Rocks at Port Douglas, Queensland

These are some personal observations, just thinking aloud, and part of my learning process and fascination with geology. I have a lot of questions to ask about the rocks at Port Douglas on the Queensland coast in Australia! They are marked by a GeoCache site which says they are a batholith. A batholith is formed deep under the earth’s crust where molten magma from superheated, melted rocks, cools slowly and forms granite made up of fairly large crystals. In eastern Australia the batholith formations, known collectively as the Kennedy Province, were created between 330 and 255 million years ago  – following the earlier formation of the Hodgkinson Province which was created between 440 and 360 million years ago, and into which the batholith magma eventually intruded.

I have seen a batholith before – at Peggy’s Cove in Nova Scotia – and the the rocks I photographed at Port Douglas are very different from the rocks exposed at Peggy’s Cove – at least the ones around the edges of the formation in Port Douglas, notwithstanding that the two outcrops of bedrock are in two separate continents and have been subjected to very different erosional and weathering processes. Peggy’s Cove rocks have been smoothed and polished by ice sheets (glaciated) and their surfaces remain clean in a temperate climate. At Port Douglas, on the other hand, the rocks have eroded out and weathered in the wet tropics climate which has led to different erosional characteristics and a surface obscured in many parts by black bio-film.

Batholiths are made of granite. I think I can see granite in some areas of the Port Douglas outcrop on which the Lookout stands. A lot of what I believe to be granite is covered in black biofilm (possilbly cyanobacteria and lichen) and is colonised by organisms like barnacles so that the details are obscured. However, most of the detailed close-up shots I took of the rocks, particularly those around the edges of the feature, including loose boulder lying on the waters’ edge, did not seem at all like granite to me. There are various colours, textures and features as shown in the photographs in this post. I have been wondering to myself, speculating, whether these rocks may represent the junction between the granite of the Kennedy Province batholith and the Hodgkinson Province rocks into which they intruded, showing further changes to the earlier overlying (and already much altered, stretched, compressed and vulcanised) metasedimentary rocks.

The geological map of the area describes the outcrop of bedrock in the Port Douglas environs as Larramore Metabasalt Member which is part of the Hodgkinson Province rocks. I suspect that some of my photographs may be showing these metabasaltic rocks, or metasedimentary rocks with evidence for explosive volcanic activity and volcanic intrusions. I have read Rocks, Landscapes and Resources of the Wet Tropics by Berndt Lottermoser et al (2008) published by the Geological Society of Australia, Queensland Division, and have found it very useful. However, a more relevant account of the port Douglas geology might be given in another book which I have been trying to track down: Rocks and Landscapes of the Cairns District by W. F. Willmott and P. J. Stephenson (1989) published by The Queensland Department of Mines and Energy but it is out of print. I think it might be useful in helping me answer some of the questions I’m posing.

Rocks at Waterside, New Brunswick

Red Triassic rocks in the cliff at Waterside beach, New Brunswick

Waterside beach in New Brunswick is a UNESCO Fundy Biosphere Reserve Amazing Place. The red rocks here are Triassic in age, like the ones at St. Martins further to the south along the western shore of the Bay of Fundy. The Bay of Fundy occupies the Fundy Basin which lies between the Provinces of Nova Scotia and New Brunswick in Canada. The Fundy Basin contains scattered outcrops of Mesozoic Period conglomerate, sandstone, shale. mudstone and basalt flows. Remnants of Middle to Late Triassic sedimentary rocks form small crescent shaped outcrops 2.5 km long and 2.3 km wide, along the New Brunswick shore at Maces Bay, Saint John, St Martins, Martins Head, and Waterside at Chignecto Bay. These deposits lie unconformably over Carboniferous rocks in a broad synclinal structure that has an axis gently dipping southwestwards towards the Gulf of Maine (Ballard & Uchupi 1945).

The rocks at Waterside belong to the Fundy Group which is part of the Newark Supergroup. The broad rock bands seen in the vertical cross-sections of the cliff are amazingly different in colour, composition and texture; and include coarser conglomerates as well as finer-grained sandstones. The layers were originally formed when rivers flowing into a major water body slowed down, and deposited their heavy load of sediment in an alluvial fan that gradually grew further out (prograded) into the water. Over time the sediments built up to considerable depths and became consolidated into rock. This rock was eventually raised above water level  by earth movements. Some of the consolidated rock layers in the cliffs at Waterside have minor stratifications showing cross-bedding, which indicates to a geologist the type and direction of the current flow that deposited them. There is also a series of large overlapping biconvex lenses of a paler, more calcareous material, the meaning of which presently eludes me.

