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The Younger Dryas interval (YD) was a period of widespread, abrupt climate change that occurred between 12,900 and 11,700 cal yr BP (10,900–10,000 14 C BP). Many sites in the Northern Hemisphere preserve a sedimentary record across the onset of the YD interval, including sites investigated in sedimentary basins located in central Mexico (Chapala, Cuitzeo, Acambay), the Basin of Mexico (Tocuila), and northern Mexico (El Cedral). Deposits consist of lacustrine or marginal lake sediments that were deposited during the Pleistocene and the Holocene. At the Tocuila and Acambay sites, Pleistocene fossil vertebrate assemblages, mainly mammoths (Mammuthus columbi), are found in association with a distinctive organic layer, sometimes called the black mat that formed during the YD. At the Chapala, Cuitzeo, Acambay, and Tocuila sites the black mats contain a suite of distinctive microscopic and mineralogical signatures and are accompanied by a sharp change in the depositional environments as supported by diatom and pollen studies reported here. The signatures include magnetic, Fe-rich microspherules, silica melted droplets with aerodynamic shapes (tektites), large amounts of charcoal, and sometimes nanodiamonds (Cuitzeo), all of which were deposited at the onset of the YD. The geochemistry of the microspherules indicates that they are not anthropogenic, authigenic or of cosmic or volcanic origin, and instead, were produced by melting and quenching of terrestrial sediments. Here, we present the stratigraphy at five field sites, the analyses of magnetic microspherules, including major element composition and scanning electron microscopy images. All of these materials are associated with charcoal and soot, which are distinctive stratigraphic markers for the YD layer at several sites in Mexico. © 2017 Springer Science+Business Media B.V.

The Valsequillo Basin in Central Mexico has been of interest due to the presence of megafauna and evidence for early human occupation, but research has been controversial. It has been suggested that extensive and deep lakes characterised the Early Pleistocene environment but sediment exposure is highly fragmentary and reliable dating has been difficult. Here we report, for the first time, Early Pleistocene palaeoenvironmental reconstructions using stable isotopes,diatoms, tephra and pollen. We studied several stratigraphic sections of mainly non-volcanic rocks, containing the 1.3 Ma Xalnene Ash as a stratigraphic marker. The isotope and other proxy data show that topographically low points in the basin were occupied by spring-fed, shallow water lakes during the Early – Mid Pleistocene, with a trend to drier conditions. The basin was a dynamic volcaniclastic environment during this period, with the production of the Toluquilla Volcano sequence and other rhyolitic-dacitic volcanic ashes interbedded with the lake sediments at the sections studied. There is no evidence from the sections for extensive and deep lakes before or after the Xalnene ash deposition. The presence of lakes in the basin during the Early Pleistocene would have made it attractive for megafauna.

We report new stratigraphic, tephrochronology and dating results from the Tocuila Mammoth site in the Basin of Mexico. At the site there is evidence for a thin meteorite airburst layer dated between 10,878 and 10,707 cal BC at the onset of the Younger Dryas (YD) cool period. The Upper Toluca Pumice (UTP) tephra marker, caused by a Plinian eruption of the Nevado de Toluca volcano, dated from 10,666 to 10,612 cal BC, is above that layer. The eruption must have caused widespread environmental disruption in the region with evidence of extensive reworking and channelling by the Lake Texcoco shoreline and contributed to the widespread death and/or extinction of megafaunal populations, as suggested by earlier authors, but the new work reinforces the view that both catastrophic events must have caused large environmental disruption in a short time period of around two hundred years. There is no evidence for megafauna (mammoths, sabre toothed cats, camels, bison, glyptodonts) after the UTP volcanic event and subsequent lahars in the Basin of Mexico. At Tocuila, although there are some in situ tephra markers in nearshore lake sediments, such as the Great Basaltic Ash (GBA) and the UTP Ash, there is evidence of much reworking of several tephra populations in various combinations. The mammoth bone accumulation is reworked in a lahar sequence (volcanic mudflow) derived from several source sediments but associated with the major UTP Plinian eruption. Paleoindian populations were also present in the Basin of Mexico during the YD period, where several Paleoindian skeletons were found associated with the UTP ash deposits, e.g. Metro Man, Chimalhuacan Man and Tlapacoya Man.

