Relative sea-level cycles and organic matter accumulation in shales of the Middle and Upper Devonian Horn River Group, northeastern British Columbia, Canada: Insights into sediment flux, redox conditions, and bioproductivity

2017 ◽  
Vol 130 (5-6) ◽  
pp. 859-880 ◽  
Author(s):  
Tian Dong ◽  
Nicholas B. Harris ◽  
Korhan Ayranci
Keyword(s):  
British Columbia ◽  
Organic Matter ◽  
Sea Level ◽  
Upper Devonian ◽  
Sediment Flux ◽  
Redox Conditions ◽  
Relative Sea Level ◽  
Organic Matter Accumulation

scholarly journals New insights into organic matter accumulation from high-resolution geochemical analysis of a black shale: Middle and Upper Devonian Horn River Group, Canada

2021 ◽  
Author(s):  
Haolin Zhou ◽  
Nicholas B. Harris ◽  
Tian Dong ◽  
Korhan Ayranci ◽  
Jilu Feng ◽  
...  
Keyword(s):  
Organic Matter ◽  
High Resolution ◽  
Second Order ◽  
Upper Devonian ◽  
Redox Conditions ◽  
Geochemical Data ◽  
Third Order ◽  
Data Set ◽  
Organic Matter Accumulation ◽  
Geochemical Proxies

Organic matter (OM) accumulation in organic matter-rich mudstones, or black shales, is generally recognized to be controlled by combinations of bioproductivity, preservation, and dilution. However, specific triggers of OM deposition in these formations are commonly difficult to identify with geochemical proxies, in part because of feedbacks that cause geochemical proxies for these controls to vary synchronously. This apparent synchronicity is partly a function of sample spacing, commonly at decimeter to meter intervals, which may represent longer periods of time than is required for the development of feedbacks. Higher resolution data sets may be required to fully interpret OM accumulation. This study applies a novel combination of technologies to develop a high-resolution geochemical data set, integrating energy-dispersive X-ray fluorescence (EDXRF) and infrared imagery analyses, to record proxies for redox conditions, bioproductivity, and clastic and carbonate dilution in millimeter-resolution profiles of 133 core slabs from the Middle and Upper Devonian Horn River shale in the Western Canada Sedimentary Basin, which provides decadal-scale temporal resolution. A comparison to a more coarsely sampled data set from the same core results in substantially different interpretations of variations in bioproductivity, redox, and dilution proxies. Stratigraphic distributions of organic matter accumulation patterns (bioproductivity-control, siliciclastic/carbonate-dilution, and redox conditions-control) show that organic enrichment events were highly varied during deposition of the shale and were closely related to second- and third-order sea-level changes. High-resolution profiles indicate that bioproductivity was the predominant trigger for organic matter accumulation in a second-order highstand, particularly during deposition of third-order transgressive systems tracts. Organic matter accumulation was largely controlled by dilution from either carbonate or clastic sediments in a second-order lowstand. Bioproductivity-redox feedbacks developed on timescales of decades to centuries.

Feasibility of sedimentation strategies for the Mekong delta to counterbalance relative sea-level rise

2021 ◽  
Author(s):  
Frances E. Dunn ◽  
Philip S. J. Minderhoud
Keyword(s):  
Land Use ◽  
Sea Level Rise ◽  
Sea Level ◽  
Mekong Delta ◽  
Sediment Deposition ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Relative Sea Level ◽  
Fluvial Sediment ◽  
Relative Sea Level Rise

<p>As one of the largest deltas in the world, the Mekong delta is home to over 17 million people and supports internationally important agriculture. Recently deposited sediment compacts and causes subsidence in deltas, so they require regular sediment input to maintain elevation relative to sea level. These processes are complicated by human activities, which prevent sediment deposition indirectly through reducing fluvial sediment supply and directly through the construction of flood defence infrastructure on deltas, impeding floods which deliver sediment to the land. Additionally, anthropogenic activities increase the rate of subsidence through the extraction of groundwater and other land-use practices.</p><p>This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise.</p>

A reconnaissance survey of late Quaternary sea levels, Bella Bella/Bella Coola region, central British Columbia coast

1978 ◽  
Vol 15 (3) ◽  
pp. 341-350 ◽  
Author(s):  
J. T. Andrews ◽  
R. M. Retherford
Keyword(s):  
British Columbia ◽  
Sea Level ◽  
Late Quaternary ◽  
Middle Part ◽  
Relative Sea Level ◽  
Marine Transgression ◽  
Sea Levels ◽  
Reconnaissance Survey ◽  
Rate Of Emergence ◽  
Bella Coola

