In January and February of 2010, beach deposits at Redcar – in an area roughly extending between the Information Center and Park Hotel – were stripped away by tidal scour revealing some infrequently exposed beds beneath the usual sand and pebbles.

At the base of the steps opposite the Information Center, and extending seaward for over 100 metres, were exposed black peat beds, springy underfoot, packed with wood fragments and even tree trunks, some in growth position. This is the Redcar Submerged Forest (aka. Peat & Forest Beds). Other minor examples survive within the Lower Tees Valley, both underlying parts of Middlesbrough and also beneath beach deposits between Seaton Carew and Hartlepool. Here the beds are known as the Hartlepool Submerged Forest.

The peat and tree trunks date from a time shortly after the last great ice-sheets (glaciers) to occupy this part of N.W. Europe retreated northward as the climate warmed c.13,000 years before present (BP). When immense ice-sheets form, like those which occupied N. Britain during the last Ice-Age, prodigious amounts of water are sequestered as ice, a process which draws down global sea-level. When the climate recovers, the ice-sheets melt and sea-level gradually rises again.

By c.10,000 years BP, ice which once occupied Northern England had retreated, and the newly exposed post-glacial landscape was recolonised by vegetation. Sea-level was still some 150 metres, or so, lower than today and the place where Redcar now stands was part of a forested upland similar in altitude to nearby Upleatham Hill!

Continued wastage of the ice-sheets farther north gradually raised sea-level until between 8,000 and 6,000 years BP, it attained its modern position in the process overwhelming the ancient forest and producing the Peat and Forest Beds. The deposit was formerly much more extensive though most of the remains have been removed by modern erosion.

These are important deposits which can tell us a great deal about the changes in global temperature, sea-level fluctuation, and vegetative cover that have occurred in the Tees Valley over that last 8,000 years or so. As such they should not be disturbed – please visit them (when exposed) but leave them for the enjoyment and edification of others.

]]> http://www.tvrigs.org.uk/archives/654/feed 0 http://www.tvrigs.org.uk/archives/554 http://www.tvrigs.org.uk/archives/554#comments Mon, 01 Feb 2010 09:12:55 +0000 admin http://www.tvrigs.org.uk/?p=554

Evaporites are non-clastic, or chemical sediments, created through the precipitation of dissolved salts from water. They most frequently occur at the site of a former large water body such as a lake or landlocked sea, on coastal plains (sabkha zones), or where rivers feed very arid desert areas. As the water involved slowly evaporates the salts become more concentrated and at well-defined concentrations they begin to recrystallise. They are different to the more conventional clastic sedimentary rocks which include mudstone, siltstone and sandstone.

Sometimes referred to as salines, these rocks form an economically important group of minerals. Sylvite (potassium sulphate) and minor amounts of halite (rock salt) are extracted by Cleveland Potash Ltd. from their mine at Boulby, near Staithes. This is Europe’s deepest shaft mine as the sylvite lies within Permian strata over a kilometer below the surface. They are some 290 million years old and were laid down when a shallow ancient sea, dubbed the Zechstein and which occupied much of northern England, underwent several cycles of evaporation and transgression. Sea water comprises ~3.5% dissolved salts of which the bulk is sodium chloride or common salt. Evaporation yields successively limestone, anhydrite (calcium sulphate), halite and finally potassium and magnesium salts. Anhydrite was formerly mined and processed at Billingham on Teesside.

Evaporite deposits can flow under pressure producing salt-domes which disturb the strata through which the pass and internally exhibit complex folding. They also retain heat and may be a target for future geothermal energy projects.

Images above show:
Sylvite – as mined at Cleveland Potash Mine, Boulby, Cleveland.
Halite – also found within Boulby Mine.
Cleveland Potash Mine, Boulby, East Cleveland. UK.
Anhydrite – once mined at Billingham on Teesside.

This mineral is able to assume almost any colour but commonly brown, yellowish-brown, or grey specimens can be found. It occurs in Britain’s Carboniferous strata as nodules and beds of impure iron carbonate known as Clay Ironstone. Once a valuable source of ore, alongside a dark carbonaceous form known as Blackband. In Cleveland the well-known ironstone through which which Teesside became a major industrial force from 1850, is of Jurassic age (c.188,000,000 years old), contains iron-rich berthierene rather than siderite, and occurs with a distinctive texture known as oolitic. An amalgamation of small rounded concentric structures, which form through the same colloidal processes as those reponsible for oolitic limestones, make up the bulk of the rock. Siderite can also be found in massive, granular, or concretionary forms, produced in a variety of environments including within hydrothermal veins along with pyrite and galena, within intrusive pegmatites, and as sedimentary Bog Iron Ore in high latitude lakes and swamps.

