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Australia: The Land Where Time Began |
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Tethys Ocean
At this time the Tethys Ocean straddled the equator, and according to
the author3 there were surface gyres that spun clockwise in
the Northern Hemisphere and anticlockwise in the Southern Hemisphere.
This pattern was the result of the Earth's rotation about its axis, the
Coriolis force. At the equator the northern and southern arms of the
supergyres combined at the equator to flow as a powerful current to the
west, pulling the water at the eastern archipelago end of the Tethys
Ocean which would have created a broad region of upwelling. The
upwelling water would have been cooler and rich in nutrients derived
from the sea floor, as well as recycling those present in the water
column above the seafloor, as occurs off the coast of Namibia and Peru.
The model of ocean circulation was produced by physical oceanographers
who believe the equatorial upwelling in Tethys would have extended about
2/3 of the way across Tethys Ocean. There would also have been 2 other
regions of upwelling in the extreme north and the extreme south of the
ocean.
Life proliferated especially in the upwelling water, and as there would
have been plenty of sunlight for the photosynthesising organisms,
leading to a rich plankton bloom that forms the basis of the food webs
in any ocean, allowing life in the ocean to proliferate greatly in the
Tethys of the Late Permian. Among the tiny consumers that fed on the
even tinier phytoplankton, or scavenging the constant rain of organic
detritus that reached the ocean floor, were seed-shrimp ostracods. There
would also have been
trilobites,
a subphylum of arthropods, on the sea floor, though they were
approaching the end of their presence in the life of the oceans, that
lasted for about 750 My. There were also
conodonts,
minnow-sized eel-like fish, that were very common, Most of the species
present were not like any that are known at present, all being from the
Palaeozoic Era, and the unique reefs that looked different from those of
the present, that were common along the margins of volcanic islands,
that harboured a rich variety of life that included such animals as
giant lamp shells and crinoids, and there would have been many schools
of fish, though the author3 describes them as 'strangely
different from those of the present'. The top marine predators then,
as now, were the sharks.
Not long after the Tethys Ocean had been separated from the
Panthalassa Ocean a
catastrophe occurred that almost wiped life from the face of the earth
at the close of the Permian, the
End Permian Mass Extinction Event.
According to the author3 by the end of the Permian the entire
supercontinent of Pangaea was under tensional stress, and quite suddenly
deep fractures were appearing all over Pangaea. He suggests this may
have been connected to the massive weight and extent of the giant
supercontinent causing
heating
of the mantle beneath it. Parts of Pangaea that had drifted over
existing hotspots would have been especially true, though he suggests
there is also the possibility that the presence of the supercontinent
caused the development of hotspots or superplumes. He also suggests that
further research is required before the situation in Pangaea and the
Earth in general, at this time.
During the Triassic
the fractures developed further until they extended through the
continental crust and became rift valleys. As these valleys widened
large amounts of sediment were deposited in them, becoming the sites of
red beds and evaporites, and as the water from the Tethys Ocean
eventually flooded them the sediment deposited was of marine origin.
They would also have been the sites where lava erupted as the valleys
widened and the future seabed on either side of the fractures extended.
They were also the sites where opening of the Tethys Ocean began, and
later, the beginnings of the North Atlantic Ocean and the South Atlantic
Oceans opened.
Where the Hudson River passes through New Jersey the banks are lined by
the cliffs of the Palisades National Park, that are almost vertical and
are composed of dark grey basaltic rocks, that in places have become
rusty brown, that are the solidified lava that was intruded into the
country rock of these rifts formed in the Triassic. This 'sill' (type of
intrusion) is typically the feeding vent for nearby lava flows. The
author3 says these rocks were the remains of one of the first
attempts at the breakup of Pangaea. Extending for more than 1000 km from
the Carolinas to Nova Scotia, the Newark Rift System is the formation
that the Palisades Sill is a part of. It was one of many rift systems
that didn't complete their development to the point where they separated
a block of continental rock enough for it to break away from the main
landmass of Pangaea.
If the attempted rift had been successful the author3
suggests Manhattan Island and New York may have ended up next to
Casablanca in Morocco. In Morocco, the Ziz Valley is a similar rift that
failed to develop. It has since been exhumed and the High Atlas
Mountains have been uplifted, raising it to its present elevated
position, exposing sediments deposited on its floor. The features
uncovered are salt deposits and sun-baked mud flats, both indicating
that a cut-off arm of the Tethys Ocean had been subjected to
evaporation. This was followed by deposits of fully marine limestone
containing gigantic ammonites, sponge mounds and reefs of algae. This
was evidence that the sea had flooded the area allowing the deposition
of turbidite sediments that are characteristic of deep water
environments. Even so, the Ziz Valley failed to complete the breakaway.
The rift that was successful in forming an ocean was the one that passed
through the Straits of Gibraltar, cutting southwest along the axis of
the Central Atlantic Ocean of the present. When the Tethys Ocean flooded
in it came from the east, past Morocco and Nova Scotia, extending as far
south as Florida and the Bahamas. Laurasia then began slowly drifting
away from Gondwana.
