Fossil Fence Post EarthCache
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At GZ there is a fossil of what appears to be a piece of wood embedded into rock.
PLEASE NOTE: Although the cache is rated 1/1.5, the cache is located on a rock platform which is subject to tidal and storm inundation. Do not attempt the cache under adverse conditions. Also please note the unstable nature of the nearby cliffs.
The geology of the Illawarra may be described by grouping and subgroupings which in order, top to bottom, start at Hawkesbury Sandstone, Narrabeen Group of shales and sandstone, Illawarra Coal Measures including Bong Bong Basalt and Minnamurra Latite, and the Shoalhaven Group including Cambewarra Latite, Budgong Sandstone, Bumbo Latite, (and again) Budgong Sandstone. These rocks are reported as being of the triassic and permian ages with the lower rocks of the earlier permian era. [Reference 1]
"Coal measures" are the number of coal seams known under names such as "Bulli Seam", "Wongawilli Seam" and others at varying depths. Latite is a tough volcanic rock "akin to basalt". [Reference 2] The coal seams and the latites and basalts occur in various layers.
The latites in the above listing are a part of the Gerringong Volcanics. The lower levels outcrop at GZ.
Fossils are found in this area with the excellent examples of particularly marine fossils to be found at GC21VQR "Fossilised Gerroa (Earthcache)" some 3.6 km approximately south.
The major element at this site is a wood fossil. It is to be found embedded in Budgong Sandstone which may be nominally a sedimentary rock, however this rock has strong connections with the latites which are nominally igneous rocks created during volcanic activity.
There are a number of marine fossils in the general area of this site as well. The fossils may have been formed after a major event such as inundation and covering. Given the close association of the rock type that the fossil is embedded in, and volcanism asscociated with the "Gerringong Volcanics" group, it would seem that heat would also have been a factor in this fossil's formation.
In order to claim this cache, you have a number of tasks.
1. a) Measure the size of the major fossil element at GZ.
b) Determine the alignment in degrees from North of the major axis of the major fossil element.
Email the answers to these to me at my geocaching.com profile.
2. Try to find another fossil in the general area. There are small marine fossils to be found well within 50m of GZ. If possible, photograph it, record its coordinates and upload these to your log.
You may like to provide a personal visit photograph such as your GPSr, yourself or your group and upload this with your log. Also, if the weather is good, bring your swimmers and towel and enjoy a swim in the nearby rock pool.
Major References:-
1. Fuller L., Mills K.; "Native Trees of Central Ilawarra"; Weston & Co. Publishers 1985.
2. Young, R. W., "The Illawarra Escarpment" (1979). Wollongong Studies in Geography. Paper 2. (available as a download from the University of Wollongong Research Online (visit link)
Additional Hints
(Decrypt)
Ubj ovt vf srapr cbfg?