The latest NIGL Annual Report can be downloaded. This section highlights some of our high-impact papers as they go to press. A full list of NERC staff publications and outputs can be found in the NERC Open Research Archive (NORA)
Journal of Paleolimnology – December 2014
Lake Prespa, in the Balkans, contains an important palaeo-archive in a key location for understanding Quaternary climate variability in the transition between Mediterranean and central European climate zones. Previous palaeoenvironmental research on sediment cores indicates that the lake is highly sensitive to climate change and that diatoms are likely to be strong palaeohydrological proxies. Here, we present new results from diatom analysis of a ca. 91 ka sequence, core Co1215, which spans the time from the end of the last interglacial to the present. Fluctuations in the diatom data were driven primarily by changes in lake level, as a function of shifts in moisture availability. Warmer interglacial (MIS 5, MIS 1) and interstadial (MIS 3) phases exhibit higher lake levels in spite of enhanced evaporative concentration, underlining the importance of changes in precipitation regimes over time. Low lake levels during glacial phases indicate extreme aridity, common to all Mediterranean lakes. Evidence for fluctuations in trophic status is linked, in part, to lake-level change, but also reflects nutrient enrichment from catchment processes. MIS 5a is characterized by the highest lake productivity in the sequence, but low lake levels, which are ascribed primarily to very low precipitation.
On a suborbital timescale, the diatoms provide evidence for correlation to the millennial-scale variability recorded in the Greenland oxygen isotope records and clearly reflect the impact of the Heinrich H6, H5 and H3–1 ice-rafting events, suggesting the dominant influence of North Atlantic forcing in this region. Although the highest-amplitude shift in the diatom assemblages occurs during the time of H4 (40–38 ka), it may be superimposed upon the impact of the 39.28 cal ka BP Campanian Ignimbrite volcanic eruption. Diatoms from Lake Prespa core Co1215 display the first strong evidence for the impact of Italian volcanic activity on lacustrine biota in this region. Results emphasize the complexity of diatom response thresholds in different studies across the region. In the case of Lake Prespa, the results highlight the important role of precipitation for maintaining the hydrological balance of the lake, and indirectly, its biodiversity.
Cvetkoska, A., Levkov, Z., Reed, J.M., Wagner, B., Panagiotopoulos, K., Leng, M.J., Lacey, J.H. 2014. Quaternary climate change and Heinrich Events in the southern Balkans: Lake Prespa diatom palaeolimnology from the last interglacial to present. Journal of Paleolimnology.
Journal of Hydrology – November 2014
Palaeo-hydrological interpretations of lake sediment proxies can benefit from a robust understanding of the modern lake environment. In this study, we use Nar Gölü, a non-outlet, monomictic maar lake in central Turkey, as a field site for a natural experiment using observations and measurements over a 17-year monitoring period (1997-2014). We compare lake water and sediment trap data to isotopic, chemical and biotic proxies preserved in its varved sediments. Nar Gölü underwent a 3 m lake-level fall between 2000 and 2010. δ18Olakewater is correlated with this lake-level fall, responding to the change in water balance. Endogenic carbonate is shown to precipitate in isotopic equilibrium with lake water and there is a strong relationship between δ18Olakewater and δ18Ocarbonate, which suggests the water balance signal is accurately recorded in the sediment isotope record. Over the same period, sedimentary diatom assemblages also responded, and conductivity inferred from diatoms showed a rise. Shifts in carbonate mineralogy and elemental chemistry in the sediment
record through this decade were also recorded. Intra-annual changes in δ18Olakewater and lake water chemistry are used to demonstrate the seasonal variability of the system and the influence this may have on the interpretation of δ18Ocarbonate. We use these relationships to help interpret the sedimentary record of changing lake hydrology over the last 1,725 years. Nar Gölü has provided an opportunity to test critically the chain of connection from present to past, and its sedimentary record offers an archive of decadal- to centennial-scale hydro-climatic change.
