Scientific Webinars

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).

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.

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.