Earth:Malvern Quartzite
| Malvern Quartzite Stratigraphic range: early Cambrian ~530 Ma[1] Template:Period fossil range | |
|---|---|
| Type | Formation |
| Underlies | Hollybush Sandstone |
| Overlies | Warren House Formation |
| Thickness | ~50–300 ft (15–91 m)[2] |
| Lithology | |
| Primary | Quartzite |
| Other | Conglomerate |
| Location | |
| Region | Worcestershire |
| Country | United Kingdom |
| Type section | |
| Named by | T. Groom |
| Location | Midsummer Hill |
| Year defined | 1902[3] |
The Malvern Quartzite, previously referred to as the Hollybush Quartzite and Conglomerate, is a Cambrian aged geologic formation in the Malvern Hills of Worcestershire. It is primarily composed of quartzites and conglomerates, and contains a sparse record of brachiopod fossils.
History and naming
Before the formation was fully described and formally named in 1899 and 1902, the conglomerate rocks of the formation were found as far back as 1811 by the Scottish geologist Leonard Horner in the Gullet Pass area.[4] Sometime later in 1839, feldspathic grit would be noted to be present in the Midsummer Hill area by Roderick Murchison. In 1849, John Phillips would record some more conglomerate rocks wrapping around and descending down the northern edge of Raggedstone Hill, towards Hollybush Pass to the North. This was later observed again by Holl in 1865 on the western side of Raggedstone Hill, as well as in Gullet Pass, although he would assign the occurrence in Gullet Pass to the Llandovery series. And in 1889, just 10 years before the first formal description and naming, William Samuel Symonds would also find more evidence of conglomerate rocks on the western and northern sides of Raggedstone Hill, including such rocks on the western side of Midsummer Hill also.[3]
When it was formally described in 1899, the formation was originally referred to as the "Hollybush Quartzite and Conglomerate" or "Hollybush Conglomerate and Quartzite", commonly truncated to just "Hollybush Quartzite".[5] The name would only remain for 3 years, when in 1902, Groom would see it formally renamed to the "Malvern Quartzite", as per a suggestion from Professor Charles Lapworth.[3]
Geology
The Malvern Quartzite is predominately composed of conglomerate rocks and quartzite, the namesake mineral of the formation. The quartzite is grey in colouration, ranging from compact to coarse-grained, with the cementing mineral being either silica or limonite. The conglomerate rocks are composed of few pebbles of a white milky quartz coated in a thin film of limonite, ranging from pea to hazel-nut sized, and are also predominately spherical to elongate in shape. Whilst the rock has been noted to understandably be primarily composed of clear, interlocking quartz crystals, of crystalline minerals have also been found, including feldspar, chalcedony, zircon, tourmaline, occasional glauconite, as well as apatite.[6] The overall thickness of the formation remains uncertain due to difficulty in ascertaining the disposition of known beds, with outcrops at Winter Combe possibly measuring between 50–65 ft (15–20 m) in thickness, whilst conglomerate rocks at Midsummer Hill possibly range anywhere between 200–300 ft (61–91 m) in thickness.[3]
Dating
Whilst it has not been properly dated, the Malvern Quartzite has been correlated to other formations across Avalonia, including being correlated to the base of the Swithland Formation in Leicestershire, the Bonavista Formation in Newfoundland, the Striped Blue Shales in Wales, the Home Farm Member in Nuneaton, the Withycombe Formation also in Worcestershire, and the Lower Comley Sandstone in Shropshire. This roughly sees it dated to somewhere around 530 Ma.[1]
Paleobiota
The Malvern Quartzite contains a small collection of shelly fossils, namely brachiopods, such as Micromitra,[7] and hyoliths such as Hyolithus.[8]
Color key
|
Notes Uncertain or tentative taxa are in small text; |
Lophotrochozoa
| Lophotrochozoa | |||||
|---|---|---|---|---|---|
| Genus | Species | Notes | Images | ||
| Hyolithus[8] |
|
Hyolith. | |||
| Kutorgina[8] |
|
Kutorginid brachiopod. |  | ||
| Micromitra[2][7][9] |
|
Paterinid brachiopod. | |||
| Obolella[8][2][7] |
|
Obolellid brachiopod. | |||
|
Obolellid brachiopod. Species would be reassigned to Broeggeria as B. salteri in 1902.[10] | ||||
| Broeggeria[10][11] |
|
Elkaniid brachiopod. | |||
References
- ↑ 1.0 1.1 McIlroy, D.; Brasier, M. D.; Moseley, J. B. (March 1998). "The Proterozoic–Cambrian transition within the ‘Charnian Supergroup’ of central England and the antiquity of the Ediacara fauna". Journal of the Geological Society 155 (2): 401–411. doi:10.1144/gsjgs.155.2.0401.
