I think the authors have got it wrong......
When referring to the Anglian glaciation (MIS 12) the authors say that it is referred to as the "Irish Sea Glaciation" -- however, I am not sure anybody has used that term since the 1940s, and within recent decades all authors have used the standard UK terminology as used in this article. The "Older Drift" v "Newer Drift" debate was a rather sterile one, plagued by too many assumptions about too many different things, including the imaginary South Wales End Moraine. Good riddance to it.
The points about the Wolstonian are interesting and stimulating, and I hope this debate continues.
On the above map showing ice limits in the Bristol Channel - Celtic Sea arena, I'm mystified by the continuing use of that strange Devensian line running southwards from western Pembrokeshire, because it makes no glaciological sense. Ice in unconstrained situations like this always spreads laterally, and the ice edge is always perpendicular to the prevailing direction of ice flow, not parallel to it. The suggested extension eastwards towards the coasts of Devon and Cornwall is much more sensible. There is a suggestion here that Wolstonian ice may have pressed onto the coasts of Devon and Cornwall and flooded across the Somerset Levels; that, I think, is a perfectly reasonable hypothesis........
The suggestion that the coasts of Carmarthen Bay (including much of Gower) were ice-free during the Devensian seems to me to be very unreliable, given the mass of evidence recently presented on this blog and elsewhere.
When it comes to the debate about an extensive Early Devensian glaciation in the Bristol Channel arena, the authors cite only two studies in support of it, based largely on the evidence of cosmogenic dating on Lundy Island. Well, I think those dates must be in error, and there is nothing in the stratigraphy of Quaternary sediments around the Bristol Channel coasts to support the idea. If ice had affected Lundy Island in the Early Devensian, it must also have affected the coasts and inland areas of Pembrokeshire -- but the sediment sequence shows no trace of Devensian ice action prior to the LGM. The sequence is ALWAYS (from the bottom up) raised beach >> rockfalls and coarse slope breccia>> Irish Sea or local lodgement till and meltout deposits including fluvioglacial sands and gravels>> thin slope breccia incorporating some glacial components>> colluvium and modern soil.
I suggested this sequence in my doctorate thesis in 1965, and all of the evidence collected since then confirms its essential reliability.
If there had been two Devensian glacial episodes this sequence would have been much more complex, at least in some localities. There are some ancient till deposits, as I have demonstrated on this blog, but they are currently not well understood, and because they are solidly cemented and impossible at present to tie into the regional sequence I have suggested that they are very old -- probably pre-Ipswichian in age.
Anyway, I look forward to further discussion on all of this.
=====================
European Glacial Landscapes
Maximum Extent of Glaciations
2022, Pages 245-253
Chapter 34 - Britain and Ireland: glacial landforms prior to the Last Glacial Maximum
Philip L.Gibbard
A younger, pre-Devensian Stage (Last Glacial Cycle, LGC) glaciation took place during the late Middle Pleistocene and is referred to as the Wolstonian Stage in Britain which is correlated with the Saalian Stage in continental Europe (Gibbard, 1991). The Wolstonian Stage is now known to span multiple glacial cycles (MIS 10–6) with the Late Wolstonian glaciation equivalent to that during MIS 6 (=Late Saalian Substage). During the 1980s the representation and impact of this glacial episode was questioned, see review by Gibbard (1991), but its significance has been progressively established extent over the subsequent three decades (e.g., Clark et al., 2012; Gibbard and Clark, 2011; Gibbard et al., 2018; Gibson, 2019).