Dean, J.R., Eastwood, W.J., Roberts, C.N., Jones, M.D., Yiğitbaşıoğlu, H., Allcock, S.L., Woodbridge, J., Metcalfe, S.E., Leng, M.J., In press. Tracking the hydro-climatic signal from lake to sediment: a field study from central Turkey. Journal of Hydrology.
Climate of the Past – October 2014
Oxygen isotope analyses of different size fractions of Pliocene diatoms (δ18Odiatom) from the Bering Sea show no evidence of an isotope offset and support the use of bulk diatom species samples for palaeoceanographic reconstructions. Additional samples containing concentrations of sponge spicules produce δ18O values several per mille (‰) lower than δ18Odiatom with a calculated mean offset of 3.9‰ ± 1.5. This difference is significantly greater than modern-day variations in water δ18O through the regional water column. Despite the potential for oxygen isotope disequilibrium within δ18Osponge, there appears to be some similarity between δ18Osponge
and a global stacked benthic δ18Oforam record. This highlights the potential for δ18Osponge in palaeoenvironmental research at sites where carbonates are not readily preserved.
Snelling, A. M., Swann, G. E. A., Pike, J., and Leng, M. J. Pliocene diatom and sponge spicule oxygen isotope ratios from the Bering Sea: isotopic offsets and future directions, Clim. Past, 10, 1837-1842, doi:10.5194/cp-10-1837-2014, 2014.
Geology – September 2014
Late Cenozoic climate history in Africa was punctuated by episodes of variability, characterized by the appearance and disappearance of large freshwater lakes within the East African Rift Valley. In the Baringo-Bogoria basin, a well-dated sequence of diatomites and fluviolacustrine sediments documents the precessionally forced cycling of an extensive lake system between 2.70 Ma and 2.55 Ma. One diatomite unit was studied, using the oxygen isotope composition of diatom silica combined with X–ray fluorescence spectrometry and taxonomic assemblage changes, to explore the nature of climate variability during this interval. Data reveal a rapid onset and gradual decline of deepwater lake conditions, which exhibit millennial-scale cyclicity of 1400–1700 yr, similar to late Quaternary Dansgaard-Oeschger events.
These cycles are thought to reflect enhanced precipitation coincident with increased monsoonal strength, suggesting the existence of a teleconnection between the high latitudes and East Africa during this period. Such climatic variability could have affected faunal and floral evolution at the time.
Wilson, K.E., Maslin, M.A., Leng, M.J., Kingston, J.D., Deino, A.L., Edgar, R.K., Mackay, A.W. 2014. East African lake evidence for Pliocene millennial-scale climate variability. Geology.
Journal of Quaternary Science – August 2014
Analysis of the oxygen isotope composition of diatom silica is a commonly used tool for palaeoclimate reconstruction that recent studies have demonstrated may be complicated by the presence of non-diatom detrital material. Such contamination can mask any true climate-driven signal, leading to spurious results. Analysis of the 2.6-Ma Barsemoi diatomites from the East African Rift Valley highlights the presence of both tephra and clay in purified samples. Here we present a new method for assessing the relative contribution and geochemical composition of contamination components where sedimentary samples may be affected by more than one type of contamination. This approach shows that the incorporation of analytical techniques, such as X-ray fluorescence spectrometry, coupled with statistical modelling,
can be used to develop a three end-member model to successfully resolve climate-driven changes in δ18Odiatom. Mass-balance corrections made to δ18Odiatom data demonstrate the importance of adopting quantitative geochemical analysis in tandem with the δ18O analysis of biogenic silica, to obtain accurate and meaningful results for palaeoclimate reconstruction.