A preliminary relative sea level curve that covers the last 10 200 years is derived for the area of the islands and outer mainland centered on Bella Bella and Namu, the central coast of British Columbia. The curve shows postglacial emergence of 17 m over this period. The rate of emergence was ~0.6 m/100 year about 9000 BP, and present sea level was attained between 7000 and 8000 BP. Relative sea level continued to fall until the last few hundred to one thousand years BP when a marine transgression led to a rise of sea level and resultant erosion of many coastal Indian middens. Marine limits on the outer islands may reach 120 m asl, whereas in the middle part of the fiord country observed delta surfaces are lower (54–75 m asl). Elevations of raised deltas then attain ~150 m at fiord heads. A readvance of the ice front ≤ 12 210 ± 330 BP (GSC-1351) is suggested by the stratigraphy of one section.

scholarly journals Constraints on the Organic Matter Accumulation of Lower Cambrian Niutitang Shales in the Middle Yangtze Region, South China

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 1) ◽  
Author(s):  
Xing Niu ◽  
Yini Liu ◽  
Detian Yan ◽  
Mingyi Hu ◽  
Zixuan Liu ◽  
...  
Keyword(s):  
Organic Matter ◽  
Sea Level ◽  
South China ◽  
Primary Productivity ◽  
Lower Cambrian ◽  
Hydrothermal Activity ◽  
Oxic Condition ◽  
Organic Matter Accumulation ◽  
Niutitang Formation ◽  
And Sea Level

Abstract The lower Cambrian Niutitang shales, as one of target intervals with the greatest potential for shale gas exploration and development, have attracted much attention. Nevertheless, the organic matter enrichment mechanisms of the lower Cambrian Niutitang shales need further study, especially in the hydrothermal active zone. In this study, samples from ND1 well in western Hubei Province, middle Yangtze region, South China, were investigated for the controlling factors of organic matter accumulation of Lower Cambrian Niutitang shales by detailed petrographic, mineralogic, and geochemical proxies. The results show that hydrothermal activity and sea level fluctuation controlled the redox conditions and paleoproductivity of seawater and ultimately controlled the organic matter accumulation of Niutitang formation. In the Niu-1 member, the intense hydrothermal events lead to a suboxic to anoxic environment, which is conducive to the organic matter preservation. However, low sea level strengthens the restriction of water mass and reduced nutrient upwelling into the shelf, leading to decreased marine primary productivity, which was ultimately responsible for depleted organic matter accumulation in the Niu-1 member. In the Niu-2 member, the anoxic-euxinic environment and high paleoproductivity, driven by continuous hydrothermal activity and rising sea level, were the main factors controlling the enrichment of organic matter. In the Niu-3 member, the dysoxic to oxic condition plus low primary productivity, caused by the disappearance of hydrothermal activities and sea-level fall, resulted in the unfavorable organic matter accumulation. The results of this paper enrich the model of organic matter enrichment in the lower Cambrian black shale in the middle Yangtze region.

Relative sea-level changes and the development of a Cambrian transgression

1993 ◽  
Vol 130 (2) ◽  
pp. 245-256 ◽  
Author(s):  
T. McKie
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Sediment Yield ◽  
Sediment Flux ◽  
Sea Level Changes ◽  
Relative Sea Level ◽  
Fluvial Sediment ◽  
Accommodation Space ◽  
Condensed Section ◽  
Lower Palaeozoic

AbstractThe Lower Cambrian in northwest Scotland is one example of a Lower Palaeozoic ‘orthoquartzite-carbonate’ succession deposited on a slowly subsiding, peneplained Precambrian basement during a period of relative sea-level rise. This particular setting led to the development of a very wide, low gradient shelf which was extremely sensitive to minor sea-level changes. The basal quartz arenite section (Lower Member-Pipe Rock) is a transgressive, tide-dominated systems tract, but lacks a systematic parasequence architecture because of three factors: a fluvial sediment flux was insufficient to induce shoreline progradation, accommodation space was limited during sea-level falls (which are commonly expressed by widespread erosional surfaces), and sediment yield to the shelf by transgressive reworking was a major contributor towards the preserved stratigraphy. The storm-dominated Fucoid Beds represent a condensed section and also show the effects of rapid and widespread facies belt oscillations because of the low shelf gradient. An overlying highstand systems tract is also lacking, partly due to the absence of a large fluvial sediment yield and also due to lowstand and transgressive reworking. An erosively based tidal sandsheet at the top of the Fucoid Beds, interpreted to be a lowstand systems tract, therefore rests directly on the condensed section of the underlying sequence. This was in turn reworked into linear tidal sandbanks (Salterella Grit) during slow sea-level rise, prior to the next major transgression. The limited accommodation space therefore introduced a preservational bias towards deepening-upward trends on a parasequence and sequence scale. The oscillations in facies belts, episodic subareal exposure and the potential to remove substantial portions of systems tracts suggests that Lower Palaeozoic ‘orthoquartzite’ successions may exhibit regular and abrupt vertical shifts in depositional environment which, given their subtle lithological character, may require detailed analysis to identify. Such successions may also display incomplete development of several components of transgressive-regressive sequence architecture.

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