Devonian Limestones Research Articles

Morphogenesis of a new landform responsive to superimposed sulphate and carbonate buried karsts in western Canada

AbstractThis case study documents the morphogenesis of a new karstic landform consisting of a calcareous tufa mound with a gypsum caprock that developed at La Saline Lake, an oxbow of the Athabasca River in northeast Alberta, Canada. The development of this novel tiered carbonate‐sulphate mound architecture resulted from emplacement above the largest known buried salt dissolution collapse‐subsidence karst system, which was superimposed by an overlying buried carbonate karst. Dissolution of halite‐anhydrite beds of the Middle Devonian Prairie Evaporite, 200 m below, resulted in extensive subsidence and brecciation of the overlying Upper Devonian carbonate karst. The development of the calcareous tufa mound resulted from meteoric‐driven groundwater mixed with glacial meltwater directed along the shallowly buried karstic carbonate terrain of Middle‐Upper Devonian limestone, which floors the McMurray Formation, the main reservoir unit of the Lower Cretaceous Athabasca Oil Sands. The flow of the carbonate‐saturated groundwater responsible for the emplacement of the tufa mound at the surface was abruptly redirected along a deeper pathway in response to dissolution collapse‐subsidence adjustments within the buried salt karst of the Prairie Evaporite. The redirected groundwater flow deeper encountered an anhydrite‐dominated segment of the salt dissolution trend within the Prairie Evaporite Formation, 200 m below. The migration up‐section of sulphate‐saturated brine onto the surface of the previously formed tufa mound resulted in the emplacement of a gypsum caprock as a new landform.

Towards a better understanding of the geochemical proxy record of complex carbonate archives

Carbonate archives record a brief snapshot of the ambient Earth’s surface conditions at their deposition. However, the geologically reasonable extraction and interpretation of geochemical proxy data from ancient, diagenetically altered rock archives is fraught with problems. Three issues stand out: the dichotomy between petrographic and geochemical alteration; the lack of quantitative age constraints for specific diagenetic phases resulting in a poorly constrained admixture of local, basin-wide and over-regional (far-field) features; and an often insufficient understanding of the temperatures and compositions of diagenetic fluids. Here, the archive of Devonian marine limestones exposed to multiple far-field diagenetic events is used as an example to explore the above-listed issues. Methods applied include petrography, micro XRF, fluid inclusion data, clumped isotopes, δ13C and δ18O isotopes, 87Sr/86Sr ratios and quartz trace element data. Devonian limestones studied here were overprinted by two cross-cutting regional fault zones (T ≈ 230 °C) by multiple events between the Variscan Orogeny and the late Paleogene. The following processes are recorded: (i) protolith deposition and partial dolomitisation during rapid burial in the Middle/Late Devonian (T ≈ 180 °C); (ii) deep burial to ca 6.5 km and tectonic/hydrothermal overprint during the Variscan Orogeny in the Carboniferous (T ≈ 90–230 °C); (iii) rapid uplift to 1–2 km burial depth at the end of the Variscan Orogeny and hypogene karstification (T ≈ 50 to 100 °C) initiated by regional geology in the Permian/Triassic; (iv) tectonic/hydrothermal overprint during the opening of the Proto-Atlantic Ocean between the Early Jurassic and the Early Cretaceous (T ≈ 50 to 130 °C); (v) tectonic/hydrothermal overprint including renewed hypogene karstification and hydrothermal calcite cement precipitation (T ≈ 50 to 180 °C) during Alpine Orogeny between the Late Cretaceous and late Paleogene. Despite this complex series of diagenetic events, the protolith limestones largely preserved their respective Middle/Late Devonian dissolved inorganic carbon (DIC) and 87Sr/86Sr signatures. This study documents that geochemical proxy data, placed into their petrographic, paleotemperature, and local to over-regional context, significantly increases the ability to extract quantitative information from ancient carbonate rock archives. Research shown here has wider relevance for carbonate archive research in general.

