Abstract Changes in terrestrial environments across the Cretaceous-Paleogene boundary, including plant ecology and carbon and water-cycling, remain poorly defined. Fluvial sediments spanning the Cretaceous-Paleogene (K-Pg) boundary of southern Saskatchewan, Canada contain well preserved plant wax n-alkanes that provide a means of reconstructing changes to plant ecology and carbon and water cycling during this mass extinction event. We measured n-alkane carbon (δ13C) and hydrogen (δ2H) isotope ratios in two sedimentary sections and applied established fractionation factors to estimate the isotopic compositions of precipitation and bulk sedimentary organic matter sources. We also analyzed the distribution of n-alkanes as an indicator of the relative abundance of aquatic and terrestrial plants. We find a consistent shift towards a greater relative abundance of longer-chain n-alkanes across the boundary, implying a persistent increase in the relative abundance of terrestrial plants in the sedimentary basin. This is consistent with an increase in birch and elm palynomorphs immediately above the boundary. We hypothesize the extinction of all large herbivores at the boundary may have facilitated this transition to a terrestrial angiosperm dominated flora immediately after the boundary. We also find that the region was characterized by isotopically light precipitation, with δ2H values between −95‰ to −160‰ but do not observe evidence for major millennial-scale changes in regional precipitation isotopic composition spanning the boundary. n-Alkanes derived from both aquatic and terrestrial plants at one site display an upward trend in δ13C values of approximately 2‰ across the K-Pg boundary. This suggests millennial-scale local or global carbon-cycle variability altering either plant carbon isotope fractionation or the carbon isotope composition of dissolved inorganic carbon and atmospheric CO2. Overall our results suggest that carbon and water cycle changes associated with the K-Pg impact in terrestrial environments in western Canada were short-lived, but ecological shifts in plant communities were longer-lasting.

中文翻译：

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从植物蜡脂分布和同位素测量推断加拿大西部白垩纪-古近纪边界陆地生态系统的变化

摘要 白垩纪-古近纪边界的陆地环境变化，包括植物生态学以及碳和水循环，仍然不清楚。横跨加拿大萨斯喀彻温省南部白垩纪-古近纪 (K-Pg) 边界的河流沉积物含有保存完好的植物蜡正构烷烃，可提供一种在这次大灭绝事件期间重建植物生态和碳和水循环变化的方法。我们测量了两个沉积剖面中的正烷烃碳 (δ13C) 和氢 (δ2H) 同位素比率，并应用确定的分馏因子来估计降水和大量沉积有机质源的同位素组成。我们还分析了正构烷烃的分布，作为水生和陆生植物相对丰度的指标。我们发现跨越边界的长链正构烷烃的相对丰度持续转变，这意味着沉积盆地中陆生植物的相对丰度持续增加。这与边界正上方的桦树和榆树孢粉体的增加是一致的。我们假设边界处所有大型食草动物的灭绝可能促进了边界后立即向陆生被子植物主导的植物群的转变。我们还发现，该地区的特征是同位素轻降水，δ2H 值在 -95‰ 到 -160‰ 之间，但没有观察到跨越边界的区域降水同位素组成在千年尺度上发生重大变化的证据。来自一个地点的水生和陆生植物的正构烷烃在跨越 K-Pg 边界的 δ13C 值上显示出大约 2‰ 的上升趋势。这表明千年尺度的局部或全球碳循环变异改变了植物碳同位素分馏或溶解无机碳和大气 CO2 的碳同位素组成。总体而言，我们的结果表明，与加拿大西部陆地环境中 K-Pg 影响相关的碳和水循环变化是短暂的，但植物群落的生态变化则更持久。