Terrestrial Palaeoecology and Global Change

356 Valentin A. Krassilov. Terrestrial Palaeoecology
a
b
c
d
Fig. 143. The Lesser Kuril Islands, a segment of the island-arc system emerging at about the Cretaceous/
Tertiary boundary: (a) view of Tyatya Volcano of the present-day island arc, (b) view of the Cretaceous/
Palaeocene island-arc basaltic sequence, (c) a giant pillow structure in the transboundary basaltic complex, (d)
fossiliferous shales with foraminifers, marine mollusks and terrestrial plant remains overlain by lavobreccias.
of island-arc volcanics (Kepezhinskas & Defant, 2001) while the Alaskan-type concentric
ultramafic-mafic intrusions contain economic platinoid resources 20 times exceeding
the Alpine ophiolite estimates (Garuti et al., 1997; Kepezhinskas & Defant, 2001).
Thus, in both the PTB and KTB situations, the iridium enrichment might have been
owing to:
– Global regressions inflicting erosion cycles, with an increased terrestrial runoff as a
source of iridium in marine deposits;
– Weathering of ultramafic bodies (in particular the harzburgites, an economic source
of iridium) tectonically exhumed and uplifted during the Maastrichtian (V.7);
– Volcanic activity tapping the mantle sources over the continental margin/island arc
belts, with voluminous ignimbrite eruptions carrying ultramafic xenoliths rich in platinoids
(the Maastrichtian of Sikhote Alin and elsewhere in the circum-Pacific belt :V.6.1);