Scientific Webinars

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).

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.

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.

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.

Please find out more information using the links below:

• https://www.sciencedirect.com/science/article/pii/S0012825219306233#ab0005
• Patagonian Ice Sheet
• PATICE interactive map