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The English Zechstein and related topics introduction

G.M. Harwood & D.B. Smith

This volume is the printed record of EZ 82, a USSR, a combination which created a lively workshop on the results of recent research on discussion meeting. strata of the English Zechstein and related topics. In a volume dealing with so many diverse The workshop comprised a six-day field study aspects by many authors we claim no unifying meeting on Permian rocks at outcrop in north- theme than that of relevance to the Zechstein. We east England and a three-day indoor discussion have divided the papers herein on a geographical meeting in the Department of Geology at the basis, with papers 2-11 dealing primarily with University of Nottingham. Twenty-one research topics within the United Kingdom, papers 12-15 and review papers were presented at this meeting. within Germany and papers 16-21 within Poland Most of these were written up for this volume with the final contribution, paper 22, describing which has been further supplemented by the Upper Permian sediments from the Urals. Within inclusion of papers submitted by two Polish each geographical section the papers are pre- workers who were unable to attend the work- sented, as far as is possible, in stratigraphical shop. order. The field meeting commenced with visits to the The first section, United Kingdom papers, classic exposures of Upper Permian reef-margin commences with revision of nomenclature for the and slope carbonate rocks in County Durham Upper Permian strata in eastern England (Smith, and adjoining areas and continued to exposures Harwood, Pattison and Pettigrew). This revision of nearshore and shelf carbonates and continen- has been thought necessary for some time, par- tal sediments in Yorkshire, Derbyshire and Nott- ticularly as strata in different Zechstein cycles had inghamshire. A guide to the exposures visited, similar, or confusing, nomenclature in different which also included background information on areas of eastern England. The EZ 82 workshop their stratigraphical, environmental and palaeo- provided the impetus to produce a revised geographical significance, was prepared for the nomenclature, which is detailed here and includes participants; copies of this guide may be obtained definitions and type localities. from The Secretary, Department of Geology, The The remaining papers in the United Kingdom University of Nottingham, Nottingham NG7 section are mostly concerned with carbonate 2RD (1986 price s including postage). strata at, or near, outcrop within eastern Eng- The pattern of the workshop was based on that land. One exception is the paper by Turner and of a highly successful meeting of Zechstein Magaritz, who have carried out detailed minera- workers in Poland in 1978 (Depowski et al. 1981) logical, chemical and stable isotope analyses on at which the growing school of Polish workers, one core from the Marl Slate, taken just offshore amongst others, presented their research results of County Durham. They detail a close correla- to an international audience with research inter- tion between lithological and geochemical para- ests in the Upper Permian. About the same time, meters, including stable isotope values. Saprope- the discovery, possible sourcing potential, plus lic units, at the base of sub-cycles within the Marl exploitation of hydrocarbons in Zechstein strata Slate, are characterized by high contents of iron, in Poland, Denmark, Germany, The Nether- quartz silt and organic carbon with strongly lands, England and the southern North Sea had negative oxygen isotope values. Turner and stimulated Fuchtbauer & Peryt (1980) to put Magaritz conclude these are indicative of fresh- together a collection of papers dealing primarily water influxes which promoted productivity, with Zechstein carbonate rocks (Contr. Sedim. 9, water stratification and regional anoxic condi- 1980). A steady trickle of papers on many aspects tions, thus forming the base of each sub-cycle. of the nature and evolution of Permian strata in They also conclude that the increase in base Europe, together with the processes that shaped metals (notably copper and zinc) away from the them, was also appearing in other journals, sapropelic units indicates these metals to be more providing further evidence of increased interest in associated with the marine conditions re-estab- these sometimes enigmatic rocks. The EZ 82 lished in the upper parts of each sub-cycle. workshop brought together both Zechstein Schweitzer presents an excellent systematic workers from many parts of Europe plus review of all the species of higher plants that have researchers who were working on similar carbo- been described from the Zechstein strata of nate-evaporite basins from the USA to the England and Germany and includes one new Downloaded from http://sp.lyellcollection.org/ by guest on September 25, 2021

