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Australia: The Land Where Time Began |
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Biogeography – Panbiogeography, Tectonics and
Evolution Clade ages are the basis of modern analyses, which
are calibrated by using the known fossil record, though in most groups
this is misleading and identifications in the fossil record, though
extant groups, that were morphology-based, were often misconstrued.
Alternatively, the best of the molecular data - the clades and their
distribution - are synthesised with revolutionary developments in hard
rock geology – the radiometric dates for tectonic events, in a
panbiogeographic approach. Calibration of a range of nodes with tectonic
events is involved in this synthesis, though this process can be
complicated by the tectonic events often being episodic or of long
duration, such as some of the main events in Australasia, including the
continental crust rifting in the formation of the Tasman and Coral Sea
basins. In an event that lasted from 84 Ma to 55 Ma the rifting zone
propagated northwards, with the result that the communities of biota
were gradually separated. The actual breakup was the final step in a
long extension process, and it is suggested by many distributions that
much of the differentiation associated with rifting resulted from the
pre-breakup deformation and magmatism. Also important in biogeography
are failed rifts such as the Moonlight Tectonic Zone in New Zealand, in
southern Africa the Lebombo Monocline, and in central Africa, the
Cretaceous rift system. Crustal shortening and thickening have led to other
events in the region of the Tasman Sea and Coral Sea, and some of these
processes are of long duration. A collision along the northern margin of
the Australian plate in New Guinea in the Palaeocene, 58 Ma, the
collision in the Eocene, 44-34 Ma, that is preserved in New Caledonia,
and in the Oligocene, 26-25 Ma, in the North Island of New Zealand are
suggested by Heads1 to all possibly be part of a single
collisional event that migrated to the south along the plate boundary
(Glen & Meffre, 2009). Here, subduction zone rollback towards the
Pacific has resulted from collision between forearc crust and
continental fragments; new basins being created and arc-continent
collision. As the uppermost geological stratum life has proven
to be stickier than believed, with populations surviving episodes of
marine flooding, volcanism, glaciation, desertification, uplift,
subsistence, as well as other events. Remnants of weedy taxa have also
persisted in gullies, cracks in rocks, on nunataks, underground and many
other habitats that are regarded as marginal. Even local tectonic
changes, such as faulting, are capable of affecting living populations
of groups in a non-weedy phase of their evolution leading to
differentiation, at the other extreme. In New Zealand, New Caledonia,
New Guinea and the Philippines, strike-slip movement, which developed
under transpressional regimes, and has also led to biogeographic
differentiation and disjunction. Heads, Michael, 2014,
Biogeography of Australasia: A
Molecular Analysis, Cambridge University Press
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |