Rob Newton | University of Leeds (original) (raw)

Papers by Rob Newton

Geological Magazine, 1998

New δ13Corg analyses of two boundary sections between the late Permian Kapp Starostin Formation a... more New δ13Corg analyses of two boundary sections between the late Permian Kapp Starostin Formation and the early Triassic Vardebukta Formation of western Spitsbergen confirm field evidence that their contact is a conformable one. Thus, contrary to previous reports, some Spitsbergen sections contain a complete record of the environmental and faunal changes during the crisis interval of the end Permian mass extinction. No environmental deterioration is recorded in the late Permian until near the end of the terminal Changxingian Stage, whereupon the abundant siliceous sponge fauna of the Kapp Starostin Formation disappears along with the deep-burrowing fauna responsible for the Zoophycus trace fossil. A low diversity dysaerobic trace fossil assemblage is briefly developed before a transition to finely laminated, pyritic facies immediately beneath the Permo-Triassic boundary. Analysis of the S/C ratios from the laminated strata suggests that free H2S was present in the water column (euxini...

Earth and Planetary Science Letters, 2004

Carbonate-associated sulphate (CAS) extracted from a Permo^Triassic succession at Siusi in northe... more Carbonate-associated sulphate (CAS) extracted from a Permo^Triassic succession at Siusi in northern Italy is shown to preserve a true seawater-sulphate isotope record. Two periods of increasing N 34 S and N 18 O in CAS provide evidence for increased oceanic anoxia in the Late Permian and the Early Triassic. These two anoxic episodes are separated by an event characterised by the addition of isotopically light sulphur and oxygen to the oceanic sulphate pool. Simple mass balance calculations suggest that this sulphate originates from the reoxidation of bacterially derived H 2 S during oceanic mixing, rather than a volcanogenic source. A dramatic fall in CAS-N 18 O directly above the P^T boundary, not accompanied by a large change in CAS-N 34 S, records an oceanic deoxygenation event probably caused by the release of methane from gas hydrates, subsequently recorded in the carbonate-carbon isotope record. The decline of Early Triassic oceanic anoxia is not recorded by a fall in CAS-N 34 S, but is preserved by declining CAS-N 18 O. This is because of an increase in the flux of reactive iron to the oceans during the Early Triassic anoxic episode, triggered by the demise of land plants. This permanently removes a greater proportion of light sulphur from the oceanic sulphate reservoir as pyrite, and means that the heavy residual sulphate-sulphur isotope signature of Griesbachian anoxic seawater is preserved as a geochemical 'fossil' until the beginning of the Middle Triassic.

Geological Magazine, 2016

Globally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon i... more Globally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon isotope excursion, sea-level changes and trilobite extinctions. Here we examine the sedimentology, sequence stratigraphy and carbon isotope record of this interval in the Cambrian strata (Durness Group) of NW Scotland. Carbonate carbon isotope data from the lower part of the Durness Group (Ghrudaidh Formation) show that the shallow-marine, Laurentian margin carbonates record two linked sea-level and carbon isotopic events. Whilst the carbon isotope excursions are not as pronounced as those expressed elsewhere, correlation with global records (Sauk I – Sauk II boundary andOlenellusbiostratigraphic constraint) identifies them as representing the local expression of the ROECE and DICE. The upper part of the ROECE is recorded in the basal Ghrudaidh Formation whilst the DICE is seen around 30m above the base of this unit. Both carbon isotope excursions co-occur with surfaces interpreted to rec...

1944 Pan-Arctic drivers of glacial microbial community structure and function STEFANIE LUTZ, ALEX... more 1944 Pan-Arctic drivers of glacial microbial community structure and function STEFANIE LUTZ, ALEXANDRE M. ANESIO, ARWYN EDWARDS, ROB NEWTON, FIONA GILL AND LIANE G. BENNING Cohen Laboratories, School of Earth & Environment, University of Leeds, Leeds, UK, s.lutz@leeds.ac.uk, r.j.newton@/f.gill@/l.g.benning@leeds.ac.uk GFZ German Research Centre for Geosciences, Helmholtz Centre Potsdam, Potsdam, Germany School of Geographical Sciences, University of Bristol, Bristol, UK, a.m.anesio@bristol.ac.uk Institute of Biological, Environmental & Rural Sciences, Aberystwyth University, Aberystwyth, UK, aye@aber.ac.uk

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

Seymour Island, in the James Ross Basin, Antarctica, contains a continuous succession of latest C... more Seymour Island, in the James Ross Basin, Antarctica, contains a continuous succession of latest Cretaceous sediments deposited in a shallow marine environment at high latitude, making it an ideal place to study environmental changes prior to the K-Pg mass extinction. We measured major and trace elements and conducted petrographic analysis of two sections from the Maastrichtian-Danian López de Bertodano Formation of Seymour Island. Several lines of evidence point to intermittently anoxic to euxinic conditions during deposition, including the presence of pyrite framboids with a size distribution suggesting syngenetic formation in the water column, and enrichments in several trace elements, including molybdenum, arsenic, copper, zinc, and chromium. Molybdenum enrichments are clearly associated with enrichments in manganese and authigenic iron, suggesting "shuttling" of redox sensitive trace elements across a chemocline that fluctuated across the sediment-water interface. Comparisons with modern systems suggest relatively high-frequency redox variability, possibly over approximately annual timescales, which may be related to the annual cycle of polar sunlight and associated seasonal changes in primary productivity. Glauconitic horizons are associated with more reducing conditions, including at the K-Pg boundary, though this does not appear to be a uniquely euxinic interval; similar degrees of trace element enrichment are seen in other highly glauconitic intervals. While euxinia may have contributed to low diversity in the lowermost 'Rotularia Units', redox conditions do not seem to have been the primary control on the transition to a mollusc dominated fauna in the latest Maastrichtian. Redox conditions show little to no response to the eruption of the Deccan Traps or Maastrichtian climatic changes. Instead, intermittent euxinia appears to have been a characteristic feature of this high-latitude environment during the Cretaceous-Paleogene transition.

Nature Communications, 2016

The Arctic is melting at an unprecedented rate and key drivers are changes in snow and ice albedo... more The Arctic is melting at an unprecedented rate and key drivers are changes in snow and ice albedo. Here we show that red snow, a common algal habitat blooming after the onset of melting, plays a crucial role in decreasing albedo. Our data reveal that red pigmented snow algae are cosmopolitan as well as independent of location-specific geochemical and mineralogical factors. The patterns for snow algal diversity, pigmentation and, consequently albedo, are ubiquitous across the Arctic and the reduction in albedo accelerates snow melt and increases the time and area of exposed bare ice. We estimated that the overall decrease in snow albedo by red pigmented snow algal blooms over the course of one melt season can be 13%. This will invariably result in higher melt rates. We argue that such a 'bio-albedo' effect has to be considered in climate models.

Nature communications, May 26, 2016

Debate continues about the nature of the Cretaceous-Paleogene (K-Pg) mass extinction event. An ab... more Debate continues about the nature of the Cretaceous-Paleogene (K-Pg) mass extinction event. An abrupt crisis triggered by a bolide impact contrasts with ideas of a more gradual extinction involving flood volcanism or climatic changes. Evidence from high latitudes has also been used to suggest that the severity of the extinction decreased from low latitudes towards the poles. Here we present a record of the K-Pg extinction based on extensive assemblages of marine macrofossils (primarily new data from benthic molluscs) from a highly expanded Cretaceous-Paleogene succession: the López de Bertodano Formation of Seymour Island, Antarctica. We show that the extinction was rapid and severe in Antarctica, with no significant biotic decline during the latest Cretaceous, contrary to previous studies. These data are consistent with a catastrophic driver for the extinction, such as bolide impact, rather than a significant contribution from Deccan Traps volcanism during the late Maastrichtian.

PALAIOS, 2012

The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform s... more The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform settings from western Tethys (Hungary and Hydra, Greece). The age model for these sections is poorly resolved and we have constructed a d 13 C chemostratigraphic correlation scheme, supported by conodont and foraminifer data, which attempts correlation with the well-dated events in China. This reveals the timing of events was similar in all Tethyan regions: extinction losses in the middle of the Capitanian produced late Capitanian assemblages in Hungary and Hydra with a distinctive late Permian character (for example, they lack large fusulinaceans). There is no evidence for an extinction event at the end of the Guadalupian (Capitanian) suggesting that previous claims for an end-Guadalupian mass extinction are based on poorly dated records of a mid-Capitanian event. Base level was stable through much of the middle-late Permian transition with the exception of a major regression within the Capitanian Stage. The subsequent transgression established widespread shallow-water carbonate deposition, such as the Episkopi Formation in Hydra and the Nagyvisnyó Limestone Formation in Hungary.

Solid Earth Discussions, 2012

The Upper Pliensbachian-Toarcian (Jurassic) sedimentological, palaeontological and geochemical (b... more The Upper Pliensbachian-Toarcian (Jurassic) sedimentological, palaeontological and geochemical (belemnite 87 Sr/ 86 Sr, δ 13 C and δ 18 O) record is examined in two Eastern Tethyan (Bulgarian) locations. This interval contains the well-known Early Toarcian ocean anoxic event (T-OAE) and its manifestation and temporal context is examined in Bulgaria. Many of the features characteristic for the SW European sections were identified: collapse of carbonate platform productivity at the Pliensbachian/Toarcian boundary, the T-OAE (a short pulse of anoxic deposition in the Falciferum ammonite Zone), an Early Toarcian rapid warming event seen in the belemnite δ 18 O record that peaked around the Falciferum/Bifrons ammonite zonal boundary. The long-recognized positive δ 13 C excursion in the late Falciferum ammonite Zone is also seen but a precursor, sharp δ 13 C negative excursion seen around the Tenuicostatum/Falciferum ammonite zonal boundary in many organic carbon records is not evident in the belemnite data, a curious absence noted from other belemnite records. Subsequent fluctuations of the 87 Sr/ 86 Sr, δ 13 C and δ 18 O suggest there may be a further perturbation of the global isotopic systems. On the other hand, belemnite Sr isotope values from Bulgaria are in accord with those seen in Western Europe and hence its value for chronostratigraphy.

Water Science and Technology, 2010

A pilot-scale primary maturation pond was spiked with 15N-labelled ammonia (15NH4Cl) and 15N-labe... more A pilot-scale primary maturation pond was spiked with 15N-labelled ammonia (15NH4Cl) and 15N-labelled nitrite (Na15NO2), in order to improve current understanding of the dynamics of inorganic nitrogen transformations and removal in WSP systems. Stable isotope analysis of δ15N showed that nitrification could be considered as an intermediate step in WSP, which is masked by simultaneous denitrification, under conditions of low algal activity. Molecular microbiology analysis showed that denitrification can be considered a feasible mechanism for permanent nitrogen removal in WSP, which may be supported either by ammonia-oxidising bacteria (AOB) or by methanotrophs, in addition to nitrite-oxidising bacteria (NOB). However, the relative supremacy of the denitrification process over other nitrogen removal mechanisms (e.g., biological uptake) depends upon phytoplanktonic activity.

