Image analysis and estimation of porosity and permeability of Arnager Greensand,Upper Cretaceous,Denmark

Arnager Greensand consists of unconsolidated, poorly sorted fine-grained, glauconitic quartz sand, often silty or clayey, with a few horizons of cemented coarse-grained sand. Samples from the upper part of the Arnager Greensand were used for this study to estimate permeability from microscopic images. Backscattered Scanning Electron Microscope images from polished thin-sections were acquired for image analysis with the software PIPPIN®. Differences in grey levels owing to density differences allowed us to estimate porosity, clay and particle content. The images were simplified into two phases, pores and particles, and the specific surface of the solid phase was calculated. We used the Kozeny Equation to calculate the permeability. The petrophysical properties, porosity and permeability obtained from image analysis were compared to results using laboratory methods. The 150x magnification of the image can not resolve the microporosity within the clay fraction, so we suggest that the imaged porosity at 150x magnification is close to the effective porosity for permeability assessment. The Heporosity, however, represents the total porosity of the Arnager Greensand. For permeability estimation, a local permeability was calculated for each image. For calculation of the plug scale permeability, we compare three different averaging methods: arithmetic, harmonic, and geometric mean. In every case the calculated permeability overestimates the measured permeability. Only the lowest calculated local permeabilities corresponds to the measured permeabilities, suggesting that the overall permeability for these samples is governed by the least permeable parts.     

The stratigraphy of the Gault and Upper Greensand Formations (Albian stage,Cretaceous) of the Dorset and East Devon Coast World Heritage Site,U.K.

The Upper Greensand Formation, in part mainly underlain by the Gault Formation and overlain by the Chalk Group, has extensive cliff outcrops in the Dorset and East Devon Coast World Heritage Site (WHS). The argillaceous Gault, up to 20 m thick in the Isle of Purbeck, is poorly exposed due to its involvement in extensive landslides, but the exposures of Upper Greensand are the most complete in England. The Gault (Middle Albian) rests unconformably on progressively older Jurassic and Triassic strata when traced westwards and becomes more arenaceous in the same direction. On the east Devon coast, the Upper Greensand comprises up to 55 m of sandstones and calcarenites that were deposited in fully marine, shallow-water environments. The formation is divided into three members there (Foxmould, Whitecliff Chert and Bindon Sandstone) each bounded by a prominent erosion surface. The full thickness of the Upper Greensand, up to 60 m, was formerly exposed in cliffs in the Isle of Purbeck in and adjacent to the steeply dipping limb of the Purbeck Monocline. The lower (Foxmould) part of the succession is similar to that in east Devon, but the upper part (White Nothe Member) is lithologically different and probably the correlative of only the Bindon Sandstone. Much of the fauna of the Gault and Upper Greensand of the WHS is not age-diagnostic with the result that the ages of parts of the succession are still poorly known. However, diverse ammonite assemblages recorded from a few thin beds in the lower and highest parts of the succession show that all except one of the Albian ammonite zones is present.     

The stratigraphical distribution of mid-Cretaceous Foraminifera near Ventnor, Isle of Wight

Ventnor No. 2 Borehole, located near Ventnor, Isle of Wight, penetrated the basal part of the Chalk Group and the Selborne Group before terminating in the upper part of the Lower Greensand Group (Sandrock Formation). The borehole was examined for Foraminifera, and although they were not seen in the Sandrock Formation and Monks Bay Sandstone Formation, the remainder of the borehole yielded moderately low diversity assemblages dominated by agglutinated species. Foraminiferal zones 3-6 (H dentatus to M. fallax/M. rostratum macrofaunal zones) were identified in the Gault Formation and zones 6 (lower) to 6a (M. fallax/M. rostratum to A. briacensis macrofaunal zones) were identified in the Upper Greensand Formation. Assemblages from the overlying West Melbury Marly Chalk Formation were used to identify foraminiferal zones BGS1-BGS3 (M. mantelli and M. dixoni macrofaunal zones).     

Sedimentary structures in the Lower Greensand of the Weald,England, and Bas-Boulonnais,France

Study of the cross-stratification and other sedimentary structures in the Lower Greensand of the Weald, England, and Bas-Boulonnais, France, indicates that the sediments were deposited by the lateral migration of sand waves in a neritic sea. Comparison of the Lower Greensand sea with the modern North Sea was attempted. If those sediments were deposited as a result of tidal current similar to the present-day North Sea then the Lower Greensand shoreline could be deduced as running northwest-southeast, indication that the western part of the London Platform was submerged.     

