Terrestrial Palaeoecology and Global Change

Chapter 5. Tectonic factors of global changes
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lomon et al., 1975; Hamilton, 1988). With continental blocks amassed to the north of the
equator, the decoupling of hemispheres by a giant shear belt is enhanced by the difference
in their crust densities.
V.5.2 Cretaceous O/D faulting and magmatic activity
Except the equatorial shear faults of the Amazon system in Brazil – Cameroon
Line in Africa, a few presently or recently active fault zones were magmatic in the
Cretaceous. Over the African rift system, the Cenozoic and Cretaceous volcanics
only locally overlap in the northern segments. On the other hand, many presently
quiescent continental and sea floor lineaments are fossil magmatic ridges of Cretaceous
age. They belong to both O- and D-systems, of non-random distribution over
the globe.
The O-faults over high northern latitudes, such as the North Sea Rift System, the Ob’
Bay – Pur Rift of Siberia, the Lomonosov Ridge – Verkhoyansk Range System of the
Arctics, etc. (Fig. 59) had controlled the Triassic rifting and trap magmatism of cratonic
areas followed by a shallow subsidence of epirift basins in the Cretaceous.
Active O-faulting between 30°N and the equator involved the intracontinental Gulf of
Aqaba-Jordan rift system and a series of regularly spaced meridional faults traversing
the oceanic crust between Madagascar and Andaman Islands, with such prominent linear
features as the Chagos – Laccadive Ridge, Indrani, Indra, 86° Ridge, East Indian
(90°) Ridge, Investigator, etc. (Fig. 60). Their inland extensions (the Kambay Graben)
are marked by the Cretaceous traps at the intersection with the diagonal Narmada – Son
rift zone of Deccan Plateau.
Fossilized O-faults are recognizable in the Pacific as well. Here they are represented
by the submerged meridional Shirshov Ridge and its parallel Emperor Ridge that extends
from Aleutian Islands to the Hawaii and is traceable further south to intersection with
the latitudinal Marcus-Neccer Ridge. Cretaceous volcanics are found on all these ridges
(Jackson & Schlanger, 1976; Saito & Osima, 1977).
At the same time, the D-faults were more conspicuously active over the mid-latitudes.
The Mongolian (Kerulen) basaltic province and its outliers in Transbaikalia and
Heilongjiang are controlled by the NW – SE Mongolo-Okhotskian system, intermittently
active since the Precambrian (Buchan et al., 2001). In the Atlantic, the Southeastern
Newfoundland Ridge, New England Seamounts, Walvis, Rio Grande, all magmatic in the
Cretaceous, are segments of the D-system. An extensive diagonal rift zone is traceable
over the Red Sea – Vardar Rift – Rhine Graben (Zytko, 1982). It is intersected by the
submerged Owen Ridge extended inland as the Naramada – Son fault system. To the
south, a no less extensive oceanic D-system comprises the Kerguelen – Crozet – Broken
Ridge – Diamantina fault zones marked by the Cretaceous volcanic ridges (Guilfy,
1973; Silantyev et al., 1983).