Global and Planetary Change, 2010

Fabric and pyrite framboid size analysis of Permian to Jurassic samples from the Mino-Tamba terra... more Fabric and pyrite framboid size analysis of Permian to Jurassic samples from the Mino-Tamba terrane of Japan provide an 80 myr redox history from the Panthalassa Ocean. Fully oxygenated conditions dominated but were punctuated by three phases of anoxia (euxinia) during the Permo-Triassic boundary, the late Early Triassic (Spathian Stage) and the late Early Jurassic (Toarcian Stage). A Permo-Triassic superanoxic event of 10 myr duration is thus resolved into a complex redox history of dysoxic-anoxic background conditions punctuated by short-lived euxinic pulses. Both the end-Permian and Toarcian anoxic episodes began abruptly with the development of siliceous claystones, characterized by a framboid-dominated pyrite fraction and no organic C enrichment, interpreted to record euxinic conditions. These facies are overlain by organic-rich shales with slightly larger framboids, more crystalline pyrite and bioturbation indicating accumulation beneath a better-ventilated, higher productivity water column. Thus, an initial phase of oceanwide stagnation was followed by improved circulation attributed to the onset of warm saline bottom water circulation. Five radiolarian crises during our study interval show a complex relationship with redox conditions. The latest Permian mass extinction coincided with the onset of ocean euxinia but two other crises (Middle Permian and end Triassic), occurred during fully oxygenated intervals. Radiolarian radiation events are also not consistently linked with redox conditions: diversification in the early Late Permian coincides with the onset of weakly dysoxic conditions, late Early Triassic and late Early Jurassic radiations coincide with euxinic events, and the basal Jurassic radiation occurred during a fully oxic phase.

Applied Geochemistry, 2011

This study demonstrates that only a combination of a chromous chloride reduction with dual sequen... more This study demonstrates that only a combination of a chromous chloride reduction with dual sequential extraction schemes can clearly separate the proportions of Se present in the sulphide versus the organic pools in shales. The data reveals that even small amounts of pyrite outcompete the organic matter for the available Se and pyrite oxidation will control the release of selenium during shale weathering.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

This is a repository copy of Trilobite extinctions, facies changes and the ROECE carbon isotope e... more This is a repository copy of Trilobite extinctions, facies changes and the ROECE carbon isotope excursion at the Cambrian Series 2-3 boundary, Great Basin, western USA.

Naturwissenschaften, 2012

Nitrogen isotope signatures (δ 15 N) provide powerful measures of the trophic positions of indivi... more Nitrogen isotope signatures (δ 15 N) provide powerful measures of the trophic positions of individuals, populations and communities. Obtaining reliable consumer δ 15 N values depends upon controlling for spatial variation in plant δ 15 N values, which form the trophic 'baseline'. However, recent studies make differing assumptions about the scale over which plant δ 15 N values vary, and approaches to baseline control differ markedly. We examined spatial variation in the δ 15 N values of plants and ants sampled from eight 150-m transects in both unlogged and logged rainforests. We then investigated whether ant δ 15 N values were related to variation in plant δ 15 N values following baseline correction of ant values at two spatial scales: (1) using 'local' means of plants collected from the same transect and (2) using 'global' means of plants collected from all transects within each forest type. Plant δ 15 N baselines varied by the equivalent of one trophic level within each forest type. Correcting ant δ 15 N values using global plant means resulted in consumer values that were strongly positively related to the transect baseline, whereas local corrections yielded reliable estimates of consumer trophic positions that were largely independent of transect baselines. These results were consistent at the community level and when three trophically distinct ant subfamilies and eight abundant ant species were considered separately. Our results suggest that assuming baselines do not vary can produce misleading estimates of consumer trophic positions. We therefore emphasise the importance of clearly defining and applying baseline corrections at a scale that accounts for spatial variation in plant δ 15 N values.

Earth-Science Reviews, 2006

Stable isotope ratios of sulfur (d 34 S) and oxygen (d 18 O) in marine sulfate respond to changes... more Stable isotope ratios of sulfur (d 34 S) and oxygen (d 18 O) in marine sulfate respond to changes in fluxes and processes in the global sulfur cycle. The two isotope systems respond on different time scales to different factors affecting the global sulfur cycle. Sulfur isotopes respond primarily to the relative fluxes of weathering-derived sulfate to the oceans versus the net flux of sulfur exported from the oceans as pyrite in marine sediments. At the present day, this response is relatively slow (~20 Ma) because of the large size of the marine sulfate reservoir; ancient oceans had lower sulfate concentrations and thus sulfate residence times may have been shorter. The d 34 S of marine sulfate is also sensitive to the development of a significant reservoir of H 2 S in ancient stratified oceans. Sulfate-oxygen isotopes respond primarily to changes in the cycling of sulfur in the oceans and marine sediments. Sulfur disproportionation, oxic and anaerobic sulfide oxidation all impart different d 18 O signatures to marine sulfate; the relative importance of these different processes is in turn controlled by the distribution of redox conditions and microbial ecology of sea-floor sediments. The mutual interpretation of changes in marine sulfate d 34 S and d 18 O can thus give rather precise information on the nature of changes in global sulfur cycling. Recently, records of isotope compositions of ancient marine sulfate have become available through the analysis of carbonate-associated sulfate (CAS) in limestones and marine biogenic barite, both of which provide far more continuous records than previous data based primarily on marine evaporite sulfate minerals.