2 G.M. Harwood & D.B. Smith species. This flora is characterized by conifers tricted whereas later events were more pervasive. which had reached a surprisingly advanced stage These later events, during early burial, were of polygenetic development and resemble some dominated by dolomitization and subsequent Recent conifers much more closely than Lower partial replacement by evaporites. Harwood con- Permian flora. Conifer woods display distinct cludes that three major dolomite types are present growth rings indicating rhythmic climatic within the Cadeby Formation and that these changes, perhaps on an annual cycle. Schweitzer formed in penecontemporaneous hypersaline demonstrates that the Zechstein transgression lagoons, from reflux of hypersaline fluids after was a significant turning point in floral evolution initial deposition and cementation and from in northern Europe and that floral development mixed water circulation in some nearshore areas. was uniform in both German and English areas of She documents several near-surface events, the Zechstein basin. The most abundant plant including anhydrite to gypsum transformation remains have been discovered in the Marl Slate with later gypsum dissolution, leaching of the and the equivalent Kupferschiefer. carbonates and dedolomitization. Kaldi concen- Well preserved specimens of the conodont trates his paper on the upper, Sprotbrough Merrillina divergens, separated and described by Member of the Cadeby Formation. He defines Swift, have been recovered from English Zech- five types of dolomite within this member, pene- stein Cycle 1 carbonate rocks (EZ1 Ca) in north- contemporaneous supratidal dolomite, primary east England. Swift reports a uniform collection dolomite precipitates within semi-restricted from each locality which can be assigned to just lagoons, early and late dolomite cements within six elements. This low diversity is typical of the ooid shoal facies and local dolomite cements Zechstein Cycle 1 (Z1) strata throughout Eng- within open shelf carbonates and a later perva- land, Germany and Poland and the recognition of sive, replacive, coarsely crystalline dolomite, the a symmetry transition between the elements is one result of mixing of fresh and marine waters. factor used to conclude that these elements are the Harwood and Kaldi thus differ as to the cause of apparatus of a single species. Swift surmises that the replacive dolomitization phase, but unite in the dominance of a single species reflects difficult that this was the major diagenetic event within the living conditions in a wholly, or partially, Cadeby Formation. Kaldi also documents the enclosed basin with fluctuations in sea-level and formation of evaporites both within supratidal salinities. sediments and as a later replacive phase. He The upper member, the Sprotbrough Member, concludes that porosity evolution was dependent of the Zechstein Cycle 1 carbonate, the Cadeby both on the nature of the primary sediments and Formation (EZlb Ca--the former Upper Subdi- on their diagenetic history. Together the papers vision of the Lower Magnesian Limestone) con- present a good introduction to the complex tains evidence of a former ooid shoal complex diagenetic history of these sediments. which was present over most of its outcrop area. In a different approach to the Cadeby Forma- Kaldi describes large-scale cross-stratified bed- tion, Harwood and Smith describe mineralization forms within this complex, including hummocky occurrences throughout the formation at out- cross-stratification, fan-shaped bedding, convex- crop. They demonstrate that the majority of upwards cross-stratification and contempora- mineralized localities cluster within four geo- neous erosion surfaces. He presents data on graphical areas. An underlying structural control palaeocurrent styles and azimuths and concludes is envisaged as a channelway for mineralizing that the predominant current direction was from fluids in three of these areas; in the fourth, the north-east, but that periodic storms produced mineralization appears to be the result of spillover lobes orientated towards the north-west. upwards leakage of formation fluids. Minerals Kaldi adds that although sandwave topography present include lead, zinc and copper sulphides must have controlled local currents by channell- with barite and minor fluorite; occurrences are in ing or refracting flows, the exact manner in which vugs and breccias of sedimentary origin with the sandwaves originated could not be deter- extremely rare examples of vein mineralization. mined. An extensive thin bed, the Trow Point Bed, at Diagenesis within the Cadeby Formation (EZ1 the top of the Zechstein Cycle 1 carbonate (EZ1 Ca) is the subject of two papers. In the first, Ca) in north-east England forms the subject of Harwood distinguishes the timing of different Smith's paper. This bed is present on the lower diagenetic events from penecontemporaneous part of the basin margin slope and is continuous through burial diagenesis to those events asso- over an uneven surface, resulting from a submar- ciated with uplift of the formation during the ine slide, with a local relief of up to 15 m. The bed Cenozoic. She includes evidence that shows early, contains oncoids, peloids, algal laminations and penecontemporaneous events to be facies-res- columnar stromatolites and is similar, and is in a Downloaded from http://sp.lyellcollection.org/ by guest on September 25, 2021

