Zechstein Limestone Research Articles

Variable alteration of organic matter in relation to metal zoning at the Rote Fäule front (Lubin-Sieroszowice mining district, SW Poland)

Drill core samples of the Lower Zechstein strata in the Lubin-Sieroszowice Cu-mining district (SW Poland) were collected at different distances to the oxidized zone (Rote Fäule), developed around the Zary Pericline. The sampled intervals include Kupferschiefer, underlying Weissliegendes sandstone and overlying Zechstein Limestone from Rote Fäule zones, adjacent Cu-mineralized strata, and drill cores from the Pb/Zn-mineralized zone more distant to the Rote Fäule front. The Kupferschiefer samples show differences in base metal and noble metal contents, accompanied by variations in the molecular composition of hydrocarbons. Organic matter is characterized by the soluble organic matter (SOM) yields, and relative proportions of saturated and aromatic hydrocarbons of the SOM. Our results provide evidence for an oxidative alteration of organic matter in Kupferschiefer samples within and adjacent to the Rote Fäule zones. The extent of this alteration is reflected by differences in the composition of the saturated and aromatic hydrocarbon fractions of the soluble organic matter. In contrast to Kupferschiefer from Pb/Zn-mineralized areas, short-chain n-alkanes dominate the saturated hydrocarbons of oxidized samples. With decreasing distance to the Rote Fäule zone, compositional changes of the aromatic hydrocarbon fractions are characterized by the increase in concentration of polycyclic aromatic hydrocarbons and elevated ratios of phenanthrene to methylphenanthrenes, resulting in a decrease of the methylphenanthrene index (MPI 1). In highly oxidized samples, the increase in the ratio of phenanthrene to methylphenanthrenes concentrations due to demethylation reactions appears to be reversed, probably caused by degradation of phenanthrene as well as the methylphenanthrenes. Organic matter of noble metal-bearing Kupferschiefer from the Rote Fäule front is characterized by high abundances of polycyclic aromatic hydrocarbons (PAHs) and sulfur- and oxygen-bearing PAHs. This result might argue for a concomitant transport of the PAHs and the noble metals in ascending oxidizing solutions, and a contribution of metal-organic complexes in mobilisation and transport of gold. The regional base metal zonation in the Kupferschiefer inside the mines, is explained by redox controlled metal precipitation from oxidizing brines through decreasing Eh-conditions during its infiltration into the reduced Kupferschiefer. Short-scale zonation in Au and Pt/Pd-contents at the oxidized-reduced interface is consistent with that model of ore formation. Organic geochemical maturation parameters argue for maximum temperatures during Kupferschiefer diagenesis between 100 and 120°C. Comparable temperatures are assumed for the ore fluids responsible for Cu mineralization near Rote Fäule.

On the neutron properties of Main Dolomite and Zechstein Limestone

Measurements of the macroscopic thermal neutron absorption cross section and slowing-down power were conducted on 75 specimens taken from the Main Dolomite and Zechstein Limestone formations as they occur in 10 prospect boreholes located in different regions of Polish Lowland. The specimens chosen for this study represented lagoonal, barrier and fore-barrier facies of Main Dolomite as well as barrier and reef facies of Zechstein Limestone. Slowing-down power measurements enabled the determination of water content in the solid phase of specimens. Histogram distribution functions for the macroscopic thermal neutron cross section and bound water content of analysed specimens are presented.

Mixed evaporative and meteoric water dolomitization: isotope study of the Zechstein Limestone (Upper Permian), southwestern Poland

Dolomites of the Zechstein Limestone in western Poland have high 13C values, characteristic of the Zechstein carbonates, and there is some variation in 18O profiles. Dolomites are mostly stoichiometric and well ordered and are characterized by variable crystal textures. The area studied underwent constant burial since the Late Permian and the isotopic curves, despite their complexity, show distinct regularities and signals of meteoric water input that in most cases could occur only during the Permian. Moldic porosity, interpreted as originated shortly after dolomitization, commonly occurs. Stratigraphic patterns and facies analyses suggest that dolomitization phases occurred at the top of each (eustatically controlled) subcycle of the Zechstein Limestone in association to subaerial exposures. Most of the dolomites, therefore, originated during the Permian.A significant proportion of the dolomites originated via meteoric—marine mixing during deposition of the Zechstein Limestone. The mixing mechanism was closely related to sea-level falls. Conventionally, evaporite-related dolomites are believed to have originated in a sabkha environment and/or by the reflux mechanism. The Zechstein Limestone case suggests that the mixing of evaporative and meteoric water may be responsible for dolomitization of other evaporate-related carbonates.

