70 m shoreline

Fox-Strangways (1892) accepted the impounding of a glacial lake in the Vale of Pickering, but did not determine the level of a shoreline. It can be inferred, however, that this shoreline must have been at an elevation of at least 68.6 m O.D., which is his recorded level for the Hutton Buscel terrace. In discussing the field evidence for two glacial lakes in the Vale of Pickering, Straw (1979) defined an early lake at 70 m O.D. and a lower lake at 45 m O.D. Mapping by Straw (1979, fig. 3.3) included outwash gravels extending from West Ayton to Wykeham below 70 m O.D. that were referred to as a kame terrace.

The validity of the 70 m shoreline is confirmed by field observations made during the mapping program for this study (2016–2017). A shoreline was mapped at c. 70 m O.D. on the southern side of the Vale of Pickering, south of East and West Heslerton (Fig. 2), between outcropping Chalk Group and chalk-gravel alluvial fans. An extension of this shoreline was later confirmed from LiDAR interpretation (Fig. 6a). The character of this shoreline is comparable with a terrace mapped by de Boer et al. (1958) near Market Weighton, later named as the 52 Metre Strandline by Penny (1974). On the northern side of the Vale of Pickering a similar shoreline was mapped at c. 70 m O.D. between Ruston and Forge Valley, separating Jurassic bedrock from gravels (Fig. 3).

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Fig. 6.

(a) Digital elevation model of the southern margin of the Vale of Pickering, showing the erosional gullies in the hummocky chalk-gravel alluvial fans between the 70 and 45 m shorelines, extending from the Knapton gravel pit to east of Ganton. (b) Digital elevation model of the Hutton Buscel terrace and the Wykeham moraine: the terrace extends c. 4 km from Ruston to East Field gully and is bounded along much of its northern edge by the trace of a subsurface erosional cliff. The DEMs are constructed from Ordnance Survey (OS Terrain 5) LiDAR surveys with 5 m resolution. © Crown copyright 2013 – all rights reserved.

Perhaps the most conclusive evidence for the 70 m shoreline is provided on a bench above Crambe [SE 7328 6485] (Fig. 8), where laminated clays exposed in a pit at c. 65 m (Fig. 7l) are situated below a ‘washing line’ at c. 70 m that segregates silt from flanking till.

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Fig. 7.

Illustrations of terraces and alluvial fans mapped in the Vale of Pickering with some of the associated depositional sequences. (a) Remnant of the 70 m terrace south of East Heslerton [SE 928 760]. The remnant mound is about 2 m high. (b) 60 m terrace on the southern face of the Hutton Buscel terrace [SE 988 853]. The summit of the Hutton Buscel terrace is about 70 m O.D. (c) 45 m terrace defining the base of the Hutton Buscel terrace near Hutton Buscel [SE 971 836]. The feature has been enhanced by road work. (d) The back-wall of the 40 m terrace (landscaped) forming the edge of a school playing field near Pickering [SE 793 843]. The mini-goalposts are about 1.5 m high. (e) The 40 m terrace near the Newton Dale outlet [SE 795 842]. The fence line is about 1.5 m high. (f) Part of the valley-confined Newton Dale alluvial fan rising up the back-wall of the 40 m terrace [SE 797 848]. (g) Part of the Thornton Dale alluvial fan, valley, confined by the back-wall of the 40 m terrace [SE 838 838]. (h) Water-worn, locally derived limestone gravel, possibly part of a littoral deposit, south of Thornton-le-Dale [SE 832 824]. Note the green pen for scale is about 15 cm. (i) The back-wall of the 25 m terrace east of Malton [SE 793 719]; it rises about 1.5 m. (j) Faceted sandstone boulder derived from boulder beds under the 32 m terrace south of Pickering [SE 789 832]. Note the 12 cm spectacles for scale. (k) Coarse gravels in a cultivated field on the Howl Dale alluvial fan [SE 814 834]. The spectacle case, top left, is 13 cm. (l) Laminated clays exposed in a temporary pit near the Crambe crossroad [SE 730 657]. The pit is about 80 cm deep. (m) The Jurassic cliff rising to c. 70 m O.D. on the northern side of East Field gulley [SE 990 857]. (n) The eroded Jurassic platform at c. 55 m O.D. in East Field gulley. The platform is about 5 m high. The red arrows mark the base of the diamicton. (o) The diamicton in East Field gulley. Note the ivy leaves for scale.

