Glendonites and authigenic carbonates in Arctic Alaska from the Cretaceous to the present: environmental and climatic significance

In the Colville Foreland Basin of Arctic Alaska, non-skeletal carbonates rarely occur in Mesozoic and Cenozoic strata. However, glendonites and other cold-water authigenic carbonates are found at specific intervals within the basin fill, forming a unique archive of geochemical, environmental, and climatic conditions at the time of precipitation. New discoveries of glendonites in Lower Cretaceous strata (informal pebble shale unit and Kuparuk Formation), with ages constrained by biostratigraphy and/or nearby ash Isotope Dilution Thermal Ionization Mass Spectrometry (ID-TIMS) zircon dates, provide evidence of cold temperatures during an overall hothouse interval. These occurrences are generally coeval with others previously described elsewhere in the Arctic, supporting the ‘cold snap’ model for early Cretaceous paleoclimate. In younger (Oligocene–Miocene) strata at Carter Creek, newly acquired clumped isotope (Δ47 and Δ48) data from glendonites yield cold paleotemperatures (generally 0–6° C), demonstrating that well-preserved specimens can record quantitative environmental information even after the transformation from ikaite to more stable forms of calcium carbonate. Further, Carter Creek glendonites (δ13C values typically -20 to less than -40‰ Vienna Peedee Belemnite standard) also occur in association with isolated pods of authigenic fine-grained carbonate sediments, which contain evidence of a unique macrofauna and are characterized by isotopically light carbon. These deposits are therefore interpreted as being associated with ancient methane seeps, which may be related to warming following the Mi-1 glaciation circa 24 Ma, with glendonite growth taking place during shorter ‘cold snaps’ within this interval. This occurrence adds additional evidence to the previously hypothesized linkages between glendonites and methane and between seep carbonates and deglaciation and potentially documents an active petroleum system in the Miocene of the Alaska North Slope. Thus, the glendonite examples described here and their sedimentary context allow for new aspects of the basin’s history to be ascertained in a way not possible with other types of sedimentary deposits.