PALAIOS, 2012

The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform s... more The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform settings from western Tethys (Hungary and Hydra, Greece). The age model for these sections is poorly resolved and we have constructed a d 13 C chemostratigraphic correlation scheme, supported by conodont and foraminifer data, which attempts correlation with the well-dated events in China. This reveals the timing of events was similar in all Tethyan regions: extinction losses in the middle of the Capitanian produced late Capitanian assemblages in Hungary and Hydra with a distinctive late Permian character (for example, they lack large fusulinaceans). There is no evidence for an extinction event at the end of the Guadalupian (Capitanian) suggesting that previous claims for an end-Guadalupian mass extinction are based on poorly dated records of a mid-Capitanian event. Base level was stable through much of the middle-late Permian transition with the exception of a major regression within the Capitanian Stage. The subsequent transgression established widespread shallow-water carbonate deposition, such as the Episkopi Formation in Hydra and the Nagyvisnyó Limestone Formation in Hungary.

The late Pliensbachian-Toarcian (Jurassic) sedimentological, paleontological and geochemical (bel... more The late Pliensbachian-Toarcian (Jurassic) sedimentological, paleontological and geochemical (belemnite 87 Sr/ 86 Sr, δ 13 C and δ 18 O) record is examined in two Eastern Tethyan (Bulgarian) locations. This interval contains the well-known early Toarcian ocean anoxic event (T-OAE) and its manifestation and temporal context is examined in Bulgaria. Many of the features seen in south-western Europe are identified: collapse of carbonate platform productivity at the Pliensbachian/Toarcian boundary, the T-OAE (a short pulse of euxinic deposition in the Falciferum Zone), an early Toarcian rapid warming event seen in the belemnite δ 18 O record that peaked around the Falciferum/Bifrons Zone boundary. The long-recognized positive δ 13 C excursion in the late Falciferum Zone is also seen but a precursor, sharp δ 13 C negative excursion seen around the Tenuicostatum/Falciferum Zone boundary in most organic carbon records is not seen in the belemnite data, a curious absence noted from other belemnite records. Subsequent perturbations in 87 Sr/ 86 Sr, δ 13 C and δ 18 O suggest that there may be more global isotopic excursions in the Early Jurassic. On the other hand, belemnite Sr isotope values from Bulgaria are in accord with those recorded in Western Europe and hence, demonstrating its value as a chronostratigraphic tool. (L.S. Metodiev), i.savov@see.leeds.ac.uk (I.P. Savov), d.r.grocke@durham.ac.uk (D.R. Gröcke), P.B.Wignall@leeds.ac.uk (P.B. Wignall), r.j.newton@leeds.ac.uk (R.J. Newton), polina_a@geology.bas.bg (P.V. Andreeva), e_koleva@geology.bas.bg (E.K. Koleva-Rekalova).

Palaeogeography, Palaeoclimatology, Palaeoecology, 2005

The Khunamuh Formation of the Guryul Ravine section in Kashmir provides one of the most detailed ... more The Khunamuh Formation of the Guryul Ravine section in Kashmir provides one of the most detailed deep-water records of the end-Permian mass extinction in Perigondwanan palaeolatitudes. Examination of pyrite framboid size distributions and sediment microfabric reveals a distinct change in the uppermost Permian strata from nonlaminated, pyrite-free silty mudstones to finely laminated, silty shales rich in framboidal pyrite around 1 m above the base of the formation. The size frequency distribution of the framboids is identical to populations from severely oxygen-restricted modern depositional environments. This change to dysoxic benthic conditions coincides with the rapid demise of diverse Permian brachiopod and bryozoan assemblages. Thus, the link between extinction and anoxia is clearly seen at Guryul Ravine and it provides an interesting contrast to other Perigondwanan sections developed in shallower water where both the onset of anoxia and the extinction occurred somewhat later in the earliest Triassic. D

Palaeogeography, Palaeoclimatology, Palaeoecology, 2010

Conodont, C isotope and fossil and facies data are presented for the Capitanian (Middle Permian) ... more Conodont, C isotope and fossil and facies data are presented for the Capitanian (Middle Permian) mass extinction record seen in platform carbonates (Maokou and Wuchiaping formations) of South China, where limestones interdigitate with the volcanic succession of the Emeishan large igneous province. The Maokou Formation provides an extinction record marked by the loss of keriothecal-walled fusulinaceans and a turnover in calcareous algae. In sections within the Emeishan province this crisis occurs at the base of the oldest record of volcanism from the Jinogondolella altudaensis conodont zone (of mid-Capitanian age). Around the periphery of the Emeishan province this extinction level lies within the upper part of the Maokou Formation at a level where platform carbonate deposition was frequently interrupted by thick volcanic ash depositional events. The assemblages of the uppermost Maokou Formation are characterised by typical "Late Permian" taxa although these levels still lie within the Middle Permian (Guadalupian Series). "Disaster" taxa, such as Earlandia and Diplosphaerina are locally prolifically abundant in the aftermath of the mass extinction. The crisis is particularly noteworthy amongst photosynthetic taxa such as calcareous algae and fusulinaceans that probably harboured photosymbionts. Therefore, a kill mechanism involving cooling from explosive volcanism and potentially acid rain from sulphate aerosols appears appropriate. A composite δ 13 C carb curve, calibrated against a high-resolution conodont biostratigraphy reveals a major intra-Capitanian negative excursion (of N 5‰) superimposed on typically heavy (4-5‰) Middle Permian values. This curve can also be recognised in Panthalassan seamount carbonates of Japan although this requires reassignment of apparently Upper Permian limestones to the Middle Permian. In both China and Japan the Capitanian mass extinction occurs during the early stage of this major, intra-Capitanian negative excursion. Assuming typical platform carbonate accumulation rates, the records of the Maokou Formation suggest δ 13 C carb values fell at ∼0.01‰/kyr suggesting a catastrophic origin (such as gas hydrate destabilisation) is unlikely, although a volcanic source is possible.

