Dynamic palaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah

摘要: Garson, D.E., Gaines, R.R., Droser, M.L., Liddell, W.D. & Sappenfield, A. 2011: Dynamicpalaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah. Le-thaia, DOI:10.1111⁄j.1502-3931.2011.00266.xBurgess Shale-type faunas provide a unique glimpse into diversification metazoanlife during Cambrian. Although anoxia has long been thought to be pre-requisitefor this particular type soft-bodied preservation, palaeoenvironmental conditionsthat regulated extraordinary have not fully constrained. In particular,the necessity bottom water anoxia, considered pre-requisite, sub-ject recent debate. study, we apply micro-stratigraphical, ichnologicalapproachtodeterminebottom wateroxygen conditionsunder,which BurgessShale-typebiotas were preserved Middle Mudstones theSpence are characterizedby fine scale (mm-cm)alternation between laminated andbioturbated intervals, suggesting high-frequency fluctuations oxygena-tion. Whilst background oxygen levels high enough support continuousinfaunal activity, brief intervals improved conditions punctuatethe succession. A diverse skeletonized benthic fauna, including various polymerid trilo-bites, hyolithids, brachiopods ctenocystoids suggests that complex dysoxic benthiccommunity was established times when werepermissive. Burgess within is largely confinedto non-bioturbated horizons, prevailed wherethese fossils preserved. However, some found weaklyto moderately bioturbated (Ichnofabric Index 2 3). This Bur-gess strongly favoured by but may notrequire it all cases. h Anoxia, Shale, type-preservation, LangstonFormation, Member,Utah.Daniel E. Garson [daniel.garson@gmail.com], Department Earth Sciences, University ofCalifornia, Riverside, CA 92521, USA; Robert R. Gaines [Robert.Gaines@pomona.edu],Geology Department, Pomona College, 185 Sixth St., Claremont, 91711, MaryL. Droser [mary.droser@ucr.edu], California,Riverside, W. David Liddel [dave.liddell@usu.edu], ofGeology, Utah State University, Logan, UT 84322-4505, Aaron Sappenfield[aaron.sappenfield@email.ucr.edu], manuscript received on 14 September 2010; acceptedon 04 February 2011.