Scientific Webinars

Global marine archives from the early Pleistocene suggest that glacial-interglacial cycles, and their corresponding sea-level cycles, have predominantly a periodicity of ~ 41 kyrs driven by Earth’s obliquity. However, in Taiwan, clastic shallow-marine strata from the early Pleistocene challenge the idea of a “41-kyr world”. The studied strata revealed precession-dominated sea-level fluctuations during the early Pleistocene, independent of a global ice-volume proxy. Preservation of this signal is possible due to the high-accommodation creation and high-sedimentation rate in the basin, enhancing the completeness of the stratigraphic record.

Macrofossils have the potential to provide significant sedimentological data, from aiding the interpretation of depositional settings, understanding the processes operating to concentrate fossils, palaeocurrent interpretation, to diagenetic analysis and much more. Join us to learn more about how to leverage your lamellibranchs, exploit your echinoids and generally put your palaeo to work.

Investigations of tsunami sedimentology has expanded dramatically in recent years following the devasting ‘Boxing Day’ Indian Ocean Tsunami in 2004. Tsunamis cause significant coastal erosion and can deposit sand sheets on coastal plains. In this talk we demonstrate the potential to trace tsunami sands and associated erosional scours in the shallow subsurface using ground-penetrating radar (GPR). We will include examples form the 2004 Indian Ocean Tsunami in Thailand and Indonesia as well as the Storegga tsunamis in Scotland and the Shetland Islands.

Seds Online Student Webinar (SOSW 4): Exploring sediment transport dynamics from source to sink

Presenters: Nikhil Sharma (University of Geneva), Octria Prasojo (University of Glasgow) Jing Lyu (University of Bremen) Maximilian Droellner (Curtin University)

The carbonate factories model, as defined at the beginning of this century, provides a subdivision of marine carbonate sediment production-systems based on the style of carbonate precipitation. The main factors controlling marine carbonate precipitation are light, water temperature, nutrients, salinity, substrate and carbonate saturation. Site-specific controls influencing the systems comprise ocean currents, upwelling and non-upwelling systems, ocean-atmosphere systems, atmospheric systems, shallow-water dynamics, and terrestrial sediment and water input.

The sequence stratigraphic patterns differ for the individual factories. The Tropical factory being light dependent is characterized by higher sediment production when the platform tops are flooded (highstand shedding). It displays decoupled sediment wedges with the partial infill of accommodation in the shallow-water realm and major sediment export towards the slopes and surrounding basins. The Cold-Water Coral factory is marked by in situ production and deposition with limited sediment export forming single cold-water coral spots or sediment accumulation ridges. The Cool-Water factory has a siliciclastic equivalent style of sediment distribution with lowstand-dominated, shelf edge wedges and a shaved-off shelf during sea-level highstands. Slope shedding marks the Microbial factory in which sediment production occurs within the upper slope realm of the flat-topped platforms both during highstands and lowstands in sea-level. This allows for fairly continuous sediment production exhibiting minor impact of sea-level changes, but with progradation, aggradation, and retrogradation of the system being only limited by local environmental changes. Planktic factory sediment production may vary in accordance with variations in sea-level providing time lines, systems tracts boundaries, in the pelagic realm.

In summary, each factory is branded by an individual set of features, e.g. production window, sediment production and export, morphologies and slopes. It is this unique set of variables marking each factory that determines the factory-dependent response to small-scale and large-scale environmental changes through space and time as shown in the sequence stratigraphic development.

Humans are becoming increasingly active and increasingly recognized as geomorphic agents, and a key value of Earth surface processes research is its relevance to society. As 21st century landscapes evolve at unprecedented rates, knowledge of human-landscape interactions is needed to design effective management strategies for sedimentary basins. In this talk, I present findings from sediment dating and archaeological investigations in the Mississippi Delta, USA, a delta that has experienced rapid land loss over the past century. I use these results to describe the relationship of prehistoric settlement patterns to delta evolution and offer insights into prehistoric, contemporary, and future human-landscape interactions in the Mississippi Delta and other coastal sedimentary basins.

Brine, with salinities reaching six times that of seawater, occurs as groundwater throughout the subsurface of the McMurdo Dry Valleys and the Victoria Land Basin, Antarctica. This brine, derived from seawater freezing, is responsible for widespread precipitation of calcite, dolomite and aragonite cement and alteration of skeletal grains in Cenozoic glaciomarine strata. Relationships among depth, sediment age, and cement precipitation temperature suggest that cement—and brine—likely formed during discrete periods of cooling and ice sheet expansion.

Viruses are very much in the news these days, unfortunately, but what about their geological history? Are viruses preserved in the fossil record, considering they are so small and you cant even see them ? If they are, how does that happen and how far back do they go? And what about the roles of viruses in the environment? Are they significant or were they just the nasty invisible parasites we regard them to be today, disrupting life as we know it ? Or are they both – good and bad?

Seds Online Great Debate

Topic: Autogenic Processes in Sedimentary Systems are Just Part of the allogenic spectrum

Arguing for the motion: Andre Strasser (Université de Fribourg), David De Vleeschouwer (University of Bremen)

Arguing against the motion: Sam Purkis (University of Miami), Anthony Shillito (Oxford University)

Tidal meandering channels are ubiquitous features of coastal landscapes. Their migration produces point-bar deposits characterized by inclined heterolithic stratification, fining-upward vertical trends, abundance of fine-grained sediments, and tidal rhythmites. Although these criteria are widely accepted, facies models for tidal point bars still lack a 3D perspective and overlook the along-bend variability of sedimentary processes. In this seminar, we will focus on a hypertidal point bar belonging to the upper-intertidal domain of the Mont-Saint-Michel Bay (France), and we will look at the sedimentology of a 3D time-framed accretionary package formed between 28/03/2012 and 29/11/2012. Integration between Lidar topographic time-series data, geomorphological field surveys and sedimentary-core data shows that over this time the bar expanded alternating depositional phases along its seaward and landward sides. The maximum thickness of deposits was accumulated in the bar apex zone, and just landward of it, where the largest amount of mud was also stored. High accretion rate of the bar apex zone endorsed also a better preservation of tidal rhythmites, which are almost missing from deposits accumulated along the bar sides (i.e. close to riffles). We suggest that alternating depositional loci and high sediment accretion at the bend apex zone emerge due to a combination of factors, including: i) the spatio-temporal asymmetric nature of tidal currents, which influenced deposition and preservation of flood and ebb deposits along the bend; and ii) the development of low-energy conditions at the apex due to ebb and flood flow configuration, which also promoted mud settling.