Geological Magazine, 1998

New δ13Corg analyses of two boundary sections between the late Permian Kapp Starostin Formation a... more New δ13Corg analyses of two boundary sections between the late Permian Kapp Starostin Formation and the early Triassic Vardebukta Formation of western Spitsbergen confirm field evidence that their contact is a conformable one. Thus, contrary to previous reports, some Spitsbergen sections contain a complete record of the environmental and faunal changes during the crisis interval of the end Permian mass extinction. No environmental deterioration is recorded in the late Permian until near the end of the terminal Changxingian Stage, whereupon the abundant siliceous sponge fauna of the Kapp Starostin Formation disappears along with the deep-burrowing fauna responsible for the Zoophycus trace fossil. A low diversity dysaerobic trace fossil assemblage is briefly developed before a transition to finely laminated, pyritic facies immediately beneath the Permo-Triassic boundary. Analysis of the S/C ratios from the laminated strata suggests that free H2S was present in the water column (euxini...

Earth and Planetary Science Letters, 2004

Carbonate-associated sulphate (CAS) extracted from a Permo^Triassic succession at Siusi in northe... more Carbonate-associated sulphate (CAS) extracted from a Permo^Triassic succession at Siusi in northern Italy is shown to preserve a true seawater-sulphate isotope record. Two periods of increasing N 34 S and N 18 O in CAS provide evidence for increased oceanic anoxia in the Late Permian and the Early Triassic. These two anoxic episodes are separated by an event characterised by the addition of isotopically light sulphur and oxygen to the oceanic sulphate pool. Simple mass balance calculations suggest that this sulphate originates from the reoxidation of bacterially derived H 2 S during oceanic mixing, rather than a volcanogenic source. A dramatic fall in CAS-N 18 O directly above the P^T boundary, not accompanied by a large change in CAS-N 34 S, records an oceanic deoxygenation event probably caused by the release of methane from gas hydrates, subsequently recorded in the carbonate-carbon isotope record. The decline of Early Triassic oceanic anoxia is not recorded by a fall in CAS-N 34 S, but is preserved by declining CAS-N 18 O. This is because of an increase in the flux of reactive iron to the oceans during the Early Triassic anoxic episode, triggered by the demise of land plants. This permanently removes a greater proportion of light sulphur from the oceanic sulphate reservoir as pyrite, and means that the heavy residual sulphate-sulphur isotope signature of Griesbachian anoxic seawater is preserved as a geochemical 'fossil' until the beginning of the Middle Triassic.

Geological Magazine, 2016

Globally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon i... more Globally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon isotope excursion, sea-level changes and trilobite extinctions. Here we examine the sedimentology, sequence stratigraphy and carbon isotope record of this interval in the Cambrian strata (Durness Group) of NW Scotland. Carbonate carbon isotope data from the lower part of the Durness Group (Ghrudaidh Formation) show that the shallow-marine, Laurentian margin carbonates record two linked sea-level and carbon isotopic events. Whilst the carbon isotope excursions are not as pronounced as those expressed elsewhere, correlation with global records (Sauk I – Sauk II boundary andOlenellusbiostratigraphic constraint) identifies them as representing the local expression of the ROECE and DICE. The upper part of the ROECE is recorded in the basal Ghrudaidh Formation whilst the DICE is seen around 30m above the base of this unit. Both carbon isotope excursions co-occur with surfaces interpreted to rec...

1944 Pan-Arctic drivers of glacial microbial community structure and function STEFANIE LUTZ, ALEX... more 1944 Pan-Arctic drivers of glacial microbial community structure and function STEFANIE LUTZ, ALEXANDRE M. ANESIO, ARWYN EDWARDS, ROB NEWTON, FIONA GILL AND LIANE G. BENNING Cohen Laboratories, School of Earth & Environment, University of Leeds, Leeds, UK, s.lutz@leeds.ac.uk, r.j.newton@/f.gill@/l.g.benning@leeds.ac.uk GFZ German Research Centre for Geosciences, Helmholtz Centre Potsdam, Potsdam, Germany School of Geographical Sciences, University of Bristol, Bristol, UK, a.m.anesio@bristol.ac.uk Institute of Biological, Environmental & Rural Sciences, Aberystwyth University, Aberystwyth, UK, aye@aber.ac.uk

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

Seymour Island, in the James Ross Basin, Antarctica, contains a continuous succession of latest C... more Seymour Island, in the James Ross Basin, Antarctica, contains a continuous succession of latest Cretaceous sediments deposited in a shallow marine environment at high latitude, making it an ideal place to study environmental changes prior to the K-Pg mass extinction. We measured major and trace elements and conducted petrographic analysis of two sections from the Maastrichtian-Danian López de Bertodano Formation of Seymour Island. Several lines of evidence point to intermittently anoxic to euxinic conditions during deposition, including the presence of pyrite framboids with a size distribution suggesting syngenetic formation in the water column, and enrichments in several trace elements, including molybdenum, arsenic, copper, zinc, and chromium. Molybdenum enrichments are clearly associated with enrichments in manganese and authigenic iron, suggesting "shuttling" of redox sensitive trace elements across a chemocline that fluctuated across the sediment-water interface. Comparisons with modern systems suggest relatively high-frequency redox variability, possibly over approximately annual timescales, which may be related to the annual cycle of polar sunlight and associated seasonal changes in primary productivity. Glauconitic horizons are associated with more reducing conditions, including at the K-Pg boundary, though this does not appear to be a uniquely euxinic interval; similar degrees of trace element enrichment are seen in other highly glauconitic intervals. While euxinia may have contributed to low diversity in the lowermost 'Rotularia Units', redox conditions do not seem to have been the primary control on the transition to a mollusc dominated fauna in the latest Maastrichtian. Redox conditions show little to no response to the eruption of the Deccan Traps or Maastrichtian climatic changes. Instead, intermittent euxinia appears to have been a characteristic feature of this high-latitude environment during the Cretaceous-Paleogene transition.

