Lithostratigraphic Groups Research Articles

Characterisation of the fracture- and karst-controlled geothermal reservoir below Munich from geophysical wireline and well information

The Upper Jurassic carbonate aquifer in the German Molasse Basin (S Germany) below Munich is the focus of exploitation of geothermal energy. To implement geothermal wells, meaningful prediction of reservoir quality (e.g., volume, temperature, location of aquifers, porosity, permeability) is required. However, permeability of this aquifer is often highly heterogeneous and anisotropic, as in other karst- and fracture systems. Based on geophysical well logs from six wells, a 3D porosity model, and side-wall cores, we provide a comprehensive characterisation of the reservoir. We investigate the correlation between rock porosity and matrix permeability, and the impact of hyper-facies on fractures and karstification. We locate and analyse hydraulic active zones and compare them with hydraulic inactive zones within equivalent depth ranges, to characterise promising exploration targets. We show that fracture system parameters vary strongly between wells and within a single well. However, we observe local trends between the fracture systems and rock properties. For instance, fracture intensities and compressional wave velocity increase, while porosity decreases, in dolomitic reefal build-ups (massive facies). We observed substantial karstification dominantly within the massive facies. The main indicators for hydraulic active zones in the reservoir seem to be karstification, fractures, and fault zones. Although matrix porosity has neglectable impact on permeability, the identified hydraulic active zones appear more frequently in sections with higher porosity. We conclude, similar to previous studies, that the massive facies is a suitable exploitation target. Despite the favourable conditions within the massive facies, the strongest hydraulic active zones are nevertheless in the bedded facies, often considered as aquitard, directly below the top of the reservoir within the lithostratigraphic group of the Purbeck, at the transition between the Jurassic and the Cretaceous.

Geology, Geochemistry, and Geochronology of the Giant Rio Tinto VMS Deposit, Iberian Pyrite Belt, Spain

Abstract The Rio Tinto deposit is a giant volcanogenic massive sulfide deposit (VMS) that contains more than 500 Mt of pyrite-rich massive sulfides and more than 2 Gt of mineralized stockwork. Three broad lithostratigraphic groups occur in the regional stratigraphy: the phyllite-quartzite group, the volcano-sedimentary complex, and the Baixo Alentejo Flysch Group. These three major packages reflect the evolution of a depositional environment from a stable platform to deposition in pull-apart continental basins during oblique subduction and collision and coeval synorogenic flysch sequence. The volcano-sedimentary complex, which hosts massive sulfide mineralization at Rio Tinto, can be divided into four major units: (1) the Mafic Siliciclastic Unit, (2) the Lower Sedimentary Unit, (3) the Felsic Unit, and (4) the Upper Sedimentary Unit. The Felsic Unit is further subdivided based on new U-Pb zircon geochronology into three distinct subunits. Felsic Unit I (ca. 356 Ma) includes dome complexes dominated by rhyodacite and reflects the onset of felsic magmatism in the region. Felsic Unit II (ca. 352–348 Ma) represents the main interval of volcanic activity, also dominated by rhyodacite domes and related aprons, and is associated with widespread VMS mineralization. Felsic Unit III (ca. 340 Ma) reflects a late pulse of rhyolitic volcanism. Massive sulfides occur as two different styles of mineralization: (1) replacive ores as discordant pipes hosted by glass-rich felsic rocks and enclosed by a large zone of stockwork-like mineralization and (2) overlying shale-hosted exhalative mineralization in small anoxic basins, probably formed during the collapse of the volcanic domes of Felsic Unit II in the Middle-Late Tournaisian. New lithogeochemical data illustrate two types of mafic rocks in the Mafic Siliciclastic Unit: a basaltic andesite and a high–Ti-Zr basalt, both of tholeiitic affinity. Using immobile element ratios (heavy rare earth elements [HREEs], Al, Y, Zr, and Ti) of the Felsic Unit, fundamental differences have been recognized between the subunits. The unmineralized Felsic Unit I is characterized by high Zr content (225–300 ppm) and a pronounced Eu negative anomaly, and probably represents the most fractionated rocks. Felsic Unit II is characterized by Zr values between 50 and 200 ppm. The low Zr values of the mineralized unit contrast with the typically high Zr values of the felsic rocks related to volcanogenic massive sulfides elsewhere and, at a regional scale, can help to discriminate potentially fertile domes from barren volcanism.

