Linda and Roger's Bunhybee Grasslands
This is a page within Roger and Linda's
Bunhybee Grasslands Web-Site.
Bunhybee Grasslands is a 49ha/120-acre conservation property 35km south of Braidwood,
in sthn N.S.W.
This is a first-cut attempt to build some information about the geology underlying the property.
The purpose is not abstract science, but part of a process of understanding about the soil-types.
The content was developed from an hour or two's web-surfing, and at this stage nothing more.
- An area map should be available from the
- This report from the mid-1950s says that:
- "quartz felsite [a very fine grained volcanic
rock that may or may not contain larger crystals] forms the valleys of
the Jerrabattgulla Creek" (p.6)
- "The 'Upper Shoalhaven Granite' is a biotite [a
common phyllosilicate mineral within the mica group] granite [a
common type of felsic intrusive igneous rock that is granular and phaneritic
in texture] and has a mapped length of sixty-four miles.
"Its most northerly
two miles east of Lake Bathurst Railway Station
and it extends to the southern edge of the Canberra 4-mile sheet; its
average width is eight miles. It is obscured by the Devonian
volcanics north of Krawaree and by the Devonian lavas and Tertiary
sediments north-west of Lambert.
"A notable pendant or screen of Silurian(?)
strata extends of average width two miles ... south from Mount
Fairy for a distance of twenty-four miles.
"The granite is cut
by the Jerrobattgulla Fault which,is fifty miles long. It is
strongly sheared in parts especially alongside contacts with sediments,
and is probably of Bowning age" (p.10)
- "Granite to the north-west of the [Jerrabattgulla Creek] fault
exposed in a quarry is sheared and mineralised"
- This report from 1980 says that:
- "At Jerrabattgulla Creek, basalts dated at 19.1±0.4
m.y. were extruded along a 5 km length of the active Shoalhaven Faultline;
about, 30m of vertical movement has taken place along the fault since
the basalts were deposited". Presumed translation. There was a volcano
close by c.20m years ago
- A map from a
study of the Shoalhaven catchment identifies the area as "Goulburn
- This map shows that the nearest entries
on the NSW soil
and land information database
are 1500m SW (Gilston?) and 500m
N (Di Izzard's property) – with:
- 6 inches of "fine sandy clay loam" (!? –
maybe well down the slope towards the creek?) and
- "highly weathered
rock rhyolite layer" [an igneous, volcanic rock,
of felsic (silica-rich) composition] from 1m deep downwards"
- Within the Land History page, we have that
an Appraisement of 5 C.P.'s on the eastern side of the road [Bunhybee and
its neighbour Parlour?] was undertaken on
1907 – p.1, p.2, p.3. ...
The physical characteristics
of the 5 Lots (as a whole) was "Reasonably level land, with a gradual
Western Slope". The character of the soil and sub-soil was Poor
clayey soil. Stoney to Rockey. Clay"
report says that, in the area to the S and/or E, "The
granodiorite [a phaneritic texture intrusive igneous rock
similar to granite, but containing more plagioclase feldspar than orthoclase
feldspar] is probably Early Devonian [400m years ago] and has been deformed
in the Carboniferous"
- We've observed on
the property (with no geological competency whatsoever):
- white, limestone-looking
(Clay is a pretty generic term: "a fine-grained natural rock or soil
material that combines one or more clay minerals with traces of metal
oxides and organic matter")
- multiple small granite-looking outcrops
- a small number of conglomerate rocks (fallen/tossed
from Bunhybee Peak?)
- A Geological Study about 10km South of Bunhybee, from Uni
of Adelaide, and another
output from that study
This is a page within the Bunhybee Grasslands Web-Site, home-page
here, and site-map here
Contact: Linda or Roger
Created: 17 October 2015; Last Amended: 18