The Kupferschiefer Cu–Ag ore deposits in Poland: a re-appraisal of the evidence of their origin and presentation of a new genetic model

The Kupferschiefer stratiform copper deposits in central Europe have long been considered a classic example of syngenetic mineralization. However, metal zoning and host-rock relationships determined during exploration around the recently discovered Lubin district orebodies in southwest Poland suggest that the ore may instead be late diagenetic. The mineralization occurs as thin, extensive blankets of sulphides in the pyritic, organic-rich basal units of the Late Permian Zechstein restricted marine sequence and in the eolian Weissliegendes sandstone at the top of the Early Permian Rotliegendes continental rift sequence of bimodal volcanic rocks and redbeds. It is directly underlain and controlled by irregular, oval zones of Rote Fäule (RF), a barren oxidized and reddened portion of the normally dark grey, pyritic basal Zechstein rocks. In plan view, the metals occur as successive belts enriched in copper (+ silver), lead, and zinc, which developed laterally from and encircle the RF zones. The ore transgresses the depositional strike of the basal Zechstein and can occur in any sedimetary facies. In section, the ore cuts across sedimentary layering from the Zechstein limestone down through the Kupferschiefer shale (Ks) into the sand stone below. Framboidal, presumably very early diagenetic, pyrite is the dominant sulphide above and lateral to the ore zones; over most of the basin, the Ks is pyritic and not anomalously high in metals compared with similar shale elsewhere. In the ore bodies, Cu, Ag, Pb, and Zn are significantly above the typical background contents, implying that these metals have been introduced. Metal contents in the RF are within the range of background contents of the Ks, suggesting that the metal source is external to the Ks. The RF–copper zones are coincident with underlying buried basement highs and occur only above Rotliegendes sediments with underlying volcanic rocks, indicating a possible genetic connection. The metal zones generally dip away from the highs toward the basin centres, suggesting convective, rather than throughgoing, fluid flow. Sulphides, as disseminations and streaks, commonly replace earlier calcite cement and lenses, lithic fragments, and quartz grains. Horizon tal and vertical dilatant veinlets of calcite and copper sulphides appear to have formed after lithification and contemporaneously with the disseminations and streaks, but not by remobilization of existing sulphides. The veinlet orientations are believed to be Kimmerian age (mid-Triassic to Late Jurassic), and the orebodies are cut and displaced, but not remobilized, by fractures and dikes of inferred Alpine (Cretaceous) age. Published sulphur-isotope ratios indicate that the copper sulphides were not formed in isotopic equilibrium with the pyrite, but adequate sulphur- and lead-isotope information on the ore deposits is not available to support an early or late diagenetic timing. The paleomagnetic age of the stable chemical remanence of the RF is Middle Triassic, supporting a late diagenetic origin of the ore coincident with a second rifting event. On account of these asso ciations and controls, it is proposed that the RF–ore systems were formed by converting Na–Ca–CI Rotliegendes formational brines. The metals were leached from the Rotliegendes volcanic detritus and carried in solution as chloride complexes through the redbeds up the flanks of the buried basement highs to the reduced pyritic Ks above. The fluids oxidized the original Ks pyrite to form the Rote Fäule, and the ore sulphides were precipitated on the far side of this subhorizontal oxidation–reduction front. This late diagenetic mineralizing event likely occurred during the Triassic, when rapid burial and increased heat flow, associated with the opening of the Tethys ocean to the south, generated natural gases and vertical fractures in the Ks and increased convective fluid velocities in the Rotliegendes basins.