Following Shotton (1953, 1968, 1976, 1983a,b, 1989), Wolstonian glacial sequences were identified over a large area in the West and Central Midlands (Rice, 1968, 1981; Rice and Douglas, 1991). These deposits indicate extensive glaciation of the region as far south as the Cotswold Hills in Gloucestershire and the Jurassic escarpment further east. The Midlands’ Wolston Formation includes two till units, the Thrussington and Oadby Members, with sands and gravels deposited below, between and above glaciogenic sediment (Shotton, 1953). The Thrussington Till consists of mainly Triassic-derived material, whereas the Oadby Till contains sediments of predominantly later Mesozoic provenance. These components indicate deposition by ice from western and eastern sources, respectively. The Thrussington Till was deposited as far east as Melton Mowbray and Rugby, and its meltwater formed a large ice-dammed lake between Leicester and Market Bosworth, in which up to 25 m of laminated clays and silts (the Bosworth Member) accumulated. The Oadby Till was subsequently deposited over much of the Eastern Midlands as far north as Nottingham and Derby, and as far west as Stratford-upon-Avon. It also extends southward to Moreton-in-Marsh.
In Eastern England the advancing Wolstonian ice-lobe deposited till in Lincolnshire and excavated the Fenland basin during the Late Wolstonian Substage (Straw, 1991, 2005; Gibbard et al., 2009, 2018). The limit of this Fenland Tottenhill ice lobe is marked by a group of glaciotectonic push moraines (Fig. 34.3) and deposits of a series of glaciofluvial delta-fan and related sediments deposited as ice-marginal deltas in a glacially dammed lake (Lake Paterson). This maximum ice-marginal position (the “Skertchly Line”) extended eastward close to the present Norfolk coast where Evans et al. (2019)report optically stimulated luminescence (OSL) ages that indicate an MIS 6 age for the emplacement of sediments in the ice-marginal ridge at Stiffkey, Norfolk.
Figure 34.3. Glaciotectonic push moraines marking the limits of the Late Wolstonian (MIS 6) Fenland ice lobe. MIS, Marine Isotope Stage.Adapted from Gibbard, P.L., West, R.G., Hughes, P.D., 2018. Pleistocene glaciation of Fenland, England, and its implications for evolution of the region. Royal Society Open Science 5 (1), 170736 (Gibbard et al., 2018).
Although originally recognised in the English Midlands, this Late Wolstonian glaciation has been identified in Yorkshire, Lincolnshire, western part of East Anglia, the Bristol Channel, and the Welsh Borderlands (Fig. 34.1). Elsewhere, poorly dated glacial deposits of restricted lateral extent have also been attributed to this glaciation and are typically found outside the Devensian glaciation (LGC) limit. Examples include the Bridlington Member or Basement Till of East Yorkshire, the Warren House Till on the coast of County Durham (the Warren House Formation: contra Davies et al., 2011), the Oakwood Formation at Chelford, Cheshire, the Ridgacre Formation, the reddish brown till-like Fremington Member of Barnstaple Bay, North Devon, the Kenn Till of Northern Somerset, the Pilkenzane Formation of Lancashire, the Thornsgill Formation of Thornsgill (Lake District), the Balby Formation at Balby and Brayton Barff in the Vale of York, and the Bakewell Formation at Shining Bank Quarry, North Derbyshire (Gibbard and Clark, 2011).
Offshore, a glacial limit has been established based on the extent of tunnel valleys and a ridge-like push-morainic landform has been identified north of East Anglia (the Norfolk High) and has been shown to continue eastward in the North Sea to join the Netherlands’ Drenthe glaciation maximum limit proposed by Moreau et al. (2012)and Moreau (2010) (cf. Gibbard et al., 2009). Comparison with the Netherlands’ sequence reveals a remarkable parallelism of events during this glaciation. In particular, Wolstonian glacial advances are generally contemporaneous with the major glacial advance during the Drenthe Stadial, the most extensive advance of the Late Saalian Stage (MIS 6), during which the southwest margin of the Eurasian Ice Sheet reached a maximum stillstand position in the Central Netherlands (Laban and van der Meer, 2004; Busschers et al., 2007, 2008). The contemporaneity is established through recent OSL dating both in Britain and the Netherlands (Busschers et al., 2008; Gibbard et al., 2018, 2021; Gibbard and Clark, 2011; Gibson, 2019).
