| 1. |
- Bunce, Colin, et al.
(författare)
-
Loess in Britain and Ireland: Formation, modification and environmental significance, a review in memory of John Catt (1937–2017)
- 2022
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier. - 0016-7878. ; 133:6, s. 501-517
-
Forskningsöversikt (refereegranskat)abstract
- Loess was first identified in England as early as the mid-19th century, although these deposits were later mapped as ‘brickearth’ or ‘head-brickearth’ by the British Geological Survey. Much of this material was subsequently recognised and named as loess again by soil scientists, most notably by J.A. Catt. The early reports of loess were mostly located in southeast England, however, more recently loessic deposits have also been reported from the north of England, possibly in Scotland, and as far west as western Ireland. Catt also appreciated that these deposits are the western limits of a broad cover of loess stretching across Eurasia. Here, contrasting models for the possible origin, transport pathways and reworking of these deposits are presented. While some of these British deposits are primary in situ loess, a range of processes has likely affected many of them, including periglaciation, Holocene climatic, and human impacts. Luminescence dating has confirmed British loess to be primarily of late Pleistocene age, however, examples of older loess are also reviewed. Deposits in southeast England are the thickest and best expressed today, and these have yielded significant insight into both the mechanism of the hydroconsolidation (collapse) of loess and landscape evolution in northwest Europe during the Last Glacial Period. The thin and regional nature of British and Irish loess may make it an excellent material for studying loess formation, with advantages over the thicker deposits of typical loess of central Europe, where the impact of smaller scale landscape processes may be less obvious.
|
|
| 2. |
- Chandler, Benjamin M. P., et al.
(författare)
-
Re -interpretation of 'hummocky moraine' in the Gaick, Scotland, as erosional remnants : Implications for palaeoglacier dynamics
- 2021
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 132:4, s. 506-524
-
Tidskriftsartikel (refereegranskat)abstract
- Many glaciated valleys in Scotland contain distinctive, closely spaced ridges and mounds, which have been termed 'hummocky moraine'. The ridges and mounds are widely interpreted as ice-marginal moraines, constructed (luring active retreat of mainly temperate glaciers. However, hummocky terrain can form by various processes in glacial environments, and it may relate to a range of contrasting glaciodynamic regimes. Thus, detailed geomorphologic-al and seclimentological studies of hummocky surfaces in Scottish glaciated valleys are important for robust interpretations of former depositional environments and glacier dynamics. In this contribution, we examine irregularly shaped ridges and mounds that occur outside the limits of former Loch Lomond Readvancc ( Younger Dryas;-12D-11.7 ka) glaciers in the Gaick, Central Scotland. These ridges and mounds are intimately associated with series of sinuous channels, and their planform shape mimics the fon-n of the adjacent channels. Available exposures through ridges in one valley reveal that those particular ridges contain lacustrine, subglacial, and glaciofluvial sediments. The internal sedimentary architecture is not related to the surface morphology; thus, we interpret the irregularly shaped ridges and mounds as erosional remnants (or interfluves). Based on the forms and spatial arrangement of the associated channels, we suggest that the ridges and mounds were generated by a combination of ice-marginal and proglacial glaciofluvial incision of glaciogenic sediments. The evidence for glaciofluvial incision, rather than ice-marginal moraine formation, al pre-Loch Lomond Reaclvance glacier margins in the Gaick may reflect differences in glaciodynamic regimes and/or efficient debris delivery from the glader margins to the glaciofluvial systems.
|
|
| 3. |
- Donovan, Stephen K., et al.
(författare)
-
Echinoids as hard substrates : Varied examples from the Oligocene of Antigua, Lesser Antilles
- 2017
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 128:3, s. 326-331
-
Tidskriftsartikel (refereegranskat)abstract
- A collection of unremarkably preserved fossil irregular echinoids from the Upper Oligocene (Chattian) Antigua Formation of Antigua, Lesser Antilles, nonetheless provides evidence of a range of palaeoecological interactions. A dead test of the heart urchin Eupatagus sp. formed a hard substrate for the attachment of gregarious Thecidellina? sp., a thecidoid brachiopod. Although obligate encrusters, these brachiopods more commonly occur as disarticulated valves free of the substrate in the Antillean fossil record. Elongate pits in test fragments were formed, variously, before and after the death of the host echinoids. These depressions on the external surface were formed either by invertebrates excavating domiciles or by claws or teeth; the echinoid later reclaimed the pits and grew new tubercles in the base. Post-mortem pits lack such new tuberculation. A test of Eupatagus sp. bears the boring Oichnus isp., formed either by a predator (gastropod?) or after the death of the echinoid (domicile), and a serpulid worm tube which grew on the test subsequent to the echinoid's death. The echinoid fauna of the Antigua Formation has been easy to collect and specimens are to be found in many museums; they now await re-examination to reveal palaeosynecological data analogous to that determined from the fragments discussed herein.
|
|
| 4. |
- Donovan, Stephen K., et al.