Holocene footprints have been reported from several locations around the UK coast preserved within inter-tidal sediments. These sediments are normally fine-grained silts, sands and clays. Here we report potential human footprints preserved in the lower of two inter-tidal peat units exposed on the foreshore at Kenfig in South Wales. The lower peat layer pre-dates 3810 ± 40 BP and its maximum age is constrained by two dates, one of 4930 ± 50 BP and another of 5110 ± 50 BP. The prints may have formed at any point within this time interval. Both peat units formed in a salt marsh, or fen environment, as indicated by the analysis of both diatoms and pollen and have been tentatively assigned to the middle Wentlooge Formation within the Holocene lithostratigraphy established for the Severn Estuary Holocene sequence. The footprints were digitised using an optical laser scanner and are compared to other Holocene human footprints exposed on the Sefton Coast in North West England. In comparison the Kenfig prints have poor anatomical form which may be the result of both the substrate and post-depositional modification. The paper demonstrates the value of using optical laser scanning in the data capture and analysis of transitory archaeological and geological trace evidence.

Hominin footprints offer evidence about gait and foot shape, but their scarcity, combined with an inadequate hominin fossil record, hampers research on the evolution of the human gait. Here, we report hominin footprints in two sedimentary layers dated at 1.51 to 1.53 million years ago (Ma) at Ileret, Kenya, providing the oldest evidence of an essentially modern human–like foot anatomy, with a relatively adducted hallux, medial longitudinal arch, and medial weight transfer before push-off. The size of the Ileret footprints is consistent with stature and body mass estimates for Homo ergaster/erectus , and these prints are also morphologically distinct from the 3.75-million-year-old footprints at Laetoli, Tanzania. The Ileret prints show that by 1.5 Ma, hominins had evolved an essentially modern human foot function and style of bipedal locomotion.

Human and animal footprints found in the Valsequillo Basin were formed on the upper bedding planes surfaces of a volcanic ash (Xalnene Ash) deposited by a subaqueous volcano along the shores of a Pleistocene lake. The footprints were made on lake shorelines and the exposed lake floor during low stands associated, either with water displacement during the volcanic eruption, or due to climatically-driven fluctuations in the water balance. The Xalnene Ash has been dated to at least 40 K BP and consequently the human footprints provide evidence for much earlier colonization of the Americas than is often accepted. The methodology used to record, analyze and conserve these footprints used three-dimensional laser scanning, with sub-millimeter precision. This data were used to reproduce polymer models of individual footprints using the application of rapid-prototyping technology. This technology has wide significance for the study of ichnofacies in general. The characteristics of the human footprints and some pro...

We present new data on the stratigraphy, dating and tephrochonology at the most important Paleoindian sites in the Basin of Mexico. These include: a) Peñon Woman III, with the oldest directly radiocarbon dated human remains (10,755 ± 75 BP); b) Tlapacoya, with two human crania dated to just over 10 ka BP; c) Tocuila, an important mammoth site with incorporation of fossils and suggested bone tools within the Upper Toluca Pumice (UTP) lahar (volcanic mudflow). The Tocuila site also includes potential evidence for a layer associated with the Younger Dryas meteorite airburst, with charcoal, iron microspherules, micro-tektites (melted glass) and volcanic ash, dated to 10,800 ± 50 BP and d) the Santa Isabel Iztapan mammoths I and II with lithics of Scottsbluff, Lerma and Angostura types and obsidian prismatic blades but lacking the characteristic fluted Clovis type points normally associated with mammoth kills and butchering and dated after the Pumice with Andesite (PWA) layer between 14,500 BP and 10,900 BP, before the Younger Dryas interval. These results show that these lithic traditions in Central Mexico are older than in the Great Plains of USA. Several tephra markers are recognised in the sites that help to constrain the stratigraphy and dating of the archaeological sequences. However tephra reworking in marginal lake sites is present and has been carefully considered, especially for the PWA tephra.\ud \ud Keywords\ud Late Pleistocene; Mexico; Tephra; Dating; Mammoths; Paleoindians

A review of the Valsequillo archaeological finds from the last century is given, such as the cranial remains (Dorenburg and Ostrander skulls), the engraved bone fragments, butchering marks, green bone fractures and flint points and scrapers. However, most of these finds are now missing. Their original dating is reviewed, along with the controversial Uranium Series and Fission Track dates from Hueyatlaco. Further relative dating techniques, such as the use of diatoms and bone assemblages, are discussed. Recently human and animal footprints from the Xalnene Ash at Toluquilla quarry have been described, mapped and dated by optically stimulated luminescence, and there has been new dating of the Valsequillo Gravels by AMS radiocarbon dating of molluscs and electron spin resonance of mammoth bone. The Xalnene Ash dates have proved controversial and the dating issues are reviewed. A suggested dating framework for the Valsequillo sequence in which the archaeological artefacts and footprints are found is given and all the stratigraphy with archaeological remains is considered to be Late Pleistocene in age.

