Zechstein Research Articles

Stratigraphy of the Lower Werra Cycle (Z1) in West Germany (preliminary results)

Summary 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.

Plate and intraplate processes of Hercynian Europe during the late paleozoic

It is speculated that until Late Carboniferous time the region of Hercynian Europe was occupied by an elongated island arc system underlain by a segment of continental crust. In the Upper Carboniferous, two subduction zones are assumed to have extended from the north and south beneath Hercynian Europe. An extensive zone of hot, partially molten upper mantle lay above and between these, and diapiric uprise of portions of this material led to separation of mafic magmas, widespread partial melting in the lower and middle crust, high temperature-low pressure metamorphism in crustal rocks, and regional uplift and extension of the crust, as indicated by intermontane troughs and their associated volcanic rocks. In Visean to Westphalian time Hercynian Europe collided with both the large neighbouring plates North America-Europe and Africa. During these diachronous collisions and owing to reduced rigidity of the relatively hot island arc crust, the irregular continental margins of the larger and thicker continental plates induced oroclinal bending of Hercynian Europe. After the collision processes had been terminated, processes of upper mantle activity continued, causing further crustal uplift and even, enhanced crustal extension for several tens of million years into the Lower Permian. Decline of the upper mantle activity beneath Hercynian Europe is indicated by crustal subsidence and formation of a peneplain in Permian time followed by the Upper Permian transgression of both the Zechstein sea and the Tethys sea which mark the end of the Hercynian geodynamic cycle.

The Permian Weissliegend of NW Europe: The partial deformation of aeolian dune sands caused by the Zechstein transgression

The Weissliegend is a European sandstone unit of largely late Early Permian age. It is underlain by the Early Permian Rotliegend red desert sandstones and is overlain by the conventionally accepted basal bed of the Zechstein-the bituminous marine shales of the Kupferschiefer. The Weissliegend sandstones are characteristically white or grey in colour and have been recognised beneath the North Sea, in Germany and in Poland. Equivalents, which are red or yellow in colour, occur in NE England and at the southern edge of the Moray Firth Basin in Scotland. From an examination of cliff and quarry exposures in Britain, and of drill cores from southern North Sea gas wells, it is now believed that the bulk of the Weissliegend sandstones (and their equivalents) were originally deposited as aeolian dunes. These dune sands, however, were later modified by a widespread event, the Zechstein transgression, which caused their partial homogenisation, the creation of large-scale soft-sediment deformation structures, and the local and minor reworking of some of the dune flanks. The preferred mechanism of deformation is interpreted as: (1) entrapment of large pockets of air within the bodies of the dunes by flanking and overlying wetted dune sands; (2) venting of the air pockets when the rising internal air pressures overcame the weight of the hydrostatic head of water and the capillary (cohesive) strength of the overlying wetted sands; (3) the rapid replacement of air by water, which caused liquidisation of the original dune laminae; and (4) the associated collapse and final consolidation of the sands into a tigher packing configuration. Deformations seem to be more developed in former transverse dunes than in seif dunes. The reason may be that the relatively tightly packed low-angle accretion bedding common on the flanks of seif dunes is more resistant to deformation than the looser avalanche sands that form a major part of transverse dunes. Limited reworking of former dune sands was probably best developed on the steep lee slopes of transverse dunes and the steeper upper slopes of seif dunes. The lack of reddening of the Weissliegend sandstones-proper is attributed to a combination of their accumulation above the Rotliegend water table, to the rapidity of the Zechstein transgression, and to the anoxic state of the early Zechstein sea floor. The Weissliegend sands, unlike the underlying Rotliegend into which they grade, were thus never in a diagenetic environment that was conducive to reddening. Finally, it is recommended that the term Weissliegend be dropped in any formational sense. It should only be retained for the Weissliegend proper, and their equivalents, to denote a complex facies association dominated by (1) the uppermost Early Permian Rotliegend dune sands (now partly deformed) that lay above the water table just prior to the Zechstein transgression, together with (2) the minor erosional marine products caused by that transgression. The latter, sensu stricto, are Zechstein sandstones of earliest Late Permian age.

