Conventional Radiography, Xeroradiography, Tomography, and Contrast Enhancement in the Study of Laminated Sediments. Preliminary Report

Koivisto, Erkki; Saarnisto, Matti

doi:10.2307/520966

Cited by 13 publications

(5 citation statements)

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“…The presence of N. Kemnitz et al: Evidence of changes in sedimentation rate fine lamination is evidence that macrofaunal activity on or in the sediment has been minimal to absent. Savrda et al (1984) documented the transition from laminated to bioturbated sediments as corresponding to a change in oxygen concentration in the bottom water, which is the chief control of benthic macrofauna presence (Levin, 2003). However, two things are necessary to produce laminated sediments.…”

Section: Introductionmentioning

confidence: 99%

Evidence of changes in sedimentation rate and sediment fabric in a low-oxygen setting: Santa Monica Basin, CA

et al. 2020

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Abstract. The Southern California Bight is adjacent to one of the world's largest urban areas, Los Angeles. As a consequence, anthropogenic impacts could disrupt local marine ecosystems due to municipal and industrial waste discharge, pollution, flood control measures, and global warming. Santa Monica Basin (SMB), due to its unique setting in a low-oxygen and high-sedimentation environment, can provide an excellent sedimentary paleorecord of these anthropogenic changes. This study examined 10 sediment cores, collected from different parts of the SMB between spring and summer 2016, and compared them to existing cores in order to document changes in sedimentary dynamics during the last 250 years, with an emphasis on the last 40 years. The 210Pb-based mass accumulation rates (MARs) for the deepest and lowest oxygen-containing parts of the SMB basin (900–910 m) have been remarkably consistent during the past century, averaging 17.1±0.6 mg cm−2 yr−1. At slightly shallower sites (870–900 m), accumulation rates showed more variation but yield the same accumulation rate, 17.9±1.9 mg cm−2 yr−1. Excess 210Pb sedimentation rates were consistent with rates established using bomb test 137Cs profiles. We also examined 14C profiles from two cores collected in the deepest part of the SMB, where fine laminations are present up to about 450 yr BP. These data indicate that the MAR was slower prior to ∼1900 CE (rates obtained were 9 and 12 mg cm−2 yr−1). The δ13Corg profiles show a relatively constant value where laminations are present, suggesting that the change in sediment accumulation rate is not accompanied by a change in organic carbon sources to the basin. The increase in sedimentation rate towards the Recent occurs at about the time previous studies predicted an increase in siltation and the demise of a shelly shelf benthic fauna on the SMB shelf. X-radiographs show finely laminated sediments in the deepest part of the basin only, with centimeter-scale layering of sediments or no layering whatsoever in shallower parts of the SMB basin. The absence of finely laminated sediments in cores MUC 10 (893 m) and MUC 3 (777 m) suggests that the rate at which anoxia is spreading has not increased appreciably since cores were last analyzed in the 1980s. Based on core top data collected during the past half century, sedimentary dynamics within SMB have changed minimally during the last 40 years. Specifically, mass accumulation rates, laminated sediment fabric, extent of bioturbation and % Corg have not changed. The only parameter that appeared to have changed in the last 450 years was the MAR, with an apparent > 50 % increase occurring between ∼1850 CE and the early 1900s. The post-1900 CE constancy of sedimentation through a period of massive urbanization in Los Angeles is surprising.

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Section: Introductionmentioning

confidence: 99%

Evidence of changes in sedimentation rate and sediment fabric in a low-oxygen setting: Santa Monica Basin, CA

et al. 2020

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“…Kodak NMB film was used with an exposure of 35 kV and 250 mAs and a focus-film distance of 75 cm (cf. Koivisto & Saarnisto 1978). The radiograph is shown in Fig.…”

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Composition and formation of laminated sediments in Diss Mere, Norfolk, England

Peglar

Fritz

Alapieti

et al. 1984

Boreas

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The chemical and biological composition of laminated lake‐sediments deposited between about 2,500 and 5,500 years B.P. in Diss Mere, Norfolk, England is described. The distribution of Ca, Fe, S, and Si in pale and dark laminae is established by energy‐dispersive X‐ray microanalysis. The pale laminae consist primarily of calcium carbonate and the dark layers contain mainly Fe, S, Si, and dark organic material. The diatom composition of 16 individual light and dark laminae shows no consistent differences between light and dark layers. There are, however, higher frequencies of chrysophycean cysts in seven of the eight dark layers, suggesting these layers were deposited in late summer or fall. Pollen analyses of the pale and dark layers show that pollen percentages of early‐flowering trees and shrubs are highest in the dark laminae and that pollen values of late‐flowering plants are highest in the pale layers. The biological data indicate that the pale layers were formed in the late spring and early summer, whereas the dark laminae were deposited in late summer, fall, winter, and the early spring. Seasonal supply of CaCO3 was the major variable responsible for couplet formation.

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“…It enables the documentation of ne-scale variations in the sediment structure (e.g. Koivisto & Saarnisto 1978;Axelsson 1983;Saarinen & Saarnisto 1998). As expressed by Axelsson (1983), the method is 'a fast, non-destructive scanning and recording technique, which may reveal sediment structures that are not revealed by other methods of analysis'.…”

Section: X-ray Densitometrymentioning

confidence: 99%

Comparing X‐ray densitometry and BSE‐image analysis of thin section in varved sediments

Ojala¹,

Francus²

2002

Boreas

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Francus, P. 2002 (March): Comparing X-ray densitometr y and BSE-image analysis of thin section in varved sediments. Boreas, Vol. 31, pp. 57-64. Oslo. ISSN 0300-9483 .A 10-cm long section from varved sequence of Lake Nautajärvi, Finland, has been analysed using both X-ray densitometr y and image analysis of Backscattered Scanning Electron microscope Images (BSEI) of thin sections. Lake Nautajärvi's clastic-organi c varves appear in X-ray images as a successio n of dark and pale stripes, pale ones being the spring detrital minerogeni c layers and dark ones organic matter laid down during the time of summer, autumn and winter ice cover. Owing to the sharp contrast of the minerogeni c spring layer, a semiautomatic tree-ring width and density measurement DendroScan system was applied to obtain seasonal /annual data of relative X-ray density. Mean density of BSEI was also acquired . Then BSEI were processe d to produce black and white images, where white pixels represent the clay-rich sedimentar y matrix and black pixels the particles in the matrix: silt-or sand-sized , terrigenou s grains, authigenic particles and diatoms. Measurements of the size of the detrital particles forming the varves were obtained. For each varve, mean grey-level values in BSEI correlate d well with the mean grey-level values of X-ray images, but grain size obtained on BSEI did not correlate with any parameters computed from X-ray radiography .

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Conventional Radiography, Xeroradiography, Tomography, and Contrast Enhancement in the Study of Laminated Sediments. Preliminary Report

Cited by 13 publications

References 0 publications

Evidence of changes in sedimentation rate and sediment fabric in a low-oxygen setting: Santa Monica Basin, CA

Evidence of changes in sedimentation rate and sediment fabric in a low-oxygen setting: Santa Monica Basin, CA

Composition and formation of laminated sediments in Diss Mere, Norfolk, England

Comparing X‐ray densitometry and BSE‐image analysis of thin section in varved sediments

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