OR/14/029 Assumptions, geological rules and limitations - Revision history

Dbk: /* Model images */

2015-03-11T16:16:30Z

Model images

← Older revision		Revision as of 17:16, 11 March 2015
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	==Model images==		==Model images==
	Figures 11 and 12 show views of the units as modelled in GSI3D.		Figures 11 and 12 show views of the units as modelled in GSI3D.
	[[Image:029_fig11.jpg\|thumb\|center\|600px\|The bedrock units to the base of the Chalk (in green) as modelled in GSI3D, viewed from the southwest. The legend is shown in Figure 2.]]		[[Image:029_fig11.jpg\|thumb\|center\|600px\|'''Figure 11''' The bedrock units to the base of the Chalk (in green) as modelled in GSI3D, viewed from the southwest. The legend is shown in Figure 2.]]

	[[Image:029_fig12.jpg\|thumb\|center\|600px\|The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]		[[Image:029_fig12.jpg\|thumb\|center\|600px\|'''Figure 12''' The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]


	[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 06]]		[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 06]]

Dbk: Protected "OR/14/029 Assumptions, geological rules and limitations" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)) [cascading]

2015-03-11T15:41:39Z

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Dbk at 09:24, 10 March 2015

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			{{Template:OR/14/029}}
	__NOTOC__		__NOTOC__
	==Assumptions, geological rules and limitations==		==Assumptions, geological rules and limitations==

Dbk at 12:34, 9 March 2015

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	[[Image:029_fig12.jpg\|thumb\|center\|600px\|The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]		[[Image:029_fig12.jpg\|thumb\|center\|600px\|The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]

	~~= name="_TOC_250005"8 Uncertainty =~~

	~~The model is not easy to assess in terms of uncertainty because the borehole data, reference material and geological knowledge that went into the model are difficult to represent. The~~
	~~</div> <br clear="all">~~

	borehole data used in the model is displayed in Figure 6. However, whilst showing the distribution and density of boreholes, this does not convey the depth of the borehole, the quality of the log itself or the reliability of the borehole coding.

	~~= name="_TOC_250004"Glossary =~~

	''BGS Lexicon ''The Lexicon of Named Rock Units is a list of geological units that appear on all BGS geological maps, with details on their lithologies. This is accessible via the BGS website at[http://www.bgs.ac.uk/Lexicon : http://www.bgs.ac.uk/Lexicon]



	''Bid file ''GSI3D borehole identity file derived from the SOBI database (see below), which stores the locations of boreholes as eastings, northings and start heights



	~~''Blg file ''GSI3D borehole log file, which stores the interpretation downloaded from the Borehole Geology database~~



	~~''BoGe ''BGS Borehole Geology database for the standardised entry of data recorded on borehole logs~~



	~~''DiGMapGB-50 ''Digital 1:50 000 geological map data~~



	''DTM ''Digital Terrain Model – a model of surface of the solid Earth (generally the boundary between geosphere and atmosphere or hydrosphere). This is traditionally derived from OS contours and spot heights and should therefore exclude all buildings, trees, hedges, crops, animals etc. Sometimes also referred to as a ‘bald earth’ model



	~~''Envelope ''Defined here as the extent, or coverage, of a geological unit in plan view, forming a 2D distribution map of the particular unit, or presence/absence map~~



	~~''Fence ''''Diagram ''The completed framework of cross-sections~~



	~~''GDI ''Geoscience Data Index, an ArcGIS platform for displaying BGS data, including boreholes, with links to scans, and geological map polygons~~



	~~''Georeferenced ''ArcGIS process where a scanned image is registered to British National Grid~~



	~~''GOCAD''''® ''3d geological modelling package utilised mainly for bedrock modelling.~~



	~~GOCAD® Consortium web site: [http://www.gocad.org/w4/index.php/consortium/consortium http://www.gocad.org/w4/index.php/consortium/consortium]~~



	''GSI3D ''Geological Surveying and Investigation in 3D, a geoscience modelling software package. GSI3D Research Consortium web site: [http://www.gsi3d.org.uk/ http://www.gsi3d.org.uk]



	''SOBI ''Single Onshore Borehole Index, a database where location details of borehole logs are stored, giving positional information in x, y and z with respect to British National Grid



	~~''TIN ''Triangular Irregular Network – a digital elevation surface with triangle- shaped cells, rather than grid squares~~

	[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 06]]		[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 06]]

Dbk: /* name="_TOC_250006"model */

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name="_TOC_250006"model

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	[[Image:029_fig12.jpg\|thumb\|center\|600px\|The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]		[[Image:029_fig12.jpg\|thumb\|center\|600px\|The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]

