Scientific Webinars

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.