Gravity currents span a broad spectrum of flows with complex variable transport and depositional processes which the community has greatly improved it’s understanding of over the past few decades. However there remains a substantial gap in our understanding of very coarse grained flows with broad grain-size mixtures around the steep slopes typical of active rift margins. In this talk we’ll visit some superb exposures from the Gulf of Corinth rift, Greece and compare these to subsurface and other outcrop examples to highlight this diversity of processes that may occur as a result of the very broad grain-size range within such flows and what this could mean for the role of momentum in governing sediment bypass of different sizes beyond base of slope breaks.
Ancient climate conditions cannot be directly measured, and are rather inferred from proxy data. Proxies are not direct indicators for changes in temperature, precipitation or evaporation, but rather provide indirect evidence for how temperature and hydrological changes impacted the Earth surface or biota. Most widely used climate proxies are geochemical or biological and provide information on mean annual temperature and mean annual precipitation. Here we utilise river sedimentary facies as proxies for precipitation intensity and intermittency, and produce a more realistic representation of past and future precipitation change.
Coastal sediments can extend observations of relative sea-level changes beyond the instrumental and historical record. Extending observations with sedimentological data is important at sites without long tide gauge records and limited geological observations. In this seminar I will show how late Holocene mangrove sediment sequences provide us with a record of anomalous relative sea-level rise in Micronesia in the western Pacific Ocean.
Fluvial carbonates, i.e. tufas and associated carbonate facies, are widespread in the Quaternary record. At present, they are developed in varied climate and geological conditions, being abundant in mid latitude regions. Results from periodic studies comprising hydraulics, hydrochemistry, geochemistry and sedimentology of modern tufa depositing streams, have demonstrated these carbonate deposits are sensitive to such a wide variety of parameters acting at different time scales; interestingly enough is the fact that laminated deposits represent high-resolution records. Therefore, fluvial carbonate deposits represent multiproxy tools to investigate past climate and environmental conditions (relative to the depositional context) at different temporal and spatial scales. The presentation compares present and past records from several basins.
Storm events annually devastate coastal areas around the world. However, instrumental records of these events in many locations are relatively short. This webinar will describe the science of paleotempestology and discuss the climatic implications learned from comparing sites in different regions.
The nitrogenous nutrient in the modern (and most oxygenated) ocean is dominated by nitrate. However, nitrate can be quickly removed during water column deoxygenation. Oceanic nitrate inventory can be greatly reduced during ocean anoxic events. This occurred during the onset of the end-Permian mass extinction and was followed by a shift in oceanic nutrient-N inventory from nitrated dominated to ammonium dominated state. The consequences included a boom of diazotrophs and potentially ammonium toxicity affecting marine animals.
This presentation documents coupled field, analytical and experimental work with a focus on carbonate diagenesis. Case examples range from speleothems to burial diagenetic carbonates. The potential and limits of state-of-the-art experimental work and its bearing on ancient carbonate archives are documented and discussed.
Two years ago the the global lockdown accelerated the adoption of virtual field trips. This presentation will review ongoing research on how VFTs compare to traditional trips, what works and what doesn’t, learning outcomes and student satisfaction.
Ocean currents control the growth style of isolated tropical carbonate platforms because surface and contour currents shape the flanks of these edifices. Currents redistribute the off-bank–transported sediment, reduce sedimentation by particle sorting or winnowing, erode slopes, and even are a major driver of carbonate platform drowning. The flanks of isolated carbonate platforms are not only shaped by mass gravity deposits, but equally by contourites with distinct drift and moat geometries which produce specific stacking patterns of platform flank deposits reflecting combined current and gravity processes. This talk will illustrate several examples of such current-controlled tropical carbonate platform systems.
(1) Fatemeh Izaditame, University of Delaware, Climate change impacts on contaminated coastal sediment
(2) Valeria Ruscitto, Sapienza Università di Roma
The contribution of the shallow water record to understanding causes and effects of MECO (Middle Eocene Climatic Optimum)
(3) Matthew Staitis, University of Edinburgh
Accessing the sedimentary record of ocean acidification occur prior to the K/Pg mass extinction
Calcium and clumped isotopes are affected by carbonate recrystallization in fundamentally different ways, and are affected by different factors. Here, they are used to study an evolving carbonate margin (Present day western Bahamian slope), in order to quantify the rate of recrystallization and the degree of fluid flow into the margin. Results show that, with the onset of drift deposits in the Straits of Florida, fluid flow into the margin increased a great deal, demonstrating the importance of larger platform structure in governing the nature of diagenetic reactions.
