Defining geo-habitats for groundwater ecosystem assessments: an example from England and Wales (UK)

Groundwater ecosystems comprising micro-organisms and metazoans provide an important contribution to global biodiversity. Their complexity depends on geology, which determines the physical habitat available, and the chemical conditions within it. Despite this, methods of classifying groundwater habitats using geological data are not well established and researchers have called for higher resolution habitat frameworks. A novel habitat typology for England and Wales (UK) is proposed, which distinguishes 11 geological habitats (geo-habitats) on hydrogeological principles and maps their distribution. Hydrogeological and hydrochemical data are used to determine the characteristics of each geo-habitat, and demonstrate their differences. Using these abiotic parameters, a new method to determine abiotic habitat quality is then developed. The geo-habitats had significantly different characteristics, validating the classification system. All geo-habitats were highly heterogeneous, containing both high quality habitat patches that are likely to be suitable for fauna, and areas of low quality that may limit faunal distributions. Karstic and porous habitats generally were higher quality than fractured habitats. Overall, 70% of England and Wales are covered by lower quality fractured habitats, with only 13% covered by higher quality habitats. The main areas of high quality habitats occur in central England as north–south trending belts, possibly facilitating dispersal along this axis. They are separated by low quality geo-habitats that may prevent east-west dispersal of fauna. In south-west England and Wales suitable geo-habitats occur as small isolated patches. Overall, this paper provides a new national-scale typology that is adaptable for studies in other geographic areas.     

Controlling factors for the spatial variability of soil magnetic susceptibility across England and Wales

We review the nature and importance of soil factors implicated in the formation of secondary ferrimagnetic minerals in soils and palaeosols worldwide. The findings are examined with respect to temperate regions through a comprehensive analysis of over 5000 samples of surface soil from England and Wales taken from a 5 × 5 km grid. Over 30 soil and environmental attributes are considered for each sample as proxies for soil forming factors. Measurements of low field magnetic susceptibility (mass specific) and frequency dependent susceptibility (mass specific and percentage) on each sample provide estimates of the concentration and grain size of ferrimagnetic minerals.Maps of soil magnetism across England and Wales show non-random distributions and clusters. One subset of data is clearly linked to contamination from atmospheric pollution, and excluded from subsequent analyses. The concentration of ferrimagnetic minerals in the non-polluted set is broadly proportional to the concentration of minerals falling into the viscous superparamagnetic domain size range (~ 15–25 nm). This set shows clusters of high magnetic concentrations particularly over specific parent materials such as schists and slates, mudstones and limestones.Bivariate analyses and linear multiple regression models show that the main controlling factors are parent material and drainage, the latter represented by soil drainage classes and particle size. Together these two factors account for ~ 30% of the magnetic variability in the complete dataset. A second group of factors, including climate (mean annual rainfall), relief (slope and altitude), and organisms (land use, organic carbon and pH) have subordinate control. Climate, as represented by mean annual temperature, and also pedogenic time are deemed not relevant at these spatio-temporal scales.The findings are consistent with a largely abiotic system where the role of iron-reducing bacteria appears minor. At coarse spatial and temporal scales, secondary ferrimagnetic mineral formation is controlled by the weathering capacity to supply Fe to the surface soil. At finer scales, soluble Fe precipitates as ferrihydrite before transformation in response to periodically anaerobic conditions into other minerals including nanoscale magnetite.     

The invertebrate ecology of the Chalk aquifer in England (UK)

The Chalk is an important water supply aquifer, yet ecosystems within it remain poorly understood. Boreholes (198) in seven areas of England (UK) were sampled to determine the importance of the Chalk aquifer as a habitat, and to improve understanding of how species are distributed. Stygobitic macro-invertebrates were remarkably common, and were recorded in 67 % of boreholes in unconcealed Chalk, although they were not recorded in Chalk that is concealed by low-permeability strata and thus likely to be confined. Most species were found in shallow boreholes (<21 m) and boreholes with deep (>50 m) water tables, indicating that the habitat is vertically extensive. Stygobites were present in more boreholes in southern England than northern England (77 % compared to 38 %). Only two species were found in northern England compared to six in southern England, but overall seven of the eight stygobitic macro-invertebrate species found in England were detected in the Chalk. Two species are common in southern England, but absent from northern England despite the presence of a continuous habitat prior to the Devensian glaciation. This suggests that either they did not survive glaciations in the north where glaciers were more extensive, or dispersal rates are slow and they have never colonised northern England. Subsurface ecosystems comprising aquatic macro-invertebrates and meiofauna, as well as the microbial organisms they interact with, are likely to be widespread in the Chalk aquifer. They represent an important contribution to biodiversity, and may influence biogeochemical cycles and provide other ecosystem services.     

