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.
Whitings, or occurrences of fine-grained carbonate within the water column, have been observed in modern environments with salinities ranging from fresh to marine conditions, and thick deposits of lime mud are described throughout the geological record. Despite their ubiquity, the trigger for whitings has been a conundrum under debate for more than eighty years. This talk will review the trigger for whitings atop the Great Bahama Bank and call upon hydrodynamic simulation and geochemical modelling to explore the diverse triggers of the lime mud factory. The results have implications for the interpretation of whitings mud in the geological record, including the geochemical signatures within it.
The Archean Pilbara Block in Australia is known to host some of the oldest fossils in Earth history. This presentation focuses on microbially induced sedimentary structures (MISS) in clastic sabkha deposits of the Dresser Formation. Similarities of modern and fossil MISS suggest that already in the early Archean time complex microbial ecosystems existed.
The genesis of rhythmically alternating carbonate lithologies is a fundamental process which is not fully understood. In this presentation different models for their genesis, biases introduced by diagenetic processes, and solutions to handle data extracted from limestones and marls are discussed.
Full characterization of drill core and outcrops is time-consuming and requires multiple analytical techniques. Hyperspectral imaging can provide high-resolution spectra that may be interrogated for continuous mineralogical data, total organic carbon, and crystal size, to aid in strategizing an effective approach to sampling. Shortwave infrared (SWIR – 1 to 2.4 µm) and longwave (LWIR; 8 to12 µm) spectral imagery of shale drill core at a sub-millimeter per pixel scale reveals previously undetected trace fossils and sedimentary structures as well as distinct populations of amorphous and crystalline silica. Hyperspectral imaging can also be performed on outcrops and cliff faces, and is particularly useful in highlighting diagenetic phases in carbonates, where mimetic replacement and a lack of colour variation between mineral phases can result in an incomplete assessment of paragenesis. In an example of Cambrian dolomites from Western Canada, SWIR is used on an outcrop almost entirely composed of dolomite to detect individual phases, based on composition and crystal size.
Mixed siliciclastic-carbonate sediments result from the interaction of a siliciclastic input and a coeval carbonate production. Mixed deposits consist of a suite of different types of mixing between the two components, from bed to stratigraphic scales, producing a high vertical and lateral lithological variability. Although mixed deposits are very diffuse in the geological record, studies about these deposits are scrappy and not well encoded. Accordingly, mixed deposits can represent a labyrinth for researchers who want to investigate them for the first time. The aim of the talk is to highlight main aspects and their peculiarities.
Bedforms are the morphological patterns on the sediment bed originating from coherent structures in fluid flows. The classical grouping of bedforms into the lower and upper regimes follows the transition from subcritical to supercritical flow as the Froude number passes a critical value. The revival of academic interest in supercritical flows and their products over the past two decades is attributed to the most recent addition to the supercritical palette: cyclic steps. This alternating pattern of subcritical and supercritical flow results from the flow overstepping the boundary between stable and unstable behaviour as predicted by the Vedernikov number. Waves at the upper flow boundary are key to understanding the transitions between the stable subcritical (ripples and dunes), stable supercritical (antidunes) and unstable supercritical (cyclic steps) regimes. In this talk we review our knowledge on the sedimentological aspects of supercritical flows and explore which questions remain to be answered.
The deep marine Hikurangi Channel, located off the east coast of New Zealand, is a colossus. More than four times longer than any other located at an active continental margin, this trench-axis conduit can be traced for ~2000 km. Rapid continental uplift and frequent earthquakes associated with Hikurangi Subduction Margin and volcanic eruptions in the Taupō Volcanic Zone, together with active temperate weather systems mean that vast amounts of terrestrial, volcanic and shelfal sediment, nutrients, and (today) pollutants, are focussed through several canyons that feed the Hikurangi Channel. Recurrent powerful, sediment-laden underwater flows, known as turbidity currents, over the last 40,000 years, have left a remarkable and highly expanded greater than 100 m thick turbidite record that is allowing us to unravel the earthquake and volcanic signal of this margin over Quaternary timescales. Here I will discuss results from a large group of researchers working on understanding the Quaternary sedimentary systems of the Hikurangi Subduction margin. This will include preliminary results from IODP site 1520, together with multiple Holocene aged short cores (< 10 m thick).
A Virtual Outcrop (VO) is a 3D photorealistic model of a cliff or quarry that captures the geological features. Most recently, model sharing across the web has become possible through generic sharing sites such as Sketchfab and purpose-built sites like V3Geo.com. In this presentation we review the history for virtual outcrops and briefly discuss how they are collected, processed and how to access data that is available for public usage. We will then take a short virtual fieldtrip to the Book Cliffs of Eastern Utah, primarily to illustrate some of our learnings on the topic. We will conclude with a short discussion on the mechanics of how to build a VFT using publicly available data in LIME.