A Mid‐Triassic paleomagnetic age of the Kupferschiefer mineralization in Poland, based on a revised apparent polar wander path for Europe and Russia

Extensive mineralization occurs in southwest Poland as zoned blankets of Cu‐Ag‐(Pb‐Zn) sulphides in the Kupferschiefer and Zechstein Limestone across the base of the Late Permian Zechstein restricted marine sequence, and in the Weissliegendes sandstone at the top of the Early Permian Rotliegendes continental volcanic and siliciclastic sequence. The Rote Fäule (RF) zone, an oxidized, hematitic equivalent of the normally pyritic basal Zechstein, directly underlies the copper ore and is part of the metal zoning. Although the origin has generally been considered to be syngenetic, geologic controls of the RF‐ore systems in Poland suggest a late diagenetic origin by converting metalliferous brines migrating through the Rotliegendes clastic redbeds up along basement highs, oxidizing the pyritic Kupferschiefer to form the RF, and precipitating base and precious metals on the reduced side of this oxidation‐reduction front. A paleomagnetic study of the ore zone in five mines in Poland, the RF zone in three mines, and of the barren pyritic basal Zechstein from outcrops and quarries in Poland, Germany, and England was undertaken to determine the absolute age of the mineralization. In the barren pyritic rocks and the copper sulphide ore, thermal demagnetization and vector subtraction revealed an unstable low‐temperature first‐remanence component (76.9°N, 12.2°E; A63 = 1.6°), parallel to the ambient field, and a second, higher temperature component (82.6°N, 145.9°E; A63 = 1.9°), which could be Miocene (10–20 Ma) or, less likely, Cretaceous (110 Ma) or Jurassic (180 Ma). This second component is erased at 350°–400°C and is thought to be carried by a product of weathering after Alpine age uplift and erosion. No primary magnetization could be isolated in the copper or pyritic zones. The RF hematite, however, contained a very stable third, reversed component (49.0°N, 157.2°E; A63 = 2.2°) which was revealed typically between 500° and 620°C, and is considered to represent a secondary chemical remanent magnetization acquired during the mineralizing process. In order to date the isolated magnetic components, Carboniferous to Neogene apparent polar wander (APW) paths for Europe and Russia were constructed using paleopole catalogs. Mean paleopoles every 10 Ma from 350 to 0 Ma, with A63 circles of confidence, were calculated as running averages using overlapping 20‐ and 30‐Ma time intervals. The RF pole, corresponding to the third remanence component, coincides extremely well with a Middle Triassic age of 240 Ma on the 20‐Ma APW path and a Late Triassic age of 230 Ma on the 30‐Ma APW path. Statistical analysis yields upper and lower age limits of 250 and 220 Ma. This Triassic paleomagnetic age supports the proposed late diagenetic origin of the Kupferschiefer ore deposits, and suggests that the RF‐ore systems were formed immediately after Triassic continental rifting associated with the opening of the Tethys ocean to the south—a likely source of the thermal anomaly necessary to initiate adequate convective velocities within the Rotliegendes clastic basins.

Genesis of Kupferschiefer Cu-Ag deposits by convective flow of Rotliegendes brines during Triassic rifting

Extensive and rich Cu-Ag sulfide mineralization occurs in Poland across the contact between the Upper Permian Zechstein restricted marine sequence and the Lower Permian Rotliegende continental volcanic and clastic sequence. Geologic evidence suggests that the mineralization was formed during late diagenesis when metalliferous brines migrated through the Rotliegende, leaching metals from the volcanic detritus, and up the flanks of basement highs, possibly along fracture porosity, to the pyritic Kupferschiefer and Zechstein limestone above. Thick evaporites in the lower Zechstein preclude a vertical flow-through model, but metal zoning attitudes suggest that the brines overturned where the Rotliegende pinched out against the highs and moved laterally along the base of the Zechstein toward the basin centers, presumably to sink back down into the Rotliegende, completing a convection cell. A Middle Triassic paleomagnetic age for the metal zoning and Kimmerian attitudes of dilatant sulfide veinlets indicate that the mineralizing event coincided with continental rifting associated with the opening of the Tethys ocean.Slow unicellular convection may be commonplace in sandstone basins where small lateral temperature gradients, delta T, exist, but greater velocities are necessary to form large orebodies. An anomalous tensional and thermal event, such as rifting, can increase velocities by increasing permeability, slope angle, or delta T. The paleothermal structure of southwestern Poland was determined by modeling the conductive heat flow in 14 one-dimensional geologic sections which described the evolution of the basin architecture for 10 m.y. in the Early Triassic. Rifting was simulated by increasing the lower boundary condition from 500 degrees to 1,000 degrees C at 25 km. This thermal pulse produced a surprisingly high delta T of 25 degrees C across the Lubin ore district solely from differences in thermal conductivities between the basement high (4.2 W/m degrees C), the sandstone (2.5 W/m degrees C), and the shale basin center (1.25 W/m degrees C). Unicellular convection patterns would be induced by the lateral boundary conditions of warm basement highs and cold shale centers and by the greater horizontal permeability. These cells were 15 to 20 km long, 400 m high, and subhorizontal.A slope angle of 2 degrees and a permeability of 1 D produces a convection velocity of 13 cm/yr which, with a copper solubility of 1,000 mg/kg in 20 to 30 percent Ca-Na-Cl brines in equilibrium with hematite, can form the Lubin deposit in less than 6 m.y. Using a fracture permeability of 2 D and a solubility of 300 mg/kg, the time needed is less than 10 m.y. The Konrad mine can be formed in similar time periods. Without the continuous recycling of the brine inherent in convective flow (20 times or more), the metal solubilities needed to form the Lubin deposits by a flow-through model would be unreasonably high.Natural gases likely migrated along with the metalliferous brines and helped convection by creating secondary porosity and increasing the buoyancy of the fluids. Because the fluids are recirculated and not expelled, convection provides a way in which secondary migration of methane and petroleum can occur effectively in solution as well as in separate phases.

