Ti tech beta ti ls 432 thin cover golf ball

TECH SOLUTIONS, INC. 4D TECHNOLOGY CORPORATION. 4E THIN FILMS, INC. APPLIED TRAINING SOLUTIONS LLC BALL AEROSPACE & TECHNOLOGIES CORP. BALLANTINE. ti-q golf-ball-tested-hitting-bal-q ls-q D F Ball J Bulat D J Evans I N Gale H W Haslam (Front cover) Cover photograph: Depth contours to the base of the Permo-Triassic. The ore body was thin and. balls with a mean diameter of μm. The Bréchet, Direct bonding of titanium layers on ti tech beta ti ls 432 thin cover golf ball, Microsystem Technologies Predel, Si—Ti .

Continental Shelf Programme

Median concentrations in ppm of Cu, Pb, and Zn in the MMG and the SSG in the Cheshire Basin, and the calculated total metal content in Mt of the basin fill, based on extrapolation of present-day concentrations to the volume of rocks prior to erosion. A model based on fresh groundwater predicts that the fluid flow is topographically driven, with recharge zones in the south-east and discharge to the west and north; the MMG forms a relatively impermeable layer, and the underlying aquifers are under confined conditions.

However, if the dissolution of evaporites, such as those of the MMG, is simulated, the flow of the high-density brines created is downwards in the centre of the basin reversing the freshwater flow directions and outwards towards the basin margins. Sorption, particularly to oxide surfaces, depends on pH and redox conditions, since both metal speciation and the nature of the surface depend on these variables.

This could explain the preferential removal of Cu relative to Zn into ore fluids and, consequently, its much greater importance in the ores. The results of the Cheshire Basin study provide new insights into the formation of its copper-lead-baryte deposits and probably SCDs generally, especially those of continental red-bed type.

Geochemical, isotopic, petrological and modelling studies all suggest that one component of the ore fluid was a density-driven brine derived from bitterns in the MMG. Flow may have been initiated by compaction-driven dewatering of the MMG via the SSG during mesodiagenesis, and was associated with the development of an anhydrite or halite cement in the SSG throughout the basin.

The metalliferous brines derived from the MMG may also have scavenged metals from the underlying SSG, as they migrated both downwards and laterally towards the basin-margin faults. The SSG is predominantly aeolian, however, and may have contained lower quantities of Cu and other metals on authigenic hematite, clays or calcite.

These authigenic phases were, in part, formed by the alteration of detrital ferromagnesian and other primary minerals during eodiagenesis. Basins containing higher proportions of argillites or sediments rich in diagenetically altered ferromagnesian minerals may have higher metal contents. Such a mixing model may also explain the spatial zonation of ore minerals in the known deposits, in which Cu mineralisation tends to extend further from faults than the Pb-Zn mineralisation.

Additional features of the deposits which can be explained by the mixing model are: local bleaching of sandstones; quartz overgrowths; and baryte concentrations near faults. The complex metal-sulphide parageneses of the deposits possibly reflect chemical evolution of the red-bed formation fluids, owing to variations in redox conditions and sorption characteristics of iron oxides during diagenesis.

The temporal and spatial distribution of sulphide minerals in the Cheshire Basin deposits is thus consistent with precipitation during an interplay between a chemically evolving red-bed formation fluid and mixing-controlled redox processes near to basin-margin faults. Best estimates for the timing of mineralisation suggest a late-Triassic to early-Jurassic event coincident with a major phase of extension.

The present-day predominance of secondary supergene Cu-mineral assemblages is probably linked to Cenozoic uplift and the influx of low salinity, oxygenated groundwaters into the SSG. The strongly faulted eastern and north-eastern parts of the basin appear to have provided fluid-flow conditions favourable for the development of ore bodies.

The major north-trending normal faults may have created ore-fluid migration pathways by structurally juxtaposing the SSG and the MMG, but it is possible that the subvertical transfer faults were of greater importance. The latter structures trend roughly east—west, cutting and locally offsetting the larger north—south normal faults, and may have exerted an important influence on the development of ore bodies.

Steeply dipping fractures probably formed more effective conduits to fluids rising from the underlying Carboniferous basement rocks than the more gently inclined normal faults, as the latter would tend to be closed by the weight of their hangingwall blocks. Prospectivity for mineralisation of Alderley Edge type is considered to be lower in the extreme south-west of the basin, which is underlain by Lower Palaeozoic and Lower Carboniferous rocks and where faults trending north-east basement Caledonide trend may have been less suitable for fluid flow.

In the north-west of the basin, isotopic evidence, indicative of an increased proportion of reducing fluids from organic-rich rocks, suggests a greater influence of fluids derived from underlying organic-rich Carboniferous basement. One of the factors affecting the prospectivity of the basin is the timing of ore-forming events. The evidence presented here suggests that mineralisation cannot be simply related to the flow of diagenetic fluids in the context of progressive basin evolution but was related instead to later tectonism associated with reactivation of basin-bounding fault systems after cementation and lithification had occurred.

Regional considerations, particularly evidence from more fully preserved sedimentary sequences to the south of the basin, indicate that extensional basin subsidence continued through early Jurassic times, with renewed extension in the late Jurassic and early Cretaceous associated with sea-floor spreading in the southern part of the North Atlantic region.

It seems most likely that the known mineralisation in the Cheshire Basin occurred sometime during the late Triassic post MMG times to early Jurassic period of extension. Ti tech beta ti ls 432 thin cover golf ball In addition to minor quantities of glacial sand, boulder clay and building stone in the SSG , there are important resources of halite in the Northwich and Wilkesley Halite Formations of the MMG.

The quantity of halite in Cheshire has been estimated at km 3 and forms a vast future resource, notably in the area of the Prees Syncline. Many of these Permo-Triassic sandstones have considerable secondary porosity due to dissolution of early diagenetic cements. The MMG halites and mudstones are excellent seals, where sufficiently thick.