The timing, route and origin of the first colonization to the Americas remains one of the most contentious topics in human evolution. A number of migration routes have been suggested and there are different views as to the antiquity of the earliest human occupation. Some believe that settlement happened as early as 30 ka BP, but most of the currently accepted early sites in North America date to the latest Pleistocene, related to the expansion of the Clovis culture, while the oldest directly radiocarbon dated human remains are 11.5 ka BP. In this context new evidence is presented in this paper, in the form of human footprints preserved in indurated volcanic ash, to suggest that Central Mexico was inhabited as early as over 40 ka BP. Human and animal footprints have been found within the upper bedding surfaces of the Xalnene volcanic ash layer that outcrops in the Valsequillo Basin, south of Puebla, Mexico. This ash layer was produced by a subaqueous monogenetic volcano erupting within a palaeo-lake, dammed by lava within the Valsequillo Basin during the Pleistocene. The footprints were formed during low stands in lake level along the former shorelines and indicate the presence of humans, deer, canids, big felids, and probably camels and bovids. The footprints were buried by ash and lake sediments as lake levels rose and transgressed across the site. The ash has been dated to at least 40 ka BP by OSL dating of incorporated, baked lake sediments.

Original article can be found at: http://www.sciencedirect.com/science/journal/00370738 Copyright Elsevier B.V. [Full text of this article is not available in the UHRA]

Remapping of the Quaternary geology of the Isle of Man, and consequent revision of the stratigraphic succession, identifies three glacigenic formations each separated by a major unconformity. The oldest formation, the Shellag, represents an extensive ice advance beyond the island limits to the Last Glacial Maximum (LGM). The overlying formation, the Orrisdale, represents a major readvance episode during retreat from the LGM and is associated with the construction of the Bride Moraine and the deposition of extensive proglacial subaqeous sediment. Examination of the sedimentology and micropalaeontology of these sediments indicates that the water body was most likely lacustrine and not marine. Application of sequence stratigraphy to the overlying Jurby Formation identifies evidence for three further phases of readvance, each off-lapping one another into the margin of the lake basin via a complex system of ice-contact subaqueous fans and outwash fan-deltas. The Jurby Formation is dated by organic sediments overlying it as older than 18.5–14.4 kyr BP and provides an ice-marginal correlative for Heinrich event 1 readvance limits identified 50 km to the west in eastern Ireland.

Two sets of well-preserved human footprints have been found in tufa sediments in the Cuatrociénegas Basin, NE Mexico, and here we present their U-series dates of 10.55 ± 0.03 ka and 7.24 ± 0.13 ka. The former are the oldest known footprints in Mexico, although their exact location is unknown, the latter form part of a trackway with eleven in situ human footprints. Oxygen (and to a lesser extent) carbon isotope data from the sediments suggest that the tufa with in situ footprints formed during a transition to a wetter (less arid) period, while pollen evidence indicates the basin floor presence of pecan (Carya) and willow (Salix sp.) before the onset of regional Chihuahuan Desert aridity. These footprints confirm the presence of humans, possibly nomadic hunter–gatherer groups, which persisted until the 18th Century AD.

Applying the principles of structural geology and sedimentology to glacial depositional features indicates that the High-Arctic provides the best analogues for late glacial landforms in the British uplands.

This paper provides the first comprehensive description and interpretation of Pleistocene glacigenic deposits exposed in a cliff section at Thurstaston on the Wirral Peninsula, NW England. The section occupies a strategic position where the Irish Sea ice sheet impinged on the English Midlands and North Wales coast. The section comprises six lithofacies: diamicton, gravel, sand, laminites, mud and cobble pavements. The diamicton lithofacies can be divided into an upper, clast-poor sandy diamicton and multiple units of a lower, clast-rich sandy diamicton. Both diamictons exhibit cobble pavements. The two diamicton lithofacies are distinguished on the basis of textural composition, clast lithology, clast shape, clast surface features and clast macrofabrics. Between the diamicton lithofacies are interbeds of sands and gravels of variable thickness. Minor mud and laminites also occur in close association with the sands and gravels. Both the diamictons are interpreted as basal, deformation tills with the interbeds of the sand, gravel and mud lithofacies as indicators of subglacial meltwater flow and ponding. The cobble pavements are interpreted as the result of clasts sinking within, or to the base of, the deforming layer. The sedimentary succession at Thurstaston is best explained by the advance and subsequent recession of a single terrestrially based ice sheet during the Late Devensian. There is no evidence at Thurstaston to suggest a glaciomarine origin for the Late Devensian deglaciation sediments on this margin of the Irish Sea basin. The evidence at Thurstaston points to constructional deformation with the net accretion of till and interbeds caused by the upward migration of the deforming layer base.

