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Passler J.-F.,Friedrich - Alexander - University, Erlangen - Nuremberg | Jarochowska E.,Friedrich - Alexander - University, Erlangen - Nuremberg | Ray D.C.,Neftex | Munnecke A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Worton G.,Dudley Museum and Art Gallery
Estonian Journal of Earth Sciences | Year: 2014

A microbial origin has been proposed for matrix-supported, low-diversity buildups reported from different palaeocontinents during the onset of the Mulde positive carbon isotope excursion. We have investigated a small aphanitic buildup from the Lower Quarried Limestone Member of the Much Wenlock Limestone Formation, exposed at Whitman’s Hill (Herefordshire), corresponding to the central part of the Midland Platform (UK). Up to 50% of the rock volume in this buildup consists of mottled micrite. The SEM studies revealed that the micrite is largely detrital and does not show features characteristic of calcareous cyanobacteria or leiolites. The aphanitic character of the buildup is suggested to be controlled by the depositional rate, and the widespread occurrence of matrix-supported reefs in this interval to be driven by a mid-Homerian rapid eustatic transgression. © 2014, Estonian Academy Publishers. All rights reserved. Source

Gladkochub D.P.,Russian Academy of Sciences | Nicoll G.,Neftex | Stanevich A.M.,Russian Academy of Sciences | Mazukabzov A.M.,Russian Academy of Sciences | And 5 more authors.
Doklady Earth Sciences | Year: 2013

The first data on the age of detrital zircons are given for Late Precambrian terrigenous rocks of the Baikal Group and Ushakovka Formation of the southern flank of the Siberian Craton. The ages obtained for 348 zircons cover the Paleoarchean to Late Ediacaran period, demonstrate the dynamics of change of sources of the clastic material in the sedimentation basin, and mark the changes of the Late Precambrian tectonic regimes. The age of the youngest group of detrital zircons extracted from the rocks of the Kachergat Formation allows us to restrict the upper age limit of accumulation of the rocks of the Baikal Group to the Late Ediacaran (Late Vendian). © 2013 Pleiades Publishing, Ltd. Source

Smith N.J.,Neftex | Kokelaar B.P.,University of Liverpool
Bulletin of Volcanology | Year: 2013

Lithofacies architecture analysis is applied to the most proximal exposures of the 273 ka Poris Formation, in the Diego Hernandez caldera wall of Las Cañadas. Here, the succession records an opening Plinian phase followed by generation of a pyroclastic density current (PDC) that was partly blocked by near-vent topography. The upper part of the current surmounted the barrier and deposited an ignimbrite veneer. During a hiatus in energetic flow, ash and various ash aggregates were deposited from a hybrid cloud comprising parts of both the Plinian and the co-ignimbrite plumes. Phreatomagmatic explosions then generated currents rich in fine-grained lithics; current waxing with local erosion was followed by pulsing-unsteady waning, recorded in repeated sets of graded tuff. Reversion to magmatic activity was marked by hybrid deposition, as coarse pumice fallout and juvenile ballistics entered pyroclastic currents to form stratified pumice-block tuff. Increasingly energetic flow is recorded in 9 m of mainly massive lapilli tuff that includes evidence of widespread scour and bypass; lithic-rich layers record incremental onset of edifice disruption due to magma withdrawal. Laterally variable stratification and load structures show that the PDC was unsteady and highly non-uniform at times, with locally rapid aggradation of gas-rich ignimbrite. Climactic edifice disruption is marked by a lithic-block layer in erosional contact with the underlying ignimbrite, recording intense pyroclastic current activity and widespread bypass of material to distal volcano slopes. Pumice-block breccia, 10 m thick and with blocks up to 1.2 m in diameter, forms the top of the succession and registers modification of the magmatic plumbing. The timing of collapse to form a major summit depression is uncertain. However, the abrupt termination of the proximal aggradation of coarse breccia, with no record there of any waning-stage pyroclastic currents, suggests subsidence at that time, conceivably with formation of a caldera that contained late-erupted material. © 2013 Springer-Verlag Berlin Heidelberg. Source

Jarochowska E.,Friedrich - Alexander - University, Erlangen - Nuremberg | Munnecke A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Frisch K.,Neftex | Ray D.C.,University of Ottawa | Castagner A.,Goethe University Frankfurt
Lethaia | Year: 2016

The late Wenlock is characterized by two global regressive-transgressive eustatic cycles in association with a double-peaked positive carbon isotope excursion. The onset of the excursion coincides with an extinction event affecting graptolites (the lundgreni event) and proposed to affect conodonts (the Mulde Event) and proliferation of non-skeletal carbonates. In order to test the hypothesized relationships between eustatic and ecological changes, the tropical carbonate Homerian succession in Podolia has been examined with respect to conodont, sequence and δ13C stratigraphy. Four depositional sequences (DS) have been identified. The onset of the δ13C excursion occurs at the boundary between DS1 and DS2, corresponding to a forced regression of proposed glacioeustatic origin. The following rapid eustatic transgression associated with the highest δ13C values of 5.2‰ includes a higher-order shallowing episode recorded in Podolia as normal regression and a boundary between DS2 and DS3. This interval is distinguished by the presence of oncoids and thrombolitic buildups. The latest Wenlock eustatic fall and the corresponding second peak of the δ13C excursion corresponds in Podolia to a stratigraphic gap. The first δ13C peak (top of DS1 and DS2) corresponds to the O. bohemica longa conodont Zone, the interval between the two peaks (DS3) - to K. ortus absidata and C. murchisoni zones, and DS4 is tentatively placed in the lowermost Ludlow Series. The record of relative sea-level changes in Podolia is consistent with reconstructions based on successions in England and Sweden. The moderate drop in conodont taxonomic richness may reflect the primary depositional control over their proposed extinction. © 2016 The Lethaia Foundation. Source

Hughes H.E.,University of Plymouth | Ray D.C.,Neftex | Brett C.E.,University of Cincinnati
GFF | Year: 2014

δ13Ccarb data from the Tortworth and Woolhope inliers, Midland Platform, UK, provide a record of part of the early Sheinwoodian (Ireviken) carbon isotope excursion. The shallow-marine mixed carbonate/siliciclastic successions exhibit a maximum δ13Ccarb value of +5.8‰ VPDB. Values begin to increase sharply at the Pycnactis Band, a prominent flooding surface, and decrease over a transgressive sequence between the Woolhope and Coalbrookdale formations. The study provides an improved chronostratigraphic correlation across the Sheinwoodian of the Midland Platform (Avalonia) and further afield, and highlights the power of integrated chemostratigraphy and sequence stratigraphy in the absence of well-developed biostratigraphy. © 2014 © 2014 Taylor & Francis. Source

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