A Miocene palynoflora preserved by karstic subsidence in Anglesey and the origin of the Menaian Surface

Walsh, Peter; Morawiecka, Iwona; Skawińska-Wieser, Krystyna

doi:10.1017/s0016756800024560

Cited by 16 publications

(22 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Further north and west, residual deposits and Tertiary outliers have been carefully examined. Again, conclusions from such studies conflict with earlier assumptions (Battiau-Queney 1984;Walsh et al 1987Walsh et al , 1996Walsh 1999). Finally, detailed mapping of surfaces and the interpretation of drainage patterns has suggested some convincing alternatives to the Wooldridge & Linton model (see Pinchemel 1954;Small 1964Small , 1980Jones 1980Jones , 1983Jones , 1999a.…”

contrasting

confidence: 67%

See 1 more Smart Citation

The history of the major rivers of southern Britain during the Tertiary

Gibbard

Lewin

2003

JGS

View full text Add to dashboard Cite

The evolution of the drainage system of lowland Britain is discussed on the basis of available geological evidence, including that from terrestrial sites and that which has more recently become available from offshore exploration of the North Sea, the English and Bristol Channels, and the Irish Sea. Tertiary stratigraphy throws considerable light on landform and river development. Paleocene destruction of a chalk cover, which seems to have been incomplete in western Britain, was accompanied by basin sedimentation under a tropical climate. The major elements, the Thames, Solent, Hampshire (?proto-Avon) river, Irish Sea river and possibly an early Trent river, existed almost throughout the Cenozoic. The influence of Atlantic rifting and thermal doming in NW Britain appears to have been stronger and more temporally focused than the persistent flexuring that determined and maintained Tertiary drainage lines in the SE. Here also the folded Mesozoic terrains on the surface contrast with the more dominant block-faulted relief of the Palaeozoic 'oldlands'. The rivers of the SE can be shown to have extended or reduced their lengths in response to relative sea-level change and gentle warping. Drainage antecedence, the destruction of the Solent system and the breaching of the English Channel are also evident. By contrast, the major river systems of the west are now entirely submerged. Long-term stability of the drainage pattern reflects a persistent tectonic regime in the south, with a subdued low-relief landscape having a weathered regolith and dense vegetation cover. Meandering river channels and alluvial styles predominated, although channel forms varied according to sediment load, slope and discharge variability. Coarse gravel-dominated accumulations are rare and localized. Chemically stable lithologies dominate the clastic component throughout. It is apparent that the deeply incised river valleys seen today are related to high, predominantly coarse sediment yields, encouraged by substantial, rapid climate changes in the Pleistocene. This emphasizes the significance of mechanical compared with chemical weathering for the rate and nature of landscape dissection, and the modifications that have arisen as a result of glaciation, frost-climate weathering, rapidly changing climates and sea levels. The stratigraphical evidence here reviewed is at variance with older, largely geomorphologically based landform evolution models ('denudational chronology'), but gives considerable support to the recent proposals emphasizing the significance of Paleocene erosion, and enduring low-relief landscapes and drainage systems evolving alongside fold development during the Paleogene. Given the depobasin evidence now available, postulated fluvially active episodes can, and must, be linked to contemporaneous deposition. Some at least of the many controversies involving the identity of erosion surfaces, the dating of them using only residual deposits and weathering mantles, and the selection of particular Tertiary episodes as ones of landscape...

show abstract

contrasting

confidence: 67%

“…The results continue to provoke reassessments of the geomorphology of southern England (Jones 1980(Jones , 1981(Jones , 1999a and beyond (e.g. Walsh et al 1987Walsh et al , 1996Walsh 1999;Mignón & Goudie 2001).…”

mentioning

confidence: 90%

The history of the major rivers of southern Britain during the Tertiary

Gibbard

Lewin

2003

JGS

View full text Add to dashboard Cite

show abstract

“…Much of eastern Anglesey, North Wales and the adjacent offshore continental shelf is underlain by Carboniferous as well as Devonian and Mesozoic strata (Howells, 2007;Jackson et al, 1995), consistent with a largely local to Irish Sea source for at least part of the finer grained component to both diamictons. A Miocene palynoflora has also been recorded onshore on Anglesey preserved as a result of karstic subsidence of a large block of limestone within the Gwna Mélange exposed at Trwyn y Parc (SH 372 941) near Cemaes Bay (Walsh et al, 1996). These data suggest that the sparse Devonian, Mesozoic and Paleogene palynofloras are absent in the sandy Irish Sea diamicton, even though this deposit apparently contains a greater proportion of far-travelled pebble to cobble sized clasts.…”

Section: Provenance Of the Diamictons On Angleseymentioning

confidence: 87%

Periglacial disruption and subsequent glacitectonic deformation of bedrock: an example from Anglesey, North Wales, UK

Phillips

Lee

Riding

et al. 2013

Proceedings of the Geologists' Association

View full text Add to dashboard Cite

The deformed metasedimentary bedrock and overlying diamictons in western Anglesey, NW Wales, record evidence of glacier-permafrost interactions during the Late Devensian (Weichselian). The locally highly brecciated New Harbour Group bedrock is directly overlain by a bedrock-rich diamicton which preserves evidence of having undergone both periglacial (brecciation, hydrofracturing) and glacitectonic deformation (thrusting, folding), and is therefore interpreted as periglacial head deposit. The diamicton locally posses a welldeveloped clast macrofabric which preserves the orientation of the pre-existing tectonic structures within underlying metasedimentary rocks. Both the diamicton and New Harbour Group were variably reworked during the deposition of the later Irish Sea diamicton, resulting in the detachment of bedrock rafts and formation of a pervasively deformed glacitectonite. These structural and stratigraphic relationships are used to demonstrate that a potentially extensive layer of permafrost developed across the island before it was overridden by the Irish Sea Ice Stream. These findings have important implications for the glacial history of Anglesey, indicating that the island remained relatively ice-free prior to its inundation by ice flowing southwards down the Irish Sea Basin. Palynological data obtained from the diamictons across Anglesey clearly demonstrates that they have an Irish Sea provenance. Importantly no Lower Palaeozoic palynomorphs were identified, indicating that it is unlikely that Anglesey was overridden by ice emanating from the Snowdon ice cap developed on the adjacent Welsh mainland. Permafrost was once again re-established across Anglesey after the Irish Sea Ice Stream had retreated, resulting in the formation of involutions which deform both the lower bedrock-rich and overlying Irish Sea diamictons.

show abstract

“…A widespread planation surface of presumed middle Miocene age ('Reskajeage surface') is recognised across western Britain and beyond (Walsh et al, 1987(Walsh et al, , 1996Walsh, 1999). In north-east Scotland kaolin weathering took place in the middle Miocene under temperatures of 15 ± 5 °C (Hall et al, 2015).…”

Section: Neogenementioning

confidence: 99%

Filling the North Sea Basin: Cenozoic sediment sources and river styles

Gibbard¹,

Lewin²

2016

Geol. Belg.

View full text Add to dashboard Cite

ABSTRACT. The history of the infilling of the North Sea is outlined, with particular focus on sediment sources and river inputs. In simple terms (for the detail is complex), these sources changed from domination by northwesterly sources from the Shetland area (Paleocene to Eocene), to a geographically more uniform basin-centred pattern, and then northerly input following Fennoscandian uplift (Oligocene and Neogene). Baltic inputs followed via an 'Eridanos (Baltic) River' (Miocene), with cold-climate coarser sediment inputs, and lacustrine episodes resulting from ice damming (Pleistocene). River styles in each of these phases are discussed, with the Cenozoic at first being dominated by low energy fluvial deposition (channel sands, chemically weathered clays, and organic sedimentation) in fluctuating climates. Cold climates in the latest Neogene and Quaternary are seen as major determinant of a change in fluvial style, though these are also associated with tectonic effects, as in Scandinavia. The mediating role of vegetation, relating also to temperature and precipitation, is also likely to have been significant. Narrow valley incision followed the Middle Pleistocene Transition, as well as an increasing importance of Rhine-Meuse sources that had begun earlier.

show abstract

A Miocene palynoflora preserved by karstic subsidence in Anglesey and the origin of the Menaian Surface

Cited by 16 publications

References 15 publications

The history of the major rivers of southern Britain during the Tertiary

The history of the major rivers of southern Britain during the Tertiary

Periglacial disruption and subsequent glacitectonic deformation of bedrock: an example from Anglesey, North Wales, UK

Filling the North Sea Basin: Cenozoic sediment sources and river styles

Contact Info

Product

Resources

About