Potential hydrocarbon source rocks include Dinantian Brigantian basinal shales, early Namurian shales Holywell Shales , Westphalian oil-shales and cannel coals oil-prone and bituminous coals gas-prone , all of which outcrop on the periphery of the Cheshire Basin.

These are well known source rocks in other oil provinces and some of them are likely to be present at depth beneath the Cheshire. These source rocks have undergone two phases of burial, firstly during Carboniferous basin formation and secondly during Permo-Triassic and later burial; thermal modelling suggests that both phases were sufficient to have resulted in hydrocarbon generation.

Consideration of thermal gradients, thermal modelling, burial history and possible migration pathways enables several structural leads to be identified in the Helsby Sandstone, Collyhurst Sandstone and Carboniferous sandstone formations. Hydrocarbons generated from Carboniferous times to the present day are likely to be trapped beneath the base Permian unconformity, by Ruabon Etruria Marl seals.

Drilling to test late Namurian and early Westphalian reservoirs can be justified. However, wells sited on early Namurian and older rocks are not recommended because these rocks have unfavourable reservoir characteristics. Although not a primary target, testing of the Helsby Sandstone should not be ignored. The mineralisation model requires a contribution from Carboniferous fluids and suggests that sealed traps may occur down-dip of mineralised structures in several areas:.

The main prospective areas for Carboniferous reservoirs are: near Wigan and in the subsurface around Runcorn; where basal Westphalian Sandstone unconformably overlies Dinantian rocks; on the possible extension of the Derbyshire High north-west from Buxton to the Alderley—Stockport area; and downdip of the Milton Green inlier and on the block between the Wem and Hodnet faults.

The design includes five modules: mineralogy-petrology-diagenesis; provenance; structure; fluid flow; and mineralisation. The user is guided by data-selection menus based on criteria such as lithostratigraphy or borehole depth. The GIS performs spatial manipulation and display of information, whilst the knowledge base of the expert system, which encapsulates the expertise of the specialists involved, analyses the data.

They provide capabilities such as defining the 3-D spatial extent based on criteria such as the occurrence of a particular mineral or assemblage of minerals and mapping the uncertainty levels of provenance sources within specific horizons.

Several types of mineral deposit, including red-bed copper, Mississipi Valley-type MVT lead—zinc, sedimentary exhalative sedex lead-zinc, and some uranium deposits, along with petroleum and natural gas, can be related to the tectonic and thermal evolution of sedimentary basins.

The deposits form as a result of the flow of brines or hydrocarbons in response to hydrostatic gradients related to topographic relief, compaction, osmotic pumping, thermal gradients, and deformation and tectonism. Sedimentary basins are also host to resources of coal and evaporitic minerals such as gypsum, halite and potash , and contain important groundwater resources and, in some basins, low-enthalpy geothermal resources.

Moreover, in Britain and much of western Europe, the principal centres of population and industrial and agricultural activity are in areas underlain by major sedimentary basins. Considerable progress has been made in recent years in basin analysis e. McKenzie, ; Royden, ; Kuznir and Ziegler, , modelling of the geochemical and fluid flow in basins e.

Bethke, , , ; Bethke et al. Walker, , and the formation of associated mineral deposits, especially base metals Roberts and Sheahan, ; Boyle et al. The present study is aimed at applying these findings to understanding the formation of resources Cu-Pb-Ba, halite and hydrocarbons associated with the Cheshire Basin of north-west England, which contains mainly red-bed sandstones and, higher in the sequence, mudstones and evaporites.

The Cheshire Basin was selected as being representative of the basins formed in the Permo-Triassic rift systems which cut north—south across the British Isles and the continental shelf and which host important resources hydrocarbons, industrial minerals and water onshore and offshore.

The aim was to develop an integrated approach to the resource analysis of red-bed sedimentary basins generally, based on analysis of the large range of datasets held by the BGS. The study used advanced basin analysis, and geochemical and fluid-flow modelling. The results were integrated with information on the geology, geophysics, stratigraphy and palaeogeography of the basin and on the geochemistry, diagenesis and heavy-mineral suites of the basin fill.

The data were compiled in digital form and plotted and presented using software developed in BGS as well as proprietary software. Work to develop an expert system for interactive resource analysis of sedimentary basins using multidataset analysis by GIS, based on the Cheshire Basin study, was initiated. It is hoped that this report will not only provide new methods for assessing the resources of red-bed sedimentary basins, but also stimulate fresh discussion on all aspects of the geology of Permo-Triassic rift system basins in Britain and elsewhere.

The Cheshire Basin is a major Permo-Triassic extensional basin within a complex north—south-trending rift system Figure 1 which stretches for about km from the English Channel Basin in the south to the East Irish Sea Basin and beyond in the north. Offshore, similar Permo-Triassic rift systems underlie the North Sea. In Permo-Triassic times the Cheshire Basin marked a particularly rapidly subsiding segment of the rift system, and has a preserved Permo-Triassic sediment thickness of almost m.

The Permo-Triassic rocks of the basin, particularly the Sherwood Sandstone Group, have been the focus of detailed investigation because of their importance as reservoirs for hydrocarbons, water and geothermal resources. The Cheshire Basin was selected for detailed study because it is one of the few onshore basins with some unexplored potential for hydrocarbons especially for gas , it contains important water and halite resources, and, unlike many British Permo-Triassic basins, it contains Cu-Pb-Zn mineralisation.

Modelling the formation of the ore deposits can provide considerable information on palaeo- and present-day fluid flow of importance for resource analysis of British Permo-Triassic basins generally. The mineralisation which occurs largely around the margins of the basin is of a sedimentary continental red-bed copper association.

The most important occurrence is at Alderley Edge, where Cu, Pb, and Zn, with minor amounts of Ag, Co, V, Ni and Mn, occur as disseminations or in fault breccias, mainly in three conglomerate and sandstone units near the top of the Lower Triassic Sherwood Sandstone Group Warrington, The mineral association is characteristic of the continental red-bed copper association Ixer and Vaughan, ; Naylor et al.