Nature Communications, 2016

The Arctic is melting at an unprecedented rate and key drivers are changes in snow and ice albedo... more The Arctic is melting at an unprecedented rate and key drivers are changes in snow and ice albedo. Here we show that red snow, a common algal habitat blooming after the onset of melting, plays a crucial role in decreasing albedo. Our data reveal that red pigmented snow algae are cosmopolitan as well as independent of location-specific geochemical and mineralogical factors. The patterns for snow algal diversity, pigmentation and, consequently albedo, are ubiquitous across the Arctic and the reduction in albedo accelerates snow melt and increases the time and area of exposed bare ice. We estimated that the overall decrease in snow albedo by red pigmented snow algal blooms over the course of one melt season can be 13%. This will invariably result in higher melt rates. We argue that such a 'bio-albedo' effect has to be considered in climate models.

Nature communications, May 26, 2016

Debate continues about the nature of the Cretaceous-Paleogene (K-Pg) mass extinction event. An ab... more Debate continues about the nature of the Cretaceous-Paleogene (K-Pg) mass extinction event. An abrupt crisis triggered by a bolide impact contrasts with ideas of a more gradual extinction involving flood volcanism or climatic changes. Evidence from high latitudes has also been used to suggest that the severity of the extinction decreased from low latitudes towards the poles. Here we present a record of the K-Pg extinction based on extensive assemblages of marine macrofossils (primarily new data from benthic molluscs) from a highly expanded Cretaceous-Paleogene succession: the López de Bertodano Formation of Seymour Island, Antarctica. We show that the extinction was rapid and severe in Antarctica, with no significant biotic decline during the latest Cretaceous, contrary to previous studies. These data are consistent with a catastrophic driver for the extinction, such as bolide impact, rather than a significant contribution from Deccan Traps volcanism during the late Maastrichtian.

PALAIOS, 2012

The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform s... more The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform settings from western Tethys (Hungary and Hydra, Greece). The age model for these sections is poorly resolved and we have constructed a d 13 C chemostratigraphic correlation scheme, supported by conodont and foraminifer data, which attempts correlation with the well-dated events in China. This reveals the timing of events was similar in all Tethyan regions: extinction losses in the middle of the Capitanian produced late Capitanian assemblages in Hungary and Hydra with a distinctive late Permian character (for example, they lack large fusulinaceans). There is no evidence for an extinction event at the end of the Guadalupian (Capitanian) suggesting that previous claims for an end-Guadalupian mass extinction are based on poorly dated records of a mid-Capitanian event. Base level was stable through much of the middle-late Permian transition with the exception of a major regression within the Capitanian Stage. The subsequent transgression established widespread shallow-water carbonate deposition, such as the Episkopi Formation in Hydra and the Nagyvisnyó Limestone Formation in Hungary.

Solid Earth Discussions, 2012

The Upper Pliensbachian-Toarcian (Jurassic) sedimentological, palaeontological and geochemical (b... more The Upper Pliensbachian-Toarcian (Jurassic) sedimentological, palaeontological and geochemical (belemnite 87 Sr/ 86 Sr, δ 13 C and δ 18 O) record is examined in two Eastern Tethyan (Bulgarian) locations. This interval contains the well-known Early Toarcian ocean anoxic event (T-OAE) and its manifestation and temporal context is examined in Bulgaria. Many of the features characteristic for the SW European sections were identified: collapse of carbonate platform productivity at the Pliensbachian/Toarcian boundary, the T-OAE (a short pulse of anoxic deposition in the Falciferum ammonite Zone), an Early Toarcian rapid warming event seen in the belemnite δ 18 O record that peaked around the Falciferum/Bifrons ammonite zonal boundary. The long-recognized positive δ 13 C excursion in the late Falciferum ammonite Zone is also seen but a precursor, sharp δ 13 C negative excursion seen around the Tenuicostatum/Falciferum ammonite zonal boundary in many organic carbon records is not evident in the belemnite data, a curious absence noted from other belemnite records. Subsequent fluctuations of the 87 Sr/ 86 Sr, δ 13 C and δ 18 O suggest there may be a further perturbation of the global isotopic systems. On the other hand, belemnite Sr isotope values from Bulgaria are in accord with those seen in Western Europe and hence its value for chronostratigraphy.

Water Science and Technology, 2010

A pilot-scale primary maturation pond was spiked with 15N-labelled ammonia (15NH4Cl) and 15N-labe... more A pilot-scale primary maturation pond was spiked with 15N-labelled ammonia (15NH4Cl) and 15N-labelled nitrite (Na15NO2), in order to improve current understanding of the dynamics of inorganic nitrogen transformations and removal in WSP systems. Stable isotope analysis of δ15N showed that nitrification could be considered as an intermediate step in WSP, which is masked by simultaneous denitrification, under conditions of low algal activity. Molecular microbiology analysis showed that denitrification can be considered a feasible mechanism for permanent nitrogen removal in WSP, which may be supported either by ammonia-oxidising bacteria (AOB) or by methanotrophs, in addition to nitrite-oxidising bacteria (NOB). However, the relative supremacy of the denitrification process over other nitrogen removal mechanisms (e.g., biological uptake) depends upon phytoplanktonic activity.