A composite Llandovery δ13Ccarb record from the Michigan Basin, USA

Abstract A new high-resolution, composite δ13Ccarb curve for the Michigan Basin, USA, was constructed using two stratigraphically overlapping subsurface cores that span the complete Llandovery interval. The Llandovery succession of the Michigan Basin measures between 140 m and 265 m thick and is represented by three lithostratigraphic groups: the Cataract (Manitoulin formation and Cabot Head Shale), the Burnt Bluff (Lime Island, Byron, and Hendricks formations), and the Manistique (Schoolcraft and Cordell formations). The composite δ13Ccarb curve exhibits five positive carbon isotope excursions (CIEs). Conodont and 87Sr/86Sr data suggest that the CIEs correlate with the Hirnantian, Early Aeronian, Late Aeronian, Valgu, and Ireviken global excursions. The new composite δ13Ccarb curve from the Michigan Basin represents the most stratigraphically complete, single-basin Llandovery record worldwide. The composite δ13Ccarb curve permits the ages of three Llandovery lithostratigraphic groups to be chronostratigraphically determined within ca. 1 Ma resolution. The composite δ13Ccarb curve also implies that the Ordovician–Silurian boundary in the Michigan Basin is located at the top of the Manitoulin formation and not at the base of the Manitoulin formation, which is consistent with recent findings from Manitoulin Island, Ontario. From the regional perspective, the high-resolution composite δ13Ccarb curve provides a valuable tool for delineating the depositional history of the Michigan Basin during the Llandovery. From a global perspective, the new composite δ13Ccarb curve sheds light on the dynamics of the global carbon cycle, particularly during the Rhuddanian, which is rarely preserved in other carbonate basins worldwide.

Dating detrital zircon from the gold-bearing Ventersdorp Contact Reef in the Ventersdorp Supergroup of South Africa

The Ventersdorp Contact Reef (VCR) at the base of the >4.5 km-thick volcanosedimentary Ventersdorp Supergroup unconformably overlies the Witwatersrand Supergroup and is the second youngest mineable reef in the Witwatersrand Goldfields. The volcanic rocks of the Ventersdorp Supergroup are predominantly mafic, affected by low-grade thermal metamorphism and difficult to date. Only the Makwassie Formation in the upper Platberg Group of the main Ventersdorp repository has been reliably dated on four felsic volcanic samples at 2720 ± 2 Ma. The actual timing of Ventersdorp volcanism and the duration of the three recognised lithostratigraphic groups remains enigmatic, despite much research and heroic attempts to synthesize the available data.In this work detrital zircon grains from VCR conglomerates were U-Pb dated in order to improve the time constraints on the Klipriviersberg Group at the base of the Ventersdorp Supergroup. The six youngest grains in VCR samples were reliably dated at 2799 ± 9 Ma. The Klipriviersberg Group and the Ventersdorp Supergroup is thus younger than 2808 Ma and the supergroup is older than the 2642 Ma Vryburg Formation at the base of the Transvaal Supergroup.Comparisons of detrital grain dates confirm that the VCR was largely derived from erosion products of the underlying Witwatersrand Supergroup, however the youngest VCR grains are ~20 Ma younger and may have been derived directly from magmatic rocks in the provenance or a felsic facet of the synchronous komatiitic Klipriviersberg volcanism.Multi-grain analyses of discordant grains show that recent lead loss is predominant. However about 5% of the data show the effect of complex Mesoproterozoic lead loss, which can yield ages as much as 150 Ma too young in 10% discordant data. This was found in grains with high Th-induced radiation damage, providing a criterion for data rejection.The proposed large igneous provinces dated between 2791 and 2683 Ma, based mainly on dated mafic dykes, which are not in contact with supracrustal Ventersdorp rocks, do fit the established time constraints and might provide a key to Ventersdorp chronostratigraphy. However only the proposed 2754–2709 Ma Platberg volcanic province is based on reliably dated Platberg Group volcanic rocks.

Deciphering the geodynamic evolution of the Dinaric orogen through the study of the ‘overstepping’ Cretaceous successions

AbstractAlong the Dinaric–Hellenic orogen, the Late Jurassic – Early Cretaceous ophiolite obduction over the Adria continental margin was sealed by sedimentation of clastic terrestrial deposits rapidly followed by a widespread carbonate platform system since the Early Cretaceous period. These Cretaceous sediments presently crop out over areas of varying extension, from several hundred kilometre wide undeformed continuous covers to small-scale tectonic slivers involved in the tectonic stack following the latest Cretaceous–Palaeogene collision. These deposits are unconformably sedimented above the units formed by the Late Jurassic to Early Cretaceous nappe stacking above the eastern Adria continental margin. We studied these deposits in a large area between western Serbia and eastern Bosnia. In the studied area, these deposits are divided into three lithostratigraphic groups according to their age, depositional environment and type of underlying basement. The Mokra Gora Group sediments (upper Aptian–Maastrichtian) were deposited on top of previously obducted and weathered ophiolites, the Kosjerić Group (Cenomanian–Campanian) overlies composite tectonic units comprising obducted ophiolites and their underlying continental basement portions, while the Guča Group (Campanian–Maastrichtian) exclusively rests on top of continental basement. The reconstructed sedimentary evolution of these groups, together with the comparison with the syn- and post-obduction deposits at the front of the ophiolitic nappe(s) in a wider area of the internal Dinarides (e.g. Pogari Group and Bosnian flysch), allowed us to clarify the obduction mechanisms, including their tectonic context, the changes in depositional environments and the timing of depositional and tectonic events, and, in a wider view, shed light on the geodynamic evolution of the Dinaric belt.

