OR/12/032 Geology - Revision history

Ajhil: /* Charmouth Mudstone Formation */

2021-08-06T08:47:59Z

Charmouth Mudstone Formation

← Older revision		Revision as of 09:47, 6 August 2021
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	The Charmouth Mudstone reaches almost 300 m in thickness in the Worcester Basin, though 250 m may be a more usual figure. On the East Midlands Shelf, thinner successions of about 100 to 150 m are typical. Northwards from the Leicester area, it is thinner still as a result of passage of the lower beds into the upper part of the Scunthorpe Mudstone Formation, and combined overall condensation towards the Market Weighton High. The Charmouth Mudstone is made up of grey mudstone with sporadic thin bands and nodules of limestone, some of which are markedly shelly. The upper part (say 50 to 70 m) is generally slightly more silty than the lower beds, and these higher beds may contain occasional sideritic ironstone nodules and beds, particularly in the north where the Dyrham Formation is absent. In this northern area, more or less coincident with the development of the Scunthorpe Mudstone Formation, the formation was formerly known as the Brant Mudstone (Brandon et al., 1990<ref name="Brandon 1990"></ref>). It includes one or more fine sandstone beds near the base (Sandrock or Brandon Sandstone) and this part of the succession resembles equivalent beds in the upper part of the Siliceous Shale Member of the Cleveland Basin.		The Charmouth Mudstone reaches almost 300 m in thickness in the Worcester Basin, though 250 m may be a more usual figure. On the East Midlands Shelf, thinner successions of about 100 to 150 m are typical. Northwards from the Leicester area, it is thinner still as a result of passage of the lower beds into the upper part of the Scunthorpe Mudstone Formation, and combined overall condensation towards the Market Weighton High. The Charmouth Mudstone is made up of grey mudstone with sporadic thin bands and nodules of limestone, some of which are markedly shelly. The upper part (say 50 to 70 m) is generally slightly more silty than the lower beds, and these higher beds may contain occasional sideritic ironstone nodules and beds, particularly in the north where the Dyrham Formation is absent. In this northern area, more or less coincident with the development of the Scunthorpe Mudstone Formation, the formation was formerly known as the Brant Mudstone (Brandon et al., 1990<ref name="Brandon 1990"></ref>). It includes one or more fine sandstone beds near the base (Sandrock or Brandon Sandstone) and this part of the succession resembles equivalent beds in the upper part of the Siliceous Shale Member of the Cleveland Basin.

	Whilst the Charmouth Mudstone of this region has not been subdivided into members, study of boreholes, particularly downhole geophysical logs, shows a remarkably uniform internal stratigraphy throughout the region. Various more calcareous units form geophysical marker bands which are useful for correlation; these include the so-called 70 and 85 Markers indicated on Figure 2.2 (see for example Horton and Poole, 1977<ref name="Horton 1977">~~Horton~~, A, and ~~Poole~~, E G. 1977. The lithostratigraphy of three geophysical marker horizons in the Lower Lias of Oxfordshire. ''Bulletin of the Geological Survey of Great Britain'', No. 62, 13–24.</ref>; Horton et al., 1987<ref name="Horton 1987">HORTON, A, POOLE, E G, WILLIAMS, B J, ILLING, V C, and HOBSON, G D. 1987. Geology of the country around Chipping Norton. Memoir for the 1:50 000 geological sheet 218 (England and Wales). ''British Geological Survey''. HMSO, London.</ref>). At outcrop, these are seen as units of mudstone, several metres thick, bearing abundant limestone nodules, and lenticular, often very shelly limestones.		Whilst the Charmouth Mudstone of this region has not been subdivided into members, study of boreholes, particularly downhole geophysical logs, shows a remarkably uniform internal stratigraphy throughout the region. Various more calcareous units form geophysical marker bands which are useful for correlation; these include the so-called 70 and 85 Markers indicated on Figure 2.2 (see for example Horton and Poole, 1977<ref name="Horton 1977">HORTON, A, and POOLE, E G. 1977. The lithostratigraphy of three geophysical marker horizons in the Lower Lias of Oxfordshire. ''Bulletin of the Geological Survey of Great Britain'', No. 62, 13–24.</ref>; Horton et al., 1987<ref name="Horton 1987">HORTON, A, POOLE, E G, WILLIAMS, B J, ILLING, V C, and HOBSON, G D. 1987. Geology of the country around Chipping Norton. Memoir for the 1:50 000 geological sheet 218 (England and Wales). ''British Geological Survey''. HMSO, London.</ref>). At outcrop, these are seen as units of mudstone, several metres thick, bearing abundant limestone nodules, and lenticular, often very shelly limestones.