Permian

In North-West Europe two mega-basins began their development during Late Carboniferous to Early Permian: The South Permian Basin stretching from eastern England into Poland , and the North Permian Basin reaching from Scotland into Denmark. These two basins were separated by the Mid North Sea High and the Ringkøbing-Fyn High which came into existence early in Permian. The initial phase of subsidence was accompanied by extensive subaerial volcanism. This was followed by a period of oxidation and erosion under desert conditions and deposition of red beds and sabkha sediments in the two Permian basins (fig. 19). These rocks are included in the Rotliegendes Group as originally established by Werner (1786). Continuous subsidence and transgression of the sea, but with a restricted connection to the ocean, lead to the formation of the evaporites of the Zechstein Group.

A gliding reptile from the Upper Permian of North East England

In July 1978 an unusual fossil reptile was discovered by D. Hall and myself 1.5 cm above the base of the Upper Permian Marl Slate at Eppleton Quarry near Hetton-le-Hole, Tyne and Wear (NZ 351484). The sapropelic Marl Slate, the first member of the English Zechstein succession, is a marine deposit well known for its fossil fish (mainly palaeoniscids) and land-derived plants1. The only recorded reptilian remains Consist of two incomplete skeletons of Protorosaurus2. The new find is an incomplete skeleton (the skull, forelimbs and most of the tail have been destroyed by quarrying), 17 cm long, of a terrestrial reptile washed into the Zechstein Sea. It is especially interesting for its elongated and jointed dorsal ribs interpreted as an adaptation for the support of two membranes to enable the reptile either to parachute or more probably glide in a manner similar to the modern gliding lizard Draco of South East Asia3.

Rapid marine transgressions and regressions of the Upper Permian Zechstein Sea

Evidence bearing on the rates of transgression and regression of the early Zechstein Sea in NE England is reviewed and the hypothesis that this sea was formed virtually instantaneously when the Boreal Ocean broke into and flooded a chain of sub-sea-level inland drainage basins is restated. Subsequent formation of a thick marginal carbonate wedge was apparently followed by an unusually rapid marine recession, the cause of which is postulated as evaporative drawdown after renewed isolation of the Zechstein Sea. The possibility of other rapid Zechstein transgressions and recessions is briefly discussed.

THE MARL SLATE AND BASAL PERMIAN BRECCIA AT MIDDRIDGE, CO. DURHAM

SUMMARY A study of the stratigraphy and palaeontology of the Basal Permian Breccia and Marl Slate at Middridge, south-east Durham, was recently made possible by the reopening of an old quarry. The Permian Breccia here, although originally deposited under terrestrial (desert) conditions, was subsequently partially redistributed during the transgression of the Zechstein Sea. Numerous specimens of invertebrates, fish and plants were collected and the assemblages as a whole demonstrate that the Marl Slate is of a near shore facies in this part of Durham. Sessile, shallow water invertebrate fossils are relatively abundant at the top of the Breccia and in a laminated limestone within the Marl Slate. Many of these fossils represent several years of in situ growth which contradicts the accepted palaeoenvironmental interpretation of seasonal toxic conditions. It is suggested that toxic conditions were less severe in the near shore environment which probably acted as a refuge for the deep and shallow water faunas during periods of unfavourable conditions in the offshore area. This interpretation is supported by other exposures of the Marl Slate in south Durham which yield a sparse invertebrate assemblage in contrast to the exposures to the north-east which yield few or no invertebrates and an essentially deep water fish fauna.

