Stable isotope paleohydrology and chemostratigraphy of the Albian Wayan Formation from the wedge-top depozone, North American Western Interior Basin
Stable isotope paleohydrology and chemostratigraphy of the Albian Wayan Formation from the wedge-top depozone, North American Western Interior Basin
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北美西部内陆盆地楔顶沉积带 Albian Wayan 组的稳定同位素古水文学和化学地层学
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发表时间：
2016
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通讯作者：
J. Walker
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作者：
Jeffrey B. Ross;G. Ludvigson;A. Möller;L. González;J. Walker
了解白垩纪温室世界气候系统中大气水分和热量传输的作用是地球系统科学的一个重大挑战。利用北美中白垩统古赤道至古北极纬度古土壤的稳定同位素古水文资料，对阿尔bian水循环的氧同位素质量平衡进行了研究。在北纬40°~ 50°范围内，以菱铁矿质古土壤为主，表明古环境具有正的降水-蒸发（P-E）平衡。塞维尔造山带背风面出现局部例外，楔顶沉积带的钙质古土壤在地形雨影中记录了负P-E平衡的古环境。爱达荷州大雁组（WF）的地层剖面取自楔顶沉积带。单元由m级泥岩古土壤堆积而成，由m级砂岩-粉砂岩层分隔。对6个发育良好的古土壤的b层进行了碎屑锆石采样，确定了最大沉积时代。其中第一个来自WF的U-Pb协和年龄为101.0±1.1 Ma。同一WF剖面δ13C值在- 24‰~ 27‰VPDB范围内呈上升递减的地层趋势，与晚Albian C15 c同位素段具有相关性。WF的成土碳酸盐岩主要由泥晶方解石组成，其碳氧同位素值沿大气方解石线排列，δ18O值在- 9.47‰~ - 8.39‰VPDB之间。在大约42°N的古纬度，这些MCL值计算出的古降水值为8.12‰~ 7.04‰VSMOW，这一范围与北美相同古纬度的其他代用物的估算结果一致。这些结果表明，尽管存在地形雨影效应，该地区经向大气水汽输送过程与大陆其他地区更为湿润的中纬度古环境相似。
Understanding of the role of atmospheric moisture and heat transport in the climate system of the Cretaceous greenhouse world represents a major challenge in Earth system science. Stable isotopic paleohydrologic data from mid-Cretaceous paleosols in North America, from paleoequatorial to paleoArctic latitudes, have been used to constrain the oxygen isotope mass balance of the Albian hydrologic cycle. Over the range from 40°–50°N paleolatitude, sideritic paleosols predominate, indicating paleoenvironments with positive precipitation-evaporation (P-E) balances. Local exceptions occur on leeward side of the Sevier Orogen, where calcic paleosols in the wedge-top depozone record paleoenvironments with negative P-E balances in the orographic rain shadow. Stratigraphic sections in the Wayan Formation of Idaho (WF) were sampled from the wedge-top depozone. The units consist of stacked m-scale mudstone paleosols separated by m-scale sandstone-siltstone beds. Sections were sampled for organic carbon isotope profiles, and B-horizons from 6 well-developed paleosols were sampled for detrital zircons to determine maximum depositional ages. The first of these from the WF has produced a U-Pb concordia age of 101.0±1.1 Ma. This same WF section has produced a stratigraphic trend of upwardly decreasing δ13C values ranging from–24‰ upwards to–27‰ VPDB, suggesting correlation to the late Albian C15 C-isotope segment. Pedogenic carbonates from the WF principally consist of micritic calcite, with carbon-oxygen isotope values that array along meteoric calcite lines (MCLs) with δ18O values that range from–9.47‰ up to–8.39‰ VPDB. At approximately 42°N paleolatitude, these MCL values produce calculated paleoprecipitation values of–8.12‰ to–7.04‰ VSMOW, a range that is consistent with the estimates produced from other proxies at the same paleolatitudes across North America. These results indicate that despite the orographic rain shadow effect, the processes of meridional atmospheric moisture transport in this locale were similar to those in more humid mid-latitude paleoenvironments elsewhere in the continent.