scholarly journals Stratigraphy and geochemical composition of the Cambrian Alum Shale Formation in the Porsgrunn core, Skien–Langesund district, southern Norway.

2018 ◽  
Vol 66 ◽  
pp. 1-20
Author(s):  
Niels Hemmingsen Schovsbo ◽  
Arne Thorshøj Nielsen ◽  
Andreas Olaus Harstad ◽  
David L. Bruton
Keyword(s):  
Gamma Ray ◽  
Geochemical Composition ◽  
Middle Cambrian ◽  
Alum Shale ◽  
Carbon Isotope Excursion ◽  
Lower Ordovician ◽  
Shale Formation ◽  
Sedimentary Succession ◽  
Southern Norway ◽  
Spice Event

The fully cored BHD-03-99 borehole (hereafter referred to as the Porsgrunn borehole and core) penetrated Ordovician and Cambrian strata in the Skien–Langesund district, southern part of the Oslo region in Norway. Hand-held X-ray fluorescence (HH-XRF) measurements combined with spectral gamma ray and density core scanning of the Middle Cambrian – Furongian Alum Shale Formation have been made and compared with similar measurements obtained on Alum Shale cores from Scania (southernmost Sweden) and Bornholm (Denmark). The Porsgrunn drill site is located in an area that was only mildly overprinted by Caledonian tectonics and represents one of the few sites in the Oslo area where a nearly untectonised sedimentary succession can be studied in terms of thickness and geochemistry. The Alum Shale Formation is 28.8 m thick in the Porsgrunn core, excluding the thickness of five 0.9–5.5 m thick dolerite sills of assumed Permian age. In the Alum Shale Formation the bulk densities are around 2.7 g/cm3 with a slightly decreasing trend up through the formation. The shale has total organic carbon (TOC) values up to 14 wt%, which is comparable to the TOC levels for the Alum Shale elsewhere in the Oslo area and for dry gas matured Alum Shale in Scania and Bornholm. The basal Furongian is characterised by a gamma ray low and an increase in Mo interpreted to reflect the Steptoean Positive Carbon Isotope Excursion (SPICE) event. The Porsgrunn core data suggest that the Mo concentration remained high also after the SPICE event. Characteristic, readily identified features in the gamma log motif are named the Andrarum gamma low (AGL), base Furongian gamma low (BFGL), Olenus triple gamma spike (OTGS) and the Peltura gamma spike (PGS). No Lower Ordovician Alum Shale is present. The 14.8 m thick Furongian part of the Alum Shale represents the Olenus, Parabolina, Leptoplastus, Protopeltura and Peltura trilobite superzones judging from log-stratigraphic correlations to Scania and Bornholm. The Middle Cambrian interval is 14.0 m thick and includes the Exsulans Limestone Bed and 1.4 m of quartz sandstone. A 0.3 m thick primary limestone bed may be an equivalent to the Andrarum Limestone Bed. The succession represents the Paradoxides paradoxissimus and P. forchhammeri superzones. The Alum Shale Formation rests atop the 13.0 m thick Lower Cambrian Stokkevannet sandstone (new informal name) that in turn directly overlies the basement. Overall, the stratigraphic development of the comparatively thin Alum Shale Formation resembles the condensed sequence seen on Bornholm.

scholarly journals Gamma-ray log correlation and stratigraphic architecture of the Cambro-Ordovician Alum Shale Formation on Bornholm, Denmark: Evidence for differential syndepositional isostasy

2018 ◽  
Vol 66 ◽  
pp. 237-273 ◽  
Author(s):  
Arne Thorshøj Nielsen ◽  
Niels Hemmingsen Schovsbo ◽  
Kurt Klitten ◽  
David Woollhead ◽  
Christian Mac Ørum Rasmussen
Keyword(s):  
Gamma Ray ◽  
Uranium Content ◽  
Middle Ordovician ◽  
Alum Shale ◽  
Stratigraphic Architecture ◽  
Lower Ordovician ◽  
Stress Changes ◽  
Shale Formation ◽  
Thickness Variations ◽  
The Individual

