Ichron Ltd

Northwich, United Kingdom

Ichron Ltd

Northwich, United Kingdom

Time filter

Source Type

Jarvis I.,Kingston University | Lignum J.S.,Kingston University | Lignum J.S.,Ichron Ltd | Grcke D.R.,Durham University | And 2 more authors.
Paleoceanography | Year: 2011

Oceanic Anoxic Event 2 (OAE2), spanning the Cenomanian-Turonian boundary (CTB), represents one of the largest perturbations in the global carbon cycle in the last 100 Myr. The δ 13C carb, δ 13C org, and δ 18O chemostratigraphy of a black shale-bearing CTB succession in the Vocontian Basin of France is described and correlated at high resolution to the European CTB reference section at Eastbourne, England, and to successions in Germany, the equatorial and midlatitude proto-North Atlantic, and the U.S. Western Interior Seaway (WIS). 13C (offset between δ 13C carb and δ 13C org) is shown to be a good pCO 2 proxy that is consistent with pCO 2 records obtained using biomarker δ 13C data from Atlantic black shales and leaf stomata data from WIS sections. Boreal chalk δ 18O records show sea surface temperature (SST) changes that closely follow the 13C pCO 2 proxy and confirm TEX 86 results from deep ocean sites. Rising pCO 2 and SST during the Late Cenomanian is attributed to volcanic degassing; pCO 2 and SST maxima occurred at the onset of black shale deposition, followed by falling pCO 2 and cooling due to carbon sequestration by marine organic productivity and preservation, and increased silicate weathering. A marked pCO 2 minimum (∼25% fall) occurred with a SST minimum (Plenus Cold Event) showing >4C of cooling in ∼40 kyr. Renewed increases in pCO 2, SST, and δ 13C during latest Cenomanian black shale deposition suggest that a continuing volcanogenic CO 2 flux overrode further drawdown effects. Maximum pCO 2 and SST followed the end of OAE2, associated with a falling nutrient supply during the Early Turonian eustatic highstand. Copyright 2011 by the American Geophysical Union.


Molyneux S.G.,British Geological Survey | Delabroye A.,French National Center for Scientific Research | Delabroye A.,Ichron Ltd | Wicander R.,Central Michigan University | Servais T.,French National Center for Scientific Research
Geological Society Memoir | Year: 2013

Early to mid Palaeozoic marine phytoplankton are represented by acritarchs and associated forms, which had a global distribution from the early Cambrian to the early Carboniferous (Mississippian). Palaeozoic phytoplankton assemblages show varying degrees of cosmopolitanism and endemism through time. A high degree of cosmopolitanism was evidently characteristic of the Cambrian and much of the Late Ordovician, Silurian and Devonian, but provincialism was more marked in the Early Ordovician and Hirnantian (latest Ordovician), the latter at a time of major palaeoenvironmental perturbations. Distribution patterns of Palaeozoic phytoplankton are attributed to a number of interacting factors, including palaeolatitude, palaeotemperature, oceanic circulation patterns, the disposition of continents, differentiation between oceanic and cratonic (distal-proximal) assemblages, and sedimentary environments and facies. There are indications that biogeographical ranges of taxa shift over time. Moving our understanding of Palaeozoic phytoplankton biogeography forward requires (1) targeted investigation of regions and time periods for which no or little data exist, (2) quantitative analysis of data to investigate how similarity between regions varies through time and how this might correlate with other datasets such as carbon isotope stratigraphy or sea-level, and (3) rigorous application of well-defined time slices to compare coeval assemblages, at least within the limits of resolution © The Authors 2013.


