High latitude meteoric δ 18 O compositions from the Cenomanian Bastion Ridge Formation, Axel Heiberg Island, Canadian Arctic Archipelago: a palaeoclimate proxy from the Sverdrup Basin

Abstract

AbstractStable isotope analyses of a siderite-cemented siltstone from the Cenomanian Bastion Ridge Formation, Axel Heiberg Island, Canada, produce a range of δ18O values from −21.9 to −18.4‰ Vienna Pee Dee Belemnite (VPDB), and δ13C values ranging from 2.0 to 4.4‰ VPDB. A meteoric siderite line of −18.95 ± 0.33‰ VPDB is calculated from siderite cements of the authigenic component. At estimated palaeolatitude of 68–72° N and palaeotemperature range from 12.6 to 13.7°C, the calculated δ18O range of palaeoprecipitation is −23.3 to −23.0‰ Vienna Standard Mean Ocean Water (VSMOW). This result is compatible with other published meteoric water δ18O datasets from Cretaceous Arctic studies, but is near the lower end of the range of estimated δ18O values. The modern δ18O empirical relationship of Dansgaard and Earth System models simulating meteoric δ18O values does not yield results for palaeopolar regions that match proxy δ18O datasets. Orographic effects of contemporaneous mountain belts and seasonal biases in groundwater recharge have been proposed to explain this paradox regarding depleted meteoric water δ18O values from proxy data in greenhouse worlds. Evidence for local to regional orographic effects and alpine snowmelt biasing groundwater recharge is lacking for the Sverdrup Basin deposits, further indicating that the Dansgaard relationship does not apply to ancient greenhouse worlds.