Teredolites Leymerie in the Lower Greensand Group (Cretaceous) of the Isle of Wight and the problematic ichnology of reworked clasts

Nineteenth-century references to clavate borings in woody substrates in the Lower Greensand of the Isle of Wight used a variety of names, but Teredo (a wood-boring bivalve, not a boring), Teredolithes (a junior synonym of Teredolites) and Gastrochaena (a bivalve borer of rock and shelly substrates, not a boring in wood) are all nomenclatorially incorrect. Borings in a beach clast derived from the Lower Greensand Group and recently collected from Sandown Bay, Isle of Wight, are referred to Teredolites isp. cf. T. longissimus Kelly and Bromley. This specimen confirms the presence of Teredolites in the Lower Greensand Group and demonstrates a common ichnological problem of beach clasts; borings, either fossil or modern, are incompletely preserved, making confident classification below the level of ichnogenus problematic.     

New evidence of the Cretaceous overstep of the Mendip Hills,Somerset, UK

The Mendip Hills, located on the north-western margin of the Wessex Basin, clearly show the onlap of Upper Triassic to Middle Jurassic sediments onto folded Palaeozoic strata. Recent field mapping on the crest of the Beacon Hill pericline at Tadhill, near Frome, augmented by a suite of shallow boreholes, proved up to 6.2 m of glauconitic grey and green silty sand. These glauconitic sands rest unconformably on Silurian volcanic rocks and Devonian sandstone. Lithological and ipalaeontological analyses of these glauconitic sands indicate that they are part of the Lower Cretaceous Upper Greensand Formation. This provides the first evidence for the Albian transgression across the Mendip Hills. The implications for the Cretaceous overstep on the margins of the Wessex Basin, and the analogies with the Upper Greensand succession in Devon are discussed.     

The palynology and geology of the Lower Cretaceous (Aptian–Albian) of Munday’s Hill Quarry,Bedfordshire, UK

Early Cretaceous sediments of Aptian–Albian age outcrop at Munday’s Hill Quarry, Bedfordshire, England. Previous papers describing the section have resulted in different terminologies being applied. The Lower Cretaceous in Bedfordshire is represented by sediments belonging to the Lower Greensand Group and the Gault Clay Formation. Within the Lower Greensand Group in the study area the Woburn Sands Formation, are of Aptian–Albian age. Selected samples have been analysed for palynology. The analysis reveals diverse palynomorph assemblages, including well-preserved dinoflagellate cysts and sporomorphs. Comparison of the assemblages with published records indicates that the lower samples are of Late Aptian age. Forms recorded include common Kiokansium unituberculatum, Cerbia tabulata, Aptea polymorpha and Cyclonephelium inconspicuum. An Early Albian age is indicated for the uppermost sample.     

Stratigraphy and micropalaeontology of the upper cretaceous of Western Australia

The distribution, relationships, and stratigraphical significance of the microfaunas (mainly foraminifera) in the Upper Cretaceous deposits of Western Australia are discussed, and palaeogeography and palaeoecology considered.Formations deposited during the Cenomanian-Turonian are the Gearle Siltstone and Alinga Greensand and perhaps the Molecap Greensand. Among the foraminifera recorded are the stratigraphically restricted planktonic formsGlobotruncana (Praeglobotruncana)stephani subspp. andG. helvetica.The Gingin Chalk and the lower part of the Toolonga Calcilutite were deposited during the Santonian. These formations contain the crinoid generaMarsupites andUintacrinus, several species ofGlobotruncana andNeoflabellina, andBolivinoides strigillata. Santonian beds are known in sub-surface sections as far north as the area of the Warroora Anticline.The Toolonga Calcilutite extends up into the lower Campanian, andGlobotruncana arca appears in the fauna. The occurrence of Campanian beds in the Perth Basin cannot be proved; most of the Poison Hill Greensand may be of this age. On foraminiferal evidence, deposition of the Korojon Calcarenite began during the Campanian. Important species identified areGlobotruncana arca,Cibicides voltziana andBolivina incrassata.The upper beds of the Korojon Calcarenite and the Miria Marl are of Maestrichtian age. The Miria Marl contains the speciesGlobotruncana stuarti,G. citae andG. contusa. The upper beds of the Poison Hill Greensand may range into the Maestrichtian.Published by permission of the Director, Bureau of Mineral Resources, Geology and Geophysics, Canberra, Australia.     