Meteorite impacts have long been debated as a cause of mass extinction on Earth. When they hit, meteorite impacts load the atmosphere with dust and cover the Earth’s surface with debris. This is thought to trigger ‘Impact Winter’, whereby sunlight is blocked from reaching the earth’s surface leading to catastrophic ecosystem collapse. The bigger the hit, the more severe the effects. But does it really work like that? In this talk I’ll show you that there is actually no correlation between size of impact and extinction intensity over 600 Myrs of multicellular life. Instead, it is the mineralogy of the target rocks that dictates extinction intensity, in particular their K-feldspar content. Weird. To find out how this benign mineral triggers mass extinctions, you’ll have to come along to the seminar!
In this talk I will provide an overview of recent work that has focused on quantifying how ecological changes have altered rates of carbonate production on modern coral reefs and the impacts for reef growth potential under sea-level rise. The talk will also review the options and challenges that exist in quantifying associated rates of reef sediment generation – a sedimentary component of reefs that contributes not only to reef-building, but also to proximal beaches and islands.
The ability to build very steep slopes is a characteristics of carbonate platforms. Microbially mediated fusing of grains and subsequent prismatic early cementation construct the margins of these edifices that are often obstacles for ocean currents along continental margins. Rock fall, margin collapse, slope canyons and slope failures are common features of carbonate slopes but cascading density currents as well as bottom and surface currents also shape the sediment distribution on the slope and in the adjacent basin. Depositional slope models largely ignore the current-related deposition. The talk will illustrate the extreme height of carbonate escarpments and the related processes using the carbonate platforms in the Florida Bahamas region.
Svalbard is a paradise for geologists, with high Arctic vegetation-free outcrops offering insights into the geological evolution of the archipelago. The short field season and remote outcrops, however, require a different approach than traditional fieldwork. The emergence of cost-efficient consumer UAVs and structure-from-motion photogrammetry has allowed us to digitize a growing number of Svalbard’s outcrops and openly share these through the Svalbox database. The available digital models are presented in the context of regional geoscientific data, including terrain models, geological maps and subsurface data. As such, Svalbox brings the Svalbard geological paradise also to geoscientists living in the lower latitudes.
Microbial carbonates dominated in the Phanerozoic during times of skeletal biota crises and environmental perturbations. High-relief platforms with steep slopes and margins with microbial boundstone reefs are non actualistic examples of highly productive carbonate systems largely representative of the late Palaeozoic, Triassic and Jurassic depositional record. This review explores the controls on facies character, depositional geometry and architecture of several examples of high-relief carbonate platforms evaluating the responses of the microbial carbonate factory, stratal geometry and platform growth to changes in accommodation.
The absence of known prehistoric underwater cultural heritage (UCH) sites on the inner continental shelf of Australia stands in stark contrast to the thousands of sites revealed elsewhere in the world. Two recent claims – Dortch et al. (D2019) and Benjamin et al. (B2020) – put forward the first in situ (i.e., primary context) marine UCH sites in the shallow waters of the Dampier Archipelago, NW Australia. Each paper argued that the stone artefact scatters are at least 7000 years old and are submerged (D2020) or intertidal (D2019) because of post-glacial sea-level rise. Huge international publicity resulted.
From the data published in D2019 and B2020, we use oceanography, sedimentary processes and geological logic to assess the explicit and implicit assumptions and uncertainties of these claims. We include results of new hydrodynamic modelling, data on coastal erosion and bathymetric data of northern Flying Foam Passage, which together help contribute to a reinterpretation of the sites’ sedimentary settings and the archaeology.
These and similar sites in the region (and elsewhere) would benefit from a thorough appraisal of past and present coastal processes to produce a sedimentologically defensible understanding of site formation processes. Even if the artefacts are not in original position, if investigated appropriately and dated effectively, they would still inform our understanding of process and change and might then inform us about past cultures.
The ongoing global Climate Crisis has sparked a strong interest in climate reconstructions and models of geological periods with high atmospheric CO2 concentrations.
But how much do we really now about the dynamics of Earth’s past climate and coastal ecosystems on the human timescale?
Now that concern is rapidly rising about the catastrophic effect of extreme weather events and seasonality, especially to our sensitive and economically important coastal areas, biogenic carbonate producers like mollusks (clams and snails) rise to the occasion as ideal archives for environmental and ecosystem change at the timescale that matters: days to decades.
In this talk, I will try to answer the question: What can these beautifully preserved shells teach us about the occurrence of extreme weather and seasonality under various climate states?