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The upper Permian Cadeby Formation in the Boston Spa area, West Yorkshire, UK
Abstract
Undescribed carbonate exposures in the Boston Spa area have been studied in detail in order to give a comprehensive account of the stratigraphy and facies there of the upper Permian (Lopingian Series) Cadeby Formation of the Zechstein Group. The Cadeby Formation was deposited close to the western margin of the Zechstein Basin, in the Yorkshire sub-basin. All the strata in the study area are of shallow water origin, and are thought to have close analogues with modern carbonate sediments in the Arabian/Persian Gulf. The Cadeby Formation comprises the Wetherby Member overlain by the Sprotbrough Member. The contact between the members is here placed at the Hampole Discontinuity, which marks a subaerial erosion surface. The Wetherby Member includes bryozoan patch reefs and was deposited on a marginal carbonate shelf of the Zechstein Basin. The Hampole Beds, which are here placed at the base of the Sprotbrough Member, were deposited during a period of relatively low basin-wide sea-level. They include features that suggest deposition in intertidal and supratidal environments. Influxes of fine clays gave rise to thin mudstones within the Hampole Beds. Particularly around Wetherby, there are also several impersistent mudstones in the strata above the Hampole Beds. These are considered to have been deposited during regression; the associated dolomites have features typical of supratidal conditions, such as fenestrae and microbial laminae, indicative of local temporary emergence. Shallow subtidal dolomites of the Sprotbrough Member above the Hampole Beds include cross-stratification that indicates sandwaves. A lens of clastic material near the top of the formation at Wetherby is interpreted as a flash flood deposit, probably sourced from emergent areas to the west. The upper beds of the Sprotbrough Member show dedolomitization, brecciation and karstic weathering, precursors to the deposition of the terrestrial red clays of the overlying Edlington Formation. Minor post-Permian barite mineralization is found and its distribution is related to underlying structural features. © 2017 The Author(s). Published by The Geological Society of London for the Yorkshire Geological Society. All rights reserved.
... The Hampole beds consist of interbedded dolomite mudstones and siliciclastic mudstones, although Smith (1995) only observed these from a distance. The base of the Sprotbrough Member is formally defined within the Hampole beds (Smith et al. 1986), but as this usage contravenes lithostratigraphical practice, the base has more recently been taken at the position of the Hampole discontinuity (Tymon et al. 2017). In this informal usage, the Hampole beds form the lowermost part of the Sprotbrough Member. ...
Seventeen samples from the Cadeby Formation (Lopingian, Permian, EZ1) of Cadeby Quarry near Doncaster, South Yorkshire, UK, yielded organic residues including phytoclasts, cuticle, unstructured tissue and generally well-preserved palynomorphs. The palynomorph assemblages are dominated by taeniate and non-taeniate bisaccate
pollen including Klausipollenites schaubergeri, Limitisporites rectus, Lueckisporites virkkiae and Taeniaesporites noviaulensis. The assemblages are generally similar to those from the English Midlands described from Kimberley Railway Cutting
and the Haughton Hall Borehole, Nottinghamshire and those from the Marl Slate Formation (lower EZ1) of the Durham Sub-basin at Claxheugh Rock and Crime Rigg Quarry and to the mid EZ1 of the Salterford Farm Borehole and Woolsthorpe Bridge Borehole. The excellent preservation of the assemblages allows the recognition that Dicappipollenites Tiwari & Vijaya 1995 is a junior synonym of Lueckisporites Potonié & Klaus emend. Clarke 1965.
The presence of rare microphytoplankton and microforaminiferal test linings indicate a neashore marine environment. The clastic (and organic) content of the Cadeby Formation, part of a dominantly carbonate succession, may represent erosion and transport of material from the hinterland reflecting a wetter climatic period, though the
alternation of clastic and carbonate sedimentation in the section at Cadeby suggests some wet/dry palaeoclimatic cyclicity.