Global and Planetary Change, 2010

Fabric and pyrite framboid size analysis of Permian to Jurassic samples from the Mino-Tamba terra... more Fabric and pyrite framboid size analysis of Permian to Jurassic samples from the Mino-Tamba terrane of Japan provide an 80 myr redox history from the Panthalassa Ocean. Fully oxygenated conditions dominated but were punctuated by three phases of anoxia (euxinia) during the Permo-Triassic boundary, the late Early Triassic (Spathian Stage) and the late Early Jurassic (Toarcian Stage). A Permo-Triassic superanoxic event of 10 myr duration is thus resolved into a complex redox history of dysoxic-anoxic background conditions punctuated by short-lived euxinic pulses. Both the end-Permian and Toarcian anoxic episodes began abruptly with the development of siliceous claystones, characterized by a framboid-dominated pyrite fraction and no organic C enrichment, interpreted to record euxinic conditions. These facies are overlain by organic-rich shales with slightly larger framboids, more crystalline pyrite and bioturbation indicating accumulation beneath a better-ventilated, higher productivity water column. Thus, an initial phase of oceanwide stagnation was followed by improved circulation attributed to the onset of warm saline bottom water circulation. Five radiolarian crises during our study interval show a complex relationship with redox conditions. The latest Permian mass extinction coincided with the onset of ocean euxinia but two other crises (Middle Permian and end Triassic), occurred during fully oxygenated intervals. Radiolarian radiation events are also not consistently linked with redox conditions: diversification in the early Late Permian coincides with the onset of weakly dysoxic conditions, late Early Triassic and late Early Jurassic radiations coincide with euxinic events, and the basal Jurassic radiation occurred during a fully oxic phase.

Applied Geochemistry, 2011

This study demonstrates that only a combination of a chromous chloride reduction with dual sequen... more This study demonstrates that only a combination of a chromous chloride reduction with dual sequential extraction schemes can clearly separate the proportions of Se present in the sulphide versus the organic pools in shales. The data reveals that even small amounts of pyrite outcompete the organic matter for the available Se and pyrite oxidation will control the release of selenium during shale weathering.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

This is a repository copy of Trilobite extinctions, facies changes and the ROECE carbon isotope e... more This is a repository copy of Trilobite extinctions, facies changes and the ROECE carbon isotope excursion at the Cambrian Series 2-3 boundary, Great Basin, western USA.

Naturwissenschaften, 2012

Nitrogen isotope signatures (δ 15 N) provide powerful measures of the trophic positions of indivi... more Nitrogen isotope signatures (δ 15 N) provide powerful measures of the trophic positions of individuals, populations and communities. Obtaining reliable consumer δ 15 N values depends upon controlling for spatial variation in plant δ 15 N values, which form the trophic 'baseline'. However, recent studies make differing assumptions about the scale over which plant δ 15 N values vary, and approaches to baseline control differ markedly. We examined spatial variation in the δ 15 N values of plants and ants sampled from eight 150-m transects in both unlogged and logged rainforests. We then investigated whether ant δ 15 N values were related to variation in plant δ 15 N values following baseline correction of ant values at two spatial scales: (1) using 'local' means of plants collected from the same transect and (2) using 'global' means of plants collected from all transects within each forest type. Plant δ 15 N baselines varied by the equivalent of one trophic level within each forest type. Correcting ant δ 15 N values using global plant means resulted in consumer values that were strongly positively related to the transect baseline, whereas local corrections yielded reliable estimates of consumer trophic positions that were largely independent of transect baselines. These results were consistent at the community level and when three trophically distinct ant subfamilies and eight abundant ant species were considered separately. Our results suggest that assuming baselines do not vary can produce misleading estimates of consumer trophic positions. We therefore emphasise the importance of clearly defining and applying baseline corrections at a scale that accounts for spatial variation in plant δ 15 N values.

Earth-Science Reviews, 2006

Stable isotope ratios of sulfur (d 34 S) and oxygen (d 18 O) in marine sulfate respond to changes... more Stable isotope ratios of sulfur (d 34 S) and oxygen (d 18 O) in marine sulfate respond to changes in fluxes and processes in the global sulfur cycle. The two isotope systems respond on different time scales to different factors affecting the global sulfur cycle. Sulfur isotopes respond primarily to the relative fluxes of weathering-derived sulfate to the oceans versus the net flux of sulfur exported from the oceans as pyrite in marine sediments. At the present day, this response is relatively slow (~20 Ma) because of the large size of the marine sulfate reservoir; ancient oceans had lower sulfate concentrations and thus sulfate residence times may have been shorter. The d 34 S of marine sulfate is also sensitive to the development of a significant reservoir of H 2 S in ancient stratified oceans. Sulfate-oxygen isotopes respond primarily to changes in the cycling of sulfur in the oceans and marine sediments. Sulfur disproportionation, oxic and anaerobic sulfide oxidation all impart different d 18 O signatures to marine sulfate; the relative importance of these different processes is in turn controlled by the distribution of redox conditions and microbial ecology of sea-floor sediments. The mutual interpretation of changes in marine sulfate d 34 S and d 18 O can thus give rather precise information on the nature of changes in global sulfur cycling. Recently, records of isotope compositions of ancient marine sulfate have become available through the analysis of carbonate-associated sulfate (CAS) in limestones and marine biogenic barite, both of which provide far more continuous records than previous data based primarily on marine evaporite sulfate minerals.