Most models for such ore deposits depend on a diagenetic brine-expulsion model e. Gustafson and Williams, ; Brown, ; Naylor et al. Two sub-types of sedimentary copper deposits are distinguished by Eckstrand , paralic marine Kupferschiefer type and continental red-bed type. In the former, anoxic marine rocks are associated with red beds, while in the latter the anoxic rocks are of fluvial or lacustrine origin.

The Cheshire Basin deposits have the closest similarity to the latter group, examples of which are the Dorchester deposit in New Brunswick, Dzhezkazgan in Kazakhstan and Nacimiento in New Mexico. In both sub-types, copper is precipitated by reduction in anoxic sediments, diagenetic pyrite being a common reductant, whereas in the copper deposits of the Cheshire Basin it has been suggested that hydrocarbons, including methane, acted as the reducing agent responsible for precipitation of the ore Warrington, Such models derive from the classic work of Walker , , , in the south-west USA and Mexico, showing that the continental red-beds are first-cycle, immature sediments deposited in oxidising conditions.

They owe their red colour to the early diagenetic alteration of ferromagnesian minerals to hematite and other iron oxyhydroxides. The alteration is associated with the release of Cu and other elements held in primary minerals onto hematite and clays from which they can be mobilised to form ore deposits.

The present study examines the exploration criteria and metallogenic models previously proposed for SCDs and suggests important modifications for the development of prospectivity and resource analysis criteria for such mineralisation in sedimentary basins generally.

The Permo-Triassic red beds of the UK are host to commercially valuable evaporites, including sylvite Cleveland , anhydrite and gypsum Cheshire, Cumbria and Nottinghamshire and halite Cleveland and Cheshire. In the Cheshire Basin, the resources of halite from the two major salt-bearing formations the Northwich Halite and Wilkesley Halite formations have been estimated to be of the order of 28 cubic miles Pugh, Brine extraction, presently by controlled pumping in the Holford and Warmingham Brinefields, is from the Northwich Halite Formation; salt is also mined from the 'Bottom Bed' of this formation.

A total of 5. Future resources are vast, particularly in the virtually untapped area of the Prees Syncline, where both halite-bearing formations are present over large areas. There is also potential for formation of deep cavities for storage of gas or liquids in the deeper parts of the syncline. The presence of halite in the Cheshire Basin is important not only as a resource, but also as a control on fluid flow and for metallogenic modelling.

Red beds are important hydrocarbon reservoirs in many parts of the world. Producing fields from Triassic reservoirs in basins adjacent to Cheshire, at Formby and in the East Irish Sea, together with oil shows in the Needwood Basin in the Midlands, indicate that both oil and gas have been generated over a wide area.

In the East Midlands oilfields the source and the reservoirs are of Carboniferous age, and in this study we consider not only the prospectivity of the Permo-Triassic but also that of the Upper Carboniferous rocks beneath the Cheshire Basin. Permo-Triassic red beds are major sources of potable water in Cheshire, Lancashire and Nottinghamshire, and are exploited as geothermal reservoirs in the Wessex Basin.

Utilisation of groundwater resources has played an important role in the urban and industrial development of the Cheshire Basin. The Permo-Triassic sandstones are prolific aquifers, exploited largely where they are not confined by the overlying Mercia Mudstone Group and younger formations. Recharge to the aquifer is, in places, restricted by thick drift cover, and groundwater generally flows towards the major rivers draining the basin.

Beneath the large conurbations, groundwater has been over-exploited historically, leading to depression of the water table below sea level. This has resulted in saline intrusion, particularly along the Mersey Estuary and the Manchester Ship Canal. Vegas odds for the masters Reduction or cessation of pumping in the last few decades has led to rising groundwater levels, particularly beneath Liverpool, in part in response to the contribution made by leaking sewers and water mains.

The present-day shallow groundwater flow system overlies a deeper saline groundwater system, which appears to be driven by the density of brines derived from the overlying halite deposits in the central and south-eastern part of the basin. Chapter 2 of the volume gives an account of the stratigraphy of the Permian to Lower Jurassic basin fill, including sections on the regional setting, biostratigraphy and sedimentology.

The basin structure and its evolution are discussed in Chapter 3, based on the interpretation of seismic reflection data calibrated by borehole information and on geophysical modelling of gravity and aeromagnetic data. In Chapter 5 the diagenesis of the basin is discussed, based on new petrographic, clay mineralogical, geochemical organic and inorganic , isotope sulphur, carbon and oxygen and fluid-inclusion data.

Hydrogeological and hydrogeochemical models consistent with the evolution of the Cheshire Basin and its diagenesis and geochemistry are then presented in Chapter 6. All these data are used to model the metalliferous mineral occurrences in the basin in Chapter 7, which also presents a resource analysis for halite, hydrocarbons and water, as well as Cu-Pb-Zn-Ba and includes a review of known resources, mining and extraction history, resource models, exploration criteria and prospectivity of the basin.

The report concludes Chapter 8 with an account of development work on an Expert System for resource analysis of red-bed sedimentary basins generally. The solid geology of the Cheshire Basin is poorly exposed because of an extensive cover of glacial drift. Because of these two factors nearly all of the samples studied for the project were obtained from boreholes or from underground mines.

There was little borehole core from the basin in the BGS collections at the start of the project. A search was therefore made for borehole core from external sources. One set, in the north of the basin, extending into the Wirral and the Lancashire coastal strip in the area between the Cheshire Basin and the East Irish Sea Basin came from the EA North West Region , while the other, in the south of the basin, formed part of Shropshire groundwater investigations and was held by EA Midlands Region.

Further cores were obtained from site investigations for the A road improvement link to Manchester Airport from Allott and Lomax and the Weaverham bypass Soil Mechanics and from mineral exploration for evaporites. All of this material is currently held in the core storage facility of the BGS and it is intended that a representative set of borehole cores will be retained.

