The challenges and opportunities of addressing particle size effects in sediment source fingerprinting: A review

publisher: Elsevier articletitle: The challenges and opportunities of addressing particle size effects in sediment source fingerprinting: A review journaltitle: Earth-Science Reviews articlelink: http://dx.doi.org/10.1016/j.earscirev.2017.04.009 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved

The implications of regional variations in rainfall for reconstructing rainfall patterns using tree rings

Haines, HA ORCiD: 0000-0003-0019-4151Copyright © 2017 John Wiley & Sons, Ltd. In Australia, multidecadal periods of floods and droughts have major economic consequences. Due to the short duration of Australian instrumental precipitation records, it is difficult to determine the patterns of these multidecadal periods. Proxy records can be used to create long-term rainfall reconstructions for regions that are lacking instrumental data. However, the spatial extent over which single-site proxy records can be applied is poorly understood. Southeast Queensland (SEQ) is an area where tree rings can be used to reconstruct long-term rainfall patterns, but their regional representation is unknown. In this study, the spatial variability in rainfall across SEQ is investigated from 1908 to 2007 using 140 instrumental rainfall stations. Pearson correlation analysis between stations is used to create groups at the r = 0.80, 0.85, and 0.90 correlation levels, and then annual deviations from the mean are determined. These patterns indicate that rainfall is not uniform across SEQ but can be broken into 2 main spatially consistent groups. Each of these groups is broken down into several subgroups with higher correlation levels. Long-term streamflow records are found to be correlated to rainfall patterns local to the streamflow stations, indicating that analysis of extreme events should consider spatial precipitation variability. Finally, the only currently available proxy rainfall reconstruction for the region, a 140-year Toona ciliata tree ring width record from Lamington National Park, is compared to rainfall groups at different correlation levels across all of SEQ. The correlation between the reconstruction and the rainfall station groupings is best for the groups within which the tree-ring record is spatially located, and this correlation improves as rainfall group correlation increases. Correlation is nearly nonexistent for groupings located at a distance from the tree-ring site. These results demonstrate the importance of assessing the spatial variability of precipitation so that the spatial applicability of proxy records can be assessed.Associated Grant Code:LP12020009

Optical dating of Holocene sediments from a variety of geomorphic settings using single grains of quartz

This paper presents an improved method for the optical dating of Holocene sediments from a variety of geomorphic settings. We have measured the equivalent dose (D-e) in individual grains of quartz, using green laser light for optical stimulation, and have simulated the D-e distributions for multiple-grain 'synthetic' aliquots using the single-grain data. For 12 samples of known (independent) age, we show that application of a 'minimum age model' to the single-grain and 'small' (10-grain) aliquot D-e data provides the most accurate estimate of the burial dose for nine of the samples examined (3 aeolian, 5 fluvial, and I marine). The weighted mean D-e (as obtained using the 'central age model') gives rise to burial age overestimates of up to a factor of 10 for these nine samples, whether single grains, small aliquots, or 'large' (100-grain) aliquots are used. For the other three samples (two aeolian and one fluvial), application of either the minimum age model or the central age model to the single-grain, small aliquot, and large aliquot D-e data yields burial ages in accord with the independent age control. We infer that these three samples were well bleached at the time of deposition. These results show that heterogeneous bleaching of the optical dating signal is commonplace in nature, and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition. We also show that grains sensitive to infrared (IR) stimulation can give rise to low D-e values, which will result in significant underestimation of the burial dose and, hence, of the age of deposition. We demonstrate that use of a modified single-aliquot regenerative-dose protocol incorporating IR stimulation prior to green light stimulation deals effectively with contamination by IR-sensitive grains. We conclude that application of the modified protocol to single grains or small aliquots of quartz, using the lowest D-e population to estimate the burial dose, is the best means of obtaining reliable ages for Holocene sediments from a wide range of depositional environments.No Full Tex

Progress towards single-grain optical dating of fossil mud-wasp nests and associated rock art in northern Australia

