We present a multi-proxy investigation of a lower Carnian basinal succession from Polzberg in the Northern Calcareous Alps (Lower Austria). A section comprising a unique Konservat-Lagerstätte was ...studied based on bio- and chemostratigraphy along with geophysical methods, yielding a detailed and robust stratigraphic calibration of the Polzberg succession. The Polzberg section revealed the paleoceanographic history and helped to identify a global climatic reversal, the Carnian Pluvial Episode. The age of the Upper Triassic Reingraben formation in the Northern Calcareous Alps is refined as the Austrotrachyceras austriacum Zone within the lower Carnian (Julian 2). Ammonoids and conodonts provide a detailed biostratigraphic subdivision that serves as a basis for analyses of the faunal distribution and the paleoenvironmental evolution of the Upper Triassic Reifling Basin. The succession includes lithological and facies changes similar to those of coeval units in the Tethys. The Carnian was characterized by a weak (~ 1‰) positive δ
C trend, punctuated by a negative shift during the lower Carnian corresponding to the initiation of the Carnian Pluvial Episode, a period representing the onset of early/late Carnian transitional global greenhouse conditions. Organic maturity parameters and the conodont alteration index (CAI) show that the thermal overprint of the Polzberg section is low. Biomarker proxies suggest that the organic matter of the uppermost Göstling formation is a mixture of marine and terrestrial material deposited in a dysoxic environment. Within the overlaying Reingraben formation, the amount of marine biomass decreased gradually upwards. Oxygen-depleted conditions, probably due to water-column stratification, continued during deposition of the Reingraben formation. Bacterial sulfate reduction played a major role in organic matter degradation.
The Carnian Pluvial Episode was a phase of global climatic change and biotic turnover that occurred during the early Late Triassic. In marine sedimentary basins, the arrival of huge amounts of ...siliciclastic sediments, the establishment of anoxic conditions, and a sudden change of the carbonate factory on platforms marked the Carnian Pluvial Episode. The sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as, for example, an extinction among ammonoids and conodonts in the ocean, and a turnover of the vertebrate fauna and the flora on land. Multiple negative carbon-isotope excursions were recorded during the Carnian Pluvial Episode in both organic matter and marine carbonates, suggesting repeated injection of 13C-depleted CO2 into the ocean–atmosphere system, but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood. We here review the existing carbon-isotope records and present new data on the carbon-isotope composition of organic carbon in selected sections of the western Tethys realm that record the entire Carnian Pluvial Episode. New ammonoid, conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections. The results provide biostratigraphically constrained composite organic carbon-isotope curves for the Carnian, which sheds light on the temporal and causal links between the main carbon-isotope perturbations, and the distinct environmental and biotic changes that mark the Carnian Pluvial Episode. The carbon-isotope records suggest that a series of carbon-cycle perturbations, possibly recording multiple phases of volcanic activity during the emplacement of the Wrangellia Large Igneous Province, disrupted Carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years.
In the early Late Triassic a period of increased rainfall, named the Carnian Pluvial Event (CPE), is evidenced by major lithological changes in continental and marine successions worldwide. The ...environmental change seems to be closely associated with a negative carbon isotope excursion that was identified in a stratigraphic succession of the Dolomites (Italy) but the temporal relationship between these phenomena is still not well defined. Here we present organic-carbon isotope data from Carnian deep-water stratigraphic sections in Austria and Hungary, and carbonate petrography of samples from a marginal marine section in Italy. A negative 2–4‰ δ13C shift is recorded by bulk organic matter in the studied sections and is coincident with a similar feature highlighted in higher plant and marine algal biomarker carbon-isotope records from the Dolomites (Italy), thus testifying to a global change in the isotopic composition of the reservoirs of the exchangeable carbon. Our new observations verify that sedimentological changes related to the CPE coincide with the carbon cycle perturbation and therefore occurred synchronously within the western Tethys. Consistent with modern observations, our results show that the injection of 13C-depleted CO2 into the Carnian atmosphere–ocean system may have been directly responsible for the increase in rainfall by intensifying the Pangaean mega-monsoon activity. The consequent increased continental weathering and erosion led to the transfer of large amounts of siliciclastics into the basins that were rapidly filled up, while the increased nutrient flux triggered the local development of anoxia. The new carbonate petrography data show that these changes also coincided with the demise of platform microbial carbonate factories and their replacement with metazoan driven carbonate deposition. This had the effect of considerably decreasing carbonate deposition in shallow water environments.
•New δ13CTOC data from Carnian (Late Triassic) sections of the western Tethys basins•A negative δ13CTOC shift always coincides with the onset of the Carnian Pluvial Event.•C-cycle disruption led to the abrupt sedimentological changes observed in the studied basins.