In a sedimentological sense a fluvial to tidal transition zone can be defined in rivers as a zone that separates the upstream fluvial from the downstream estuarine zone. Characteristic sedimentary structures within this zone are notoriously difficult to recognize. This study demonstrates the influence of tidal modulation within the most proximal part of the fluvial-tidal transition zone (i.e. the 'backwater zone') of an ancient fluvial system. Criteria have been established to differentiate between purely fluvial facies and those modulated by tidal energy. The stratigraphic interval from which the data were derived is the Lourinhã Formation (Late Jurassic) of the Lusitanian Basin, Western Portugal. An analysis of sedimentary features at four key localities has identified a temporal spectrum of tidal influence ranging from the daily modulation of fluvial flows to the effects of tidal bore passage. A combination of quantitative and qualitative data reveals systematic changes in the internal architecture of dune-scale bedforms deposited in a channel-floor setting. The key co-occurring features are: (i) increasing-decreasing organic particle concentration; (ii) increasing-decreasing bottomset thickness; (iii) increasing-decreasing foreset dip and shape (from convex to concave); and (iv) increasing-decreasing brinkpoint height. Collectively, these features are interpreted as having been produced by successive fluctuations in flow regime conditions from lower (during flood tidal retardation) to higher (during ebb tidal drawdown) current velocities. Bedforms showing these features occur in both meandering fluvial channels and straighter distributary systems. In addition, several examples of a specific type of stepped erosion surface and draping sediment have been recognized, the interpretation of which strongly suggests generation by the passage of tidal bores. If this interpretation is correct, then it represents one of the first published examples of tidal bore propagation in ancient fluvial systems. Palaeoclimatic evidence (cellular analysis of woody tissue, palaeosol character and plate reconstruction) indicates a warm, seasonal, winter wet to summer dry climate during deposition of the Lourinhã Formation. From this evidence it is suggested that tidal modulation and tidal bore effects are more likely to develop in the 'dry season', when fluvial flow in the main river channels was reduced. © 2010 The Authors. Journal compilation © 2010 International Association of Sedimentologists.


Taylor A.M.,Ichron Ltd | Gowland S.,Ichron Ltd | Leary S.,Statoil | Keogh Kevin J.,Statoil | Martinius A.W.,Statoil
Geological Journal | Year: 2014

The c. 700m thick succession of continental-brackish-marine deposits forming the Lourinhã Formation, cropping out along the coast of western Portugal between Baleal and Santa Cruz, has been correlated using laterally persistent shelly marker beds. Three shelly units record the episodic establishment of relatively short-lived, brackish-marine embayments, transgressing from the southwest, onto a low-lying coastal plain. The succession displays systematic changes in facies types and stacking patterns reflecting differences in fluvial style, bedload character and palaeontological content. Based on these observations, four new members for the Lourinhã Formation are proposed: the Sáo Bernardino, Porto de Barças, Areia Branca and Ferrel members. New biostratigraphical data indicate that the Lourinhã Formation is Late Kimmeridgian to earliest Early Tithonian in age. This age has also been obtained from the underlying mixed carbonate and clastic deposits of the Abadia Formation at Consolação. As a result, these latter sediments are now re-assigned to the Alcobaça Formation, a lithostratigraphical term currently in use in other areas of the Lusitanian Basin. Improved regional mapping of the Lourinhã Formation has established a new sub-basin within the western parts of the Lusitanian Basin. This sub-basin, now named the Consolação Sub-basin, is bounded to the east by the Lourinhã-Caldas de Rainha (L-C) fault zone and to the west by the Berlengas Horst. © 2013 John Wiley & Sons, Ltd.


Khanna N.,University of St. Andrews | Khanna N.,Ichron Ltd | Godbold J.A.,University of Southampton | Austin W.E.N.,University of St. Andrews | And 2 more authors.
PLoS ONE | Year: 2013

Culturing experiments were performed on sediment samples from the Ythan Estuary, N. E. Scotland, to assess the impacts of ocean acidification on test surface ornamentation in the benthic foraminifer Haynesina germanica. Specimens were cultured for 36 weeks at either 380, 750 or 1000 ppm atmospheric CO 2. Analysis of the test surface using SEM imaging reveals sensitivity of functionally important ornamentation associated with feeding to changing seawater CO2 levels. Specimens incubated at high CO2 levels displayed evidence of shell dissolution, a significant reduction and deformation of ornamentation. It is clear that these calcifying organisms are likely to be vulnerable to ocean acidification. A reduction in functionally important ornamentation could lead to a reduction in feeding efficiency with consequent impacts on this organism's survival and fitness. © 2013 Khanna et al.