Magmatic Evolution of the Ordovician Snowdon Volcanic Centre, North Wales (UK)

The Ordovician Snowdon Volcanic Centre (SVC) of North Walescomprises a bimodal basalt–subalkaline/peralkaline associationemplaced around a caldera within a shallow marine environment.The tectonic setting was associated with closure of the LowerPalaeozoic Iapetus Ocean and cessation of ocean plate subduction.The SVC volcanic products include basaltic lavas and pyroclasticrocks, rhyolitic pyroclastic flow deposits, high-level intrusions,domes, and flows, together with reworked equivalents. A programmeof detailed field mapping, sampling, and chemical analysis hasbeen used to evaluate the structure and magmatic evolution ofthe SVC volcanic system. SVC basalts show a range in chemicalcharacteristics between volcanic arc type and within-plate,ocean island basalt (OIB) type. Subalkaline, silica-oversaturatedintermediate intrusions (icelandites) and five chemically distinctgroups of extrusive and intrusive subalkaline/peralkaline rhyolites(termed A1, A2, B1, B2, and B3) were emplaced during the evolutionof the SVC. This evolution was driven by material and thermalinput from basaltic magma. The SVC basaltic lavas were derivedas partial melts from a heterogeneous volcanic arc to OIB-typespinel lherzolite mantle and experienced up to 60% olivine gabbrofractionation during storage in sill networks in the sub-crustor lower crust. Some magma batches experienced further fractionalcrystallization ({small tilde}70%) and minor crustal contamination({small tilde}10%) to yield the icelandites. Trace element andNd isotope data do not favour an origin for the rhyolites bypartial or total fusion of likely crustal material, and thefive rhyolite groups are regarded as distinct homogeneous batchesof magma derived from varied basaltic magmas. The icelanditesand peralkaline rhyolites (group B3) result, respectively, from{small tilde}50% and {small tilde}80–90% zircon-free fractionalcrystallization of SVC basalts. The subalkaline rhyolites (groupsA1 and B1) result from {small tilde}80–90% fractionalcrystallization of subduction-related basalts similar to thoseof Ordovician basalts which pre-date the Lower Rhyolitic TuffFormation, and groups A2 and B2 were formed by mixing and homogenizationof A1, B1, and B3 magma batches. These data and interpretationsprovide the basis of a model for the complex evolution of asilicic magma system below the SVC caldera around the time ofcessation of Caledonian subduction in North Wales. Rhyolitemagma chambers were short lived and discontinuous; the largestwas probably disc shaped and was almost entirely evacuated duringa >60-km³ ash-flow eruption.     

The Petrology of an Adamellite-Porphyrite from the New England Bathylith (New South Wales)

The paper presents an account of the occurrence, petrography,mineralogy, and geochemistry of several intrusions of adamellite-porphyrite,an early member of the New England Bathylith (N.S.W.). The rockis composed of phenocrysts of quartz, andesine, hornblende,biotite, augite (and minor orthopyroxene) which are set in afine-grained quartzofeldspathic groundmass. Compositions ofsilicate phenocrysts (which reveal widespread evidence of cataclasis)accord with coexisting phases of an assemblage appropriate tointermediate rocks. Xenolith mineralogy is similar to equivalentminerals occurring as phenocrysts. The recalculated bulk compositionof a rock represented by the modal andesine, hornblende, biotite,augite, and magnetite of the adamellite-porphyrite is similarto the composition of a biotite–diorite; the compositionof the quartzo-feldspathic groundmass plots in the low-meltingregion of the NaAISi₃O₈-KAISi₃O₈-SiO₂-H₂O system. Evidence ispresented to indicate a hybrid origin for the adamellite-porphyritewhereby disrupted biotite-diorite was invaded and mixed withlow-melting silicic alkalic liquid.     

