The North structure is a discontinuous, partially flooded elliptical basin 250 m in diameter and defined by arcuate scarps. It is located in Annapolis County, Nova Scotia, approximately 1 km north of the Bloody Creek structure, a possible 400 m-diameter elliptical impact crater. Geophysical surveys indicate that raised scarps border a broadly elliptical basin with depth/diameter ratios similar to those at the Bloody Creek structure. Percussion coring and probing indicated that the basin is in-filled with 3.5 m of lacustrine sediment and peat overlying post-glacial alluvial sediment and diamicton. Samples collected proximal to the rim of the structure contain kink-bands in feldspar and biotite and possible planar microstructures in quartz and feldspar. The elliptical nature and similar, anomalous morphometries of the North and Bloody Creek structures indicate that two, low-angled, genetically linked impacts may have taken place at the site. Both structures are interpreted to be post-Pliocene (<2.6 Ma), based on the unlikelihood of their preservation during Cretaceous-Paleogene regional peneplanation. RÉSUMÉLa structure d'impact du North Group est une cuvette elliptique discontinue et partiellement inondée d'un diamètre de 250 mètres, définie par des escarpements arqués. Elle se situe dans le comté d' Annapolis, en Nouvelle-Écosse, à environ 1 km au nord de la structure de Bloody Creek, un possible cratère d'impact de forme elliptique mesurant 400 mètres de diamètre. D'après les levés géophysiques, les escarpements soulevés bordent une cuvette largement elliptique dont les rapports entre la profondeur et le diamètre sont semblables à ceux de la structure de Bloody Creek. Les activités de carottage à percussion et de sondage d' exploration ont permis de savoir que l'intérieur de la cuvette était rempli d'une couche de 3,5 mètres de sédiments lacustres et de tourbe, qui recouvrent du diamicton et des sédiments alluvionnaires d' origine post-glaciaire. Le contenu des échantillons prélevés dans le milieu proximal de la bordure de la structure révèle des bandes froissées dans le feldspath et la biotite et de possibles microstructures planaires dans le quartz et le feldspath. Si l' on se fie à la nature elliptique et à la morphométrie anormale similaire des structures du North Group et de Bloody Creek, il se pourrait que deux impacts d'un angle peu prononcé et génétiquement liés aient eu lieu à cet endroit. Les deux structures seraient, d'après les interprétations, postérieures au Pliocène (<2,6 Ma), car les probabilités qu' elles aient été préservées pendant la pénéplanation régionale du Crétacé-Paléogène sont plutôt faibles.[Traduit par la redaction] ATLANTIC GEOLOGY 51, 044-050 (2015) 0843-5561|15|00044-050 $1.80|0

Rationale The isotopic composition of hydrocarbons trapped in rocks on the microscale (fluid inclusions, mineral grain boundaries, microfractures) can provide powerful information on geological and biological processes but are an analytical challenge due to low concentrations. We present a new approach for the extraction and carbon isotopic analysis of methane (CH4) and hydrocarbons in trapped volatiles in crystalline rocks. Methods An off‐line crusher with cryogenic trapping and a custom‐made silica glass U‐trap were attached to an external injector port on a continuous flow gas chromatograph/combustion/isotope ratio mass spectrometer to demonstrate the accuracy, reproducibility, and sensitivity of δ13C measurements for CH4. Results The method can isotopically characterize CH4 in crushed rock samples with concentrations as low as 3.5 × 10−9 mol/g of rock, and both sample and isotopic standards are analyzed with an accuracy and reproducibility of ±0.5‰. High H2O/CH4 ratios of 98 to 500 have no effect on measured δ13CCH4 values. The method is successfully applied to natural samples from the north range of Sudbury Basin, Ontario, Canada. The δ13C isotopic signatures of CH4 trapped microscopically in rock from the north range overlap significantly with that of CH4 contained in larger scale flowing fracture fluids from the same part of the Sudbury Basin, indicating a potential genetic link. Conclusions A novel method for δ13CCH4 analysis was developed for the extraction of nanomole quantities of CH4 trapped microscopically in rocks. The technique has an accuracy and reproducibility comparable to that of on‐line crushing techniques but importantly provides the capability of crushing larger rock quantities (up to 100 g). The benefit is improved detection levels for trace hydrocarbon species. Such a capability will be important for future extension of such crushing techniques for measurement of 2H/1H for CH4, clumped isotopologues of CH4 and other trapped volatiles species, such as C2H6, C3H8, C4H10, CO2 and N2.

No abstract