100 research outputs found
The geochemistry and petrogenesis of the lower paleozoic granitoids of North Wales
The Lower Paleozoic rocks of North Wales are penetrated by numerous bodies of dolerite and intermediate-acid material which are closely associated with pillow basalts, acid and basic tuffs and ignimbrites. Igneous activity occurred throughout the Ordovician although in Snowdonia and Lleyn it reached a climax during the Caradoc stage. The present study has considered the granitoids of Snowdonia and Lleyn which are intruded as stocks, laccoliths and high level plugs (<5 km2) into clastic and volcaniclastic sediments.
A substantial body of new chemical data has been obtained for over thirty intrusions. Twenty-four major and trace elements were determined on each sample by X-ray fluorescence techniques and the rare earth abundances of forty-five selected samples were measured using a radiochemical neutron activation procedure.
Three distinctly different types of granitic material are recognised and their possible evolutionary mechanisms are discussed in detail. On the basis of the geochemistries of the various sampled intrusions it is concluded that they were all ultimately derived from the mantle by partial melting. One group originated from the remobilisation of calc-alkaline plutons formed by hydrous melting of the mantle wedge above a destructive plate margin. The other two groups, it is argued, evolved from tholeiitic basaltic magma by low-pressure fractional crystallisation. The goochemical affinity between some Caradocian andesitic material from Lleyn and the tonalitic-granitic intrusions of the same area has provided good evidence against a view that the latter were emplaced late in the Caledonian cycle (Silurian-Devonian).
A paleo-tectonic reconstruction of the North Wales region is presented and it is claimed that the area evolved as a volcano-tectonic rift zone, a precursor of a back-arc basin
Lake sedimentary DNA accurately records 20th Century introductions of exotic conifers in Scotland
Summary:Sedimentary DNA (sedDNA) has recently emerged as a new proxy for reconstructing past vegetation, but its taphonomy, source area and representation biases need better assessment. We investigated how sedDNA in recent sediments of two small Scottish lakes reflects a major vegetation change, using well-documented 20th Century plantations of exotic conifers as an experimental system. We used next-generation sequencing to barcode sedDNA retrieved from subrecent lake sediments. For comparison, pollen was analysed from the same samples. The sedDNA record contains 73 taxa (mainly genus or species), all but one of which are present in the study area. Pollen and sedDNA shared 35% of taxa, which partly reflects a difference in source area. More aquatic taxa were recorded in sedDNA, whereas taxa assumed to be of regional rather than local origin were recorded only as pollen. The chronology of the sediments and planting records are well aligned, and sedDNA of exotic conifers appears in high quantities with the establishment of plantations around the lakes. SedDNA recorded other changes in local vegetation that accompanied afforestation. There were no signs of DNA leaching in the sediments or DNA originating from pollen
A new Holocene record of geomagnetic secular variation from Windermere, UK
Paleomagnetic
secular
variation
(PSV)
records
serve
as
valuable
independent
stratigraphic
correlation
and
dating
tools
for
marine
and
terrestrial
sediment
sequences,
and
enhance
knowledge
of
geomagnetic
field
dynamics.
We
present
a
new
radiocarbon-dated
record
(WINPSV-12K)
of
Holocene
geomagnetic
secular
variation
from
Windermere,
updating
the
existing
1981
UK
master
PSV
curve.
Our
analyses
used
continuous
U-channel
samples
taken
from
the
center
of
four
sediment
cores
retrieved
from
Windermere
in
2012.
The
natural
remanent
magnetization
(NRM)
of
each
U-channel
was
measured
before
and
after
stepwise
alternating
field
(AF)
demagnetization
on
a
superconducting
rock
magnetometer
at
intervals
of
0.5-cm
or
1-cm.
The
NRM
data
reveal
a
stable
and
well-defined
primary
magnetization.
Component
declinations
and
inclinations
estimated
using
Principal
Component
Analysis
(PCA)
of
NRM
data
from
the
four
Windermere
cores
correlate
well
on
their
independent
radiocarbon
age
models.
The
four
records
were
stacked
using
a
sliding
window
bootstrap
method,
resulting
in
a
composite
Holocene
PSV
record
(WINPSV-12K).
On
millennial
timescales
WINPSV-12K
correlates
well
with
other
records
from
Western
Europe
and
the
northern
North
Atlantic
to
a
resolution
of
∼
1
kyr,
given
age
uncertainties
and
spatial
variability
between
records.
WINPSV-12K
also
compares
well
to
the
CALS10k.2
and
pfm9k.1a
model
predictions
for
Windermere.
Key
regionally-significant
PSV
inclination
features
of
WINPSV-12K
which
correlate
with
other
North
Atlantic
records
include
peaks
at
5–6,
8.5,
and
10 cal ka BP,
and
a
trough
at
7calkaBP.
Key
PSV
declination
features
include
the
eastward
swing
from
5.5–2.3 cal ka BP
followed
by
a
major
westward
excursion
at
2.3 cal ka BP,
peaks
at
1.1
and
7calkaBP,
and
troughs
at
5.4
and
8.2 cal ka BP,
with
the
caveat
that
an
estimated
magnetic
lock-in
delay
of
at
least
100–200 yr
is
present.
