[Taxacom] Annual NZ Biogeographers' Exam. Q 1

John Grehan calabar.john at gmail.com
Thu Jan 5 12:34:20 CST 2017


Annual NZ Biogeographers’ Exam


Question 1. What is the biogeographic significance of the inland Castle
Hill basin for the origin of its coast plants?


“In Castle Hill basin, Late Cretaceous coal measures including sandstone,
mudstone, and muddy coal lie with angular unconformity on Torlesse terrane
basement. The coal measures are covered by glauconitic sandstone
(greensand) deposited during a Late Cretaceous-Eocene marine transgression
(Gage, 1970). The coal measures and the greensand are diachronous and mark
a slow, westward migration of the coastline over a land surface of low
relief. Eocene uplift interrupted deposition in the east and south, but
elsewhere deposition proceeded until the mid-Oligocene, when limestone was
deposited and submarine volcanoes were active. Sedimentation then ceased in
the center of the area, while there was renewed elevation and tilting in
the soot and east. Marine sediments of the Enys Formation accumulated early
in the Miocene, but the sea finally withdrew later in the Miocene and Early
Pliocene.


Cockayne (1899, 1906) cited several common coastal plants found inland at
the lower Waimakariri Gorge, and he attributed their presence there to the
“former extension of the coast-line inland.” Cockayne (1906) also discussed
other localities, such as Castle Hill and Weka Pass, where coastal plants
occur on inland limestone, and he concluded: “If such a distribution is
correlated with the marine origin of the rocks, then it is evident that
species can exist under special conditions for enormous periods of time.”
Cockayne (1906) recognized that the observed pattern was not caused by the
ecological or physiological effects of the limestone (some of the species
are not restricted to limestone), but by its history and tectonic context.
The same process of inland stranding could also mean that the shore biota
of the Late Cretaceous-Eocene inland seas, along with members of the forest
represented by the coal, has direct descendants in the present landscape.”


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