|
Department of Geology and Geophysics, The University of Adelaide, SA 5005, Australia
Sonic velocities from the Danian Chalk, the Upper Cretaceous Chalk, the Lower Cretaceous Greensand/Gault Clay, and the Triassic Mercia Mudstone were used to quantify apparent exhumation (i.e. amount of missing section) in the Celtic Sea/Southwestern Approaches (southern Irish, southwestern United Kingdom, and northwestern French continental shelves). Analysis of all four of these stratigraphic units yields similar results. Since it is unlikely that sedimentological and/or diagenetic processes are responsible for similar amounts of overcompaction in the chalks, shaly sandstones and shales analysed, burial at depth greater than that currently observed is the most likely cause of overcompaction (anomalously high velocities). The use of lithologies other than shales in thus validated. The consistency of results from units of Triassic to Danian age suggests that Tertiary exhumation was of sufficiently great magnitude to mask any earlier Mesozoic periods of exhumation, and that the maximum Mesozoic-Cenozoic burial depth in the Celtic Sea/Southwestern Approaches was attained prior to Tertiary exhumation.
The recognized in version axes of the Brittany Basin, Southwest Channel Basin and North Celtic Sea Basin are highs in apparent exhumation. However, highs in apparent exhumation of approximately 1 km also occur in the uninverted St. Mary’s and Plymouth Bay Basins, and on the margins of the Armorican and Cornubian platforms and the Pembroke Ridge (Fig. 1). Tertiary exhumation was regional and not restricted to inversion axes, and thus had a thick-skinned origin. Heterogeneous lithospheric compression is the geodynamic model preferred to account for the regional exhumation of the Celtic Sea/Southwestern Approaches. The identification of regional exhumation
...
This 250-word extract was created in the absence of an abstract.