Geochronology and geochemistry of Palaeozoic intrusive rocks in the Rockvale region,southern New England Orogen,New South Wales

Palaeozoic intrusive rocks of the New England Batholith from the Rockvale district in the southern New England Orogen form three distinct associations: (i) the Carboniferous Rockvale Adamellite, a member of the Hillgrove Suite of deformed S‐type granitoids; (ii) a small I‐type igneous complex on the northwestern margin of the Rockvale Adamellite: several members of this complex have similar chemical compositions to the most mafic members of the Moonbi Suite of New England Batholith I‐types; and (iii) a suite of dyke rocks ranging in composition from calc‐alkaline lamprophyre through hornblende and biotite porphyrite to aplite. Ion‐microprobe U‐Pb zircon analysis indicates intrusion of the Rockvale Adamellite at 303 ±3 Ma (weighted mean ²⁰⁶Pb/²³⁸U age; 95% confidence limits). Preliminary investigation of zircon inheritance within the Rockvale Adamellite is consistent with chemical and isotopic indications of derivation of New England Batholith S‐type granitoids from a relatively juvenile protolith. Deformation of the Rockvale Adamellite occurred after complete crystallization of the pluton and prior to emplacement of dykes and I‐type intrusives. K‐Ar biotite and hornblende ages show broadly synchronous intrusion of I‐type magmas and lamprophyre dykes at ca 255 Ma, indicating that mantle magmatism associated with lamprophyres was contemporaneous with the crustal production of I‐type melts. Chemical similarities between the most mafic Moonbi Suite members and calc‐alkaline lamprophyres may also indicate a direct mantle contribution to some I‐type magmas.     

The ordovician (caradoc) volcanic rocks of montgomery,Powys, N. Wales

The Ordovician (Caradoc, Soudleyan) rocks of Montgomery, Powys are shales interbedded with locally conglomeratic volcaniclastic sediments composed of andesitic detritus. New formal lithostratigraphic units are proposed: Montgomery Volcanic Group comprising in ascending order: Castle Hill Shale Formation, Castle Hill Conglomerate Formation and Quarry Sandstone and Shale Formation. The volcaniclastic strata are reinterpreted as deposits of a submarine volcaniclastic fan system sourced by contemporaneous andesitic island volcanism. The observed diagenetic sequence is typical of marine volcanic sandstones and was dominated by hydration reactions related to the degradation of abundant unstable volcanic detritus. Diagenesis has resulted in the virtual destruction of original porosity in the volcaniclastic rocks.     

Deep groundwater flow and geochemical processes in limestone aquifers: evidence from thermal waters in Derbyshire, England, UK

Thermal waters potentially provide information on geochemical processes acting deep within aquifers. New isotopic data on groundwater sulphate, inorganic carbon and strontium in thermal and non-thermal waters of a major limestone aquifer system in Derbyshire, England, UK, are used to constrain sulphate sources and groundwater evolution. Shallow groundwaters gain sulphate from oxidation of sulphide minerals and have relatively ¹³C-depleted dissolved inorganic carbon (DIC). Thermal waters have relatively high Sr/Ca and more ¹³C-enriched DIC as a result of increased water–rock interaction. In other respects, the thermal waters define two distinct groups. Thermal waters rising at Buxton have higher Mg, Mn and ⁸⁷Sr/⁸⁶Sr and lower Ca and SO₄, indicating flow from deep sandstone aquifers via a high permeability pathway in the limestone. By contrast, Matlock-type waters (97% of the thermal flux) have elevated sulphate concentrations derived from interaction with buried evaporites, with no chemical evidence for flow below the limestone. About 5% of the limestone area's groundwater flows to the Matlock group springs via deep regional flow and the remainder flows via local shallow paths to many non-thermal springs. Gypsum dissolution has produced significant tertiary porosity and tertiary permeability in the carbonate aquifer and this is an essential precursor to the development of karstic drainage.