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Fig. 8.

Map of part of the 70 m shoreline near Crambe, southwest of Kirkham Priory, showing the location of a pit that exposed laminated clays.

The Hutton Buscel terrace (65 m terrace)

The Hutton Buscel terrace is defined here as a planar surface at about 65 m O.D., below the 70 m shoreline (Figs 3 and 6b). It extends from east of Forge Valley to Ruston, where it abruptly terminates against a 10 m scarp of Corallian Group limestone (Fig. 6b), and is dissected by an erosional 60 m O.D. terrace west of Yedman Dale and by extensive terracing at 50 m O.D. between Hutton Buscel [SE 9733 8415] and Forge Valley (Fig. 3). For most of its length the terrace has a southerly facing scarp falling to 45 m O.D., while its northern boundary appears to have a steeply dipping erosional contact against Corallian Group limestone. Kendall (1902) considered the surface of the terrace to fall slightly from east to west, but this was not apparent during mapping for this study (Fig. 3). Coarse gravels with slabs of limestone give the terrace a crude bedded character near Forge Valley, but these deposits, now largely removed by quarrying, pass laterally to sand and grit near Hutton Buscel.

The origin of the terrace has been in dispute since Fox-Strangways (1880, 1892) suggested it had formed as a beach or shoreline terrace. This model was rejected by Kendall (1902) on the basis that a corresponding feature was not present on the southern side of the valley, and he considered the landform to be a ‘deformed delta’ marginal to a glacier; Straw (1979) and Eddey et al. (2017) refer to it as a kame terrace.

A conspicuous terrace equivalent to the Hutton Buscel terrace is not preserved on the southern side of the Vale, but the Hutton Buscel terrace has much in common with the chalk-gravel alluvial fans below the Chalk Group escarpment so they might have had similar origins. Three observations are relevant: (1) both deposits are bounded by terraces at 70 and 45 m O.D. (Figs 3 and 6); both deposits are imprinted by 60 m O.D. and 50 m O.D. terraces; both deposits seem to have feeder channels leading into them: Sawdon Dale, Bee Dale and Yedman Dale to the Hutton Buscel terrace (Fig. 3) and valleys south of East and West Heslerton to the chalk- gravel fans (Fig. 2). The failure to preserve a more conspicuous terrace might be attributed to the bedrock of water-saturated Chalk Group (not the case for the Hutton Buscel terrace) allowing erosion caused by the emanation of spring water.

These observations are inconsistent with the origin of a well-documented kame terrace, such as the Brampton kame belt described by Livingstone et al. (2010). Perhaps a major problem to overcome to confirm a kame terrace at Hutton Buscel is its location adjacent to the 70 m O.D. shoreline, and the need to explain the 60 and 50 m O.D. terraces on the southern face of the landform, if they are not of lacustrine origin, as is the case of similar terraces in the chalk-gravel fan below the Chalk Group escarpment. Kendall & Wroot (1924) interpreted the 60 m O.D. terrace as a groove cut by a stream running parallel to the hillside, but a lacustrine origin for the Hutton Buscel terrace has to be more likely rather than searching for a unique event.

60 m terrace

This forms a significant erosion level, particularly between Ruston and West Ayton (Fig. 3) where it has dissected the Hutton Buscel terrace into small tabloid mounds separated by narrow steep-sided shallow valleys. Near Forge Valley, the shoreline forms a conspicuous bench on the southern face of the terrace (Fig. 7b). Although not conspicuously terraced along its entirety, the shoreline has been recorded north of Seamer [TA 0163 8361] and north of Eastfield [TA 0386 8399] in the Mere valley, where it passes laterally into a fluvial terrace (Fig. 3). It also forms a planar level at the summit of the Wykeham moraine and on Gallows Hill [SE 9520 8285] where the surface is underlain by a gravel lag.

On the southern slopes of the Vale of Pickering (Fig. 2) the terrace has been noted in the valley south of West Heslerton, but elsewhere in this region the terrace in the chalk-gravel fans is absent probably due to extensive erosion.

