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首页> 外文期刊>Palaios: An International Journal of the Society of Economic Paleontologists & Mineralogists >ANATOMY OF A CONCRETION: LIFE, DEATH, AND BURIAL IN THE WESTERN INTERIOR SEAWAY
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ANATOMY OF A CONCRETION: LIFE, DEATH, AND BURIAL IN THE WESTERN INTERIOR SEAWAY

机译：结论的解剖：西方内陆海域的生命，死亡和野性

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摘要

Concretions are the most characteristic mode of fossil occurrence in the Upper Cretaceous Western Interior of the United States. An in-depth analysis of a single concretion from the upper Campanian Pierre Shale, South Dakota, drawing upon sedimentology, paleontology, shell preservation, degree of encrustation, and geochemistry allows us to determine a time frame for the accumulation and burial of the organisms and the process of cementation and diagenesis of the concretion. The concretion is very fossiliferous and dominated by mollusks. Large ammonites are commonly broken up with pieces missing from the adapical end of the body chamber. This breakage pattern is widely interpreted as evidence of lethal damage, implying introduction into the burial site via predation. In contrast, smaller ammonites are nearly complete and may have died due to smothering in resuspended sediment produced by bottom currents. The concretion is rich in cephalopod jaws, which mostly appear as isolated occurrences, usually deformed, with the calcite covering (aptychus) missing. The preservation of jaws suggests that the organic debris did not remain in the taphonomically active zone for more than a few years. The concretion, thus, represents a time-averaged deposit of organisms derived from the local community. In contrast, host sediments contain fewer fossils, most of which are crushed. Oxygen and carbon isotopic composition of samples in the concretion and the host sediments reveals a two-stage diagenetic history of the concretion. First, cementation probably occurred at shallow burial depths in early diagenesis in association with the decomposition of organic matter and the oxidation of methane. Second, alteration of the shelly material and the formation of calcite crystals filling the empty chambers of ammonites probably occurred during later diagenesis in contact with meteoric water.
机译：固结是美国上白垩统西部内陆化石发生的最典型方式。根据沉积学，古生物学，壳保护，结壳程度和地球化学，对南达科他州坎帕尼亚上层皮埃尔页岩的单个凝结物进行了深入分析，使我们能够确定生物体堆积和埋葬的时间框架。胶结和成岩过程。粪便是化石，以软体动物为主。大的铵通常被分解成从体腔的顶头末端丢失的碎片。这种破损模式被广泛地解释为致命损害的证据，这意味着通过掠食将其引入墓地。相比之下，较小的炸药几乎完整，可能由于底部水流产生的悬浮沉淀物窒息而死亡。该结石富含头足类下颌，多数以孤立的形式出现，通常变形，方解石覆盖物（aptychus）缺失。颌骨的保存表明，有机碎屑在几年来没有保留在胶体活性区域中。因此，该固结物代表了当地社区生物的平均时间沉积。相反，宿主沉积物包含的化石较少，其中大多数被压碎了。固结和宿主沉积物中样品的氧和碳同位素组成揭示了该固结的两阶段成岩史。首先，胶结作用可能发生在成岩初期的浅埋深度，这与有机物的分解和甲烷的氧化有关。其次，在后来的成岩作用中，与流态水接触时，可能发生了壳状物质的改变和方解石晶体的形成，这些方解石晶体填充了空洞的炸药。

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