Iron-boracite from the English Zechstein

Iron-boracite from the English Zechstein

Petrology of the Permian Yellow Sands of northeastern England and their North Sea Basin equivalents

The Permian Yellow Sands of northeastern England and the Permian Weissliegendes of the English North Sea Basin are petrologically defined as multicycle, moderately sorted, subrounded graywackes, subgraywackes and subarkoses with post-depositionally etched and overgrown grains. These sandstones were derived by the marine reworking of the Permian Rotliegendes and transported from the east to the southwest. Petrologic data show that these Upper Permian sandstones were deposited in a shallow marine environment and that the commonly held aeolian dune interpretation for them should be rejected. Their formation during the transgression of the Zechstein Sea places them within the Zechstein sequence and therefore they are Thuringian in age rather than Saxonian.

Petrology of the Weissliegendes sandstones in the Harz and Werra-Fulda areas, Germany

The Weissliegendes and adjacent related Permian sediments from the Harz and Werra-Fulda areas are petrologically described. The Weissliegendes sandstones are classified as moderately sorted, multicycle subgraywackes and orthoquartzites. Petrographic data indicate that the Weissliegendes and Zechsteinkonglomerate were derived in large part from the underlying Rotliegendes. Textural and stratification data show that the Weissliegendes sandstones were deposited in a shallow marine depositional environment and that the aeolian dune origin for the sandstones should be rejected. Rotliegendes sands and gravels were reworked by the transgressive Zechstein Sea, producing the sands of the Weissliegendes and the lag gravels of the Zechsteinkonglomerate. These two closely related units are time equivalent facies which represent the initial stage of the Zechstein Series.

Zechstein lead-bearing shales in the Fore-Sudetian monocline in Poland

Zechstein lead-bearing shales in the Fore-Sudetian monocline in Poland

Permian Rotliegendes of Northwest Europe: ABSTRACT

The basal Permian Rotliegendes redbeds of the North Sea area, in the Northwest Europe Permo-Triassic basin, contain some of the world's largest gas reserves. Groningen field, The Netherlands, discovered in 1959, has proved plus probable gas reserves of 66.7 Tcf (1,904 × 109 m3). Smaller Netherlands and northwestern Germany fields contain proved plus probable gas reserves of 8.4 Tcf (240 × 109 m3); North Sea gas fields have 22.5 Tcf (700 × 109 m3). The Northwest Europe Permo-Triassic basin is north of the Variscan mountain chain, which was folded during Pennsylvanian time and which extends from the southern British Isles to central Germany. North of the Variscan mountain chain is a block-faulted foreland on which the Mid-North Sea and Fyn-Grinsted highs formed. The WNW-ESE-trending Northwest Europe Permo-Triassic basin is between these highs on the north and the Variscan chain on the south. A second Permo-Triassic basin, whose boundaries are not defined, may lie north of the Mid-North Sea and Fyn-Grinsted highs. The sediments of the basal sedimentary unit of the Permo-Triassic basin, the Rotliegendes, were derived mainly from the Variscan mountain chain. As this mountain chain rose and was eroded, increasingly arid conditions predominated. As a result, the Rotliegendes is primarily a desert deposit, though marginal fluviatile and local evaporitic sediments are present. When the arid climatic depositional conditions and desert origin of the subsurface Rotliegendes were recognized, it became imperative to develop criteria for the recognition of different desert-arid sedimentary facies, so that an exploratory program could be developed. Modern desert studies were made, and three major sedimentary facies were recognized: (1) wadi (intermittently flowing streams) gravel and sand which border highl nds; (2) eolian sand, derived from deflation of wadi deposits and outcrops, forms barchan dunes (probably formed from intermediate-velocity winds) and linear (seif) dunes, parallel with the dominant wind direction (probably formed from high-velocity winds); and (3) sabkha deposits of both the inland (wadi or oasis types) and coastal varieties, including both layered and interstitial evaporitic deposits. All three facies have been recognized in the Rotliegendes. Generally, the wadi facies are basal or peripheral within the basin. Most are broad alluvial fans along the northern flank of the Variscan mountain chain. The eolian facies is widespread--some as thick as 660 ft (200 m). The lack of linear dunes suggests intermediate wind-velocity values. Directional data indicate a west-to-east wind flow, as in the modern horse-latitude deserts. Sabkha facies also are widespread, particularly in the upper and central parts of the basin. These include interior-desert sabkha deposits, where wadi waters reached the surface, as well as coastal sabkha deposits, the precursors of the later Permian Zechstein sea. Although the environmental conditions which produced the Rotliegendes persisted locally, these environmental conditions eventually were replaced by the rapid transgression of the Zechstein sea when the basal Kupferschiefer (Copper shale) and associated marine evaporite deposition began. End_of_Article - Last_Page 1969------------