At its purest, siderite forms rhombohedral crystals with a vitreous (inclining to pearly) lustre, perfect cleavage, a white streak, and uneven fracture. An allied mineral Hydrated Iron Oxide or Limonite (FeO(OH)·nH2O), commonly forms pseudomorphs (perfect copies) of siderite crystals.

It is however more usually found in the local area as red-weathering nodules within grey mudstone scars, exposing part of the Cleveland Ironstone Formation that crops out on the foreshore at Jet Wyke, Staithes. In the 1700s, such nodules were collected from the scars by local villagers and loaded onto boats which eventually disgorged their cargoes at furnaces on Tyneside, long before the significance of the Cleveland Ironstone Formation was suspected.

Images above are of:
Manganoan Siderite with Albite;
Siderite Pseudomorphosis in Limonite with quartz;
Red Siderite Nodule in Grey Mudstone at Staithes.

Use of this mineral can be traced back to c.3,000BC, when the Ancient Egyptians used it as a kind of cosmetic known as Kohl applied around the eyes. The dark marks it produces played the dual role of both reducing the glare of the powerful desert sun, and also as a fly repellent which helped reduce the instance of disease. Though it was used in this manner by the Egyptians, being an ore of lead it is also harmful to health causing lead poisoning. Galena is also a semiconductor (like silicon in today’s computers) and was used to detect radio signals in early receivers as a point-contact diode.

Mining for lead in Britain probably pre-dates the Roman occupation, but it was during their tenure here that the mineral appears to have first been extracted on a large scale. In many places small areas of Roman workings can still be found today. The Romans located the ore by looking for a small white flower, Spring Sandwort (Minuartia verna), also known as Leadwort; This flower grows on land heavily polluted by lead and other associated heavy metals. Where the Romans noticed this plant growing they would scrape back the soil and grass to locate the vein or rake of lead which was then extracted and smelted.

Lead is often found in hydrothermal veins and is associated with silver, pyrite, calcite, fluorspar and barites, all of which are useful by products known as gangue minerals.

The images above show a large boulder with Galena, the flower Spring Sandwort, and a fist-sized sample of Galena with flourite.

More correctly, the Mica Group of minerals are sheet silicates. This means that instead of growing as a large crystal they form in lots of very thin layers. The minerals are often transparent and in the past were used as a substitute for glass. It is a widely distributed mineral occurring in igneous, metamorphic, and sedimentary rocks and can form the planet’s largest-known crystals reaching several tens of metres in length, particularly within granitic pegmatites.

China is the greatest world producer of mica, with the largest deposits being found on the Indian sub-continent, USA, South Korea, and Canada. The mineral has multifarious uses including within Geiger-Müller Tubes, heating elements, capacitors, refractory windows (isinglass), in toothpaste, and adds a bright shimmer to make-up.

Throughout the ages, fine powders of mica have been used for various purposes, including decorative purposes. The coloured body paints used by Hindus of North India during holi festival contain fine small crystals of mica. The majestic Padmanabhapuram palace, 65 km (40 miles) from Trivandrum in India, has colored mica windows.

Mica occurs in the Tees Valley most commonly as small specks within the Jurassic sedimentary strata and is generally indicative of the sediment being deposited in quiet water conditions.

Around 58 million years ago, as the Atlantic oceanic basin formed, adjacent areas of crust became stretched and weaknesses could be exploited by molten material (magma) being forced into the crust by pressure from below. This magma cooled very quickly surrounded by local rocks and became the Cleveland Dyke.

Stretching for c.350 miles between Mull in Western Scotland and the Tees Valley and North Yorkshire the hot magma cooled to form a dark blue-grey, finely crystalline rock referred to by geologists, more correctly, as dolerite. Dolerite is chemically similar to basalt, the major difference being that basalt is erupted at the Earth’s surface, whereas dolerite solidifies within the Earth’s crust.

