High frequency un-mixing of soil samples using a submerged spectrophotometer in a laboratory setting—implications for sediment fingerprinting

Purpose This study tests the feasibility of using a submersible spectrophotometer as a novel method to trace and apportion suspended sediment sources in situ and at high temporal frequency. Methods Laboratory experiments were designed to identify how absorbance at different wavelengths can be used to un-mix artificial mixtures of soil samples (i.e. sediment sources). The experiment consists of a tank containing 40 L of water, to which the soil samples and soil mixtures of known proportions were added in suspension. Absorbance measurements made using the submersible spectrophotometer were used to elucidate: (i) the effects of concentrations on absorbance, (ii) the relationship between absorbance and particle size and (iii) the linear additivity of absorbance as a prerequisite for un-mixing. Results The observed relationships between soil sample concentrations and absorbance in the ultraviolet visible (UV–VIS) wavelength range (200–730 nm) indicated that differences in absorbance patterns are caused by soil-specific properties and particle size. Absorbance was found to be linearly additive and could be used to predict the known soil sample proportions in mixtures using the MixSIAR Bayesian tracer mixing model. Model results indicate that dominant contributions to mixtures containing two and three soil samples could be predicted well, whilst accuracy for four-soil sample mixtures was lower (with respective mean absolute errors of 15.4%, 12.9% and 17.0%). Conclusion The results demonstrate the potential for using in situ submersible spectrophotometer sensors to trace suspended sediment sources at high temporal frequency.

Some Aspects of Sedimentology of the Wanganui Basin, North Island, New Zealand

<p>The thesis comprises studies of the marine Pleistocene sediments of the Wanganui Basin, North Island, New Zealand. Part I deals with the chronology of the sediments and correlation of horizons within and outside the basin, by dating glass shards from tephra horizons using the fission-track method. Correlation to similar tephras from Hawke's Bay, to deep-sea cores taken 1000km east of New Zealand and to the central North Island volcanic district is attempted. These fission-track ages fill a dating gap that previously existed in the New Zealand marine Quaternary sequence. Thirteen tephras were examined in the Wanganui Basin and were found to range in age from 1.50 [plus or minus] 0.21m.y.B.P. (Ohingaiti Ash) to 0.28 [plus or minus] 0.05m.y.B.P. (uppermost Finnis Road Ash). These tephras record major rhyolitic eruptive phases in the central volcanic region. The most significant eruptive phase began 1.06 [plus or minus]0.16m.y.B.P. with the deposition of the Makirikiri Tuff sediments, continued to 0.88 [plus or minus]0.13m.y.B.P. and is tentatively associated with the older ignimbrites of the King Country, west of Lake Taupe. A volcanically quiet period followed when no volcanic glass was deposited in the sediments, until 0.74 [plus or minus] 0.09m.y.B.P. Several large eruptions then occurred between 0.74 and 0.28m.y.B.P. The age of the Plio-Pleistocene boundary, at the base of the Hautawan Stage in the Wanganui Basin is 1.87m.y.B.P. The age of the base of the Nukumaruan is 1.55m.y.B.P., the Okehuan, 1.06m.y.B.P., the Castleclifflan 0.45m.y.B.P., and the Hawera Series is less than 0.38m.y.B.P. Palaeomagnetic stratigraphy was determined for the upper Nukumaruan and lower Okehan sequence in the Rangitikei River. Viscous components of magnetism were removed from the samples by thermal demagnetising, extreme care being needed to obtain consistent results. Independent dates from the palaeomagnetic stratigraphy substantially confirm the fission-track dates. The Bruhnes-Matuyama boundary is clearly defined between the Rewa and Potaka Pumice Members (aged 0.74 and 0.61m.y.B.P. respectively) of the Kaimatira Pumice Send Formation. The Jaramillo event was not recognised and is probably represented in part of the sequence where sediments are too coarse and friable to yield palaeomagnetic cores. Part II deals with the detailed sedimentology of the lower Okehuan Stage sequence which is composed of two volcaniclastic formations, the Makirikiri Tuff and Kaimatira Pubmice Sand, separated by a non-volcaniclastic siltstone formation, the Okehu Siltstone. Interpretations of the Sedimentary structures in the Makirikiri Tuff and the Kaimatira Pumice Sand Formation confirm previous conclusions of shallow water deposition based on palaeontological evidence. Some structures also indicate the high rate of sediment accumulation during deposition of the volcancic sediments. Size analysis statistics show influence of source material and processes acting on the sediment during transport and deposition. Rapid sediment accumulation is emphasised by poor sorting, and processed inferred from the sedimentary structures are confirmed by the grain size analyses of the same structures. Analysis of the attitude of large and small scale cross-stratification reveals a complex polymodal palaeocurrent pattern, as might be expected of shallow water to intertidal sequences. Although often bipolar-bimodal, the dominant sediment transport appears to have been from west to east, similar to the direction of current movement along the Wanganui coast today. Size and petrography of clasts from the conglomeratic horizons indicated sediment sources both from the central volcanic region of North Island and from the Mesozoic "greywackes" of the axial mountain ranges which were emergent and probably significantly elevated at the time when the sediments were accumulating. No volcanic debris was deposited with the Okehu Siltstone. The mineralogy of the sands points to the same sediment sources but also indicates that some metamorphic material was being introduced most likely from South Island. Part III of the thesis represents a pilot study undertaken to determine whether isotopic differences in fossil shell composition could be used to distinguish shells that grew in fully marine water from those that grew in less saline conditions. Carbon and oxygen isotope ratios were determined on shells from three formations whose environments had been adequately studied by paleontologists. The horisons chosen were the Waipuru Shellbed, the Tewkesbury Formation and the Tainui Shellbed. Agreement with the palaeontological evidence and thus distinction between the fully marine and the fresh water contaminated marine environments was possible with the technique.</p>

