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Positive δ13C carb excursions are correlated through an upper Turinian to lower Chatfieldian carbonate-platform succession along the axis of the Ottawa Embayment and into outliers of the northern Ottawa-Bonnechere graben in central Canada. Successive Turinian excursions (E1 and E2) are lithostratigraphically constrained by erosional surfaces and hosted within the Watertown and overlying L'Orignal formations, respectively, the latter coeval with the Selby Formation in the adjacent northern Appalachian Basin. The excursions coincide with periods of regional transgression, but geographic patterns of 13C depletion versus enrichment coincide with structurally defined areas of stratigraphically condensed and preferentially thickened formation successions, respectively. Differential subsidence is interpreted to have created bathymetric variation resulting in intrabasinal restriction of seawater exchange between these areas, with preferential C org recycling with stratigraphic condensation. By early Chatfieldian time, segmentation of the once regional carbonate platform (L'Orignal Formation) produced a regional mosaic of low-energy muddy carbonate banks (Rockland Formation) and a deeper water platform (lower Hull Formation) settings subject to fluctuating high to low energy current flow. Excursion E3 occurs in both successions, but 13C enrichment is associated only with the bank-top muddy facies. This may identify preferential photosynthetic drawdown of 12C across the bank tops due to limited seawater exchange across the bank-deeper platform boundaries. Excursions E1 to E3, and a younger excursion (E4) in the Hull Formation, are correlated with varying confidence with excursions across southern Laurentia, excursion E3 being the local expression of the Guttenberg δ13C excursion. Our study supports local modulation of regional, if not global, δ13C excursions arising from structurally controlled changes in oceanography and productivity. • Turinian and early Chatfieldian δ13C excursions occur in the Ottawa Embayment. • Lithostratigraphic constraints reveal local excursion truncation, notably the GICE. • Lateral variation in excursion magnitude reflects local syndepositional controls. • Local controls modulate regional to global isotopic signals. [ABSTRACT FROM AUTHOR]

Abstract: Tree-ring analyses have contributed significantly to investigations of past climate. Stable isotope climate proxies (δ18O, δD and δ13C values) enhance traditional ring-width data, although poor preservation of ancient wood has tended to limit development of stable isotope proxy records to the Holocene and the Late Pleistocene. Here we apply stable isotope techniques to wood that represent the remains of Mixed-Coniferous Boreal Vegetation preserved in Early Pliocene (4–5Ma) deposits at Strathcona Fiord, Ellesmere Island, Canada (ca. 78°N). Four well-preserved tree trunks, identified through wood anatomical characteristics as Larix (larch), from this high Arctic site provide annually resolved sequences of up to 250years from which we developed a high-resolution record of Pliocene climate. Stable oxygen isotope values, in conjunction with ring-width measurements were used to derive annually resolved temperature records for this site. Our ring-width and isotope-based reconstructions provide an annually resolved record, up to 250years, of temperature and indicate growing season (JJ) temperatures (15.8±5.0°C) 11.8±5.1°C, and mean annual temperatures (MAT) (−1.4±4.0°C) 18.3±4.1°C warmer than present. Estimated isotope values of precipitation of −16.3±2‰ (δ18O) and −150.1±8.9‰ (δD) were calculated from the isotopic values of wood cellulose. Relative humidity estimated from both δ13C and δD records ranged from 60 to 80%. Paleotemperature, source water and humidity estimates are comparable to those of a modern Boreal Forest growing ca. 15–20° south of modern Ellesmere Island. [Copyright &y& Elsevier]

Abstract: Three curves delineating δ 13C variations across the Early Cambrian Sekwi Formation carbonate ramp, Mackenzie Mountains, Northwest Territories, Canada, are incorporated into a biostratigraphic and sequence stratigraphic framework that provides a higher resolution temporal and spatial framework for the Sekwi Formation. The three δ 13C curves were correlated across a range of depositional environments, from tidal flat to deep subtidal on the Sekwi carbonate ramp. Eight δ 13C “cycles” in the curves (A–H) were correlated across the basin, complimenting the sequence stratigraphic framework. The most complete δ 13C curve from the Sekwi Formation correlates well with a composite Early Cambrian δ 13C curve from the Siberian Platform. However, the differing magnitude and absolute timing of some of the correlative isotopic excursions records the influence of regional tectonism, sea level changes, and diagenesis on the Sekwi ramp. Additionally, the Sekwi Formation δ 13C curve has more high-frequency variations than the Siberian curve, due in part to the higher sample density used to construct the Sekwi curve. The Early–Middle Cambrian boundary was not sampled in this study, but a large negative isotopic excursion in the very latest Early Cambrian coincides with a regional drowning that may be correlative throughout western Laurentia, but recognizing this event globally is problematic. [Copyright &y& Elsevier]