Geochemical and microbiological variability of aerobic and anaerobic sediments along a bifurcated sulphate‐saturated brine spring in western Canada

AbstractA tufa mound developed at La Saline Lake, an oxbow of the Athabasca River in the Athabasca Oil Sands deposit of north‐east Alberta, is characterised by an unusual emplacement of a gypsum caprock. This two‐tiered architecture resulted from the bicarbonate‐saturated groundwater flow along Upper Devonian limestone being redirected deeper and encountering the halite–anhydrite dissolution trend within the underlying Middle Devonian Prairie Evaporite Formation, 175 to 200 m below. Migrations up‐section of sulphate‐saturated brine resulted in the gypsum caprock on the tufa mound and discharge of a sulphate‐saturated brine spring with total dissolved solids of ca 80,000 mg/L. The brine spring is bifurcated with flows to the south‐west and north‐west. Calcite–gypsum thrombolytic bottom sediments along the south‐western branch were covered by a halite deposit and subsequently a gypsum crust with a microbial community dominated by the cyanobacteria Coleofasciculus chthonoplastes. The thrombolite contact zone with the halite–gypsum encrustation has a more diversified community with the cyanobacteria Dactylococcopsis. Cyanobacterial mats that wrap around the bulbous gypsum crust protuberances distributed along the brine pool bottom surfaces have significant eukaryotic diversity, represented by the heterotrophic Ochrophyte Paraphysomonas. In contrast, sediments accumulated along the adjacent spring branch flow to the north‐west were thicker and clogged by abundant decomposed and fermented floral debris, unlike the deposit accumulated along the south‐western branch. This resulted in an oxygen‐depleted anaerobic environment dominated by sulphate‐reducing bacteria resulting in a calcite‐rich and sulphate‐starved anaerobic sediment with ca 20% elemental sulphur and emanation of H2S gas.

Morphogenesis of Hollow Bulbous Gypsum Structures Along a Brine Spring in Northeast Alberta

Abstract The stromatolite tufa mound at La Saline Lake developed along the Athabasca River Valley in northeast Alberta consists of a 30 m-high structure with a multi-meter thick caprock of stratified gypsum. The gypsum caprock developed when the meteoric-charged groundwater channeled along shallowly buried Upper Devonian limestone was redirected deeper and encountered anhydrite beds of the Middle Devonian Prairie Evaporite Formation, only 175–200 m below. Discharge of the sulfate-saturated brine from the central vent of the gypsum caprock eventually ceased and the flow was redirected to the western lakefront bank of the tufa mound. This active brine spring, characterized by total dissolved solids level of ∼79,000 mg/L, is channeled along a 25 m gully toward La Saline Lake. The bottom sediment in each of the interconnected brine pools along the gully consists of a 2–4 cm-thick calcite-gypsum thrombolite and an overlying gypsum crust. This sulfate crust developed as densely packed arrays of hollow botryoidal to hemispheroidal and bulbous gypsum protuberances, each 0.5–1.5 cm long, that extend upward into the brine. This is the first documented example of bulbous protuberances of gypsum that developed within brine pools with hollow interiors. The unusual hollowness of these bulbous gypsum protuberances resulted from the rapid encasement of gas bubbles that ascended from the underlying thrombolite ooze and were trapped within the overlying microbial mats and meshwork of gypsum crystallites on the surface of the bottom pool sediment. Nanoscale biomineralization of gypsum developed along the parallel arrays of microbial stalks within the enveloping mat, resulting in a meshwork of parallel aligned crystallites that encased the surfaces of the trapped bubbles. Continued abiotic gypsum precipitation transitioned the abiotic crystallites into enlarged needle-form crystallites distributed as parallel arrays along curvilinear growth surface laminae. Sufficient rigidity on the bubble surfaces precluded implosion-collapse or detachment. Strontium adsorption widely stabilized the acicular crystals, inhibiting complete coalescence as gypsum spar.

Physical properties of Devonian limestones from selected deposits in the context of frost resistance

Physical properties of Devonian limestones from selected deposits in the context of frost resistance

New biostratigraphic evidence of Upper Devonian deposits by metamorphosed conodonts from Sidi Bou Othmane area of central Jebilet, Morocco and their paleogeographic implications

This report is dedicated to the Sidi Bou Othmane limestones outcrops, which are exposed in the Central Jebilet. This area experienced strong Hercynian metamorphism and deformation. Strongly metamorphosed and recrystallized conodonts point to Frasnian-Famennian ages, which are reported from this region for the first time. Based on conodont data, we thus revise the age of the Sidi Bou Othmane limestones, which are definitely Late Devonian in age instead of Mississippian (late Viséan) as reported in previous publications. Six stratigraphic intervals from the Middle falsiovalis to marginifera utahensis Zones are identified. The colour alteration index of conodonts (CAI) is very high and varies from CAI 6 to CAI 8, indicating a thermal gradient from 360 °C to over 600 °C for the conodont bearing strata, which is consistent with the isograds obtained in previous publications. Transgressive Upper Devonian limestones discontinuously overlie Ordovician psammites, beginning with a variably thick polymict conglomerate. This unconformity provides evidence of a regional exhumation and erosional event of the Ordovician strata in the Central Jebilet, prior to Upper Devonian transgression. Together with the Koudiat Laabid limestones at Jebel Gueliz in the south, these Upper Devonian outcrops, locally covered by upper Viséan Sarhlef Schists, suggest that the upper Viséan basin of Central Jebilet was divided in a N–S elongated paleogeographical highland formed by the Ordovician and Devonian bedrock. The proposed paleogeographic configuration could explain the lithological differences between the slate deposits to the west and the flysch-like deposits to the east. The exhumation/erosion of Ordovician strata in the Sidi Bou Othmane area may be related to the Eovariscan block faulting and the preorogenic extension of the Meseta domain.

Copper-Bearing Mineralisation in the Upper Devonian Limestones: A Case Study from the Historical Teresa Adit in the Świętokrzyskie Mountains, Poland

The studied copper ore deposit is located in Miedzianka Mountain (Świętokrzyskie Mountains, central Poland). This deposit was exploited from the 13th century to the 1950s; therefore numerous historical adits are currently present. One of these is Teresa adit (established in 1805), consisting of underground mining corridors and natural cave developed in the Upper Devonian limestones, partially transformed by mining works. Samples of copper- and rock-forming minerals in limestones collected at seven sites within the richest copper-bearing mineralisation in this adit were studied with petrographic investigation of thin sections, micro-area chemical analysis (EDS), and XRD. This study shows the presence of various minerals: (a) Cu-Fe sulphides (relics of chalcopyrite) and Cu sulphides (covellite, chalcocite), (b) Cu-Fe oxides (cuprite and hematite), (c) Ca and Cu carbonates (calcite, azurite, and malachite), (d) clay minerals (Fe-Mg illite), and (e) micro-crystalline silica (quartz). For the first time in the studied deposit, we described chalcopyrite relics in cuprite pseudomorphosis, hematite with admixture of vanadium in pinkish-creme veins in limestones, and the presence of an admixture of Fe-Mg illite and microcystaline silica within cracks of limestones. In addition, for the first time, unit cell parameters of malachite and azurite from Miedzianka Mountain were determined, indicating very low substitutions of atoms other than Cu in their structures. We suppose that the minerals studied were formed during three types of copper mineralisation processes: (a) hydrothermal (relics of chalcopyrite), (b) secondary weathering (chalcocite, covellite, cuprite, hematite), and (c) adsorptive mineralisation (azurite, malachite). The latter stage is related to residuum, which consists of a mixture of Fe-Mg illite and micro-crystalline quartz, which was formed during the dissolution of limestones in karst processes in some crevices. We proposed a model of the formation of copper carbonates in the adsorption stage of the copper-bearing mineralisation in Miedzianka Mountain deposits. Two generations of calcite veins (older—red calcite and younger—crème-pinkish calcite) were also detected. Mineralogical–petrographical studies of samples revealed a high scientific and educational value. Due to the fact that the Teresa adit is planned to be made available to geotourists, this work is worth presenting to the public either in the adit and/or in a local museum in Miedzianka village.

Devonian upper ocean redox trends across Laurussia: Testing potential influences of marine carbonate lithology on bulk rock I/Ca signals

The Devonian is characterized by major changes in ocean-atmosphere O2 concentrations, colonialization of continents by plants and animals, and widespread marine anoxic events associated with rapid δ13C excursions and biotic crises. However, the long-term upper ocean redox trend for the Devonian is still not well understood. This study presents new I/Ca data from well-dated Lower Devonian through Upper Devonian limestone sections from the Great Basin (western Laurussia) and the Illinois Basin (central Laurussia). In addition, to better address potential influences of lithology and stratigraphy on I/Ca redox signals, I/Ca data are reported here as carbonate lithology-specific. Results indicate that lithologic changes do not exert a dominant control on bulk carbonate I/Ca trends, but the effects of some diagenetic overprints cannot be ruled out. For the Illinois Basin, low I/Ca values (more reducing) are recorded during the Pragian to Emsian and increased but fluctuating values are recorded during the Eifelian to Givetian. The Great Basin I/Ca trends suggest local upper oceans were more reducing in the Lochkovian, more oxic in the Pragian-Emsian, return to more reducing in the Eifelian, then to increasingly more oxic, but fluctuating in the Givetian-Frasnian. The local I/Ca variations at Great Basin likely share more similarity with global upper ocean condition (compared to the Illinois Basin) based on its position adjacent to the Panthalassic Ocean and its temporal co-variation with global environmental volatility trends. The overall reducing and variable redox conditions of local upper ocean (if not a diagenetic signal) during the Middle and Late Devonian of Great Basin coincide with evidence of increased global environmental volatility suggesting seawater redox may have been an important part of environmental instability at this time.

A comprehensive genetic model for the world’s largest Sb deposit (Xikuangshan, China)

AbstractThe Mesozoic (160–130 Ma), fault-controlled Xikuangshan Sb deposit within Devonian limestone strata of Hunan Province, Southern China is the world’s largest Sb deposit containing a proven reserve of ~2.5 m Sb. Although mined for over a century, its genesis remains poorly understood. Here we use new He-Ar isotope data of hydrothermal stibnite and both new and existing C-O-Sr-Nd isotopes of hydrothermal calcite with known stages to decipher its genesis and the major constraints on mineralization intensity. The 3He/4He and 40Ar/36Ar ratios of fluid inclusions trapped in stibnite are from 0.01 to 0.04 Ra (Ra: atmospheric 3He/4He ratio) and 304–1077, respectively, indicating the ore-forming fluids at Xikuangshan were dominated by air-saturated meteoric groundwater after interaction with crustal rocks. Ore-stage calcite C and O isotopes indicated that most CO2 in the fluids was acquired from marine carbonate rocks by dissolution; whereas Sr and Nd isotopes differed from deposited Devonian country rocks but were similar to the underlying regional Proterozoic clastic rocks in the region. Calcite from early and late stages showed a strong positive correlation between δ18O and 87Sr/86Sr, consistent with the mixing between the circulating groundwater and compounds released from the Proterozoic rocks due to extensive fluid-rock interaction. The 3He/Q ratios of the fluid inclusions are low, varying from 4.3 to 18.5 × 10−15 cm3 standard temperature and pressure (STP) J−1, indicating deep-seated magma could have provided heat by conduction but no volatiles into the ore-forming fluids. Based on these new results, we suggest that deep-seated granitic magma heated the down-going meteoric groundwater along fault zones, after which the groundwater extensively interacted with and extracted Sb from the Proterozoic Sb-rich rocks to form Sb-rich fluids. The Sb-rich fluids then ascended through regional faults and deposited Sb as stibnites at favorable structural traps to form the Xikuangshan Sb deposit. This study highlights that extensive water-rock interaction is essential to form the deposit, and more intensive water-rock interaction at an early stage allowed for early-stage mineralization yielding higher Sb reserves (>80%) at Xikuangshan.

Dendritické vrtby v miskách ramenonožců ze středního devonu (eifelu) pražské pánve (Barrandien, Česká republika)

Three ichnospecies of dendritic borings (Clionolithes cf. cervicornis, C. isp. A, and C. isp. B) were observed in abundant brachiopod shells in the Třebotov Formation (lowermost Eifelian, zone Polygnathus partitus) in two Prague localities (Praha-Holyně, “V rokli”, and Praha-Barrandov, street “K Barrandovu”). Borings are generally small-sized, of about 1 mm, but they can reach up to 4 mm. Borings are preserved inside thick translucent walls of brachiopods smooth shells (Trigonatrypa holynensis, Xenomartinia monoseptoides and Clorinda sp.). Borings are very frequent (almost in all examined shells), but never pass through a whole wall thickness of a brachiopod. Two or even more borings, commonly of a different type, are preserved on an individual shell. Both valves of articulated specimen may be bored, while the shell interior is devoid of borings neither shows any response to the boring activity such as uneven internal biomineralization. Majority of tunnels bores inside the shell wall, and the borings are opened by small irregular central pit. As more than a half of examined shells were infected, bioerosion likely had a negative impact on the shell preservation. Our study shows that the brachiopod infestation was selective. Only thick calcitic shells were bored, while thinner shells or exopunctate brachiopods (Holynatrypa, Peridalejina, Prokopia) were not a target of the borers. Similarly, crinoid and other echinoderm ossicles do not show any signs of a boring. A different dendritic boring referred to as Clionolithes radicans was observed on a shell of brachiopod coming from the Acanthopyge Limestone (Choteč Formation, Eifelian) from Zadní Kobyla locality near Koněprusy. The stellate trace is substantially larger (4.3 mm × 2.8 mm) than borings from the Třebotov Limestone, with deep and externally open canals. Borings from the Třebotov Limestone come from so-called “white beds”. These soft beds originated by weathering of a hard limestone, leaving loose generally small bioskeletal remains of echinoderms, gastropods, brachiopods, ostracods, dacryoconarids and other invertebrate groups. Dacryoconarid shells and crinoid ossicles dominate. The life assemblage occupied a deeper weakly hypoxic perireef environment below the fotic zone. The dendritic boring from the Acanthopyge Limestone comes from a completely different environment. Associated diverse and generally large brachiopods, fragmented fenestrate bryozoans and abraded tabulate and rugose corals (including Calceola sandalina) indicate a shallow-water highenergy reef environment. This is the first report of dendritic borings from the Eifelian of the Prague Basin. It confirms not only so far unknown presence of their borers in the area, but also reveals that their activity can be observed in the weakly lithified Devonian limestones in the area.

From shallow into deep sea: Sedimentary facies and U-Pb zircon ages in the early Paleozoic Noric Group at Veitsch (Eastern Greywacke Zone, Austria)

Abstract The low-grade metamorphic early Paleozoic basement of the Veitsch area presents a wide variety of sedimentary facies domains. The first domain consists of thick metadacites of Middle Ordovician age (Blasseneck Porphyroid), overlain by fine-grained metaclastics of the Rad Formation (Late Ordovician to Silurian) and Devonian limestones and calcitic marbles (Kaiserstein and Kaskögerl Formation, respectively). Rhyolitic to dacitic magmatism initiated at ca. 479 Ma (LAMC-ICP-MS U-Pb zircon data) and lasted until ca. 444 Ma. The second domain comprises metaclastics of the Stocker Formation (Early Ordovician to Silurian), characterized by thin volcanics and volcaniclastics of andesitic and rhyolitic composition. U-Pb zircon data give Middle Ordovician age (463 Ma – 468 Ma). The third domain, exposed northwest of Veitsch, consists of thick metadacites (Blasseneck Porphyroid, ca. 478 Ma), followed by (siliceous) phyllites which grade into turbiditic metasediments (Sommerauer Formation, Late Ordovician to Devonian?). Clastic sediments of the Stocker and Sommerauer Formations were sourced from northern Gondwana showing a prominent Pan-African detrital zircon peak at ca. 640 Ma. Middle to Upper Ordovician volcanics (ca. 462 Ma – 448 Ma) represent the second source. Tectonic reconstruction leads us to the arrangement of three facies domains. A shallow marine shelf facies is located in the present days southwest. A marginal basin with volcanic islands on a sloping continent, and a deep-water environment containing turbidites are situated further to the northwest. The present arrangement of these facies domains is explained by eo-Alpine and Variscan thrust tectonics.

Impact of mechanical stratification on the structural style of the Lublin Basin, SE Poland: results of seismic interpretation and implications for quantification of deformation within the frontal parts of thin-skinned fold-and-thrust belts

We demonstrate how lithological and mechanical stratification of Ediacaran–Carboniferous sedimentary package governs strain partitioning in the Lublin Basin (LB) which was incorporated in the marginal portion of the Variscan fold-and-thrust belt. Based on the geometry of seismic reflectors, the pre-Permian–Mesozoic sedimentary sequence was subdivided into two structural complexes differing in structural style. The lower one reveals forelandward-vergent imbrication, while the upper one comprises fold train, second-order deformations, and multiple local detachments. Lithological composition of the upper structural complex controlled geometry, kinematics, and position of compressional deformations in stratigraphic profile. System of foreland-vergent thrusts which links lower and upper detachment developed due to efficiency of simple shear operating in heterogeneous clastic-carbonate-evaporitic strata of the Lower–Upper Devonian age. Internal homogeneity promoted the formation of conjugate sets of thrusts in Silurian shales and Upper Devonian limestones. Structural seismic interpretation combined with sequential restoration revealed localised thickening of Devonian strata and up to 5% difference in length of Devonian horizons. This mismatch is interpreted as a manifestation of distributed shortening, including layer-parallel shortening (LPS), which operated before or synchronously to the initiation of folding. The amount of distributed strain is comparable with numbers obtained in external parts of other fold-and-thrust belts. The outcomes derived from this study may act as a benchmark for studying variability in a structural style of multilayered sequences which were incorporated in the external portion of other fold-and-thrust belts.

The Miedzianka Mountain Ore Deposit (Świętokrzyskie Mountains, Poland) as a Site of Historical Mining and Geological Heritage: A Case Study of the Teresa Adit

There are numerous traces of mining activity in the Miedzianka Mountain (Świętokrzyskie Mountains, Poland), because copper and silver ores have been mined in this region since at least the 13th century. The history of scientific research on the Miedzianka Mountain ore deposit spans almost 200 years. Almost 40 minerals have been found: ore minerals of Cu and Fe, and also secondary minerals, including carbonates, sulphates and even very rare arsenates, phosphates and vanadates. Three new minerals have been found, staszicite, lubeckite and miedziankite, but their chemical composition has not been precisely determined and therefore their names have not been approved by the International Mineralogical Association (IMA). The Miedzianka Mountain deposit is an important area on the map of educational activities. It is included in the “Świętokrzyskie Archaeological and Geological Trail” as a site of historical (mining and metallurgy) and natural (geological sciences) heritage. Despite the large potential, none of the underground workings (adits and shafts) are currently available to the public. Our research and exploration of the Teresa adit, which is one of the historical underground complexes of the Miedzianka Mountain, show that this adit displays a wide spectrum of topics in the field of mineralogy, geology and mining history. The Teresa adit, which is a 523 m system of underground corridors, contains 270 m of natural karst caves altered by mining works and is constituted of Upper Devonian limestones, locally cut by cherry shales. In several sites of the adit unique features can be observed, such as: (1) old mining works—galleries carved in the rock back in the 19th century; (2) interesting vein mineralization with secondary-colored copper carbonates and multi-colored calcite veins; (3) mineralization with azurite domination; and (4) karst phenomena (coatings, flowstone, dripstones and stalactites) in a cave part of the adit. The sites with unique features suggest that the Teresa adit is highly suitable to be presented to tourists. That is why we propose seven sites on the underground route that could be the basis for further projects to create a “geotouristic trail” in the Teresa adit. The proposal to make the Teresa adit available to tourists is in line with the tendency to protect the post-industrial landscape associated with former mining activities.

Tracing the Provenance of the Devonian Limestone of Telen River, East Kalimantan

H. Witkamp found an outcrop with Devonian Limestone in East Kalimantan in 1925. In 1989, an expedition run by Institute of Technology Bandung (ITB) reinvestigated the outcrop and concluded that the Devonian Limestones in Telen River were boulders within a Permian formation. This paper gives a wider overview on the distribution of Devonian rocks in Asia Pacific region and discusses their possible origin.Based on the distribution map of Devonian rocks in the region, the Devonian limestone in Borneo is very isolated. The closest Devonian limestones are about more than 2000 km away. Probably the Devonian limestone in Telen River has been separated away from its origin by significant tectonic movement. There are several theories and models related to the formation history of this area, which makes it very complex. To understand the origin of these limestones, the geology needs to be restored to their time and place of deposition of the Devonian limestone.

Alignment of saline springs with evaporite karst structures in northeast Alberta, western Canada: analogue for cretaceous hypogene brine seeps to the surface

Meteoric and glacial meltwater charged groundwater, mixed with dissolved salts from Devonian sources at depth, discharged as saline springs along topographic lows of the Athabasca River Valley, which downcuts into the Cretaceous Athabasca oil sands deposit in northeast Alberta, western Canada. These Quaternary saline seeps have TDS measurements, isotope signatures and other chemical characteristics indicative of the groundwater flows coming in contact with Prairie Evaporite (M. Devonian) salt beds, 200 m below the surface. Migrations up-section of groundwater with dissolved chloride and sulphate salts occurred along salt dissolution collapse breccia zones that cross-cut Upper Devonian limestone strata. Seeps discharged along the karstic Devonian limestone paleotopography, the unconformity surface flooring the Lower Cretaceous McMurray Formation. Saline to brine springs along the Athabasca River Valley have TDS measurements that can exceed 100,000 mg/L. Quaternary salt removal was insignificant compared to the voluminous removal of the 80-130 m thick salt section for 1000s km2 during the Early Cretaceous configuration of the Devonian paleotopography, which partially controlled depositional patterns of the overlying McMurray Formation, principal host rock of the Athabasca oil sands. Little is known of the storage or disposition of voluminous brines that would have resulted from this regional-scale removal of the salt beds below the Athabasca deposit during the Cordilleran configuration of the foreland Alberta Basin. Holocene dissolution trends and discharges at the surface as saline springs are proposed as a modern analogue for voluminous Early Cretaceous brine seeps to the surface along salt dissolution collapse breccia zones, concurrent with deposition of the McMurray Formation. This model links several characteristics of the McMurray Formation as responses to Aptian brine seeps to the surface. These include: (1) the emplacement of a drainage-line silcrete along the margins of the Assiniboia PaleoValley, now partially exhumed by the Athabasca River Valley, (2) distribution of brackish-water burrowing organisms, and (3) diagenesis of calcite-cemented sand intervals.

Chemical and boron isotopic compositions of tourmaline at the Dachang Sn-polymetallic ore district in South China: Constraints on the origin and evolution of hydrothermal fluids

The Dachang Sn-polymetallic ore district in South China is the second largest tin district in the world with a tin reserve of over one million tonnes. Zn-Cu skarn and stratiform, massive, and vein Sn-Pb-Zn ores are all present in this district. This has led to a debate as to whether the Sn orebodies were formed by Cretaceous magmatic-hydrothermal replacement or Devonian submarine exhalative-hydrothermal sedimentation. Here, we present a systematic investigation of the major, trace element, and boron isotopic compositions of different types of tourmaline in the Dachang ore district. Tourmaline disseminated in the Longxianggai granite and pegmatite veins belongs to the schorl series and has high contents of Li, Zn, and Ga. The δ11B value of primary magma of the Longxianggai granite is estimated to be about −13‰, close to the global average δ11B value (−11‰) for S-type granites. Tourmaline from quartz-tourmaline veins in the Longxianggai granite has similar chemical composition to the magmatic tourmaline and likely formed from hydrothermal fluids exsolved from the evolved granitic melt. The δ11B value of the initial hydrothermal fluids is also calculated to be about −13‰. Tourmalines from the skarn and sulfide ores in the Lamo deposit have higher Mg/(Mg+Fe) and lower Na/(Na+Ca) ratios and higher contents of Be, Ge, Sr, and Sn than magmatic tourmaline. These patterns likely reflect input of elements derived from the host Devonian limestone. The δ11B values of the hydrothermal fluids are estimated to be between −13 and −10‰, suggesting evolved magmatic-hydrothermal fluids related to the Longxianggai granite. Tourmalines from the stratiform and vein ores in the Changpo-Tongkeng deposit are extremely Mg-rich and mostly belong to the dravite series. They have high contents of Sc, V, Cr, Sr, and Sn and show positive Eu anomalies. The δ11B values of these B- and Sn-rich fluids are estimated to be between −15 and −10‰, suggesting that the fluids also have a magmatic-hydrothermal origin. These fluids are most likely derived from the same granitic magma source, but may have interacted with the Devonian volcanic rocks.

The Heritage Interest of the Koudiat Ferjane Outcrops of Jebel Ardouz in the M’zoudia Region and Their Protection

The Jebel Ardouz massif west of Marrakech (M’zoudia region) is one of a few Paleozoic outcrops that arises from the Pliocene-Quaternary Houaz plain (Kebir, Lahalima, Alamma, and Ferjane). Locally, the first tree hills capped by the Devonian limestones have been exploited by the Asmar cement plant since 1974. The Koudiat Ferjane, not yet exploited, consists of undeformed and unmetamorphosed Devonian rocks. The exposed limestones have been sampled in order to determine their conodont microfauna. The samples delivered the best-preserved conodonts of the Jebilet region and attest the only reef structure of the Middle Devonian (Givetian) platform in the area, witnessing the expansion of the Prototethys between Gondwana and Laurussia. For the numerous sedimentological, paleontological, and paleoenvironmental features, the easily accessible Koudiat Ferjane represents a unique geological heritage site. It deserves protection for geotourism and education, both for scientific purposes and for the general public, and must therefore be preserved and protected from the upcoming destruction.