The Key Role of Aptian-Albian Marine Fossils from Eastern Heilongjiang in Marine-Nonmarine Stratigraphic Correlation

The alternating marine and nonmarine coal-bearing Lower Cretaceous successions are well developed in eastern Heilongjiang, northeastern China, including the Jixi Group in the west and the Longzhaogou Group in the east. The correlation of these two lithostratigraphic groups with the nonmarine Jehol Group is important for dating the exceptionally well-preserved Jehol Biota. The Early Cretaceous marine fossils recovered from eastern Heilongjiang include ammonites, bivalves, radiolarians, foraminifers and dinocysts. During the early Aptian transgression the ammonite fauna entered the Hulin and Mishan areas and the bivalve Aucellina fauna in the Jixi area. This enables correlation of the marine lower part of the Chengzihe Formation of the Jixi Group with the Qihulin Formation of the Longzhaogou Group.

Lower Serpukhovian (Steshevian) foraminifers and algae from exotic limestone clasts of Nötsch (Eastern Alps, Austria)

The >1,000 m-thick Carboniferous sedimentary succession of Nötsch is divided into the Erlachgraben, Badstub, and Nötsch formations with poorly constrained precise ages, but probably constituting a continuous lithostratigraphic Group deposited from the latest Viséan to the early Bashkirian, thus including a complete Serpukhovian succession. We date the early Serpukhovian (Steshevian) in exotic limestone clasts of the Badstub Fm. based on algae and foraminifers. These limestone clasts have been reworked from a carbonate shelf, indicating that they are older than the Badstub Fm. Microfacies and fossil assemblages indicate that a shallow marine carbonate shelf was developed at the northern margin of the deep-sea basin of Nötsch. The assemblages include the red alga Hortonella, rare green algae, and incertae sedis algae Praedonezella, Aoujgalia, and Frustulata; howchiniid and lasiodiscid foraminifers; atypical endothyrids, probably belonging to Semiendothyra emend.; rare Janischewskina; taxonomically disputable eostaffellids (including Eostaffellina aff. paraprotvae) and pseudoendothyrids; attached forms transitional between pseudolituotubid Fusulinata and calcivertellid Miliolata; and probably the oldest known free Miliolata. Newly described taxa include the incertae sedis algae Praedonezella sebbarae nov. sp. and the foraminifers Pseudoendotaxis nov. gen., Quasilituotuba serpens nov. sp., Q. pseudospiroides nov. sp., and Eoglomospiroides carnica nov. sp. Revised foraminiferal taxa include Pseudolituotubidae, Quasilituotuba cf. serpuchoviensis nov. comb., and Q. ex gr. extensa nov. comb. The studied material provides information about the phylogeny of the first Miliolata and permits the reconstruction of the lineage of Pseudolituotubidae and Calcivertellidae, between the classes Fusulinata and Miliolata. The palaeobiogeography of Austria during the Serpukhovian is not yet clearly established, but relationships with the Saharan and Mediterranean Provinces exist, and especially with the Donbass. Fewer relationships are conspicuous with England, the Moscow Basin or the Urals.

Reorganisation of the Triassic stratigraphic nomenclature of northern Switzerland: overview and the new Dinkelberg, Kaiseraugst and Zeglingen formations

In the context of the harmonisation of the Swiss stratigraphic scheme (HARMOS project), the stratigraphic nomenclature of the Triassic sedimentary succession of northern Switzerland has been reorganised to six formations (from base to top): Dinkelberg, Kaiseraugst, Zeglingen, Schinznach, Bankerjoch, and Klettgau Formation. The first three are formally introduced in this paper. The Dinkelberg Formation (formerly «Buntsandstein») encompasses the siliciclastic, mainly fluvial to coastal marine sediments of Olenekian to early Anisian age. The formation is some 100 m thick in the Basel area and wedges out towards southeast. The Kaiseraugst Formation (formerly «Wellengebirge») comprises fossiliferous siliciclastic and carbonate sediments documenting a marine transgressive—regressive episode in early Anisian time. It starts with sandstone, dolomite, continues with subtidal limestone and marl and ends with bituminous shale and supratidal dolomite. Thickness decreases from approximately 50 m in the High Rhine area to 10 m in the south and east. In the Lake Constance area, a transition to the siliciclastic marginal facies of the Vindelician High (Eschenbach Formation in Germany) is documented by borehole evidence. The Zeglingen Formation (formerly «Anhydritgruppe») documents a regressive marine evaporitic megacycle during the Illyrian (late Anisian). At most places, except in far eastern Switzerland, it starts with massive halite deposits. It continues with sulfate and marl sequences and ends with littoral stromatolitic dolomite. In the WSW–ENE trending depot centre total formation thickness is 150 m and more, and thickness of salt layers reaches up to 100 m. In the High Rhine area, the thickness is reduced due to subrecent subrosion. At some places evidence points to syn- to early-post-diagenetic erosion. For practical reasons, the six formations are organised in three lithostratigraphic groups: Buntsandstein Group (with the Dinkelberg Formation), Muschelkalk Group (combining the Kaiseraugst, Zeglingen and Schinznach Formations) and Keuper Group (combining the Bankerjoch and Klettgau Formations).

Synthesis and revision of the lithostratigraphic groups and formations in the Upper Permian?-Lower Jurassic Newark Supergroup of eastern North America

The Upper Permian? - Lower Jurassic Newark Supergroup of eastern North America has a strikingly uniform succession of lithologic units. This uniformity is seen regardless of whether these units are characterized on the basis of their lithostratigraphy, allostratigraphy, biostratigraphy, or chemostratigraphy. After deposition, these units were broken up tectonically and attacked erosionally; parts of them survive today only within localized, down-faulted areas. Many lines of evidence compellingly demonstrate that most or all of these remnant units once were physically continuous between remaining outcrops. It is needlessly confusing to give every remnant of each unit a different name in each area where it persists simply because it is now physically isolated by erosion from other portions of the same unit. Instead, these units should be defined within a regional lithostratigraphic framework that emphasizes their common origins and original stratigraphic continuity. To this end, the formation-level stratigraphy of the Newark Supergroup is reduced from 58 locally applied and locally defined formations to a succession of only 16 uniformly defined and regionally recognizable formations. In all cases the oldest name validly applied to each formation is given priority over more recently erected synonymous names, which are either abandoned or, in a few cases, changed in rank to a member of one of the formations recognized here. The Newark Supergroup is here organized into four regionally recognizable groups, each subdivided into regionally recognizable formations. In ascending order, the Upper Permian?-Middle Triassic Acadia Group (new name) includes the Honeycomb Point Formation, Chedabucto Formation, Economy Formation, and Evangeline Formation. This group is preserved only in the Canadian Fundy and Chedabucto basins. The Upper Triassic (Carnian-Norian) Chatham Group includes the Doswell Formation, Stockton Formation, Lockatong Formation, and Passaic Formation. The Upper Triassic-Lower Jurassic (upper Rhaetian-lower Hettangian) Meriden Group includes the Talcott Formation, Shuttle Meadow Formation, Holyoke Formation, East Berlin Formation, and Hampden Formation. The term "Agawam Group," previously proposed to encompass all Newark Supergroup strata above the highest basalt of the Meriden Group, is here abandoned and replaced with the name "Portland Group" for the same suite of strata. The Lower Jurassic (upper Hettangian-lower Sinemurian) Portland Group includes a lower Boonton Formation, an overlying Longmeadow Sandstone (here reinstated), and the Mount Toby Conglomerate, which laterally intertongues with both the Boonton Formation and the Longmeadow Sandstone.

Aquifer community structure in dependence of lithostratigraphy in groundwater reservoirs.

Groundwater microbiology with respect to different host rocks offers new possibilities to describe and map the habitat harboring approximately half of Earths' biomass. The Thuringian Basin (Germany) contains formations of the Permian (Zechstein) and Triassic (Muschelkalk and Buntsandstein) with outcrops and deeper regions at the border and central part. Hydro(geo)chemistry and bacterial community structure of 11 natural springs and 20 groundwater wells were analyzed to define typical patterns for each formation. Widespread were Gammaproteobacteria, while Bacilli were present in all wells. Halotolerant and halophilic taxa were present in Zechstein. The occurrence of specific taxa allowed a clear separation of communities from all three lithostratigraphic groups. These specific taxa could be used to follow fluid movement, e.g., from the underlying Zechstein or from nearby saline reservoirs into Buntsandstein aquifers. Thus, we developed a new tool to identify the lithostratigraphic origin of sources in mixed waters. This was verified with entry of surface water, as species not present in the underground Zechstein environments were isolated from the water samples. Thus, our tool shows a higher resolution as compared to hydrochemistry, which is prone to undergo fast dilution if water mixes with other aquifers. Furthermore, the bacteria well adapted to their respective environment showed geographic clustering allowing to differentiate regional aquifers.

Piggy-back Supervolcanoes—Long-Lived, Voluminous, Juvenile Rhyolite Volcanism in Mesoproterozoic Central Australia

The Talbot Sub-basin is one of several bimodal volcanic depositional centres of the Mesoproterozoic Bentley Basin in central Australia. It is dominated by rocks of rhyolitic composition and includes ignimbrites, some forming large to super-eruption size deposits. Ferroan, incompatible trace element enriched, A-type compositions, anhydrous mineralogy and clear evidence for local rheomorphism indicate high eruption temperatures, with apparent zircon-saturation temperatures suggesting crystallization at >900 degrees C. Comagmatic basalt is of mantle origin with minor Proterozoic basement contamination. The rhyolites cover the same range of Nd isotope compositions (epsilon(Nd(1070)) +1.24 to -0.96) and La/Nb ratios (1.2-2.1) as the basalts (epsilon(Nd(1070)) +2.1 to -1.1: La/Nb 1.2-2.3) and are compositionally far removed from all older basement and country-rock components (average epsilon(Nd(1070)) = -4, La/Nb = 10). The rhyolites and basalts are cogenetic through a process probably involving both fractional crystallization of mafic magmas and partial melting of recently crystallized mafic rock in a lower crustal intraplate, extraction of dacitic magmas to a voluminous upper crustal chamber system, and separation of rhyolite by processes involving rejuvenation and cannibalization of earlier chamber material. More than 230 000 km(3) of parental basalt is required to form the >22 000 km(3) of preserved juvenile rhyolite in the Talbot Sub-basin alone, which represents one of the most voluminous known felsic juvenile additions to intracontinental crust. Zircon U-Pb age components are complex and distinct from those of basement and country rock and contain antecrystic components reflecting dissolution-regrowth processes during periodic rejuvenation of earlier-emplaced chamber material without any significant interaction with country rock. The overall duration of magmatism was >30 Myr but can be divided into between two and four separate intervals, each probably of a few hundred thousand years' duration and each probably reflecting one of the distinct lithostratigraphic groups defined in the sub-basin. Neither the composition nor style of felsic and mafic volcanism changes in any significant way from one volcanic event to the next and the range of zircon U-Pb ages indicates that each period utilized and cannibalized the same magma chamber. This volcanism forms a component of the 1090-1040 Ma Giles Event in central Australia, associated with magma-dominated extension at the nexus of the cratonic elements of Proterozoic Australia. This event cannot be reasonably reconciled with any putative plume activity but rather reflects the >200 Myr legacy of enhanced crustal geotherms that followed the final cratonic amalgamation of central Australia.

Early MIS 3 occupation of Mochena Borago Rockshelter, Southwest Ethiopian Highlands: Implications for Late Pleistocene archaeology, paleoenvironments and modern human dispersals

Between 70 and 50 ka BP, anatomically modern humans dispersed across and out of Africa to eventually populate all inhabitable continents. Knowledge of paleoenvironments and human behavioral patterns in Africa prior to and during these dispersals is crucial for understanding how and why hunter-gatherers were able to adapt rapidly to the new environments they encountered. However, few well-dated sites from this time period are known from the Horn of Africa, one of the purported staging areas for population movements into southern Arabia and Asia. Excavations at Mochena Borago Rockshelter, situated on the western slopes of a dormant volcano where the SW Ethiopian Highlands meet the Ethiopian Rift, have yielded the first securely dated archaeological sequence for later periods of the dispersal. Three major lithostratigraphic groups incorporating occupational episodes have yielded charcoal radiocarbon ages ∼53–38 ka calBP; deeper deposits have been tested but remain undated. Archaeological assemblages consist mainly of obsidian flaked stone artifacts manufactured from small, minimally prepared, single- to multi-platform flake cores; radially prepared cores are rare and blade cores are absent. Small unifacial to bifacial points from non-radial cores dominate the earliest shaped tool assemblages, and backed pieces first appear by ∼45 ka calBP. By ∼43 ka calBP, scrapers and backed pieces are predominant, rather than points. However, there is little evidence for technological change other than the appearance of bipolar technology. Mochena Borago's archaeological sequence thus cannot be neatly classified as Middle Stone Age, Later Stone Age or “transitional” and calls into question some of the principles by which archaeologists have attempted to classify African toolmaking traditions.

Cenozoic volcanism and extension in northwestern Mesa Central, Durango, México

The Santiago Papasquiaro region is located in the northwest portion of the Mesa Central and is characterized by Tertiary Sierra Madre Occidental lithology. Geologic mapping and dating of key units using U-Pb laser ablation method on zircons has identified three different lithostratigraphic groups. These include: (1) early Eocene felsic volcanic rocks, consisting of the Antigua ignimbrite [51.75 +0.35/-0.45 Ma]; (2) late Eocene - early Oligocene felsic to intermediate volcanic rocks, consisting of the Altamira ignimbrite [38.8 ± 1.0 Ma], El Cazadero andesite [ages of 37.2 +0.30/-0.40 Ma and 35.95 +0.45/-0.5 Ma], a dioritic intrusion, the Venadita rhyolite, Puente Negro ignimbrite [34.0 +0.50/-0.70 Ma], Los Fresnos ignimbrite and Balin ignimbrite [33.2 +0.50/-0.20 Ma]; and (3) late Oligocene to Quaternary sedimentary and volcanic mafic rocks comprising the Santiago sedimentary formation, basalts equivalent to Metates Formation and Neogene to Quaternary continental non-consolidated deposits. Within the studied area, the main volcanic pulse of the Sierra Madre Occidental volcanic province corresponds to the second group, which lasted ca. 5 Ma. Older rocks are represented by a single outcrop of the Antigua ignimbrite, and the younger units are mainly continental clastic sediments intercalated with sporadic mafic alkaline volcanic rocks that record a major change in the tectonic regime. Extension that began in late Eocene - Oligocene gradually tilted the late Eocene – early Oligocene volcanic sequence and formed the NNW-trending Santiago Papasquiaro half-graben, which is the northernmost and earliest structure of the Rio Chico-Otinapa graben. NW-striking faults of the San Luis-Tepehuanes fault system were synchronous with the development of the Santiago Papasquiaro half-graben. The deformation propagated gradually to the south, forming the NNW Rio Chico-Otinapa graben by the early-middle Miocene, and to the east-southeast in the Santiaguillo graben. A recent minor extensional deformation accommodated by NE-striking faults was probably related to seismic deformation of the Nuevo Ideal zone, approximately 40 km southeast of the study area.

The Mount Wright Arc: A Cambrian subduction system developed on the continental margin of East Gondwana, Koonenberry Belt, eastern Australia

The Mount Wright Arc, in the Koonenberry Belt in eastern Australia, is associated with two early to middle Cambrian lithostratigraphic groups developed onto the Late Neoproterozoic volcanic passive margin of East Gondwana. The Gnalta Group includes a calc-alkaline basalt-andesite-dacite suite (Mount Wright Volcanics), interpreted to represent the volcanic component of the arc. Volcaniclastic Gnalta Group rocks now buried in the Bancannia Trough represent the continental back-arc, developed immediately behind the arc in a manner analogous to the modern Taupo Volcanic Zone of New Zealand. East of the Gnalta Group is the Ponto Group, a deep marine sedimentary package that includes tholeiitic lavas (Bittles Tank Volcanics) and felsic tuffs, interpreted as part of a fore-arc sequence. The configuration of these units suggests the Mount Wright Arc developed on continental crust in response to west-dipping subduction along the East Gondwana margin, in contrast with some models for Cambrian convergence on other sections of the Delamerian Orogen, which invoke east-dipping subduction and arc accretion by arc-continent collision. This convergent margin was deformed by the middle Cambrian Delamerian Orogeny, which involved initial co-axial shortening followed by sinistral transpression, and oroclinal folding around the edge of the Curnamona Province.

Rare earths and yttrium hydrostratigraphy along the Lake Kinneret–Dead Sea–Arava transform fault, Israel and adjoining territories

Rare earth elements and Y (REY) have been analysed in 49 groundwaters from localities in the areas of Lake Kinneret and the Jordan and Arava Valleys. These waters originate from various aquifers and the REY abundances are expected to be controlled by the aquifer rocks. The REY pattern allow one to distinguish interaction of waters with basalts, basalt-limestone interaction zones (silicified limestones), limestones from the Judea and Avdat Groups (Upper Cretaceous and Eocene, respectively), and sandstones of the Lower Cretaceous Kurnub Group. Groundwater from the Quaternary alluvial fill (Dead Sea Group) are either controlled by Judea Group limestone or Kurnub Group sandstone. The REY patterns show characteristic features for each group. In hydrogeological systems, the rocks of natural replenishment areas are usually not the same as rock units from which the waters are collected. This becomes evident by comparing the lithostratigraphic groups from which the waters were collected and the hydrochemical grouping according to REY patterns with their characteristic trends and anomalies. In many cases, there is a correspondence between the lithostratigraphic and the hydrochemical grouping; in other cases, the 2 groupings disagree. This disagreement proves inter-aquifer flow of groundwater. In some cases, the geologically derived aquifers rocks of origin, differ from those indicated by REY patterns. Thus, applying the REY grouping, new fundamental information for hydrological models can be given and sources of salinisation can be elucidated.

Influence of the Ainslie Detachment on the stratigraphy of the Maritimes Basin and mineralization in the Windsor Group of northern Nova Scotia, Canada

The Late Devonian to Lower Permian Maritimes basin of eastern Canada developed as a late to post-tectonic extensional basin following the Early Devonian Acadian orogenic event and is subdivided into five main lithostratigraphic groups. The principal host to base metal mineralization is the Visean Windsor Group, which is also the only marine-dominated interval within the basin. The Windsor Group is a thick accumulation of evaporites, carbonates, and siltstone, deposited during passive regional subsidence and intracontinental submersion of a tectonically thinned crust. Earlier rift deposits consist of the nonmarine coarse clastic sediments of the underlying Tournaisian Horton Group, and the Horton to Windsor succession defines a typical rift and sag transgressive event. The Macumber and stratigraphically equivalent Gays River Formations are the marine basal carbonate units to the Windsor Group and contain numerous Pb-Zn-Ba occurrences in central and northern Nova Scotia. These carbonate units are overlain by thick evaporite deposits of the Lower Windsor Group, consisting of gypsum, anhydrite, and salt. In northern Nova Scotia the evaporite-carbonate contact at the top of the basal carbonates is the locus of intense shear and brecciation which developed in relation to the Ainslie detachment. This detachment is a stratigraphically controlled regional-scale flat-lying extensional fault that affected the hydrodynamic regime and mineralizing environment in the Carboniferous Maritimes basin. Movement on the detachment has stripped away thick evaporitic units and excised the entire Windsor Group across wide areas, effectively breaching a regional aquiclude. With shearing, permeability was locally enhanced through brecciation, creating a favorable environment for mineralization. Significant thickness variations within underlying coarse clastic rocks and pinch outs of the Horton Group aquifer also focused basin fluids.The detachment is rooted in a master basement normal fault which occurs offshore along the southeast margin of the Gulf of St. Lawrence, with the basement fault displaying up to 10 to 12 km of offset. Structural evidence from onshore exposures in the uplifted or horsted regions of mainland Nova Scotia and Cape Breton Island indicate that much of this movement was transferred horizontally along the Ainslie detachment. Thin-skinned gravitational sliding produced large rafts of allochthonous strata which progressively draped over the edge of basement normal faults during extension, resulting in tectonic salt build-up in the main offshore graben and a salt massif. Buttressing at the front end of the raft within the graben produced seismically imaged large amplitude buckle folds above the detachment.As well as a regionally extensive planar low-strength or low-viscosity layer, large-scale detachment faults require high fluid pressures to sustain motion of the allochthonous sheets. Abnormal fluid pressures are known to occur beneath evaporites, which is the site of nucleation for the Ainslie detachment. Fluid focusing along the detachment is suggested from the structural style, and evidence is provided by widespread synkinematic calcite + or - fluorite-barite-pyrite veins which occur in the calc-mylonite and breccia.

The Permian in Northern Bulgaria. I. Formal lithostratigraphy related to the Lower Permian

Two lithostratigraphic groups, corresponding to Lower Permian and Upper Permian, have been distinguished after stating the principles of division of the Permian sediments. In the first group, called North-Bulgaria Group, are distinguished: a variegated clayey-terrigenous formation, Nanevo and Komunari Formations (Lower Rotliegendes?), Severci Formation (Upper Rotliegendes?) and Bdin and Dolna Zlatica Formations (undivided Rotlegendes), as well as Kamen Briag, Bajacevo and Balgarevo Members in Nanevo Formation and Bononia, Delejnska and Rasovo Members in Bdin Formation. The officially distinguished lithostratigraphic units are documented by eight type sections and two reference sections, which are described according to drill-holes, taking into consideration the requirements of the Stratigraphic Code. The variegated clayey-terrigenous formati on comprises red and grey-green sandstones, silt stones and argillites. In the Nanevo Formation, from the bottom upwards, dominate various middle-acid volcanites and tuffs (Kamen Brjag Member), conglomerates, sandstones and a small amount of silt stones with tuffs and redeposited volcanic material (Bajačevo Member) and hypoargillitcs, hyposiltstones, a small amount of impure gravel-sandy rocks (Bălgarevo Member). Polygenetic brecc iaconglumcrates. conglomerates, red and black grey sandstones and siltstones alternate in the Komunari Formation (by a lateral disappearance of the psephilic rocks). The Belin Formation mainly contains conglomerates with carbonate fragments (with a small amount of admixtures of volcanic fragments, mainly in the Bononia Member), the composit ion of the Delcjnska Member being hypoa lcuropclitic. The Dolna Zlatica Formation is built of brown-reddish, mainly massive argillites and clayey siltstones with rare bedded interbeds consisting of siltstones and grained sandstones. Breccia conglomerates, sandstones and siltstones (a small amount of argillites), the psephites bearing fragments of sediments (carbone ones inclusive), low-metamorphic and volcanic rocks, are in an alternation in the Severci Formation. The Severci Formation overlies an eroded surface, while the other formations interfinger laterally with a correlation of the separate triads of members. The Komunari Formation is spread over the southern margin of the estern part of North Bulgaria, the Dolna Zlatica Formation - in the Tiirnovo Depression and the areas around, the Nanevo Formation - in the Bulgarian Coastal Dobrudza and around the North-Bulgaria Swell, the Severci Formation - in NE Bulgaria. Lower Permian, in the Bulgarian pari of the Moesian area, has a more detailed lithostratigraphic division than on the territory of Romania. The majority of the formations and members described may have analogues in the drill-holes north of the Danube.