Some Aspects of Sedimentology of the Wanganui Basin, North Island, New Zealand

<p>The thesis comprises studies of the marine Pleistocene sediments of the Wanganui Basin, North Island, New Zealand. Part I deals with the chronology of the sediments and correlation of horizons within and outside the basin, by dating glass shards from tephra horizons using the fission-track method. Correlation to similar tephras from Hawke's Bay, to deep-sea cores taken 1000km east of New Zealand and to the central North Island volcanic district is attempted. These fission-track ages fill a dating gap that previously existed in the New Zealand marine Quaternary sequence. Thirteen tephras were examined in the Wanganui Basin and were found to range in age from 1.50 [plus or minus] 0.21m.y.B.P. (Ohingaiti Ash) to 0.28 [plus or minus] 0.05m.y.B.P. (uppermost Finnis Road Ash). These tephras record major rhyolitic eruptive phases in the central volcanic region. The most significant eruptive phase began 1.06 [plus or minus]0.16m.y.B.P. with the deposition of the Makirikiri Tuff sediments, continued to 0.88 [plus or minus]0.13m.y.B.P. and is tentatively associated with the older ignimbrites of the King Country, west of Lake Taupe. A volcanically quiet period followed when no volcanic glass was deposited in the sediments, until 0.74 [plus or minus] 0.09m.y.B.P. Several large eruptions then occurred between 0.74 and 0.28m.y.B.P. The age of the Plio-Pleistocene boundary, at the base of the Hautawan Stage in the Wanganui Basin is 1.87m.y.B.P. The age of the base of the Nukumaruan is 1.55m.y.B.P., the Okehuan, 1.06m.y.B.P., the Castleclifflan 0.45m.y.B.P., and the Hawera Series is less than 0.38m.y.B.P. Palaeomagnetic stratigraphy was determined for the upper Nukumaruan and lower Okehan sequence in the Rangitikei River. Viscous components of magnetism were removed from the samples by thermal demagnetising, extreme care being needed to obtain consistent results. Independent dates from the palaeomagnetic stratigraphy substantially confirm the fission-track dates. The Bruhnes-Matuyama boundary is clearly defined between the Rewa and Potaka Pumice Members (aged 0.74 and 0.61m.y.B.P. respectively) of the Kaimatira Pumice Send Formation. The Jaramillo event was not recognised and is probably represented in part of the sequence where sediments are too coarse and friable to yield palaeomagnetic cores. Part II deals with the detailed sedimentology of the lower Okehuan Stage sequence which is composed of two volcaniclastic formations, the Makirikiri Tuff and Kaimatira Pubmice Sand, separated by a non-volcaniclastic siltstone formation, the Okehu Siltstone. Interpretations of the Sedimentary structures in the Makirikiri Tuff and the Kaimatira Pumice Sand Formation confirm previous conclusions of shallow water deposition based on palaeontological evidence. Some structures also indicate the high rate of sediment accumulation during deposition of the volcancic sediments. Size analysis statistics show influence of source material and processes acting on the sediment during transport and deposition. Rapid sediment accumulation is emphasised by poor sorting, and processed inferred from the sedimentary structures are confirmed by the grain size analyses of the same structures. Analysis of the attitude of large and small scale cross-stratification reveals a complex polymodal palaeocurrent pattern, as might be expected of shallow water to intertidal sequences. Although often bipolar-bimodal, the