The Upper Permian Zechstein Supergroup has the potential to play an important role in the UK's future energy production and energy transition. However the Supergroup is comparatively poorly understood in the UK, particularly the link between the onshore and offshore geology. In this paper we re-evaluate available data in order to present a consistent regional interpretation of the Z1 to Z3 Zechstein Supergroup cycles. This review is based on an interpretation and re-evaluation of 620 offshore wells located in the UK portion of the SW Southern North Sea and 83 onshore wells located in Yorkshire and Lincolnshire (eastern England). The Zechstein Supergroup was interpreted in each well, and the data was used to compile seven SW-NE oriented correlation panels which show the development of the Supergroup in the study region. Five isopach maps for key formations in the Zechstein Supergroup were created, together with depositional environment maps for each of the main Zechstein carbonate formations. In combination, these regional-scale maps and diagrams have resulted in a consistent interpretation of the Zechstein Supergroup over an area which extends from the onshore outcrop in the west to the UKCS boundary in the Southern North Sea in the east.
A review of the exposures in the Cadeby Formation, Upper Permian (Lopingian Series) in South Yorkshire by the Sheffield Area Geology Trust revealed groups of previously undescribed sites near the base of the Sprotborough Member, at, and just above, the Hampole Discontinuity. These sites indicate: a wider degree of palaeoenvironmental variation along the Hampole Discontinuity surface than was previously evident; that the discontinuity surface is not laterally continuous; and imply some caution is needed when using these exposures as marker horizons. The field data is used to inform a palaeoenvironmental reconstruction for the period of the Hampole regression. A complex of near-offshore pools and islands, an area of partly exposed shoal and lagoon, and an embayment are identified.
Cavities, pores and crystal pseudomorphs which are lined or filled by calcite are ubiquitous in Raisby Formation dolostones at outcrop in north-east England. Their distribution in most exposures is random on a metre scale. On a smaller scale, cavities, pores and crystal pseudomorphs are most numerous in bioclastic and resedimented beds. Deep borehole cores of the Raisby Formation contain nodules and euhedral crystals of gypsum and anhydrite of very similar size and shape to the cavities and pseudomorphs. This indicates that calcium sulphates were once abundant in the Raisby Formation at outcrop, but almost all have been removed subsequently.
Calcium sulphate minerals were formed early in the diagenetic history of the Raisby Formation, predominantly by selective replacement of carbonate rocks. Gypsum was precipitated first, probably as a by-product of dolomitization, by brines refluxing basinwards through the Raisby Formation from the hypersaline Zechstein Sea during deposition of the Edlington Formation and the Hartlepool Anhydrite Formation. Later, replacive anhydrite formed following both pressure-solution and dehydration of the gypsum. During further burial, some anhydrite was replaced by barite, dolomite and sphalerite. Upon uplift of the Raisby Formation during the Tertiary, anhydrite rehydrated to porphyroblastic gypsum and this was then dissolved by meteoric groundwaters. The resultant pores were lined or filled by two generations of calcite and also, locally, by kaolinite. The earlier calcite generation is luminescent and was precipitated partly as a passive cement and partly by replacement of surviving gypsum and anhydrite, a reaction thought to have been mediated by sulphate-reducing bacteria. The later calcite generation is predominantly non-luminescent and was precipitated from near-surface meteoric groundwaters.
The successions of carbonate-evaporite basins, which are periodically cut off from the world ocean, are considered in terms of their sequence stratigraphy. Two basin types are distinguished: those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation. It is argued that, following relative sea-level falls, sequences begin with the evaporites, precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin-centre halite fills in the second. The evaporites pass up into carbonate sediments which are mainly deposited on shallow-water platforms around the basin during transgressive and highstand systems tracts. The concepts and models developed are applied to the Zechstein (Upper Permian) strata of northeast England and adjoining North Sea. Seven sequences are proposed, with some containing thin parasequences. The sequence approach to carbonate-evaporite basins, which considers both basin margin and basin centre facies, gives a more encompassing perspective of sedimentation than the traditional cycle concept, with its emphasis on the basin centre.
