Biofacies and age of Cambrian trilobite associations of the Diringde reef complex (northern Siberian Platform, Russia)

The Diringde reef complex (Kotuy River Basin, Southwest of the Anabar Region, northern Siberian Platform, Russia) has formed during the late mid-Cambrian-early Furongian at the shelf margin of the epicontinental marine basin. Two detached carbonate buildup complexes originated. The southern mid-Cambrian buildup complex is replaced laterally by shale-carbonate rocks of the open basin slope. The northern mid-Cambrian-Furongian buildup complex passes laterally into the inner shelf dolomites. The trilobite associations of the central parts of both buildup complexes consist of rare endemic polymerids, distributed mainly in interbeds between algal buildups. The trilobite associations in narrow facial transition zones (reef flanks) to surrounding stratified deposits differ in having more abundant polymerids, higher taxonomic diversity, and include also agnostoids. The trilobite associations are similar to the assemblage of the reef-dominated mid-Cambrian-Furongian Chukuka Formation that is widespread in the neighboring South Anabar Region. The associations from the reef flank of the southern buildup complex consist mainly of species distributed in Cambrian shallow-water deposits of the Saami, Sakha, Nganasany and Tavgi horizons in the Kulyumbe River reference section, northwestern Siberian Platform. The trilobite assemblages of deeper water deposits of the Eyra Formation that are found on the open marine side of the Diringde reef complex combine typical elements of mainly endemic, shallow-water associations of the southern buildups and the slope basin associations with various cosmopolitan pre-Furongian agnostoids enabling international correlations.