Rubinstein C.V.,CONICET | de la Puente G.S.,National University of Comahue | Delabroye A.,Ichron Ltd | Astini R.A.,National University of Cordoba
Review of Palaeobotany and Palynology | Year: 2015

The Hirnantian "glacial horizon" has been recognized across the Central Andean Basin (Puna, Cordillera Oriental, Sierras Subandinas and Sistema de Santa Bárbara) in northwestern Argentina. It is represented by glaciofluvial to glaciomarine facies which unconformably overly Lower to Middle Ordovician stratigraphic units. In the Caspalá area, in the eastern margin of the Cordillera Oriental, the glacial deposits are assigned to the Caspalá Formation. The Lower Silurian postglacial deposits of the Lipeón Formation sharply truncate the underlying Caspalá Formation. Miospores, chitinozoans and acritarchs have been recorded across the Ordovician/Silurian boundary. Marine palynomorphs dominate the studied section. The Late Ordovician miospore assemblage is fairly diverse.It contains permanent tetrads and dyads, spores physically separated from cryptospore polyads, laevigate and ornamented hilate spores, and trilete spores. The trilete spores Ambitisporites avitus, Aneurospora? sp., Chelinospora cf. prisca and Leiotriletes spp. occur in the Caspalá Formation together with chitinozoans dated as early to late Katian. If land-derived palynomorphs were considered autochthonous, their age would be Hirnantian. The trilete spores of the Caspalá Formation constitute their oldest record in South America, representing the advent of vascular plants in the region. The Lipeón Formation yielded Telychian trilete spores dated by chitinozoans, constituting the earliest evidence of Silurian vascular plants of Argentina. The diversity and abundance of miospores decrease in the Lipeón Formation in accordance with the disappearance of terrestrial ecosystems due to the global transgression after the melting of the Hirnantian glaciers. Acritarchs in both the Caspalá and the Lipeón formations support the chitinozoan dating. Whereas chitinozoans and acritarchs show affinities with Gondwanan and peri-Gondwanan regions, the studied miospores confirm the cosmopolitism of Late Ordovician-earliest Silurian microfloras. The new miospore data, particularly those related to the incoming and evolution of hilate/trilete spores, question previous palaeogeographic and palaeoclimatic interpretations about the origin and adaptive radiation of vascular land plants. © 2015 Elsevier B.V.


Ruckwied K.,Royal Dutch Shell | Gotz A.E.,Rhodes University | Gotz A.E.,Kazan Federal University | Jones P.,Ichron Ltd
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2014

The Permian formations of the South African Karoo Basin play a crucial role in understanding Gondwana's climate history during this time of major global changes. In this paper we present two data sets, one from the coal-bearing Vryheid Formation (Witbank Basin) and one from the Whitehill and Upper Prince Albert formations of the DP 1/78 core (NE Karoo).Our main goal was to study the vegetation changes during this period of global warming and test if the climatic signals could be used to correlate the basinal Ecca group facies with the fluvio-deltaic coal-bearing strata of the Witbank Basin. The palynological record of the No. 2 Coal Seam of the Vryheid Formation indicates a cold climate, fern wetland community, characteristic of lowland alluvial plains, and an upland conifer community in the lower part of the coal seam. Up section, these communities are replaced by a cool-temperate cycad-like lowland vegetation and gymnospermous upland flora. The data set of the DP 1/78 core is interpreted to represent a cool to warm temperate climate represented by a high amount of Gangamopteris and Glossopteris elements.Both data sets are very different in their composition, which can be explained by the differences in depositional environment; however, our findings reveal a different age of the studied assemblages and thus also suggest that both data sets represent different stages in the transition from icehouse to greenhouse during Permian times. As the stratigraphic correlation between the Main Karroo Basin and the peripheral basins is still under discussion, this paper provides new data to underpin the stratigraphic placement of the Whitehill Formation relative to the coal-bearing Vryheid Formation. © 2014 Elsevier B.V.


Lee D.E.,University of Otago | Lindqvist J.K.,University of Otago | Beu A.G.,Institute of Geological & Nuclear Sciences | Robinson J.H.,University of Otago | And 3 more authors.
New Zealand Journal of Geology and Geophysics | Year: 2014

A new fossil locality of Late Oligocene (Duntroonian) age at Cosy Dell farm, Waimumu, southern New Zealand has yielded a diverse array of exceptionally well-preserved fossils derived from rocky shore, sandy beach and estuarine habitats. A lag deposit of Jurassic Murihiku basement boulders and cobbles is overlain by richly fossiliferous, locally concretionary, pebbly shellbeds. The fauna is remarkable for its taxonomic diversity. It includes thick-shelled bivalves and large gastropods, an abundance of juveniles and micromolluscs, and species with nacreous shell and colour patterns preserved. More than 350 species of molluscs are present, including 10 chitons, 90 bivalves and 250 gastropods. Other notable components of the biota include > 125 ostracod species, barnacles, foraminifera, brachiopods, bryozoans, echinoderms, hermatypic corals, otoliths and penguin bones. Oyster-encrusted and pholad-bored boulders, and intertidal and estuarine species indicate proximity to a rocky coastline and estuary, confirming the presence of land in southern New Zealand during Late Oligocene times. © 2014 © 2014 The Royal Society of New Zealand.