50 m terrace

Forming only a minor bench on the southern face of the Hutton Buscel terrace between Hutton Buscel and Forge Valley and on the Jurassic slope east of Forge Valley (Fig. 3), this terrace, near Crossgates [TA 0292 8398], has been tentatively mapped as the boundary between Jurassic bedrock and the cover of glaciofluvial sediments and lacustrine deposits (note that on the British Geological Survey 1998, 1:50 000 Scarborough sheet, this boundary has been placed at a lower elevation, closer to the 40 m contour). In the Mere valley, north of Eastfield, the 50 m terrace forms a wide platform between Eastfield and The Mere [TA 0345 8598] (Fig. 3). Subsequent erosion below the 50 m terrace has resulted in the outlier of glaciofluvial gravel at Gallows Hill (near Ruston), now separate from the main Wykeham moraine (Fig. 3).

45 m terrace

The back-wall of the 45 m terrace of the 45 m lake, which is equivalent to the 42/45 m terrace on Figure 3, is a pronounced feature at the base of the Hutton Buscel terrace below Hutton Buscel (Figs 3 and 7c). Eastwards, the terrace is less robust and has only been recognized north of Seamer (Fig. 3). In the Mere valley, however, the terrace again takes the form of a planar surface on both sides of the valley, flanking the railway line and forming a base for part of the A64 road (Fig. 3).

Between East and West Heslerton, the 45 m terrace, although not appearing to have a distinctive erosional back-wall, does form a well-defined contact between the rather hummocky older chalk-gravel alluvial fans and the planar sandy surface of the younger alluvial fans or Sherburn Sands (Fig. 2, see below). This contact, which is continuous with the edge of fluvial channels that extend back into the chalk, has therefore partly evolved from fluvial erosion. Straw (1979) has referred the 45 m terrace to a lower Lake Pickering level.

42 m terrace

A 42 m O.D. terrace, which rises into the 45 m terrace, has only been mapped along the northern side of the Vale of Pickering between Pickering and Thornton-le-Dale, although not as a continuous feature (Fig. 5). Despite this, it is possible that the terrace is more widely preserved than the mapping indicates, as it was also noted in places above the 40 m O.D. terrace on the western side of Malton (Fig. 4).

The 42 m O.D. terrace is particularly significant as it could mark not only the maximum elevation of Glacial Lake Humber (Fairburn & Bateman 2016) but also the maximum elevation of the younger low-level phase of Glacial Lake Pickering (Straw 1979) if it is equivalent to the 45 m O.D. terrace, with the level difference being due only to a minor eastward rise in apparent lake elevation.

40 m terrace

This terrace, which forms a continuous bench between Pickering and Thornton-le-Dale (Fig. 5) and between Ruston and Eastfield (Fig. 3) has also been mapped adjacent to the A64 between East Knapton [SE 8819 7593] and East Heslerton (Fig. 2) and on the western side of Malton (Fig. 4). It is the most conspicuous terrace of Glacial Lake Pickering as it has eroded a prominent back-wall (enhanced by landscaping) that can be observed below the Pickering school [SE 7926 8432] (Fig. 7d) and along the western wall of the Newton Dale outlet (Fig. 7e). This back-wall also forms a diminishing boundary in both Newton Dale and Thornton Dale between in-valley alluvial fans and Coralline Group bedrock (Fig. 7f and g). The terrace also extends into Forge Valley and north of Eastfield adjacent to the A64 before it terminates against the rising Mere valley floor south of grid reference [TA 0311 8522] (Fig. 3).

35 m terrace

The 35 m terrace is not a distinctive feature in the mapped areas as it was not recognized north of the A64 near the East Heslerton sand and gravel pit [SE 9173 7698], possibly owing to low regional relief, difficult to trace in the Malton urban area (Fig. 4), poorly defined near Thornton-le-Dale, and noted only in a few locations near the southern edge of the area mapped in Figure 3 between Wykeham and Crossgates. It was, however, mapped with confidence below the Pickering school (Fig. 5), in places on the Jurassic dip slope east of Pickering (Fig. 5) and adjacent to the Malton to York road (Fig. 4). A 35 m O.D. terrace was not recognized in Glacial Lake Humber (Fairburn & Bateman 2016), but it is possibly equivalent to the well-presented 33 m O.D. terrace of that lake, the difference in elevation being due to a short-lived restriction near Kirkham Priory, where a 35 m O.D. terrace has been observed by the author (see also 34–36 m OD terrace of Eddey & Lincoln 2017), or to an apparent minor elevation rise of the lake surface due to an isostatic effect.