Wilson, K.E., Leng, M.J., Mackay, A.W. 2014. The use of multivariate statistics to resolve multiple contamination signals in the oxygen isotope analysis of biogenic silica. Journal of Quaternary Science
Journal of Archaeological Science – August 2014
The discovery of the mortal remains of King Richard III provide an opportunity to learn more about his lifestyle, including his origins and movements and his dietary history; particularly focussing on the changes that Kingship brought. We analysed bioapatite and collagen from sections of two teeth which formed during Richard's childhood and early adolescence, and from two bones: the femur (which averages long-term conditions), and the rib (which remodels faster and represents the last few years of life). We applied multi element isotope techniques to reconstruct a full life history. The isotopes initially concur with Richard's known origins in Northamptonshire but suggest that he had moved out of eastern England by age seven, and resided further west, possibly the Welsh Marches. In terms of his diet, there is a significant shift in the nitrogen, but not carbon isotope values, towards the end of his life, which we suggest could be explained by an increase
in consumption of luxury items such as game birds and freshwater fish. His oxygen isotope values also rise towards the end of his life and as we know he did not relocate during this time, we suggest the changes could be brought about by increased wine consumption. This is the first suggestion of wine affecting the oxygen isotope composition of an individual and thus has wider implications for isotope-based palaeodietary and migration reconstructions.
Lamb, A.L., Evans, J.E., Buckley, R., Appleby, J. 2014. Multi-isotope analysis demonstrates significant lifestyle changes in King Richard III. Journal of Archaeological Science, 48, 5–14.
Archaeofauna – August 2014
The exploitation of marine molluscs by Mediterranean hunter-gatherers increased from the Upper Palaeolithic onwards, although their role in subsistence has rarely been investigated fully. An ideal area to address this issue is the archipelago of the Egadi Islands, most of which were isolated by Post-Glacial sea level rise. Here we report on the results of the study of the mollusc assemblage recovered during the 1972 excavations at Grotta d'Oriente, a cave on Favignana, occupied from the Late Pleistocene to the middle Holocene. Marine molluscs, including principally rocky shore intertidal gastropods (Patella and Osilinus), were taken to the cave for consumption throughout its occupation, sporadically in the early Mesolithic, but more frequently and throughout the year in the late Mesolithic and early Neolithic. Progressive isolation resulted in intensification of shellfish exploitation, but not, however, in
long-term over-exploitation of all intertidal marine gastropods, despite their vulnerability to human predation. The archaeozoological and isotopic data suggest that shellfish were a useful source of protein for the occupants of Grotta d'Oriente, but that the main role of marine molluscs was probably to provide nutrients not readily available in the terrestrial foods which constituted the bulk of the diet.
Marcello, M., Thomas, K., Crema, E.R., Leng, M.J. 2014. A matter of taste? Mode and periodicity of marine mollusc exploitation on the Mediterranean island of Favignana (Egadi Islands, Italy) during its isolation in the early Holocene. Archaeofauna, 23, 133-147.
International Journal of Earth Sciences – August 2014
Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high–resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial–Holocene transition represented by low TIC and TOC contents, (2) the early to mid–Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene–Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing δ18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the bes–dated and highest resolution archive
of past Late Glacial and Holocene climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north–eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring–summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history.
Lacey, J.H., Francke, A., Leng, M.J., Vane, C.H., Wagner, B. 2014. A high resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania). International Journal of Earth Sciences. DOI 10.1007/s00531-014-1033-6.
Geology – July 2014
The Paleocene–Eocene Thermal Maximum (PETM), ca. 56 Ma, was a major global environmental perturbation attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. Geochemical records of tropical sea-surface temperatures (SSTs) from the PETM are rare and are typically affected by post-depositional diagenesis. To circumvent this issue, we have analyzed oxygen isotope ratios (δ18O) of single specimens of exceptionally well-preserved planktonic foraminifera from the PETM in Tanzania (δ19°S paleolatitude), which yield extremely low δ18O, down to <–5‰. After accounting for changes in seawater chemistry and pH, we estimate from the foraminifer δ18O that tropical SSTs rose by >3 °C during the PETM and may
have exceeded 40 °C. Calcareous plankton are absent from a large part of the Tanzania PETM record; extreme environmental change may have temporarily caused foraminiferal exclusion.