Around this time the region from Yucatan along the Panamanian Isthmus
was being cut by the Panthalassa Ocean that flooded in from the west. A
proto-Gulf of Mexico had begun to form, but spreading stopped before
completion. The salt deposits characteristic of many early rifts was
formed as these early seas evaporated. The salt deposits in the Gulf of
Mexico are very thick, leading the author3 to suggest that
there were probably many cycles of flooding and evaporation. He says
that long after these evaporites had been buried beneath hundreds or
even thousands of metres of sediment from the adjacent land, the great
weight of the sediment caused them to deform. As the salt is of lower
density than the overlying sediment they are buoyant, finger-like
protrusions of salt, salt domes, forced their way up through the
sediment. There are places where the salt has forced it way to the
surface through several kilometres of sediment to flow out onto the sea
floor. This bizarre behaviour of salt under pressure has led directly to
the seafloor of the northern part of the Gulf of Mexico being pockmarked
with a maze of domes and hollows. This feature is common in buried
evaporites around the world, being easily visible on seismic profiles.
After the spreading ceased in the Gulf of Mexico it began to the south
of Yucatan Peninsula leading to the formation of a proto-Caribbean.
Spreading eventually opened a passage around Florida and Cuba that
allowed the waters of the Tethys and Panthalassa to mix forming a single
massive ocean. At first the gap between the 2 supercontinents that
resulted from the breakup of the former single, much larger,
supercontinent was the Tethys Seaway, but the gap continued to expand.
The author3 has suggested that the joining of all the
landmasses to form Pangaea was one of the main causal factors Triassic
as life recovered from its near extinction, one of the main episodes of
evolutionary radiation.
The author3 has listed a number of effects of the breakup of
Pangaea:
A greatly increased space was made available by the collective effect of
these factors for the adaptive radiation to take place on a grand scale
as many new ecological niches became available for the experimentation
and diversity that developed. The base of the food chain in the oceans
and on the land had improved supply of food as levels of primary
production increased. The seas in the Jurassic were extremely fecund,
the author3 stating that 'there was a remarkable growth
and vibrancy of the ocean world while dinosaurs ruled the land'. Portrait of
the Tethys Sea At the opening of the Cainozoic India was
approaching eastern Asia, the Middle East was approaching Russia and
Africa was colliding with Europe. The Tethys Ocean was to become a
narrow seaway between continents in the Era. Following the KT extinction event the remaining
taxa didn’t recover immediately following the great environmental
changes that had taken place at the end of the Cretaceous. The author3
suggests it probably took about 1-5 My for life to recover from this
near-death experience, though the nature and duration of the recovery
varied for different groups. There were great losses among the oceanic
plankton, many fewer species being present after the KT boundary than
before, the species numbers of coccoliths being greatly reduced, and
among the foraminifera only the smaller species survived the mass
extinction event. The
dinoflagellates and diatoms had been less affected, diversifying and
recolonising the oceans so that the basic food stock of the oceans was
replenished. Some animals, such as bivalves, sea snails, crabs, sea
urchins, bryozoans and teleosts that had survived the extinction event
began the next era in prominent positions in the new ecology. Shortly
after new forms evolved to occupy particular niches, such as sand
dollars, a flattened sea urchin the size of a biscuit that are the only
sea urchins able to burrow into the sand of beaches. And corals
displaced the rudists, though the author3 suggests their
diversification appears to have taken longer. Desert
dollars The pyramids of Giza are made of blocks of the
nummulitic limestone of the Giza Plateau, a rock type that had been
deposited in the Tethys Ocean 40-50 Ma. Nummulites are small fossils
that have a disc shape, that are found in various sizes from a few
millimetres to a few centimetres across, with an ornamentation of a
spiral pattern on their outer shell, though many have been smoothed by
exposure to sand and wind to such an extent that this pattern is no
longer apparent on the shells. They are single-celled benthic
foraminifers, among the largest known, that used calcium carbonate to
construct their disc-like, multichambered shells. They were completely
different from the smaller related forms that lived in the plankton and
ate coccoliths. The nummulitic limestone was formed of lithified thick
shell banks and dunes that were in turn formed by the sweeping into
these banks and dunes of the animals that appear to have carpeted the
seafloor in shallow, warm water. The same type of limestone is also present in North
Africa and the Middle East. The northern shoals of Tethys have been
traced through southern Europe and central Asia by their distinctive
signatures, occasionally in the form of white cliffs more than 20 m in
height. On the Black Sea coast, a bit inland, there is a
double line of nummulitic crags that sparkle in bright sunlight. Light
reflecting from tiny calcite spar crystals forming the strong cement
holding the individual animals together is the source of the sparkles.
It was these same crags that were the ‘jaws of the Valley of Death’ that
had doomed the ‘Charge of the Light Brigade’ in the Battle of Balaclava
in 1854. Sex in the
Tethys Marine fish and invertebrates lay enormous numbers
of eggs at a time. Mackerel eggs average about 100,000 per clutch, hake
up to 1,000,000, haddock 3,000,000, and cod up to 9,000,000. Among
marine snails some lay 20,000,000 eggs at a time and oysters up to
500,000,000 eggs. The mortality rate among these organisms is extremely
high at about 99%. The author3 suggests that in the Tethys
Ocean the production rate of its inhabitants would probably have been at
similar levels. In the Badlands of Alberta, Canada, that had been
on the northern margin of the Tethys Ocean around the time of its
greatest expansion, an extremely well preserved female turtle has been
found that had 5 eggs still inside her, near a nest containing 26 eggs.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |