Impact of Ship Traffic on the Characteristics of Shelf Sediments: An Anthropocene Prospective

Humans have been sailing across seas and oceans for thousands of years. However, the story of large ships capable of affecting coastal ecology and shelf sedimentary processes is only about 100 years old. Modern large seagoing vessels with a draft of 10–20 m can cause resuspension of seabed sediment, erosion of the channel slope and shoal, enhancement of seafloor sediment activity and thickening of the active layer, thereby having a significant impact on seabed topography and sedimentation processes. However, little is known about the effects of this anthropogenic agent on shelf sedimentation due to limited observational data. Here, two sediment cores were collected from a shipping lane used by vessels of 5,000- to 50,000-ton off the coast of China to analyze their sedimentary properties, with focus on both the grain size and elements. It was found that ship disturbance selectively modified the sedimentary record, with the fine-grained sediment becoming increasingly unstable. In addition, there was a reduction in grain size of sediment finer than 6.25 Φ, which decreased by 11% after the disturbance by ship. Biogenic elements that were closely related to the ecological environment were significantly altered, with Br/Cl, Si/Ti, and Ca/Ti ratios all becoming significantly smaller. This indicated that frequent disturbance caused by ships had reduced the productivity in the waters near the shipping lane. In terms of sensitivity to the effects of ship navigation, the sedimentation response was relatively rapid and began to emerge from the commencement of ship navigation, whereas the ecological response became evident later than the sedimentation response and only appeared after a significant growth in the maritime transportation of China. Following the comparison of the two sediment cores, we propose that the constant rate of supply (CRS- with ship disturbance)–constant initial concentration (CIC- without ship disturbance) dual dating model be used to establish a dating framework in waters frequently disturbed by ship. This type of anthropogenic sedimentary dynamic process and its sedimentary–ecological effects deserve attention on this era where there is a surge in shipping globally. Shipping lanes present an excellent area for quantitative studies on the impacts of human activity and defining the Anthropocene in the context of shipping.

The 2011 Tohoku-oki tsunami-induced sediment remobilization on the Sendai shelf, Japan, from a comparison of pre- and post-tsunami surface sediments

Tsunamis are generally considered to disturb the seafloor, rework surface sediments, and change seafloor environments. However, the response of the seafloor to such extreme wave events has not been fully elucidated. Herein, we compare the surface sediments before and after the 2011 Tohoku-oki tsunami on the Sendai shelf and demonstrate that both sandy and muddy sediments were significantly reworked on the shelf. Muddy sediments (> 10 cm thick) were redeposited as graded mud with no or little bioturbation, characterizing the offshore muddy tsunami deposit, while well-sorted sand was found as the sandy tsunami deposit. This redeposited layer could also be retained in the shelf mud sequence. The results imply that the high friction velocity of the tsunami wave and its long-term effect on Sendai Bay might contribute to the large sediment reworking. Part of the resuspended mud moved offshore to the slope area as turbidity currents. Thus, the tsunami is an important mechanism not only for shelf sedimentation but also for deep-sea sedimentation along active plate margins. The detection of 134Cs derived from the Fukushima Daiichi Nuclear Power Plant accident in the redeposited mud indicates that the suspended shelf water state was maintained for some days after the tsunami.

Shales of Palaeo-Mesoproterozoic Vindhyan Basin, central India: insight into sedimentation dynamics of Proterozoic shelf

The Vindhyan Supergroup represents the largest Proterozoic sedimentary basin fill in the Indian shield. In addition to some significant palaeobiological discoveries, the sedimentary sequence of the Vindhyan, particularly its argillaceous intervals, holds crucial information for our understanding of sedimentation dynamics in Proterozoic clastic shelves. Here we attempt an extensive, although not exhaustive, review of the physical characteristics of six argillaceous (shale) intervals (Arangi, Koldaha, Rampur, Bijaygarh, Rewa and Sirbu shale) from the Son valley sector, Vindhyan Basin, augmented with new observations to unravel the status of current understanding in terms of palaeo-flow dynamics, shelf sedimentation processes and dispersal pattern, depositional cyclicity and basinal tectonics. The sedimentary attributes of Vindhyan shales reveal their deposition largely in relative bathymetry fluctuating from distal shoreface or inner shelf (near to fair-weather wave base) to distal shelf below storm wave base. More often than not, the Vindhyan shelf was storm-infested and the operation of both storm-generated return flow and Coriolis-force-guided geostrophic currents are documented from different stratigraphic intervals of argillaceous successions. The thick arenaceous intervals interrupting the deposits of the Koldaha, Rewa and Sirbu shales at multiple stratigraphic levels indicate the presence of a fan delta and braided fluvial system during intermittent regressive stands of sea level or event deposition during a sea-level highstand, respectively. Based on facies pattern and flow vectors, a rift-related half-graben model is inferred for Arangi and Koldaha shale and a low-gradient stable-shelf model with well-defined energy gradient is proposed for successions from Rampur shale onwards.

