Издатель: U.S. Department of the Interior Minerals Management Service Alaska Outer Continental Shelf Region , Место издания: Anchorage, Alaska , Год издания: 1994

Investigation of abundant fossils found in many sections of boundary beds between Pliensbachian and Toarcian time clearly show a differentiation in communities of benthos in the terminal Pliensbachian, a crisis of biota in the beginning early Toarcian, and a new succession of benthic communities in the Toarcian. The composition of the boundary beds is the same all around the Siberian Platform. Lower Toarcian black shales ("Kiterbyutsk Clay"), which overlap the Pliensbachian, are extraordinary persistent along strike and are possibly very similar to lower Toarcian shales in Western Europe, the Canadian Arctic, and Northern Alaska. The lithologic composition and geochemical parameters of the lower Toarcian shales are homogeneous throughout Northern Siberia, and the distribution of benthic assemblages in the boundary beds is in agreement with them. The great turnovers take place in macro- and microbenthos communities; the differentiation of biota in the ecological zones is reduced, the variety of trophical groups is decreased, and, at the beginning of the early Toarcian, opportunist species dominate. The paleogeography of Siberian seas in "Kiterbyutian" time may be in agreement with the second Hallam model for bituminous clay accumulation.