REFERENCES

Powers, Sidney (1916) The Acadian Triassic, The Journal of Geology, Volume XXIV, Number 1.

Ballard, R.D., and Uchupi, Elazar, 1972, Carboniferous and Triassic rifting: A preliminary outline of the tectonic history of the Gulf of Maine: Geological
Society of America Bulletin, v. 83, no. 8, p. 2285-2302.

Luttrell, Gwendoline W. (1989) Stratigraphic Nomenclature of the Newark Supergroup of Eastern North America – A lexicon and correlation chart of Newark Supergroup stratigraphic nomenclature, including a review of the origin and characteristics of the early Mesozoic basins of eastern North America,  U.S. Geological Survey Bulletin 1572, United States Government Printing Office, Washington.

Nadon, G. C. and Middleton G. V. (2011) The stratigraphy and sedimentology of the Fundy Group (Triassic) of the St Martins area, New Brunswick, Canadian Journal of Earth Sciences 02/2011, 22 (8), 1183-1203.

Rocks at St. Martins, New Brunswick

The rocks at St Martins in New Brunswick, on the coast of the Bay of Fundy in Canada, are around 250 million years old and belong to the earliest and oldest part of the Triassic Period. The Triassic Period lasted from 251 to 199 million years ago. In fact some of the rocks may be so old that they extend as far back as the previous geological period – the Permian.

Two rock types outcrop in the cliffs here. The Quaco Formation is represented by light-coloured coarse boulder conglomerate while the red sandstone belongs to the Honeycomb Point Formation. It is possible to see where the two types of rock make contact in the cliff at the east end of the beach just past the water-side restaurants. Both types of rock are fairly soft and susceptible to erosion by the pounding of the waves. The sea works particularly at vulnerable areas like the bedding surfaces between the angled strata. It is here that the waves eventually form shallow sea caves by washing away the rocks. Very few fossils are found in these rocks. They are too old to have dinosaur fossils although possible reptile footprints have been found. However, Triassic rock layers like those at St Martins pass right under the waters of the Bay of Fundy and emerge on the other side in Nova Scotia near Parrsboro and Blomidon, where fossils of the oldest dinosaurs in the North American Continent have been found.

The beach at St Martins is composed of rounded pebbles with many different colours and patterns. They look their brightest and most interesting close to the water’s edge. The wet pebbles look completely different from the dull dry pebbles higher up the shore. The pebbles represent many rock types and are presumably mostly derived from two sources: the adjacent cliffs, especially the conglomerate, and the thick layer of glacial deposits that overlies much of the terrain in this part of the world.

All the information in this post was obtained from the very informative local signs on the beach. St Martins [GPS: 45.21.42N, 65.31.4.W] is one of many sites of geological interest in the region and forms part of the Stonehammer GEOPARK. Stonehammer produce a downloadable St Martins geology fact sheet and also a St Martins geology map.

Rocks at Clogher Bay 3

Silurian rock at Clogher Bay in Dingle

View of cliffs at Clogher Bay with human figure for scaleThis is the third in a series of photographs of Silurian rocks from Clogher Bay. A brief examination of the literature indicates that the rocks in these pictures belong to the Drom Point Formation which has accumulated to a depth of 300 metres and is part of the Dunquin Group of Silurian Period strata in Ireland. The Drom Point and Croagh-marhin Formations consist of shallow-marine, fossiliferous siltstones and very fine to fine grained sandstones.

Rock colour and texture boulders and cliff in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rock colour and texture with Chondrites trace fossils in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rock colour and texture in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rock colour and texture in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rock colour and texture with preserved sand ripples in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rock colour and texture in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rock colour and texture in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rock colour and texture in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rock colour and texture in Silurian Period silt stones and sandstones from the Drompoint Formation in Dingle

Rocks at Clogher Bay 2

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

This is the second in a series of photographs of rocks at Clogher Bay on the Dingle Peninsula in the West Coast of Ireland, and they belong to the Dunquin Group from the Silurian Period. Clogher Bay is just south along the coast from Ferriters Cove which has featured in earlier postings.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.