Yellow Rock is located only a short drive from Portland. It is located in Nelson Bay.
Nelson Bay is a 4 km wide, south facing, rocky bay lying between Cape Sir William Grant and Cape Nelson. Deep inside the bay are three remnants of a once larger beach. Today the bay consists of 50 to 90 m high cliffs, composed largely of dune calcarenite sitting on top of basalt bases and rock platforms. Behind the beaches, the cliffs rise steeply to heights of 30 to 40 m and are capped with a veneer of dune sand. The dunes were deposited when a larger beach and backing sand ramp occupied the back of the bay, approximately 6000 years ago.
Calcarenite is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) sand-size (0.0625 to 2 mm in diameter), carbonate grains. The grains consist of sand-size grains of either corals, shells, ooids, intraclasts, pellets, fragments of older limestones and dolomites, other carbonate grains, or some combination of these. Calcarenite is the carbonate equivalent of a sandstone.
The term calcarenite was originally proposed in 1903 by Grabau as a part of his calcilutite, calcarenite and calcirudite carbonate classification system based upon the size of the detrital grains composing a limestone. Calcarenites can accumulate in a wide variety of marine and nonmarine environments. They can consist of grains of carbonate that have accumulated either as coastal sand dunes (eolianites), beaches, offshore bars and shoals, turbidites, or other depositional settings.
Calcarenite
Questions
Q1 Describe Yellow Rock in your own words.
Q2 How does the Yellow Rock differ to the "beach" that you are standing on?
Q3 WP2 will bring you to the base of a small cliff. What significant difference can you see here in the rock and what shape is it? (above head height and at least 30cm thick)
Q4 At WP2, face Yellow Rock so the water is at your left. Describe the direction of the weathering of the rock (eg pointing at the ground).
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References ~ greatsouthwestwalk.com & wikipedia