The Hanson Ranch (HR) Bonebed is a monodominant assemblage of Edmontosaurus annectens and infrequent remains of other vertebrates within the Lance Formation of northeastern Wyoming. This bonebed, which has yielded more than 13,000 specimens from five Main Quarries over the last 25 years, is interpreted to have formed by deposition of a clastic debris flow, generating a normally-graded, fossil-dense assemblage. To clarify the geochemical history of the HR Bonebed and assess its mode of formation independent of traditional taphonomic means, we conducted trace element analyses of 12 bones from the assemblage using laser ablation-inductively coupled plasma mass spectrometry. A majority of the examined bones were found to exhibit rapidly-declining rare earth element (REE) profiles, indicative of brief exposure to groundwaters, modest overall trace element uptake, and minimal late-diagenetic alteration. However, noteworthy variations were also identified among the specimens. In particular, both positive and negative redox anomalies were identified at the cortical margins and whole-bone level, indicating variable exposure within and among specimens to both reducing and oxidizing conditions. Several of the examined specimens, especially those of taxa other than Edmontosaurus, also exhibit less fractionation among REEs and more homogenous internal compositions. We infer these contrasts to arise from more protracted pore-fluid interactions for some specimens than others, and thus that select bones were attritionally added into the assemblage during transport to the final site of burial. These collective findings independently support prior taphonomic inferences that the bonebed horizon primarily hosts a partially-reworked or short-distance-transported mass death assemblage, and that this depositional history has imparted infrequent attritional signatures into specimens preserved in the bonebed. Our data thereby establish a baseline for comparison for many other fossil sites within the Lance Formation in the region, similar study of which can illuminate the suite of paleoenvironments and diagenetic settings recorded by these highly-fossiliferous strata.

中文翻译：

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Hanson Ranch Edmontosaurus 骨床的微量元素 taphonomy 通过运输大规模死亡组合支持其起源


汉森牧场 （HR） 骨床是怀俄明州东北部兰斯组内 Edmontosaurus annectens 和其他脊椎动物的罕见遗骸的单一优势组合。在过去的 25 年里，这个骨床从五个主要采石场产生了 13,000 多个标本，被解释为是由碎屑碎石流沉积形成的，产生了正常等级的化石密集组合。为了阐明 HR 骨床的地球化学历史并评估其独立于传统 taphonomic 手段的形成模式，我们使用激光消融-电感耦合等离子体质谱法对组合中的 12 块骨头进行了痕量元素分析。发现大多数检查的骨骼表现出迅速下降的稀土元素 （REE） 特征，表明短暂暴露于地下水，总体微量元素吸收适中，晚期成岩作用改变最小。然而，在标本中也发现了值得注意的变化。特别是，在皮质边缘和全骨水平上发现了阳性和阴性氧化还原异常，表明标本内部和标本之间对还原和氧化条件的暴露程度不同。一些被检查的标本，尤其是 Edmontosaurus 以外的分类群的标本，也表现出较少的 REE 分馏和更均匀的内部组成。我们推断这些对比是由于某些标本比其他标本更持久的孔隙液相互作用引起的，因此，在运输到最终埋葬地点的过程中，选定的骨骼被消耗性地添加到组合中。 这些集体发现独立地支持了先前的 taphonomic 推断，即骨床层位主要承载着部分返工或短距离运输的大规模死亡组合，并且这种沉积历史为保存在骨床中的标本赋予了不常见的磨损特征。因此，我们的数据为该地区 Lance 组内的许多其他化石遗址的比较建立了基线，对这些化石含量很高的地层的类似研究可以阐明这些高度化石地层记录的一系列古环境和成岩环境。