32 m terrace

It is probable that this terrace, although a distinctive feature running parallel to the Pickering to Thornton-le-Dale road (Fig. 5), marks only a temporary stand of Glacial Lake Pickering at the foot of the faulted Corallian Group outcrop (British Geological Survey 2000). To the southwest of Newton Dale it is much less distinct (Fig. 5). It is, however, significant as it forms the northern edge of gravel and boulder beds that underlie much of central Pickering, where the deposit resembles a littoral zone reworked from an older Newton Dale alluvial fan (see below).

30 m terrace

Around Malton, this terrace, like the 35 m O.D. terrace, is generally obscured in the urban area and is only clearly observed adjacent to the Malton to Old Malton road (Fig. 4). It is more conspicuous near Pickering (Fig. 5), where it forms the southern edge of the gravel and boulder beds forming the 32 m O.D. terrace, and south of Thornton-le-Dale with locally derived littoral gravels (Fig. 7h) possibly reworked downslope from the 35 and 40 m terraces.

North of West Heslerton (Fig. 2) and to the west of the sand and gravel pit, a 30 m O.D. terrace may be indicated by a transition from silty to more clayey soils.

25 m terrace

Indicating an appreciable shrinkage of Glacial Lake Pickering, with emergence from the lake of the higher ground around Malton (Fig. 4), the 25 m O.D. terrace is one of the more visible of the lake's terraces as it has a conspicuous back-wall (Fig. 7i). Generally outside the built-up area of Malton the terrace can be mapped with certainty for at least 2 km between Malton and Old Malton (Fig. 4).

Modern alluvium

While modern river alluvium of the River Derwent forms a terrace at c. 20 m O.D. through Malton (Fig. 4), a slightly higher terrace was noted (although not mapped) in a few locations between 22 and 23 m O.D. in the river valley. These remnants of an older river terrace could be the equivalent of one mapped in the Ouse valley near York (Fairburn & Bateman 2016), believed to be an alluvial extension of the 5 m O.D. terrace of Lake Humber.

Thornton Dale

In contrast to Newton Dale, there is no evidence of fanglomerates in Thornton Dale, unless a comparable deposit is present in the subsurface and lacks any topographic expression. The dale does, however, contain an in-valley alluvial fan similar to the younger sandy fan in Newton Dale (Fig. 5) and as in Newton Dale, the rising fan north of Thornton-le-Dale, is contained by the back-wall of the 40 m O.D. terrace (Fig. 7g). South of Thornton-le-Dale the gently dipping surface of the fan, which contains minor drainage channels, expands to more than 1 km in width as it merges with the 30 m O.D. terrace of Glacial Lake Pickering (Fig. 5). As in Newton Dale, the alluvial fan must be younger than the imprinting of the 40 m O.D. terrace of Glacial Lake Pickering.

Howl Dale

In contrast to both Newton Dale and Thornton Dale, the Howl Dale alluvial fan can be mapped in its entirety from its emergence at the foot of the Jurassic dip slope down to its terminal deposition below the 30 m O.D. terrace of Glacial Lake Pickering (Fig. 5). It is also apparent from the boundaries of the fan that it represents a destructive event eroded through the 40 m O.D. terrace of Glacial Lake Pickering (Fig. 5). Clasts recorded from the fan gravel below its point of emergence include both rounded and faceted quartz and sandstone pebbles as well as larger flat cobbles of locally derived limestone (Fig. 7k). The deposit could be of comparable age to the Newton Dale and Thornton Dale alluvial fans.

Hutton Buscel

The Hutton Buscel alluvial fans that supplied sediment to the 65 m Hutton Buscel terrace originated from feeder channels, namely Sawdon Dale, Bee Dale and Yedman Dale, cut into the Jurassic dip slope (Fig. 3). This gravelly, sandy sediment consisting largely of small sub-rounded to faceted pebbles of sandstone ranging in size from 2 to 4 cm is believed to be of glacial origin. In an examination of this sediment at Yedman Dale and Hutton Buscel, Kendall (1902) identified pebbles of Jurassic sandstone and limestone with some pebbles of Cheviot andesite, greywacke, jasper and granite. The presence of such lithologies, not of local provenance, could indicate derivation from unmapped older tills on the North York Moors.

Heslerton

Mapping between East and West Heslerton has outlined two sets of alluvial fans below the Chalk Group escarpment: an older set of hummocky fans eroded by gullying and shoreline terracing and a younger set of fans that have produced more planar landforms.