Aze, T., Pearson, P.N., Dickson, A.J., Badger, M.P.S., Bown, P.R., Pancost, R.D., Gibbs, S.J., Huber, B.T., Leng, M.J., Coe, A.L., Cohen, A.S., and Foster, G.L. 2014. Extreme warming of tropical waters during the Paleocene–Eocene Thermal Maximu. Geology, 42.
Science of the Total Environment – July 2014
Peri-urban floodplains are an important interface between developed land and the aquatic environment and may act as a source or sink for contaminants moving from urban areas towards surface water courses. With increasing pressure from urban development the functioning of floodplains is coming under greater scrutiny. A number of peri-urban sites have been found to be populated with legacy landfills which could potentially cause pollution of adjacent river bodies. Here, a peri-urban floodplain adjoining the city of Oxford, UK, with the River Thames has been investigated over a period of three years through repeated sampling of groundwaters from existing and specially constructed piezometers. A nearby landfill has been found to have imprinted a strong signal on the groundwater with particularly high concentrations of ammonium and generally low concentrations of nitrate and dissolved oxygen. An intensive study of nitrogen dynamics through the use of N-species chemistry, nitrogen isotopes and dissolved nitrous oxide reveals that there is little or no denitrification in the majority of the main landfill plume, and neither is the ammonium significantly
retarded by sorption to the aquifer sediments. A simple model reveals that up to 15% of the ammonium loading at the study site and over the length of the reach could increase in-stream concentrations by nearly 40%. Catchment management plans that encompass floodplains in the peri-urban environment need to take into account the likely risk to groundwater and surface water quality that these environments pose.
Gooddy, D.C., Macdonald, D.M.J., Lapworth, D.J., Bennett, S.A., Griffiths, K.J. Nitrogen sources, transport and processing in peri-urban floodplains, Science of the Total Environment 494-495 (2014) 28-38.
Anthropocene Review – July 2014
We consider whether the Anthropocene is recorded in the isotope geochemistry of the atmosphere, sediments, plants and ice cores, and the time frame during which any changes are recorded, presenting examples from the literature. Carbon and nitrogen isotope ratios have become more depleted since the 19th century, with the rate of change accelerating after ∼AD 1950, linked to increased emissions from fossil fuel consumption and increased production of fertiliser. Lead isotope ratios demonstrate human pollution histories several millennia into the past, while sulphur isotopes can be used to trace the sources of acid rain.
Radioisotopes have been detectable across the planet since the 1950s because of atmospheric nuclear bomb tests and can be used as a stratigraphic marker. We find there is isotopic evidence of widespread human impact on the global environment, but different isotopes have registered changes at different times and at different rates.
Dean, J.R, Leng, M.J., Mackay, A.W. 2014. Is there an isotopic signature of the Anthropocene? The Anthropocene Review.
Stratigraphical Basis for the Anthropocene – June 2014
Humankind has pervasively influenced the Earth’s atmosphere, biosphere, geosphere, hydrosphere and cryosphere, arguably to the point of fashioning a new geological epoch, the Anthropocene. To constrain the Anthropocene as a potential formal unit within the Geological Time Scale, a spectrum of indicators of anthropogenically-induced environmental change is considered, and shown as stratigraphical signals that may be used to characterize an Anthropocene unit, and to recognize its base. This volume describes a range of evidence that may help to define this potential new time unit and details key signatures that could be used in its definition. These signatures include lithostratigraphical (novel deposits, minerals and
mineral magnetism), biostratigraphical (macro- and micro-palaeontological successions and human-induced trace fossils) and chemostratigraphical(organic, inorganic and radiogenic signatures in deposits, speleothems and ice and volcanic eruptions). We include, finally, the suggestion that humans have created a further sphere, the technosphere, that drives global change.