The Anisian amber from the “Voltzia beds” of the Recoaro area, produced by Voltzia recubariensis, represents the most ancient Triassic amber known so far. The discovery of amber in the Anisian ...localities of Kühwiesenkopf/Monte Prà della Vacca and Piz da Peres, in the Dolomites area, fills a gap in the amber fossil record and gives an important contribution to the knowledge of Triassic amber. The finding of amber droplets, both dispersed in the sediment and anatomically connected to shoot fragments of V. recubariensis, demonstrates that during the Anisian this species was a major resin-producer and that the favorable conditions for the preservation of resin and plant remains were present at regional scale. The contribution of Voltziales to Middle Triassic resin production in Northern Italy is also testified by the Ladinian amber from the “Wengener Schichten” of Wengen/La Valle, produced by Voltzia ladinica, whereas the Late Triassic amber was mainly produced by cheirolepidiaceous conifers. The finding of organic body trapped in the amber of Kühwiesenkopf/Monte Prà dalla Vacca is noteworthy, although difficult to interpret, and shows once again its capability to entrap and preserve witnesses of past life. Moreover, the correspondence between the Triassic amber occurrences and regional/global scale humid shifts, suggests a cause-and-effect relationship, in which the rise of amber production/preservation potential is related to climate/environmental changes, particularly in marginal marine/costal environments.
The End-Triassic Extinction event (ETE) has been recognized in numerous sections worldwide and it is usually marked by three negative carbon isotope excursions (NCIEs), named “precursor” (P-NCIE), ...“initial” (I-NCIE) and “main” (M-NCIE) negative carbon isotope excursions. These three NCIEs are significant characteristics of this time interval, and they are likely related to the emplacement of the Central Atlantic Magmatic Province (CAMP) that is considered the main trigger of the ETE. Stable carbon isotope excursions, commonly related to biotic turnovers and extinctions, play an important role in stratigraphic correlations, particularly around the Triassic-Jurassic boundary (TJB). This time interval records the disappearance of conodonts, elements of a feeding apparatus belonging to marine organisms that populated the Paleozoic-early Mesozoic seas, and which became extinct across the TJB. So far, the interpretation of conodont extinction has remained ambiguous, as the timing of its last occurrence was debated which in turn hindered our understanding of the main cause(s) that could have led to their disappearance. Here we present and compare integrated data of nine TJB sections from different areas, Tethys and Panthalassa, and different depositional environments, i.e. shallow vs deep water or proximal vs distal shelf. Each of these sections record both the last occurrences of latest Triassic conodont taxa and pronounced changes in the carbon isotopic composition of organic matter across the TJB interval. Our analysis of chemo- and integrated biostratigraphic correlation suggests that the final extinction of the taxon Conodonta was asynchronous.
The Carnian Pluvial Episode (Late Triassic) was a time of global environmental changes and possibly substantial coeval volcanism. The extent of the biological turnover in marine and terrestrial ...ecosystems is not well understood. Here, we present a meta-analysis of fossil data that suggests a substantial reduction in generic and species richness and the disappearance of 33% of marine genera. This crisis triggered major radiations. In the sea, the rise of the first scleractinian reefs and rock-forming calcareous nannofossils points to substantial changes in ocean chemistry. On land, there were major diversifications and originations of conifers, insects, dinosaurs, crocodiles, lizards, turtles, and mammals. Although there is uncertainty on the precise age of some of the recorded biological changes, these observations indicate that the Carnian Pluvial Episode was linked to a major extinction event and might have been the trigger of the spectacular radiation of many key groups that dominate modern ecosystems.
Arthropods in amber from the Triassic Period Schmidt, Alexander R; Jancke, Saskia; Lindquist, Evert E ...
Proceedings of the National Academy of Sciences - PNAS,
09/2012, Letnik:
109, Številka:
37
Journal Article
Recenzirano
Odprti dostop
The occurrence of arthropods in amber exclusively from the Cretaceous and Cenozoic is widely regarded to be a result of the production and preservation of large amounts of tree resin beginning ca. ...130 million years (Ma) ago. Abundant 230 million-year-old amber from the Late Triassic (Carnian) of northeastern Italy has previously yielded myriad microorganisms, but we report here that it also preserves arthropods some 100 Ma older than the earliest prior records in amber. The Triassic specimens are a nematoceran fly (Diptera) and two disparate species of mites, Triasacarus fedelei gen. et sp. nov., and Ampezzoa triassica gen. et sp. nov. These mites are the oldest definitive fossils of a group, the Eriophyoidea, which includes the gall mites and comprises at least 3,500 Recent species, 97% of which feed on angiosperms and represents one of the most specialized lineages of phytophagous arthropods. Antiquity of the gall mites in much their extant form was unexpected, particularly with the Triassic species already having many of their present-day features (such as only two pairs of legs); further, it establishes conifer feeding as an ancestral trait. Feeding by the fossil mites may have contributed to the formation of the amber droplets, but we find that the abundance of amber during the Carnian (ca. 230 Ma) is globally anomalous for the pre-Cretaceous and may, alternatively, be related to paleoclimate. Further recovery of arthropods in Carnian-aged amber is promising and will have profound implications for understanding the evolution of terrestrial members of the most diverse phylum of organisms.