Landform–sediment assemblages associated with two ice-dammed lakes, one active and one fossil, at Heinabergsjokull in southeast Iceland are described. The current ice-dammed lake (Vatnsdalur) is dominated by a large aggradational terrace, as well as an excellent suite of shorelines. The second fossil ice-dammed lake dates from the Neoglacial maximum of Heinabergsjokull (c. 1887) and drained during the late 1920s. This lake is associated with a suite of shorelines and ice-marginal glaciolacustrine fans. The sedimentology of one of these fans is described. Between 50 and 70% of the sediment succession is dominated by ice-rafted sediment, although rhythmites, matrix-rich gravels, sands and graded sand–silt couplets are also present. A range of intra-formational, soft-sediment deformation structures are present, consistent with liquefaction and deformation associated with loading, current shear, and iceberg calving. The landform–sediment assemblages described from Heinabergsjokull provide important data for the interpretation of Pleistocene ice-dammed lakes.

The available published and unpublished archaeological record (human and animal bones, artefacts, footprints) is collated and reviewed in relation to the stratigraphic succession and palaeoecology for Mid-Holocene marginal coastal environments around Liverpool Bay. Two stratigraphic levels with human and animal footprint trails are described from Formby Point and whilst the upper level was formed between c 4000–3600 years B.P. (during the later Neolithic-early Bronze Age), the lower level is older. The animal and bone assemblages and the archaeological artefact evidence for this coastal region are reviewed. The implications of these finds for inter-tidal zone archaeology for this region are assessed but it appears that there is no evidence for major Mesolithic coastal human or animal activity, except for the North Wales coast, although there are major concentrations of Neolithic animal, human and artefacts remains. During the Bronze to Iron Age dunes were present and probably grazed. Metal artefacts have been located from several sites but there is a lack of associated pottery evidence throughout the Holocene. This may mean that settlements were inland and coastal areas were only visited for grazing, hunting and fishing.

Human and animal footprints and tracks exposed in the intertidal zone on the Formby coast are described. Their distribution, age and stratigraphic and palaeoecological setting in relation to Holocene coastal environmental change is discussed. The regional significance of these prints and their relationship to human and animal bones found in the intertidal zone is discussed and their relationship to the local archaeological record is summarised.

The interpretation of glacigenic diamictons is a subjective process, for which quantitative support is frequently sought from parameters such as clast shape and fabric. It has been widely suggested that different glacigenic diamicton facies possess distinct clast-fabric signatures. This paper examines this concept using a data set of 111 clast fabrics, and a synthesis of published results. Eigenvalues are calculated and compared for a variety sedimentary facies. It is concluded that clast fabric alone is not able to discriminate between different glacigenic facies, and it is argued that clast fabric offers little quantitative support in the interpretation of glacigenic sediments. It is suggested, therefore, that although clast fabric may continue to have a role as an indicator of relative strain at specific sites, its use in the discrimination of glacigenic facies is limited. Consequently, we should be much more selective in undertaking such analyses in the future. Copyright © 1999 John Wiley & Sons, Ltd.

Well-rounded gravels are described from moraine-mound complexes, diamicton forefields and modern englacial thrusts at the margins of four glaciers on the northern side of Broggerhalvoya, northwest Spitsbergen. Their shape charcteristics are compared with modern and fossil glacigenic, modern beach and Early Weichselian beach gravels from this peninsula. The best discriminators of the well-rounded gravels have been found to be the percentage-frequency roundness histograms, the roundness mid-point and roundness range diagrams and the sphericity-roundness plots. It is concluded that the gravels have been derived by englacial thrusting from Early Weichselian or last interglacial beaches in the inner parts of the fjord and in the low level cirques when sea level reached at least 50m a.s.l. and deposited the beach gravels. The discrimination between gravel in basal diamictons, proglacial outwash and modern beaches is difficult as the reworking has resulted in little particle shape change. The potential major problem caused by reworking in the glacial environment is emphasised, especially when clast shape comparisons from modern environments to older sediments are used.

