Introduction
Sub-divisions in the Quaternary of the British Isles.
The Quaternary Period is the shortest division of time in the geological column covering only the last 2.6 million years or so of Earth’s history. The period is characterised by extraordinary changes in global climate producing several major phases of ice-sheet advance, (glacial), and retreat (interglacial) across lower latitudes than permanent ice cover is restricted to today. Many minor cycles of advance and retreat are superimposed upon each major phase making deposits of this age difficult to interpret and correlate between different areas.
Furthermore, each re-advance more-or-less erases the evidence of any preceding glacial activity exacerbating the problems facing Quaternary geologists. Because of this analysis of pollen grains (palynology) and oxygen isotopes provide some of the best clues to the different environments under which deposits of this age accumulated.
The Quaternary can be sub-divided into two series, the Pleistocene – which covers all deposits between 2.6 million years and around 20,000 years ago (locally), and the Holocene – encompassing deposits from around 20,000 years ago to the present day.
Solid rocks of the Tees Valley district below c.300m are covered by till, sand and gravel laid down by wastage of the local ice-sheet at the close of the most recent glacial episode. The youngest deposits in the district are the Flandrian sand dunes and estuarine silts, sands and clays currently being deposited around the the mouth of the River Tees.
Devensian
The most recent ice-sheet to occupy the Tees Valley did so during the Devensian Stage of the Pleistocene, between around 120,000 and 20,000 years before present, when ice advanced on the area from seats in the Lake District to the west, and Scotland to the north. Pressure, applied by Scandinavian ice from the North Sea Basin, affected the advance locally by forcing the Scottish ice stream inland at suitable low points in the landscape.
View of Freeborough Hill looking south east from Stanghow Ridge.
Some landforms, such as Freeborough Hill, were sculpted as the ice-sheet carved up the original landscape during advance. Others, such as Cat Nab at Saltburn, resulted as the ice melted and the material which had been acquired en-route was unceremoniously dumped. Immense amounts of melt water, unable to escape in any other direction, flowed along the ice margins forming temporary lakes where conditions allowed. Longer-lived water bodies tended to fill until they eventually overflowed, the escaping streams often cut distinctive channels which were abandoned as flow rates diminished. Water also travelled through, beneath and upon the ice-sheet where conditions allowed.
The most extensive evidence of former occupation by ice-sheets is a thick deposit of boulder clay (or till) which cloaks the landscape, softening its contours to heights of between 250 and 300 metres above sea level. This material has also in-filled some of the pre-Devensian features producing buried valleys, most notably at Upgang and Saltwick Bay, near Whitby.
Boulder clay is a mixture of clay-, silt- and sand-sized particles (dubbed rock flour) within which grit, pebbles and boulders are embedded. It forms as an ice-sheet advances and tears up the bedrock over which it passes. Large boulders enhance ice’s abrasive ability and are gradually pulverised by movement of the ice to form rock flour. When ice-sheets eventually melt the boulder clay left behind contains fragments of rock acquired en-route which are non-native to the district in which the clay ends up being deposited. These erratics provide important clues to the source and route taken by the originating ice.
Holocene
Since the retreat of the Devensian ice-sheets, around 20,000 years ago in the Tees Valley and Cleveland, many changes have occurred to the landscape. On both sides of the River Tees, at Seaton Carew and Redcar, are ancient peat deposits buried beneath the sands on the beaches. These date from around 8,000 years ago.
As water becomes locked up in the form of ice, so sea levels fall. Even though ice had left the area by 8,000 years ago, sea levels were still much lower than they are today. Up to 150m lower. Forest extended far seaward from Teesside at this time, it was later occupied by early human resettlers. Finds at Seaton Carew include signs of flint-working, a skull, wattle-work and much more, and the Peat & Forest Beds have been designated a SSSI. No such work has been undertaken at Redcar despite the ongoing sea-defence work and these valuable deposits are likely to be lost.
Tree-trunk in the Redcar Peat & Forest Beds.
Eventually, c.6,000 years ago, sea levels rose to (roughly) their present levels and the former forest was overwhelmed. The only clues to its former existence these two patches of peat on either side of the River Tees estuary. As these deposits contain evidence of past sea-level change, they are a valuable resource for the study of future sea-level rise.
« Tertiary
©2011 Tees Valley RIGS Group.