dominant sediment transport appears to have been from west to east, similar to the direction of current movement along the Wanganui coast today. Size and petrography of clasts from the conglomeratic horizons indicated sediment sources both from the central volcanic region of North Island and from the Mesozoic "greywackes" of the axial mountain ranges which were emergent and probably significantly elevated at the time when the sediments were accumulating. No volcanic debris was deposited with the Okehu Siltstone. The mineralogy of the sands points to the same sediment sources but also indicates that some metamorphic material was being introduced most likely from South Island. Part III of the thesis represents a pilot study undertaken to determine whether isotopic differences in fossil shell composition could be used to distinguish shells that grew in fully marine water from those that grew in less saline conditions. Carbon and oxygen isotope ratios were determined on shells from three formations whose environments had been adequately studied by paleontologists. The horisons chosen were the Waipuru Shellbed, the Tewkesbury Formation and the Tainui Shellbed. Agreement with the palaeontological evidence and thus distinction between the fully marine and the fresh water contaminated marine environments was possible with the technique.</p>

Supplemental Material: Detrital zircon geothermochronology reveals pre-Alleghanian exhumation of regional Mississippian sediment sources in the southern Appalachian Valley and Ridge Province

<div>Figure 4 is interactive. Hover over each sample set (right) to see stacked on composition-age fields (left) (A) 250–500 Ma and (B) 800– 1200 Ma. Layers may be viewed separately or in combination using the capabilities of the Acrobat (PDF) layering function (click “Layers” icon along vertical bar on left side of window for display of available layers; turn layers on or off by clicking the box to the left of the layer name). Figure 5 is interactive. Hover over the Th/U>75 (black-red) box and Th/U<75 (green) box in the lower part of the figure to view subset KDEs of each sample. Layers may be viewed separately or in combination using the capabilities of the Acrobat (PDF) layering function (click “Layers” icon along vertical bar on left side of window for display of available layers; turn layers on or off by clicking the box to the left of the layer name).<br></div>

Supplemental Material: Detrital zircon geothermochronology reveals pre-Alleghanian exhumation of regional Mississippian sediment sources in the southern Appalachian Valley and Ridge Province

<div>Figure 4 is interactive. Hover over each sample set (right) to see stacked on composition-age fields (left) (A) 250–500 Ma and (B) 800– 1200 Ma. Layers may be viewed separately or in combination using the capabilities of the Acrobat (PDF) layering function (click “Layers” icon along vertical bar on left side of window for display of available layers; turn layers on or off by clicking the box to the left of the layer name). Figure 5 is interactive. Hover over the Th/U>75 (black-red) box and Th/U<75 (green) box in the lower part of the figure to view subset KDEs of each sample. Layers may be viewed separately or in combination using the capabilities of the Acrobat (PDF) layering function (click “Layers” icon along vertical bar on left side of window for display of available layers; turn layers on or off by clicking the box to the left of the layer name).<br></div>