Neptunist concepts in ore genesis

Mineralization of middle Permian sedimentary rocks of western Europe (Kupferschiefer and correlatives) is not prominent in rocks containing penecontemporaneous vein deposits. Solutions from a deep-seated source formed the vein deposits, and where they emerged at the surface, beneath the waters of the Zechstein sea, their remaining metal contents were precipitated under foul-bottom conditions.

Biogenic primary sulfide of the Permian Kupferschiefer and Marl Slate

Pyrite spheres in the Permian Kupferschiefer of the Mansfeld district, Germany, and the Marl Slate of northeast England (also a deposit of the early Zechstein sea) are shown to enclose remains of Pyritosphaera barbaria (mainly) or other fossil microorganisms considered to have been responsible for precipitation of primary iron sulfide in fetid bottom muds. At a later stage in diagenesis of the sediments, the iron of the authigenic pyrite was replaced by other metals (whose source has not been determined), leading to formation of the Kupferschiefer copper, zinc, and lead ores.

SYNGENETIC AND DIAGENETIC MINERALIZATION IN YORKSHIRE

Summary The bedded iron ores, sulphide-bearing black shales and evaporites of Yorkshire are described. The presence of abundant decaying vegetable or animal matter is held to be fundamental to the formation of both the clayironstones of the Coal Measures and the sideritic chamosite-oolites of the Jurassic, to provide the required conditions of low pH, low pH and available CO 2 . Oxide, silicate-carbonate, carbonate and sulphide facies are recognized in the Cleveland ores and associated rocks, and the primary chamosite ooliths are held to have been formed in the region between the carbonate and oxide zones rather than near the sulphide facies. It is noted that Al and Si in solution are necessary, in addition to Fe++, for the formation of the silicate ores. Hypotheses, including that of Borchert, for the transportation and precipitation of the iron are considered, and an attempt is made to assess the role of diagenesis in this type of mineral concentration. A consideration of the zonal distribution of minerals within the Permian evaporites leads to a suggestion that a straits or submerged bar lay to the north-west between the Zechstein Sea and the open ocean. The zones tended to migrate towards the margin of the basin as deposition proceeded. Boundaries between the various members of the evaporite sequences are considered to be markedly diachronous. Emphasis is laid upon the massive and complex effects of later, probably diagenetic, changes under the influence of migrant concentrated brines.

Some aspects of the new red desert in britain

AbstractA number of points of interest and controversy in British Permo‐Trias stratigraphy are discussed. Evidence is put forward to suggest that the location of the British area in relation to the poles was very different from that of the present day. The origin of the red colouration in the dune sands is discussed. An attempt is made to reconstruct the outcrop geology of northern England in New Red times, and from this deductions are drawn about the extent of the Zechstein sea. The nature of the false‐bedding in the dune sands is analysed and conclusions are drawn about the extent of the sand sea and the regional pattern of prevailing winds. The relation between false‐bedding and true dip is discussed in an appendix.