Quaternary
Introduction
Sub-divisions in the Quaternary of the British Isles.
The Quaternary Period is the shortest division of time in the geological column covering only the last 2.6 million years or so of Earth’s history. The period is characterised by extraordinary changes in global climate producing several major phases of ice-sheet advance, (glacial), and retreat (interglacial) across lower latitudes than permanent ice cover is restricted to today. Many minor cycles of advance and retreat are superimposed upon each major phase making deposits of this age difficult to interpret and correlate between different areas.
Furthermore, each re-advance more-or-less erases the evidence of any preceding glacial activity exacerbating the problems facing Quaternary geologists. Because of this analysis of pollen grains (palynology) and oxygen isotopes provide some of the best clues to the different environments under which deposits of this age accumulated.
The Quaternary can be sub-divided into two series, the Pleistocene – which covers all deposits between 2.6 million years and around 20,000 years ago (locally), and the Holocene – encompassing deposits from around 20,000 years ago to the present day.
Solid rocks of the Tees Valley district below c.300m are covered by till, sand and gravel laid down by wastage of the local ice-sheet at the close of the most recent glacial episode. The youngest deposits in the district are the Flandrian sand dunes and estuarine silts, sands and clays currently being deposited around the the mouth of the River Tees.
Devensian
The most recent ice-sheet to occupy the Tees Valley did so during the Devensian Stage of the Pleistocene, between around 120,000 and 20,000 years before present, when ice advanced on the area from seats in the Lake District to the west, and Scotland to the north. Pressure, applied by Scandinavian ice from the North Sea Basin, affected the advance locally by forcing the Scottish ice stream inland at suitable low points in the landscape.
View of Freeborough Hill looking south east from Stanghow Ridge.
Some landforms, such as Freeborough Hill, were sculpted as the ice-sheet carved up the original landscape during advance. Others, such as Cat Nab at Saltburn, resulted as the ice melted and the material which had been acquired en-route was unceremoniously dumped. Immense amounts of melt water, unable to escape in any other direction, flowed along the ice margins forming temporary lakes where conditions allowed. Longer-lived water bodies tended to fill until they eventually overflowed, the escaping streams often cut distinctive channels which were abandoned as flow rates diminished. Water also travelled through, beneath and upon the ice-sheet where conditions allowed.
The most extensive evidence of former occupation by ice-sheets is a thick deposit of boulder clay (or till) which cloaks the landscape, softening its contours to heights of between 250 and 300 metres above sea level. This material has also in-filled some of the pre-Devensian features producing buried valleys, most notably at Upgang and Saltwick Bay, near Whitby.
Boulder clay is a mixture of clay-, silt- and sand-sized particles (dubbed rock flour) within which grit, pebbles and boulders are embedded. It forms as an ice-sheet advances and tears up the bedrock over which it passes. Large boulders enhance ice’s abrasive ability and are gradually pulverised by movement of the ice to form rock flour. When ice-sheets eventually melt the boulder clay left behind contains fragments of rock acquired en-route which are non-native to the district in which the clay ends up being deposited. These erratics provide important clues to the source and route taken by the originating ice.
Holocene
Since the retreat of the Devensian ice-sheets, around 20,000 years ago in the Tees Valley and Cleveland, many changes have occurred to the landscape. On both sides of the River Tees, at Seaton Carew and Redcar, are ancient peat deposits buried beneath the sands on the beaches. These date from around 8,000 years ago.
As water becomes locked up in the form of ice, so sea levels fall. Even though ice had left the area by 8,000 years ago, sea levels were still much lower than they are today. Up to 150m lower. Forest extended far seaward from Teesside at this time, it was later occupied by early human resettlers. Finds at Seaton Carew include signs of flint-working, a skull, wattle-work and much more, and the Peat & Forest Beds have been designated a SSSI. No such work has been undertaken at Redcar despite the ongoing sea-defence work and these valuable deposits are likely to be lost.
Tree-trunk in the Redcar Peat & Forest Beds.
Eventually, c.6,000 years ago, sea levels rose to (roughly) their present levels and the former forest was overwhelmed. The only clues to its former existence these two patches of peat on either side of the River Tees estuary. As these deposits contain evidence of past sea-level change, they are a valuable resource for the study of future sea-level rise.
« Tertiary
©2011 Tees Valley RIGS Group.