In Ireland the equivalent of the Wolstonian Stage is the Munsterian Stage. The Munsterian Stage is reviewed in the study of Knight et al. (2004) who noted that the evidence for ice limits and flow directions associated with this glaciation is not clear and based mainly on erratic carriage and the presence of striae and subdued glacial landforms found outside well-marked Midlandian (LGC) end moraines. The fact that ice is now known to have completely covered Ireland in the LGC does raise doubts about the presence of surface glacial features relating to this penultimate glacial cycle. In terms of deposits, it is likely that deposits previously interpreted Munsterian are in fact Midlandian in age (Warren, 1985; Eyles and McCabe, 1991; Coxon 1993).
Maximum Extent of Glaciations
2022, Pages 245-253
Chapter 34 - Britain and Ireland: glacial landforms prior to the Last Glacial Maximum
Philip L.Gibbard
Philip D.Hughes
Chris D.Clark
Neil F.Glasser
Matt D.Tomkins
https://doi.org/10.1016/B978-0-12-823498-3.00050-9Get rights and content
Abstract
The most extensive ice sheets over Britain and Ireland formed during the Middle Pleistocene in the Anglian Stage [Marine Isotope Stage (MIS) 12] and the Late Wolstonian Substage (MIS 6). The landforms and associated sediments are widely preserved in Southern England but are largely absent from the rest of Britain and Ireland because the last ice sheet covered these areas. Despite the restricted evidence, the Middle Pleistocene glaciations had a profound impact on the landscapes of Britain and Ireland. For example, Britain became an island for the first time in Anglian Stage and the Middle Pleistocene Ice Sheets essentially determined the modern drainage of Southern England. Early pre-Last Glacial Maximum glacier advance in the Devensian Stage [MIS 5d-2; Last Glacial Cycle (LGC)] is elusive but significant ice cover is indicated in the sedimentological and geomorphological records early in the LGC, in MIS 4 and 3, in several parts of both Britain and Ireland.
https://doi.org/10.1016/B978-0-12-823498-3.00050-9Get rights and content
Abstract
The most extensive ice sheets over Britain and Ireland formed during the Middle Pleistocene in the Anglian Stage [Marine Isotope Stage (MIS) 12] and the Late Wolstonian Substage (MIS 6). The landforms and associated sediments are widely preserved in Southern England but are largely absent from the rest of Britain and Ireland because the last ice sheet covered these areas. Despite the restricted evidence, the Middle Pleistocene glaciations had a profound impact on the landscapes of Britain and Ireland. For example, Britain became an island for the first time in Anglian Stage and the Middle Pleistocene Ice Sheets essentially determined the modern drainage of Southern England. Early pre-Last Glacial Maximum glacier advance in the Devensian Stage [MIS 5d-2; Last Glacial Cycle (LGC)] is elusive but significant ice cover is indicated in the sedimentological and geomorphological records early in the LGC, in MIS 4 and 3, in several parts of both Britain and Ireland.
Summary
Following Shotton (1953, 1968, 1976, 1983a,b, 1989), Wolstonian glacial sequences were identified over a large area in the West and Central Midlands (Rice, 1968, 1981; Rice and Douglas, 1991). These deposits indicate extensive glaciation of the region as far south as the Cotswold Hills in Gloucestershire and the Jurassic escarpment further east. The Midlands’ Wolston Formation includes two till units, the Thrussington and Oadby Members, with sands and gravels deposited below, between and above glaciogenic sediment (Shotton, 1953). The Thrussington Till consists of mainly Triassic-derived material, whereas the Oadby Till contains sediments of predominantly later Mesozoic provenance. These components indicate deposition by ice from western and eastern sources, respectively. The Thrussington Till was deposited as far east as Melton Mowbray and Rugby, and its meltwater formed a large ice-dammed lake between Leicester and Market Bosworth, in which up to 25 m of laminated clays and silts (the Bosworth Member) accumulated. The Oadby Till was subsequently deposited over much of the Eastern Midlands as far north as Nottingham and Derby, and as far west as Stratford-upon-Avon. It also extends southward to Moreton-in-Marsh.
