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.
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
Topic: Sea Level Drowns Reefs
Arguing for the motion: Cecilia Lopez-Gamundi, Elias Samankassou
Arguing against the motion: Edward Matheson, Peter Burgess
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.
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).
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.
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”
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.
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.
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.
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.
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.
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.
Seds Online Great Debate
Topic: The Recent Really is the Key to the Past
Arguing for the motion: Jeff Peakall (University of Leeds) and Shahin Dashtgard (Simon Fraser University)
Arguing against the motion: William McMahon (University of Cambridge) and Cathy Hollis (University of Manchester)
When we look at modern, Alpine glacial landscapes, we are struck by the abundance of chaotic and poorly sorted material, bearing large boulders. This material is diamict: unsorted, boulder-bearing material that is fashioned into a variety of familiar glacial landforms called moraines, and sometimes streamlined structures (drumlins). Earth has experienced many glaciations, and has a rich record of diamictites stretching from about 2.2 Ga to the present day. However, even superficial investigation reveals that the records of many glacial periods such as the Cryogenian and Late Ordovician are greatly contrasting. Cryogenian rocks crop out spectacularly in places like South Australia, Namibia, Scotland and the western USA. They are associated with no convincing glacially striated pavements anywhere in the world. This is in spite of these being associated with a so-called “snowball Earth”. Spectacular, thick diamictites are interbedded with abundant dropstone-bearing strata and thus testify to a glacial influence, but not all diamictites are glacial and many record mass failures of slopes in a marine environment. By contrast, there is a high abundance of these features recording subglacial erosion in Late Ordovician and Late Carboniferous records. Huge networks of palaeo-ice streams can be mapped from satellite data, to allow detailed ice sheet reconstruction. The deposits of the Late Ordovician glaciation are predominantly sandstone, supercritical flow deposits are abundant, and most of the subglacial record records shearing of soft-sediment rather than “traditional” scratches on bedrock. Examples of these deposits are in Morocco, Algeria, Libya and Saudi Arabia. The Late Carboniferous record includes palaeo-fjord systems (e.g. in Namibia and Argentina) with polished bedrock surfaces that closely resemble Pleistocene fjord systems. Approaching the glacial record often requires “out of the box” thinking, because the present is not always the key to the past. This begs the question as to which glacial period, if any, is truly representative in terms of a glacial sedimentary record on Earth. So, do we really know what a glacial deposit looks like?
Ever since the contourite revolution of the 1960s the distinction between contourites, turbidites and hemipelagites in modern and ancient deepwater systems has been controversial. This is partly because: (a) the processes themselves show a degree of overlap as part of a continuum, so that the deposit characteristics also overlap; (b) the three facies types commonly occur within interbedded sequences of continental margin deposits; and (c) much erroneous and misleading material has been published over the past five decades. However, the nature of these end-member processes and their physical parameters are becoming much better known, and the occurrence, architecture and seismic attributes are now well established. Good progress has also been made in recognising differences between end-member facies in terms of their sedimentary structures, facies sequences, ichnofacies, sediment textures, composition and microfabric. These characteristics can be summarised in terms of standard facies models, and the variations from these models that are typically encountered in natural systems. Nevertheless, it must be acknowledged that clear distinction is not always possible on the basis of sedimentary characteristics alone, and that uncertainties should be highlighted in any interpretation. Controversy remains and clearly focused new research is much needed.
Geological models are important in aiding our interpretation of the rock record, particularly where outcrops, or subsurface data, is sparse. Conceptual models have been built and published for distributive fluvial systems (e.g. fluvial fans) where a predictive downstream and temporal changes in fluvial characteristics (e.g. channel body size) are present. However, few studies have assessed how much variability is observed across such systems and therefore should be present within our predictive models. This talk will present work that assesses how much variability can be present within facies models. Focusing on recently collected data from the Huesca distributive fluvial system (Spain) with comparison to the well-documented Salt Wash distributive fluvial system (SW USA).
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.