Erratum to “The Albian-Cenomanian boundary at Eggardon Hill, Dorset (England): An anomaly resolved?” [Proc. Geol. Assoc. 120 (2009) 108-120]

Re-examination of the classic exposures of the Eggardon Grit (topmost Upper Greensand Formation) at Eggardon Hill, Dorset shows that the upper part of this unit has a more complex stratigraphy than has been previously recognised. The Eggardon Grit Member, as described herein, is capped by a hardground and associated conglomerate, and is entirely of Late Albian age. The hardground is probably the lateral equivalent of the Small Cove Hardground, which marks the top of the Upper Greensand succession in southeast Devon. The conglomerate is overlain by a thin sandy limestone containing Early Cenomanian ammonites. This limestone is almost certainly the horizon of the Early Cenomanian ammonite fauna that has previously been attributed to the top of the Eggardon Grit. The limestone is regarded as a thin lateral equivalent of the Beer Head Limestone Formation (formerly Cenomanian Limestone) exposed on the southeast Devon coast. The fauna of the limestone at Eggardon suggests that it is probably the age equivalent to the two lowest subdivisions of the Beer Head Limestone in southeast Devon, with a remanié fauna of the Pounds Pool Sandy Limestone Member combined with indigenous macrofossils of the Hooken Nodular Limestone Member. The next highest subdivision of the Beer Head Limestone in southeast Devon (Little Beach Bioclastic Limestone Member), equates with the ammonite-rich phosphatic conglomerate of the ‘Chalk Basement Bed’, which caps the Beer Head Limestone at Eggardon, and which was previously regarded as the base of the Chalk Group on Eggardon Hill.Petrographic analysis of the Eggardon Grit shows that lithologically it should more correctly be described as a sandy limestone rather than sandstone. The original stratigraphical definition of the unit should probably be modified to exclude the softer, nodular calcareous sandstones that have traditionally been included in the lower part of the member.Without the apparently clear evidence of unbroken sedimentation across the Albian-Cenomanian boundary, suggested by the previous interpretation of the Eggardon succession, it is harder to argue for this being a prevalent feature of Upper Greensand stratigraphy in southwest England. Correlation of the Eggardon succession with successions in Dorset and southeast Devon reveals a widespread regional break in sedimentation at the Albian-Cenomanian boundary. The sand-rich facies above this unconformity represent the true base of the Chalk Group, rather than the ‘Chalk Basement Bed’ of previous interpretations.Selected elements of regionally important Upper Greensand ammonite faunas previously reported from Shapwick Quarry, near Lyme Regis, and Babcombe Copse, near Newton Abbot, are newly figured herein.     

Anatomy of the stratigraphical boundary between the Arnager Greensand and Arnager Limestone (Upper Cretaceous) on Bornholm,Denmark

The complex boundary between the Arnager Greensand Formation and the Arnager Limestone Formation on the island of Bornholm (Denmark) has been studied for almost a century. Despite this effort, the hiatus represented by the boundary remains poorly constrained. Using a considerable number of processed samples and thin sections the uppermost Arnager Greensand Formation is confirmed as Thalmanninella reicheli Zone age (early Middle Cenomanian) and the overlying Arnager Limestone Formation is probably early Coniacian in age. No evidence of macrofossil and microfossil assemblages indicative of the late Cenomanian or the Turonian have been recorded and there is no palaeontological or sedimentological evidence of the global late Cenomanian (Bonarelli or OAE 2) anoxic event. The significant mid-Cenomanian to early Coniacian hiatus reflects a period of sediment starvation along the line of the Sorgenfrei-Tornquist Zone in the vicinity of Bornholm.     

The Albian–Cenomanian boundary at Eggardon Hill,Dorset (England): an anomaly resolved?