Stable carbon-isotope geochemistry of fossilized tree resin (amber) potentially could be a very useful tool to infer the composition of past atmospheres. To test the reliability of amber as a proxy ...for the atmosphere, we studied the variability of modern resin δ13C at both local and global scales. An amber δ13C curve was then built for the Cretaceous, a period of abundant resin production, and interpreted in light of data from modern resins. Our data show that hardening changes the pristine δ13C value by causing a 13C-depletion in solid resin when compared to fresh liquid–viscous resin, probably due to the loss of 13C-enriched volatiles. Modern resin δ13C values vary as a function of physiological and environmental parameters in ways that are similar to those described for leaves and wood. Resin δ13C varies between plant species and localities, within the same tree and between different plant tissues by up to 6‰, and in general increases with increasing altitudes of the plant-growing site. We show that, as is the case with modern resin, Cretaceous amber δ13C has a high variability, generally higher than that of other fossil material. Despite the high natural variability, amber shows a negative 2.5–3‰ δ13C trend from the middle Early Cretaceous to the Maastrichtian that parallels published terrestrial δ13C records. This trend mirrors changes in the atmospheric δ13C calculated from the δ13C and δ18O of benthic foraminiferal tests, although the magnitude of the shift is larger in plant material than in the atmosphere. Increasing mean annual precipitation and pO2 could have enhanced plant carbon-isotope fractionation during the Late Cretaceous, whereas changing pCO2 levels seem to have had no effect on plant carbon-isotope fractionation. The results of this study suggest that amber is a powerful fossil plant material for palaeoenvironmental and palaeoclimatic reconstructions. Improvement of the resolution of the existing data coupled with more detailed information about botanical source and environmental growing conditions of the fossil plant material will probably allow a more faithful interpretation of amber δ13C records and a wider understanding of the composition of the past atmosphere.
The palynological analysis on a continuous shallow-marine succession of the western Tethys realm allows a better characterization of the Carnian (late Triassic) paleofloristic and paleoclimatic ...scenario. The classic succession of the “Raibl Group”, once the “Raibler Schichten”, in the Southern Alps (northern Italy) was investigated. Ammonoids and conodonts constrain the age of the fossil-rich terrigenous-carbonate sequence to the Julian and Tuvalian, the Julian/Tuvalian boundary lying in the upper part of the Tor Formation. In order to document the pollen biostratigraphy and the paleoecologic trends of this late Triassic interval, results of qualitative and quantitative spore and pollen analysis are presented. The new combination
Converrucosisporites tumulosus (Leschik) Roghi is proposed.
The recognition of three palynological assemblages facilitates realistic regional palynostratigraphical correlation of Carnian successions in the Southern Alps. Quantitative analysis of the pollen/spore assemblages is used to confirm humid environmental conditions during latest Julian and earliest Tuvalian times.
Within the Venetian Pre-Alps, the Borcola Pass connects the Posina (Vicenza province) and the Terragnolo (Trento province) valleys. The Posina valley is located north of Schio (Vicenza) within the ...Italian Southern Alps structural unit. In this area, the injection of Paleogene basaltic dykes along fault/fractures in the late Triassic Dolomia Principale unit has produced a local metamorphism of the dolomite rock into a marble characterized by the presence of brucite veins. This marble was studied in the eighteenth century by the famous Italian scientist Giovanni Arduino, who understood its metamorphic origin. In fact, the marble is always associated with sub-vertical basaltic dykes intruded into the carbonate rocks of the Pre-Alps. Arduino performed also chemical experiments on the marble. The reading of the description of the experiments induced later authors (e.g., Maraschini, von Morlot, Mc Kenzie) to infer that Arduino unknowingly discovered the mineral called dolomite. In this work, we propose that the abandoned Borcola Quarry should be nominated as a geosite, to allow its conservation and popularization and to preserve the memory of a probably minor, yet informative step in the long-lived history of the discovery of dolomite. In addition, this site presents other reasons of interest, such as petrography, mineralogy, structural geology, industrial archeology, and eco-geotourism. The proposed geosite is therefore of great importance in terms of its multidisciplinary scientific value, aesthetic appeal, and educational value.
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