The Goban Spur of the Northeast-Atlantic Margin during Late Cretaceous Times

Abstract

The Late Cretaceous depositional history of the continental margin across the Goban Spur can be divided into two episodes, sediment records of which are separated by an upper Campanian unconformity traceable from the foot to the top of the margin. Below the unconformity, there was no deposition at the shallowest site (548), and deposition of relatively short sequences of foraminiferal and nannofossil-bearing white chalks, with indications of hiatuses or condensation, took place at the two sites of intermediate depth (549 and 551). The varied clay-mineral associations show a marked terrigenous influx superimposed on the mostly biogenic calcareous sedimentation. A 1-m-thick bed of carbonaceous shale and radiolarian chert interbedded with low-TOC white chalks was drilled at the boundary between the Cenomanian and the Turonian of Sites 549 and 551. Interpretations of this lithology are discussed. Above the unconformity, layers of nearly pure chalks (upper Campanian to Maestrichtian), with frequent signs of redeposition, blanket the whole margin, except for the steeper slopes like the Pendragon Escarpment. The Albian ocean crust drilled at Site 550 lay farther from the contemporary shore line than the other drill sites. In the Cenomanian the still narrow oceanic trough received nearly pure calcareous mudstones under alternating conditions of poorly and normally oxygenated bottom water. A sediment gap at Site 550 spans the upper Cenomanian and the whole of the Turonian. From the lower Senonian to the lower Paleocene, chalky turbidites are interbedded within hemipelagic mudstones. Deposition probably took place beneath the CCD in the early Senonian. The mineralogical composition of the hemipelagic part of these turbidites shows a significantly greater terrigenous influence than coeval deposits at shallower sites.

Biostratigraphical correlation of the Campanian–Maastrichtian boundary: Lägerdorf–Hemmoor (northwestern Germany), DSDP Sites 548A, 549 and 551 (eastern North Atlantic) with palaeobiogeographical and palaeoceanographical implications

“…The isotherms were constructed assuming a boundary horizon between the warmer, near-surface water an colder, deep water at 200-500 m depth (Schonfeld, Sirocko & J0rgensen, 1991). The palaeobathyrnetry after Graciansky & Bourbon (1985) was corrected after Masson, Montadert & Scrutton, (1985). The palaeotemperatures are expressed in degrees Celsius.…”

“…Inoceramus prisms from the Goban Spur DSDP Sites are well preserved but slightly corroded. Due to the palaeoenvironmental setting it remains, however, possible that some of them were redeposited and derive from shallower areas (Graciansky & Bourbon, 1985).…”

“…The Tethyan oceanic realm includes the shelf seas, continental slopes and abyssal plains of the young North Atlantic, the Bay of Biscay and Tethys (Butt, 1981;Cepek et al 1985;Graciansky & Bourbon, 1985). Typical sediments are pelagic chalks and limestones, marls and claystones, turbidites and related deposits.…”

“…From the viewpoint of the planktonic foraminiferal zonation, this boundary has to be drawn at the level of extinction of Globotruncanita calcarata (Cushman) . Pachydiscus neubergicus, however, first occurs in the Boreal realm in the Lower Lower Maastrichtian (Schulz et al 1984;Kennedy & Summesberger, 1986, while Belemnella lanceo- Based on Wonders (1980), Ziegler (1982), Cepek et al (1985), Graciansky & Bourbon (1985), Tyson & Funnell (1987).…”

“…These sections provide a sufficient palaeodepth and oceanic characteristics to have allowed access of Tethyan planktonic foraminifers to this area (Graciansky & Bourbon, 1985;Graciansky & Poag, 1985). The ranges of planktonic foraminifers are correlated in these borings with those of benthic foraminifers and calcareous nannoplankton.…”