	====Dyrham Formation====		====Dyrham Formation====

Ajhil: /* Cleveland Ironstone Formation */

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Cleveland Ironstone Formation

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	====Cleveland Ironstone Formation====		====Cleveland Ironstone Formation====
	The Cleveland Ironstone is well displayed at its type section on the coast near Staithes ([NZ 788 189] to [NZ 794 183]) (Howarth, 1955<ref name="Howarth 1955">HOWARTH, M K. 1955. Domerian of the Yorkshire coast. ''Proceedings of the Yorkshire Geological Society'', Vol.30, 147–175.</ref>; 1973; Hesselbo and Jenkyns, 1995<ref name="Hesselbo 1995">HESSELBO, S P, and JENKYNS, H C. 1995. A comparison of the Hettangian to Bajocian successions of Dorset and Yorkshire. 105–150 ''In:'' Field geology of the British Jurassic. Taylor, P D (editor). ''(Bath: The Geological Society of London.)''</ref>) and also at Hawsker Bottoms [NZ 953 073] and Kettle Ness [NZ 832 161]. About 29 m thick at Staithes, it generally falls within the range 20 to 35 m throughout the Cleveland Basin, though it thins markedly towards the margins to west and south, being only a few metres thick near Thirsk. This thinning is a result of a more condensed sequence with some parts absent, notably one near the top which separates the '''Penny Nab Member''' from the succeeding '''Kettleness Member''' (Howard, 1985<ref name="Howard 1985">~~Howard~~, A S. 1985. Lithostratigraphy of the Staithes Sandstone and Cleveland Ironstone formations (Lower Jurassic) of north-east Yorkshire. ''Proceedings of the Yorkshire Geological Society'', Vol. 45, 261–275.</ref>). Whilst dominated by mudstone, argillaceous siltstone and silty sandstone, it characteristically contains beds of siderite and berthierine-rich, often somewhat nodular, ooidal ironstone which occurs at the tops of sedimentary rhythms. Where the succession is fully developed, there are six named ironstone bands, typically 0.3 to 1 m thick, the thickest and most persistent being the ‘Main Seam’ close to the top of the formation (in the Kettleness Member). The ironstone bands are best developed in the Guisborough-Loftus area near Middlesbrough, where they form up to 20 per cent of the thickness of the formation and once formed the basis of a thriving iron and steel industry ([[OR/12/032 Industrial applications #Iron \|''see'' Iron]]). There, the Main Seam, where not removed by mining, locally exceeds 3 m in thickness.		The Cleveland Ironstone is well displayed at its type section on the coast near Staithes ([NZ 788 189] to [NZ 794 183]) (Howarth, 1955<ref name="Howarth 1955">HOWARTH, M K. 1955. Domerian of the Yorkshire coast. ''Proceedings of the Yorkshire Geological Society'', Vol.30, 147–175.</ref>; 1973; Hesselbo and Jenkyns, 1995<ref name="Hesselbo 1995">HESSELBO, S P, and JENKYNS, H C. 1995. A comparison of the Hettangian to Bajocian successions of Dorset and Yorkshire. 105–150 ''In:'' Field geology of the British Jurassic. Taylor, P D (editor). ''(Bath: The Geological Society of London.)''</ref>) and also at Hawsker Bottoms [NZ 953 073] and Kettle Ness [NZ 832 161]. About 29 m thick at Staithes, it generally falls within the range 20 to 35 m throughout the Cleveland Basin, though it thins markedly towards the margins to west and south, being only a few metres thick near Thirsk. This thinning is a result of a more condensed sequence with some parts absent, notably one near the top which separates the '''Penny Nab Member''' from the succeeding '''Kettleness Member''' (Howard, 1985<ref name="Howard 1985">HOWARD, A S. 1985. Lithostratigraphy of the Staithes Sandstone and Cleveland Ironstone formations (Lower Jurassic) of north-east Yorkshire. ''Proceedings of the Yorkshire Geological Society'', Vol. 45, 261–275.</ref>). Whilst dominated by mudstone, argillaceous siltstone and silty sandstone, it characteristically contains beds of siderite and berthierine-rich, often somewhat nodular, ooidal ironstone which occurs at the tops of sedimentary rhythms. Where the succession is fully developed, there are six named ironstone bands, typically 0.3 to 1 m thick, the thickest and most persistent being the ‘Main Seam’ close to the top of the formation (in the Kettleness Member). The ironstone bands are best developed in the Guisborough-Loftus area near Middlesbrough, where they form up to 20 per cent of the thickness of the formation and once formed the basis of a thriving iron and steel industry ([[OR/12/032 Industrial applications #Iron \|''see'' Iron]]). There, the Main Seam, where not removed by mining, locally exceeds 3 m in thickness.