Application of environmental magnetism to trace sediment sources contributing to Kruger National Park reservoirs

Sediment source fingerprinting using environmental magnetism has successfully differentiated between sediment sources in different regions of South Africa. The method was applied in the natural landscape of the Kruger National Park to trace sediment sources delivered to four reservoirs (Hartbeesfontein, Marheya, Nhlanganzwani, Silolweni) whose contributing catchments were underlain by a range of igneous, metamorphic, and sedimentary rocks. This research attempted to evaluate the impact of vegetation, lithology, and particle size controls on the ability of magnetic signatures to discriminate between lithology-defined potential sources. Potential source samples were collected from each lithology present in all catchments, except for the Lugmag catchment where the lithology was uniform, but the vegetation type varied significantly between woodland and grassland. One sediment core was taken in each of the four catchment reservoirs where there was more than one lithology present in order to unmix and apportion contributing sediment sources. Sampling time in the field was often restricted to short periods, dependent on anti-poaching activities and movement of free-roaming wildlife across the Park. This occasionally led to the sub-optimal collection of enough source samples to capture source signature variability. Mineral magnetic parameters were unable to discriminate between vegetation-defined sediment sources in the Lugmag catchment (homogenous underlying lithology) but were able to discriminate between lithology-defined sediment sources (to varying degrees) in the other four catchments. The contributions of each lithology-defined sediment source were estimated using a straightforward statistical protocol frequently used in published literature that included a Mann-Whitney U or Kruskal-Wallis H test, mass conservation test, discriminant function analysis, and an (un)mixing model. A contribution from each lithology source to reservoir sediment was estimated. Connectivity was a significant factor in understanding erosion in each of the catchments. Both longitudinal (e.g., drainage density) and lateral connectivity (e.g., floodplain - river) were important. Travel distance of eroded sediment to reservoirs was also an essential element in two of the four catchments. There are no defined floodplains, so channel bank soils are very similar to the catchment soils. Therefore, channel bank storage potential would be similar to the storage potential within the catchment. Vegetation played a crucial role in protecting soils, by reducing ii erosion potential as well as trapping and storing sediment, thereby interrupting lateral connectivity. Underlying geology and soils are determining factors of vegetation type and density. A published study estimated catchment area-specific sediment yields for different KNP catchments, including the Hartbeesfontein, Marheya, Nhlanganzwani and Silolweni catchments. The published data was used in combination with the (un)mixing model source contribution estimates of this thesis to determine specific sediment yields by lithology, i.e., for each catchment source. The polymodal particle size characteristics of the sample material led to an investigation into particle size controls on the ability of magnetic signatures to discriminate between potential sources. Due to time constraints, only the Hartbeesfontein and Marheya catchments were tested for grain size differences. For each catchment, one bulk sample was created for each lithology source. This bulk sample was divided into 10 subsamples. The samples were then fractionated into four particle size fraction groups: coarse (250 – 500 μm), medium (125 – 250 μm), fine (63 – 125 μm), and very fine (<63 μm). Reservoir samples were also bulked to create 10 down-core samples for each reservoir, and the samples were also fractionated into the four fraction groups. The same statistical protocol was applied to the fractionated samples and contribution estimates were obtained by lithology for each particle size fraction group. The goodness of fit and uncertainty of the (un)mixing model varied in each catchment, with the two measures of accuracy often showing an inverse relationship. The fractionated modelling estimated the same primary source in the two catchments as in the unfractionated modelling. However, additional information on the secondary and tertiary sources was obtained. Connectivity remained a significant factor in interpreting the results of the fractionated analysis. Specific sediment yields were estimated for each catchment source per particle size fraction group. These sediment yields provided a deeper understanding of sediment transport through a catchment and which particle size groups are most important in catchment erosion. An original contribution to research was made by estimating source contribution estimates for the four reservoirs, quantifying sediment yields for each catchment lithology and then for each catchment lithology by particle size. Mineral magnetic tracing of the catchments was applied for the first time in this region of South Africa.