PSV
variations
on
1–3 kyr
timescales
are
interpreted
to
represent
strengthening
and
weakening
of
the
North
American
versus
the
Siberian
and
European–Mediterranean
high-latitude
flux
lobes,
based
on
the
close
similarities
between
the
North
Atlantic
regional
records
and
the
antiphase
existing
in
the
East
Asian
Stack
record
and
the
North
East
Pacific
inclination
stack.
WINPSV-12K
provides
a
regionally-important
new
PSV
reference
curve
whose
prominent
features
may
serve
as
stratigraphic
markers
for
North
Atlantic
paleo-records
Assessing the role of the "estuarine filter" for emerging contaminants : pharmaceuticals, perfluoroalkyl compounds and plasticisers in sediment cores from two contrasting systems in the southern U.K.
The environmental occurrence, fate and ecotoxicity of emerging contaminants (ECs) has been the subject of increasing research, policy and public concern over the past two decades. While a wide range of publications have examined the environmental persistence and sediment/soil interactions of ECs following their discharge into aquatic environments, the extent to which ECs are sequestered in estuarine sediments, and the impact of this on their environmental persistence and supply to the ocean, in comparison remains unclear. This Article examines the environmental concentrations of seven, relatively water-soluble and environmentally mobile, ECs (including pharmaceuticals, perfluoroalkyl compounds, and plasticisers) in dated intertidal saltmarsh cores from two contrasting estuarine sites in the southern U.K. (one heavily urbanised/industrial, the other non-urbanised). Mean sediment EC concentrations are similar in both estuarine systems (in the range 0.1 (acetaminophen) to 17 (4-hydroxyacetophenone) ng/g dry weight). Despite their variable reported Log Kow values (from ca. 0.5 to > 7), the ECs are all apparently mobile in the marsh systems studied, and where subsurface concentration maxima are present these most likely relate to local flushing or diffusive processes and cannot be clearly linked to likely input trends or changes in sediment geochemistry (including sedimentary organic carbon content). The “estuarine filter” here, at least with respect to intertidal saltmarsh sediments, shows reduced potential to sequester the seven ECs examined and mediate their supply to coastal and shelf environments
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Sediment structure and physicochemical changes following tidal inundation at a large open coast managed realignment site
Managed realignment (MR) schemes are being implemented to compensate for the loss of intertidal saltmarsh habitats by breaching flood defences and inundating the formerly defended coastal hinterland. However, studies have shown that MR sites have lower biodiversity than anticipated, which has been linked with anoxia and poor drainage resulting from compaction and the collapse of sediment pore space caused by the site's former terrestrial land use. Despite this proposed link between biodiversity and soil structure, the evolution of the sediment sub-surface following site inundation has rarely been examined, particularly over the early stages of the terrestrial to marine or estuarine transition. This paper presents a novel combination of broad- and intensive-scale analysis of the sub-surface evolution of the Medmerry Managed Realignment Site (West Sussex, UK) in the three years following site inundation. Repeated broad-scale sediment physiochemical datasets are analysed to assess the early changes in the sediment subsurface and the preservation of the former terrestrial surface, comparing four locations of different former land uses. Additionally, for two of these locations, high-intensity 3D-computed X-ray microtomography and Itrax micro-X-ray fluorescence spectrometry analyses are presented. Results provide new data on differences in sediment properties and structure related to the former land use, indicating that increased agricultural activity leads to increased compaction and reduced porosity. The presence of anoxic conditions, indicative of poor hydrological connectivity between the terrestrial and post-inundation intertidal sediment facies, was only detected at one site. This site has experienced the highest rate of accretion over the terrestrial surface (ca. 7 cm over 36 months), suggesting that poor drainage is caused by the interaction (or lack of) between sediment facies rather than the former land use. This has significant implications for the design of future MR sites in terms of preparing sites, their anticipated evolution, and the delivery of ecosystem services
Palaeoseismology from microfabric and geochemical analysis of lacustrine sediment, Windermere, UK
Lake sediments commonly contain detrital layers that record events such as floods or earthquakes but these may be disturbed or partially destroyed by bioturbation. Here we use a novel combination of techniques to relate microscopic sediment fabric features to lake-basin scale processes. X-radiography and micro-XRF of cores are complemented by backscattered electron imagery and energy dispersive X-ray microanalysis of resin-embedded sediment. Together, the microfabric and geochemical methods enable the identification of clay-layer mass transport deposits despite bioturbational mixing of the original end members. Two cores with robust radionuclide chronologies contain correlative clay layers dated to 1979 (1974–1982) and 1979–1980 (1973–1986) respectively. These clay layers likely represent the distal turbidite generated by a major mass flow deposit identified from multibeam swath bathymetry and sediment grab sampling. A likely trigger for the mass flow and associated turbidity current is the 4.7 ML 1979 Carlisle earthquake. The lake basin slope was likely preconditioned for failure by increased sedimentary biogenic gas production and sediment in-wash as a result of anthropogenic activities, coupled with sediment disruption and dredging. This study highlights the effectiveness of microstratigraphic techniques in the recognition and characterisation of event layers in sediments where bioturbative disruption has occurred