Re-examination of the classic exposures of the Eggardon Grit (topmost Upper Greensand Formation) at Eggardon Hill, Dorset shows that the upper part of this unit has a more complex stratigraphy than has been previously recognised. The Eggardon Grit Member, as described herein, is capped by a hardground and associated conglomerate, and is entirely of Late Albian age. The hardground is probably the lateral equivalent of the Small Cove Hardground, which marks the top of the Upper Greensand succession in southeast Devon. The conglomerate is overlain by a thin sandy limestone containing Early Cenomanian ammonites. This limestone is almost certainly the horizon of the Early Cenomanian ammonite fauna that has previously been attributed to the top of the Eggardon Grit. The limestone is regarded as a thin lateral equivalent of the Beer Head Limestone Formation (formerly Cenomanian Limestone) exposed on the southeast Devon coast. The fauna of the limestone at Eggardon suggests that it is probably the age equivalent to the two lowest subdivisions of the Beer Head Limestone in southeast Devon, with a remanié fauna of the Pounds Pool Sandy Limestone Member combined with indigenous macrofossils of the Hooken Nodular Limestone Member. The next highest subdivision of the Beer Head Limestone in southeast Devon (Little Beach Bioclastic Limestone Member), equates with the ammonite-rich phosphatic conglomerate of the ‘Chalk Basement Bed’, which caps the Beer Head Limestone at Eggardon, and which was previously regarded as the base of the Chalk Group on Eggardon Hill.Petrographic analysis of the Eggardon Grit shows that lithologically it should more correctly be described as a sandy limestone rather than sandstone. The original stratigraphical definition of the unit should probably be modified to exclude the softer, nodular calcareous sandstones that have traditionally been included in the lower part of the member.Without the apparently clear evidence of unbroken sedimentation across the Albian–Cenomanian boundary, suggested by the previous interpretation of the Eggardon succession, it is harder to argue for this being a prevalent feature of Upper Greensand stratigraphy in southwest England. Correlation of the Eggardon succession with successions in Dorset and southeast Devon reveals a widespread regional break in sedimentation at the Albian–Cenomanian boundary. The sand-rich facies above this unconformity represent the true base of the Chalk Group, rather than the ‘Chalk Basement Bed’ of previous interpretations.Selected elements of regionally important Upper Greensand ammonite faunas previously reported from Shapwick Quarry, near Lyme Regis, and Babcombe Copse, near Newton Abbot, are newly figured herein.     

Chertification histories of some Late Mesozoic and Middle Palaeozoic platform carbonates

A consistent pattern for the silica sources, depositional environments and timing of chertification was observed in a diverse suite of five Late Mesozoic and Middle Palaeozoic carbonate sequences; the (1) Upper Greensand (Cretaceous) and (2) Portland Limestone (Jurassic) of southern England, (3) the Ramp Creek Formation (Mississippian) of southern Indiana, and the (4) lower Helderberg Group (Devonian) and (5) Onondaga Limestone (Devonian) of New York State. Nodular chert formation in all five limestone sequences occurred in sediments that were largely uncemented. Ghosts of pre-chertification carbonate cements are present in some chert nodules but are volumetrically minor. In every limestone sequence except the Upper Greensand, chertification occurred after burial to a depth sufficient for intergranular pressure solution and mechanical grain deformation of carbonate sand. Nodular chert is most abundant in subtidal, normal marine wackestones and mudstones that were deposited at or below fair-weather wave base, and is absent or rare in supratidal, intertidal and high-energy subtidal limestones and dolomites. An intraformational sponge spicule silica source for chert nodules is suggested by direct evidence, such as calcitized sponge spicules in the host limestone, and circumstantial evidence, such as ghosts of sponge spicules in chert nodules and a correlation of chert abundance with depositional environment. Most molds of siliceous sponge spicules were apparently obliterated by post-chertification intergranular compaction. We propose that these general trends for the depositional environments, silica sources and timing of chertification are representative of most Mesozoic to Middle Palaeozoic platform limestones.     

Edentulous pterosaurs from the Cambridge Greensand (Cretaceous) of eastern England with a review of Ornithostoma Seeley, 1871

A re-examination of fossil material from the Late Cretaceous Cambridge Greensand Member (CGM) of the West Melbury Marly Chalk Formation revealed a number of new specimens of edentulous pterosaur jaw fragments previously identified as shark fin spines and fish jaws and accessioned under the epithet ‘cestraciontid finray’ and ‘jaws of fish’. These are now recognised as pterosaurian jaw tips and referred to Ornithostoma sedgwicki Seeley, 1891 and Azhdarchoidea indet. This material increases the diversity of edentulous pterosaurs from the CGM.The edentulous pterosaur Ornithostoma sedgwicki Seeley, 1891 from the Cretaceous Cambridge Greensand of eastern England is reviewed. The holotype specimen is confirmed as a fragment of a premaxilla/maxilla of a non-tapejarid azhdarchoid on account of the conspicuous curvature of the dorsal and occlusal margins posteriorly and the presence of small neural foramina on the lateral margins. Neural foramina are not seen on jaws of members of the Pteranodontia, a group to which O. sedgwicki was included previously. The referral of O. sedgwicki to Azhdarchoidea eliminates the single known Lower Cretaceous occurrence of Pteranodontidae, restricting the temporal range of this taxon to the Upper Cretaceous. Postcranial material referred to O. sedgwicki from the type horizon is regarded as indeterminate Pterosauria.     