The recurrence of the same types of sequence stratigraphic surface through geologic time defines cycles of change in accommodation or sediment supply, which correspond to sequences in the rock record. These cycles may be symmetrical or asymmetrical, and may or may not include all types
of systems tracts that may be expected within a fully developed sequence. Depending on the scale of observation, sequences and their bounding surfaces may be ascribed to different hierarchical orders. Stratal stacking patterns combine to define trends in geometric character that include
upstepping, forestepping, backstepping and downstepping, expressing three types of shoreline shift: forced regression (forestepping and downstepping at the shoreline), normal regression (forestepping and upstepping at the shoreline) and transgression (backstepping at the shoreline). Stacking
patterns that are independent of shoreline trajectories may also be defined on the basis of changes in depositional style that can be correlated regionally. All stratal stacking patterns reflect the interplay of the same two fundamental variables, namely accommodation (the space available
for potential sediment accumulation) and sediment supply. Deposits defined by specific stratal stacking patterns form the basic constituents of any sequence stratigraphic unit, from sequence to systems tract and parasequence. Changes in stratal stacking patterns define the position and timing
of key sequence stratigraphic surfaces. Precisely which surfaces are selected as sequence boundaries varies as a function of which surfaces are best expressed within the context of the depositional setting and the preservation of facies relationships and stratal stacking patterns in that
succession. The high degree of variability in the expression of sequence stratigraphic units and bounding surfaces in the rock record means ideally that the methodology used to analyze their depositional setting should be flexible from one sequence stratigraphic approach to another. Construction
of this framework ensures the success of the method in terms of its objectives to provide a process-based understanding of the stratigraphic architecture. The purpose of this paper is to emphasize a standard but flexible methodology that remains objective.
Describes the suite of carbonate rocks known as the Magnesian Limestone, which formed near the margins of shallow tropical sea during the last few million years of the Permian. Indicates formation in a complex mosaic of tropical, shallow-water marine sub-environments, ranging from lagoons to barrier bars, reefs to basin-margin slopes. Following an introductory chapter, chapter 2 describes a selected site in the north-west of England; chapter 3 describes 17 localities in the Durham area of NE England; and chapter 4 covers 10 sites in the Yorkshire area. -after Author
Patch-reefs commonly 10-25m across and 3-8m thick are abundant in dolomitized skeletal oolite of the Upper Permian Lower Magnesian Limestone in Yorkshire, England, and are themselves dolomitic. They are roughly circular or oval in plan and irregular in section. A widespread coquina near the base of the formation may have provided a stable foundation for reef forming organisms. Most of the reefs comprise an untidy assemblage of sack-shaped bodies ('saccoliths') , each composed mainly of closely-packed sub-parallel remains of the ramose bryozoa Acanthocladia (generally predominant) and Thamniscus in a finely crystalline dolomite matrix. The reefs probably were formed entirely under water on a broad shallow tropical carbonate marine shelf. Mud-trapping and binding by bryozoa was the main constructional process, with encrusting foraminifers and early submarine cements adding stiffening and bulk. In upper parts of the formation the reefs are composed largely or wholly of algal stromatolitic dolomite.-from Author
New evidence from fluid inclusion compositions and simple physical modelling provide important constraints on the genesis of the ores of the Alston Block in northern England. Evidence from fluid inclusions shows that probably at least four, hydrothermal fluids were involved, two of which are formed by evaporation of seawater, in some cases well beyond halite saturation. Some of the high-temperature fluid dissolved evaporites during its evolution. Physical modelling shows that neither compactional dewatering of the adjacent Carboniferous sedimentary basins nor compressional tilting and throughflow within the Northumberland Trough could have contributed significantly to the hydrothermal fluids of the orefield. Most of the high temperature hydrothermal flow must have been generated by penetrative circulation of surface brines to 8 to 10 km depth in the basement, with the upflow focused and accelerated by the high heat production of the Weardale Granite that unconformably underlies the Carboniferous rocks of the Alston Block. The orefield is considered to have formed during the Upper Permian by the following sequence of events. Initially, fluid movement in the basement was prevented by sealing of pre-existing cracks, and temperatures rose at depth. An episode of extension allowed saline water, probably from the Upper Permian Zechstein Sea, to penetrate deep into the basement, reacting with the rocks there, and becoming heated to as much as 200°C. Penetration to 10 km took a few tens of thousands of years. The granite, at 300°C at that depth, up to 100°C hotter than the surrounding basement, acted to focus the flow, and to generate concentric zones of increasing temperature fluid towards the centre. Once the basement had become cooled, the flow slowed, cracks became sealed, and the episode of hydrothermal circulation and orc formation was complete.
