Stable Isotope Tracers of Cretaceous Arctic Paleoprecipitation

Abstract

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.

Exploring the Deuterium Excess of Cretaceous Arctic Paleoprecipitation Using Stable Isotope Composition of Clay Minerals from the Prince Creek Formation (Maastrichtian) in Northern Alaska

“…This could be the result of geographic, orographic, or geochronological differences between the paleosol and bentonite localities. Regardless, these oxygen isotope estimates of meteoric water fall within previously reported data from paleosol siderites, dinosaur tooth enamel phosphate, and pedogenic clay minerals [4,5], and both the bentonite and paleosol localities record deuterium excess despite the large shift in oxygen isotopic composition of meteoric water.…”

“…Clay mineral analyses by Salazar-Jaramillo et al [14] showed no ordering of illite during I/S interstratification analyses of paleosols in the Prince Creek Formation, suggesting little or no diagenetic transformations of illite [46]. Furthermore, the results presented in Figure 5 indicate reasonable oxygen and hydrogen isotopic values of estimated meteoric water that are within the range of previously published isotopic estimates of meteoric water from the Prince Creek Formation using alternative proxies, including pedogenic siderite, dinosaurian tooth enamel phosphates, and n-alkane biomarkers [5].…”

“…0.3825; [43,44]) indicate a maximum burial temperature of 48 • C, which is too low to have caused substantial diagenetic changes in paleosol mineralogy [45]. This is also confirmed by studies conducted by Ludvigson et al [5], which indicated organic matter sampled from the Prince Creek Formation had very low thermal maturity and the n-alkane biomarkers were suitable for δD and δ 13 C isotopic analyses as their values had not been thermally altered. Additionally, there are well-preserved micromorphological features present in the paleosols [14] and the paleosols remain unlithified.…”

“…The results from this previous research revealed low δ 18 O of paleoprecipitation corresponding to higher δD than would be expected, given modern relationships of δ 18 O and δD plotting along the Global Meteoric Water Line [5]. However, the question became if this deuterium excess recorded in n-alkane biomarkers was the result of photosynthetic and samples from each locality and their exact stratigraphic position are indicated by stars in Figure 2.…”

“…In an effort to resolve this conflict, new research has focused on collecting and analyzing samples that can reveal the relationship of paleotemperature and stable isotopic (δ 18 O and δD) composition of paleoprecipitation. This work includes studies on pedogenic siderite, dinosaurian tooth enamel phosphates, and pedogenic clay minerals producing δ 18 O data and n-alkane biomarkers producing δD data from terrestrial deposits that capture the Cretaceous record in the Arctic [4,5].…”