Introduction comparable stratigraphic position, to deposits phy of the Lower Werra Cycle Carbonate (Z 1 Ca) described from Germany, Poland and the south- in West Germany. This paper was submitted after ern North Sea. Smith concludes that the similari- the EZ 82 workshop and is a direct consequence ties of these occurrences suggest that, although of the field excursions before the oral presen- both German and Polish equivalents are con- tations. In visits to exposures in Yorkshire, Paul siderably thicker, they are possible correlatives. was shown the Hampole Discontinuity, first He further surmises that the Trow Point Bed described by Smith (1968). This seemed similar to accumulated in water depths of 25-100 m in oxic some German exposures and, on return to his conditions and may have been much more exten- native country, Paul carried out preliminary field- sive than is apparent at outcrop today. work resulting in documentation, here, of the Evidence for present-day dissolution of gyp- 'Solhops Discontinuity'. Paul concludes this to be sum from both Zechstein Cycle 1 and Cycle 2 equivalent to the Hampole Discontinuity in evaporites in North Yorkshire is given by eastern England. Furthermore, he takes it to Cooper. The timing of the subsidence resulting represent an extensive regression of the Zechstein from this dissolution within the last few hundred Sea, leading to subaerial exposure of marginal years has been documented from newspaper areas of the Zechstein basin. This paper is articles, unpublished notebooks and previous included in this volume both because it resulted published papers; subsidence during Pleistocene from the workshop itself and because of its glaciations is evidenced by Late Devensian and implications on basin-wide changes in sea-level. Flandrian lacustrine deposits over some tens of Richter-Bernburg's two papers concentrate on square kilometres. Cooper demonstrates the the evaporites within the Zechstein sequence. The linearity of many of the subsidence hollows, author has worked with Zechstein material for which he concludes is due to a subsurface joint- many years and has probably seen more Zech- controlled cave and fissure system where active stein sediments, both at outcrop and in core, than dissolution is taking, or has taken, place. He also any other researcher in this field. In the first of demonstrates that the eastern limit of the subsi- two papers he discusses some of the problems of dence-prone belt is marked by the transition of anhydrite sedimentation in Zechstein Cycles 1 the secondary gypsum to anhydrite with depth; and 2 (Z1A and Z2A). He documents five sub- the western limit is where the gypsum, or its cycles in the Werraanhydrit (Z1A) throughout residue, crops out. Cooper's paper is the last in Germany which are correlatable with similar the United Kingdom section of this volume and evaporites within the southern North Sea. Lami- makes a valuable contribution to this aspect of nites near the base of the Basalanhydrit (Z2A) can the Zechstein strata. be traced throughout the German Zechstein The remaining sections of the volume contain basin, although higher within the sequence they papers on the Zechstein elsewhere in northern are abruptly replaced by flaser, or more nodular, Europe, plus one paper on the carbonate-evapor- anhydrite. This change takes place at a lower ite deposits of the Urals. The German papers are position near the basin margins, a factor Richter- contributed by two authors, Paul and Richter- Bernburg suggests may indicate an alteration in Bernburg. In the first of his two papers, Paul the depositional environment in those areas. considers the effects of a basin and schwellen Richter-Bernburg also introduces three new de- topography, inherited from the Variscan regime, scriptive terms for use in study of evaporite on sedimentation within the lower Zechstein sequences in his paper. cycles in Germany. He shows that although the One correlation of Zechstein cycles between basinal Kupferschiefer facies are similar through- Germany, Denmark and England is presented in out the Zechstein, different facies, including red Richter-Bernburg's second paper. Using criteria shales and fossiliferous dolomitized carbonates, including similarities in distribution, thickness are present around the basin rim and on schwellen and lithology of the evaporites, along with a within the basin. In the Zechstein Cycles 1 and 2 change in colour, he suggests that the strata of the carbonates (Z1 and Z2 Ca) reefs and other Don and Aislaby Groups of eastern England are biogenic sediments dominate the basin margins equivalent in age to those of the Werra Cycle in and biogenic sediments were also abundant on Germany and that those of the Teesside Group the schwellen (or palaeohighs). Paul further de- are correlatives of the German Stassfurt scribes how evaporite deposition in both cycles sequence. This correlation is at variance with that was much greater on the palaeohighs and the of both Smith et al. (1974) and Taylor (1980) and basin rims, increasing the relief between palaeo- provoked active discussion when it was pre- high and basin floor with consequent sediment sented; short discussion contributions are instability. included after the paper. In a second paper Paul describes the stratigra- Although two of the Polish authors were able Downloaded from http://sp.lyellcollection.org/ by guest on September 25, 2021

