Terrestrial Palaeoecology and Global Change

154 Valentin A. Krassilov. Terrestrial Palaeoecology
of the Palaeocene to Eocene graywacke–olistostrome complex and the overlying tuffs
of Barbados (S.N. Davies, 1971).
The (long ignored) structural similarity of the Antilles and the Canaries – Cape Verde
belt, as well as their asymmetry, is of the same nature as those of the western and
eastern Pacific structures (above).
The Scotia Block, like the Caribbean, is surrounded by island arcs bridging the thrust
complexes of Teirra del Fuego (Navarino Island) to those of Antarctic Peninsula (V.6.3)
and projecting to the South Atlantic as the eastern counterpart of the African Agulhas
arc. They are dissected by a series of transcurrent faults, including the better known
Magallanes, Bransfield and South Sandwich fault zones (Fig. 68). A combination of the
left-lateral (the northern fault zones) and right-lateral (the southern periphery) transcurrent
faulting might generate the pull-apart basins of the modern Scotia Sea. However
there is little evidence of its origin by a back-arc spreading as suggested by Alvarez
(1982) and Barker et al. (2001).
One can argue that island arcs, if at all present in the Atlantic, are of a much lesser
extent than in the Pacific. However, in addition to the emergent arcs, there are submerged
marginal structures that might have been active arcs in the past. Incidentally, the
Ivory Coast – Ghana marginal ridge marks a shear zone of thrust Cretaceous sediments
(Huguen et al., 2001; the alleged relation of marginal shear to continental separation is
not supported by geological evidence). On seismic evidence, the marginal evaporitic
basins of Sierra Leone, Gabon and Angola are fringed by buried arcuate ridges, e.g., the
Longa – Cabo Ledo Ridge fringing the Cuanza Basin (Sheridan et al., 1969; Franks &
Nairn, 1973; Cooper, 1978). They form a nearly continuous series traceable to the metamorphic
Agulhas Arc over the southern extremity of Africa.
Their western counterpart is a series of submerged morphologically and/or magnetically
distinct positive structures extending over the shelf margin from Newfoundland to
Bahamas (Uchupi & Milliman, 1971). Some of them, such as the J-anomaly Ridge on
the northern flank, are topped by the partly subaerial mid-Cretaceous basalts (Tucholke
& Ludwig, 1982). This ridge system has been once interpreted as a buried island-arc belt
(Watkins & Geddes, 1965), the most plausible of several possible explanations. In the
South Atlantic, a similar system of buried arcs borders the shelf basins of Argentina
between Colorado to San Jorge (Zambrano & Urien, 1970).
The Arctic Ocean consists of the larger Amerasian and Eurasian basins subdivided
by a series of parallel ridge/trough structures, with a spreading zone over the Gakkel
Ridge belonging to the same fault system as the fossil Alpha-Mendeleev and Lomonosov
ridges. The periphery of the Arctic Ocean bears evidence of tectonic activity in the
mid-Palaeozoic and the Cretaceous – Palaeogene, in reference to which we can speak
of the mobile peri-Arctic belt involving both the Caledonian and Laramid structures. The
Caledonian thrust belts of Norway, Novaya Zemlya, Svalbard, Greenland, submerged
Lomonosov Rise (with the post-orogenic Devonian molassoids and Cretaceous continental
deposits: Herron et al., 1974; Grantz et al., 2001).), Brooks Range and the Parry