Joggins Rock Textures 10

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Natural fracture patterns and subtle colour transitions in rocks at Joggins Fossil Cliffs

Joggins Rock Textures 10 – Natural fracture patterns and subtle colour transitions in rocks at Joggins Fossil Cliffs on the Bay of Fundy in Nova Scotia, Canada.

Joggins Rock Textures 9

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Iron-stained water running down cliff strata

Joggins Rock Textures 9 – Iron-stained water running down a cliff face at Joggins Fossil Cliffs on the shore of the Bay of Fundy in Nova Scotia, Canada.

Joggins Rock Textures 8

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Coal seam with fossil-bearing limestone

Joggins Rock Textures 8 – Junction of a coal seam with a limestone layer packed tight with small fossil fragments, mostly bivalve shells, at Joggins Fossil Cliffs on the shore of the Bay of Fundy in Nova Scotia, Canada.

A Visit to Crystal Cliffs Beach

Beach stone with range tinted gypsum crystal in limestone at Crystal Cliffs Beach

Crystal Cliffs Beach lies a few miles from Antigonish on the north coast of Nova Scotia, Canada. It overlooks St George’s Bay close to the Northumberland Strait. It consists of a sand and pebble spit that dams back the water of Ogden’s Brook to form a large shallow lake known as Ogden’s Pond. The waters are tidal as there is a narrow inlet/outlet to the sea. In winter, the lake is more extensive as evidenced by the quantity of dead vegetation visible in marginal marshy areas. The ripples of the slowly moving water in the Pond reflected intricate patterns of blue sky and white clouds.

Boulders and pebbles dominate the upper levels of the spit, along with blanched driftwood, and sparse vegetation such as marram grass. The lower levels are mostly coarse sand. Occasional mammal bones rest on the tide line, perhaps from a seal. Cobble-size and larger beach stones of limestone, sandstone, and conglomerate are strewn across the shore – but the most noticeable and are the ones with orange and white crystals of gypsum that have come from the nearby cliffs that give the beach its name. The cliffs are composed of Early Carboniferous Limestone belonging to the Windsor Group with substantial gleaming surfaces of white gypsum. Viewed from the sea by kayak, the cliffs are said to be a marvellous sight. The only part visible from the beach at high tide, at this particular time, showed a relatively recent and massive rock fall defacing that outcrop.

The sea water lapping against the sand, on this crisp and sunny spring day, was crystal clear, revealing through a distorting lens of saline the multitudes of coloured pebbles on the seabed. The wave-textured surface made abstract patterns of sunlit reflections. It was a beautiful place to experience.

Rocks at Wasson Bluff

Wasson Bluff is famous. A site with an international reputation. It is located to the east of Parrsboro on the northern shore of the Minas Basin in Nova Scotia, Canada, and is best known for its fossils and its fascinating geology. Canada’s oldest dinosaur skeletons are being excavated in earliest Jurassic sedimentary rocks at Wasson Bluff Palaeontological Protected Site. Within these rocks an important vertebrate fauna including jaw bones and skulls of a rare protomammal, Pachygenelus were discovered, and also bones and scales of the lizard-like reptile Clevosaurus, a crocodile-like reptile Protosuchus, fish scales and prosauropod dinosaurs (Donohoe et al. 2005).

The bluff consists of complexly faulted and tilted sedimentary rocks and basalt. Most of the rocks of the Bluff itself are composed of brownish Jurassic North Mountain Basalt with evidence of hexagonal cooling joints. Much of it is brecciated. The basalt boulders that have fallen to the beach include many with pockets and streaks of various minerals; the green deposits seen in the photographs of boulders on the beach may be the mineral celadonite. A fault brings the mostly brecciated basalt into contact with The Triassic Partridge Island Member of the Upper Blomidon Formation. The Blomidon Formation rock is described as well-bedded grey, red and purple sandstone and mudstone with the Partridge Island Member of it being conglomeritic but fining upwards to siltstone but beneath the basalt. This junction of rock types can be seen in images 1 and 17 in the gallery of photographs above this text and image 25 in the gallery below.

Carboniferous Parrsboro Formation “red bed” strata are exposed for a short distance to the east of the bluff and on the east of the small stream that traverses a narrow, steep sided, tree-lined valley before it crosses the beach.

Further east along the beach, the soft red Jurassic period McCoy Brook Formation rocks which originated as sediments associated with rivers, lakes, and wind-blown sand dunes form a low crumbling cliff and can be seen in the photographs as the brighter red rocks often with white stripes and patches.

The local Fundy Geological Museum conducts tours of the site and works with academics on fossil excavations at the site every summer.

Please note that all the identifications attached to the photographs of the rocks are tentative and subject to verification – I am just an interested natural historian and not a professional geologist.

REFERENCES

Donohoe, H.V.Jr., White, C.E., Raeside. R.P., and Fisher, B.E. 2005. Geological Highway Map of Nova Scotia, Third Edition. Atlantic Geoscience Society Special Publications #1.

Nova Scotia Field Guide, Arthur D. Storke Memorial Expedition, Department of Earth and Environmental Sciences, Columbia University in the State of New York, August 23 to September 2, 2012.

Water-worn Limestone 2

Weathered limestone rock layers on the Worms Head Causeway in Gower, South Wales.

The limestone further east along the Worms Head Causeway shore, towards Tears Point, displays the results of a number of erosion agents leading to some curious formations. The clean, smooth surfaces of mounded and hollowed shapes result from mechanical abrasion where the rock is pounded by stones carried in the waves; by chemical and physical erosion caused by micro-organisms and marine invertebrates (bio-karst surfaces made by such organisms as lichens, limpets, and sea urchins); and acid dissolution by rainwater when the tide is out, especially around the edges of pools, in natural fissures like joints and bedding planes, and areas where water constantly drains – resulting in what is called karst topography. Small circular pits (image 48) of dissolved limestone readily connect with each other, soon enlarging into bigger pools that are known as kamenitzas – which in turn can interconnect with other pools as seen in the images below (particularly images 49, 50, and 51).

Water-worn Limestone 1

Water-worn limestone rock layers on the Worms Head Causeway in Gower, South Wales.

The Carboniferous sedimentary strata outcropping on the landward shore of the Worms Head Causeway at Rhossili show differential erosion by the sea. Some areas of the Black Rock Limestone Subgroup are clean, smooth and worn down whilst others are sharp and jagged with encrusting biofilms and barnacles. This is partly due to the varying compositions and relative hardness of the different strata, and partly to the way in which the waves with their rock-bearing loads seek lines of least resistance in the shore with each tidal ebb and flow. Areas of weakness, for example, between bedding planes and in minor faults with veins of soft white crystalline calcite and red haematite, are more vulnerable to repeated abrasion. This has led to the formation of numerous channels, gullies, and basins among other more resistant rock outcrops. Rounded pebbles and cobbles frequently lying within the hollowed areas evidencing their role in wearing the bedrock away. Mechanical abrasion allied to varying rock resistance is not the only way that the limestone is altered. Elsewhere on the causeway, limestone acid dissolution and marine organisms are the most common agents of natural change in surface texture and sculpturing, creating karstic and bio-karstic limestone topography.