ENVIRONMENTAL BIAS OF FOSSIL KONSERVAT LAGERSTÄTTEN THROUGH THE PHANEROZOIC

Fossil Konservat Lagerstätten (FKL) provide the only evidence of soft-bodied or lightly sclerotized organisms, which are otherwise unknown in the fossil record. Therefore, these deposits are critical to determining the evolutionary history of certain groups, accurate paleoecology and taxonomic composition of communities, and the true diversity of life through time. However, there are environmental biases that influence the preservation of FKL, thereby limiting their occurrence and impacting the kinds of information available.

Cambrian Burgess Shale- and Chengjiang-type FKL represent typical marine environments containing common and diverse shelly taxa in addition to the soft-bodied organisms. In contrast, post-Cambrian FKL never represent typical marine settings, but rather are found in restricted sedimentary environments, whether marine or nonmarine.

This is clearly demonstrated by FKL in Silurian rocks of the Great Lakes region of North America. These occurrences are not confined to a single time interval or geographic area but are related to short-term sedimentary events (e.g., hypersalinity, anoxia) within atypical environments (e.g., sediment traps) that contained few shelly taxa. With the exception of the soft-bodied organisms, these strata, which are commonly well laminated, would otherwise appear nearly barren. In contrast, FKL are absent from the classic Silurian reefs and other shallow-shelf environments in the area that contain an abundance and high diversity of shelly taxa.

Although these restricted conditions mediate the early diagenetic mineralization that allows soft tissue preservation, they also indicate the absence of bioturbation. Conversely, post-Cambrian FKL are absent where conditions are conducive to bioturbation and its concomitant sediment disruption, i.e., normal marine settings; deeper bioturbation may have been limited in the Cambrian. As a result, little is known about the soft-bodied component of normal marine ecosystems after the Cambrian. Consequently, there may be major gaps in the evolutionary story of these environments through most of the Phanerozoic.