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The continuously cored record from Deep Sea Drilling Project Site 608 has been used as a reference stratigraphy with which to compare the results of all previous dredge and rock core sampling of the King's Trough tectonic complex. Some dredge hauls from the axis of King's Trough and Palmer Ridge contain lithologic and stratigraphic units that are absent at Site 608 either because they predate basement formation at the drill site or because they fall within the range of the major upper Eocene-lower Oligocene hiatus that drilling penetrated. Combining the data sets confirms and refines previous models of formation for the complex that involve rifting of an aseismic ridge or hot-spot trace that began its development at the Mid-Atlantic Ridge in the early Eocene (about 56 Ma). Two major intraplate tectonic events subsequently affected this ridge: (1) in the late Eocene (about 32 Ma), intrusion of trachytic rocks along fault planes, uplift, and explosive volcanicity near sea level; and (2) in the early middle Miocene (about 20 Ma), extensional rifting and subsidence of the basins and deeps of the complex through step-faulting. Palmer Ridge became isolated as a sliver of exposed deep ocean crust during this subsidence. We refrain from discussing new plate kinematic models for the Northeast Atlantic and western Europe, but point out that, whereas the ridge uplift and intraplate volcanism was coeval with the main phase of the Pyrenean orogeny, the extension and rifting of the King's Trough complex was independent of events on the European margin. The complex does not appear to have been a plate boundary at any time. INTRODUCTION King's Trough comprises a 450-km-long chain of roughly parallel basins and flanking ridges, trending WNW-ESE, which is a prominent feature of the North Atlantic seafloor some 700 km northeast of the Azores (Fig. 1). Basins within the complex are anomalously deep when compared with the regional depth and age of ocean crust in the surrounding area, and the flanking ridges are anomalously shallow (Searle and Whitmarsh, 1978). The question of the origin of this unusual bathymetry east of the Mid-Atlantic Ridge (MAR) has attracted geophysical and geological study for over two decades, since the main basin at 44°N, 22°30' W was first described in Laughton (1965). The possibility that this intraplate complex, might, in fact, represent a former plate boundary means that it has been incorporated into various models of the evolution of the North Atlantic (LePichon and Sibuet, 1971; Williams and McKenzie, 1971; Vogt and Avery, 1974; Kristofersson, 1978; Grimaud et al., 1982 and 1983). Kidd et al. (1982) used a GLORIA long-range sidescan sonar survey for regional geological control of a transponder-navigated dredging and coring program. Their results were used to test models for the origin of King's Ruddiman, W. R, Kidd, R. B., Thomas, E., et al., Init. Repts. DSDP, 94: Washington (U.S. Govt. Printing Office). 2 Addresses: (Kidd, present address) Dept. of Geology, University College of Swansea, Singleton Park, Swansea, Glamorgan SA2 8PP Wales, United Kingdom; (Ramsay) Dept. of Geology, University College of Swansea, Singleton Park, Swansea, Glamorgan SA2 8PP Wales, United Kingdom. Trough, based largely upon geophysical data, that had been proposed by Searle and Whitmarsh (1978). The consensus of these investigations was that the tectonic complex developed by a combination of initial spreading from an elevated part of the mid-ocean ridge ("hot spot") and subsequent rifting, extension, and subsidence of the WNW-ESE trending ridge that had formed. There was no continuous stratigraphic record in the area that could be brought together with the dredge and rock core data. No matter how precisely located this sampling program had been, there were major stratigraphic uncertainties to hamper the interpretation and construction of tectonic models (Kidd et al., 1982). In the DSDP Leg 94 paleoenvironmental transect, there was a requirement for a site located astride the southernmost penetration of polar water during the glacial periods. This requirement brought with it the opportunity to drill to basement on the south flank of the King's Trough complex (Fig. 2). In this chapter, we bring together the results of DSDP Site 608 with the previous dredge and rock core data, using the same biostratigraphic time scales of Berggren, Kent, and Flynn (1985a) and Berggren, Kent, and Van Couvering (1985b). We will look for the temporal and spatial amplification of the regional geology that the earlier sampling can now provide. We will consider some of the postdrilling results of other studies in this volume that deal with Site 608 as well as some findings of concentrated geophysical and geologic studies on the south flank of the complex that derive from a program of feasibility studies for high-level radioactive waste disposal (Kidd et al., 1983).

The Geology and Formation of the King's Trough Complex in the Light of Deep Sea Drilling Project Site 608 Drilling