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Resumen Las aguas termales potencialmente proporcionan información sobre procesos geoquímicos que actúan a profundidad en acuíferos. Nuevos datos isotópicos de sulfatos, carbón inorgánico y estroncio en aguas termales y no-termales de un acuífero importante de caliza en Derbyshire, Inglaterra se utilizan para delinear las fuentes de sulfato y la evolución de aguas subterráneas.Las aguas subterráneas no muy profundas adquieren sulfato a través de la oxidación de minerales de sulfuro y poseen carbón inorgánico disuelto (DIC) relativamente deplatado de ¹³C. Las aguas termales muestran un ratio Sr/Ca relativamente alto y poseen (DIC) más enriquecido en¹³C, como resultado de la mayor interacción de roca-agua. En otros aspectos, los aguas termales definen dos grupos distintivos. Las aguas termales que ascienden en Buxton tienen mas Mg, Mn y ⁸⁷Sr/⁸⁶Sr y menos Ca and SO₄, indicando flujo de acuíferos de areniscas profundas por un sendero de alta permeabilidad en la caliza.En contraste el tipo de agua - Matlock (97% del flujo termal) posee altas concentraciones de sulfato, derivado por interacción con evaporitas enterradas, sin evidencia química de flujo debajo de la caliza. Aproximadamente 5% del agua del área de la caliza se fluye al grupo de manantiales de Matlock a través de un flujo regional profundo y el resto fluye por senderos locales poco profundos a muchos de los manantiales no-termales. La disolución de yeso ha producido porosidad terciaria importante así como permeabilidad en el acuífero de carbonato y este es un precursor esencial del desarrollo de drenaje kárstico.

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Résumé Les eaux thermales peuvent apporter des informations sur les processus géochimiques dans les aquifères profonds. De nouvelles données isotopiques sur les sulfates présents dans les eaux souterraines, le carbone inorganique et le strontium dans les eaux thermales et non thermales d'un système aquifère calcaire majeur dans le Derbyshire, Angleterre, Royaume Uni, sont utilisées pour comprendre les sources de sulfates et l'évolution des eaux souterraines. Les eaux souterraines phréatique s'enrichissent en sulfate via l'oxydation des minéraux sulfatés et ont un Carbone Inorganique Dissous (DIC) relativement appauvri en¹³C. Les eaux thermales ont un rapport Sr/Ca relativement plus élevé et un DIC plus enrichi en¹³C, du fait de l'interaction accrue des eaux avec les roches. En d'autres mots, les eaux thermales définissent deux groupes distincts. Les eaux thermales remontant à Buxton ont un Mg, un Mn et un rapport ⁸⁷Sr/⁸⁶Sr plus hauts, mais un Ca et SO₄ plus faible, indiquant un écoulement à travers les zones perméables des aquifers gréseux. Par contraste, les eaux du type de Matlock (97% du flux thermique), possèdent des concentrations élevées en sulfates, provenant de l'interaction des eaux avec les évaporites enfouies, tandis qu'il n'existe aucune évidence chimique d'un écoulement sous les calcaires. Sur environ 5% de la surface des calcaires, les eaux souterraines alimentent des sources non-thermales. La dissolution du Gypse a produit une porosité tertiaire significative et une perméabilité dans les aquifères calcaires, et ceci est un précurseur essentiel au développement du drainage karstique.

     

Graphite morphologies from the Borrowdale deposit (NW England,UK): Raman and SIMS data

Graphite in the Borrowdale (Cumbria, UK) deposit occurs as large masses within mineralized pipe-like bodies, in late graphite–chlorite veins, and disseminated through the volcanic host rocks. This occurrence shows the greatest variety of crystalline graphite morphologies recognized to date from a single deposit. These morphologies described herein include flakes, cryptocrystalline and spherulitic aggregates, and dish-like forms. Colloform textures, displayed by many of the cryptocrystalline aggregates, are reported here for the first time from any graphite deposit worldwide. Textural relationships indicate that spherulitic aggregates and colloform graphite formed earlier than flaky crystals. This sequence of crystallization is in agreement with the precipitation of graphite from fluids with progressively decreasing supersaturation. The structural characterization carried out by means of Raman spectroscopy shows that, with the exception of colloform graphite around silicate grains and pyrite within the host rocks, all graphite morphologies display very high crystallinity. The microscale SIMS study reveals light stable carbon isotope ratios for graphite (δ ¹³C = −34.5 to −30.2‰), which are compatible with the assimilation of carbon-bearing metapelites in the Borrowdale Volcanic Group magmas. Within the main mineralized breccia pipe-like bodies, the isotopic signatures (with cryptocrystalline graphite being lighter than flaky graphite) are consistent with the composition and evolution of the mineralizing fluids inferred from fluid inclusion data which indicate a progressive loss of CO₂. Late graphite–chlorite veins contain isotopically heavier spherulitic graphite than flaky graphite. This agrees with CH₄-enriched fluids at this stage of the mineralizing event, resulting in the successive precipitation of isotopically heavier graphite morphologies. The isotopic variations of the different graphite morphologies can be attributed therefore, to changes in the speciation of carbon in the fluids coupled with concomitant changes in the XH₂O during precipitation of graphite and associated hydrous minerals (mainly epidote and chlorite).     

