Scientific Webinars

130 years of natural and anthropogenic modifications of the Venice lagoon unravel morpho-sedimentary evolution of tidal meanders

Alvise Finotello - University of Venice

Most tidal channels in both estuarine and lagoonal environments have a tendency to meander, yet very few studies have analyzed their morphometric characteristics and morphodynamic evolution. In spite of recent breakthroughs in numerical, experimental, and field techniques, an investigation on the full spectrum of the processes controlling tidal-meander evolution remains challenging. The Venice Lagoon (Italy) offers a unique opportunity to shed light on this topic, because a long record of morphological and sedimentary data is available, which allows one to relate tidal channel evolution to the hydrodynamic and morphological changes undergone by the lagoon. In particular, during the last 130 years, feedbacks between rising relative sea levels and anthropogenic interventions have caused severe modifications of the hydrodynamics and morphology of the Lagoon. Here we investigate how these modifications fed back into the morphodynamic evolution of a meandering tidal channel located in the northern Lagoon. Combining extensive datasets of aerial photographs, topographic and bathymetric survey, geophysical investigations, sedimentary core analysis, and numerical modeling, we illustrate how changes in local hydrodynamics determined the evolution of the study channel by inducing adjustments of both its cross-sectional areas and bed morphologies, thereby ultimately impacting meander planform dynamics. We also discuss how alterations in sediment transport regime affected tidal point-bar sedimentology, and suggest that wave-enhanced concentrations of suspended sediment during slack water conditions could have hampered the formation of high-relief bedforms.

Roles of oceanography and orbital forcing in greenhouse climates

Sietske Batenburg - University of Barcelona

In climates that were warmer than at present, orbital parameters exerted a strong control on environmental conditions, which often resulted in the deposition of rhythmic sedimentary sequences. Especially in the marine realm, such successions reveal the pacing of past climates and can provide detailed time scales for climate perturbations. Ocean circulation played a major role in greenhouse climates by distributing heat and nutrients. I aim to disentangle the role of geography, for example through the opening of gateways, from the role of a warmer climate on the behaviour of ocean currents.

Discontinuity in equilibrium wave–current ripple dimensions on mixed clay-sand substrates

Xuxu Wu - University of Hull

We conducted a large-scale flume experiment to investigate combined-flow ripple development on mixed sand-clay beds. The experiment results reveal a threshold bed clay content controlling the generation of two distinct types of equilibrium ripples: large ripples are comparable with clean-sand counterparts and relatively small and flat ripples reflect strong bed cohesion preventing ripple growth. Additionally, we find clay loss at relatively deeper layer below the large equilibrium ripples due to strong clay winnowing under combined flow. This possibly reduces rippled bed stability.

Disentangling the controls and orbital pacing of South-East Atlantic carbonate deposition since the Oligocene (30-0 Ma)

Anna Joy Drury - University College London

In this study we use XRF core scanning to approximate carbonate content at Wallis Ridge in the Southeast Atlantic. We then look at how the patterns of carbonate deposition in this region have changed over the last 30 million years, and see what this record can tell us about how climate, the cryosphere and the carbon cycle interacted since the early Oligocene.

Submarine channel-lobe transition zones in an ancient passive-margin turbidite system

Lilian Navarro - Cape Breton University, University of Ottawa

Deep-water turbidite systems have been the focus of much research during several decades, particularly much work has been done on slope channels and associated levees and basin-floor depositional lobes, but with much less attention devoted to the channel to lobe transition zone (also known as CLTZ) that separates them. Based on detailed lithological and architectural analyses of an interval consisting of intercalated, sheet-like, sandstone-rich strata that transition upward to channelized sandstones bounded by mudstone-rich strata of the Neoproterozoic, passive-margin Windermere turbidite system in the southern Canadian Cordillera, this study provide new insights into the spatial and temporal development of an ancient channel-lobe system and its related CLTZ (s), which are here interpreted to be largely linked to major changes in sediment supply and related flow characteristics (such as flow efficiency, and bypassing versus depositional character).

