Carbon isotope record for the onset of the Lomagundi carbon isotope excursion in the Great Lakes area, North America

AbstractGlobally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon isotope excursion, sea-level changes and trilobite extinctions. Here we examine the sedimentology, sequence stratigraphy and carbon isotope record of this interval in the Cambrian strata (Durness Group) of NW Scotland. Carbonate carbon isotope data from the lower part of the Durness Group (Ghrudaidh Formation) show that the shallow-marine, Laurentian margin carbonates record two linked sea-level and carbon isotopic events. Whilst the carbon isotope excursions are not as pronounced as those expressed elsewhere, correlation with global records (Sauk I – Sauk II boundary andOlenellusbiostratigraphic constraint) identifies them as representing the local expression of the ROECE and DICE. The upper part of the ROECE is recorded in the basal Ghrudaidh Formation whilst the DICE is seen around 30m above the base of this unit. Both carbon isotope excursions co-occur with surfaces interpreted to record regressive–transgressive events that produced amalgamated sequence boundaries and ravinement/flooding surfaces overlain by conglomerates of reworked intraclasts. The ROECE has been linked with redlichiid and olenellid trilobite extinctions, but in NW Scotland,Olenellusis found after the negative peak of the carbon isotope excursion but before sequence boundary formation.

Download Full-text

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

10.21203/rs.3.rs-1042905/v1 ◽

2021 ◽

Author(s):

Aisha H. Al-Suwaidi ◽

Micha Ruhl ◽

Hugh C. Jenkyns ◽

Susana E. Damborenea ◽

Miguel O. Manceñido ◽

...

Keyword(s):

High Resolution ◽

Carbon Isotope ◽

Volcanic Ash ◽

Lower Jurassic ◽

Zircon Geochronology ◽

Organic Carbon Isotope ◽

Carbon Isotope Excursion ◽

Isotope Record ◽

Age Model ◽

Zonal Boundary

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.

Download Full-text

Carbon isotopes, stratigraphy, and environmental change: the Middle–Upper Cambrian Positive Excursion (SPICE) in Port au Port Group, western Newfoundland, Canada

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2018-0025 ◽

2018 ◽

Vol 55 (11) ◽

pp. 1209-1222 ◽

Cited By ~ 3

Author(s):

Rosalia Barili ◽

Joyce Elaine Neilson ◽

Alexander Thomas Brasier ◽

Karin Goldberg ◽

Tatiana Pastro Bardola ◽

...

Keyword(s):

North America ◽

Environmental Change ◽

Carbon Isotope ◽

Carbon Isotopes ◽

Carbonate Rocks ◽

Isotopic Signature ◽

Upper Cambrian ◽

Carbon Isotopic ◽

Carbon Isotope Excursion ◽

Diagenetic Environment

In many basins, Upper Cambrian carbonate successions display intervals with a positive carbon isotope excursion (CIE) of up to +5‰. In North America, this marks the boundary between the Sauk II–III super-sequences. A Steptoean positive carbon isotope excursion (SPICE) locality previously identified in the Port au Port peninsula, western Newfoundland, has been revisited and an additional potential SPICE locality found. In both locations, a CIE is found to be associated with a prominent bioherm and sandstone layer within a sequence of carbonate rocks. At March Point columnar stromatolites occur, whereas at Felix Cove thrombolites can be seen. In the latter, the sandstone immediately overlies the thrombolites coincident with the CIE, whereas at March Point a dolomitized grainstone occurs above the stromatolites. The sandstone at this locality post-dates the CIE. Although lower than the SPICE in some localities, a positive CIE is present in both sections: March Point (+1.1‰) and Felix Cove (+1.8‰). Additionally, δ13Corg rises from −30.0‰ to −22.0‰ at March Point and from −27‰ to −24.0‰ at Felix Cove and, in accordance with previously published work, we suggest that this could be the SPICE. Comparison of the stratigraphy and petrography between the two localities suggest that both depositional and diagenetic factors could have influenced the nature of the interpreted SPICE in Newfoundland. It is also possible that the local carbon isotopic signature may have been influenced by a semi-restricted depositional and early diagenetic environment related to the paleogeographic configuration rather than the global marine excursion.

Download Full-text