	~~= name="_TOC_250006"model =~~

	A rockhead elevation surface derived from the combined base of all modelled superficial and artificial units has an elevation range of +254.87m OD to -25.24m OD (Figure 13). This rockhead elevation surface has a cell size of 100m and caps the bedrock part of the geological model. It was generated by calculating in GSI3D using the complete superficial and anthropocene model on a tile by tile basis, buffering each area by 200m to ensure a small overlap. The resulting rockhead surfaces were combined into the single surface in GIS. Where modelled anthropocene and/or superficial deposits are absent, this rockhead elevation surface corresponds to the Digital Terrain Model. This surface was calaculated in GSi3D and exported



	~~to GOCAD''®'''' ''in order to cap the model of the faulted bedrock units.~~















	~~[[File:.jpg\|517px]]'''Rockhead'''''' ''''''elevation (m)'''~~

	~~<p align="right">[[File:.png\|29px]]254.87</p>~~















	~~<p align="right">-25.24</p>~~





















	'''Figure 13. 3D view of the calculated rockhead elevation surface calculated as an ascii grid with a 100m cell size. The highest elevations are in red and the lowest in blue, vertical exaggeration is x 10.'''



	~~''' '''~~



	~~''' '''~~

	= name="_TOC_250005"8 Uncertainty =		= name="_TOC_250005"8 Uncertainty =

Dbk: /* =Model images */

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=Model images

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	The given methodology for attributing subcrop lines with z-coordinates means that the resolution of the DTM surface is propagated into the subsurface		The given methodology for attributing subcrop lines with z-coordinates means that the resolution of the DTM surface is propagated into the subsurface

	==Model images=		==Model images==
	Figures 11 and 12 show views of the units as modelled in GSI3D.		Figures 11 and 12 show views of the units as modelled in GSI3D.
	[[Image:029_fig11.jpg\|thumb\|center\|600px\|The bedrock units to the base of the Chalk (in green) as modelled in GSI3D, viewed from the southwest. The legend is shown in Figure 2.]]		[[Image:029_fig11.jpg\|thumb\|center\|600px\|The bedrock units to the base of the Chalk (in green) as modelled in GSI3D, viewed from the southwest. The legend is shown in Figure 2.]]

Dbk at 12:30, 9 March 2015

2015-03-09T12:30:20Z

← Older revision		Revision as of 13:30, 9 March 2015
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			__NOTOC__
	==Assumptions, geological rules and limitations==		==Assumptions, geological rules and limitations==
	===Assumptions and rules===		===Assumptions and rules===

Dbk: /* =Model images */

2015-03-09T12:29:21Z

=Model images

← Older revision		Revision as of 13:29, 9 March 2015
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	[[Image:029_fig12.jpg\|thumb\|center\|600px\|The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]		[[Image:029_fig12.jpg\|thumb\|center\|600px\|The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]


	= name="_TOC_250006"model =		= name="_TOC_250006"model =

Dbk at 12:28, 9 March 2015

2015-03-09T12:28:53Z

← Older revision		Revision as of 13:28, 9 March 2015
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	~~<div> name~~=~~"_TOC_250009"~~		==Assumptions, geological rules and limitations==
			===Assumptions and rules===
	Wherever possible, the model matches the corresponding 1:50 000 scale geological map sheets. However, where mismatches occur between the interpretation of boreholes and the geological mapping, the borehole have been used in preference. Therefore, the vast majority of the model matches DiGMapGB-50, but with minor amendments, these have not been carried over into an updated DiGMapGB-50 version at this stage. The most significant changes are to the pattern of subcrop of the bedrock units at rockhead.		Wherever possible, the model matches the corresponding 1:50 000 scale geological map sheets. However, where mismatches occur between the interpretation of boreholes and the geological mapping, the borehole have been used in preference. Therefore, the vast majority of the model matches DiGMapGB-50, but with minor amendments, these have not been carried over into an updated DiGMapGB-50 version at this stage. The most significant changes are to the pattern of subcrop of the bedrock units at rockhead.



	As described above the artificial ground units were updated specifically for the model and have not been incorporated into the released version of DiGMapGB-50 at present. This was carried out as a desk study using modern Ordnance Survey topographic maps and aerial photographs, with emphasis given to cuttings and embankments along major transport routes. Backfilled workings are not included, unless indicated on the relevant published geological maps.		As described above the artificial ground units were updated specifically for the model and have not been incorporated into the released version of DiGMapGB-50 at present. This was carried out as a desk study using modern Ordnance Survey topographic maps and aerial photographs, with emphasis given to cuttings and embankments along major transport routes. Backfilled workings are not included, unless indicated on the relevant published geological maps.



	Sub-alluvial gravel is modelled beneath river alluvium as a separate geological unit wherever it is identified in boreholes. This gravel is modelled as River Terrace Deposits Undivided (rtdu) in the majority of the model, as in most areas it is uncertain which river terrace gravel occurs beneath the alluvium. The sub-alluvial gravel is modelled as Shepperton Gravel Member (shgr), the very lowest terrace in the sequence in areas where it crops out adjacent to the modern floodplain alluvium.		Sub-alluvial gravel is modelled beneath river alluvium as a separate geological unit wherever it is identified in boreholes. This gravel is modelled as River Terrace Deposits Undivided (rtdu) in the majority of the model, as in most areas it is uncertain which river terrace gravel occurs beneath the alluvium. The sub-alluvial gravel is modelled as Shepperton Gravel Member (shgr), the very lowest terrace in the sequence in areas where it crops out adjacent to the modern floodplain alluvium.



	Tidal River or Creek Deposits (trd) are mapped as a thin strip on each side of the River Thames and its tributaries from easting 539980 (around Silvertown) downstream to easting 568570 (Tilbury Marshes). These tidal deposits have not been differentiated from alluvium in this model, due to the close similarity in their lithologies and the gradational nature of their relationship.		Tidal River or Creek Deposits (trd) are mapped as a thin strip on each side of the River Thames and its tributaries from easting 539980 (around Silvertown) downstream to easting 568570 (Tilbury Marshes). These tidal deposits have not been differentiated from alluvium in this model, due to the close similarity in their lithologies and the gradational nature of their relationship.

	== ~~name~~=~~"_TOC_250008"~~ ==		===Model limitations===

	Whilst every effort has been made to ensure accuracy, with the model constructed using a framework of cross-sections according to standard GSI3D workflow and procedures, not every available borehole was used in the model. Some variation may therefore occur between the depth of units modelled and depths recorded in boreholes that do not occur in the sections.		Whilst every effort has been made to ensure accuracy, with the model constructed using a framework of cross-sections according to standard GSI3D workflow and procedures, not every available borehole was used in the model. Some variation may therefore occur between the depth of units modelled and depths recorded in boreholes that do not occur in the sections.

			Where mismatches in the geological linework occur at 1:50 000 scale geological sheet boundaries, precedence is given to the most recently surveyed sheet, with the older linework adjusted to the newer version. Current BGS Lexicon codes are used in the model whereas DiGMapGB-50 data uses some older nomenclature. Artificial ground, mass movement deposits (landslide deposits), tufa and head are drawn in the cross-sections, but are excluded from the final model volume calculation because the cross- sections alone provide insufficient information to calculate these units due to their complex distribution, size and shape.

	Where mismatches in the geological linework occur at 1:50 000 scale geological sheet boundaries, precedence is given to the most recently surveyed sheet, with the older linework adjusted to the newer version. Current BGS Lexicon codes are used in the model whereas DiGMapGB-50 data uses some older nomenclature.
	~~</div> <br clear="all"> <div>~~
	Artificial ground, mass movement deposits (landslide deposits), tufa and head are drawn in the cross-sections, but are excluded from the final model volume calculation because the cross- sections alone provide insufficient information to calculate these units due to their complex distribution, size and shape.



	This model is intended for use at around 1:50 000 resolution, in line with the corresponding DiGMapGB-50 geological map data, and is not recommended for site specific use.		This model is intended for use at around 1:50 000 resolution, in line with the corresponding DiGMapGB-50 geological map data, and is not recommended for site specific use.



	The throw along modelled faults is often very small and may show undue ‘waviness’. The underlying reason for this is lack of data to support placing a fault at the modelled location.		The throw along modelled faults is often very small and may show undue ‘waviness’. The underlying reason for this is lack of data to support placing a fault at the modelled location.



	The given methodology for attributing subcrop lines with z-coordinates means that the resolution of the DTM surface is propagated into the subsurface		The given methodology for attributing subcrop lines with z-coordinates means that the resolution of the DTM surface is propagated into the subsurface

	= ~~name~~=~~"_TOC_250007"~~ images =		==Model images=
			Figures 11 and 12 show views of the units as modelled in GSI3D.
	Figures 11 and 12 show views of the units as modelled in GSI3D		[[Image:029_fig11.jpg\|thumb\|center\|600px\|The bedrock units to the base of the Chalk (in green) as modelled in GSI3D, viewed from the southwest. The legend is shown in Figure 2.]]