	The base of the formation is clearly marked by a rapid downward transition from shaly mudstone with scattered sideritic nodules to the siltstone or sandstone of the Staithes Sandstone Formation. The top is similarly readily apparent, being taken at the top of the highest ironstone bed or nodule band, which is succeeded by grey mudstone of the Whitby Mudstone Formation.		The base of the formation is clearly marked by a rapid downward transition from shaly mudstone with scattered sideritic nodules to the siltstone or sandstone of the Staithes Sandstone Formation. The top is similarly readily apparent, being taken at the top of the highest ironstone bed or nodule band, which is succeeded by grey mudstone of the Whitby Mudstone Formation.

Ajhil: /* Dyrham Formation */

2021-08-06T08:46:58Z

Dyrham Formation

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	====Dyrham Formation====		====Dyrham Formation====
	The Worcester Basin is the type area of this unit, named after the village of Dyrham [ST 741 758], to the east of Bristol (Kellaway, 1960<ref name="Kellaway 1960">~~Kellaway~~, G A. 1960. 1:10 560 Geological Sheet ST 67 SE. Geological Survey of Great Britain (England and Wales).</ref>). It tends to form moderately steep slopes of an escarpment capped by the Marlstone Rock Formation. It is typically about 40 to 60 m thick in the Basin, though seldom more than 30 m thick on the Shelf. It can be traced as far north as the Grantham area, beyond which its characteristic sandy and silty lithologies do not appear to be developed and equivalent strata are included in the Charmouth Mudstone (Figure 2.2).		The Worcester Basin is the type area of this unit, named after the village of Dyrham [ST 741 758], to the east of Bristol (Kellaway, 1960<ref name="Kellaway 1960">KELLAWAY, G A. 1960. 1:10 560 Geological Sheet ST 67 SE. Geological Survey of Great Britain (England and Wales).</ref>). It tends to form moderately steep slopes of an escarpment capped by the Marlstone Rock Formation. It is typically about 40 to 60 m thick in the Basin, though seldom more than 30 m thick on the Shelf. It can be traced as far north as the Grantham area, beyond which its characteristic sandy and silty lithologies do not appear to be developed and equivalent strata are included in the Charmouth Mudstone (Figure 2.2).

