Abstract

The distribution and character of Upper Cretaceous rocks of the Celtic Sea is discussed on the basis of newly released well data and shallow seismic surveys.

At the beginning of Cenomanian time shallow water sands and carbonates were being deposited over much of the area. These were rapidly succeeded by deeper water silts and argillaceous chalks in the South Celtic Sea Basin, a pelagic connection existing at this time with the Anglo-Paris Basin via the Bristol Channel.

A mid-Cenomanian transgressive pulse caused significant drowning of the positive areas around the Celtic Sea, establishing pure chalk sedimentation over most of the region, possibly allowing shallow water sediments to persist only in the west.

Important circulation changes occurred at this time, open circulation being established across the Celtic Sea shelf. Significant mid-Cenomanian modifications in sedimentation have been recorded around the North Atlantic borderlands.

In Turonian to Maastrichtian times the Celtic Sea was dominated by a pelagic water mass and white chalk was developed throughout. An important change in consistency (degree of lithification) and microfauna occurs at the Coniacian-Santonian boundary, reflecting an important change in the character and depth of this water mass. A stratigraphical hiatus is suggested at this level.

Latest Cretaceous and Early Tertiary regression and inversion tectonics resulted in the removal of Upper Cretaceous sediments from positive areas around the Celtic Sea, but only removed limited amounts from the Celtic shelf.

Aptian (Austrian) and mid-Cenomanian regional tectonic pulses with associated eustatic regressions are noted in the Celtic Sea and adjacent areas. These events we suggest to be related to the onset of sea floor spreading in the Bay of Biscay and Rockall Trough, respectively. The end-Coniacian event may have a similar significance.

The change from pre-Aptian fault controlled subsidence to post-mid-Cenomanian downwarping is also related to this crucial mid-Cretaceous phase of activity along this section of the Atlantic passive continental margin.