C.N. Waters, J.A. Zalasiewicz, M. Williams, M.A. Ellis and A.M. Snelling. 2014. A Stratigraphical Basis for the Anthropocene. Special Publication 395. http://nora.nerc.ac.uk/506924/.
International Journal of Earth Sciences – May 2014
Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial–Holocene transition represented by low TIC and TOC contents, (2) the early to mid-Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene–Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing δ18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of
short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of past Late Glacial and Holoce climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring–summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history.
Lacey, J.H., Francke, A., Leng, M.J., Vane, C.H., Wagner, B. 2014. A high–resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania). International Journal of Earth Sciences. DOI 10.1007/s00531-014-1033-6.
Journal of Quaternary Science – May 2014
The oxygen isotope composition of diatom silica (δ18Odiatom) is increasingly being used to reconstruct climate from marine and lacustrine sedimentary archives. Although diatoms are assumed to precipitate their frustule in isotopic equilibrium with their surrounding water, it is unclear whether internal processes of a given species affect the fractionation of oxygen between the water and the diatom. We present δ18Odiatom data from two diatom size fractions (3–38 and >38μm) characterized by different species in a sediment core from Heart Lake, Alaska. Differences in δ18Odiatom between the two size fractions varies from 0 to 1.2‰, with a mean offset of 0.01‰ (n=20). Fourier transform infrared spectroscopy confirms our samples consist of pure biogenic silica (SiO2) and δ18Odiatom trends are not driven by contamination. The maximum offset is outside the range of error, but the mean is within analytical error of the
technique (±1.06‰), demonstrating no discernible species-dependent fractionation in δ18Odiatom. We conclude that lacustrine δ18Odiatom measurements offer a reliable and valuable method for reconstructing δ18Owater. Considering the presence of small offsets in our two records, we advise interpreting shifts in δ18Odiatom only where the magnitude of change is greater than the combined analytical error.
Bailey, Hannah L.; Henderson, Andrew C.G.; Sloane, Hilary J.; Snelling, Andrea; Leng, Melanie J.; Kaufman, Darrell S. 2014. The effect of species on lacustrine δ18Odiatom and its implications for palaeoenvironmental reconstructions. Journal of Quaternary Science, 29 (4). 393-400.
Scientific Drilling – May 2014
The Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project is an international research initiative to study the influence of major geological and environmental events on the biological evolution of lake taxa. SCOPSCO drilling campaigns were carried out in 2011 and 2013. In 2011 we used gravity and piston coring at one of the five proposed drill sites, and in 2013 we undertook deep drilling with the Deep Lake Drilling System (DLDS) of Drilling, Observation and Sampling of the Earth's Continental Crust (DOSECC). In April and May 2013, a total of 2100 m sediments were recovered from four drill sites with water depths ranging from 125 to 260 m. The maximum drill depth was 569 m below the lake floor in the centre of the lake. By retrieving overlapping sediment sequences, 95% of the sediment succession was recovered. Initial data from borehole logging, core logging and geochemical measurements indicate that the sediment
succession covers >1.2 million years (Ma) in a quasi-continuous sequence. These early findings suggest that the record from Lake Ohrid will substantially improve the knowledge of long-term environmental change and short-term geological events in the northeastern Mediterranean region, which forms the basis for improving understanding of the influence of major geological and environmental events on the biological evolution of endemic species.
Wagner, B., Wilke, T., Krastel, S., Zanchetta, G., Sulpizio, R., Reicherter, K., Leng, M., Grazhdani, A., Trajanovski, S., Francke A., Lindhorst, K., Cvetkoska, A., Reed, J.M., Zhang, X., Lacey, J.H., Wonik, T., Baumgarten, H., Vogel, H. 2014. The SCOPSCO drilling project recovers more than 1.2 million years of history from Lake Ohrid. Scientific Drilling, 17, 19-29.