A new look at the Lower Greensand using ground–penetrating radar

The Wobum Sands Formation is Aptian to Albian in age and forms part of the lower Greensand Group, which crops out in the Weald Basin, East Anglia and the Isle of Wight. The sands are thought to have accumulated in a narrow tidal seaway connecting the Boreal Sea to the Tethys Ocean and early North Atlantic Ocean. Here I present new information on the geometry and internal character of large sedimentary structures exposed in sand pits near Leighton Buzzard, which have been imaged using ground–penetrating radar.     

The geochemistry of boron and its isotopes in groundwaters from marine and non-marine sandstone aquifers

The geological evolution of B in two UK sandstone aquifers is followed from precipitation chemistry through to groundwaters in both the unconfined and confined zones. Measurements have been made of major element geochemistry, B concentrations and B isotopic ratios. The isotopic measurements were carried out using ICP/MS following a simple preconcentration step. Isotopic measurements of rainfall show a bimodal distribution and it is suggested that enriched signatures are characteristic of Atlantic air over Britain and depleted signatures representative of continental air. In the marine Lower Greensand aquifer dissolution of glauconite results in the mobilisation of B and a correlation with SO₄ suggests that this dissolution is related to the oxidation of pyrite which appears to be the SO₄-forming reaction in the aquifer. In the non-marine Hastings beds isotopic ratios and a correlation with HCO₃ suggest that B is associated with the dissolution of ferroan carbonates. In both aquifers the geochemical evolution of B is complex and more information is needed on the behaviour of B isotopes during evapotranspiration and groundwater recharge.     

庐山第四纪地质一瞥

内容提要本文简要介绍庐山地区一次短暂的考察中所观察到的有关这一地区第四纪地质和冰川作用的一些现象。其目的不在试图以此解决庐山的古冰川问题,而只是想提出一点多少与前人不同的想法。     

Characterization of building materials from the aqueduct of Antioch-on-the-Orontes (Turkey)

The Roman aqueduct of Antioch-on-the-Orontes (Turkey), a city located near the junction between the active Dead Sea fault and the East Anatolian fault, has been damaged several times due to historical earthquakes, as mentioned in ancient texts. The traces of repairs are studied in order to identify their potential seismic origin. The deformations of the structure were characterised thanks to a LIDAR scan. Several bricks were sampled on different parts of the city's aqueducts, on the original structure and on repaired parts. The bricks were characterized through a petrological approach. ¹⁴C and archaeomagnetism were tested on the bricks in order to constrain the age of their production. The synthesis of all the data showed a local origin for the bricks, and led to the identification of several manufacturing techniques and several types of production, thus, confirming the potentiality of this approach to date and characterise post-seismic repairs.     

卤(盐)井维修施工技术探讨

卤（盐）井是岩盐矿山水采方式的主要手段,建井成本高,且每眼井对应一定范围的可采地下资源,对问题卤井的修复具有较广泛意义。根据本矿区卤井维修工程实例,介绍卤井维修施工中一些关键工艺和施工经验。     

Distinctive azhdarchoid pterosaur jaws from the mid-Cretaceous Cambridge Greensand of eastern England and the Kem Kem Group of Morocco

An isolated jaw fragment from the Late Cretaceous (Cenomanian) Cambridge Greensand Member of the West Melbury Marly Chalk Formation previously identified as a cestraciontid shark fin spine is referred to the pterosaur clade Azhdarchoidea on account of its lateral and occlusal foramina and edentuly. The specimen differs from the azhdarchoid Ornithostoma sedgwicki from the same deposit in having flat lateral surfaces and an acute dorsal/ventral apex. The specimen is similar in overall morphology to CAMSM B40085 from the same horizon and probably represents the corresponding jaw but from a different individual. Likely these specimens represent a new taxon but are considered too fragmentary to diagnose at present. A remarkably similar and distinctive morphology is found in unnamed pterosaur jaws from the Kem Kem Group (?Albian-Cenomanian) of Morocco, supporting the idea of faunal similarity between these two distant localities.