The Cambro–Ordovician Alum Shale Formation on Bornholm, Denmark, is in total 26.7 to ≥ 34.9 m thick in nine boreholes, but may be up to ~39 m thick. The well sections are correlated using gamma-ray logs supplemented in some boreholes with resistivity and sonic logs. The gamma radiation of the ‘hot’ Alum Shale Formation primarily reflects the uranium content, which is moderately high in the Miaolingian (≈ middle Cambrian) and Tremadocian (Lower Ordovician), and very high in the Furongian (≈ upper Cambrian). The log pattern is calibrated with the detailed biozonation established in the Gislövshammar-1 and -2 wells in south-eastern Skåne, Sweden. Except for the Eccaparadoxides oelandicus Superzone, all superzones known from the Alum Shale in Scandinavia are also developed on Bornholm, but not all zones. On Bornholm, the Miaolingian interval is 7.2–11.9 m thick, the Furongian is 16.4–22.8 m thick and the Tremadocian is 2.5–4.0 m thick. The Miaolingian strata exhibit no systematic thickness variations across southern Bornholm, whereas the Furongian Parabolina, Peltura and Acerocarina Superzones and, less pronounced, the Tremadocian, show increased condensation towards the south-east. In comparison with Skåne, the Alum Shale Formation is overall strongly condensed on Bornholm, but different stratigraphic levels show variable developments. The Miaolingian Paradoxides paradoxissimus Superzone is thus extremely condensed and incomplete, whereas the Paradoxides forchhammeri Superzone has almost the same thickness as in Skåne, and locally is even thicker. The Furongian Olenus and Parabolina Superzones are slightly thinner than in Skåne while the Protopeltura, Peltura and Acerocarina Superzones are half as thick or less. The Tremadocian is also much thinner on Bornholm. The Furongian Olenus scanicus–O. rotundatus and Parabolina brevispina Zones seem to be developed on Bornholm, and a thin ‘Leptoplastus neglectus’ Zone is also possibly present. The ‘Parabolina megalops’ Zone in the upper part of the Peltura Superzone appears to be absent. It is impossible to distinguish the individual thin zones in the lower part of the Acerocarina Superzone using wireline logs. A thin veneer of the Lower Ordovician Tøyen Formation, hitherto considered absent on Bornholm, is described from the Billegrav-2 core. It may also be present in the uncored Sømarken-3 and -4 wells. The Middle Ordovician Komstad Limestone Formation thins from c. 4.0–4.7 m in the Læså area to 0.1– c. 2.5 m in the Øleå area. The general decrease in thickness of Cambro–Ordovician strata from Skåne to Bornholm and also within Bornholm from the Læså to the Øleå area is inferred to reflect isostatic uplift of the southern margin of Baltica commencing with the terminal 'early' Cambrian Hawke Bay Event and lasting until the Late Ordovician. In detail, several uplift and subsidence phases can be discerned. The isostatic adjustments are surmised to reflect stress changes related to ongoing plate tectonic processes in the adjacent closing Tornquist Sea.

Skeletal carbonate productivity and phosphogenesis at the lower–middle Cambrian transition of Scania, southern Sweden

2009 ◽  
Vol 147 (1) ◽  
pp. 59-76 ◽  
Author(s):  
J. JAVIER ÁLVARO ◽  
PER AHLBERG ◽  
NIKLAS AXHEIMER
Keyword(s):  
Primary Productivity ◽  
Microbial Mats ◽  
High Energy ◽  
Nutrient Supply ◽  
Energy Conditions ◽  
Southern Sweden ◽  
Middle Cambrian ◽  
Alum Shale ◽  
Shale Formation ◽  
Reducing Environment

AbstractThe lower–middle Cambrian transitional interval of Scania is largely represented by condensed limestone beds, lithostratigraphically grouped in the Gislöv Formation (1–5.7 m thick), and the Forsemölla and Exsulans Limestone beds (lower part of the Alum Shale Formation, up to 4 m thick). The strata display a combination of skeletal carbonate productivity, episodic nucleation of phosphate hardground nodules, and polyphase reworking recorded on a platform bordering the NW corner of Baltica. The shell accumulations can be subdivided into three deepening-upward parasequences, separated by distinct erosive unconformities. The parasequences correspond biostratigraphically to the Holmia kjerulfi, Ornamentaspis? linnarssoni and Ptychagnostus gibbus zones, the latter two generally being separated by a stratigraphic gap that includes the middle Cambrian Acadoparadoxides oelandicus Superzone. Except for the Exsulans Limestone, the carbonates reflect development of a prolific epibenthic biota, dominated by filter-feeding nonreefal chancelloriid–echinoderm–sponge meadows, rich in trilobites and brachiopods, and which were subjected to high-energy conditions. The absence of microbial mats or veneers encrusting the erosive surfaces of these event-concentration low-relief shoal complexes may be related to long hiatal episodes resulting in microboring proliferation. High levels of nutrient supply resulted in high primary productivity, eutrophic conditions, glauconite precipitation, phosphogenesis (in some case microbially mediated) and microendolithic infestation. An early-diagenetic mildly reducing environment is suggested by the presence of authigenic (subsequently reworked) pyrite, which contrasts with the syndepositional normal oxygenated conditions reflected by macroburrowing and the abundance of benthic fossils.