	[[~~File~~:.jpg\|~~557px]]~~



	~~'''Figure 11~~ The bedrock units to the base of the Chalk (in green) as modelled in GSI3D, viewed from the southwest. The legend is shown in Figure 2.~~'''~~
	~~</div> <br clear="all"> <div>~~
	~~''' '''~~



	~~[[File:.jpg\|571px~~]]



	~~'''Figure 12 The GSI3D model of bedrock and superficial deposits, viewed from the southwest.'''~~



	~~''' '''~~

			[[Image:029_fig12.jpg\|thumb\|center\|600px\|The GSI3D model of bedrock and superficial deposits, viewed from the southwest.]]

	~~''' '''~~

	= name="_TOC_250006"model =		= name="_TOC_250006"model =

Dbk: Created page with "
name="_TOC_250009" Wherever possible, the model matches the corresponding 1:50 000 scale geological map sheets. However, where mismatches occur between the interpretat..."

2015-03-09T12:24:18Z

Created page with "<div> name="_TOC_250009" Wherever possible, the model matches the corresponding 1:50 000 scale geological map sheets. However, where mismatches occur between the interpretat..."

New page

<div> name="_TOC_250009"

Wherever possible, the model matches the corresponding 1:50 000 scale geological map sheets. However, where mismatches occur between the interpretation of boreholes and the geological mapping, the borehole have been used in preference. Therefore, the vast majority of the model matches DiGMapGB-50, but with minor amendments, these have not been carried over into an updated DiGMapGB-50 version at this stage. The most significant changes are to the pattern of subcrop of the bedrock units at rockhead.

As described above the artificial ground units were updated specifically for the model and have not been incorporated into the released version of DiGMapGB-50 at present. This was carried out as a desk study using modern Ordnance Survey topographic maps and aerial photographs, with emphasis given to cuttings and embankments along major transport routes. Backfilled workings are not included, unless indicated on the relevant published geological maps.

Sub-alluvial gravel is modelled beneath river alluvium as a separate geological unit wherever it is identified in boreholes. This gravel is modelled as River Terrace Deposits Undivided (rtdu) in the majority of the model, as in most areas it is uncertain which river terrace gravel occurs beneath the alluvium. The sub-alluvial gravel is modelled as Shepperton Gravel Member (shgr), the very lowest terrace in the sequence in areas where it crops out adjacent to the modern floodplain alluvium.

Tidal River or Creek Deposits (trd) are mapped as a thin strip on each side of the River Thames and its tributaries from easting 539980 (around Silvertown) downstream to easting 568570 (Tilbury Marshes). These tidal deposits have not been differentiated from alluvium in this model, due to the close similarity in their lithologies and the gradational nature of their relationship.

== name="_TOC_250008" ==

Whilst every effort has been made to ensure accuracy, with the model constructed using a framework of cross-sections according to standard GSI3D workflow and procedures, not every available borehole was used in the model. Some variation may therefore occur between the depth of units modelled and depths recorded in boreholes that do not occur in the sections.

Where mismatches in the geological linework occur at 1:50 000 scale geological sheet boundaries, precedence is given to the most recently surveyed sheet, with the older linework adjusted to the newer version. Current BGS Lexicon codes are used in the model whereas DiGMapGB-50 data uses some older nomenclature.
</div> <br clear="all"> <div>
Artificial ground, mass movement deposits (landslide deposits), tufa and head are drawn in the cross-sections, but are excluded from the final model volume calculation because the cross- sections alone provide insufficient information to calculate these units due to their complex distribution, size and shape.

This model is intended for use at around 1:50 000 resolution, in line with the corresponding DiGMapGB-50 geological map data, and is not recommended for site specific use.

The throw along modelled faults is often very small and may show undue ‘waviness’. The underlying reason for this is lack of data to support placing a fault at the modelled location.

The given methodology for attributing subcrop lines with z-coordinates means that the resolution of the DTM surface is propagated into the subsurface

= name="_TOC_250007" images =

Figures 11 and 12 show views of the units as modelled in GSI3D

[[File:.jpg|557px]]

'''Figure 11 The bedrock units to the base of the Chalk (in green) as modelled in GSI3D, viewed from the southwest. The legend is shown in Figure 2.'''
</div> <br clear="all"> <div>
''' '''

[[File:.jpg|571px]]

'''Figure 12 The GSI3D model of bedrock and superficial deposits, viewed from the southwest.'''