Upper Jurassic carbonate buildups in the Miechów Trough, southern Poland – insights from seismic data interpretations

The geometry and internal architecture of the Upper Jurassic carbonate depositional system in the epicontinental basin of central and western Europe and within the northern margin of the Tethyan shelf are hitherto only partly recognized, especially in areas with thick Cretaceous and younger cover such as the Miechów Trough. In such areas, seismic data are indispensable for the analysis of a carbonate depositional system, in particular for the identification of the carbonate buildups and the enveloping strata. The study area is located in the central part of the Miechów Trough that in the Late Jurassic was situated within the transition zone between the Polish part of the central and western European epicontinental basin and the Tethys Ocean. This paper presents the results of the interpretation of 2D seismic data calibrated by deep wells that document the presence of large Upper Jurassic carbonate buildups. The lateral extent of particular structures is in the range of 400–1000 m, and their heights are in the range of 150–250 m. The interpretation of seismic data revealed that the depositional architecture of the subsurface Upper Jurassic succession in the Miechów Trough is characterized by the presence of large carbonate buildups surrounded by basinal (bedded) limestone and marly-limestone deposits. These observations are compatible with depositional characteristics of well-recognized Upper Jurassic carbonate sediments that crop out in the adjacent Kraków–Częstochowa Upland. The presented study provides new information about carbonate open-shelf sedimentation within the transition zone in the Late Jurassic, which proves the existence of a much more extensive system of organic buildups which flourished in this part of the basin. The results obtained, due to the high quality of available seismic data, also provide an excellent generic reference point for seismic studies of carbonate buildups in other basins and of different ages.

Sedimentological and physical properties of the submarine mine tailings deposit of Portmán Bay, SE Spain

<p><strong>Sedimentological and physical properties of the submarine mine tailings deposit of Portmán Bay, SE Spain</strong></p><p><strong> </strong></p><p>Andrea Baza-Varas, Jaime Frigola, Marc Cerdà-Domènech, Anna Sànchez Vidal and Miquel Canals</p><p>CRG Marine Geosciences, Dept. of Earth and Ocean Dynamics, Faculty of Earth Sciences, University of Barcelona, Spain</p><p>[email protected], [email protected], [email protected], [email protected],  [email protected]</p><p> </p><p>About 57 Mt of mine tailings were dumped directly into the sea from 1957 to 1990 as a result of the open pit exploitation of Pb and Zn ores in Sierra de Cartagena - La Unión district, SE Spain. This led to the infilling of Portmán Bay and a seaward shoreline advance of ~ 600 m associated to the development of a submarine extension of the resulting deposit. Whereas several investigations have been carried out in the emerged portion of the tailings deposit, little information exists on the dimensions and properties of its submerged portion. Nowadays, a restoration project intends to move back the shoreline by ~250 m by dredging part of the subaerial deposit.</p><p> </p><p>This contribution focuses on the sedimentological and physical properties of the materials forming the submerged deposit from where accumulation patterns could be derived. With this purpose a number of up to 4 m long gravity cores where obtained from R/V Ángeles Alvariño during the 2018 NUREIEVA-MAR1 research cruise. Subsequently, Multi Sensor Core Logger (MSCL) measurements were performed on whole and split sections in order to obtain the physical properties of the materials, namely gamma-density, magnetic susceptibility, p-wave velocity and non-contact resistivity. Furthermore, split core sections were visually described and imaged.</p><p> </p><p>This led to the identification of 4 main units in the sampled materials. From bottom to top, Unit 1 consists of light-colored, bioclast-rich fine-medium sands indicative of pre-dumping inner shelf sedimentation. Unit 2 appears only in some distal cores (~ 1.3 km from shore) collected at water depths of about 40 m and is composed of brown-dark grey silty clays with abundant black patches. All measured physical properties display low and homogeneous values. This unit could be interpreted as of transitional character in between pre-dumping conditions and the first arrival of mine waste. Unit 3 is made of highly laminated clayey silts punctuated by dark sand layers and its physical properties show generally high and oscillating values. Unit 3 corresponds to the mine tailings in stricto sensu. Finally, the upper Unit 4 is composed of bioturbated homogeneous sandy silts with generally diminishing values for most of the measured physical properties. This unit results from the reworking of materials from the top of the tailings deposits mixed with post-dumping sedimentary particles.</p><p> </p><p>The physical properties and elements measured have a diagnostic character in differentiating the mine tailings from former deposits and from materials resulting from reworking after the cessation of dumping. Our results also provide clues on the seaward extension of the mine tailings deposit as shown by its seaward thinning recorded in the investigated sediment cores, which is a consequence of increasing distance from the discharge point on the shore and of waste dispersal and accumulation patterns in the shallow marine environment.</p>

Upper Jurassic carbonate buildups in the Miechów Trough, Southern Poland – insights from seismic data interpretation

The geometry and internal architecture of the Upper Jurassic carbonate depositional system in the epicontinental basin of western and central Europe, and within the northern margin of the Tethyan shelf are hitherto only partly recognised, especially in areas with thick Cretaceous and younger cover such as the Miechów Trough. In such areas, seismic data are indispensable for analysis of a carbonate depositional system, in particular for identification of the carbonate buildups and the enveloping strata. The study area is located in the central part of the Miechów Trough that in the Late Jurassic was situated within the transition zone between the Polish part of western and central European epicontinental basin and the Tethys Ocean. This paper presents the results of interpretation of 2D seismic data calibrated by deep wells that document the presence of large Upper Jurassic carbonate buildups. The lateral extent of particular structures is in the range of 400–1000 m, and their heights are in range of 150–250 m. Interpretation of seismic data revealed that the depositional architecture of the subsurface Upper Jurassic succession in the Miechów Trough is characterised by the presence of large carbonate buildups surrounded by basinal (bedded) limestone-marly deposits. These observations are compatible with depositional characteristics of well-recognised Upper Jurassic carbonate sediments that crop out in the adjacent Kraków-Częstochowa Upland. The presented study provides new information about carbonate open shelf sedimentation within the transition zone in the Late Jurassic, which proves the existence of much more extensive system of organic buildups which flourished in this part of the basin. Obtained results, due to high quality of available seismic data, provide also an excellent generic reference point for seismic studies of carbonate buildups from other basins and of different ages.