摘要：Through much of the earlier part of the Middle Cenomanian the sea-levels in western Asia, northern Europe and the Western Interior of the U.S.A. were lower than during the later Early Cenomanian and most of the later Middle Cenomanian. In north-west Europe the first sign of this Mid-Cenomanian Eustatic Low was just before the end of the Zone of Cunningtoniceras inerme. There was then an abrupt and strong fall of sea-level at the base of Milankovitch couplet C 1, early in the Subzone of Turrilites costatus. Sea-level continued to be low through couplets C 1 to C 3 for some 60,000 years: this is the Mid-Cenomanian Regressive Trough. In western Germany it has been distinguished as the Primus Event. In north Texas and the Western Interior of the U.S.A. the Trough occurred in the Zone of Conlinoceras tarrantense which can be dated as 95.78 [plus-minus] 0.61 Ma.A later regressive trough occurred at the start of the Subzone of Turrilites acutus, which is marked by the Mid-Cenomanian Event in Germany. The overall lower sea-level from late in the Zone of C. inerme to early in the Subzone of T. acutus is the Mid-Cenomanian Eustatic Low. It lasted some 300,000 years.