The geology of the Madina-Kouta basin (Guinea-Senegal) and its significance for the geodynamic evolution of the western part of the West African Craton during the upper proterozoic period

Abstract The Madina-Kouta basin is a southward extension of the upper Proterozoic Taoudeni basin. This sedimentary basin formed in a SW-NE tectonic fault zone in the Leo shield at ∼ 1000-800 Ma. The deposits indicate a quiet and slightly subsiding area. An important uncorformity allows us to distinguish two lithostratigraphic groups: the Segou Group below and the Madina-Kouta Group above. Sedimentation in this area ended with the Late Proterozoic glaciation 650-620 Ma. The correlations with the Taoudeni basin show a close relationship between the foreland area and the Mauritanides/Bassarides fold belt during the Pan-African I cycle (800-650 Ma). In particular we suppose that the lower part of the Taoudeni basin deposits which correlate with the Madina-Kouta Group (group of Souroukouto) is on the passive margin of the Pan-African I rift, and the post-Madina-Kouta deposits in the Taoudeni basin (Group of Bakoye) correspond to the molassic stage of the Pan-African I fold belt (rift closure stage).

Superimposed upper proterozoic collision-controlled orogenies in the Mozambique Orogenic Belt of Kenya

The geological history of the northernmost part of the Mozambique Orogenic Belt, exposed in north-central Kenya, is described. A basement of ∼ 1200-Ma (Kibaran) migmatites is overlain by altered sediments with lateral and vertical facies changes defining eight lithostratigraphic groups. There is no evidence for any Archaean-early Proterozoic crust within the mapped part of the orogenic belt. A tectonothermal (Samburuan-Sabachian) event in the amphibolitegranulite facies at ∼ 820 Ma produced major recumbent folds with ductile thrusting to interleave the basement, metasedimentary cover and slices of oceanic metavolcanic complexes. There was syntectonic emplacement of crustal melt granites and metabasic dykes. We interpret this tectonothermal event to be related to plate collision, oblique to the north-south orogenic strike, between the Archaean Tanzanian craton in the west and an eastern Kibaran craton. A one-dimensional manifestation of the suture between these cratonic areas is possibly exposed at West Pokot in western Kenya. Post-collisional greenschist-amphibolite facies (Baragoian-Barsaloian) deformation at between 620 and 570 Ma produced regional upright folds and vertical ductile strike-slip shear zones striking subparallel to the orogenic strike. The metamorphism culminated during the intrusion of syntectonic granites. High-level open folding and brittle shears record the final events of the orogeny. Uplift and cooling, which extended beyond the confines of the orogen, are dated by ubiquitous mineral ages of ∼ 500-480 Ma. Whereas the roughly contemporaneous (Pan-African) Nubian Shield to the north preserves large segments of island arc/ophiolitic material, in the Mozambique Orogenic Belt this volcanic material was mostly consumed during the Upper Proterozoic oblique continent-continent collision. The roots of the collision zone are now exposed in the highgrade Mozambique Orogenic Belt and contrast with the higher exposure levels seen in the Nubian Shield.

Post-breakup stratigraphy of the Kaikoura Synthem (Cretaceous-Cenozoic), continental margin, southeastern New Zealand

The stratigraphy and structure of the Kaikoura Synthem (Cretaceous—Cenozoic) is synthesised from available seismic records and well reports on the continental margin of southeastern South Island. Four seismic sequences are distinguished, corresponding to lithostratigraphic groups that can also be recognised nearby on land: Matakea Group (Cretaceous), Onekakara Group (late Cretaceous—Oligocene), Kekenodon Group (Late Oligocene—Miocene), and Otakou Group (Miocene—Recent). These sequences achieve maximum thickness within three sedimentary basins underlying the continental shelf (Canterbury and Foveaux Basins) and slope (Great South Basin). The Great South Basin is separated from the Canterbury and Foveaux Basins across the WaipounamouFaultSystem, anortheasterly oriented zone of faults which controlled rifting and Matakea Group sedimentation along the western edge of a Cretaceous aulacogen now manifest as the Bounty Trough. The Canterbury andFoveaux Basins contain transgressive sequences (Onekakara Group) that were deposited in response to post-rifting thermal subsidence of the margin. By the mid Cenozoic, land areas were greatly reduced, and at peak transgression there was the development of a widespread Oligocene unconformity (Marshall Unconformity at the base of the Kekenodon Group). Subsidence continued until the Miocene, though punctuated by phases of mild faulting and volcanism in thePaleocene, Middle Eocene and Late Eocene–Oligocene. Regression commenced in the Miocene (Otakou Group), consequent upon uplift of the Southern Alps along the Alpine plate boundary in the west. Crustal deformation attained a climax in eastern Otago in the late Middle Miocene, with substantial volcanism and block faulting.