Bioturbation in Burgess Shale-type Lagerstätten — Case study of trace fossil–body fossil association from the Kaili Biota (Cambrian Series 3), Guizhou, China Jih-Pai Lin a,b, ⁎, Yuan-Long Zhao c , Imran A. Rahman d , Shuhai Xiao e , Yue Wang c a Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China b Dept. of Geology and Geophysics, Yale University, New Haven, CT 06511, United States c College of Resource and Environment Engineering, Guizhou University, Guiyang 550003, China d Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK e Dept. of Geosciences, Virginia Tech, Blacksburg, VA 24061, United States abstract article info Article history: Received 6 November 2009 Received in revised form 18 March 2010 Accepted 23 March 2010 Available online 31 March 2010 Keywords: Cambrian Ichnofossils Fecal pellets Sediment reworking Konservat-Lagerstätten Cruziana, Gordia, Planolites, Rusophycus, and Trichophycus are common ichnological elements of the Kaili Biota. New discoveries based on the examination of 323 specimens include eldoniids, echinoderms, trilobites, monoplacophorans, and non-biomineralizing arthropods that are associated with trace fossils. Based on the observed effects of bioturbation on the preservation of five different animal groups, it is clear that infaunal scavengers/deposit feeders were periodically active on the Kaili sea floor and were able to reach historic layers yielding exceptionally preserved fossils. In general, the average level of infaunal activity is absent to moderate (Ichnofabric Index [i.i.] = 1 to 3) in the Kaili substrate; by contrast, the “Phycodes beds” are completely disturbed by infaunal activity (i.i. = 5). Observed burrow diameter ranges from diminutive (∼ 0.2 mm) to normal (up to 4.2 mm). Computed tomography allows us to visualize the precise geometry of the trace fossil–body fossil association in three dimensions. We concluded that although some Kaili infaunal animals could bore through the biomineralized echinoderms, they did not appear to have scavenged upon these echinoderms based on our three-dimensional reconstruction. Furthermore, Kaili burrowers can reach the historic layers containing exceptionally preserved fossils without altering soft-tissue preservation. On the other hand, we used conventional techniques to reveal that one burrow is filled with fecal pellets (100– 200 μm) at its terminal end. Because most burrows are filled with yellow/brown “coarse sediment”, and because there is no compositional difference between the fecal pellets and the surrounding coarse sediment within the burrow, the origin of the yellow/brown “coarse sediment” is interpreted here as parautochtho- nous and/or autochthonous and as a result of sediment reworking by deposit (or suspension) feeders. The relative scarcity of soft-part preservation in the Kaili Biota compared to the older Chengjiang Biota and the younger Burgess Shale Biota may be the result of post-burial bio-disturbance due to the relatively high intensity of local bioturbation. It is plausible that oxygenation in deeper sediments (facilitated by bioturbation) allowed carcasses in the Kaili biota to undergo a more extensive period of ‘normal’ decay prior to final burial than in other Cambrian Konservat-Lagerstätten. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Exceptionally preserved fossils offer unique insights into the evolutionary history of life. It is striking that there are more exceptionally preserved marine deposits in the Cambrian than in the entirety of the remaining Phanerozoic (Conway Morris, 1985, 1990; Robison, 1991; Allison and Briggs, 1993b; Butterfield, 1995; Conway Morris, 1998; Butterfield, 2003; Donoghue and Dong, 2005; Seilacher et al., 2005; Donoghue et al., 2006; Maas et al., 2006; Bambach et al., 2007), and the abrupt decline of exceptional fossil deposits after the Cambrian is a subject of considerable debate. Bioturbation has been suggested as one of the major limiting factors of these so-called Burgess Shale-type (BST) deposits (Allison and Briggs, 1993a; Allison and Brett, 1995; Bottjer et al., 2000; Orr et al., 2003; Gaines and Droser, 2005; Gaines et al., 2005) (however this is not universally accepted, see e.g., Aronson, 1992, 1993; Powell et al., 2003). Furthermore, ichnofauna (Appendix A) has been studied for more than a decade within the strata of Kaili Biota that yields exceptionally preserved fossils (e.g., Zhao et al., 2005) and represents an important transitional community temporally (Zhu et al., 2006) between the older Chengjiang Biota (e.g., Hou et al., 2004) and the younger Burgess Shale Biota (e.g., Briggs et al., 1994). Investigations of trace fossils alone, however, cannot address all of the issues relating to BST preservation. Palaeogeography, Palaeoclimatology, Palaeoecology 292 (2010) 245–256 ⁎ Corresponding author. Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China. E-mail address: jplin@hotmail.com (J.-P. Lin). 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.03.048 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo