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.
Clinothems are the building blocks of basin margin successions, and can be subdivided into three physiographic segments: shelf (topset), slope (foreset) and basin floor (bottomset). These segments are defined according to the position of sedimentary transition zones, like the shelf-edge rollover and base of slope. These are zones with breaks in clinoform gradient, and their stratigraphic record and trajectory provide information about the balance between accommodation versus sediment supply, and sedimentary process interactions. However, the complete record of individual clinothems is rarely documented, mainly due to outcrop or subsurface dataset limitations. The Karoo Basin, in South Africa, exposes exhumed basin-margin scale clinothems with local across-strike control, which allows a) to provide sub-seismic characterization of topset-foreset-bottomset deposits along the same basin margin clinothem; b) to locate sedimentary transition zones and study the facies distribution both down depositional dip and across depositional strike; c) to establish the sequence stratigraphy of a margin transitioning from erosional- to accretionary-dominated; and d) to discuss wider implications for stratigraphic models of basin evolution.
Cyclothems are stratal rhythyms comprising repetitive vertical successions of sandstones, heterolithic (thinly interbedded) sandstones and mudrocks, mudrocks, limestones, and coals, in many cases with pedogenic overprinting of these lithologies. They record repetitive alternations of shallow marine and coastal to nonmarine environments of deposition. They are typical of Carboniferous and Permian paleotropical successions across Euramerica. Controversy endures as to whether cyclothems were formed under external forcing or rather were the product of mainly autogenic processes. Careful mapping and correlation of cyclothem strata and use of a sequence stratigraphic methodology allows a fuller understanding of these enigmatic rhythms. Depositional sequences can be identified and correlated over 100s of km, based on the recognition of regionally extensive disconformity surfaces and the continuity of key marker beds. Erosional surfaces preserve deeply incised valleys, separated by relatively flat interfluves represented by pedogenically modified strata. Sequences bounded by these surfaces are < 2 to > 30 m in thickness, varying considerably in thickness and facies composition but nonetheless preserving predictable arrays of facies that record deepening and shallowing trends. Because of the limited thickness of cyclothems, it is difficult to apply the accommodation succession concept to these deposits. Rather, cyclothem sequences are thin, incomplete, condensed, strongly top-truncated, and have a ragged blanket geometry. Although the term “cyclothem” has been used in a variety of contexts, a definition of the term limited to successions that were deposited (1) on low-gradient pericontinental shelves in paleotropical regions, (2) as far-field products of Gondwanan glacial growth and decay at various timescales, and (3) under conditions of low sediment supply in most cases, and (4) under low accommodation limited by slow, passive subsidence is herein preferred.
Sedimentology of tidal meanders has received comparably much less attention than that of river meanders, and facies models for tidal point bars were developed in the shade of their fluvial counterparts, driven by the simplistic assumption that tidal and fluvial meanders are characterized by similar planform morphologies and dynamics, together with accretional and erosional processes along the inner and outer bank, respectively. This general lack of attention for tidal meanders runs parallel with their scarce documentation in the ancient record, a knowledge gap that contrasts with their widespread incidence in modern coastal plains, where they play a fundamental control on landscape evolution. Knowledge about tidal meanders and their deposits is even weaker when considering those developed in coastal regions characterized by a microtidal regime (e.g Mediterranean Basin, Gulf of Mexico and the Baltic Sea). The Venice Lagoon (Northeastern coast of Italy) includes a wide spectrum of meandering channels developed in a microtidal regime, and provides a unique laboratory to investigate their morphodynamic evolution and the related sedimentary products. The Venice Lagoon has a total surface of about 550 km2 and represents the largest brackish water body of the Mediterranean Basin. The Lagoon has an elongated shape trending NE-SW and has mean water depth of tidal flat and subtidal platform of about 1.5 m. It is connected to the sea through three inlets, where the maximum water excursion is ±0.75 m around Mean Sea Level. Nowadays, the Lagoon does not receive any relevant fluvial sediment supply, and is surrounded by densely-vegetated saltmarshes. Tidal channels are up to 15 m deep and form a complex network that drains saltmarshes, tidal flats and adjacent subtidal platforms. This talk will provide an overview on morphological and sedimentological processes concurring to shape these channels and build up related pointbar bodies. Specifically, it will illustrate planform geometries and migration rates of channel bends developed at different scales, and will depict depositional geometries developed under the interaction between lateral migration and vertical aggradation. The signature of tidal processes will be shown and compared with that recorded in deposits accumulated where tidal range is higher. Finally, stratal architecture and sedimentary facies distribution in subtidal pointbars will be also described.
The Patagonian Ice Sheet was an ice sheet characterised by a wide variety of environments, including glaciolacustrine, land-terminating lowland lobes, high mountain glaciers and glaciomarine environments. It dammed large lakes that grew as it receded, which were an important control on ice dynamics. Here we present an overview of the variety of sediment-landform assemblages produced, and use these together with 1669 published ages to reconstruct Patagonian Ice Sheet evolution over the last 35,000 years, from the Last Glacial Maximum to the present day. We use these datasets to untangle the climatic and ice dynamical controls on ice recession, and find that current recession, driven by a persistent negative phase of the Southern Annular Mode, is exceptional within the Holocene.
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Human energy expenditure in the Anthropocene (starting ~1950CE) is ~22 zetajoules (ZJ), and exceeds all human energy expended across the prior 11,700 years of the Holocene (at ~14.6 ZJ), largely through the combustion of fossil fuels. The global warming effect during the Anthropocene is more than an order of magnitude greater still. Global human population and their productivity and energy consumption are highly correlated and with most changes impacting the global environment: number of large dams; shrimp farming; industrial production of plastic, cement, ammonia, copper, gypsum, salt, iron, steel, sulfur, helium, aluminum; mineral species; atmospheric gases (CO2, N2O, CH4); terrestrial freshwater budgets; and surface temperatures, sea levels, and ice masses. This extraordinary outburst of energy and productivity demonstrates how it is that the Earth System in the past 70 years has departed from its Holocene state, forcing abrupt physical, chemical and biological changes to the Earth’s stratigraphic record that can be used to justify the proposal for naming a new epoch – the Anthropocene.
Aggradational bedforms, from dunes to cyclic steps, are the subject of dozens of papers each year, producing lots of startling discoveries. These bedforms tell us about the flows that formed them and in turn aid interpretation and prediction. In contrast, sole structures have been almost entirely neglected for 50 years; unloved, ignored, and whose only role is to tell geologists which way the flow went. Here we present a new process model of flutes and tool marks in deep-marine environments that tackles a host of long-standing conundrums, and examines under what flow types these structures form. We finish by looking at the implications of the work including a revised Bouma Sequence diagram.
Bedforms are a key tool to reconstruct sedimentary processes in modern and ancient environments. This talk will present novel mixed sand-mud bedforms which have different shapes and sizes compared to pure-sand bedforms, and are found in the fringe of submarine fans. These striking mixed sand-mud bedforms are interpreted to be produced by sediment gravity flows with transient-turbulent fluid dynamics, due to the presence of cohesive clay. The presence and spatial trends in mixed sand–mud bedform types may be an important tool in interpreting fan fringe environments.
The scientific endeavours of the Apollo Lunar missions provided two important, yet apparently contradictory, pieces of information. The lunar rock samples aged the Moon at 4.5Gy, whilst laser ranging measurements of present day lunar recession, facilitated by reflectors left on the Moon, imply an age of only 1.5Gy. It is evident that least one of these estimates must be wrong! We now know that Earth, because of its current continental configuration, has a very energetic tide. Because the dissipation of tidal energy act as a break on Earth’s rotation and thus forces the moon to recede, it is also a first order controller of lunar distance. Is it possible that the motion of continents has changed the tides enough on geological scales to facilitate a weaker tide that can reconcile the two age estimates of the moon? Here, I am hoping to answer this question by going on journey through Earth’s history and estimating the tidal energetics for a series of interesting time slices. I will also touch upon what the consequences may have been for other parts of the Earth system and for other planets.
The threat posed by plastic pollution to ecosystems and human health is under increasing scrutiny and the amount of mismanaged plastic waste entering the environment is growing at a staggering rate. In particular microplastics (plastic particles <1 mm in size) have been discovered in every sedimentary system on the planet and thus became a new type of sediment particle. As such, sedimentology represents an important and powerful tool to understand and predict the transport, dispersal, and ultimate fate of microplastics in different environments. However, due to the complex shapes and low densities the transport and sedimentation behavior of this new sediment particle may differ significantly from those of natural sediments. The presence of microplastics in the environments poses new challenges for the field of sedimentology, but may also provide opportunities to better understand the dynamics of sedimentary systems. In this talk I will provide an overview on global plastic-pollution, microplastic as a new and unique sediment particle, and on microplastics in seafloor sediments.
Based on a recent review of the literature a data base of absolute values of short term (<3my) Cretaceous sea level rises and falls has been created. This shows an overall amplitude range of 5 to >65m, organised in four broad trends. The potential of aquifer eustasy has been investigated using climate modelling which showed a maximum impact of 5 to 10 meters. This leaves Glacio-eustasy as the key driver for short term high magnitude sea level changes in the Cretaceous.
The Halimeda algal bioherms of the Great Barrier Reef, Australia represent the largest living, actively accumulating Halimeda deposits worldwide. Following the Holocene post-glacial marine transgression, these bioherms kicked off the outer-shelf carbonate factory some 2000 years earlier than the nearby coral reefs. Recent multi-disciplinary work has revealed new insights into their surface geomorphology, subsurface architecture and depositional environment that may be of interest to those working on their fossil counterparts.