Scientific Webinars

The southeastern Caribbean Margin has been tectonically active throughout much of the Miocene to present with the Caribbean plate obducting the Atlantic plate to the east and obliquely colliding with the South American plate to the south. Mix in two of the largest continent-draining river systems in the world; the Orinoco and the Amazon Rivers, and you have huge sedimentation rates over-filling the basin, generating enormous mass failure, and over-pressuring the subsurface to build mountain of mud on the seafloor. All of these elements interact to produce an area of the world that is likely the most sedimentologically dynamic of anywhere on Earth. A mega-merge of ~50,000 sq km of 3D seismic data, some of which reaches nearly 20,000 m (60,000 feet) deep, is enabling us to view the seismic geomorphologic evolution of this enigmatic and energy rich province as never before. Extensional faults, mobile mud withdrawal and transtensional pull-apart processes produce enormous amounts of accommodation. This accommodation has been filled for the past 15 million years by deltaic progradation, tectonic-activity and over-accumulation triggered mass failures, and alongshore-current transported sediments. This talk will visit the processes and deposits of a basin that does not play by passive margin rules. Where leveed channels weave their way 250 km basinward through extremely complex and enormous seafloor topography to deposit in the Orinoco Fan. This region holds the entire post-Cretaceous history of the northern South American continent and new explorers are now reaching beneath the decollement of the plates (!) to search for Cretaceous age turbidite reservoirs.

Recent time-lapse bathymetric data from modern deep-water channels reveal steeper gradient steps or knickpoints that can migrate rapidly upstream at rates of 100s m to kms per year. But what sort of fingerprint might these leave in the geological record? The knickpoints can erode down metres to 10s metres and hence should exhume relative stiff substrates, they typically have a vee-shaped planform and hence should perturb the flow field of turbidity currents passing over them, and as they migrate rapidly upstream, the flow state should evolve ‘at a point’ from supercritical as the higher gradient knickpoint migrates past followed by a hydraulic jump zone and then subcritical flow. In this talk, we will review the characteristics of a range of curious small scale (10s cm) scour-and-fill structures in the axial sandy facies filling Bashkirian turbidite channels in the upper (and more proximal) Ross Sandstone Fm, western Ireland, and consider a possible link to cyclic steps and knickpoint migration.

The length and dimensions of submarine channels can rival or exceed the largest rivers on land, and they produce the largest sediment accumulations on Earth.  However, there were previously no direct flow-measurements at the end of a submarine channel in the deep-sea. This led to the assumption that sediment transport to the end of submarine channels occurred for only a small (< 0.5%) fraction of the time, via infrequent but unusually powerful and erosive ‘canyon-flushing’ flows. However, here we show the termination of the Congo Submarine Channel is active for ~15% of the time, during a 14-month period without canyon-flushing flows, with individual flows lasting for a week to a month. This is despite the channel’s termination being situated >1,000 km from shore (measured along the channel-axis) at a water-depth of ~5 km. The flux of sediment from the end of this submarine channel rivals that supplied by the Congo River to its head. Frequent, sustained and exceptionally (~100%) efficient transfer of sediment and organic carbon transfer thus occurs over extremely long distances. This leads to unusual deep-sea ecosystems, and rapid (~10 km/yr) submarine channel extension due to a previously unknown mechanism involving non-erosional mud-flows rather than coalescing erosional scours.

A turbidity current measured at the end of the Congo Canyon-Channel at 5,000m water depth and some 1,000 km from the coastline

Interpretation of past environments from carbonate rocks is a challenging endeavor. Remains of different groups, taphonomy, chemical, and physical processes all result in an integrated hodgepodge which may be interpreted in more than one way. But this ambiguity is rarely fully acknowledged or accounted for. This talk will examine the inherent non-uniqueness in carbonate facies and what we can still infer from them, nevertheless.

Dryland fluvial systems exhibit interesting sedimentary facies and the spatial extents and downstream variations in sedimentary architecture can be quantified. However, reservoir models capturing the detail and variations of these depositional systems are limited. In this webinar we will travel (virtually) to the southwestern USA to examine the Lower Jurassic Kayenta Formation and investigate how the detailed sedimentary architecture of this dryland fluvial system can affect reservoir characterisation and fluid migration for CO2 storage.

The Lower Mississippi River near Natchez, USA, has experienced a prolific series of floods over the past 15 years that have resulted in overbank sedimentation in the embanked floodplain. Analysis of overbank sediment samples following floods coupled with floodplain sediment cores indicates that depositional thicknesses, rates, grain sizes, organic carbon, and nutrient concentrations vary with sub-basin inputs, flood magnitude and duration, and historical trends associated with land-use and flood mitigation efforts.

Investigating taphonomic processes affecting calcareous remains of invertebrates near the sediment-water interface and in the mixed layer in Holocene and Anthropocene marine environments on the basis of postmortem age-frequency distributions is informative about how mixing and disintegration change downcore, how they affect preservation potential and stratigraphic resolution, and whether taphofacies can be informative about how much time do the skeletal-bearing deposits actually contain (taphonomic clock). This talk will several approaches that can be used to assess the taphonomically-active zone, with empirical examples from the northern Adriatic Sea and the southern California shelf.

Sediments have long been a source of invaluable information about the Earth’s life history. The advent of ancient sedimentary DNA has opened a new window into this history. New opportunities include tracking the distribution of specific species across time and space and reconstructing entire ecosystems dating back as far as 2 million years. Today, the field is on the cusp of taking another transformative step in studying the past —tracking evolutionary processes of a broad spectrum of organisms, from viruses and bacteria to higher plants and animals. Achieving this breakthrough depends on developing novel wet lab and computational methods. Sedimentary microfossils lie at the centre of these efforts. Diverse, abundant, and well-preserved in various depositional environments worldwide, microfossils originate from organisms across the tree of life. As such, microfossils hold the potential to provide an unprecedentedly detailed study of evolutionary histories from sediments. However, this potential comes with challenges, including the complexities of isolating microfossils from sediments at scale and efficiently retrieving their DNA. This talk will introduce the exciting opportunities and practical challenges of working with microfossil DNA, with pollen as a case study, and provide an overview of the methodological developments underway.