Full use was made of existing core and samples held by BGS from stratigraphical, geothermal, water and site-investigation boreholes, as well as from exploration for coal, oil and salt resources. Because groundwater abstraction or monitoring boreholes are heavily represented, there is a bias towards the permeable Permo-Triassic sandstone aquifer rocks principally those of the Sherwood Sandstone Group SSG around the margins of the Cheshire Basin.

Less borehole core was available from the Mercia Mudstone Group MMG and other formations in the centre of the basin, but MMG strata were sampled from BGS boreholes, such as Wilkesley and Crewe, and from exploration for evaporites and site-investigation boreholes. Due to the lack of available material only a limited study was made of pre-SSG strata.

The Collyhurst Sandstone, Manchester Marl and earlier strata were sampled from a small number of boreholes. To supplement the borehole material a few surface outcrop samples were collected, principally from the south of the basin, and samples were taken from the old mine workings at Alderley Edge and Clive.

The locations sampled are illustrated in Figure 2 and details are given in Table 2. Samples from the cores, or outcrops, were selected to give as wide a geographical and stratigraphical coverage as possible. A standard sample-handling scheme was devised Figure 3 to avoid conflict between the requirements of different parts of the project; wherever possible, reference material was retained prior to any destructive treatment, such as preparation of the rocks for chemical analysis, thin sections, physical properties or palynology.

In total more than samples were collected during the project, of which more than were from the SSG and over from the MMG. Particulars of each sample were recorded in a computer database. The information included location grid reference, borehole name, borehole reference number, depth etc.

Overviews of the tectonic development of Britain and neighbouring regions before and during the deposition of the Permo-Triassic sediments of the Cheshire Basin are given by, among others, Anderton et al. This section on Tectonic setting has been compiled from these accounts and from Chapter 3 of this volume. During Precambrian and Palaeozoic times, the tectonics of north-west Europe were dominated by the sequential accretion of magmatic arcs and older continental fragments against and onto the stable North American craton.

In early to middle Devonian times, oblique collision between the Laurentian and Avalonian land masses produced regional compressional deformation over much of Britain, with widespread uplift, folding and basin inversion. These important Acadian tectonic events effectively marked the end of the Caledonian orogeny in Britain, by which time closure of the mid-European Rheic and Iapetus oceans had resulted in the Armorican, Laurentian, Avalonian and Baltican terranes being fused into a single land mass, Laurasia, with Britain close to its southern margin Figure 4.

Major Acadian structures were susceptible to later reactivation and played an important part in the subsequent structural development of the region. Throughout much of north-west Europe and the Appalachians, the Variscan orogeny was a further episode in this long history of progressive accretion.

Laurasia was separated from the continent of Gondwana to the south by a proto-Tethys Ocean. Ti tech beta ti ls 432 thin cover golf ball Closure of this ocean, combined with the buffering effects of various small terranes, had, by end-Carboniferous times, created the Variscides as a collision orogenic belt. In Germany, the internal, or Moldanubian, zone of the Variscides Figure 5 shows structures dominated by a gently dipping schistosity and gneissic banding, with overthrust sheets of eclogitic and granulitic material.

The tectonic transport direction was towards the north-west. To the north-west of this zone, the Saxo-Thuringian and Rheno-Hercynian zones show lower-grade metamorphism but similarly north-west-directed shears and thrusts. Together they indicate several hundred kilometres of crustal shortening. In north-west France crustal shortening may have been considerably less, and in south-west England the shortening across Devon and Cornwall has been estimated at km.

The Variscides of southern England form a continuation of the outer, or Rheno-Hercynian, zone of the European Variscan belt and can, in part, be interpreted in terms of thin-skinned thrust tectonics, with a thrust transport direction dominantly towards the north-west or north-north-west. There is, however, evidence of thick-skinned thrust tectonics beneath north Devon, South Wales and the Mendips, where the structures trend approximately east—west, oblique to the general north-west-directed movements in the thin-skinned zones.

The Devonian and Lower Carboniferous sedimentary sequence in south-west England reflects a marine transgression from the south. Terrestrial deposits were succeeded first by shallow-marine sediments and subsequently by deep-water shales, cherts and volcanic rocks. During Namurian and Westphalian times the Variscan thrust front advanced from the south while the flysch-like sediments of the Culm were deposited in north Devon and Cornwall.

To the north of the developing Variscan fold belt in southern Britain lay a foreland on which extensional basins developed in Carboniferous times on the northern side of a persistent Wales—London—Brabant high. Extension in latest Devonian and early Carboniferous times produced a series of grabens and half-grabens in the Caledonian basement, which exerted the dominant control on early Carboniferous sedimentation to the north of the high.

In Namurian times, crustal extension progressively gave way to regional post-extensional subsidence, the early Carboniferous deposition of carbonate and detrital sediments on a block-and-basin topography being followed by the accumulation of thick, more uniform sequences of deltaic strata.

Later in the Carboniferous, subsidence was replaced by uplift, as Variscan compressive forces became progressively more dominant. The main effects of this regional Variscan compression were the reversal of Caledonian lines of weakness and structural inversion of the Carboniferous basins. Minor inversion occurred sporadically in latest Dinantian and Namurian times, but the main period of basin inversion, roughly coeval with emplacement of the Variscan thrust front, took place in Westphalian and Stephanian times.

The Variscan front now effectively forms the northern limit of the Variscan fold belt. During Devonian times, a hot semi-arid climate prevailed over much of the North Atlantic area, Britain lying close to the equator. Though Britain remained near the equator throughout the Carboniferous and early Permian, the climate changed from arid in the earliest Dinantian to semi-arid and then monsoonal in later Dinantian times.

Later in the Carboniferous, an increasingly humid tropical climate prevailed over much of north-west Europe, which ended in latest Westphalian to Stephanian times when the evidence of red beds and oxidised coal seams indicates the onset of the lengthy Permo-Triassic arid period. During Permo-Triassic times, northern Europe lay within the arid hinterland of the Pangaean supercontinent, newly formed by the collision of Laurasia and Gondwana.

