Victorians have been visiting Sorrento and its surrounding areas for rest, relaxation and recreation since the 1870s

Of the many great beaches in the region, Diamond Bay is one of the most attractive with the added bonus of being bit more sheltered than most of the 'back beaches' for surfing, diving and fun in the sun

Visitors to Diamond Bay often comment on the bay's scenic qualities but probably don't delve further into how the photogenic cliffs around the bay formed

This Earthcache is located with the permission of Parks Victoria in the Mornington Peninsula National Park and Earthcachers must abide by the National Park (Park) Regulations 2003 which include no disturbance to the site, rubbish must be removed and visitors are restricted to defined walking tracks. Dogs are permitted subject to time and seasonal restrictions and must be on a leash at all times

More information on the Mornington Peninsula National Park is available on the Parks Victoria Website or by calling 13 19 63

SITE DESCRIPTION

Rock Types

The cliffs reveal a succession of Pleistocene and Recent calcareous sand dunes, the older, lower ones being consolidated to form the rock, aeolianite. Breaks in the sequence of dune development are indicated by fossil soils (palaeosols)

Fossil Soils

There are numerous fossil soils consisting of calcareous sand grains and clay. The clay was evidently introduced as a wind-blown dust. Some palaeosols are up to one metre thick

Nine Pleistocene soils are represented, eight being terra rossas and one (at about mid-section) a rendzina. Rendzina is a dark clayey soil developed on limestone, containing a high proportion of organic (humic) and calcareous matter. Terra rossa (red earth) is a soil of varied composition, typically developed on limestone, and distinctly red in colour. Little is known concerning its variation and genesis

Blowouts in the unconsolidated dunes in the upper parts of the cliffs reveal at least two dark-coloured buried soils. Organic matter from the older one has been isotopically dated at about 5350 years B.P. using the carbon-14 method. Each terra rossa is underlain by a layer of calcium carbonate, leached from the upper part of the soil profile. One calcrete layer forms a prominent ledge halfway up the cliffs

The base of each soil is irregular, in places projecting downwards one metre or more as 'soil-pipes'. These probably formed where the underlying rock was dissolved from around the decaying roots of trees and shrubs

The soils vary in thickness and rise and fall as they are traced around the cliff faces, thus reflecting irregularities in the surface of the dunes on which they formed. In places they branch, indicating that parts of the ancient dunes remained stable, while others developed blowouts

Origin of Palaeosols

Two sets of conditions are indicated by alternation of soils and dunes. The dunes formed during unstable periods when the previous landscape was overrun by windblown sands. This may have been due to the onset of more arid times or to periodic rises in sea level

The soils developed during periods when the dunes were stabilized by vegetation. The thickest soils possible reflect thousands of years of topographic stability. At the top of the cliffs, conditions are currently unstable and the dunes are spilling inland of the vegetation, which had stabilized the preceding dune topography

References:
Clark, I. & Cook, B. (Eds.), 1988, Victorian Geology Excursion Guide, Australian Academy of Science, Canberra, p.459

To successfully log this Earthcache you are required to take a trip to Diamond Bay and email me the correct answers to the following questions:

1. What does the name of the rock, aeolianite, indicate about its method of transportation/deposition?

2. What is the dip direction of the layers in the strata (pictured below) adjacent to the stairway?
(A cardinal, primary or secondary intercardinal direction will suffice. There is no need to give an accurate bearing. Some reading/googling may be required if you don't know the difference between a dip and a strike)