CHRONOSTRATIGRAPHY OF CRETACEOUS OCEANIC REDBEDS

CORBs – Cretaceous Oceanic Red Beds – were deposited intermittently from Late Aptian to Maastrichtian and even into Paleogene. Late Cretaceous CORBs were deposited in deep epicontinental basins between colliding continents and on the craton in Spain, northwestern Germany, Austria, Poland, the Czech Republic, Romania, the Caucasus, and Tibet and in the Atlantic Basin on oceanic crust. Some CORBs have homogeneous bedding without distinct sedimentary structures and no carbonate and others are regularly bedded with nannofossil marls.

Late Aptian-Cenomanian CORBs are nannofossil-planktic foraminifer oozes deposited on the outer shelf to slope. Turonian-Santonian CORBs are epicontinental and oceanic deposits, some of which are homogenous and some are cyclically bedded. The Campanian-Maasstrichtian CORBs in epicontinental basins and on the oceanic abyssal plain are both homogeneous and cyclically bedded. Turonian-Santonian CORBs were deposited in shorter time intervals than Campanian-Maastrichtian CORBs averaging 3.04 myr versus 6.92 myr. However, the rate of Turonian-Santonian CORBs was faster on average than the Campanian-Maastrichtian, 19.51 m/myr versus 11.56 m/myr. The shorter duration and faster rates during the Turonian-Santonian may reflect active tectonic and volcanic processes.

The duration of CORB deposition was similar in epicontinental and oceanic basins averaging 4.34 myr and 5.57 myr respectively. However, the rate of sediment accumulation tended to be faster in epicontinental basins than in oceanic basins averaging 20.37 m/myr and 13.18 m/myr respectively. The higher rate in epicontinental basins reflects terrigenous runoff.

The duration of deposition of regularly bedded CORBs was about the same as of homogeneously bedded deposits averaging 4.92 myr and 5.68 m/myr respectively. But regularly bedded CORBs accumulated at a faster rate than homogeneously bedded deposits averaging 17.99 m/myr compared to 8.9 m/myr. This probably was the effect of mixed terrigenous and calcareous pelagic sediment input of bedded strata. In comparison, in the U.S. Western Interior Turonian-Santonian chalk/marl deposition averaged 24 m/myr. Regularly bedded chalk deposits in England and Italy, where clay input was minimal, were deposited at mean rates of 15 and 12 m/myr, respectively.