Mid-Cenomanian separation of Atlantic and Tethyan domains in Iberia by a land-bridge: The origin of larger foraminifera provinces?

Abstract

The Middle and Late Cretaceous shallow-water carbonate platforms widely exposed across the eastern half of the Iberian Peninsula including the Betic Cordillera, the Iberian Ranges and the Pyrenees provides an excellent material for analyzing the origin of two Iberian Late Cretaceous larger foraminifera provinces, the Betic and the Pyrenean: the former corresponds to the Tethyan domain, the latter to the Atlantic domain. The spatiotemporal distribution in the three studied areas of the larger foraminifera k-strategists, the Alveolinaceans, from the latest Albian–Cenomanian time interval suggests that separation of the two faunal provinces started during Early Cenomanian (mid-Cretaceous Global Community Maturation cycle), and the shelves of the Iberian seaway formed the boundaries of the corresponding bioprovinces. This occurred before the Betic–Pyrenean communication near the Middle–Late Cenomanian transition was interrupted by a landbridge. Therefore, the separation of the two bioprovinces cannot be due to the physical barrier created by the opening or closure of the shallow seaway across the Iberia: here it is attributed to the differences in the ecological gradients. At the end of the Cenomanian, the Cenomanian–Turonian eutrophication event eliminated all the k-strategist larger foraminifera to such a degree that all their essential k-strategy information was lost. The newly arising k-strategist foraminifera needed a considerable time (8–10 m.y.) to recover their lost genetic complexity: this occurred during the Coniacian in the following GCM cycle.