Terrestrial Palaeoecology and Global Change

180 Valentin A. Krassilov. Terrestrial Palaeoecology
Fig. 78. An interpretation of sea-level
fluctuations resulting from divergence/
convergence of mean hypsometric levels
for isostatically compensated oceanic
and continental domains under
centrifugal rotation forcing. Present:
shore-lines close to the boundary of
isostatically compensated continental
and oceanic blocks. Acceleration – divergence:
shore-lines retreat with a
rise of continents and subsidence of
oceanic depressions. Deceleration –
convergence: the opposite tendency
resulting in low continents and shallow
oceanic basins.
and elsewhere). On the other hand, global transgressions would have been synchronized
with intracontinental magamtism (traps), which is obviously the case at both the Permian/Triassic
and Cretaceous/Palaeogene boundaries.
Thus, through application of rotation geodynamics to sea-level fluctuations, we arrive
at a causal scheme providing a long-sought explanation of the antithetic pulses of the
cratonic sea-floor and continental volcanism correlating with the talassocratic and geocratic
tendencies respectively, The intermediate island-arc volcanism increases with
marginal shear over the transitional stages.
VI.2. Hypsometric curve
The above model of global sea-level changes in respect to the relative hypsometric
levels of isostatically compensated oceanic and continental lithosphere can be tested by
comparing hypsometric curves for the present geocratic versus mid-Cretaceous thalassocratic
epoch. Hypsometric curve shows how much of the earth’s surface (percentages)
is maintained at a particular hypsometric level. Hypsometric steps correspond to the
larger lithospheric domains of different density isostatically compensated in the earth’s
rotation field. The curve thus reflects isostatic situation at a given velocity of rotation.