08142 geologic 3
TRANSCRIPT
8/6/2019 08142 Geologic 3
http://slidepdf.com/reader/full/08142-geologic-3 1/2
geo LOGICFoundations in limestone
The rst curio o karst environments is not their
variety o magnicent and unusual eatures such
as stone outcrops, arches, gorges and caves, but
the presence o carbonate rock such as limestone,
dolomite and marble on the Earth’s surace. This
type o rock did not exist early in the Earth’s history
and rst appeared some 1000 million years ago,
when photosynthesis lowered the acidity o oceans
allowing calcium carbonate to orm.
In New South Wales (NSW) the majority o karst
environments are ormed rom limestone, a
sedimentary rock consisting o the cemented
remains o marine organisms such as corals,
brachiopods, stromatoporoids and crinoids, and/or
ne grained calcite (lime mud), which are all made
rom calcium carbonate (CaCO3).
This sedimentary material was deposited in the
ocean millions o years ago where it was converted
to limestone and buried under layers o rock. The
liting and aulting o the Earth’s surace exposed the
limestone to the atmosphere, where physical and
chemical weathering resulted in the developmento caves and other karst landorms.
It depends on water
Limestone caves orm in two main ways: rom
surace streams nding their way through cracks in
the ground and orming underground rivers, and
by groundwater rising up through cracks in rocks
under the infuence o heat and pressure, dissolving
out mazes and rounded chambers. Caves in NSW
have ormed rom both o these processes.
3
W at er , and the ma terials i t d issol ves an
d carries,
d r i v e t he developmen t o f k ars t en vironm
ents.
K arst forming and de velopmen t processes
Speleothem formation. ©S.Babka
Karst formation and development process. ©M.Inwood
8/6/2019 08142 Geologic 3
http://slidepdf.com/reader/full/08142-geologic-3 2/2
geo LOGIC Karst forming and development processes
Rainwater is responsible or the natural sculpturing
o limestone and many other eatures o caves such
as stalactites. This intricate process begins whenrain alls through the atmosphere and in doing
so, picks up small amounts o carbon dioxide,
which dissolve in the water droplets orming a
weak solution o carbonic acid. As the rain water
continues its journey it makes contact with the
ground, where it travels through the soil prole
picking up urther amounts o carbon dioxide and
other organic acids, increasing its level o acidity and
thereore the ability to dissolve carbonate rock. This
acidic water dissolves outcropping stone resulting
in rich patterns and displays, beore it nds its way
underground through weaknesses in the limestone.
On making its way below the surace, the water
percolates through the various cracks and ssures,
expanding them and creating holes, which over
time, evolve into the great subterranean voids that
are the trademark o karst environments.
Water is also responsible or the array o minerals
and other eatures ound in caves. Chemically
saturated water degasses as it drips, pools, fows and
percolates in the below ground karst environment,
releasing calcium carbonate (that it dissolved during
its travels), which over time, orms into towering
stalagmites, hanging stalactites, straws, columnsand cave pearls to name a ew. These ormations (or
speleothems) may also be ormed rom sediments
comprised o dust, either washed or blown into
caves, guano (bat dung) and various minerals.
Water is the engine o the karst system. It drives
the various chemical and physical processes
that create the karst landscape and provides the
medium or complex biological processes and
interactions to occur.
Published by: Department o Environment and Climate Change NSW59–61 Goulburn Street, PO Box A290, Sydney South 1232
Phone: (02) 9995 5000 (switchboard)Phone: 131 555 (environment inormation and publications requests)Phone: 1300 361 967 (national parks inormation and publications requests)Fax: (02) 9995 5999 TTY: (02) 9211 4723Email: [email protected]: www.environment.nsw.gov.au
This material may be reproduced in whole or in part, provided the meaning is unchanged and the source is acknowledged. ISBN 978 1 74122 777 2 DECC 2008/142 May 2008 Printed on environmentally sustainable paper
Roof of Orient Cave, Jenolan. ©J.Lim
Pillar – the joining of stalagmite and stalactite. ©S.Babka
Cathedral structure. ©S.Babka