- ↑ 2.0 2.1 2.2 Cobbold, Edgar Sterling (October 1920). "The Cambrian Horizons of Comley (Shropshire), and their Brachiopoda, Pteropoda, Gasteropoda, etc.". Quarterly Journal of the Geological Society of London 76 (1-4): 325–386. doi:10.1144/GSL.JGS.1920.076.01-04.10.
- ↑ 3.0 3.1 3.2 3.3 Groom, Theodore (February 1902). "The Sequence of the Cambrian and Associated Beds of the Malvern Hills". Quarterly Journal of the Geological Society of London 58 (1-4): 89–135. doi:10.1144/GSL.JGS.1902.058.01-04.10.
- ↑ Horner, Leonard (1811). "On the Mineralogy of the Malvern Hills". Transactions of the Geological Society. 1st Series (The Geological Society of London) 1: 281–321. doi:10.1144/transgsla.1.281. https://en.wikisource.org/wiki/Transactions_of_the_Geological_Society,_1st_series,_vol._1/On_the_Mineralogy_of_the_Malvern_Hills. Retrieved 18 June 2015.
- ↑ Groom, T. T. (February 1899). "The Geological Structure of the Southern Malverns, and of the Adjacent District to the West". Quarterly Journal of the Geological Society of London 55 (1-4): 129–169. doi:10.1144/GSL.JGS.1899.055.01-04.10.
- ↑ Sweeting, G.S. (January 1927). "The petrography of the Malvern Quartzite, Hollybush Sandstone, and May Hill Sandstone, exposed in the Eastnor (Herefordshire) district". Proceedings of the Geologists' Association 38 (4): 548–560. doi:10.1016/S0016-7878(27)80018-0.
- ↑ 7.0 7.1 7.2 Stubblefield, C. J. (12 March 1966). "The Malvern Lower Cambrian Strata". Nature 209 (5028): 1121–1121. doi:10.1038/2091121a0.
- ↑ 8.0 8.1 8.2 8.3 Matley, Charles Alfred (February 1902). "On the Cambrian Brachiopoda of the Malvern Hills". Quarterly Journal of the Geological Society of London 58 (1-4): 135–149. doi:10.1144/GSL.JGS.1902.058.01-04.11.
- ↑ Williams, Mark; Rushton, Adrian W. A.; Cook, Alan F.; Zalasiewicz, Jan; Martin, Adam P.; Condon, Daniel J.; Winrow, Paul (September 2013). "Dating the Cambrian Purley Shale Formation, Midland Microcraton, England". Geological Magazine 150 (5): 937–944. doi:10.1017/S0016756813000010.
- ↑ 10.0 10.1 Walcott, Charles D. (1902). "Cambrian Brachiopoda Acrotreta; Linnarssonella; Obolus; with descriptions of new species". Proceedings of the United States National Museum 25 (1299): 577–612. doi:10.5479/si.00963801.1299.577. https://repository.si.edu/server/api/core/bitstreams/7e4ed482-5a75-4d0b-a423-b4a910b7f9da/content.
- ↑ Cite error: Invalid
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