A tectonic regime of regional crustal extension became established, many of the earlier Caledonian and Variscan structures being reactivated as basin-controlling normal faults. The Cheshire Basin formed part of a north—south rift system see Figure 1 and Chapter 3 of this volume. The climate was continental, with low rainfall, and the basin was filled with a sequence of continental sediments, mostly of aeolian, fluvial and playa-lake origin.

Erosional areas lay to the east Pennines and the south-west and west Wales. Marine incursions entered from the north-west in Late Permian and Mid and Late Triassic times, and from the south and west at the end of the Triassic. It is about km long, with a maximum width of about 55 km, and covers an area of at least km 2.

The Permo-Triassic fill rests unconformably on, or is in faulted contact with, folded Carboniferous and older rocks and is contiguous with the fill of the East Irish Sea Basin EISB to the north-west, and the Stafford, Needwood and Worcester basins to the south-east and south. It consists of a dominantly arenaceous sequence to the top of the Sherwood Sandstone Group; SSG overlain by a largely argillaceous sequence with evaporites in the lower part Mercia Mudstone Group; MMG and limestones in the upper part Penarth and Lias groups.

Though the nature of the basin fill was recognised in the last century, its thickness was not proved by drilling until after A gravity survey White, broadly defined the structure of the area as a half-graben, bounded to the east by a major fault. Kent proposed depths to the basin floor of more than m in the south, near Prees, and about m further north near Northwich.

More recent geophysical studies provided a better definition of the structure of the basin and the form of its floor Gale et al. Glacial deposits are widespread in the Cheshire Basin and exposures of the basin fill are thus limited Figure 9. The dominantly arenaceous lower part of the succession is better exposed than the overlying, largely argillaceous sequence. Surface exposures have been augmented by borehole sections in parts of the basin.

The arenaceous lower part of the basin fill has been extensively drilled for water-supply purposes, largely in the peripheral areas in the north, west and south of the basin. Parts of the overlying largely argillaceous sequence have been drilled in connection with salt extraction in the Northwich—Winsford area and elsewhere.

Additionally, information is available from boreholes drilled, largely in connection with the exploration of concealed coalfield prospects, around the northern and northwestern margins of the basin, and from boreholes drilled by the. Geological Survey, principally in the Stockport, Chester and Nantwich districts geological sheets 98, , ; Figure Several deep boreholes penetrating the full basin fill have been drilled in search of hydrocarbons see below.

The form of the basin floor has been interpreted from geophysical data Gale et al. Around the northern, western and southern margins of the basin the fill rests on folded and faulted pre-Permian rocks Figure 7 , which are mostly Carboniferous up to Westphalian D in age though Ordovician rocks occur at the south-western margin, south of Oswestry. Few boreholes have proved the entire succession of the basin fill or the nature of the basin floor beneath the deeper parts of the structure.

Nearly 50 km to the north-north-east, Carboniferous shales, sandstones and coals of Westphalian age were proved from c. A small inlier of Carboniferous rocks has been proved near Chester Poole and Whiteman, ; Earp and Taylor, ; a borehole in this area Milton Green: Esso Petroleum, [SJ ] Figure 7 proved some m of Carboniferous Dinantian and Silesian rocks resting on Ordovician sediments and intrusive igneous rocks Whittaker et al.

A summary account of the distribution and structures of the pre-Permian rocks of the basin floor and in the surrounding area is given on pp. At the beginning of the Permian, Britain lay deep within the Pangaean supercontinent, in a belt of easterly winds and situated within a few degrees of the equator Smith and Taylor, The area was dominated by desert erosion and deposition.

Crustal tension, possibly associated with the onset of rifling in the North Atlantic area, led to local subsidence and the development of a series of fault-bounded basins, including the Cheshire Basin and the adjacent East Irish Sea and Stafford basins Figure 6.

To the north-east and south-west, the Cheshire Basin was surrounded by bare, rugged hills. The sands were deposited on an uneven erosional surface of mainly Carboniferous rocks, and this surface was further modified by syndepositional faulting. Early in the Late Permian, a marine incursion from the north-west into the northern part of the Cheshire Basin led to the deposition of the dolomitic and gypsiferous mudstones of the Manchester Marls Formation.

In the southern part of the basin at this time, the Bold Formation represents a continuation of the conditions that obtained during the deposition of the Collyhurst Sandstone. Towards the end of the Permian, the sea retreated and the Bold and Manchester Marls formations were succeeded by the Kinnerton Sandstone.

The Kinnerton Sandstone Formation the basal formation of the SSG consists dominantly of aeolian sands, though evidence of fluvial action suggests the presence of rivers in the interdune areas. Similar conditions continued into the Triassic. These sediments were deposited from a northward-flowing river system which entered the Cheshire Basin via the Stafford Basin.

The abundance of pebbles decreases northwards; pebble beds extend into the south-eastern extremity of the EISB, beyond which lie fluvial sandstones the St Bees Sandstone Formation similar to the Wilmslow Sandstones which, in the Cheshire Basin, overlie the Chester Pebble Beds. The Wilmslow Sandstone Formation consists of sandstones, with some siltstones and mudstones, deposited from the north-west-flowing river system, and also features dunes formed by easterly winds.

The succeeding beds of the Bulkeley Hill Sandstone Formation are only locally present, and their deposition was followed by a period of faulting and erosion, now marked by the Hardegsen disconformity. The Tarporley Siltstone Formation, the lowest formation of the MMG, was laid down in intertidal and playa environments and marks a transition to less sandy deposits.

It is followed by a sequence of formations dominated by dolomitic mudstone Boffin, Byley, Wych, and Brooks Mill Mudstone formations or halite Northwich and Wilkesley Halite formations. The land surface varied between dry, desert conditions, shallow temporary lakes, and seas or lakes of a more lasting nature in which thick halite units developed.

