The search for Orsten-type fossils in southern China

Orsten-type fossils, mainly arthropod juveniles and even tiny embryos exquisitely preserved in apatite, have been well documented from several localities in southern China. This particular type of Lagerstätte is known from just a few places around the world but has led to significant breakthroughs in the understanding of the early diversity of animals and evolution of metazoans. The original 'orsten' from southern Sweden are limestone concretions within black shales, whereas in China this kind of preservation occurs in lime mudstone thin beds and nodules interbedded with shale. Thus there is a taphonomic bias in that this kind of preservation is localized to a deeper water carbonate facies which can be regarded as concretionary due to early cementation under shallow burial. Nonetheless, we observe that even within a laterally extensive bed of the seemingly appropriate lithofacies, preservation may be highly localized. Thus, in addition to the extreme rarity of Orsten-type preservation globally, serendipity in discovering fossiliferous localities plays a significant role. Because of their predominant occurrence in the Cambrian they are also a temporally restricted window. To extract Orsten-type material from the limestone matrix, mild acetic acid digestion has been widely applied, but certain procedures can be employed to aid recovery by limiting damage to these delicate but fragile specimens. Here, we describe our method for etching out specimens and review some of the discoveries recently made in southern China.