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Miria Formation
In Australia the Miria Formation is among the
stratigraphically youngest known Cretaceous rocks to contain fossils. It
is comprised of calcarenite (uncemented chalk) sediments deposited on
the calm continental shelf that formed when the marine incursion into
the Carnarvon Basin occurred in the Late Cretaceous. In the Miria
Formation macrofossils are common, though many are incomplete. The
authors1 suggest they may
have been broken up by storm activity when deposition was occurring.
Outcrops of the Miria Formation can be recognised by phosphatic
steinkerns, that are
present in sediments that have been
weathered, though the Miria
Formation is typically not well exposed. In the Giralia Ranges to the
south of Exmouth Gulf outcrops of the Miria Formation are most
conspicuous, often being rich in fossils. An extremely diverse range of
pelagic cephalopods and benthic molluscs are indicated by faunal
records. Other fossils that have been found in the Miria Formation
deposits are mosasaurs and
sharks, as well as isolated bones of
dinosaurs and pterosaurs. An age of the Late Masstrichtian is suggested
by the Ammonites and microfossils. Warm temperatures are indicated by
plankton assemblages.
Sources & Further
reading
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Kear, B.P. &
Hamilton-Bruce, R.J., 2011, Dinosaurs in Australia, Mesozoic life
from the southern continent, CSIRO Publishing.
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Steinkerns
-the fossilised outline of a hollow organic structure such as a skull or
the shell of a mollusc that is formed by the compaction of mud or
sediment inside the structure after which the actual structure is
dissolved or disintegrates.
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