scholarly journals Anopolenus henrici Salter, a middle Cambrian (Drumian) centropleurid trilobite from the Alum Shale Formation of Scandinavia

2018 ◽  
Vol 66 ◽  
pp. 223-228
Author(s):  
Thomas Weidner ◽  
Jan Ove R. Ebbestad
Keyword(s):  
Middle Cambrian ◽  
Alum Shale ◽  
Shale Formation

Centropleurid trilobites include five genera of which Centropleura Angelin, Anopolenus Salter, Clarella Howell and Luhops Šnajdr are known from eight species in the traditional middle Cambrian (Miaolingian Series, Drumian Stage) of Sweden and Denmark (Bornholm). Beishanella Xiang & Zhang has not been recorded in Scandinavia so far, and no centropleurids have been reported from Norway. Of these taxa, only Centropleura is common in Scandinavia. Two pygidia previously identified as Centropleura sp. and Anopolenus sp. from erratics in Germany and Bornholm, respectively, as well as a new pygidum from Scania in Sweden are here identified as Anopolenus henrici Salter. Elsewhere, the species is known from Wales, Avalonian Canada, Siberia, Alaska, and Sardinia, occurring in the A. atavus and P. punctuosus zones (the former in Siberia only). The presence of this species increases the known diversity of Centropleuridae in Scandinavia and is important for correlation between Baltica and Avalonia.

scholarly journals Agraulos longicephalus and Proampyx? depressus (Trilobita) from the Middle Cambrian of Bornholm, Denmark

2015 ◽  
Vol 63 ◽  
pp. 1-11
Author(s):  
Thomas Weidner ◽  
Arne Thorshøj Nielsen
Keyword(s):  
Middle Cambrian ◽  
Alum Shale ◽  
Shale Formation

The trilobite genus Agraulos Hawle & Corda 1847 has within Scandinavia been recorded only from Bornholm, Denmark, where its representatives occur in the Middle Cambrian Paradoxides paradoxissimus Superzone of the Alum Shale Formation. Only cranidia have been found so far, representing Agraulos longicephalus (Hicks 1872) and the rare “Agraulos” depressus Grönwall 1902.

scholarly journals Revision of the mollisoniid chelicerate(?) Thelxiope, with a new species from the middle Cambrian Wheeler Formation of Utah

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e8879
Author(s):  
Rudy Lerosey-Aubril ◽  
Jacob Skabelund ◽  
Javier Ortega-Hernández
Keyword(s):  
Type Species ◽  
Taxonomic Diversity ◽  
New Taxon ◽  
Single Specimen ◽  
Common Component ◽  
Middle Cambrian ◽  
Lower Ordovician ◽  
Distinct Genus ◽  
Shale Formation ◽  
Lower Palaeozoic

The recent re-interpretation of the Lower Palaeozoic euarthropod group Mollisonia as belonging to Chelicerata has triggered a renewed interest for the poorly known family Mollisoniidae. In this contribution, we revise the anatomy, taxonomic diversity, and systematics of Thelxiope, the sister-taxon of Mollisonia. This mollisoniid genus comprises four species, and is characterized by the presence of one cephalic, seven thoracic (one per tergite), and three pygidial long sagittal spines. The type species, T. palaeothalassia Simonetta & Delle Cave, is a rare taxon in the Wuliuan Burgess Shale Formation of Canada, which can be recognized by the hypertrophy of a single of its sagittal spines, the posteriomost one. T. spinosa (Conway Morris & Robison)–a species originally assigned to a distinct genus ‘Ecnomocaris’ herein synonymised with Thelxiope–is known from a single specimen found in the Drumian Wheeler Formation of the House Range of Utah. It differs from the type-species in the hypertrophy of both the anteriormost (cephalic) and the posteriormost (third pygidial) sagittal spines. The same Wheeler strata have also yielded a single specimen of a new taxon, T. holmani sp. nov., which lacks hypertrophied sagittal spines and features blunt thoracic tergopleural tips. A putative fourth species, referred to Thelxiope sp. nov. A, extends the stratigraphical range of Thelxiope to the Lower Ordovician (Tremadocian), and its palaeographic range to West Gondwana. Currently under study, this relatively common component of the lower Fezouata Shale fauna is only briefly discussed. Features characterizing the genus Thelxiope and its components almost exclusively pertain to the sagittal spines, for the scarcity and inconsistent preservation of the Cambrian materials as-yet available preclude a confident assessment of the variability of other morphological features. The pygidium in Thelxiope and Mollisonia is not composed of four, but three tergites essentially similar to thoracic ones, except for the lack of articulations.