Chronostratigraphical and lithostratigraphical correlations of the Zechstein Limestone in Central Europe

Summary A glacioeustatic mechanism governed the sedimentation of the PZ1 Zechstein Limestone and made it possible to correlate Zechstein Limestone deposits in different areas chronostratigraphically. The chronohorizons are surfaces (uncommon) or layers up to several centimetres thick that originated in a subaerial or shallow water environment and overlie deposits formed in a subtidal environment. These chronohorizons divide the Zechstein Limestone sequences into three parts or sub-cycles. The boundary between the previously established lower and upper lithostratigraphical units of the Zechstein Limestone corresponds with that between the first and the second sub-cycles or that between the second and the third sub-cycles, or both, depending on the local palaeogeography.

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.

Former aragonitic submarine hemispheroids associated with vadose deposits, Zechstein Limestone (Upper Permian), Fore-Sudetic area, western Poland

Former aragonitic submarine hemispheroids associated with vadose deposits, Zechstein Limestone (Upper Permian), Fore-Sudetic area, western Poland

A Case Study Comparison of Wells Drilled With and Without MWD Directional Surveys on the Claymore Platform in the North Sea

Introduction Occidental Consortium, North Sea-Claymore Platform Occidental of Britain Inc. and Occidental Petroleum (Caledonia) Ltd., subsidiaries of the Occidental Petroleum Corp., are operators of a North Sea Petroleum Corp., are operators of a North Sea consortium including Getty Oil (Britain) Ltd., Allied Chemical (Great Britain) Ltd., Thomson North Sea Ltd., and the British National Oil Corp. (BNOC).In March 1972 the Occidental consortium was awarded a petroleum license for six blocks in the U.K. sector of the North Sea. In May 1974, the Claymore field was discovered. Although Claymore did not have the recoverable reserves, recovery factor, or expected daily production that nearby Piper field had, Claymore still was considered a Piper field had, Claymore still was considered a viable economic proposition, especially with the proximity of the Piper field and associated oil proximity of the Piper field and associated oil pipeline from the Piper platform to the Occidental pipeline from the Piper platform to the Occidental terminal at Flotta in Orkney.The Claymore platform is 100 miles northeast of Aberdeen, Scotland, in 364 ft of water on Block 14/19. It is a twin-derricked, steel-jacketed, drilling and production platform. The platform was designed with 36 slots to accommodate 27 producing wells, eight injection wells, and one water-disposal well. Claymore was spudded in April 1977. Six wells were predrilled and 20-in. casing was set before drilling predrilled and 20-in. casing was set before drilling into the productive zone was undertaken.Main formations in the Claymore area consist of Eocene sands and silts; Paleocene sands, clays, and shales; Cretaceous limestone, chalk, shales, and sands (productive zone); Jurassic shales and sands (productive zone); Triassic shales; Zechstein limestone (productive zone); and Carboniferous shales and sands (productive zone). A geological section of the Claymore area with typical bottomhole assemblies (BHA's) is shown in Fig. 1A.From mid-1977 to late 1978, 15 directional wells were drilled from Claymore A platform using conventional wireline tool orientation and single-shot directional surveying techniques. From Sept. 1978 to Oct. 1979 the Teleco measurement-while-drilling (MWD) system was used to provide survey data and tool orientation in the drilling of 10 wells. Teleco MWD System Teleco Oilfield Services Inc. was formed in 1972 as a joint venture of Raymond Industries Inc. and Societe Nationale Elf Aquitaine for the purpose of developing an MWD system for directional surveying. Teleco became a public-owned company in April 1979. Following extensive technological development and field testing, commercial service was initiated in Sept. 1978 in the North Sea and Gulf of Mexico. A comparative study was made on wells drilled on the Claymore platform in the North Sea with and without the measurement-while-drilling (MWD) system. This case study accurately quantified the direct tine savings and showed the second-tier benefits to be as significant as the direct savings. JPT P. 1867