Apart from infrequent fluvial sandstones, the detrital sediment was entirely fine grained, deposited as aeolian sediment structureless facies; oxidised or in shallow water laminated facies; oxidised and reduced laminae. Groundwater throughout this time contained relatively high concentrations of magnesium, leading to the precipitation of dolomite and magnesium-bearing clays in the mudstones during early diagenesis.

Nodules of gypsum also grew in the mudstones, close to the surface. Subsidence accompanied by movement along contemporary faults continued until Carnian times Wilkesley Halite , when conditions became more uniform over a wider area Warrington and Ivimey-Cook, A major marine incursion ensued. The Penarth Group consists of mudstones, fine sandstones and limestones with marine fossils, and this fauna became more diverse in the overlying Lias Group.

The stratigraphical nomenclature used is that of Hull , and Pugh , as revised by Warrington et al. In its most complete form, in the northern part of the basin, the fill comprises the Appleby, Cumbrian Coast, Sherwood Sandstone and Mercia Mudstone groups; to the south, younger deposits of the Penarth Group and the lower part of the Lias Group are also present Figure 7 and Figure 8.

Further south in the basin the formation becomes almost indistinguishable from the overlying Manchester Marls where the latter pass laterally into a more silty or arenaceous facies, as recognised in the Prees Borehole Evans et al. Where these formations become indistinguishable, their correlatives are regarded as forming the lower part of the Kinnerton Sandstone Formation of the Sherwood Sandstone Group Warrington et al.

The Collyhurst Sandstone is of continental, aeolian, origin. Palaeocurrent vectors indicate deposition under the influence of winds from an easterly direction, with the possible formation and migration of transverse dunes with barchanoid crests or, locally, of longitudinal seif dunes Thompson, , fig.

Further south, in the Stafford and Worcester basins Figure 6 , the lower part of the aeolian Bridgnorth Sandstone Formation is equivalent to the Collyhurst Sandstone. The Bridgnorth Sandstone is interpreted as having accumulated in a combination of transverse and barchanoid draas, with superimposed oblique crescentic and linear dunes, under the influence of fluctuating winds from a predominantly easterly direction Karpeta, Changes in the thickness of the formation in the Manchester area have been interpreted as evidence of syndepositional faulting Tonks et al.

However, Poole and Whiteman considered that these variations were related largely to deposition on an uneven land surface, and that the apparent relationship to fault lines was fortuitous in all but one instance. Seismic reflection data Figure 42 and Figure 43 show, however, that the Collyhurst Sandstone does thicken across faults, supporting the views of Tonks et al.

In the Manchester area the formation is locally absent but ranges in thickness up to Within the basin the formation is m thick in the Knutsford Borehole and m in the Prees Borehole Evans et al. The Collyhurst Sandstone is thus constrained only within the post-Westphalian to pre-Kazanian interval Figure 8 , though it is generally regarded as Early Permian e.

Smith et al. This newly introduced group BGS Lexicon of Named Rock Units incorporates the Manchester Marls Formation, which is recognised around the northern and north-eastern margins of the basin Figure 7 , in the Wigan, Manchester and Stockport districts geological sheets 84, 85, 98; Figure 10 Tonks et al. The Manchester Marls rest on the Collyhurst Sandstone or locally overlap that formation and rest unconformably on Carboniferous rocks e.

Tonks et al. Around Manchester the formation varies in thickness from The Manchester Marls comprise red, rarely green, dolomitic and gypsiferous mudstones. In the lower part of the formation there are lenses and thin beds of calcareous mudstone, dolomitic limestone and iron2stained limestones, containing calcareous microfaunas and shelly macrofossils indicative of a marine depositional environment Logan, ; Pattison, ; Pattison et al.

A concealed development of the Manchester Marls extends south for at least 40 km from the outcrops at the northern end of the basin Gale et al. This development is in thick in the Knutsford Borehole Evans et al. A silty and arenaceous correlative 70 m thick is recognised nearly 50 km to the south-south-west in the Prees Borehole Evans et al.

Elsewhere the formation is indistinguishable from the underlying Collyhurst Sandstone and merges with the equivalent of that formation to form the lower part of an arenaceous sequence assigned to the Kinnerton Sandstone Formation Warrington et al. An interbedded succession of aeolian sandsheet deposits and fluvial sheetflood facies in the Speke Reservoir Borehole p.

Regional studies show that the Manchester Marls accumulated marginally to a depocentre sited to the north-west, in the EISB. Towards that depocentre the formation passes laterally into concentric belts of dolomitic and anhydritic mudstones disposed around a body of halite Colter and Barr, ; Jackson et al.

The formations of this group have an extensive outcrop in the Cheshire Basin, almost surrounding that of the Mercia Mudstone Group and younger deposits Figure 7. The principal formations Warrington et al. The upward increase in sand content in the Manchester Marls and the transition into the sandstones of the SSG reflect palaeogeographical changes that resulted in the exclusion of marine influences from the northern part of the Cheshire Basin and the neighbouring EISB.

This has been correlated with the Hardegsen disconformity Trusheim, in the Middle Bunter of Germany Warrington et al. Evidence of the regional nature of this unconformity, and of its presence within the concealed SSG in the Cheshire Basin, has been compiled from geophysical studies Evans et al. Above the unconformity, the Helsby Sandstone reflects the re-establishment, in the early Mid-Triassic Warrington and Ivimey-Cook, , map Trlb , of a continental fluvial system which drained northwards into the EISB.

Continental sedimentation in the EISB Bushell, ; Stuart and Cowan, ; Cowan, ; Meadows and Beach, a, b was superseded by the deposition of fine-grained sediments with evaporites, which form the lowest part of the MMG and were deposited partly in water of marine origin.