PALAIOS, 2012

The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform s... more The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform settings from western Tethys (Hungary and Hydra, Greece). The age model for these sections is poorly resolved and we have constructed a d 13 C chemostratigraphic correlation scheme, supported by conodont and foraminifer data, which attempts correlation with the well-dated events in China. This reveals the timing of events was similar in all Tethyan regions: extinction losses in the middle of the Capitanian produced late Capitanian assemblages in Hungary and Hydra with a distinctive late Permian character (for example, they lack large fusulinaceans). There is no evidence for an extinction event at the end of the Guadalupian (Capitanian) suggesting that previous claims for an end-Guadalupian mass extinction are based on poorly dated records of a mid-Capitanian event. Base level was stable through much of the middle-late Permian transition with the exception of a major regression within the Capitanian Stage. The subsequent transgression established widespread shallow-water carbonate deposition, such as the Episkopi Formation in Hydra and the Nagyvisnyó Limestone Formation in Hungary.

The late Pliensbachian-Toarcian (Jurassic) sedimentological, paleontological and geochemical (bel... more The late Pliensbachian-Toarcian (Jurassic) sedimentological, paleontological and geochemical (belemnite 87 Sr/ 86 Sr, δ 13 C and δ 18 O) record is examined in two Eastern Tethyan (Bulgarian) locations. This interval contains the well-known early Toarcian ocean anoxic event (T-OAE) and its manifestation and temporal context is examined in Bulgaria. Many of the features seen in south-western Europe are identified: collapse of carbonate platform productivity at the Pliensbachian/Toarcian boundary, the T-OAE (a short pulse of euxinic deposition in the Falciferum Zone), an early Toarcian rapid warming event seen in the belemnite δ 18 O record that peaked around the Falciferum/Bifrons Zone boundary. The long-recognized positive δ 13 C excursion in the late Falciferum Zone is also seen but a precursor, sharp δ 13 C negative excursion seen around the Tenuicostatum/Falciferum Zone boundary in most organic carbon records is not seen in the belemnite data, a curious absence noted from other belemnite records. Subsequent perturbations in 87 Sr/ 86 Sr, δ 13 C and δ 18 O suggest that there may be more global isotopic excursions in the Early Jurassic. On the other hand, belemnite Sr isotope values from Bulgaria are in accord with those recorded in Western Europe and hence, demonstrating its value as a chronostratigraphic tool. (L.S. Metodiev), i.savov@see.leeds.ac.uk (I.P. Savov), d.r.grocke@durham.ac.uk (D.R. Gröcke), P.B.Wignall@leeds.ac.uk (P.B. Wignall), r.j.newton@leeds.ac.uk (R.J. Newton), polina_a@geology.bas.bg (P.V. Andreeva), e_koleva@geology.bas.bg (E.K. Koleva-Rekalova).

Palaeogeography, Palaeoclimatology, Palaeoecology, 2005

The Khunamuh Formation of the Guryul Ravine section in Kashmir provides one of the most detailed ... more The Khunamuh Formation of the Guryul Ravine section in Kashmir provides one of the most detailed deep-water records of the end-Permian mass extinction in Perigondwanan palaeolatitudes. Examination of pyrite framboid size distributions and sediment microfabric reveals a distinct change in the uppermost Permian strata from nonlaminated, pyrite-free silty mudstones to finely laminated, silty shales rich in framboidal pyrite around 1 m above the base of the formation. The size frequency distribution of the framboids is identical to populations from severely oxygen-restricted modern depositional environments. This change to dysoxic benthic conditions coincides with the rapid demise of diverse Permian brachiopod and bryozoan assemblages. Thus, the link between extinction and anoxia is clearly seen at Guryul Ravine and it provides an interesting contrast to other Perigondwanan sections developed in shallower water where both the onset of anoxia and the extinction occurred somewhat later in the earliest Triassic. D

Palaeogeography, Palaeoclimatology, Palaeoecology, 2010

Conodont, C isotope and fossil and facies data are presented for the Capitanian (Middle Permian) ... more Conodont, C isotope and fossil and facies data are presented for the Capitanian (Middle Permian) mass extinction record seen in platform carbonates (Maokou and Wuchiaping formations) of South China, where limestones interdigitate with the volcanic succession of the Emeishan large igneous province. The Maokou Formation provides an extinction record marked by the loss of keriothecal-walled fusulinaceans and a turnover in calcareous algae. In sections within the Emeishan province this crisis occurs at the base of the oldest record of volcanism from the Jinogondolella altudaensis conodont zone (of mid-Capitanian age). Around the periphery of the Emeishan province this extinction level lies within the upper part of the Maokou Formation at a level where platform carbonate deposition was frequently interrupted by thick volcanic ash depositional events. The assemblages of the uppermost Maokou Formation are characterised by typical "Late Permian" taxa although these levels still lie within the Middle Permian (Guadalupian Series). "Disaster" taxa, such as Earlandia and Diplosphaerina are locally prolifically abundant in the aftermath of the mass extinction. The crisis is particularly noteworthy amongst photosynthetic taxa such as calcareous algae and fusulinaceans that probably harboured photosymbionts. Therefore, a kill mechanism involving cooling from explosive volcanism and potentially acid rain from sulphate aerosols appears appropriate. A composite δ 13 C carb curve, calibrated against a high-resolution conodont biostratigraphy reveals a major intra-Capitanian negative excursion (of N 5‰) superimposed on typically heavy (4-5‰) Middle Permian values. This curve can also be recognised in Panthalassan seamount carbonates of Japan although this requires reassignment of apparently Upper Permian limestones to the Middle Permian. In both China and Japan the Capitanian mass extinction occurs during the early stage of this major, intra-Capitanian negative excursion. Assuming typical platform carbonate accumulation rates, the records of the Maokou Formation suggest δ 13 C carb values fell at ∼0.01‰/kyr suggesting a catastrophic origin (such as gas hydrate destabilisation) is unlikely, although a volcanic source is possible.