4 G.M. Harwood & D.B. Smith

to attend the EZ 82 workshop, others found it and throughout many of the slope and basin impossible to do so. We have included two deposits. He comments that throughout some additional papers in this section from these areas of Poland, in Germany and in England authors both because the authors had originally there is only one exposure surface recognized (the hoped to present these in Nottingham and 'Solhops Discontinuity' in Germany and the because of their relevance to Zechstein research. Hampole Discontinuity in eastern England) but is The first of these papers is by Oszczepalski, and is unable to determine whether this coincides with one of a series of three papers on the Copper the boundaries between his first and second sub- Shale in the area of the Foresudetic Monocline in cycles, or between the second and third, or south-western Poland. Oszczepalski, working whether one of these sub-cycles is not developed with a series of cores, has used microfacies in the other areas of the Zechstein basin. analysis combined with geochemical studies to The macrofauna present in the first three define three major facies within the Copper Shale; Zechstein cycles in Poland is summarized by a deep shelf facies, a shallow shelf facies and a Karwowski and Klapcinski. They distinguish nearshore facies. Shorewards the Copper Shale is four biozones with characteristic faunal assem- replaced by carbonate and/or terrigenous sedi- blages, which typify palaeogeographical areas ments. A great deal of detailed research has been within the Zechstein carbonates. Preservation of compiled in this paper as Oszczepalski combines the macrofauna is variable, in part dependent on both inorganic and organic geochemical results the host rock and its diagenetic history. Fauna with personal core descriptions in his analysis. discussed include bryozoans, brachiopods and In contrast, in his two papers, both presented at bivalves with gastropods, cephalopods and echi- Nottingham, Tomaszewski concentrates on the noderms being poorly represented. The authors base metal enrichment of the Copper Shale. In the include a faunal list showing stratigraphic occur- first of his papers, he comments on the genesis and rence. structure of the polymetallic ores in the area of the In a separate paper, Klapcinski describes the Foresudetic Monocline. Also working with shal- Leine Anhydrite (PZ3A) within Poland. He low cores, he has produced detailed maps show- recognizes three lithostratigraphic units within ing the distribution of the types of ore, the the anhydrite, principally based on its textural different mineral zones and the lead content characteristics. The spherulitic structure of units within the area, together with cross-sections within the anhydrite is described, with examples showing the vertical distribution of the minerali- shown in the text. This texture is recognizable zation. In the second paper, on the sedimentary throughout much of the Leine Anhydrite in environments of the lowest Zechstein sediments, Poland. Klapcinski concludes that the presence of Tomaszewski presents data from samples from this spherulitic texture in the anhydrite may underground galleries in the Lubin copper mine, provide a useful and extensive marker unit within which have been analysed for their metal content the Zechstein basin. and mineralogical components. With additional The final paper in this volume deals with a data from the mine's geological service, he has carbonate-evaporite succession outside the Zech- constructed isopach maps for the Border Dolo- stein basin, but of a similar age. Chuvashov mite and Copper Shale and also shows the presents a brief description of sediments from the amount of mineralization in the underlying white Kungurian basin of the Urals, concentrating on sandstones. Taken together, Tomaszewski's the carbonates present. He compares these to papers present a wealth of hitherto unpublished similar sediments within the Zechstein basin and data on the extent of mineralization in the Lubin also provides a stratigraphic summary which area of the Foresudetic Monocline and discuss helps to depict the evolution of the Kungurian some of the current ideas on its genesis. basin. Peryt contributes a discussion on the chronos- In compiling this volume we have rejected some tratigraphical and lithostratigraphical correla- manuscripts initially presented at the EZ82 work- tions of the Zechstein Limestone (PZ1 Ca) shop, in addition to including three papers not throughout Poland, which unfortunately he was orally presented at the meeting. We have tried to unable to present personally in Nottingham. He include as many of the foreign papers as is recognizes three sub-cycles within this carbonate, practicable as little research in this field is pub- each representing progressive shallowing lished in English; perhaps the references included upwards. In areas around the basin margin the will encourage some readers to consult the Ger- upper parts of these subcycles contain evidence of man, Polish and Russian literature. We realize subaerial exposure. Peryt uses these exposure that this represents a very small contribution to surfaces as chronostratigraphic markers which he research over the whole Zechstein basin and that traces across the carbonate platform sediments there are many areas of relevant research that are Downloaded from http://sp.lyellcollection.org/ by guest on September 25, 2021