This formation is predominantly of continental, aeolian facies. Detailed petrographical examination p. The Kinnerton Sandstone lacks fossils, but, because of its lateral equivalence to the aeolian Collyhurst Sandstone and the partly marine Manchester Marls, it is regarded as largely Permian in age Figure 8. Palaeowind vectors Thompson, , fig. In the Chester district geological sheet ; Figure 10 the upper part of the formation shows large-scale deformed cross-bedding which Thompson compared with structures described by Glennie and Buller from Permian aeolian deposits in the North Sea Basin.

In the Chester district, 14 m of very micaceous sandstones, described by Thompson as at the 'predicted horizon' of the Manchester Marls, forms a transition upwards into the Chester Pebble Beds. These sandstones may correlate with the Bold Formation, a unit recognised by geologists of the North West Water Authority in the Runcorn district geological sheet 97; Figure 10 Campbell et al.

This formation outcrops principally on the western and north-western sides of the basin but is also recognised in smaller areas in the north-east; minor outcrops in the southeast are contiguous with more extensive outcrops in the adjoining northern part of the Stafford Basin. Elsewhere, it locally rests unconformably on the Bold Formation, Manchester Marls, Collyhurst Sandstone and Carboniferous rocks and, in the south-eastern part of the basin, is overlain unconformably by the Helsby Sandstone.

The Chester Pebble Beds comprise conglomerates, pebbly sandstones and sandstones the Red Pebbly Sandstone Lithofacies of Thompson, a and are of continental origin. Horizontally bedded gravels are interpreted as representing longitudinal sheet bars, and flat- and cross-bedded gravel associations were deposited as mid-channel bars in confined braided channels with considerable bar—channel relief.

These facies types are recognised principally in the south-east. Thick cross-bedded pebbly sandstones also occur there, and persist northwards through the basin; they represent deposition in transverse bars and dunes in channels of a braided river system. Interbedded finer sediments argillaceous cross-bedded sandstones, siltstones and mudstones reflect less turbulent braided river systems dominated by transverse bars and dunes Steel and Thompson, ; Thompson, a, Palaeocurrent vectors Thompson, a, , fig.

The abundance of pebbles decreases in the downstream direction, and the formation is traceable only to the south-eastern periphery of the EISB Colter and Barr, ; Colter, ; Jackson et al. The formation is m thick in the Prees Borehole and m at Knutsford Evans et al. North-westwards, into the EISB, the formation shows a decrease in pebble content and becomes indistinguishable from sandstones of the overlying Wilmslow Sandstone Formation.

Beyond the limit of the occurrence of pebbles in the Chester Pebble Beds, the lateral equivalents of that formation and the Wilmslow Sandstone occur in the St Bees Sandstone Formation Jackson and Mulholland, , fig. Thompson considers that some 14 m of non-pebbly, argillaceous, very micaceous, cross- and planar-bedded sandstones that were mapped as the basal beds of the Chester Pebble Beds Formation in the Chester district geological sheet ; Figure 10 are equivalent to the Bold Formation.

No stratigraphically useful fossils are known from the Chester Pebble Beds which, from their position above the Late Permian Manchester Marls are assessed as Early Triassic in age Figure 8. This formation outcrops principally in the western and northern parts of the basin. Elsewhere the Bulkeley Hill Sandstone is overlapped by the Helsby Sandstone which comes to rest unconformably on, or completely cuts out, the Wilmslow Sandstone.

The Wilmslow Sandstone comprises predominantly red, fine-grained, argillaceous, cross-bedded sandstones the Soft Sandstone Lithofacies of Thompson, b , with some interbedded siltstones and mudstones. It was deposited under continental fluvial and aeolian conditions in a braided river system dominated by transverse bars and dunes. Aeolian dunes developed in interdistributary areas under the influence of easterly winds; palaeocurrent vectors from water-laid sediments indicate transport to the north-west Thompson, , fig.

The formation is m thick in the Knutsford Borehole and m thick at Prees Figure 7 and Figure 11 ; the thinner sequence encountered in the Prees Borehole is attributed to stratigraphical cut-out by normal faulting Evans et al. The Wilmslow Sandstone lacks stratigraphically useful fossils. Trace fossils, including vertebrate tracks, from the formation in its type area see Sarjeant, are significant for environmental interpretation only.

From its position beneath an inferred representative of the Hardegsen disconformity, which affects beds high in the Middle Bunter of Germany Trusheim, , , and below the Mid-Triassic Anisian Helsby Sandstone, the Wilmslow Sandstone is assessed, with the Chester Pebble Beds, as Early Triassic in age. This formation, the 'Keuper Sandstone Passage Beds' of Poole and 'Whiteman , is recognised at outcrop only in west Cheshire, where it is up to 21 m thick Poole and Whiteman, ; Earp and Taylor, ; Evans et al.

It succeeds the Wilmslow Sandstone conformably but is overlapped by the Helsby Sandstone above an unconformity that was correlated Warrington et al. Evidence of the presence of this unconformity within the concealed SSG in the Cheshire Basin, and of the concealed extent of the Bulkeley Hill Sandstone, has been compiled from geophysical studies Evans et al. The formation comprises massive, well-bedded, fairly coarse brown sandstones, with interbedded red flaggy sandstones, soft millet-seed sandstones and red-brown mudstones.

It lacks fossils, but its stratigraphical position is analogous to that of the Wilmslow Sandstone and it is similarly assessed as Early Triassic in age. This formation has an almost continuous, though faulted, outcrop which fringes that of the MMG in the northern, western and southern parts of the basin.

Small, isolated occurrences are found on the eastern side of the basin Figure 7 , adjacent to the Red Rock Fault. The Soft Sandstones, of fluvial, fluvio-lacustrine and aeolian origin, occur principally in the Wilmslow Sandstone but are also present in the Helsby Sandstone. The Red Pebbly Sandstones, representing fluvial-channel and associated overbank deposits of low- to moderate-sinuosity stream systems, occur in the Chester Pebble Beds and the Helsby Sandstone.

