Scientific Webinars

Seds Online Student Webinar (SOSW 3): New insights into coastal processes from the sedimentological record

Presenters:

Liz Mahon (University of Melbourne)

Yannis Kappelmann (University of Bremen/Leibniz Centre for Tropical Marine Research)

Laura Buhrig (University of Leeds)

Kat Wilson (The University of Texas at Austin)

While ever-improving analytical techniques and the ability to absolute date diagenetic phases are driving ever more sophisticated interpretations in carbonate sedimentology, observation-based studies have also led to huge shifts in how we perceive carbonate diagenesis. We now appreciate, but have yet to fully understand, how critically important mineral transformations and translocations in marine fluids are during even very shallow burial. What controls diagenesis in shallow meteoric systems is also being revised, and there is a rapidly growing appreciation of the extent of how hypogene fluids have the ability to modify limestones even at the seismic-scale. Thus the framework in which we interpret marine, meteoric and burial carbonate diagenesis has been, and still is, undergoing a series of paradigm shifts.

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.

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.

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.

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.

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).

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.

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”