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The Brooms Head area is situated on the far north coast of New South Wales.
You can explore the area starting from the day car park at the beach and walk up the headland or park at the Lookout ,either way you will observe the geology of the area and get spectacular views .
This pleasant beach-side locality is endowed with a rocky headland of deformed metasedimentary rocks.
These rocks exhibit a range of features ideal for demonstrating the common sedimentary structures of deep
water marine sediments, and post-depositional deformation. The rocks are Carboniferous in age aprox (299,000,000-359,000,000 years old ) and were formed far from land in a very deep ocean. They have been metamorphosed, folded and faulted
GEOLOGY FEATURES YOU MAY OBSERVE
range of metasedimentary rocks
various sedimentary structures,included graded bedding and cross bedding
numerous faults
quartz veining
sandstone dykes
weathering profiles
shallow water sandstone and conglomerate with minor coal
To check out the features please be aware that some area can be quite dangerous.
Prone to tidal influences and sporadic anomalous wave activity and falling rocks
Sites along cliff base and cliff edge should be undertaken with care .
Wear sturdy strong appropriate footwear and hold onto your childs hand .
(To get answers you require for this earthcache you do not need to go into dangerous areas)
LOCAL AND REGIONAL GEOLOGY
The Brooms Head area comprises metamorphosed and deformed Carboniferous, deep water marine rocks.
These include sandstones, siltstones and mudstones. They were formed in a very deep ocean many kilometres from land. These were transported to the edge of the continent by movement of the underlying oceanic crust toward a subduction zone which existed along the margin of the Australian landmass. The sedimentswere scraped off against the edge of the continent as the crust sank downwards into the subduction zone,forming a mass of compressed, metamorphosed and deformed rocks known as an accretionary wedge or
subduction complex. During this time Australia was moving about the surface of the earth by
continental drift, becoming part of the super continent Gondwana in the Permian , which itself began to break apart in the Jurassic Period .The accretionary wedge rocks extend inland from the present coastline for several hundred kilometres, gradually increasing in age to the west.
The rocks exposed at Brooms Head are
the Coramba beds, a Carboniferous package of sedimentary rocks formed in a deep oceanic setting, probably beneath several kilometres depth of water.
Sedimentary structures in these rocks, which can be examined on the headland, demonstrate that the sands, silts and muds were deposited close to the base of a high,steep slope on the ocean floor.
From the late Triassic period to the early Cretaceous , much of the Australian land mass was undergoing erosion and accompanying deposition on land and in some places, shallow marine seas.
In what is now northeastern New South Wales and southeastern Queensland deposition took place in the Clarence-Moreton Basin. The first materials deposited in this basin included organic-rich swamp deposits which
formed coal seams and some volcanic rocks. However, most material deposited was sand, gravel, silt and mud formed in and about rivers and their alluvial plains. Prolonged burial has converted these materials to sandstone, mudstone and siltstone.
Boulders of the basin rocks have been placed along the Brooms Head beach shoreline as a
buffer against wave erosion
Cooling events which have occurred over the past 700,000 years have been associated with
lowering of sea levels. This has resulted in the exposure of large expanses of sandy sea floor. This was subjected to wind erosion which moved the sand inland as multitudes of shifting dunes. Those dunes were to some degree stabilised by vegetation in recent millennia. These dunes of clean, white fine sand occur along the coastline, overlying the older rocks. The dunes are evident on the southern end of the headland.
Over the past tens of thousands of years, groundwater movement through the rocks and sand dunes has changed the composition of the materials it has moved through. The groundwater is derived from rainfall and salt spray. Its effect upon the rocks has been to decompose some minerals and remove the soluble products
of that decomposition. This is the process of weathering, and rocks which have undergone this process are generally bleached and relatively soft. Weathering effects can be seen on the headland. However, groundwater movement within the dunes has resulted in the accumulation of weathering-derived iron and humus at the base of the dunes to form a soft, brown, sandy rock known as coffee rock. This rock is exposed
along the southern end of the headland
The view of the end of the headland displays the variation in bedding dips due to folding in that
area. A small sea cave has been eroded into the headland between the areas of
shallow and steep dips, because that area corresponds with an anticline, the perfect site for a cave to develop.
You can continue along the track for a further 210 m to where the track enters the sandy beach,follow the beach around to the north for about 70 m to the outcrops on the western edge of the sandy beach.
A view of folded rocks to the north and spectacular iron oxide formations in weathered siltstone can be seen
This site reveals a great view of the folded rocks on the southern end of Brooms Head and displays some spectacular iron oxide veins within bleached, weathered siltstone and mudstone .The iron oxide veins are arranged in almost parallel groups, are curved and show sharp ends, suggesting that they have formed as infills within fractures which formed by fracturing of the rocks, probably by tensional forces.
Perhaps these fractures resulted from forces associated with the formation of the folds and faults in the area.
You have come this far so now to get some information required to submit your log entry
Ground zero is away from the cliff edge so safe to observe the cliff face or you may prefer to walk down onto the beach to get your answers
Q1
Explain the difference between the dip on the eastern side of the cliff and that of the one on the western side
Q2
What conditions are required to form a cave in the cliff
Q3
what colour are the rocks on the beach as you look down in the little valley from gz
Are they the same colour and size as those further around the base of the cliff and what type of rock do you think they are
Q4
At gz what are you standing on or next to that is man made (to verify that you are there at gz)
All information used in this geocache were obtained from
ozgeotours.yolasite.com>brooms-head
Please submit answers to me then you can log
I will remove log if not submitted
Happy Caching
Congratulations Earthlight on FTF
Additional Hints
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