A Jurassic Lost World: seismic imaging of the drowned topography at the base of the Louann Salt (Gulf of Mexico) reveals how the evaporite giant was deposited
28/04/2021 4:00 pm (London)
Submarine-channel meandering and salt-basin filling
05/05/2021 4:00 pm (London)
Many continental margins show submarine-channel patterns that resemble meandering rivers on land. How exactly do submarine channels evolve and disperse sediment and dissolved loads throughout the ocean? Do submarine channels migrate in a way that is similar to rivers? Whereas platforms like Google Earth Engine have enabled broadly accessible, global-scale analysis of rivers in Landsat imagery, this is difficult to do underwater. We used 3D seismic-reflection data to interpret the evolution of some of the largest submarine-channel systems ever recorded offshore Brazil. The margin offshore Brazil has complex topography, with many salt domes that have steered and deflected the submarine channels since the Cretaceous. We applied our experience in mapping and interpreting the time-lapse evolution of rivers in Landsat data to analyze the evolution of the submarine channels offshore Brazil. Our results show that early during the evolution of the submarine channel it migrated like a freely meandering river. However, as the submarine channel expanded toward nearby salt domes, its migration pattern fundamentally changed. With nowhere to expand further, the submarine channel translated downstream to produce a pattern characteristic in rivers that are confined by banks resistant to erosion.
How, when and where do ocean currents control sedimentation in deep-water environments?
19/05/2021 4:00 pm (London)
Ocean currents play an important role in transporting sediment in deep-water settings. The sedimentary deposits generated by oceanic circulation, i.e. contourites, are common morphological features along continental margins where currents encounter the seafloor. Despite their importance and increasingly recognised ubiquitous occurrence worldwide (even in lakes), the link between oceanographic processes and contourite features is poorly constrained. In this talk I will present and discuss what is known and not known about the oceanographic processes that control sedimentation in deep-marine systems.
Early Pleistocene mud tectonics and sedimentation within mud-withdrawal basins, Bawdsey, Suffolk, UK – virtual field trip and civil engineering consequences
26/05/2021 4:00 pm (London)
Deposition of basal Pleistocene, warm-water clastics (Red Crag) on top of Paleocene-Eocene marine mudrocks (London Clay s.l.) triggered a phase of intense syndepositional mud tectonics. The Red Crag was deposited in subsiding mud-withdrawal basins, separated by rising mud diapirs and mud ridges. Mud deformation ranged from plastic flow to liquefied flow, with extrusion of allochthonous mud sheets. Tidal bedforms in the Red Crag allow us to estimate the duration of deposition and mud mobilization. As the mud dewatered, upward water flow though the Red Crag changed the color of the clastic sediments, revealing the geometry of the fluid-escape pathways, with narrow conduits feeding up into surface blow-out craters. The deformation has previously been interpreted as a later, postdepositional, process during the subsequent periods of glaciation (cryoturbation), but it is clearly syndepositional with the non-glacial Red Crag. This may have important consequences for civil engineering, because it indicates that this level of the London Clay s.l. has been prone to catastrophic failure and even liquefaction (akin to catastrophic quick clay failures of coastal Scandinavia) in conditions similar to the present day. However, large engineering projects on the same substrate (offshore windfarms, nuclear power stations, etc.) have been constructed on the assumption that the mud deformation is a product of glacial conditions.
09/06/2021 4:00 pm (London)
What is left after tsunami disasters? – a sedimentological perspective
16/06/2021 4:00 pm (London)
During the two decades, tsunamis have appeared to be the most disastrous natural process worldwide. The dramatic, large tsunamis on Boxing Day, 2004 in the Indian Ocean and on March 11, 2011 offshore Japan caused catastrophes listed as the worst in terms of the number of victims and the economic losses, respectively. In the aftermath, they have become a topic of high public and scientific interest. The record of past tsunamis, mainly in form of tsunami deposits, is often the only way to identify tsunami risk at a particular coast due to the relatively low frequency of their occurrence. The identification of paleotsunami deposits is often difficult mainly because the tsunami deposits are represented by various sediment types, may be similar to storm deposits, or altered by post-depositional processes. There is no simple universal diagnostic set of criteria that can be applied to interpret tsunami deposits with certainty. Thus, there is a need to develop new methods, which would enhance the ’classical’, mainly sedimentological and stratigraphic approach. During the talk I would like to present the need for geological studies of tsunami deposits, the examples of tsunami deposits (mainly from my own studies of 2004 tsunami in Thailand, 2011 tsunami in Japan, 2000 tsunami in Greenland) and their postdepositional changes, as well as I am going to outline recent progress and application of new approaches (e.g. paleogenetics).