Upper Permian rocks exposed at Quarry Moor, Ripon, Yorkshire, comprise about 7.2 metres of thick-bedded porous oolitic dolomite overlain by about 5.5 metres of varied, mainly thin-bedded, limestones and dolomites with thin argillaceous and earthy beds. They lie at the top of the Lower Magnesian Limestone, and may include the lowest beds of the Permian Middle Marls. Algal lamination is present in the uppermost 9 metres, where textural evidence suggests that the limestones originated by calcitization of earlier dolomite rock (dedolomitization). Most of the rocks exposed were deposited at or near sea level and it is suggested that the contortion and brecciation in some of the higher beds took place during the formation, diagenesis and subsequent dissolution of displacive evaporites. The calcitization is thought to have taken place when intergranular gypsum or anhydrite was dissolved, probably near the ground surface during the current cycle of uplift and erosion.
A thin but distinctive group of mudstones and dolomites have been traced along the outcrop of the Lower Magnesian Limestone from Nottingham to Ripon and, with less certainty, into south Durham. These beds, for which the name Hampole Beds is proposed, overlie a minor discontinuity and are thought to have accumulated partly by intermittent deposition on an extensive intertidal, or supratidal, coastal flat. They constitute a useful marker between the lower and upper subdivisions of the Lower Magnesian Limestone, and extend into areas marginal to the tidal flat where the two subdivisions are otherwise inseparable. They also permit a close correlation of the rocks of these two subdivisions with, respectively, the Lower and Middle Magnesian limestones of the Durham sequence.
Upper Permian carbonates in eastern England at outcrop feature subeconomic syngenetic and epigenetic Pb-Zn-Cu-Fe-Ba-F mineralization. Pb-Zn-Fe sulphides occur in vugs and breccias of sedimentary origin whereas much barite replaces the host carbonate. Vein mineralization is rare. The majority of occurrences are within the Cadeby Formation (Lower Magnesian Limestone; EZ1 Ca).
More than 70 occurrences of mineralization have been recorded, clustered on centres at Farnham, Bramham, Edlington and Mansfield. Host carbonates at the first three of these centres overlie major cross-cutting structures in pre-Permian strata; these structures were possible flow channels for mineralizing solutions. Mineralization in the Mansfield area can be explained by the upwards leakage, on a broad scale, of formation fluids from Carboniferous strata that overlie the South Pennine basement high.
Revised names of some Upper Permian strata in eastern England are proposed and defined, together with new names for some strata previously without formal names; the new and revised names are based on nominated type localities and are intended to replace existing names that were confusing or inappropriate. We propose that the names Lower and Upper Magnesian Limestone in the Yorkshire Province be replaced by the new names Cadeby (Magnesian Limestone) Formation and Brotherton (Magnesian Limestone) Formation respectively and that the Lower and Middle Magnesian Limestone in the Durham Province should become the Raisby (Magnesian Limestone) and Ford (Magnesian Limestone) formations respectively. The Middle Marls are renamed the Edlington Formation in both provinces and the new names Sherburn (Anhydrite) Formation, Sneaton (Halite) Formation and Littlebeck (Anhydrite) Formation are proposed for the Upper Anhydrite, Upper Halite and Top Anhydrite formations. The term Roxby Formation is proposed to replace the present name Upper (or Saliferous) Marls.