Human settlement of East Polynesia earlier, incremental, and coincident with prolonged South Pacific drought
The timing of human colonization of East Polynesia, a vast area lying between Hawai‘i, Rapa Nui, and New Zealand, is much debated and the underlying causes of this great migration have been enigmatic. Our study generates evidence for human dispersal into eastern Polynesia from islands to the west from around AD 900 and contemporaneous paleoclimate data from the likely source region. Lake cores from Atiu, Southern Cook Islands (SCIs) register evidence of pig and/or human occupation on a virgin landscape at this time, followed by changes in lake carbon around AD 1000 and significant anthropogenic disturbance from c. AD 1100. The broader paleoclimate context of these early voyages of exploration are derived from the Atiu lake core and complemented by additional lake cores from Samoa (directly west) and Vanuatu (southwest) and published hydroclimate proxies from the Society Islands (northeast) and Kiribati (north). Algal lipid and leaf wax biomarkers allow for comparisons of changing hydroclimate conditions across the region before, during, and after human arrival in the SCIs. The evidence indicates a prolonged drought in the likely western source region for these colonists, lasting c. 200 to 400 y, contemporaneous with the phasing of human dispersal into the Pacific. We propose that drying climate, coupled with documented social pressures and societal developments, instigated initial eastward exploration, resulting in SCI landfall(s) and return voyaging, with colonization a century or two later. This incremental settlement process likely involved the accumulation of critical maritime knowledge over several generations
Determination of 135Cs and 137Cs in environmental samples: A review
Radionuclides of caesium are environmentally important since they are formed as significant high yield fission products (135Cs and 137Cs) and activation products (134Cs and 136Cs) during nuclear fission. They originate from a range of nuclear activities such as weapons testing, nuclear reprocessing and nuclear fuel cycle discharges and nuclear accidents. Whilst 137Cs, 134Cs and 136Cs are routinely measurable at high sensitivity by gamma spectrometry, routine detection of long-lived 135Cs by radiometric methods is challenging. This measurement is, however, important given its significance in long-term nuclear waste storage and disposal. Furthermore, the 135Cs/137Cs ratio varies with reactor, weapon and fuel type, and accurate measurement of this ratio can therefore be used as a forensic tool in identifying the source(s) of nuclear contamination. The shorter-lived activation products 134Cs and 136Cs have a limited application but provide useful early information on fuel irradiation history and have importance in health physics.Detection of 135Cs (and 137Cs) is achievable by mass spectrometric techniques; most commonly inductively coupled plasma mass spectrometry (ICP-MS), as well as thermal ionisation (TIMS), accelerator (AMS) and resonance ionisation (RIMS) techniques. The critical issues affecting the accuracy and detection limits achievable by this technique are effective removal of barium to eliminate isobaric interferences arising from 135Ba and 137Ba, and elimination of peak tailing of stable 133Cs on 135Cs. Isobaric interferences can be removed by chemical separation, most commonly ion exchange chromatography, and/or instrumental separation using an ICP-MS equipped with a reaction cell. The removal of the peak tailing interference is dependent on the instrument used for final measurement. This review summarizes and compares the analytical procedures developed for determination of 135Cs/137Cs, with particular focus on ICP-MS detection and the methods applied to interference separation
Identification and Quantification of Radionuclides in Contaminated Drinking Waters and Pipeline Deposits
There is broad international interest, particularly with Homeland Security and first-responder organizations, in developing a range of effective, robust, and rapid analytical tools to identify terrorist assaults. Accidental or intentional radionuclide contamination of drinking water supplies would have significant public health, social, political, and financial implications even where the real risk might be small given public perception. Rapid identification and assessment of the magnitude of any contamination is critical in managing any threat and ultimately in allaying public and regulator concerns and in steering subsequent remediation operations. Conventional screening techniques do not provide information of the radionuclide present, and subsequent identification techniques are too time-consuming and require some prior knowledge of the nuclide identity to permit accurate quantification. The development described here presents a novel, rapid, and effective radiometric approach using industry-standard liquid scintillation counting equipment that can both identify and quantify alpha and beta radionuclide contamination within 1 h of sample receipt. The liquid scintillation counting (LSC) or liquid scintillation analysis (LSA) method, though widely used by the life science and the 14C scientific communities since the 1960s, has greater potential than is often used. The technique developed here, which uses multiple quench parameters for nuclide identification, has been tested on both contaminated drinking waters and pipeline scales with compositions typical of those that might be encountered. It is shown to be highly effective both in terms of rapidly identifying the radionuclide and providing a measure of the quantity of radionuclide present. The whole procedure is about to be developed into an integrated analytical system for use by untrained personnel. It is notable that the development could also be readily applied as a QC procedure in routine radioanalytical measurements
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