(författare)
-
Macrostylocrinus bornholmensis Laursen, 1940, a forgotten Silurian crinoid from Denmark
- 2019
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 130:1, s. 76-80
-
Tidskriftsartikel (refereegranskat)abstract
- The monobathrid camerate crinoid Macrostylocrinus bornholmensis Laursen has an unfortunate history. It was published in a journal not commonly consulted by echinoderm workers and, worse, in time of war; written in a language not in common use for crinoid studies; and described by a stratigrapher, not an expert on pelmatozoans. These and other factors combined to ensure that M. bornholmensis has not been reassessed since it was first described almost 80 years ago, despite belonging to a genus well-known from the Lower Palaeozoic. Macrostylocrinus bornholmensis is Llandovery (Telychian) and not Wenlock as has been reported elsewhere. Diagnostic features include a column that does not bear radices close beneath the cup; a heteromorphic mesistele with five orders of regularly inserted internodals; three basal plates; smooth thecal plates with central folds following rays; and ten pinnulate free arms that are biserial distally. Macrostylocrinus bornholmensis is distinctly different in morphology from well-known, congeneric species described from the Lower Palaeozoic of northern Europe.
|
|
| 5. |
- Gierlinski, Gerard D., et al.
(författare)
-
Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?
- 2017
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 128:5-6, s. 697-710
-
Tidskriftsartikel (refereegranskat)abstract
- We describe late Miocene tetrapod footprints (tracks) from the Trachilos locality in western Crete (Greece), which show hominin-like characteristics. They occur in an emergent horizon within an otherwise marginal marine succession of Messinian age (latest Miocene), dated to approximately 5.7 Ma (million years), just prior to the Messinian Salinity Crisis. The tracks indicate that the trackmaker lacked claws, and was bipedal, plantigrade, pentadactyl and strongly entaxonic. The impression of the large and non-divergent first digit (hallux) has a narrow neck and bulbous asymmetrical distal pad. The lateral digit impressions become progressively smaller so that the digital region as a whole is strongly asymmetrical. A large, rounded ball impression is associated with the hallux. Morphometric analysis shows the footprints to have outlines that are distinct from modern non-hominin primates and resemble those of hominins. The interpretation of these footprints is potentially controversial. The print morphology suggests that the trackmaker was a basal member of the Glade Hominini, but as Crete is some distance outside the known geographical range of pre-Pleistocene hominins we must also entertain the possibility that they represent a hitherto unknown late Miocene primate that convergently evolved human-like foot anatomy.
|
|
| 6. |
- Johnson, Mark D., 1954, et al.
(författare)
-
The Ledsjo end moraine-a subaquatic push moraine composed of glaciomarine clay in central Sweden
- 2013
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 124:5, s. 738-752
-
Tidskriftsartikel (refereegranskat)abstract
- During the Younger Dryas cold event, the Scandinavian ice sheet readvanced in southwest Sweden and formed the Middle Swedish end-moraine zone (MSEMZ). Recent highway construction near Skara has created an exposure through the prominent ridge at Ledsjo. Through sketching and measurement of structural information, we have documented the internal character of the Ledsjo moraine. The moraine consists predominantly of clay with numerous sand pods and lenses, which show undeformed, brittle deformed, or fluidized structures. Based on geomorphology and structural geology, it is clear the moraine was made during two advances. As ice advanced, proglacial marine clay was subglacially mobilized by the ice and extruded at the ice margin forming a ramp of debris-flow sediment. Contemporaneously, subglacial meltwater transported sand to the margin, where the meltwater became a buoyant plume, and sand was deposited near the ice margin by currents moving away from as well as toward the ice margin. These processes resulted in interbedded sand and clay. Continued advance of the ice margin deformed this package and further pushed the assemblage into a ridge form with gravity sliding of portions of the ridge. Prior to the second advance, sand was deposited on the proximal side of the initial ridge. During readvance, this sand was thrust faulted and intruded by mobilized clay. Up ice of the intruded sands, subglacial, extensional deformation created a complex shear zone of faulted sand and clay. The Ledsjo moraine represents a subaerial example of submarine push moraines like the submerged moraines recently documented in Svalbard. (c) 2012 The Geologists' Association. Published by Elsevier Ltd. All rights reserved.
|
|
| 7. |
- Olszak, Janusz, et al.
