Lithologic repetition and deformation of the cored sediments indicate that DSDP Hole 415A penetrated a 450-meter Upper Cretaceous allochthonous unit with several imbricate repetitions of a Cenomanian shale-and-carbonate sequence above a décollement of Albian and Cenomanian shale. This unit is expressed on multichannel seismic profiles as an interval of chaotic interval signal. Its upper surface is deformed by folds which predate the overlying Tertiary turbidites. Some of these folds maintain a harmonic profile in the sequence beneath the allochthonous unit, whereas others are restricted to the top of the unit. Although some folds are asymmetric, we cannot recognize a consistent vergence. Profiles beneath the continental slope east of Site 415 indicate that the drilled sequence is only the distal portion of a much more widespread feature. The equivalent sequence beneath the lower slope is thcker and is cut by several major, landward-dipping thrust faults across which there is a minimum of 20 km of overthrusting. The thrusts have a north-south strike, as do the disharmonic folds within each individual thrust sheet. Both folds and faults are refolded by a series of east-west-trending folds parallel to the Atlas tectonic trend. The displaced unit is not present beneath the upper slope, where it passes laterally into a prominent angular unconformity. This zone represents the source area for the overthrust masses. Onshore geological evidence indicates the emergence of the western High Atlas Mountains during Late Cretaceous times, and the allochthon is interpreted as an associated belt of gravity-driven overthrusts refolded by the last phases of this tectonism. Its scale is comparable with that of some overthrust zones in orogenic chains, and its existence on a passive margin may be important to the interpretation of exposed nappe complexes. Uplift of the western Atlas, gravity sliding, folding of the allochthon, and the onset of Canary Islands volcanism can be explained by sinistral strike-slip faulting along the South Atlas fault during Late Cretaceous time.
Between 62° and 68°N on the Norwegian continental margin, the hypothesis of a Cretaceous or Permian ocean extending northwards from the Rockall Trough can be tested with data from commercial reflection seismic profiles. Two major Mesozoic basin systems occur. The Helgeland Basin is a late Triassic and early Jurassic depocentre with a thin Upper Jurassic and Cretaceous cover except in two late Cretaceous sub-basins. The Møre/lnner Vøring Basin system is a middle to late Cretaceous depocentre in which the pre-Cretaceous section is deeply buried and rarely seen on seismic profiles. The two basin systems are separated by a complex zone of faulted 'marginal highs' active in Jurassic times and reactivated during Cretaceous times. Pre-Cenomanian lavas or sills are interpreted within the Møre Basin and a pre-Cretaceous block-faulted sequence can be identified across the inner Vøring Basin except in a narrow axial zone. These features suggest the presence of an extremely narrow zone of oceanic crust of Cretaceous age. Fault patterns confirm a major tectonic episode of mid-Cretaceous age. The geology off mid-Norway supports a mid-Cretaceous age for sea-floor spreading in the Rockall Trough but suggests that the generated oceanic crust narrowed northwards and that plate motion was partially accommodated by dextral transcurrent faulting. Reconstruction of Jurassic tectonic trends in NW Europe must allow for subsequent Cretaceous distortion.
The Othris Mountains of eastern Greece contain a calcareous continental margin/ocean basin sequence exposed in a stack of Cretaceous thrust sheets. Upper Triassic to Lower Cretaceous shelf, submarine fan and basinal successions overlie shallow marine units of Lower Triassic and Permian age. In off‐shelf sequences the older sediments are separated from the younger by a horizon of alkaline ‘early‐rifting’ basalts. Ophiolites overthrust the marginal sequence. Pre‐rifting sediments are represented by a varied suite of limestones and clastics resting on metamorphic basement and include distinctive, green lithic arenites. In the thrust sheet immediately over the para‐autochthonous shelf sequence, pre‐rifting sediments are separated from the rift basalts by an intermittent horizon of calcareous sandstones and conglomerates reworked from uplifted basement and older sediments. Textural and petrographic immaturity suggests that these are probably deposits derived from fault scarps, produced in an early phase of rifting. Above the basalts in the same sheet is a suite of calciclastic sediment‐gravity‐flow deposits, apparently sedimented on a submarine fan. Progressive downslope modification of calcirudites suggests deposition from evolving, high concentration flows. Massive calcarenite facies (? grain flows) are unusually abundant; a possible reflection of a shallow palaeo‐shelf break since provenance and palaeocurrent evidence proves the clastic carbonates to have been derived from a calcareous shelf. In addition to limestone lithoclasts the calcirudites, but not the massive calcarenites, contain fragments of pre‐rifting lithologies including the distinctive arenites. Since the shelf sequence in Othris is totally nondetrital these clasts imply derivation of coarse sediment from an off‐shelf position; probably the walls of a submarine canyon. This may have occurred either by direct erosion of wall rock, or by reworking of material from an older clastic sequence. In the latter case the inferred fault‐scarp deposits are a likely source.
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