Sept 2019 Talk: Yorkshire’s ancient storms


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YORKSHIRE’S ANCIENT STORMS

ANDY HOWARD

Honorary Research Associate, British Geological Survey

About Andy Howard

Abstract: Hurricanes and typhoons are notoriously destructive storms that cause significant loss of life and livelihoods across the tropics. The Atlantic hurricane season of 2017 was notably severe. Tropical Storm Harvey caused unprecedented coastal flooding in Texas, and was followed by Hurricanes Irma and Maria, both of which reached Category 5 intensity. These record-breaking storms devastated several Caribbean island communities and wreaked havoc in the Florida Keys. Later in the season, Hurricane Ophelia took a different and unusual path, tracking northwards to bring storm force winds to Ireland and ‘apocalyptic’ red skies laden with Saharan dust to southern Britain.

Although the impact of extreme events on the geological record has long been appreciated, it was not until the early 1970s that storm deposits, or ‘tempestites’, were extensively described in the published scientific literature. This was stimulated by extensive observations of storm processes on modern continental shelf environments, notably hurricanes in the Caribbean and eastern USA, but also severe storms in the North Sea including the Great Storm of 1953. This research assessed the impacts of storm waves and surges, and described the associated effects of erosion and deposition on the seafloor and its inhabitants. Similar storm deposits were soon identified in ancient shallow marine deposits which led, in the 1980s and early 1990s, to a boom in published papers on storm deposits from all periods of the geological record.

Use of the term ‘tempestite’ in the geological literature has been almost entirely limited to the deposits of storms in shallow marine environments. However, the impact of storms in other depositional environments is equally profound. The geological record of northern England preserves extensive evidence of storms in a range of ancient depositional settings including flood plains, deltas, coastal marshes, deserts and sabkhas, as well as shallow marine continental shelves. This talk reviews examples of ancient storms preserved in several geological formations in northern England, ranging in age from early Carboniferous to mid Jurassic. The examples include successions recently demonstrated in YGS field trips and indoor meetings, and enable comparisons to be drawn with similar and dramatic storm events that have made the news at the present day. This talk will not only show how these short-lived extreme events have shaped the geological history of northern England, but also the early evolution of the diverse range of terrestrial vertebrates that inhabit our planet today.

Photo 1. Shallow marine tempestite beds in the early Jurassic Cleveland Ironstone Formation at Staithes, North Yorkshire. Tempestite beds consist of upwards-fining sandstone beds with channelled bases. The overlying ironstone seam marks a long break in sedimentation. Photo: Andy Howard, 2013.

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Photo 2. Coastal sabkha facies, siltstones and mudstones of the mid-Triassic Sidmouth Mudstone Formation (Mercia Mudstone Group), Radcliffe-on-Trent, Nottingham. Laminated greenish-grey or pale brown siltstones forming the more resistant beds were deposited by storm-driven flash floods on wet mudflats and saline lakes, while the interbedded red-brown blocky mudstones represent wind-blown dust storm deposits that accumulated on damp mudflats. Photo: Andy Howard, 2017.

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