6 - Exceptional preservation

Summary

O me, why have they not buried me deep enough?

Is it kind to have made me a grave so rough,

Me, that was never a quiet sleeper?

Alfred, Lord Tennyson, Maud

Introduction

It has been estimated that from 66 to 79% of the biota of a marine community is not normally fossilized (e.g., Lawrence, 1968; see also Allison and Briggs, 1991a, b). Despite the improbability of preservation, there are numerous instances of exceptional preservation called Lagerstätten (singular Lagerstätte). The term comes from the mining industry and, loosely translated, means “fossil-motherlodes”, or rocks that are unusually rich in paleontological information. Seilacher (1970) recognized two types of Lagerstätten: (1) Konzentrat (concentration) deposits, which form by sedimentological and biological processes that largely exclude the preservation of soft parts and include shell beds, bone beds, and crinoidal limestones (Allison, 1988c); and (2) Konservat (conservation) deposits, which are characterized by preservation of soft-bodied fossils. Thus, Konzentrat-Lagerstätten are distinguished primarily by quantity whereas Konservat deposits are distinguished by the quality of preservation (Seilacher, 1990). Both types of deposits really represent end-members of a continuum in the preservational spectrum (Allison and Briggs, 1991a, b). Chapters 1–5 have been concerned with the formation and occurrence of Konzentrat-Lagerstätten. This chapter is devoted to major Konservat-Lagerstätten (Figure 6.1), in which soft-bodied organisms are preserved. Long viewed like the curios in an antique shop, the tremendous value of Konservat deposits was recognized only relatively recently.