Linking morphodynamics of deltaic distributary networks to stratigraphic connectivity of channel bodies

Elisabeth Steel - Queen’s University

In deltaic environments, distributary channel networks serve as the primary conduits for water and sediment. Once these networks are buried and translated into the subsurface, the coarse-grained channel fills serve as likely conduits for subsurface fluids such as water, oil, or gas. This talk will focus on a new method for building synthetic stratigraphy from surface imagery and will discuss how the temporal evolution of a delta topset can be used to constrain subsurface architecture.

Seds Online Student Webinar (SOSW 2): Influences of syndepositional deformation on sedimentation

Ariana Osman, Sebastian Reimann, and David Lankford-Bravo

Ariana Osman (The University of the West Indies) “The Changing Topset Regime and Clinoform Architecture on the Paleo-Orinoco Delta, Trinidad – A Story of Eustatic and Tectonic Interaction”

Sebastian Reimann (Friedrich Schiller University Jena) “Syndepositional Intrusion of the Lomati River Sill and Liked Hydrothermalism Preserves Records of One of the Earliest Benthic Ecosystems”

David Lankford-Bravo (The University of Texas at El Paso) “Investigating Permian-Aged Deposition and Deformation at the North Onion Creek Salt Shoulder”

True substrates: the inevitable preservation of ‘human timescale’ snapshots on ancient bedding planes

Neil Davies - University of Cambridge

Rock outcrops of the sedimentary-stratigraphic record often reveal bedding planes that can be considered to be true substrates: preserved surfaces that demonstrably existed at the sediment–water or sediment–air interface at the time of deposition. These surfaces have high value as repositories of palaeoenvironmental information, revealing fossilized snapshots of microscale topography from deep time. This talk will discuss ideas about how such true substrates are preserved, what they can inform us about ancient environments and stratigraphic time at outcrop, and why they seem to be so counterintuitvely abundant in the sedimentary record.

The 3D geometry of meandering channels: Implications for the stratigraphic record

Zoltan Sylvester - The University of Texas at Austin

Meandering channels are ubiquitous on the surface of the Earth, both on land and on the seafloor. Although there is a large volume of published research on meandering, relatively simple questions – like the prediction of migration rates – are still considered highly complex problems with no simple solutions. A comparison of a simple curvature-based model of meandering with measurements from rivers and submarine channels suggests that, in systems unaffected by significant variation in erodibility, migration rates can be predicted relatively well, based on channel curvature alone. Plan-view meandering patterns in nature, both fluvial and submarine, show many of the characteristics of this model: a spatial phase lag between curvature and migration that has a characteristic length and results in autogenic downstream translation of many meander bends and in deposition of counter point bars. If along-channel changes in slope are added to the model, the implications of the 3D geometry for incising and aggrading channels become obvious as well. We use open-source code to visualize the 3D geometry and temporal evolution of the deposits of both subaerial and submarine meandering flows.

Seds Online Great Debate: Sea Level Rise Drowns Reefs

Cecilia Lopez-Gamundi, Elias Samankassou, Edward Matheson, and Peter Burgess

Seds Online Great Debate

Topic: Sea Level Drowns Reefs

Arguing for the motion: Cecilia Lopez-Gamundi, Elias Samankassou

Arguing against the motion: Edward Matheson, Peter Burgess

From calcretes to travertines: are they good neighbours?

Ana María Alonso-Zarza - Director of the Geological and Mining Institute of Spain

Continental carbonates also, controversially, often referred to as ‘non-marine carbonates’ are intriguing and deserve our full attention. These land-formed carbonates contribute to our understanding of the Earth System and its imprint in the so called ‘critical zone’. Climate, biota, CO2 fluxes, parent material, aeolian dust, hydrology and even humans, interplay to form an impressive puzzle in which necessarily calcretes and travertines must be good neighbours.

What is left after tsunami disasters? – a sedimentological perspective

Witold Szczuciński - Adam Mickiewicz University

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).

