New Chronostratigraphic Constraints on the Lower Jurassic Pliensbachian–Toarcian Boundary at Chacay Melehue (Neuquén Basin, Argentina)

Abstract The Pliensbachian–Toarcian boundary interval is characterized by a ~3‰ negative carbon-isotope excursion (CIE) in organic and inorganic marine and terrestrial archives from sections in Europe, such as Peniche (Portugal) and Hawsker Bottoms, Yorkshire (UK). A new high-resolution organic-carbon isotope record, illustrating the same chemostratigraphic feature, is presented from the Southern Hemisphere Arroyo Chacay Melehue section, Chos Malal, Argentina, corroborating the global significance of this disturbance to the carbon cycle. The negative carbon-isotope excursion, mercury and organic-matter enrichment is accompanied by high-resolution ammonite and nannofossil biostratigraphy together with U-Pb CA-ID-TIMS geochronology derived from intercalated volcanic ash beds. A new age of ~183.71 ± 0.40/-0.51 Ma for the Pliensbachian–Toarcian boundary, and 182.77 +0.11/-0.21 for the tenuicostatum–serpentinum zonal boundary, is assigned based on high-precision U-Pb zircon geochronology and a Bayesian Markov chain Monte Carlo (MCMC) stratigraphic age model.

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New high resolution geochemistry of Lower Jurassic marine sections in western North America: A global positive carbon isotope excursion in the Sinemurian?

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2014.04.023 ◽

2014 ◽

Vol 397 ◽

pp. 19-31 ◽

Cited By ~ 13

Author(s):

Sarah J. Porter ◽

Paul L. Smith ◽

Andrew H. Caruthers ◽

Pengfei Hou ◽

Darren R. Gröcke ◽

...

Keyword(s):

High Resolution ◽

North America ◽

Carbon Isotope ◽

Lower Jurassic ◽

Western North America ◽

Carbon Isotope Excursion

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High-resolution organic carbon isotope record across the Cretaceous–Tertiary boundary in south-central Alberta: implications for the post-impact recovery rate of terrestrial ecosystems and use of δ13C as a boundary marker

Canadian Journal of Earth Sciences ◽

10.1139/e06-109 ◽

2007 ◽

Vol 44 (4) ◽

pp. 529-542 ◽

Cited By ~ 9

Author(s):

François Therrien ◽

David A Eberth ◽

Dennis R Braman ◽

Darla K Zelenitsky

Keyword(s):

High Resolution ◽

Organic Carbon ◽

Carbon Isotope ◽

Terrestrial Ecosystems ◽

Terrestrial Organic Matter ◽

Sedimentary Environments ◽

South Central ◽

Organic Carbon Isotope ◽

Isotope Record ◽

Post Impact

A high-resolution study identified a δ13C excursion of –1.8 to –2.3 in terrestrial organic matter across the Cretaceous–Tertiary (K–T) boundary at two localities in the Scollard Formation of south-central Alberta, one of the northernmost occurrences of the K–T boundary in terrestrial settings. δ13C values are at their lowest within 6 cm above the K–T boundary claystone and return to pre-boundary levels within 10 cm above the boundary claystone. Statistical analyses reveal that the K–T isotopic shift in Alberta is related to the nature of floral changes that occurred across the K–T boundary. A radiometrically dated bentonite resting on the boundary-hosting Nevis coal at one of the localities permits us to estimate that the terrestrial carbon cycle recovered ~100 000 years after the K–T boundary event, a value that supports an existing hypothesis that terrestrial ecosystems recovered more rapidly than marine ecosystems. The organic carbon isotope record of the entire Scollard Formation demonstrates that the δ13C excursion across the K–T boundary did not reach anomalously low values by late Maastrichtian standards in Alberta. Furthermore, the occurrence of the K–T carbon isotope shift within a restricted stratigraphic interval (<10 cm) greatly limits the probability of its preservation in the context of terrestrial sedimentary environments. These observations suggest that, on their own, δ13C profiles may be unreliable for locating the K–T boundary (and possibly other geologically instantaneous events) and that they should be used in combination with other approaches (e.g., palynology) to identify the K–T boundary in sections lacking the boundary claystone and iridium anomaly.

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Cyclo and chemostratigraphic characteristics of the Middle Silurian in Gotland, Sweden

10.5194/egusphere-egu2020-9556 ◽

2020 ◽

Author(s):

Michiel Arts ◽

Bradley Cramer ◽

Mikael Calner ◽

Christian Rasmussen ◽

Alyssa Bancroft ◽

...

Keyword(s):

High Resolution ◽

Carbon Isotope ◽

Time Interval ◽

Carbon Isotope Excursion ◽

Core Dataset ◽

Extinction Event ◽

Age Model ◽

Extinction Events ◽

A Minor ◽

Age Constraints

<p>The cumulative work of geoscientists over the past decades has shown that the Silurian Period which was once thought as warm and climatically stable time interval is in fact punctuated by numerous paleoenvironmental perturbations or events. These Silurian events follow a similar pattern where a minor extinction event precedes a substantial carbon isotope excursion. Many theories have been brought forward to explain these events ranging from glaciations, to changes in precipitations patterns, ocean currents and ocean anoxia. Constraints on the duration and timing of these extinction events and subsequent positive carbon isotope excursions are weak, which hampers a full understanding of the processes at play.</p><p>The data from the Altajme core from Gotland, Sweden provides us with a unique opportunity to look at two of these climatic perturbations during the Silurian. The Altajme core spans both the Sheinwoodian Ireviken event and the Homerian Mulde event. The Altajme core dataset includes a litholog, high-resolution &#948;13C data, correlated bentonites with U-Pb dates and a high-resolution XRF core scan: important data required for and integrated stratigraphic study. The U-Pb-dated bentonites give us age constraints. The &#948;13C data in combination with the high resolution XRF scan gives us insights into the changes in the ocean before during and after the events, while the XRF is also used to build cyclostratigraphic age constraints for the events and for the whole core. This stratigraphic study will provide us with a palaeoclimatological insights to explain these two events and provide us with a cyclostratigraphy based age model for the Middle Silurian.</p>

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