Cummings J.P.,University of Liverpool | Cummings J.P.,Ichron Ltd | Hodgson D.M.,University of Liverpool
Sedimentary Geology | Year: 2011

The Cretaceous to Eocene aged Basque Basin in northern Spain preserves a variety of submarine fan related environments of deposition in well exposed outcrops. Here, quantitative trace fossil data is calibrated to sedimentologically defined environments of deposition. Nine environments of deposition are assigned according to sedimentary facies associations, depositional architecture and stratigraphic context. The preserved trace fossil assemblages are interpreted in terms of extrinsic palaeoecological, and intrinsic taphonomical and depositional environment controls. In channel related environments, diverse pre-depositional dominated assemblages are prevalent in marginal settings. These are replaced by low diversity post-depositional dominated assemblages in more axial positions within the system. Lobe related environments display a higher level of diversity and bioturbation intensity in more distal/off axis (lobe fringe) environments compared to the most axial lobe environments that preserve low diversity, and exclusively post-depositional assemblages (dominated by Ophiomorpha). Diverse pre- and post-depositional assemblages are common in fan fringe deposits, with less diverse assemblages dominated by post-depositional ichnotaxa (particularly Zoophycos) in basin floor fan deposits. The use of 'sub-ichnofacies' is found to only aid characterisation of trace fossil assemblages based on a general (proximal-distal) position within a submarine fan system. Tier preservation of trace fossil assemblages is almost exclusively determined by the depth of erosion that a substrate is subjected to. As such, colonisation style (pre- versus post depositional) and ethological groupings are proposed as being the most powerful tool in assisting sedimentological observations in assigning environments of deposition. © 2011 Elsevier B.V.


Ayress M.A.,Ichron Ltd | Whatley R.C.,Aberystwyth University
Palaeontology | Year: 2014

Twenty-seven species of well-preserved and abundant Early Cretaceous non-marine ostracod crustaceans were recovered from the North Falkland Basin. The assemblage is unusually diverse for a non-marine palaeoenvironment and is sourced from cuttings samples collected during 2011 drilling of wells by Desire and Rockhopper Exploration, in the northern and southern areas of the basin. Ostracoda are entirely undocumented in published accounts from this basin, and all but one species appear to be new to science. For the new taxa, one new family (Alloiocyprideidae; type genus Hourcqia) is proposed and includes Hourcqia woodi sp. nov. Four new genera are erected: Falklandicypris gen. nov.; type species F. petrasaltata sp. nov., Gangamoncythere gen. nov.; type species G. colini sp. nov., Paraplesiocypridea gen. nov.; type species P. alloios sp. nov., and Musacchiocythere gen nov.; type species M. sarunata (Musacchio, ). Nine other species are described as new and are Falklandicypris desiderata, Clinocypris epacrus, Cypria poietes, Ilhasina? leiodermatus, Looneyellopsis tuberculatus, Theriosynoecum petasmathylacus, Theriosynoecum ballentae, Timiriasevia fluitans, and Vecticypris samesi. The remainder are left in open nomenclature due to paucity of material. The ostracod assemblage is largely restricted to the southern part of the basin (wells 25/5-1 and 26/6-1). In the northern part of the basin only four species, dominated by Vecticypris samesi, are present and with one possible exception are restricted there. There appears to have been little or no interchange of species suggesting that a barrier probably existed between the northern and southern regions. The more diverse southern assemblage indicates that more favourable conditions existed to the south. Stratigraphically, a distinct change in faunal composition recorded in both southern wells is likely to be an isochronous event correlatable across the southern area, and of an age no younger than Hauterivian. © The Palaeontological Association.

Loading Ichron Ltd collaborators
Loading Ichron Ltd collaborators