British Lower Palaeozoic black shales and their palaeo-oceanographic significance

ABSTRACTSediments, mainly sandstones, conglomerates and shales, accumulated in small turbidite fans along the northern arc–trench margin of the Iapetus Ocean from middle Ordovician to Silurian time. These fans, together with the underlying pelagic facies and part of the oceanic crust, were sliced and accreted northward resulting in the Lower Palaeozoic accretionary prism which forms the Scottish Southern Uplands and the Longford-Down inlier in Ireland. North Down is the continuation of the Northern belt of the Southern Uplands of Scotland into Ireland, bounded to the S by the Orlock Bridge fault. Lithological and petrographical comparison with the rest of the Northern belt indicates closer affinities with the Southern Uplands of Scotland than with the western end of the Longford-Down inlier. Major ENE—WSW-trending Caledonian strike faults define five blocks, in which new formations of Caradoc and ? Ashgill age are defined. Pillowed spilitic rock, interpreted as a fragment of the ocean-floor, is only recognised in the Ballygrot block. Pelagic and hemipelagic black shales and cherts are overlain by arenaceous sediments in all blocks.

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Shale gas investigations in Denmark: Lower Palaeozoic shales on Bornholm

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/geusb.v23.4794 ◽

1969 ◽

Vol 23 ◽

pp. 9-12 ◽

Cited By ~ 11

Author(s):

Niels Hemmingsen Schovsbo ◽

Arne Thorshøj Nielsen ◽

Kurt Klitten ◽

Anders Mathiesen ◽

Per Rasmussen

Keyword(s):

Shale Gas ◽

Black Shales ◽

Rock Properties ◽

Groundwater Exploitation ◽

Lower Silurian ◽

Gas Source ◽

Alum Shale ◽

Lower Palaeozoic ◽

Global Sea Level ◽

Deep Exploration

The Cambrian to Lower Silurian succession in Denmark is mostly composed of organic-rich black shales that were deposited in an epicontinental sea during a period of high global sea level (Haq & Schutter 2008). The mid-Cambrian to early Ordovician Alum Shale was intensively studied in the 1980s for its source-rock properties (e.g. Buchardt et al. 1986). Recent attention has focused on its potential as an unconventional shale gas source (Energistyrelsen 2010). On southern Bornholm, many wells have been drilled through the Lower Palaeozoic succession because of its importance for groundwater exploitation. In western Denmark, only the deep exploration wells Slagelse-1 and Terne-1 have penetrated the Alum Shale, and knowledge of the unit west of Bornholm is thus very limited (Fig. 1).

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Mineralogical and hydrogeological study of "pouhons" in the lower Palaeozoic formations of the Stavelot-Venn Massif, Belgium

Geologica Belgica ◽

10.20341/gb.2021.001 ◽

2021 ◽

Vol 24 (3-4) ◽

pp. 109-124

Author(s):

Martin DEPRET ◽

Yannick BRUNI ◽

Alain DASSARGUES ◽

Agathe DEFOURNY ◽

Jean-Marc MARION ◽

...

Keyword(s):

Land Surface ◽

Iron Hydroxide ◽

Black Shales ◽

Surface Circulation ◽

Hydrogeological Study ◽

Orange Colour ◽

Lower Palaeozoic ◽

Water Springs ◽

Radon Measurements ◽

Iron Manganese

Numerous naturally CO2-rich mineral water springs, locally called pouhons, occur in the Stavelot-Venn Massif. These water springs show a particular composition with a high content of iron, manganese and lithium, and are characterised by a red-orange colour resulting from iron hydroxide precipitation near the land surface. Radon measurements have shown that these ferruginous deposits are weakly radioactive. The Upper Cambrian black shales of the La Gleize Formation are also known to display radioactive anomalies. These rocks show enrichment in HFSE (Pb, U, Y, Ce, Zr, Ti, Nb) and are depleted in transition metals (Co, Ni, Cu, Zn). Specific minerals such as florencite-(Ce), monazite-(Ce), xenotime-(Y) and zircon have been identified and are probably at the origin of the radioactive anomalies. Uranium was gradually leached from these minerals, transported in solution, and finally concentrated in ferruginous muds. These muds are mainly composed of goethite (most often amorphous), residual quartz and calcite in some samples. The most probable hypothesis is that uranium is adsorbed in small concentrations on the goethite surface. On the other hand, the Ottré Formation (Ordovician) appears to be the main source of lithium, iron and manganese. Pouhon waters have therefore probably leached rocks of various mineralogy and chemical composition during their sub-surface circulation.

