The paper presents results of paleontological, stratigraphic, and lithofacies studies of the Ordovician deposits exposed by boreholes in the western periphery of the Vilyui Basin. The studies allowed us to revise the classification of some lithostratigraphic units of the Vilyui and Markha-Morkoka facies, to give detailed lithofacies and paleontological characteristics of formations and members, and to reveal lateral changes of coeval deposits within both facies at every stratigraphic level from Lower to Upper Ordovician. We have performed correlations between lithostratigraphic and biostratigraphic units of the regional Ordovician scale for the Siberian Platform, recognized and estimated regional- and local-scale stratigraphic gaps between the Lower and Middle Ordovician and at the top of the Upper Ordovician strata. It is shown that the Ordovician deposits are in places overlain by Silurian, Upper Paleozoic, or Triassic rocks. The biostratigraphic correlation of the deposits is based on studies of conodonts, graptolites, ostracodes, brachiopods, and trilobites. Space and time relationships between lithostratons of different facies and regional biostratons are illustrated in three cross sections of the Ordovician deposits, compiled along profiles in different parts of the region.

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First page of THE ORDOVICIAN OF THE WESTERN PERIPHERY OF THE VILYUI BASIN: STRATIGRAPHY, FACIES, AND PALEONTOLOGIC CONSTRAINTS
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