	Overall, the succession is less sandy than in the Wessex Basin, being dominated by more or less silty, often finely micaceous mudstones which weather to a pale bluish grey, ochreous mottled clay. These beds were once favoured for brick making and there are several large, disused brickpits along the outcrop including the type section at Robin’s Wood Hill, near Gloucester, Gloucestershire [SO 836 149] (Ager, 1956<ref name="Ager 1956">AGER, D V. 1956. Field meeting in the central Cotswolds. ''Proceedings of the Geologists' Association'', Vol. 66, 356–365.</ref>, 1969<ref name="Ager 1969">AGER, D V. 1969. Cotswolds and Vale of Gloucester. B27-B43 in TORRENS, H S (editor) ''International Field Symposium on the British Jurassic''. Excursion No. 2 Guide for north Somerset and Gloucestershire. (Keele: Geology Department, Keele University).</ref>). Typically, the Dyrham Formation contains beds of fine-grained sand, which may be cemented into quite hard massive sandstones. These include the Subnodosus Sandstone, up to 1.5 m thick, which occurs near the top of the succession in the Gloucester to Moreton-in-Marsh area of the Cotswolds. The Capricornus Sandstone is a convenient marker for the base of the formation in this Cotswolds area, but where the sandstone is not well developed; the base of formation is gradational and hard to define.		Overall, the succession is less sandy than in the Wessex Basin, being dominated by more or less silty, often finely micaceous mudstones which weather to a pale bluish grey, ochreous mottled clay. These beds were once favoured for brick making and there are several large, disused brickpits along the outcrop including the type section at Robin’s Wood Hill, near Gloucester, Gloucestershire [SO 836 149] (Ager, 1956<ref name="Ager 1956">AGER, D V. 1956. Field meeting in the central Cotswolds. ''Proceedings of the Geologists' Association'', Vol. 66, 356–365.</ref>, 1969<ref name="Ager 1969">AGER, D V. 1969. Cotswolds and Vale of Gloucester. B27-B43 in TORRENS, H S (editor) ''International Field Symposium on the British Jurassic''. Excursion No. 2 Guide for north Somerset and Gloucestershire. (Keele: Geology Department, Keele University).</ref>). Typically, the Dyrham Formation contains beds of fine-grained sand, which may be cemented into quite hard massive sandstones. These include the Subnodosus Sandstone, up to 1.5 m thick, which occurs near the top of the succession in the Gloucester to Moreton-in-Marsh area of the Cotswolds. The Capricornus Sandstone is a convenient marker for the base of the formation in this Cotswolds area, but where the sandstone is not well developed; the base of formation is gradational and hard to define.

Ajhil: /* Dyrham Formation */

2021-08-06T08:46:39Z

Dyrham Formation

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	The Worcester Basin is the type area of this unit, named after the village of Dyrham [ST 741 758], to the east of Bristol (Kellaway, 1960<ref name="Kellaway 1960">Kellaway, G A. 1960. 1:10 560 Geological Sheet ST 67 SE. Geological Survey of Great Britain (England and Wales).</ref>). It tends to form moderately steep slopes of an escarpment capped by the Marlstone Rock Formation. It is typically about 40 to 60 m thick in the Basin, though seldom more than 30 m thick on the Shelf. It can be traced as far north as the Grantham area, beyond which its characteristic sandy and silty lithologies do not appear to be developed and equivalent strata are included in the Charmouth Mudstone (Figure 2.2).		The Worcester Basin is the type area of this unit, named after the village of Dyrham [ST 741 758], to the east of Bristol (Kellaway, 1960<ref name="Kellaway 1960">Kellaway, G A. 1960. 1:10 560 Geological Sheet ST 67 SE. Geological Survey of Great Britain (England and Wales).</ref>). It tends to form moderately steep slopes of an escarpment capped by the Marlstone Rock Formation. It is typically about 40 to 60 m thick in the Basin, though seldom more than 30 m thick on the Shelf. It can be traced as far north as the Grantham area, beyond which its characteristic sandy and silty lithologies do not appear to be developed and equivalent strata are included in the Charmouth Mudstone (Figure 2.2).