Four depositional facies are recognizable in the Sprotbrough Member of the Cadeby Formation (formerly the Lower Magnesian Limestone) in eastern England; they are sabkha, semi-restricted lagoon, oolite shoal complex and open marine shelf. Of these, the oolite shoal complex occupies most of the present outcrop in the Yorkshire Province, i.e. south of the Cleveland High. It comprises large-scale cross-stratified oolite bedforms that are interpreted as sandwaves from their size, type of sediment and internal features. The sandwaves probably originated from the concentration of wave energy by eminences on the floor of the Zechstein Sea. Biogenic structures in the sandwaves show that they were inhabited by marine organisms.
A complex pattern of palaeocurrent styles and azimuths is present within the sandwaves. At many exposures, the long axes of the sandwaves trend NW-SE, suggesting predominant currents normal to this direction. A predominant current from the NE is further indicated by the preferential abutment of SW-dipping beds on the NE flanks of bedforms; this was caused by sandwaves that climbed the backs of others. Occasional storms from the SE produced spillover lobes oriented towards the NW. Storms were also probably responsible for the formation of internal structures such as hummocky cross-stratification, fan-shaped bedding and contemporaneous erosion surfaces.
The Zechstein Limestone (Cal) of Western Germany has a clear stratigraphical subdivision. A lower unit (subcycle a) is separated from an upper unit (subcycle b) by a discontinuity, which is best exposed at the Solhops-Berg at the Harz Mountains and is here termed the 'Solhops Discontinuity'. The discontinuity was caused by an extensive regression of the Zechstein Sea which led to subaerial exposure of large areas of the Zechstein basin. Based on this discontinuity, a preliminary stratigraphy of the Lower Werra cycle in Germany is established and compared with that of the English Zechstein sequence.-Author
Extract
Chapter I. § 1. Introduction. It is my intention in the following communication to describe the principal phenomena exhibited by the great deposit of magnesian limestone which stretches on the eastern skirt of the central chain of our island, from the neighbourhood of Nottingham to the southern extremity of Northumberland. I had, in the year 1821, an opportunity of examining several portions of this deposit (especially in the county of Durham), and of verifying some interesting details connected with it which had appeared in the Transactions of the Society*. During a part of the two following summers I examined its whole western escarpment, and most of the localities which seemed likely to show its general relation, or to throw light on the structure of its subordinate parts. I venture to hope that a connected account of these observations, to which many additions have been made during subsequent visits to certain parts of the formation, may not be thought unworthy the attention of this Society.
After the production of the rocks of the carboniferous order, the earth’s surface appears to have been acted on by powerful disturbing forces, which, not only in the British Isles, but through the greater part of the European basin, produced a series of formations of very great extent and complexity of structure. These deposits (known in our own country by the name of new red sandstone and red marl, and when considered on an extended scale, comprising all the formations between the coal-measures and the lias)
All available information has been used in the preparation of a series of palaeogeographical maps. Most of the area initially lay near the western fringe of the Southern North Sea tropical desert basin, much of which was flooded at the beginning of the late Permian so as to create the epicontinental Zechstein Sea. With oscillating relative sea levels and differential subsidence, contemporary coastlines fluctuated widely whilst successive progradational carbonate shelves were constructed in the first two of four main cyclic sequences; the deposition of thick salt at the end of the second main cycle almost filled the basin, eliminating most of the earlier depositional topography and ensuring that carbonates and evaporites of the third and fourth cycles were formed in a less diverse range of coastal plain to shallow marine environments. -from Author
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