Scientific Webinars

Coralline algae are one of the most common carbonate producers in shelf environment, occurring from the poles to the equator and from the intertidal zone to the lowest limit of the photic zone. Notwithstanding their abundance (and several attempts throughout the years), they remain a relatively underused instrument for studying shallow water limestones. This is mainly caused by the complicated and ever shifting taxonomy and by the inherent difficulties in dealing with a macroscopic object which requires a microscope for proper identification. This talk aims at providing a couple of useful and time-effective strategies to use coralline algae for paleoenvironmental reconstructions focusing on the Miocene, an epoch where these carbonate producers are particularly widespread and common.

Organisms can produce minerals with highly controlled crystallographic texture, either as a necessity resulting from growth mechanism, or to achieve desired material properties. But they will not shy away from abiotic mechanisms of crystal formation when they can exploit them. What is more, the crystallographic texture of originally highly-controlled biominerals can be altered by diagenesis. As a result, instead of a clearly defined biologically controlled and abiotic minerals, there is a spectrum of textures occurring in nature. In deep-time marine minerals, the crystallographic properties and their preservation may be the key to identifying the biotic origin of a structure and even its biological affinity (microbial or metazoan). This talk will provide a short overview of Electron Backscatter Diffraction and its use in studying fossil carbonates and phosphates, including sample preparation and data analyses important in resolving the processes of their formation.

Tide-dominated and tide-influenced systems have been investigated for several decades, attracting the interest of many sedimentologists; nonetheless, these depositional systems remain poorly understood compared to their fluvial-dominated and wave-dominated counterparts. Interpreted tide-dominated successions show mismatches with their modern analogues when comparing grainsize, architectural elements, unit thicknesses and others. Sedimentary structures considered as “tidal indicators” can also commonly be found in non-tidal environments. Yet, they are often used as the only tool to infer a tidal origin for ancient systems, driving the development of (misleading) conceptual and applied models. During this seminar, I will show some examples of modern and ancient tidal systems, discussing some of the problems related to their investigation.

Bedforms and their primary current stratification are used routinely as indicator of flow type and flow strength. It has recently been advocated that sole marks could be used in a similar way, particularly for depositional, non-bypassing, flows. This presentation reveals, for the first time, that predictable relationships exist between sole mark type and size, flow type, deposit type, and depositional environment, based on field data from the Aberystwyth Grits Group (Silurian, West Wales, U.K.)

Along-slope bottom currents, and associated oceanographic processes, can trigger large- and small-scale deep-water processes that interact with other hemipelagic and gravitational processes, generating Contourites and Mixed (or Hybrid?) Depositional Systems, depending on the relative contribution of each type of process behind the scenes. The very recent explosion of examples described in either academic or industry research on the deep-marine sedimentation has no doubt contributed to a better understanding of these systems. New models are being proposed and there is a growing interest in these systems, in their origins, their deposits and evolution, their relationship with deep-sea ecosystems, geological hazard, and even their economic potential. Nevertheless, we lack some essential knowledge about their genetics, interrelations and evolution over time. This talk is intended to present the basic (confirmed or proposed) concepts regarding Contourite and Mixed Depositional Systems, offering examples from modern oceans and ancient records, from 2D and 3D seismic scales to the sedimentary facies scale, highlighting the role of bottom currents in shaping the sea-floor and controlling the sedimentary stacking patterns of deep-water sedimentary successions. Future considerations are then put forth, so that the newly enlightened audience, especially students and young researchers, may more readily to “go with the flow”.

Aeolian sedimentary systems are sensitive to changes in multiple environmental variables, including climate, sea level, sediment supply and tectonic controls. As such, the preserved sedimentary deposits of aeolian dune fields record a fingerprint of past environmental change. A combined field-based, remote-sensing and modelling approach is used to characterise a variety of different types of aeolian sedimentary system and their preserved successions. A suite of generic models is developed and applied to enable regional palaeoenvironmental reconstructions of desert systems that evolved during different periods in earth history, and in different palaeogeographic settings, in response to changing environmental conditions. These models are applied to predict sediment-system response to future environmental change, especially desertification arising from on-going climate change.

Carbonate drifts are interesting sedimentary environments for understanding past palaeoceanographic and palaeoecologic conditions. Carbonate drifts are typically studied at large scale with seismic profiles or a meter scale by sedimentological analysis, however the study of the bioturbation on such deposits can provide more detailed information about the palaeoenvironmental conditions at the seafloor.

Recent extensive geological and geophysical surveys over the world major river-dominated sea margins indicate that many rivers have developed largest proximal subaqueous deltas, with asymmetrical prodelta lobes, and elongated or detached distal masses of sediment. For example, the Amazon River’s sediment disperses >1500 km along the shore within the water depths of 60-70 m, and reaching the Orinoco River mouth; The Yangtze River sediment has transported ~800 km along the shore into the Taiwan Strait, and Yellow River sediment is deposited more than 700 km into the south Yellow Sea. Beyond the proximal depocenters near their river mouth, both the Yangtze and Yellow systems have developed a 40-m thick distal mud depocenters. The Mekong-derived sediment has also extended >250 km southwestwardly to the tip of the Ca Mau Peninsula, forming a distal mud depocenter up to 22 m thick, and extending into the Gulf of Thailand. Other major river systems, like the Irrawaddy, Mississippi, Nile, Po, Rhone, Pearl, Red, also have a large longshore-transported distal deposit with some typical underwater clinoform features. Only a few of the world major rivers are able to disperse their sediment directly or indirectly to the deep sea through the attached shelf canyon systems, like the Congo and Ganges-Brahmaputra.I will describe the unexpected discovery of pore fluids that, for the first time, appear to represent a direct archive of ancient seawater and to preserve the salinity and isotopic ratios of seawater from a past glacial period, likely the Last Glacial Maximum. These pore fluids were extracted from sediment cores from the Maldives Inner Sea, drilled in 2015 during IODP (International Ocean Discovery Program) Expedition 359 and penetrating late Oligocene to modern sediments. The composition of these fluids carries implications for glacial ocean circulation, water-rock interaction in platform systems, and preservation of carbonate sedimentary geochemistry.

I will describe the unexpected discovery of pore fluids that, for the first time, appear to represent a direct archive of ancient seawater and to preserve the salinity and isotopic ratios of seawater from a past glacial period, likely the Last Glacial Maximum. These pore fluids were extracted from sediment cores from the Maldives Inner Sea, drilled in 2015 during IODP (International Ocean Discovery Program) Expedition 359 and penetrating late Oligocene to modern sediments. The composition of these fluids carries implications for glacial ocean circulation, water-rock interaction in platform systems, and preservation of carbonate sedimentary geochemistry.