Correlation possibilities around the Jurassic/Cretaceous boundary
The present-day detailed knowledge of the zonation and the chronostratigraphic ranges of the fossils of the Mediterranean Berriasian makes it possible to re-evaluate critically the factual evidence on which the correlation of the Boreal sequence with the Tethyan standard is based. It turns out that the evidence is still very meagre and that correlation by means of marine fossils is only possible for time-intervals in which the sea level was high. Some important results of this investigation are: 1) The Valanginian age of the upper Ryazanian: the base of the Tirnovella alpillensis Subzone is stratigraphically closest to, or even coinciding with, the boundary between the lower and the upper Ryazanian and to the base of the German 'Wealden' unit 4. 2) The correlation of the English Cinder Beds with the upper Tithonian Berriasella jacobi Subzone. 3) The time-equivalence of the jacobi Subzone with the lower part of the Canadian Buchia terebratuloides Zone and with at least a part, or even the whole of the underlying Buchia fischeriana Zone, and therefore also with the upper Volgian Taimyroceras taimyrense Zone and with at least the major part, or even the whole, of the Craspedites okensis Zone. 4) The lack of any evidence for the East-European Riasanites rjasanensis Zone being older than the Mediterranean Berriasella paramimouna Subzone or younger than the Berriasella picteti Subzone. 5) The correlation of the Buchia okensis Zone with the lower part of the Berriasella paramimouna Subzone, and possibly with a small part of the Dalmasiceras dalmasi Subzone, but also with an interval in the lower part of the upper Hectoroceras kochi Zone. 6) The entire Riasanites rjasanensis Zone falling within the upper part of the Héctoroceras kochi Zone. 7) The top of the Siberian Chetaites chetae Zone being stratigraphically closest to the top of the Mediterranean Pseudosubplanites grandis Subzone and to the top of the German 'Wealden' unit 1. As the author (Hoedemaeker, 1981, 1982, 1983, 1984) has proposed to draw the base of the Valanginian at the base of the alpillensis Subzone and the top of the Tithonian at the top of the grandis Subzone, the above correlations imply that the Berriasian/ Valanginian boundary is stratigraphically closest to, or even coinciding with, the boundary between the lower and upper Ryazanian and that the Tithonian/Berriasian boundary, which is also the Jurassic/Cretaceous boundary, is closest to, or even coinciding with, the top of the chetae Zone. The Jurassic/Cretaceous boundary correlates approximately with the base of 'Wealden' unit 2 in Germany, with the approximate base of the Royal faunicycle of the English Purbeck Beds, and with a level not far above the middle of the rock interval occupied by the North American Buchia terebratuloides Zone.
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Hoedemaeker, Ph.J. (1987). Correlation possibilities around the Jurassic/Cretaceous boundary. Scripta Geologica, 84, 1–55.