Following removal of the overlying strata by erosion, primarily through glaciation, the dyke was exposed at the Earth’s surface. In the west of our region it can be traced crossing the river at Preston-on-Tees, but perhaps its most notable feature occurs near Great Ayton where the more durable rock making up the dyke, and softer Jurassic strata into which it is intruded, exhibit a phenomenon known as differential erosion. The softer sedimentary rock is preferentially removed by erosion leaving the harder whinstone to form a bold ridge called Langbaurgh Ridge.

The geater hardness of whinstone relative to sedimentary rock makes it ideal for use road-stone and cobbles, and it was for this purpose that Leeds City Council leased land around Great Ayton, where the ridge is best developed, in 1869. Large quantities of the rock were quarried at Cliff Rigg, as well as elsewhere along the length of the dyke, for example at Preston-on-Tees, Ingleby Barwick, and at a variety of locations on the North York Moors. The now-abandoned workings today form an unmistakeable scar on the landscape, though the former quarry’s remains allow geologists to study the effects of metamorphism, i.e. the baking of the surrounding sedimentary rock when the hot magma was injected.

What the Persians were actually importing was Asbestos, one of six fibrous minerals known to geologists as chrysotile, amosite, crocidolite, tremolite, anthopyllite, and actinolite.. The natural shape of the mineral as it grows is as fine fibres that are strong enough to weave into material.

Its widespead use as insulation and a fire retardant commenced with the Industrial Revolution since which time it has been used in the manufacture of concrete, bricks, pipes, gaskets, flooring, roofing, ships, aircraft, and a wealth of other products. In the 1950s it was even used by one cigarette manufacturer to produce filters!

We now know that Asbestos can be extremely harmful when the fibres become lodged in the lungs and the substance is now restricted in its use.

Alum Shale is an unremarkable, grey, thinly-bedded, pyritic mudrock that weathers readily to thin crumbly flakes, the detritus often forming steep talus slopes below the working faces in numerous alum quarries that today reside peacefully along the coast and hills of Cleveland and North Yorkshire. The quarries and boiling houses operated for over 260 years here, commencing around 1600, in the only district in Britain where rock suitable for the important industry of alum-making was, and still is, able to be extracted.

The Tethys Sea supported a diverse fauna of, now mostly-extinct, creatures amongst which can be counted a wide-range of ammonite species, belemnites, fish, and a number of large reptiles including crocodiles, ichthyosaurs and plesiosaurs. At the end of their lives, the remains of these creatures would settle on the sea-floor and occasionally become buried and preserved as fossils. Given the rock’s mode and time of creation, who amongst us could have imagined that the remains of these leviathans, tokens of antiquity from a long lost world millions of years after their lives had ended, would once again see the light of day by way of a quarryman’s hands.

Ammonites achieved their evolutionary zenith during the Jurassic as a result of which some species are only found within a very small stratigraphic range. The usefulness of this to geologists in ascertaining the relative ages of strata was noticed by alum-maker’s son Louis Hunton (1814-1838), who collected data at coastal quarries and made valuable contributions to the young science of biostratigraphy in the 19th century.

The large reptile fossils began to come to light during the 18th century at a time when the science of geology was in its infancy. They provided some of the earliest, best preserved, fossils to be examined by early palaeontologists and found their way to academic establishments across the world. Specimens of these and many more fossils can be seen today on display in Pannett Park Museum, Whitby.

The image above shows Lower Jurassic Alum Shale (grey) making up the lower part of the cliff at Rosedale Wyke, Port Mulgrave. The overlying yellow-brown sandstone belongs to the Middle Jurassic Saltwick Formation.

Locally, there are many hundreds of metres of Permian evaporite deposits, both sylvite and rock salt (halite), beneath Teesside and North Yorks which were deposited around 260 million years ago when a sea known as the Zechsteain evaporated. Middlesbrough formerly fostered a thriving salt industry, and sylvite (for use as fertiliser) and halite (essential for keeping roads ice-free in winter) are still mined locally at the Cleveland Potash mine, Boulby which descends over a kilometre beneath the surface making it Europe’s deepest mine.

Stigmaria are the remains of the roots of large tree like plants. It is a generic name for the roots and the plants could have been Lepidodendron, Lepidophloios and Sigillaria, which were tall Lycopods, often described as club mosses They could be over 30m tall and have a diameter of 2m. Their branches were draped with long grass like foliage of spirally arranged leaves and cones.

The roots of these plants were shallow branching hollow tubes. This fossil is the internal cast of one of these tubes. The dimples on the surface are the nodes that would have had a ribbon like rootlet attached.