Evidence of the middle Miocene paratethys transgression from Jurkowice-Budy site (SE Holy Cross Mountains, Poland

 Identifying ancient shores may provide valuable information concerning sea-level fluctuations and environmental changes, since they serve as a reliable marker of palaeoshorelines. This paper deals with deposits that display features of a nearshore zone. In the Jurkowice-Budy quarry (southern slopes of the Holy Cross Mountains) a sequence of clastic sediments and littoral structures linked to the transgression of the Paratethys Sea in the middle Miocene has been recognised. The discovery of bio-erosional assemblages (borings of lithophags) in Devonian limestone boulders helped to determine the littoral nature of the examined deposits and to layout a palaeocliff wall. The samples of sandy sediments were analysed by sieving procedure and interpreted using statistical parameters calculated by graphic and moment methods. Moreover, morphometric analysis of gravels and analysis of mineralogical composition under binocular microscope were performed. The results showed well-developed beach assemblages composed of pebbles, coarse-to-medium sands and silty sands derived from eroded Cambrian strata (sand-stones) located to the north of the study site.

The bio-availability and accumulation of the trace elements in rock-soil-fruit system in carbonatite regions of different stratums: Critical soil factors and transfer models

For exploring the key factors affecting trace element accumulation in crops in limestone soil derived from limestone area of different stratums, the loquat (Eriobotrya japonica Lindl.) orchard of three limestone units (Middle Devonian, Upper Devonian and Middle Cambrian) in Mengzi city of Yunnan Province, China were investigated. Loquat fruits grown on soil from Middle Devonian limestone exhibited significantly higher bio-enrichment in cadmium. The Middle Devonian (Chemical Index of Alteration [CIA] = 86.07) and Upper Devonian (CIA = 84.84) soils were more weathered than those derived from Middle Cambrian rocks (CIA = 74.42). In the Middle Devonian limestone area, Fe element (for As uptake into fruit), Al element (for Cu and Zn) and metal speciation (for Cd, extracted by diethylene triamine pentaacetic acid) in the soil were the important influencing factors. For the Upper Devonian, soil weathering was found to be the key factors controlling fruit Cu uptake, respectively. For the Middle-Cambrian-derived soils, soil Ca concentration and pH played a critical role in Cd accumulation in fruit. In conclusion, under acidic soil conditions derived from limestone, the Ca concentration and metal fraction in the soil are the pivotal factors affecting Cd accumulation of fruit, whereas the soil Fe element content control the fruit As and Pb uptake. These results are helpful to further understand the migration regularity of trace elements into fruit in different limestone geology types.

Two-dimensional inversion of CSAMT data and three-dimensional geological mapping for groundwater exploration in Tongkeng Area, Hunan Province, China

Controlled source audio-magnetotelluric (CSAMT) is an indirect and effective geophysical prospecting method in subsurface prospecting. Although CSAMT investigation tools are equipped with new techniques, it must be noted that the models obtained still do not automatically decipher the reality of groundwater in bedrock with very high resistivity contrasts. Our study proposed a new CSAMT data processing scheme, which combined the 2D modeling and 3D visualization for groundwater exploration in Tongkeng area, Hunan Province, China. To directly highlight exploitable groundwater, we used the open-source and the OCCAM2D inversion software, coupled with the geological information of the area to define the 3D imaging with emphasizing on the network of producing fractures. We deployed three CSAMT profiles with transverse magnetic (TM) mode recorded on 21 frequencies (8192 Hz to 8 Hz). The data were filtered, pre-processed and carefully analyzed from station to station. Analysis of the apparent resistivity and phase maps show the conductive zones (<150 Ωm) and resistive zones (> 500 Ωm) separated by transition zones (150 to 500 Ωm). The 2D models and stacked sections show discontinuities of fractures marked by two major faults and a main fracture in the zone interconnected by minor fractures. A 3D geological map was obtained from the result of the best models of the different lines. The ITER2DAT function was used to export the data from OCCAM2D inversion and then display it to array and depth channels data for each station. Geological and borehole ZK01 data were used to build pseudo stratigraphic drillholes based on the range of very low (<10 Ωm) to high values resistivity structures (>1500 Ωm). The 3D view shows stratigraphic discontinuity that is between carbonaceous formation and the metamorphic granites. The intruded Devonian limestone layer, which is the potential water tank, and the carbonate vein layer are constantly heated by the geothermal gradient of the area.