	Overall, the succession is less sandy than in the Wessex Basin, being dominated by more or less silty, often finely micaceous mudstones which weather to a pale bluish grey, ochreous mottled clay. These beds were once favoured for brick making and there are several large, disused brickpits along the outcrop including the type section at Robin’s Wood Hill, near Gloucester, Gloucestershire [SO 836 149] (Ager, 1956<ref name="Ager 1956">AGER, D V. 1956. Field meeting in the central Cotswolds. ''Proceedings of the Geologists' Association'', Vol. 66, 356–365.</ref>, 1969<ref name="Ager 1969">~~Ager~~, D V. 1969. Cotswolds and Vale of Gloucester. B27-B43 in TORRENS, H S (editor) ''International Field Symposium on the British Jurassic''. Excursion No. 2 Guide for north Somerset and Gloucestershire. (Keele: Geology Department, Keele University).</ref>). Typically, the Dyrham Formation contains beds of fine-grained sand, which may be cemented into quite hard massive sandstones. These include the Subnodosus Sandstone, up to 1.5 m thick, which occurs near the top of the succession in the Gloucester to Moreton-in-Marsh area of the Cotswolds. The Capricornus Sandstone is a convenient marker for the base of the formation in this Cotswolds area, but where the sandstone is not well developed; the base of formation is gradational and hard to define.		Overall, the succession is less sandy than in the Wessex Basin, being dominated by more or less silty, often finely micaceous mudstones which weather to a pale bluish grey, ochreous mottled clay. These beds were once favoured for brick making and there are several large, disused brickpits along the outcrop including the type section at Robin’s Wood Hill, near Gloucester, Gloucestershire [SO 836 149] (Ager, 1956<ref name="Ager 1956">AGER, D V. 1956. Field meeting in the central Cotswolds. ''Proceedings of the Geologists' Association'', Vol. 66, 356–365.</ref>, 1969<ref name="Ager 1969">AGER, D V. 1969. Cotswolds and Vale of Gloucester. B27-B43 in TORRENS, H S (editor) ''International Field Symposium on the British Jurassic''. Excursion No. 2 Guide for north Somerset and Gloucestershire. (Keele: Geology Department, Keele University).</ref>). Typically, the Dyrham Formation contains beds of fine-grained sand, which may be cemented into quite hard massive sandstones. These include the Subnodosus Sandstone, up to 1.5 m thick, which occurs near the top of the succession in the Gloucester to Moreton-in-Marsh area of the Cotswolds. The Capricornus Sandstone is a convenient marker for the base of the formation in this Cotswolds area, but where the sandstone is not well developed; the base of formation is gradational and hard to define.

	====Marlstone Rock Formation====		====Marlstone Rock Formation====

Ajhil: /* Marlstone Rock Formation */

2021-08-06T08:46:22Z

Marlstone Rock Formation

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	The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.		The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.

	The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">~~Hallam~~, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991).</ref>.		The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">HALLAM, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991).</ref>.

	The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.		The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.

Ajhil: /* Marlstone Rock Formation */

2021-08-06T08:45:20Z

Marlstone Rock Formation

← Older revision		Revision as of 09:45, 6 August 2021
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	The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.		The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.

	The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">Hallam, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991).</ref>		The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">Hallam, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991).</ref>.

	The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.		The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.

Ajhil: /* Marlstone Rock Formation */

2021-08-06T08:45:00Z

Marlstone Rock Formation

← Older revision		Revision as of 09:45, 6 August 2021
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	The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.		The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.

	The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">Hallam, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991)</ref>.		The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">Hallam, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991).</ref>

	The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.		The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.

Ajhil: /* Marlstone Rock Formation */

2021-08-06T08:44:12Z

Marlstone Rock Formation

← Older revision		Revision as of 09:44, 6 August 2021
Line 765:		Line 765:
	The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.		The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.

	The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">Hallam, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991).</ref>		The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">Hallam, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991)</ref>.

	The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.		The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.

