Early Palaeogene tectonics and sedimentation in the Central North Sea

Abstract

The early Palaeogene deposits of the Central North Sea have been divided by Stewart into ten depositional units, on the basis of seismic stratigraphy. These are interpreted as the products of variations in relative sea level. The units may be traced from the shelf into the basin using wireline log markers correlated within a biostratigraphic framework. These are interpreted as the signature of transgressive maxima when basinal clastic supply was at a minimum. The attitude of coal or lignite beds within the shelfal areas can be used to demonstrate a period of Palaeogene net uplift, followed by tilting and sinking of the shelf-edge and basinal areas during the later depositional episodes. Other than by a mechanism of load-induced differential compaction around buried or partially buried Mesozoic features no significiant rejuvenation of Mesozoic faults can be demonstrated. The area of uplift extended at least as far as the western limit of the Beauly Formation. The products of Stewart’s depositional episodes vary depending on the tectonic activity. During the uplift phase, thick massive basinal fans were deposited and little or no shelfal deposits are preserved. During the tilting/sinking phase thick progradational wedges were deposited, and basinal deposition was largely confined to shales with relatively small local sand systems.

Graphic correlation and sequence stratigraphy in the Palaeogene of NW Europe

“…The L A D of the dinocyst Eatonicysta ursulae (Morgenroth, 1966) marks the top of Sequence 10. Due to the high concentration of red-stained planktonic foraminifera, Stewart interprets this sequence as representing pelagic sedimentation similar to that recorded in the Rosnres Clay of Denmark (HeilmannClausen et al, 1985), conditions brought about by high relative sea levels resulting from the collapse of the Palaeocene Scottish uplift (Milton et al, 1990). The top of Sequence 10 represents a regional unconformity which is 64 'baselapped' (Stewart, 1987) by younger Eocene sediments produced by renewed tectonism (Galloway et al, 1993;Jones & Milton, 1994).…”

“…These deposits may overlie a high gamma shaly section interpreted t o represent periods where sediment is ponded in a coastal system t'o the west. The coal represents the remains of a marsh and a base level zero datum (Milton et a/., 1990).…”

“…Two depositional sequences are recognized in the shallow water section of 8/27a-1, which are below graphic correlation resolution between data terraces above the Upper Forties and Balder sequences. The thick coals at 3100 ft and 2870 ft represent the remains of a transgressive marsh, a zero base level datum, and are found over a large region of the Outer Moray Firth Basin (Milton et al, 1990). These coals are interpreted as deposits directly overlying sequence boundaries.…”

“…Stewart (lY87) followed with a 10-sequence division of the section, incorporating seismic and well data, tied to a biostratigraphic framework. Stewart's (1987) framework was related to tectonics by Milton et a / . (1990), exploring the idea of nested high and low frequency sea-level change Recently, a series of papers were published in a volume edited by Parker (19Y3) that cover a range of time scales and stratigraphic tools.…”

Sequence stratigraphy in British geology

“…In studies using subsurface data, regional correlation of supposed maximum flooding surfaces within shallow marine strata is commonly based largely on correlation of gamma-ray maxima, thought to be generated by relatively argillaceous intervals within sandstones, organic-rich intervals within mudstones, or mineralized surfaces within a condensed section (see for discussion : Milton et al 1990;Partington et al 1993a, b;Creany & Passey 1993;Armentrout et al 1993;Hesselbo 1996). Two papers within this volume address different aspects of this topic.…”