zagros. The shallow-water environment was measured in the Al Jabal al-Akhdar Mountains (Wadi Sathan section), the Saih Hatat (Wadi Sawat) and the Musandam (Wadi Shahha), and the slope carbonates of the platform margin in the Sumeini area (Wadi Maqam). Deep-water deposits from the basinal sector of the margin were studied in the Hawasina Nappes (Wadi Wasit South, Wadi Musjah and Buday’ah) and the Bata’in complex (Sal). Drowned carbonate platform (Oman Exotics) and tilted blocs of the platform have also been studied (Ba’id and Wadi Wasit block).