The effect of stress on the acoustic properties of carbonate rocks

Bart Verberne & Conxita Taberner - Shell

Authors – Bart Verberne, Luuk Kleipool, Conxita Taberner, Arjan van der Linden, Fons Marcelis, Sander Hol and Axel Makurat
Understanding acoustic velocity variations in rocks is important for operation of hydrocarbon, geothermal, and CO2-storage reservoirs. Using a triaxial loading apparatus to simulate realistic subsurface stress conditions, we measured ultrasonic wave velocities of core plug samples composed of i) near-pure calcite limestone (bulk grain density ρg ≈2.70 gcm-3), characterized by widely varying pore types, and ii) dolostone-dominated samples which are compositionally varying (ρg = [2.66-2.80] gcm-3) but which are texturally relatively uniform. Comparison of wave velocity properties at selected key stress states revealed important differences between reservoir stress conditions versus near-isostatic conditions, and between limestone samples with different pore types.

Seds Online Student Webinar (SOSW 1): Depositional Processes in Mixed Carbonate-Siliciclastic Systems

Various

Angelo Santos (McGill University) “Facies analysis of Limbunya Group in Northern Territory, Australia: A Proterozoic cyclic carbonate and siliciclastic succession”

Yu Pei (Goettingen University) “Sedimentary factories and ecosystem change across the Permian-Triassic Critical Interval”

Hermann Rivas (Heidelberg University) “Mixed-carbonate ramps in volcanic arc settings: an example from the Lower Cretaceous of southern South America (45°S)”

Buddy Price (University of Texas at Austin) “Compounding controls on mixed carbonate-siliciclastic slope and basinal sedimentation, Delaware Basin, USA”

Early Pleistocene mud tectonics and sedimentation within mud-withdrawal basins, Bawdsey, Suffolk, UK – virtual field trip and civil engineering consequences

Gillian Apps and Frank Peel - Bureau of Economic Geology

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.

How, when and where do ocean currents control sedimentation in deep-water environments?

Elda Miramontes - University of Bremen

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.

Submarine-channel meandering and salt-basin filling

Jacob Covault - The University of Texas at Austin

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.

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

Frank Peel and Gillian Apps - Bureau of Economic Geology

3D seismic imaging of the base of the giant Bajocian Louann Salt evaporite reveals, in exquisite detail, the nature of the pre-salt landscape. An arid desert terrain contains a network of incised rivers (wadis) flowing into a large, incised, meandering river, in turn flowing into a large lake in the middle of the basin. This lake was >1km deep, and its surface was ca. 750m below Bajocian sea level. At 170MA, a connection to the Tethys Ocean was opened, and the desert basin was flooded, allowing deposition of the salt in a deep-water basin. Simple calculations indicate that salt deposition was extremely rapid, with the entire multi-km thickness of salt deposited in a few tens of thousands of years.

Investigating heterogeneous geochemistry of brines and sediments from the Salar de Llamara: A case study from a polyextreme environment

Amanda Oehlert – University of Miami

The Atacama Desert is home to a variety of extreme environments. It includes salt flats, with wide ranging age, chemistry and styles of mineral deposition. One of these extreme environments is the Salar de Llamara which contains more than 400 saline lagoons and peripheral ponds locally called “Puquios”, with a diverse range in brine chemistry and sedimentation styles which appear to result from the complex interplay between physical, chemical, and biological processes. In this talk, the major characteristics of the Puquios will be presented, and heterogeneity of lagoon chemistry and five sediment cores will be evaluated to provide insight into environmental reconstruction of extreme environments.

Late Early Jurassic environmental perturbations: a shallow-water perspective

Stéphane Bodin – Aarhus University

Neritic environments, host of the highest marine biodiversity, are particularly sensitive to environmental changes. Their study allows us to understand how carbonate-producing ecosystems cope with climatic upheavals, but also shed important light on the evolution of critical parameters such as global sea-level fluctuations during these contorted times. This presentation will focus on the late Plienbachian – early Toarcian time interval, which is marked by repeated drastic environmental changes, out of which the Toarcian OAE stands as one of the most extreme environmental change of the Mesozoic. By looking at an exceptionally preserved geological record in the Central High Atlas Basin of Morocco, the role and weight of different environmental factors (such as seawater temperature, oxygen and nutrient levels, carbonate saturation state, sea-level change, etc.) on neritic carbonate production and demise will be discussed.