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Ordovician turbidites and black shales of Bennett Island (De Long Islands, Russian Arctic), and their significance for Arctic correlations and palaeogeography

Geological Magazine ◽

10.1017/s0016756819001341 ◽

2020 ◽

Vol 157 (8) ◽

pp. 1207-1237

Author(s):

Maria K. Danukalova ◽

Alexander B. Kuzmichev ◽

Nikolai V. Sennikov ◽

Tatiana Yu. Tolmacheva

Keyword(s):

Carbonate Platform ◽

Black Shales ◽

The Arctic ◽

New Siberian Islands ◽

Faunal Assemblages ◽

Lower Palaeozoic ◽

Early Palaeozoic ◽

First Time ◽

Remote Part ◽

Siberian Shelf

AbstractBennett Island stands alone in a remote part of the Arctic and information on its geology is essential to ascertain relations with other terranes in order to restore the early Palaeozoic Arctic palaeogeography. Lower Palaeozoic sedimentary rocks throughout the island were studied thoroughly for the first time. The Ordovician section (> 1.1 km thick) comprises three units: Tremadocian, lowest Floian black shale (130–140 m); Floian, lower Dapingian carbonate turbidite (> 250 m); and Dapingian, lower Darriwilian siliciclastic turbidite (> 730 m). Ordovician deposits conformably overlie Cambrian rocks deposited within the Siberian shelf, as shown earlier. Most of the Ordovician succession was formed in a deep trough that received carbonate debris from a nearby carbonate platform and silicate material from a distant landmass located to the NE (present coordinates). The Bennett Island Ordovician rocks have much in common with those of both the Central and Northern Taimyr belts. It could be tentatively suggested that both belts merged at their eastern continuation in the vicinity of De Long Islands. The whole system probably extends further eastwards. The Ordovician facies patterns and faunal assemblages in the New Siberian Islands are notably similar to those of northwestern Alaska, where the same lateral transition from turbidites to shelf limestones was reported.

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The sedimentology of Lower Palaeozoic black shales from the shallow wells Skelbro 1 and Billegrav 1, Bomholm, Denmark

Bulletin of the Geological Society of Denmark ◽

10.37570/bgsd-1988-37-13 ◽

1989 ◽

Vol 37 ◽

pp. 151-173

Author(s):

Gunver Krarup, Pedersen

Keyword(s):

Gamma Ray ◽

Average Rate ◽

Sedimentary Facies ◽

Black Shales ◽

Low Energy ◽

Upper Ordovician ◽

Middle Cambrian ◽

Facies Associations ◽

Shallow Wells ◽

Lower Palaeozoic

Previous studies of the Lower Palaeozoic shales on Bornholm have mainly been based on the outcrops along the streams. The outcrops provide data on the lateral continuity of the facies while the selection of (2-3 cm wide) cores for the present study focused the attention on the vertical sequence of facies. Cores of high quality were obtained and have been found to provide an excellent basis for a study of structures, sediment composition and diagenesis. In the outcrops of shale fossils are locally present in high numbers and such levels are also recognized in the cores. Seven sedimentary facies, ranging from black mudshale to greyish mudstone and silt-streaked shale, are distinguished in the Middle Cambrian to lowermost Silurian shales. Gamma-ray logs were run in the two wells and a convincing correlation to the cored sequence can be demonstrated. Gamma-ray logs provide thus a good means of correlation to wells where no cores have been cut. The shales are all interpreted as deposited in an epicontinental sea due to their geological setting i.e. the association with shallow water carbonates (Andrarum Limestone and Komstad Limestone) and their stratigraphical position above the shelf to shoreface sandstones of the Lresa formation. Three facies associations are distinguished: The mudshale association comprises black organic-rich shales which represent a low-energy anoxic depositional environment which prevailed in the Middle Cambrian to Lower Ordovician. The mudstone association is typical of the Middle and Upper Ordovician and represents a continuation of low-energy environments though mottling indicates that ventilation improved in certain periods. The siltshale association represents higher energy environments which were dominant in the lowermost Silurian. A well defined Upper Ordovician CU sequence probably reflects the global eustatic fall in sea level caused by the extensive glaciation in Gondwanaland. In the late Silurian the average rate of deposition increased in response to the approaching Caledonian orogeny.

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