Thompson proposed division of the Helsby Sandstone into members distinguished by the predominance of fluvial or of aeolian sediments. In view of the amount of possible interdigitation and lateral variation in thickness illustrated by Thompson b, figs 6, 7 it is more appropriate to consider these members as facies associations whose stratigraphical order may vary laterally; a similar interpretation is placed upon the constituents of the correlative Ormskirk Sandstone Formation in the EISB Meadows and Beach, a, b; see below.

In the southern part of the basin, in the Oswestry and Wem districts geological sheets and ; Figure 10 , the Ruyton and Grinshill Sandstones have historically been assigned, largely or entirely Pocock and Wray, ; Wedd et al. In the early stage of Helsby Sandstone sedimentation, braided river channels were the sites of deposition of pebbly transverse sand bars and dunes and some pebbly channel deposits during high-discharge phases.

Thompson b, has recognised parts of three distributary courses, represented by coarse pebbly members in the northern part of the basin. Sediments of the Thurstaston Member facies accumulated between these distributaries and are more widely developed across the basin; they comprise low-energy fluvial sands and some possible aeolian dunes that formed on dry interdistributary tracts.

The succeeding stage of Helsby Sandstone sedimentation witnessed the more widespread deposition of pebbly fluvial sands, of the Delamere Member facies, in distributaries of low to moderate sinuosity. Subsequently, fluvial deposition waned substantially and aeolian deposits of the Frodsham Member facies dominated the basin; localised fluvial deposits formed in discrete distributary channels, mainly in the eastern part of the basin.

Palaeocurrent studies Thompson, , , figs 9—11 indicate that aeolian facies in the formation accumulated under the influence of easterly winds and that fluvial transport was generally north-westwards. Meadows and Beach a, b have recognised seven facies associations comparable with those of Stuart and Cowan , comprising major and minor fluvial-channel sandstones, aeolian-dune and sandsheet sandstones, sheetflood deposits, and playa-lake and playa-margin deposits.

Palaeogeographical interpretations Meadows and Beach, a, fig. In the absence of stratigraphically significant fossils from formations lower in the SSG, the position of the Permian-Triassic boundary is poorly constrained. In the northern part of the basin it is within some m of strata between the highest fossiliferous beds in the Manchester Marls and the base of the Helsby Sandstone; it may, therefore, occur within the topmost Manchester Marls or the lower part of the SSG.

Further south in the basin it is considered to occur within the Kinnerton Sandstone Figure 8 Warrington et al. This group has an extensive outcrop, enclosing the outliers of the Penarth and Lias groups in the southern part of the basin and almost surrounded by the outcrop of the SSG. The lower halite-bearing unit, the Northwich Halite Formation occurs between the Bollin and Byley mudstones, and the upper unit, the Wilkesley Halite Formation, between the Wych and Brooks Mill mudstones Figure 8 and Figure 13 for lithological key.

The mudstone formations in the MMG include structure-less and laminated units. The former constitute the bulk of the Wych and Brooks Mill mudstones and the lower part of the Bollin Mudstone, and also occur within the Byley Mudstone. Laminated beds are dominant in the upper part of the Bollin Mudstone and also occur in the Byley Mudstone.

The structureless units are probably largely aeolian in origin; Arthurton suggested that relict structures in these mudstones originated as 'ploughed ground' or zardeh, an irregular surface caused by growth of halite or gypsum crystals in sediments, which acted to trap wind-blown dust. Gypsum nodules grew in the sediment, probably in slightly upraised areas where gypsiferous solutions pulsed close to ground level Shearman, The laminated units contain sedimentary structures indicative of deposition in shallow water.

This formation, formerly called the 'Keuper Waterstones', was defined by Warrington et al. The lowest formation in the MMG, it is at least m thick in the Ashley Borehole [SJ ], south of Altrincham Figure 13 and between and m thick in several boreholes elsewhere in the Cheshire Basin. The multiple seismic reflector associated with the Helsby Sandstone—Tarporley Siltstone succession Figure 32 is identifiable widely in the Cheshire Basin.

Towards the basin edge, however, m is a more common thickness for the Tarporley Siltstone, with a likelihood that the unit thins out locally on the eastern fringe near Alsager. Exposures [SJ ] to [SJ ] near North Rode viaduct on the River Dane, which are seen near the basin edge, were first noted by Ormerod ; the formation here is rich in siltstone, but contains only scattered sandstones.

The well exposed upper half of the section exposed here has been measured Figure The Tarporley Siltstone comprises a distinctive facies that consists of alternating siltstones, reddish brown and greenish grey mudstones and thin fine- to medium-grained sandstones; desiccation surfaces and pseudomorphs after halite point to arid conditions.

Cross-lamination, burrows and reptilian footprints are also recorded; Ireland et al. Examination of the Saughall Massie Borehole, however, revealed abundant sedimentary structures Figure 13 indicative of deposition in an ephemeral lake playa environment see p. In the Malpas area, a large part of the formation comprises a reddish brown cross-bedded sandstone, some m thick. This unit, the Malpas Sandstone, contains abundant windblown grains Poole and Whiteman, but includes water-laid sandstone, with current-ripple lamination and clasts of mudstone.

In the south-eastern part of the basin, near Norton in Hales [SJ ], beds of Tarporley Siltstone facies alternate with up to six sandstone units some 20 to 30 m thick, of both aeolian and subaqueous origin, with rip-up clasts and cross-bedding. This formation was defined by Wilson ; it replaces the former 'Lower Keuper Marl' and the 'lower mudstone division of the Mercia Mudstone Group' of Earp and Taylor The formation is defined as the beds between the highest sandstone interbed at the top of the Tarporley Siltstone and the base of the first bed of halite over 2 m in thickness, marking the base of the Northwich Halite.

In the northern half of the basin there is commonly a repetition of the Tarporley Siltstone facies in the overlying Bollin Mudstone. It has not been separately mapped at surface but has been identified in boreholes sunk for a road scheme north-west of Knutsford Wilson, Atlas R.

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