Data from: The same picture through different lenses: quantifying the effects of two preservation pathways on Green River Formation insects

Insects in the fossil record are generally preserved in lacustrine shales or in amber. For those in lacustrine shales, preservation is usually via keroginization or mineralization. Given the extended period of microbial decay required to generate ions for mineralization, there is a predicted inherent bias toward lower preservation quality for this pathway by most taphonomic indices compared to keroginization. This study tests this hypothesis by comparing multiple measures of preservation quality between sites with similar sedimentology in the Eocene Green River Formation of Colorado. Here, insects are either mineralized in iron oxides (likely after pyrite) at the Paleoburn site, or keroginized at the Anvil Points site. Generally, the prediction that keroginization preserves soft-bodied fossils with higher preservational quality than mineralization is affirmed, but with some caveats. Beetles, known for their robust cuticles, are proportionately more abundant at the Paleoburn site, but eight of the nine orders recorded are shared between sites. As predicted, insects show lower preservation fidelity at the Paleoburn site, but they also show higher degrees of disarticulation. This second bias should be acquired primarily during the biostratinomy stage, and not early diagenesis. Nonetheless, higher energy biostratinomic conditions may be compatible with taphonomic conditions that promote mineralization over keroginization. Comparing the inherent taphonomic bias of different preservation pathways is often difficult since fossil deposits may be preserved millions of years or thousands of kilometers apart. By studying two different preservation pathways of insects within the same formation, we can affirm that keroginization does indeed preserve recalcitrant organic matter with higher quality than pyritization/iron oxide mineralization. Additionally, some guidelines can be proposed concerning the body parts and taxa that can be compared, and for what purpose, when contrasting mineralized and keroginized soft-bodied deposits.

化石记录中的昆虫通常保存在湖相页岩（lacustrine shales）或琥珀（amber）中。对于湖相页岩中的昆虫标本，其保存途径通常为干酪根化（keroginization）或矿化作用（mineralization）。由于矿化作用需要经历较长的微生物降解过程以产生成矿所需的离子，多数埋藏学指标（taphonomic indices）显示，相较于干酪根化途径，矿化作用的保存质量存在固有偏差，即保存效果更差。
本研究针对这一假说开展验证，通过对比美国科罗拉多州始新世格林河组（Eocene Green River Formation）中沉积学特征相似的两个遗址的多种保存质量评价指标展开分析。其中，古燃烧位点（Paleoburn site）的昆虫化石以氧化铁矿化（大概率为黄铁矿化（pyritization））形式保存，而铁砧点遗址（Anvil Points site）的昆虫化石则以干酪根化方式保存。
总体而言，“干酪根化相较于矿化作用，能以更高质量保存软躯体化石（soft-bodied fossils）”这一预测得到了证实，但也存在部分限定条件。以角质层（cuticles）较为坚固著称的甲虫类在古燃烧位点的占比更高，但两个遗址共记录了9个昆虫目中的8个。正如预测，古燃烧位点的昆虫化石保存保真度更低，但同时解体程度也更高。这一额外偏差主要应形成于尸积学（biostratinomy）阶段，而非早期成岩作用（diagenesis）。不过，高能环境的尸积学条件可能与更倾向于矿化而非干酪根化的埋藏学环境相兼容。
由于不同化石产地的保存时间可能相隔数百万年，或空间跨度达数千公里，直接对比不同保存途径的固有埋藏学偏差往往极具挑战。通过在同一地层中针对昆虫的两种不同保存途径开展研究，我们证实了干酪根化确实能比黄铁矿化/氧化铁矿化作用更高质量地保存难降解有机质（recalcitrant organic matter）。此外，针对对比矿化与干酪根化软躯体沉积时可用于比较的躯体部位、类群及研究目的，本研究也提出了若干指导原则。