Ajhil: /* Marlstone Rock Formation */

2021-08-06T08:43:45Z

Marlstone Rock Formation

← Older revision		Revision as of 09:43, 6 August 2021
Line 765:		Line 765:
	The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.		The Marlstone Rock Formation is restricted to this region, although a condensed representative is present as a member of the Beacon Limestone Formation in the Mendips and Wessex Basin areas. The Marlstone Rock is generally some 2 to 4 m in thickness and reaches a maximum of 7.5 m near Banbury. Up to 10 m are reported locally in Leicestershire, but this figure includes the so-called ‘Sandrock’ developed in much of the Midlands, which is a sandstone that strictly belongs to the Dyrham Formation (see above) but was not formerly mapped separately from the Marlstone Rock proper. The Marlstone Rock typically caps a prominent escarpment throughout the region, often forming an extensive shelf like dip-slope.

	The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">Hallam, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.) </ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1.</ref>		The Marlstone Rock is typically a more or less sandy, shell-fragmental, siderite and berthierine- bearing ooidal limestone, with calcareous sandstone and mudstone partings. It is commonly highly fossiliferous, particularly with belemnites and brachiopods (''Lobothyris'' and ''Tetrarhynchia''). In the Worcester Basin the formation is not generally especially ferruginous and may appear as a greenish-grey sandstone. However, on the Shelf, the iron concentration reaches 20 to 25% and the rock weathers to a rust-brown limonitic ironstone. This was formerly worked for iron ore particularly in the Banbury area and in Leicestershire and can still be seen in abandoned quarries in these areas and also at the type section, Tilton railway cutting, east of Leicester [SK 762 055] (Hallam, 1955<ref name="Hallam 1955">Hallam, A. 1955. The palaeontology and stratigraphy of the Marlstone Rock-bed in Leicestershire. ''Transactions of the Leicester Literary and Philosophical Society''. Vol. 49, 17–35. </ref>, 1968<ref name="Hallam 1968">HALLAM, A. 1968. The Lias. 188–210 in ''The geology of the East Midlands''. Sylvester-Bradley, P C, and Ford, T D (editors). (Leicester: Leicester University Press.)</ref>; Howarth, 1980c<ref name="Howarth 1980c">HOWARTH, M K. 1980c. The Toarcian age of the upper part of the Marlstone Rock Bed of England. ''Palaeontology'', Vol. 23, 637–656.</ref>, 1992<ref name="HOWARTH 1992">HOWARTH, M K. 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. ''Monograph of the Palaeontographical Society London'': 1–106, pls 1–16. (Publ. No. 586, part of vol. 145 for 1991).</ref>

	The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.		The base of the Marlstone proper is an erosive non-sequence, and the basal bed is commonly conglomeratic enabling its identification in sections where the ‘Sandrock’ facies is present (e.g. in the type section). The top is also generally erosive, with mudstones or limestones of the Whitby Mudstone resting sharply on it.