Determining uraniferous host rocks and minerals as a source of dissolved uranium in granite aquifers near the central Ogcheon metamorphic belt,Korea

Korea has suffered from high U concentrations in some groundwater, especially in Daejeon near the central Ogcheon metamorphic belt. However, clear explanation has not been yet reported for the uranium sources in groundwater. This study is focused on identifying the potential uraniferous host rocks and finding the exact U-minerals serving as uranium sources in groundwater near Daejeon, Korea. For this work, we performed an in situ gamma ray spectrometer survey and a laboratory microscopic study with electron micro-probe analysis. The measurements for radioactive element content did not show any prominent K- and Th-anomaly spots, but they did result in several observations of considerable U-anomalies in pegmatite and hydrothermally altered granite, in which uraninite, coffinite and uranophane were found by electron micro-probe analysis. The occurrences of U-minerals are the first such discovery except in the low-grade U deposits of the Ogcheon metamorphic belt in Korea. All observed U-minerals were intimately associated with hydrothermal alteration. The remarkably low Th/U ratios in the studied uraniferous rocks also suggest that the U enrichment was genetically related to a post-magmatic hydrothermal process. However, many of the uraniferous parts were controlled by a reducing environment and occurred near the border between graphite-rich mica-schist and Jurassic leucocratic granite. The findings on these uraniferous rocks can be used in elucidating the source of highly enriched U groundwater in granite aquifers as well as in understanding the occurrence of igneous U-minerals, which has not been previously reported in Korea.     

Probable Neolithic footprints preserved in inter-tidal peat at Kenfig, South Wales (UK)

Holocene footprints have been reported from several locations around the UK coast preserved within inter-tidal sediments. These sediments are normally fine-grained silts, sands and clays. Here we report potential human footprints preserved in the lower of two inter-tidal peat units exposed on the foreshore at Kenfig in South Wales. The lower peat layer pre-dates 3810 ± 40 BP and its maximum age is constrained by two dates, one of 4930 ± 50 BP and another of 5110 ± 50 BP. The prints may have formed at any point within this time interval. Both peat units formed in a salt marsh, or fen environment, as indicated by the analysis of both diatoms and pollen and have been tentatively assigned to the middle Wentlooge Formation within the Holocene lithostratigraphy established for the Severn Estuary Holocene sequence. The footprints were digitised using an optical laser scanner and are compared to other Holocene human footprints exposed on the Sefton Coast in North West England. In comparison the Kenfig prints have poor anatomical form which may be the result of both the substrate and post-depositional modification. The paper demonstrates the value of using optical laser scanning in the data capture and analysis of transitory archaeological and geological trace evidence.     

扬子板块伊迪卡拉(震旦)纪多细胞生物的发展与烃源岩的形成

生物的生产量以及被保存的沉积有机质是烃源岩形成的重要条件。多细胞生物出现并广泛地生活于扬子地区伊迪卡拉纪陡山沱期晚期的浅海中,生物之间相互依赖和共存的多层次化和复杂化生态系统的建立,使陡山沱期成为扬子地区生命演化和发展重要时期。陡山沱期的黑色泥(页)岩在沉积时为富含水份的粥性沉积物,同时当时海洋中的氧化-还原界面较浅,生物遗体可迅速地被沉积物所覆盖而形成烃源岩。伊迪卡拉纪陡山沱期是化学、气候和环境变化的剧烈时期,也是扬子地区生命演化、有机质生产力发展和烃源岩形成的一个重要时期。     

Darwin’s deep well at Down House,England (UK)

Hydrogeology Journal - When Charles Darwin moved to Down House, England (UK), in 1842, he inherited a deep well, penetrating 325&nbsp;ft (~100&nbsp;m) into the Chalk. The groundwater from...     