scholarly journals The Furongian to Lower Ordovician Alum Shale Formation in conventional and unconventional petroleum systems in the Baltic Basin – A review

2021 ◽  
pp. 103674
Author(s):  
Hans-Martin Schulz ◽  
Shengyu Yang ◽  
Niels H. Schovsbo ◽  
Erik Rybacki ◽  
Amin Ghanizadeh ◽  
...  
Keyword(s):  
Baltic Basin ◽  
Petroleum Systems ◽  
Alum Shale ◽  
Lower Ordovician ◽  
Shale Formation ◽  
The Baltic

Integrated Cambrian biostratigraphy and carbon isotope chemostratigraphy of the Grönhögen-2015 drill core, Öland, Sweden

2018 ◽  
Vol 156 (06) ◽  
pp. 935-949 ◽  
Author(s):  
PER AHLBERG ◽  
FRANS LUNDBERG ◽  
MIKAEL ERLSTRÖM ◽  
MIKAEL CALNER ◽  
ANDERS LINDSKOG ◽  
...  
Keyword(s):  
Carbon Isotope ◽  
Global Scale ◽  
Carbonate Facies ◽  
Southern Sweden ◽  
Middle Ordovician ◽  
Alum Shale ◽  
Carbon Isotope Excursion ◽  
Upper Stage ◽  
Shale Formation ◽  
Isotope Analyses

AbstractThe Grönhögen-2015 core drilling on southern Öland, Sweden, penetrated 50.15 m of Cambrian Series 3, Furongian and Lower–Middle Ordovician strata. The Cambrian succession includes the Äleklinta Member (upper Stage 5) of the Borgholm Formation and the Alum Shale Formation (Guzhangian–Tremadocian). Agnostoids and trilobites allowed subdivision of the succession into eight biozones, in ascending order: the uppermost Cambrian Series 3 (Guzhangian) Agnostus pisiformis Zone and the Furongian Olenus gibbosus, O. truncatus, Parabolina spinulosa, Sphaerophthalmus? flagellifer, Ctenopyge tumida, C. linnarssoni and Parabolina lobata zones. Conspicuous lithologic unconformities and the biostratigraphy show that the succession is incomplete and that there are several substantial gaps of variable magnitudes. Carbon isotope analyses (δ13Corg) through the Alum Shale Formation revealed two globally significant excursions: the Steptoean Positive Carbon Isotope Excursion (SPICE) in the lower–middle Paibian Stage, and the negative Top of Cambrian Excursion (TOCE), previously referred to as the HERB Event, in Stage 10. The δ13Corg chemostratigraphy is tied directly to the biostratigraphy and used for an improved integration of these excursions with the standard agnostoid and trilobite zonation of Scandinavia. Their relations to that of coeval successions in Baltoscandia and elsewhere are discussed. The maximum amplitudes of the SPICE and TOCE in the Grönhögen succession are comparable to those recorded in drill cores retrieved from Scania, southern Sweden. The results of this study will be useful for assessing biostratigraphic relations between shale successions and carbonate facies on a global scale.

The first Early Ordovician graptolites and marine incursions in eastern Alborz, Iran

2021 ◽  
pp. 1-14
Author(s):  
Adrian W. A. Rushton ◽  
Mansoureh Ghobadi Pour ◽  
Leonid E. Popov ◽  
Hadi Jahangir ◽  
Arash Amini
Keyword(s):  
Northern Iran ◽  
Early Ordovician ◽  
Lower Ordovician ◽  
Shale Formation ◽  
Kopet Dagh ◽  
Semnan Province

Abstract Graptolites have been collected from sections through Lower Ordovician strata in northern Iran. At the Saluk Mountains, in the Kopet–Dagh region, mudrocks yielded fragmentary tubaria of Rhabdinopora sp. cf. R. flabelliformis, indicating the presence of lower Tremadocian strata there; stratigraphically, they lie between two limestone beds with the euconodont Cordylodus lindstromi. At Simeh–Kuh in the eastern Alborz Mountains (Semnan Province), upper Tremadocian – lower Floian strata include laminated dark mudstones that contain restricted graptolite faunas, mainly of small declined didymograptids; these are thought to represent incursions of plankton during periods of marine highstands. The lower major flooding surface in Simeh–Kuh coincides with an invasion of the graptolite biofacies and an incursion of Hunnegraptus? sp.; the second major flooding surface is associated with an incursion of Baltograptus geometricus. They were most probably synchronous with those in the lower part of the Hunnegraptus copiosus Biozone and at the base of the Cymatograptus protobalticus Biozone in the of the Tøyen Shale Formation succession of Västergötland, Scandinavia, suggesting that observed characters of sedimentation were eustatically controlled.

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