Holocene Sediments

13.11.07 Soil coring Seamer Meads Blockley FBphonepic213.11.07 Soil coring Seamer Meads Blockley FBphonepic3

The Flixton area has been a wetland, to greater or lesser extent since the last Glacial. As the ice-sheets retreated, a series of deposits accumulated in the wetlands and low-lying spots. Sands and gravels, such as those won for aggregate at Wykeham Quarry, are present in many parts of The Vale of Pickering but their depth and thickness vary. Lake marls (a kind of lime-rich mud) can be found in thin layers but more prominent are the thick piles of peat, several metres deep, from partly-decayed wetland vegetation. This forms the characteristic ‘black-land’ of The Carrs. 

Sediment cores at Wykeham and Flixton are so important because they can be matched up to parts of the Greenland Arctic ice core, the most complete timeline of climatic changes in the northern hemisphere. One of the more exciting methods is to isolate microscopic shards of volcanic glass from the lake sediment layers.

These ‘microtephra’ emanate from ancient volcanic eruptions and leave a distinctive signature in sediment layers all over the northern hemisphere, including the ice core records from Greenland. (Recently the volcano Eyafjallajokul in Iceland  caused a pan-European ash cloud event of exactly that kind.) Matching up these volcanic ash events with the Greenland cores is something that Dr Simon Blockley from Royal Holloway University of London specialises in.

This can be called ‘Tephra-chronology’. Dr Blockley and colleagues use Flixton as a training ground for MSc students. The sediments here are by no means fully understood – each field season there are fresh revelations about the complexity of the former wetland – its extent, its variation in depth and so on. The information gleaned from these coring studies is progressively improving our understanding of the environment our ancestors inhabited and places greater precision on the chronology of habitat and climate changes that our Stone Age ancestors at Star Carr must have experienced and adapted to.

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