Progressive und deszendente Vorgänge bei der Sedimentation der Riedel-Gruppe (Zechstein 3)

Progressive und deszendente Vorgänge bei der Sedimentation der Riedel-Gruppe (Zechstein 3)

Tiefenberechnung des Zechsteinmeeres nach dem Bromgehalt der Salze

Tiefenberechnung des Zechsteinmeeres nach dem Bromgehalt der Salze

PERMIAN EVAPORITES AND ASSOCIATED ROCKS IN TEXAS AND NEW MEXICO COMPARED WITH THOSE OF NORTHERN ENGLAND

Summary Marine evaporites form an important part of the Permian succession of the United States and of England. This paper gives a review of their geological setting, petrology, and mineralogy. The American mid-continental Permian reaches its greatest thickness in Texas and New Mexico. In Leonard and Guadaloupe times several relatively deep basins, flanked by shallow-water shelf areas, were connected by channels to each other and to an ocean to the south. Reef and bank deposits accumulated at times on the margins of the basins, and separated clastic basinal deposits from back-reef limestone-evaporite-red bed facies on the shelves. There was a general south-westward shift of areas of evaporite deposition as time went on, corresponding to a general retreat of the epicontinental seas. These conditions culminated in the development of the Capitan reef which surrounded the Delaware basin in Upper Guadaloupe time. Later the area was uplifted and tilted, and the basinal evaporites of the Ochoa (more than 4,000 ft. in thickness) were deposited, filling the Delaware basin, overlapping its margin, and covering part of the shelf. The back-reef evaporites are mineralogically simple, and show a marked lateral zoning from less to more soluble salts in a landward direction. The Castile evaporites (Lower Ochoa) provide a striking example of relatively deep-water deposition in an almost isolated basin relatively free from influx of terrestrial water. The Salado and Rustler evaporites (Upper Ochoa), which are mineralogically complex, are shallow-water basinal types, and include important deposits of potassium salts. The British Permian evaporites, deposited in the Zechstein Sea, represent a small part of a large area of deposition. There is little evidence of back-reef deposition in England. The evaporites appear to be predominantly shallow-water basinal types like those of the Salado Formation of Texas and New Mexico. They include the products of three major cycles of desiccation, and it is suggested that these correspond to the upper three of the four major cycles of Hanover and Thuringia. The lowest cycle of this German succession may be represented in north-eastern England by replacement bodies of anhydrite in the Lower Magnesian Limestone. Lateral change of facies in the English evaporites is marked, and includes the passage of evaporites into red beds, and of more into less soluble salts, in a shoreward direction. Potassium salts are confined to the Whitby district, where the marine Permian reaches its greatest thickness. Halite, anhydrite, and the carbonates progressively die out as the shore-line is approached. Vertical zoning includes the upward passage of less to more soluble salts, and repetitions of sequence are numerous, but large-scale repetitions within each major cycle are much less abundant than in the Salado. The mineralogy of the two regions is compared and found to be generally similar. Striking differences include the restriction of rinneite to the English evaporites, and the virtual absence of langbeinite, a major constituent of some of the Salado potash zones, in England. The English potash field is notably richer in quartz and clay, and poorer in magnesium sulphates (except in the Lower Evaporite Bed) than the American. Some minor constituents found only in the Salado may be expected to be found as exploration proceeds in England. Widespread replacement and recrystallisation have modified the evaporites of both regions, and their present mineral composition differs a great deal from that of the original deposits.

XXI.— Age-Relations of the Epigenetic Mineral Deposits of Britain

Finlayson’s thesis that the important British non-ferrous mineral fields were mineralized in Hercynian times is examined in the light of investigations made since 1910 and largely confirmed. It is suggested that hydrothermal fluids leaked into the Zechstein Sea and that dolomitization related to this sea preceded non-ferrous mineralization in the Southern Pennines. Pockets of “fossil” Hercynian hydrothermal waters are believed to explain certain instances of weak mineralization affecting Mesozoic strata. In Carboniferous Limestone areas deep cavernization later than the Hercynian non-ferrous epoch occurred before or during the accumulation of the ferric (haematite) ores in Tertiary times.