IGA LECTURE Wednesday, 27th April, 2011
Speaker: Dr. Shane Tyrrell (UCD)
VENUE: TCD, Museum 4, Dept. of Geology, Muesum Building, Trinity College, Dublin 2.
NOTE NEW TIME: 6.00pm , tea/coffee from 5.30pm
Sediments and sedimentary rocks represent a unique archive recording environmental change over geological timescales. Determining the provenance (or source) of the individual grains comprising sands and sandstones provides important insights into these changes. They can, for example, help constrain ancient plate tectonic configurations and palaeogeography. In this talk, two sedimentary provenance investigations are presented. The aim is to demonstrate how detailed geochemical tracing of grains can, in conjunction with other data, lead to a more complete reconstruction of past environments. Analysis of feldspar grains from Triassic sandstones in sedimentary basins along the NW European margin have shed light on the routes and pathways taken by ancient large-scale rivers. Operating within the arid interior of the Pangean Supercontinent, these drainage systems appear to have been controlled by a combination of topography and seasonal climatic fluctuations. Data from feldspars from a completely contrasting depositional setting – Quaternary glacio-marine sediments from offshore west of Ireland – have provided intriguing insight into more recent environmental change. Here, it has been possible to distinguish ice-rafted debris derived from a local source (the British Irish Ice Sheet) from that with a more distal origin (the Laurentide and Greenland Ice Sheets). These provenance data highlight the links between ice sheet instability and climatic cycles.