Climate of the Past – May 2014
The transboundary Lake Prespa (Albania/former Yugoslav Republic of Macedonia/Greece) has been recognized as a conservation priority wetland. The high biodiversity encountered in the catchment at present points to the refugial character of this mountainous region in the southwestern Balkans. A lake sediment core retrieved from a coring location in the northern part of the lake was investigated through sedimentological, geochemical, and palynological analyses. Based on tephrochronology, radiocarbon and electron spin resonance (ESR) dating, and cross correlation with other Northern Hemisphere records, the age model suggests that the basal part of core Co1215 reaches back to 92 ka cal BP. Here we present the responses of this mid-altitude site (849 m a.s.l.) to climate oscillations during this interval and assess its sensitivity to millennial-scale variability. Endogenic calcite precipitation occurred in marine isotope stages (MIS) 5 and 1 and is synchronous with periods of increased primary production (terrestrial and/or lacustrine). Periods of pronounced phytoplankton blooms (inferred from green algae and dinoflagellate concentrations) are recorded in MIS 5 and MIS 1 and
suggest that the trophic state and lake levels underwent substantial fluctuations. Three major phases of vegetation development are distinguished: the forested phases of MIS 5 and MIS 1 dominated by deciduous trees with higher temperatures and moisture availability, the open landscapes of MIS 3 with significant presence of temperate trees, and the pine-dominated open landscapes of MIS 4 and MIS 2 with lower temperatures and moisture availability. Our findings suggest significant changes in forest cover and landscape openness, as well as in the properties of the vegetation belts (composition and distribution) over the period examined. The study area most likely formed the upper limit of several drought-sensitive trees (temperate tree refugium) at these latitudes in the Mediterranean mountains.
Panagiotopoulos, K., Böhm, A., Leng, M.J., Wagner, B., Schäbitz, F. 2014. Climate variability over the last 92Ka in SW Balkans from analysis of sediments from Lake Prespa. Climate of the Past, 10, 643-660.
Journal Of Archaeological Science – May 2014
Two sets of well-preserved human footprints have been found in tufa sediments in the Cuatrociénegas Basin, NE Mexico, and here we present their U-series dates of 10.55 ± 0.03 ka and 7.24 ± 0.13 ka. The former are the oldest known footprints in Mexico, although their exact location is unknown, the latter form part of a trackway with eleven in situ human footprints. Oxygen (and to a lesser extent) carbon isotope data from the sediments suggest that the tufa with in situ footprints formed during a transition to a wetter (less arid) period, while pollen evidence indicates the basin floor presence of pecan (Carya) and willow (Salix sp.) before the onset of regional Chihuahuan Desert aridity.
These footprints confirm the presence of humans, possibly nomadic hunter–gatherer groups, which persisted until the 18th Century AD.
Feldstead, N.J., Gonzalez, S., Huddart, D., Noble, S.R., Hoffmann, D.L., Metcalfe, S.E., Leng, M.J., Albert, B.M., Pike, A.W.G., Gonzalez-Gonzalez, A., Jimenez-Lopez, J, C. 2014. Holocene-aged human footprints from the Cuatrocienegas Basin, NE Mexico. Journal of Archaeological Sciences, 42, 250-259.
Journal of Sedimentary Research – March 2014
Deep-water mudstones from ancient epicontinental settings are significant repositories for organic matter, but the detailed temporal variations of, and controls on, the abundance and type of organic matter (OM) is little studied. Using micro-petrographic and geochemical data from late Mississippian mudstones of the Widmerpool Gulf, UK, the processes that delivered fine-grained sediment to this basin during a glacioeustatic sea-level cycle are interpreted from detailed lithofacies analysis. Seven primary lithofacies are identified from core, which show specific and systematic variations in total organic carbon (TOC) content and bulk carbon isotope composition of organic material (δ13Corg). During sea-level highstands, thin-bedded carbonate-bearing mudstones are the dominant facies deposited, contain up to 6.6% TOC (average 4.6±1.3%), and have mean δ13Corg of &nda28.5±0.9‰. During phases of lower sea level, thin-bedded silt-bearing clay-rich mudstones with up to 4.1% TOC (average 2.3±0.8%; mean δ13Corg: –28.2±1.0‰) were interbedded with more organic-lean graded silt-bearing mudstones and sand-bearing silt-rich mudstones (average TOC: 1.7±0.6%) derived from turbidity currents. The latter (mean δ13Corg: –26.2±0.7‰) are closely linked to significant proportions of terrestrial plant material, while some rare plant debris- and sand-bearing mudstones produced from debris flows have more than 7.0% TOC and δ≥–26.0‰.