Sedimentology and paleoecology of the Zechstein limestone (upper Permian) in the fore-sudetic area (Western Poland)

Five main microfacies types can be distinguished within the rocks of the Zechstein Limestone (Zechstein 1, Upper Permian) of western Poland: (1) micritic; (2) biomicritic; (3) biolithitic; (4) oncolitic; and (5) a microfacies type characterized by micrites interlaminated with terrigenous clay material. The spatial distribution of these micro facies types enables us to establish five paleogeographical zones: (1) a basinal zone, characterized by thin sequences (about 5 m) of argillaceous micrites and/or deeper-water oncolites; (2) a zone of submarine elevations within the basin, composed of either thick (up to 66 m) sequences terminated by shallow-water oncolites and stromatolites, or condensed sequences (less than 2 m) containing vadose marine deposits; (3) a fore-barrier zone (5–20 m thick), mainly micritic with rare interbeds of biomicrites and oncolites; (4) a barrier zone of highly variable thickness and microfacies composition, with carbonate buildups made up of algal and bryozoan biolithites; and (5) a lagoonal zone (20–60 m thick) having a lower micritic and an upper oncolitic (and oolitic) part, both micrites and oncolites being sandy and argillaceous. The regressive nature of the microfacies sequence is marked in all these zones, but it is particularly well expressed in the barrier zone. Whereas in the lower Zechstein Limestone subtidal deposits (mainly argillaceous micrites and micrites) occur, carbonate buildups of shallow subtidal and intertidal origins are found in the upper Zechstein Limestone, while the uppermost Zechstein Limestone originated in a sabkha environment. The sedimentation model of the Zechstein Limestone in western Poland can be compared with that of the Recent carbonate sedimentation in the Persian Gulf, whereas other areas of Zechstein sedimentation have rather different morphologies.

Algal—vadose pisoliths in the Zechstein Limestone (Upper Permian) of northern Poland

Vadose marine deposits associated with stromatolites and pisoliths were found within the Zechstein Limestone (Upper Permian) of northern Poland. The nature of pisoliths is very complex and in some cases it is possible to distinguish between those of purely algal origin and those of partly algal and partly vadose origin. The latter originated from the transportation of algal oncoids from a subtidal zone of oncoid formation to supratidal flats where vadose deposits formed and then vadose and/or algal—vadose pisoliths were transported to a subtidal zone, sometimes without any appreciable sign of transportation or erosion. As a result, it is difficult to determine the genesis of each particular sedimentary particle. It seems that algal—vadose pisoliths are rather frequent in ancient environments, but so far they have been mostly identified as algal or vadose pisoliths.

I.—On Some Reptilian Teeth from the Upper Permian Cupriferous Sandstones of Kargalinsk, near Orenburg, Russia

The teeth under consideration in this paper were derived from the Kargalinsk copper mines in the government of Orenburg, Russia. These mines are in the marls and sandstones overlying conformably the Zechstein or Magnesian Limestone, and were referred by Murchison to the upper division of the Permian. Other writers have regarded them as belonging to the Lower Trias, so that the question of their horizon is still sub judice. I have elsewhere explained my reasons for believing them to form part of the Permian formation, and wishing to avail myself of the latest Russian opinions, I have recently asked Dr. Trautschold, the esteemed palæontologist of Moscow, what is the state of opinion now, and he informs me that there are as yet no positive data on which to base a Triassic hypothesis. Dr. Trautschold has visited and examined the locality, an advantage not possessed by many of those who consider the series must be Triassic, because reptilian remains of a high grade are found in them.