Ajhil: /* Cleveland Ironstone Formation */

2021-08-06T08:41:52Z

Cleveland Ironstone Formation

← Older revision		Revision as of 09:41, 6 August 2021
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	====Cleveland Ironstone Formation====		====Cleveland Ironstone Formation====
	The Cleveland Ironstone is well displayed at its type section on the coast near Staithes ([NZ 788 189] to [NZ 794 183]) (Howarth, 1955<ref name="Howarth 1955">HOWARTH, M K. 1955. Domerian of the Yorkshire coast. ''Proceedings of the Yorkshire Geological Society'', Vol.30, 147–175.</ref>; 1973; Hesselbo and Jenkyns, 1995<ref name="Hesselbo 1995">HESSELBO, S P, and JENKYNS, H C. 1995. A comparison of the Hettangian to Bajocian successions of Dorset and Yorkshire. ~~105-150~~ In: Field geology of the British Jurassic. Taylor, P D (editor). ''(Bath: The Geological Society of London.)''</ref>) and also at Hawsker Bottoms [NZ 953 073] and Kettle Ness [NZ 832 161]. About 29 m thick at Staithes, it generally falls within the range 20 to 35 m throughout the Cleveland Basin, though it thins markedly towards the margins to west and south, being only a few metres thick near Thirsk. This thinning is a result of a more condensed sequence with some parts absent, notably one near the top which separates the '''Penny Nab Member''' from the succeeding '''Kettleness Member''' (Howard, 1985<ref name="Howard 1985">Howard, A S. 1985. Lithostratigraphy of the Staithes Sandstone and Cleveland Ironstone formations (Lower Jurassic) of north-east Yorkshire. ''Proceedings of the Yorkshire Geological Society'', Vol. 45, 261–275.</ref>). Whilst dominated by mudstone, argillaceous siltstone and silty sandstone, it characteristically contains beds of siderite and berthierine-rich, often somewhat nodular, ooidal ironstone which occurs at the tops of sedimentary rhythms. Where the succession is fully developed, there are six named ironstone bands, typically 0.3 to 1 m thick, the thickest and most persistent being the ‘Main Seam’ close to the top of the formation (in the Kettleness Member). The ironstone bands are best developed in the Guisborough-Loftus area near Middlesbrough, where they form up to 20 per cent of the thickness of the formation and once formed the basis of a thriving iron and steel industry ([[OR/12/032 Industrial applications #Iron \|''see'' Iron]]). There, the Main Seam, where not removed by mining, locally exceeds 3 m in thickness.		The Cleveland Ironstone is well displayed at its type section on the coast near Staithes ([NZ 788 189] to [NZ 794 183]) (Howarth, 1955<ref name="Howarth 1955">HOWARTH, M K. 1955. Domerian of the Yorkshire coast. ''Proceedings of the Yorkshire Geological Society'', Vol.30, 147–175.</ref>; 1973; Hesselbo and Jenkyns, 1995<ref name="Hesselbo 1995">HESSELBO, S P, and JENKYNS, H C. 1995. A comparison of the Hettangian to Bajocian successions of Dorset and Yorkshire. 105–150 ''In:'' Field geology of the British Jurassic. Taylor, P D (editor). ''(Bath: The Geological Society of London.)''</ref>) and also at Hawsker Bottoms [NZ 953 073] and Kettle Ness [NZ 832 161]. About 29 m thick at Staithes, it generally falls within the range 20 to 35 m throughout the Cleveland Basin, though it thins markedly towards the margins to west and south, being only a few metres thick near Thirsk. This thinning is a result of a more condensed sequence with some parts absent, notably one near the top which separates the '''Penny Nab Member''' from the succeeding '''Kettleness Member''' (Howard, 1985<ref name="Howard 1985">Howard, A S. 1985. Lithostratigraphy of the Staithes Sandstone and Cleveland Ironstone formations (Lower Jurassic) of north-east Yorkshire. ''Proceedings of the Yorkshire Geological Society'', Vol. 45, 261–275.</ref>). Whilst dominated by mudstone, argillaceous siltstone and silty sandstone, it characteristically contains beds of siderite and berthierine-rich, often somewhat nodular, ooidal ironstone which occurs at the tops of sedimentary rhythms. Where the succession is fully developed, there are six named ironstone bands, typically 0.3 to 1 m thick, the thickest and most persistent being the ‘Main Seam’ close to the top of the formation (in the Kettleness Member). The ironstone bands are best developed in the Guisborough-Loftus area near Middlesbrough, where they form up to 20 per cent of the thickness of the formation and once formed the basis of a thriving iron and steel industry ([[OR/12/032 Industrial applications #Iron \|''see'' Iron]]). There, the Main Seam, where not removed by mining, locally exceeds 3 m in thickness.

	The base of the formation is clearly marked by a rapid downward transition from shaly mudstone with scattered sideritic nodules to the siltstone or sandstone of the Staithes Sandstone Formation. The top is similarly readily apparent, being taken at the top of the highest ironstone bed or nodule band, which is succeeded by grey mudstone of the Whitby Mudstone Formation.		The base of the formation is clearly marked by a rapid downward transition from shaly mudstone with scattered sideritic nodules to the siltstone or sandstone of the Staithes Sandstone Formation. The top is similarly readily apparent, being taken at the top of the highest ironstone bed or nodule band, which is succeeded by grey mudstone of the Whitby Mudstone Formation.