Upper Cretaceous (Santonian to late Campanian) strata from the upper 196 m at Shivugak Bluffs along the Colville River of northern Alaska preserve a paleopolar, fluvial-deltaic succession deposited along a prograding paleo-Arctic Ocean coastline. The uppermost lower Schrader Bluff Formation is best classified as a river-dominated delta based on muddy prodelta and delta-front deposits that contain abundant hyperpycnites, subaqueous terminal distributary channels, interdistributary bays, and mouth bars. This deltaic succession is overlain by distal distributaries and a braided fluvial system of the Prince Creek Formation. Channel measurements and paleo-discharge calculations from Prince Creek Formation distributaries indicate that rivers were the appropriate size and had the appropriate discharge to regularly produce hyperpycnites. Delta front and interdistributary bays transitioned into lakes and floodbasins on the lower delta plain, alongside distributary channels during delta lobe reorganization and abandonment. These floodbasins were subsequently transgressed and are overlain by proximal shelf and prodelta muds containing Phycosiphon. Overlying strata containing delta front, interdistributary bay, terminal distributary channel, distributary mouth bar, and distributary channel deposits signaled the reactivation of the delta lobe. Ultimately, these deltaic environments were incised into and became overlain by braided channel deposits during a marked drop in relative sea level and progradation of the fluvial system. Combining ichnologic and sedimentologic observations was critical to identify eleven distinct deltaic and continental paleoenvironments. This study documents the architecture and evolution of an ancient, high-latitude, muddy, river-dominated deltaic system and highlights the autogenic and allogenic processes preserved in the system.

We report estimated stable isotope compositions of depositional waters and paleoprecipitation from the Cretaceous Arctic to further elucidate the role of the global hydrologic cycle in sustaining polar warmth during that period. Estimates are based on new hydrogen isotopic analyses of n-alkane biomarkers extracted from Late Cretaceous and mid-Cretaceous terrestrial deposits in northern Alaska and the Canadian High Arctic. We integrate these new results with earlier published work on oxygen isotopic analyses of pedogenic siderites, dinosaurian tooth enamel phosphates, and pedogenic clay minerals from the same field areas. Average Late Cretaceous δD values of −143‰ VSMOW corresponded with average δ18O values of −24.1‰ VSMOW, and average mid-Cretaceous δD values of −106‰ VSMOW corresponded with average δ18O values of −22.1‰ VSMOW. The distributions of water isotope δD and δ18O values from Cretaceous Arctic deposits do not intersect with the Global Meteoric Water Line, suggesting an apparent deuterium excess ranging from about 40 to 60 per mil. We considered several possible explanations for these Cretaceous results including (1) mass-balance changes in zonal patterns of evaporation and precipitation at lower latitudes, (2) concentration of 2H in leaf tissue waters from continuous transpiration by coniferous paleofloras during the Arctic growing season, and (3) concentration of 2H in the groundwaters of methane-emitting Arctic soils.

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New mapping in the Lake Kaweah pendant of the southwestern Sierra Nevada batholith reveals a previously unrecognized nonmarine sequence of metamorphosed sedimentary and volcanic strata, defi ned herein as the Goldstein Peak Formation. The nonmarine origin distinguishes the Goldstein Peak Formation from all other Sierra Nevada metasedimentary pendants and from virtually all other coeval deposits associated with the Sierra Nevada arc. Basic structural relations, supplemented by new U-Pb zircon ages, suggest an Early Cretaceous depositional age, a time that is poorly represented within the stratigraphic record of California. This unusual age makes the Goldstein Peak Formation the youngest sedimentary deposit preserved within the metamorphic framework of the exhumed batholith, one that was deposited concurrently with some of the earliest deposits in the Great Valley forearc basin and just preceding the mid-Cretaceous Sierra Nevada arc surge. Preserved sedimentary and volcanic structures, along with whole-rock geochemistry, are consistent with deposition of Goldstein Peak conglomerates and sandstones within fl uvial and alluvial fan environments, deposition of mud-rich sediments and air-fall tuffs within a lacustrine(?) environment, and subaqueous to subaerial extrusion of basaltic to dacitic arc volcanic rocks. This volcanosedimentary section was intruded soon after deposition, with peak hornblende hornfels to low-pressure amphibolite facies metamorphism ultimately driven by intrusion of the surrounding Early Cretaceous Stokes Mountain ring dike complexes. Deposition of the nonmarine Goldstein Peak Formation within a fault-bounded, possibly transtensional, intra-arc basin during the transition from the low-standing, moderately extensional, Late Jurassic fringing arc to the high-standing, compressional mid-to Late Cretaceous arc indicates that at least one section of the Sierra Nevada arc was a fully emergent continental margin arc by the Early Cretaceous Epoch.