Irregular mounds of glacial debris, commonly referred to as 9hummocky moraine9, until recently were linked to ice stagnation during rapid climatic amelioration. However, recent work in Scotland has demonstrated that some hummocky moraine, dating from the Younger Dryas event ( c. 10 000 years BP ), was the product of deposition at active ice margins. Observations at modern high–arctic glacier margins in Svalbard (76–80°N) indicate that some moraines of this type form under a dynamic glaciological regime, mainly by thrusting in active polythermal ice undergoing strong longitudinal compression. This situation is particularly common where there is a transition from warm–based ice in the interior of a glacier to cold–based ice at the margins or snout. From their morphological similarity (rectilinear slopes facing up–glacier and irregular downglacier faces), and apparent stacking of slabs of sediment of subglacial derivation, it is concluded that some assemblages of British moraines are also the product of thrusting. This process appears to be most dominant in polythermal glaciers, rather than in temperate glaciers. On this basis, it is tentatively suggested that the Younger Dryas in Britain was characterized by a climatic regime similar to that in Svalbard today (mean annual temperature − 5°C; 400–1000 mm precipitation), and that the associated glaciers may have been of polythermal character.

The formation of a moraine mound (hummocky moraine) complex at the Neoglacial limit of Pedersenbreen, Svalbard is discussed. The moraine mounds are composed for the most part of sheared basal diami...

Traditionally, geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge (‘crevasse-fill’ ridges). They are widely regarded as a characteristic landform of glacier surges. Understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record. The geometrical ridge network at the surge-type glacier Kongsvegen in Svalbard, does not form by crevasse filling. The networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin. The transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice. The thrusts were apparently formed during a glacier surge in 1948. Longitudinal ridges form through the meltout of elongated pods of debris, which on the glacier surface are subparallel to the ice foliation and pre-date the surge. This work adds to the range of landforms associated with glacier surges.

Many glaciers in Svalbard, which tend to be thermally complex with both warm and cold ice, produced complex ‘push moraines’ or ‘thrust-moraine complexes’ at the time of their maximum neoglacial advance, and during their subsequent recession. Uvěrsbreen, which nearly reaches the coast of northwest Spitsbergen, has a push moraine 50 m high, comprising gravel and sand of fluvial origin, and diamicton derived from basal ice, as well as thrust masses of dead ice. The push moraine is almost entirely a product of the tectonic processes, especially thrusting, that occurred in the snout of the glacier and in the frozen sediments immediately in Journal of Quaternary Science front. Thrusting is probably initiated where the glacier switches from a sliding mode to a state of being frozen to the bed. Thrusting in the foreland is an extension of the same processes that occur within the ice itself, and a sole thrust probably extends from the frozen sediment that underlies the base of the glacier near its snout. Thrusting results in subglacial sediment being uplifted to a high level within the glacier or even to the surface. Subsidiary near-horizontal thrusts parallel to the bedding plane link thrusts dipping up-glacier, and result in local thickening of individual subglacial sedimentary units. Gravels incorporated in this way retain their integrity but sands are folded, whereas uplifted debris-rich basal ice is intensely folded. The distinctive tectonic style of low-dip bedding in gravels, truncated by high-angle (30–40°) thrusts, and only localised folding in less competent material, differs from most descriptions of such ridges, but may be typical of many push moraines composed principally of fluvial material.

Fridtjovbreen is an actively surging tidewater glacier in western Spitsbergen, Svalbard. This paper presents observations made at the western flank of the glacier in July 1997, when the glacier front was still advancing rapidly and was characterised by steep lateral ice cliffs. The geomorphological consequences of the surge include the formation of push moraines from toppled ice blocks along this ice cliff and the development of debris-rich thrusts. There is also evidence of glaciotectonic deformation within deformed debris-rich thrusts. Thrusts are restricted to the lateral margins and are not seen in the terminal calving cliff. On its western flank, Fridtjovbreen is over-riding Sagabreen, a small-tributary glacier. Large facies variations in this area are a result of recycling by Fridtjovbreen of material originally transported as medial moraines on Sagabreen. There are few observations of landform development at actively surging glaciers in Svalbard. The Fridtjovbreen descriptions provide documentation for post-surge landform development. More observations are required at the margins of actively surging glaciers to determine how representative Fridtjovbreen is of a surge event.

SummaryThe sand/matrix ratio technique is described and has been shown to provide a rapid method of correlating till units in the Cumberland lowland which belong to separate glacial phases. Basal tills have a relatively constant sand/silt-matrix ratio compared with flowage tills in the same locality.