133 Introduction Echinoderm ossicles have a high preservation potential as fossils. Their skeletons, however, disarticulate easily and rap- idly after death, so they are relatively rare as articulated spec- imens. Because of the fragility of the echinoderm skeletons, preservation of complete specimens requires special condi- tions. Burial has to be rapid and effective enough to prevent subsequent disruption by currents or scavengers (Donovan 1991). Echinoderms are particularly sensitive to smothering by sediments, because this effectively blocks their water-vas- cular system. Following Seilacher (1970), the results of such events have been referred to as “obrution deposits”. Tem- pestites and turbidites have commonly been suggested as physical mechanisms for the creation of exceptionally well- preserved assemblages known as Lagerstätten. Late Juras- sic examples in Europe include the Solnhofen Plattenkalk of Bavaria (Hess 1999) and the French lithographic lime- stones of Cerin (Breton et al. 1994) and Canjuers (Roman et al. 1991, 1993, 1994). However, very few echinoderm fossils have until now been reported from high-latitude deposits. Well-preserved echinoderm fossils were discovered in the Upper Jurassic of central Spitsbergen, Arctic Norway, during fieldwork expeditions of the Spitsbergen Jurassic Research Group (Natural History Museum University of Oslo and University of Alaska, Fairbanks) between 2008 and 2010. The material contains one crinoid and one echinoid species identifiable to genus level, as well as new asteroids and ophiuroid species which are currently being described by, respectively, Rousseau & Gale (in prep.) and Rousseau & Thuy (in prep.). These taxa are here referred to in open nomenclature. Using this exceptional material, the current contribution establishes the first paleoenvironmental inter- pretation of High-Boreal Mesozoic echinoderms. The Late Jurassic Arctic The Late Jurassic marine rocks that nowadays crop out in central Spistbergen were deposited in a high-latitude, cold water setting (Fig. 1A). Distinct Boreal (Arctic and northernmost Europe) and Tethyan (southernmost Europe and margins of the former Tethys seaway) marine faunal assemblages have been recog- nised through the Late Jurassic and Early Cretaceous, with the greatest faunal differentiation between Callovian and Aptian times (Gordon 1974). Changes in the distribution of ammonites and bivalves suggest episodes of faunal migra- tion between the Boreal and Tethyan realms, coupled to the opening and closing of seaways between the north and the south (Zakharov & Rogov 2003, 2004). Difficulties in correlation of the Northwest European region (Tethyan) with both tropical and polar regions have resulted in the widespread use of regional stratigraphy for the uppermost Jurassic and lowermost Cretaceous (Fig. 1B; Ogg 2005). The latest Jurassic Volgian stage, established in western Russia by Nikitin in 1881, has since been extensively used and defended—after its withdrawal from the International Stratigraphic Scale in 1991—by Russians and Boreal region workers (see Zakharov 2003). NORWEGIAN JOURNAL OF GEOLOGY An Upper Jurassic Boreal echinoderm Lagerstätte from Janusfjellet, central Spitsbergen An Upper Jurassic Boreal echinoderm Lagerstätte from Janusfjellet, central Spitsbergen Julie Rousseau & Hans Arne Nakrem Rousseau, J. & Nakrem, H.A.: An Upper Jurassic Boreal echinoderm Lagerstätte from Janusfjellet, central Spitsbergen. Norwegian Journal of Geology, vol. 92, pp 133-161. Trondheim 2012. ISSN 029-196X. A well-preserved, low-diversity assemblage of fossil echinoderms from the early Middle Volgian in the Slottsmøya Member (Agardhfjellet Formation) has been discovered at Janusfjellet, Sassenfjorden area, central Spitsbergen. Five species are recognised: the isocrinid Chariocrinus sp., the pedinoid Hemipedina sp., the forcipulate asteroid Asteriidae sp., the ophiacanthid Ophiacanthidae sp. and the ophiurid Ophiurinae sp. A depo- sitional environment model reconciling autecologic, taphonomic and sedimentary evidence is presented. The Janusfjellet Lagerstätte was formed by a single, rapid burial event during a storm, entombing together autochthonous asteroids and ophiurids, and allochthonous crinoids and echinoids on a dysoxic muddy sea-floor. Comparable echinoderm material from the Boreal Late Jurassic-Early Cretaceous is scarce, outdated and usually poorly described and illustrated. The scarcity of reported occurrences probably results from a collector bias for rare complete specimens and does not reflect the true echinoderm composition of Mesozoic high-latitude communities. Julie Rousseau, Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway. Email: julie.rousseau@nhm.uio.no. Hans Arne Nakrem, Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway. Email: h.a.nakrem@nhm.uio.no.