塔里木盆地石炭系烃源岩成熟演化研究

尽管塔里木盆地石炭系富含有机质且已发现其生成的原油,但关于石炭系烃源岩热演化研究却很薄弱。根据基础地质资料、古地温梯度和实测镜质体反射率数据,本文定量模拟了塔里木盆地6口典型井的石炭系烃源岩热演化史和这套烃源岩底界、顶界在二叠纪末期、三叠纪末期、白垩纪末期及现今成熟度的平面分布规律。塔北隆起南部、塔西南坳陷和阿瓦提凹陷在石炭-二叠纪作为沉降中心接受了巨厚的沉积物,造成这些地区石炭系烃源岩底界成熟度在二叠纪末期达到0.9%～1.3%（中-高成熟）,顶界为0.5%～0.9%（低-中成熟）,成为有利生油区。中生代时期,塔里木盆地中、东部长期处于沉降状态,石炭系烃源岩处于成熟演化阶段。白垩纪末期,塔中低凸起和满加尔凹陷的石炭系底界成熟度为0.7%～0.9%（中成熟）,顶界为0.5%～0.7%（低成熟）,而塘古孜巴斯坳陷底界成熟度为0.9%～1.1%（中-高成熟）,顶界为0.7%～0.9%（中成熟）。受羌塘地体、拉萨地体、印度板块分别与欧亚板块南缘碰撞远程效应的影响,塔西南坳陷和巴楚隆起在中生代一直处于隆升剥蚀状态,烃源岩热演化进入停滞状态。新生代以来,塔西南坳陷和阿瓦提凹陷演化为前陆盆地,再次接受了巨厚沉积物,致使石炭系烃源岩快速成熟演化,底-顶界成熟度现今已超过2.0%,进入干气阶段。满加尔凹陷石炭系烃源岩自石炭纪至今一直处于成熟演化阶段,现今达到最大,为0.8%～1.0%。另外,热史研究表明塔西南坳陷和阿瓦提凹陷石炭系烃源岩具有二次生烃潜力。本研究不仅丰富了塔里木盆地石炭系烃源岩热史研究成果,而且对油气勘探与开发具有重要的指导意义。     

Deformation of granitic rocks across the brittle-ductile transition

A microstructural analysis has been carried out on mylonites and mylonitic gneisses of the Eastern Peninsular Ranges Mylonite Zone, which were formed over a range of metamorphic conditions from lower greenschist to amphibolite facies. Composite planar fabrics in the form of C and S planes are found at all metamorphic grades. Fractured feldspars, kinked biotites and ductile deformation of quartz characterize the lower greenschist facies mylonites. At mid-upper greenschist grade orthoclase grains show dynamic recrystallization textures whereas plagioclase exhibits low temperature plasticity with only minor recovery. Biotite ribbons form by progressive rotation and coalescence of kink band segments to produce chevron fold patterns. At epidote-amphibolite grade and above, recovery processes and annealing recrystallization predominate in all minerals. Residual orthoclase porphyroclasts show strain-related myrmekite formation along those sides of the grains that face the instantaneous shortening direction. Myrmekite formation due to replacement reactions cannot explain this geometry. It is proposed that the myrmekites formed due to a combination of exsolution, replacement and strain-enhanced diffusion.     

Organic geochemistry of Miocene source rocks from the Banat Depression (SE Pannonian Basin, Serbia)

The origin, depositional environment and maturity of petroleum source rocks were determined via conventional whole rock and biomarker analysis of samples from wells in the Banat Depression, where the most important Serbian oil and gas fields are located. The organic matter (OM) in organic-rich upper Tertiary siltstones and marls consists predominantly of Type II kerogen. Numerous biomarker parameters indicated mixed algal-terrestrial OM, related to a brackish or freshwater environment, whose salinity decreased from Middle to Upper Miocene. The OM was deposited under variable redox conditions, reducing to sub-oxic.The wells in the Banat Depression experienced variable high rates of rapid heating, providing an opportunity for examining the applicability of different thermal indicators in a hyperthermal basin. Rock-Eval and numerous biomarker parameters indicate that the main stage of oil generation begins at ca.130 °C and vitrinite reflectance (Rc) ca. 0.63% and reaches a maximum at ca.145-150 °C and Rc ca. 0.72-0.75%, while the late stage of oil generation starts at ca.155 °C and ca. Rc 0.78%, which corresponds, depending on geothermal gradient, to relative depths of 2100-2300 m, 2600-2900 m and 3050-3100 m, respectively. The naphthalene and phenanthrene maturity parameters proved to be less applicable than the biomarker ratios, particularly in the early to moderate maturation range. The newly proposed parameter C(14a)-homo-26-nor-17α(H)-hopane/C₃₀hopane (C₃₀HH/C₃₀H) proved applicable to a wide range of maturity.