''' '''

''' '''

= name="_TOC_250006"model =

A rockhead elevation surface derived from the combined base of all modelled superficial and artificial units has an elevation range of +254.87m OD to -25.24m OD (Figure 13). This rockhead elevation surface has a cell size of 100m and caps the bedrock part of the geological model. It was generated by calculating in GSI3D using the complete superficial and anthropocene model on a tile by tile basis, buffering each area by 200m to ensure a small overlap. The resulting rockhead surfaces were combined into the single surface in GIS. Where modelled anthropocene and/or superficial deposits are absent, this rockhead elevation surface corresponds to the Digital Terrain Model. This surface was calaculated in GSi3D and exported

to GOCAD''®'''' ''in order to cap the model of the faulted bedrock units.

[[File:.jpg|517px]]'''Rockhead'''''' ''''''elevation (m)'''

<p align="right">[[File:.png|29px]]254.87</p>

<p align="right">-25.24</p>

'''Figure 13. 3D view of the calculated rockhead elevation surface calculated as an ascii grid with a 100m cell size. The highest elevations are in red and the lowest in blue, vertical exaggeration is x 10.'''

''' '''

''' '''

= name="_TOC_250005"8 Uncertainty =

The model is not easy to assess in terms of uncertainty because the borehole data, reference material and geological knowledge that went into the model are difficult to represent. The
</div> <br clear="all">

borehole data used in the model is displayed in Figure 6. However, whilst showing the distribution and density of boreholes, this does not convey the depth of the borehole, the quality of the log itself or the reliability of the borehole coding.

= name="_TOC_250004"Glossary =

''BGS Lexicon ''The Lexicon of Named Rock Units is a list of geological units that appear on all BGS geological maps, with details on their lithologies. This is accessible via the BGS website at[http://www.bgs.ac.uk/Lexicon : http://www.bgs.ac.uk/Lexicon]

''Bid file ''GSI3D borehole identity file derived from the SOBI database (see below), which stores the locations of boreholes as eastings, northings and start heights

''Blg file ''GSI3D borehole log file, which stores the interpretation downloaded from the Borehole Geology database

''BoGe ''BGS Borehole Geology database for the standardised entry of data recorded on borehole logs

''DiGMapGB-50 ''Digital 1:50 000 geological map data

''DTM ''Digital Terrain Model – a model of surface of the solid Earth (generally the boundary between geosphere and atmosphere or hydrosphere). This is traditionally derived from OS contours and spot heights and should therefore exclude all buildings, trees, hedges, crops, animals etc. Sometimes also referred to as a ‘bald earth’ model

''Envelope ''Defined here as the extent, or coverage, of a geological unit in plan view, forming a 2D distribution map of the particular unit, or presence/absence map

''Fence ''''Diagram ''The completed framework of cross-sections

''GDI ''Geoscience Data Index, an ArcGIS platform for displaying BGS data, including boreholes, with links to scans, and geological map polygons

''Georeferenced ''ArcGIS process where a scanned image is registered to British National Grid

''GOCAD''''® ''3d geological modelling package utilised mainly for bedrock modelling.

GOCAD® Consortium web site: [http://www.gocad.org/w4/index.php/consortium/consortium http://www.gocad.org/w4/index.php/consortium/consortium]

''GSI3D ''Geological Surveying and Investigation in 3D, a geoscience modelling software package. GSI3D Research Consortium web site: [http://www.gsi3d.org.uk/ http://www.gsi3d.org.uk]

''SOBI ''Single Onshore Borehole Index, a database where location details of borehole logs are stored, giving positional information in x, y and z with respect to British National Grid

''TIN ''Triangular Irregular Network – a digital elevation surface with triangle- shaped cells, rather than grid squares

[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model| 06]]

OR/14/029 Assumptions, geological rules and limitations - Revision history

Dbk: /* Model images */

Dbk: Protected "OR/14/029 Assumptions, geological rules and limitations" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)) [cascading]

Dbk at 09:24, 10 March 2015

Dbk at 12:34, 9 March 2015

Dbk: /* name="_TOC_250006"model */

Dbk: /* =Model images */

Dbk at 12:30, 9 March 2015

Dbk: /* =Model images */

Dbk at 12:28, 9 March 2015

Dbk: Created page with " name="_TOC_250009" Wherever possible, the model matches the corresponding 1:50 000 scale geological map sheets. However, where mismatches occur between the interpretat..."

Dbk: Created page with "
name="_TOC_250009" Wherever possible, the model matches the corresponding 1:50 000 scale geological map sheets. However, where mismatches occur between the interpretat..."