Boreskov

PP‐23The oldest Trilobite Biofacies were common in the outer shelf of the Siberian paleobasin.Trilobite Biofacies Fallotaspidoidea has occurred in several areas (the Lena River, AldanRiver, Kharaulakh mountains, etc.). The next Trilobite Biofacies Fallotaspidoidea –Eodiscoidea already found in all parts of the study territory. These Biofacies existed inAtdabanian (Early Cambrian). Protolenids trilobites (biofacies Protolenidae (Bergeroniellus,Bergeroniaspis) – Eodiscoidea) replaced Fallotaspids and Eodiscids trilobites communities inBotomian (Early Cambrian). Despite the facies differences in different parts of the platform,and some representatives Protolenids and Eodiscids trilobites held in a dominant position inthe trilobites associations to the second half of the Toyonian (Early Cambrian). Althoughspecies composition was different in the trilobites associations, Protolenids still dominatedin the first half of the Toyonian (Biofacies Protolenidae (Lermontovia, Paramicmacca),Neopagetina). But the dominant were the representatives of other genera. At this time inthe Upper‐Markha area trilobites associations was mixed, Protolenids trilobites it is notdominant (Biofacies Agraulidae – Jakutiidae – Utiidae – Paradoxididae). Differentiation oftrilobites associations occurred in the study area at the Early Middle Cambrian. Trilobitesassociations, which occupy large areas, were replaced by complexes which prevalent in smallareas of the Siberian paleobasin (Biofacies Paradoxididae – Dorypygidae – Dinesidae,Dorypygidae – Ptychopariidae – Dinesidae, Ovatoryctocara – Agnostida, Agnostida –Oryctocephalidae).Agnostids and Oryctocephalids trilobites dominated on the area where accumulatedorganic‐rich rocks. Representatives of the families Dorypygidae, Ptychopariidae,Corynexochiidae existed and dominated in other part of the Siberian platform at differenttimes. The Eastern part of the Platform is populated Trilobites Biofacies Agnostida –Anomocaridae – Dorypygidae at the end of the Amgan (Middle Cambrian). But in the Upper‐Markha area there is another Trilobite Biofacies (Anomocaridae – Corynexochiidae –Paradoxididae).References[1]. Repina L. N. Biofacies of trilobites of the taryn level of Early Cambrian on Siberian Platform. //Environment and life in the geological past (facies and organisms), 1977, Novosibirsk, pp. 51‐74 (inRussian).[2]. Pegel T. V. Evolution of trilobite biofacies in Cambrian basin of the Siberian platform. J. Paleontology, 74(6), 2000, pp. 1000‐1019.172