A new hypothesis for organic preservation of Burgess Shale taxa in the middle Cambrian Wheeler Formation, House Range, Utah
A new hypothesis for organic preservation of Burgess Shale taxa in the middle Cambrian Wheeler Formation, House Range, Utah
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DOI：
10.1016/j.palaeo.2004.07.034
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发表时间：
2005-05-02
影响因子：
3
通讯作者：
Droser, ML
中科院分区：
文献类型：
--
作者：
Gaines, RR;Kennedy, MJ;Droser, ML
寒武纪 konservat-lagerstatten 是对于我们了解显生宙生命起源最重要的化石沉积。尽管可能存在多种保存方式，但这些沉积物最常见的是以干酪化碳膜形式保存的非矿化化石，这是一种罕见但重要的埋藏学途径，此前尚未通过综合模型对任何单位进行解释。犹他州中寒武纪惠勒组是其中之一，含有丰富的非矿化组织的干酪岩化保存，这些组织发生在独特的地相中，这些地相在以下条件下积累：（1）粘土大小颗粒对硅质碎屑部分的控制，（2）靠近碳酸盐台地，导致混合碳酸盐-粘土沉积物，（3）发育良好的最低含氧量，排除了底栖殖民和穴居，以及(4) 相对接近含氧底层水，有利于生物体从宜居环境运输到有利于其保存的环境。我们认为，惠勒地层中非矿化组织的保存可能是由于降低渗透性并因此降低氧化剂通量的综合影响造成的，这反过来又可能限制了一些非矿化组织的微生物分解。这些影响包括近底缺氧、通过限制生物扰动防止沉积物灌溉；减少沉积物-水界面附近的条件，这些条件可能起到解絮凝粘土矿物的作用，从而导致面对面接触的低渗透性；早期成岩孔隙闭塞碳酸盐胶结物；不含粗颗粒，如淤泥、骨架微化石、粪便颗粒或生物碎屑。该模型可能适用于其他化石大型化石的干酪岩化保存。 (c) 2004 Elsevier B.V. 保留所有权利。
Cambrian konservat-lagerstatten are the most significant fossil deposits for our understanding of the initiation of Phanerozoic life. Although many modes of preservation may occur, these deposits most frequently contain nonmineralized fossils preserved in the form of kerogenized carbon films, a rare yet important taphonomic pathway that has not previously been explained for any unit by a comprehensive model. The middle Cambrian Wheeler Formation of Utah, one of these lagerstatten, contains abundant kerogenized preservation of nonmineralized tissues, which occurs within a distinctive taphofacies that accumulated under the following conditions: (1) domination of the siliciclastic fraction by clay-sized particles, (2) close proximity to a carbonate platform, which resulted in mixed carbonate-clay sediments, (3) a well-developed oxygen minimum precluding, benthic colonization and burrowing, and (4) relative proximity to oxic bottom-waters, facilitating transport of organisms from a habitable environment to one that favored their preservation. We propose that preservation of nonmineralized tissues in the Wheeler Formation may have resulted from a combination of influences that reduced permeability and, thus, lowered oxidant flux, which in turn may have restricted microbial decomposition of some nonmineralized tissues. Those influences include near bottom anoxia, preventing sediment irrigation by restriction of bioturbation; reducing conditions near the sediment-water interface that may have acted to deflocculate aggregations of clay minerals, resulting in low permeability face-to-face contacts; early diagenetic pore occluding carbonate cements; and an absence of coarse grains Such as silt, skeletonized microfossils, fecal pellets, or bioclasts. This model may be applicable to kerogenized preservation of macrofossils in other fossil lagerstatten. (c) 2004 Elsevier B.V. All rights reserved.