Geology has traditionally been a descriptive science with a significant portion of the data coming from observations of features at a range of scales. Modern practices in the oil industry still rely in a large part on this legacy of observational data, for instance when rock facies are used to derive regional stratigraphic trends from core data, or as a building block for petrophysical classifications. However, a recent study has shown that even experienced carbonate sedimentologists will often classify the same facies using different textural names. This problem is compounded in industry by large teams often collaborating on a project, resulting in a heterogeneous attribution of facies to similar rocks despite the use of a common classification scheme. This problem reduces the reliability of descriptive data. In this presentation, I will talk about our research applying machine learning to automatic identification of carbonate facies using the Dunham classification scheme. We used high-resolution core images from the Integrated Ocean Discovery Program (IODP) Leg 194. Core images are used to train a model written in the Python programming language using the TensorFlow machine learning library. Specifically, we used Google’s Inception V3 network as a pre-trained Convolutional Neural Network (CNNs), and applied a method called ‘transfer learning’ to train Inception V3 to recognize carbonate core images. Results show that our CNN can achieve up to 90% accuracy for identification of Mudstone to Rudstone and Crystalline Dolomite. The main misclassifications were between matrix and grain supported facies, and fine and coarse-grained facies, textures also commonly misclassified by control tests with geologists. Interestingly, the bias observed in core description by the algorithm is very similar to human biases: a tendency to give a greater weight to grains as they stand out from the matrix, called ‘saliency’. But the CNNs were able to identify facies 60 times faster than humans, and with a much greater consistency. The results of our study demonstrate the potential of artificial neural networks to reliably interpret and quantify descriptive data for the oil and gas industry, in a fast, automated, high-resolution manner. Current and future work will focus on acquiring a larger dataset of core and thin section images, improving the training of the neural network, and coupling image recognition with logging and petrophysical data estimation.
Two types of currents dominate sediment transport and deposition on continental slopes: sediment gravity flows that travel down the slope through submarine canyons, channels, and gullies; and bottom currents that are part of the ocean circulation and commonly flow along the slope. Continental slope morphologies reported from mixed sediment gravity flow – bottom current systems across the planet reflect various degrees of interaction between sediment gravity flows and bottom currents. Unfortunately, two communities of researchers have historically specialized in either gravity driven sediment transport or bottom current sediment transport. Consequently, the processes governing sediment transport and deposition in mixed systems are not clearly established and interpretations of mixed-system deposits in literature remain hypothetical and sometimes appear contradictory. In this seminar we will present the first measurements of combined contour-current and turbidity-current flows, which were obtained in laboratory experiments. The measurements demonstrate that contour currents flowing at 10 % of the turbidity current speed can pervasively deflect the turbidity current flow and prove for the first time that hybrid bottom-turbidity currents can be at the origin of asymmetric channel-levee systems. These first experiments are the starting point for discussions on the themes that need to be addressed by the deep water community to achieve an integrated understanding of sediment deposition in deep water environments by contour currents and turbidity currents.
Carbonate sedimentary rocks form through the accumulation of organisms and chemically precipitated calcium carbonate, usually on the sea floor. They preserve fragments of marine organisms, which are sensitive to temperature, salinity and seawater chemistry during their growth, and they therefore provide an exceptional record of evolutionary and climatic change through Earth’s history. Carbonate sediments are also highly reactive, dissolving and precipitating in surface water. For these reasons, despite their simple mineralogy, they have a reputation for being difficult to understand and many clastic sedimentologists approach them with caution! Nevertheless, carbonate sedimentary rocks are important for many reasons. They have been exploited for millenia for their minerals, water resources and, more recently, for cement, roadstone and hydrocarbon. Now, as we face the effects of climate change, we can use carbonate strata to understand how Earth responds to environmental stress and use this knowledge to better predict the effect of climate change on modern ecosystems. There is also growing interest in how carbonate sedimentary rocks can be used to good effect for carbon storage and geothermal heat production. This talk will provide an introduction to ‘novices’ of carbonate sedimentology to the principle processes that govern their formation and modification during lithification. It will illustrate their importance to our modern landscape and heritage and demonstrate how ancient carbonate systems can hold warnings, and solutions, to the effects of anthropogenic environmental impact.
“To see the World in a grain of sand… hold infinity in the palm of your hand and eternity in an hour” might be one of the best poetic descriptions for Luminescence Dating… sure, back in 1803, William Blake could not have imagined such scientific achievement! As a matter of fact, Optical Dating or OSL (Optically Stimulated Luminescence) has been one of the fastest growing dating methods since its development in 1985, in terms of protocol development, instrumentation and use. Who would have thought that a single ray of sunshine and the natural radioactive decay ever present in the environment would be allies for OSL signals to shine! As it uses two of the most abundant mineral grains available on the surface of the Earth (quartz & feldspars), OSL has a multitude of applications in addition to the ability to assign numerical ages to numerous environments and sedimentary deposits from the depths of the ocean to the highest peaks. In this presentation we will go over the basics of OSL Dating, and consider some of the major challenges, as well as the advantages. We will have a glimpse at the latest developments and applications, with a special focus on sedimentological and stratigraphical issues. One thing to bear in mind: OSL might not be used only for dating! The in-depth analysis of luminescence signals may give unforeseen insights into transport-deposition processes and events of both natural and anthropogenic origin.
If there were a guide book for the intergalactic sedimentologist then this would be the heavily-read chapter on terrestrial carbonates (principally those formed in soils, lakes, streams and springs). A reviewer might say that the examples used – although spanning a huge time range – are rather Earth-focussed. This largely reflects the travel budget of the author. But they would hopefully also say that this chapter is much more widely applicable to other planets, and that it contains beautiful pictures of all types of terrestrial carbonates. Readers would agree that hot-springs are great for holidays, but even the humble calcrete nodule can be invaluable for studying the co-evolution of life and environments on a planet.
Avalanches of sediment in the ocean, called turbidity currents, are among the volumetrically most important sediment transport processes globally. Due to their fast speeds, turbidity currents can break critical infrastructure, and transport organic carbon and nutrients far into the deep-sea, thus sustaining deep-sea ecosystems. Until recently, we have largely had to rely on the deposits that they left behind or small-scale flows held ‘captive’ in the laboratory to understand turbidity currents. New developments in technology now enable detailed and direct measurements of powerful flows at field scale to complement these studies. Here, we present recent measurements gathered by a large consortium of researchers from a range of shallow to deep-marine settings worldwide that provide new insights into the internal anatomy of these these flows, how they initiate, evolve and interact with the seafloor.