Here we report on investigations into optical dating of fossil mud-wasp nests as a means of constraining the ages of overlying and underlying rock paintings in northern Australia. We describe the application of a 'dual-signal' regenerative-close approach, using the easy-to-bleach ('fast') and hard-to-bleach ('slow') components of optically stimulated luminescence (OSL) emitted by individual sand-sized grains of quartz extracted from two nests: a modern nest (< 2 yr old) and a nest dated by C-14 to about 30,000 calendar years (similar to 30 ka). For the modern nest, most of the palaeodoses obtained from both the fast and slow components are consistent with a zero age, while the C-14-dated nest yielded an age of 27.1 +/- 1.5 ka from those grains that yielded concordant palaeodoses from the fast and slow components (as measured by linearly modulated OSL). Our findings indicate that a dual-signal approach permits grains that were fully bleached by sunlight at the time of nest construction, and that have since remained concealed in the light-safe 'core' of a nest. to be distinguished from (a) grains that were incompletely bleached before nest construction, and (b) grains embedded in the continuously light-exposed, exterior portion of a nest. We conclude that reliable optical ages for small mud-wasp nests associated with ancient rock art may be obtained using the dual-signal approach and the light-safe grains.No Full Tex

Wave climate, sand budget and shoreline alignment evolution of the Iluka-Woody Bay sand barrier, northern New South Wales, Australia, since 3000 yr BP

Multi-centennial fluctuations in the northern New South Wales (NSW) coastline alignment are interpreted from a detailed reconstruction of the morphological and depositional evolution of the Iluka to Woody Bay barrier during the late Holocene. The regional coastline is aligned obliquely to the south-east, inner-shelf, modal wave direction, and hence sediment is transported obliquely on the shoreface with a net northward movement. On centennial to millennial time scales, the coastline is shown to have responded to fluctuations in mean wave direction, longshore gradients in sand transport and headland sand bypassing processes. Overall, barrier progradation has been punctuated by episodes of shoreline recession and realignment throughout the late Holocene. A prolonged shoreline recessional phase occurred at ∼ 1500 yr BP in response to a rotation in modal wave direction from more southerly, towards east–south–easterly. Subsequent to this realignment, renewed shoreline progradation occurred along the east aspect coastline after ∼ 1400 yr BP whilst the north-east aspect, coastline remained in a receded alignment until after ∼ 1000 yr BP, when renewed progradation occurred. Progradation rates increased throughout the past millennium, driven by changes to the alongshore gradient in sand transport, under an implied shift to a more southerly and energetic modal wave climate. In the past 50 yrs, the north-east aspect shoreline has experienced a rapid recessional trend, which is associated with a shift in modal wave climate, to a more east–southeasterly direction, and a reduction in headland sand bypassing, The average sand supply rate to the Iluka to Woody Head section of the northern NSW shoreline is 4.1 m³/m/yr, since ∼ 3000 yr BP

Late Quaternary changes in flow-regime on the Gwydir distributive fluvial system, southeastern Australia

Ages for large palaeochannels of the Gwydir distributive fluvial system (DFS) in northern New South Wales, Australia have been determined using single grain optically stimulated luminescence. Two palaeochannel systems have been found to dominate; the here named Coocalla (43-34 ka) and Kamilaroi (19-16 ka) which have inferred palaeodischarges 25-100 times the bankfull discharges of nearby channels of the contemporary Gwydir system, which appears to have been established during the Mid-Holocene. This scale differential is very much larger than that reported for other catchments in southeastern Australia, and reflects both a decline in catchment runoff through the Last Glacial cycle and the adoption of a distributary pattern sometime after 16 ka. Actual decline in catchment runoff, determined by comparing estimated palaeodischarge with contemporary flows upstream of the DFS where flow is confined to a single channel, indicate contemporary discharge to be 0.1 times and 0.25 times that of the Coocalla and Kamilaroi, respectively. The chronology presented here shows periods of increased discharge in the Gwydir to be more or less coincident with those observed elsewhere in the Murray Darling Basin. Although no evidence of a \u27Gum Creek\u27 fluvial phase (from 35 to 25 ka) was found, the Coocalla and Kamilaroi palaeochannel systems broadly conform in age to \u27Kerarbury\u27 and \u27Yanco\u27 fluvial phases on the Murrumbidgee and Murray systems. This synchronicity with more southern catchments supports the hypothesis that La Nina - like conditions were semi-permanent for much of the Last Glacial cycle with moisture derived largely from the western Pacific Ocean