In Eastern England the advancing Wolstonian ice-lobe deposited till in Lincolnshire and excavated the Fenland basin during the Late Wolstonian Substage (Straw, 1991, 2005; Gibbard et al., 2009, 2018). The limit of this Fenland Tottenhill ice lobe is marked by a group of glaciotectonic push moraines (Fig. 34.3) and deposits of a series of glaciofluvial delta-fan and related sediments deposited as ice-marginal deltas in a glacially dammed lake (Lake Paterson). This maximum ice-marginal position (the “Skertchly Line”) extended eastward close to the present Norfolk coast where Evans et al. (2019)report optically stimulated luminescence (OSL) ages that indicate an MIS 6 age for the emplacement of sediments in the ice-marginal ridge at Stiffkey, Norfolk.
Figure 34.3. Glaciotectonic push moraines marking the limits of the Late Wolstonian (MIS 6) Fenland ice lobe. MIS, Marine Isotope Stage.Adapted from Gibbard, P.L., West, R.G., Hughes, P.D., 2018. Pleistocene glaciation of Fenland, England, and its implications for evolution of the region. Royal Society Open Science 5 (1), 170736 (Gibbard et al., 2018).
Although originally recognised in the English Midlands, this Late Wolstonian glaciation has been identified in Yorkshire, Lincolnshire, western part of East Anglia, the Bristol Channel, and the Welsh Borderlands (Fig. 34.1). Elsewhere, poorly dated glacial deposits of restricted lateral extent have also been attributed to this glaciation and are typically found outside the Devensian glaciation (LGC) limit. Examples include the Bridlington Member or Basement Till of East Yorkshire, the Warren House Till on the coast of County Durham (the Warren House Formation: contra Davies et al., 2011), the Oakwood Formation at Chelford, Cheshire, the Ridgacre Formation, the reddish brown till-like Fremington Member of Barnstaple Bay, North Devon, the Kenn Till of Northern Somerset, the Pilkenzane Formation of Lancashire, the Thornsgill Formation of Thornsgill (Lake District), the Balby Formation at Balby and Brayton Barff in the Vale of York, and the Bakewell Formation at Shining Bank Quarry, North Derbyshire (Gibbard and Clark, 2011).
Offshore, a glacial limit has been established based on the extent of tunnel valleys and a ridge-like push-morainic landform has been identified north of East Anglia (the Norfolk High) and has been shown to continue eastward in the North Sea to join the Netherlands’ Drenthe glaciation maximum limit proposed by Moreau et al. (2012)and Moreau (2010) (cf. Gibbard et al., 2009). Comparison with the Netherlands’ sequence reveals a remarkable parallelism of events during this glaciation. In particular, Wolstonian glacial advances are generally contemporaneous with the major glacial advance during the Drenthe Stadial, the most extensive advance of the Late Saalian Stage (MIS 6), during which the southwest margin of the Eurasian Ice Sheet reached a maximum stillstand position in the Central Netherlands (Laban and van der Meer, 2004; Busschers et al., 2007, 2008). The contemporaneity is established through recent OSL dating both in Britain and the Netherlands (Busschers et al., 2008; Gibbard et al., 2018, 2021; Gibbard and Clark, 2011; Gibson, 2019).
In Ireland the equivalent of the Wolstonian Stage is the Munsterian Stage. The Munsterian Stage is reviewed in the study of Knight et al. (2004) who noted that the evidence for ice limits and flow directions associated with this glaciation is not clear and based mainly on erratic carriage and the presence of striae and subdued glacial landforms found outside well-marked Midlandian (LGC) end moraines. The fact that ice is now known to have completely covered Ireland in the LGC does raise doubts about the presence of surface glacial features relating to this penultimate glacial cycle. In terms of deposits, it is likely that deposits previously interpreted Munsterian are in fact Midlandian in age (Warren, 1985; Eyles and McCabe, 1991; Coxon 1993).
No comments:
Post a Comment