Introduction 5

not included. Perhaps the greatest omissions are they answer. We are very conscious of the the areas of East Germany, Denmark, the north- problems yet to solve and of whole fields that ern Netherlands and the southern North Sea. We have been largely ignored in research. We hope also realize that many questions remain unans- that this book will go some way towards stimulat- wered and that many of the papers included in ing interest, and hence further research, on this volume perhaps raise more questions than Zechstein strata throughout the basin.

References DEPOWSKI, S., PERYT, T.M. & PIATKOWSKIT.S. 1981. SMITH, D.B., BRUNSTROM, R.G.W., MANNING, P.I., Proceedings of International Symposium on Central SIMVSON, S. & SHOTTON, F.W. 1974. Correlation of European Permian. Wydawnicta Geologiczne, the Permian rocks of the British Isles. Spec. Rep. Warszawa. geol. Soc. Lond., No. 5. FUCHTBAUER, H. 8z PERYT, T.M. 1980. The Zechstein TAYLOR, J.C.M. 1980. Origin of the Werraanhydrit in Basin with emphasis on carbonate sequences. Contr. the U.K. Southern North Sea--a reappraisal. In: Sedim. 9, Schweizerbart'sche Verbuchhandlung, FUCHTBAUER, H. & PERYT, T.M. (eds) The Zechstein Stuttgart. Basin with Emphasis on Carbonate Sequences. Contr. SMITH, D.B. 1968. The Hampole Beds--a significant Sedim. 9, 91-114. Schweizerbart'sche Verbuchhan- marker in the Lower Magnesian Limestone of dlung, Stuttgart. Yorkshire, Derbyshire and Nottinghamshire. Proc. Yorks. geol. Soc. 36, 463-74.

GILL M. HARWOOD, Department of Geology, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU. DENYS B. SMITH, 79 Kenton Road, Newcastle upon Tyne NE3 4NL.