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Graptolites were a component of the Ordovician macroplankton.
They lived at various depths in the ocean waters and are found
in a wide range of sedimentary facies. Graptolite species
are widespread globally, and most are of relatively short
stratigraphic duration. These attributes combine to make them
extremely valuable fossils for zoning and correlating strata.
Together with conodonts, they are the primary fossil group
for global correlation of Ordovician rock sequences.
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 Slab
of black shale from the Aorangi Mine Formation, near West
Haven Inlet.
The exposed bedding plane shows at least
seven species of graptolites, representing a community that
lived in deep waters (greater than 150m) of the Ordovician
ocean (470 million years ago). R.A. Cooper photo.
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Isograptus victoriae maximodivergens,
a prominent species of graptolite in the Castlemainian and Yapeenian
Stages of Northwest Nelson.
It is globally distributed and is important
for correlation and dating Ordovician rocks.
Thirty zones, two of which are divided into subzones, are recognized
in the Ordovician Systems of Australia and New Zealand. The
zones are defined in terms of the stratigraphic ranges of selected
species; zone boundaries are defined by the successive horizons
of appearance of the defining species. The Australasian graptolite
zones have proved widely applicable around the world, either
as they are, or with slight modification. They are representative
of the Ordovician low latitude belt, known as the Pacific Province.
They comprise the most detailed Ordovician graptolite zonal
scheme known. The zones range widely in duration, from 8-10
m.y. down to 0.5 m.y. or less, and average 1.47 m.y. each in
duration.
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 Isograptus
victoriae maximus, Northwest Nelson.
The bedding plane shows a monospecific
'death assemblage' - caused by the sudden death of a community
living in the ocean deep waters.
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