The δ13C values of wood fragments ranged from –27.1‰ to –24.0‰ and therefore the δ13Corg is interpreted as a function of the ratio of marine and terrestrial organic matter. More negative values in the carbonate-bearing and the clay-rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material. The data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea-level stages. Marine OM was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial OM was delivered by sediment density flows. Variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine OM. Organic-rich mudstones preserved in these marine basins are potential hydrocarbon source rocks, especially as unconventional (shale gas) reservoirs. Detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source-rock potential of basinal mudstones, and of fine-grained organic-rich sediments in general.
Konitzer, S.F., Davies, S.J., Stephensin, M.H., Leng, M.J. 2014. Depositional Controls On Mudstone Lithofacies In A Basinal Setting: Implications for the Delivery of Sedimentary Organic Matter. Journal of Sedimentary Research, 84, 198-214.
Climate of the Past – February 2014
The 74 (75) ka Toba eruption in Sumatra, Indonesia, is considered to be one of the largest volcanic events during the Quaternary. Tephra from the Toba eruption has been found in many terrestrial and marine sedimentary deposits, and acidity peaks related to the eruption have been used to synchronize ice core records from Greenland and Antarctica. Seismic profiles and sedimentological data from Lake Prespa on the Balkan Peninsula, SE Europe, indicate a lake level lowstand at 73.6 ± 7.7 ka based on ESR dating of shells. Tephrostratigraphy, radiocarbon dating and tuning of the total organic carbon content with the NGRIP isotope record, corroborate that the lake level lowstand was a short-term event superimposed on the general cooling trend at the end of MIS 5, most likely at the onset of the Greenland Stadial GS-20. Acknowledging that tectonic events or karst
processes could have triggered this lake level lowstand, the chronological correspondence between the lowstand and the Toba eruption is intriguing. Therefore a Toba-driven short-term shift to aridity in the Balkan region, leading to lake level changes and triggering spatial expansion events in one of the lake's most abundant benthic species, the carino mussel Dreissena presbensis, cannot be excluded.
Citation: Wagner, B., Leng, M. J., Wilke, T., Böhm, A., Panagiotopoulos, K., Vogel, H., Lacey, J. H., Zanchetta, G., and Sulpizio, R.: Distinct lake level lowstand in Lake Prespa (SE Europe) at the time of the 74 (75) ka Toba eruption, Clim. Past, 10, 261-267, doi:10.5194/cp-10-261-2014, 2014.
Geobiology – January 2014
Iron (Fe) oxidizing bacteria have the potential to produce morphologically unique structures that may be used as biosignatures in geological deposits. One particular example is Mariprofundus ferrooxydans, which produces extracellular twisted ribbon-like stalks consisting of ferrihydrite, co-located with organic and inorganic elements. It is currently thought that M. ferrooxydans excrete and co-precipitate polysaccharides and Fe simultaneously, however the cellular production of these polysaccharides has yet to be confirmed. Here, we report on a time series study that used scanning
transmission X-ray microscopy (STXM) and C 1s and Ca 2p near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy to investigate production of polysaccharides over the growth cycle of M. ferrooxydans.
Sarah A. Bennett, Brandy M. Toner, Roman Barco and Katrina J. Edwards. 2014. Carbon adsorption by Fe oxyhydroxide stalks produced by a lithotrophic iron-oxidizing bacteria. Geobiology DOI:10.1111/gbi.12074