Determining sedimentation rates using 137Cs in a low fallout environment dominated by channel-and cultivation-derived sediment inputs, central Queensland, Australia

Fallout 137Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of 137Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total 137Cs inventories calculated from the detailed profile data. Information on the rates of 137Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection-diffusion model to account of 137Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for 137Cs being known and without having to assume that 137Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total 137Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, 137Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites.No Full Tex

Determining floodplain sedimentation rates using 137Cs in a low fallout environment dominated by channel- and cultivation-derived sediment inputs, central Queensland, Australia

Fallout (137)Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of (137)Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total (137)Cs inventories calculated from the detailed profile data. Information on the rates of (137)Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection-diffusion model to account of (137)Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for (137)Cs being known and without having to assume that (137)Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total (137)Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, (137)Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites.</p

Changes in the rates of floodplain and in-channel bench accretion in response to catchment disturbance, central Queensland, Australia

Analysis of the changes in rates of catchment sediment storage can provide material evidence of the impact of landscape disturbance on catchment sediment flux. A number of studies have suggested increased sediment yields from the rivers draining to the Great Barrier Reef since European settlement in the mid-nineteenth century. Many of these predictions, which indicate increases between four to ten times the pre-disturbance estimates, are based on large-scale catchment modelling that make some critical assumptions about pre-disturbance erosion rates and/or sediment delivery ratios. In addition, the majority have not been validated by empirical data. This study uses single-grain OSL dating and 137Cs depth profiles to determine pre- and post-floodplain accretion rates in Theresa Creek, a subcatchment of the dry-tropical Fitzroy River basin. We demonstrate that floodplain accretion rates have increased by three to four times since European settlement (ca. A.D. 1850). Decreased rates of floodplain accretion since the mid-twentieth century at sites contributed to by gullied terrain suggest a decrease in the supply of sediment derived from gully networks. In contrast, floodplain accretion rates from areas dominated by cultivation remain high. Widespread in-channel benches deposited since European settlement are stable and appear to be important stores of large volumes of sediment. Low magnitude increases in post-disturbance floodplain sedimentation rates (3 to 4 times), in comparison to those reported from mainly temperate climates (10 to 100 times), are attributed to the naturally high sediment loads typical of dry-tropical catchments. Consequently, previous predictions of large post-disturbance increases in sediment yields from large dry-tropical catchments draining to the Great Barrier Reef are likely to be overestimates.No Full Tex

Changes in the rates of floodplain and in-channel bench accretion in response to catchment disturbance, central Queensland, Australia

Analysis of the changes in rates of catchment sediment storage can provide material evidence of the impact of landscape disturbance on catchment sediment flux. A number of studies have suggested increased sediment yields from the rivers draining to the Great Barrier Reef since European settlement in the mid-nineteenth century. Many of these predictions, which indicate increases between four to ten times the pre-disturbance estimates, are based on large-scale catchment modelling that make some critical assumptions about pre-disturbance erosion rates and/or sediment delivery ratios. In addition, the majority have not been validated by empirical data. This study uses single-grain OSL dating and 137Cs depth profiles to determine pre- and post-floodplain accretion rates in Theresa Creek, a subcatchment of the dry-tropical Fitzroy River basin. We demonstrate that floodplain accretion rates have increased by three to four times since European settlement (ca. A.D. 1850). Decreased rates of floodplain accretion since the mid-twentieth century at sites contributed to by gullied terrain suggest a decrease in the supply of sediment derived from gully networks. In contrast, floodplain accretion rates from areas dominated by cultivation remain high. Widespread in-channel benches deposited since European settlement are stable and appear to be important stores of large volumes of sediment. Low magnitude increases in post-disturbance floodplain sedimentation rates (3 to 4 times), in comparison to those reported from mainly temperate climates (10 to 100 times), are attributed to the naturally high sediment loads typical of dry-tropical catchments. Consequently, previous predictions of large post-disturbance increases in sediment yields from large dry-tropical catchments draining to the Great Barrier Reef are likely to be overestimates