(författare)
-
Revision of river terrace geochronology in the Orawa-Nowy Targ Depression, south Poland : insights from OSL dating
- 2016
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 127:5, s. 595-605
-
Tidskriftsartikel (refereegranskat)abstract
- Geochronologies of intramontane depression (basin) fluvial sedimentation enable to identify through time periods of alluviation and river erosion, and date fault movement. For these purposes the optically stimulated luminescence (OSL) dating has been applied to evaluate and to develop a geochronological framework of river terraces. We study the age of river terrace deposits of the Czarny Dunajec River and its tributaries, in the Orawa-Nowy Targ Depression situated at the contact of the Central and the Outer Carpathians; where alluvial sediment ages were derived mainly from morphostratigraphic dating. Thorough careful analysis our approach demonstrates that the OSL dates differ markedly from the previous age assignments. Alluvium of the terrace elevated 5.5–6.0 m above the present-day valley floor, in terms of cementation and lithology resembling sediments described as pre-Pleistocene, was found to have been deposited ∼34 ka ago (MIS 3). Sediments of the lower terraces, 3 m and 3.5 m high, similar in elevation and internal structure to those of the Holocene terraces, are most likely of MIS 3 and MIS 2 ages, respectively. The architecture of the terraces introduces climate as a dominant driver for terrace formation at the southern border of the depression. We conclude that the morphostratigraphic approach appears insufficient for reliable dating of river terraces, especially in areas where they might be affected by young tectonic movements. Comprehensive and credible chronostratigraphy of fluvial deposits is required, particularly in the studies of the history of the fluvial systems and seismic hazard in the Carpathians.
|
|
| 8. |
- Sahlin, Eva A. U., et al.
(författare)
-
Connectivity analyses of valley patterns indicate preservation of a preglacial fluvial valley system in the Dyfi basin, Wales
- 2009
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 120, s. 245-255
-
Forskningsöversikt (refereegranskat)abstract
- Coastal valleys in the west part of Mid-Wales, such as the Mawddach, Dysynni, Tal-y-Ilyn and Dyfi, acted as corridors for ice which drained the Welsh Ice Cap during the Devensian. Analyses of detailed digital elevation models, and interpretation of satellite images and aerial photographs, show the existence of large variations in the amount of glacial modification between these valleys. Although all the valleys are glacially over-deepened along late Caledonian fault lines, only the Dyfi basin exhibits a dendritic pattern, with V-shaped cross-profiles and valley spurs typical of valleys formed by fluvial processes. Connectivity analysis of the Dyfi basin shows that it exhibits an almost completely dendritic pattern with connectivity alpha and beta values of 0.74 and 1.01, respectively, with little glacial modification of the preglacial fluvial valley pattern in the form of glacial valley breaching. Several examples of glacial meltwater incision into a well-developed pre-existing river valley system, causing river capture across watersheds, have been identified in the Dyfi basin. The degree of preservation of the preglacial fluvial valley system within the Dyfi basin indicates limited modification by glacial processes, despite the area being subjected to glacier activity during the Late Devensian at least. It is possible that major parts of the basin were covered by cold-based or slow-moving ice, close to, or under, a migrating ice-divide, with the major ice drainage Occurring along the weaker zone of the Pennal Fault along which teh Dyfi valley is located, causing minor adjustments to the Surrounding interfluves and uplands. it is proposed here that the general river valley morphology of the Dyfi basin is of a pre-Late Devensian age.
|
|
| 9. |
- Stevens, Thomas, 1979-, et al.
(författare)
-
Detrital zircon U-Pb ages and source of the late Palaeocene Thanet Formation, Kent, SE England
- 2021
-
Ingår i: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 132:2, s. 240-248
-
Tidskriftsartikel (refereegranskat)abstract
- The sources of the Paleocene London Basin marine to fluviodeltaic sandstones are currently unclear. High analysis number detrital zircon U-Pb age investigation of an early-mid Thanetian marine sand from East Kent, reveals a large spread of zircon age peaks indicative of a range of primary sources. In particular, a strong Ediacaran age peak is associated with the Cadomian Orogeny, while secondary peaks represent the Caledonian and various Mesoproterozoic to Archean orogenies. The near absence of grains indicative of the Variscan orogeny refutes a southerly or southwesterly source from Cornubia or Armorica, while the strong Cadomian peak points to Avalonian origin for a major component of the material. Furthermore, the relatively well expressed Mesoproterozoic to Archean age components most likely require significant additional Laurentian input. Comparison to published data shows that both Devonian Old Red Sandstone and northwesterly (Avalonia-Laurentia) derived Namurian-Westphalian Pennine Basin sandstones show strong similarities to the Thanetian sand. This pattern is consistent with derivation of Thanetian material via a SE draining proto-Thames River system that was initiated in the Paleocene due to uplift of western and northwestern Britain. This river system would have incised and eroded cover sandstones and potentially also Avalonian basement of mid to north Wales and England. However, the possibility of a contribution of Laurentian grains directly from the north via longshore drift cannot be excluded by the data, and the extent to which the sediment source signatures of Paleogene sands of the London Basin are variable both geographically and over time remains unclear.
|
|