The older hummocky chalk-gravel fans, composed of chalk gravel, sand and silt, are confined below the 70 m O.D. terrace and extend down to the 45 m O.D. terrace (Figs 2 and 6a). Initial deposition of these fans must have been more extensive and have included valley-fill deposits extending back into the Chalk escarpment to elevations of nearly 80 m O.D.; subsequent fluvial erosion has re-excavated these valleys leaving only remnants of the fill on the valley sides (Fig. 7a). Lacustrine erosion of the fans is indicated by shorelines at 55, 60 and 65 m O.D. (Fig. 2). These fans, which must have originated from significant fluvial events, were probably recognized by Fox-Strangways (1880) as ‘a thick covering of sand including angular and partially rounded fragments of chalk and chalk flints’ up to 50 ft (15.2 m) thick lying at the foot of the Chalk escarpment. Remnants of extensive sub-aerial deposition also comprise isolated planar deposits on eroded interfluve areas at elevations between 80 and 85 m O.D. (Fig. 2) on the Chalk Group.

The younger sandy fans appear to have originated by fluvial erosion from valleys previously occupied by the chalk-gravel fans that breach the 70 m O.D. shoreline. These fans form a gentle, northerly sloping planar surface that extends from a depositional edge below the 45 m O.D. shoreline down to at least 30 m O.D. (Fig. 2), where the deposit becomes more silty. They are only imprinted by the 40 m O.D. shoreline and are therefore older in part than this prominent shoreline of Glacial Lake Pickering. The deposit, also referred to as the Sherburn Sands (Foster 1987), has been given a maximum optically stimulated luminescence (OSL) age of 17.6 ± 1.0 ka (Evans et al. 2016).

Forge Valley

In contrast to Newton Dale and Thornton Dale, the floor of the Forge Valley (Fig. 3), appears to form an extension of the 40 m O.D. terrace of Glacial Lake Pickering. Any alluvial fan component feeding into this terrace must be to the north of the mapped area.

The Pickering and Thornton Dale tills

Recent drilling by the British Geological Survey (Powell et al. 2016) has confirmed that deposits of till mapped by Fox-Strangways (British Geological Survey 2000) southwest of Pickering are valid and consequently refute auger drilling results recorded by Edwards (1978). Powell et al. (2016) suggest a source of the till from a plateau ice field on the North York Moors.

The Thornton Dale till was defined by Edwards (1978) as a terminal moraine associated with the earliest advance of Late Devensian ice, and Evans et al. (2016) depicted the Pickering/Thornton-le-Dale Stage as one of two scenarios, albeit the least likely, for the maximum extent of a North Sea ice lobe during the Dimlington Stadial. As noted above, though, there is no evidence that such an advance of the North Sea lobe reached this far west. However, the westerly truncation of the moraine by the Thornton Dale alluvial fan (Fig. 5) does suggest a source from Thornton Dale as there is no evidence of a glacial advance from Wykeham.

The tentative Middle Pleistocene MIS 8 age for the Pickering and Thornton Dale tills, proposed by Powell et al. (2016), provides a foundation for a re-evaluation of the glacial history of the Vale of Pickering prior to the Dimlington Stadial, and must allow some rethinking on the validity of an ice advance during this stadial elsewhere in the Vale of Pickering.

Wykeham moraine and Hutton Buscel terrace

A long-standing interpretation of the Hutton Buscel terrace (since Kendall 1902) is that it originated as a kame terrace (e.g. Straw 1979; Eddey et al. 2017). This interpretation is contrary to the current mapping (Fig. 3), however, which suggests that the terrace originated from possible sub-aqueous fans built out by glaciofluvial sediments that were deposited from feeder valleys during shrinkage of a proglacial lake from 70 m O.D. down to about 65 m O.D. Subsequent shrinkage of the lake resulted in pronounced erosional terracing at 60 m that dissected the original terrace into tabular hills and planed the surface of the Wykeham moraine (Figs 3 and 6b). The final southerly margin of the terrace resulted from truncation by the 45 m O.D. strandline. This suggested lacustrine influence is not compatible with a kame terrace and is more akin to an earlier interpretation as a raised beach (Fox-Strangways 1880). Furthermore, as the depositional and erosional model for the northern 70 m shoreline, derived from mapping, has many similarities with the southern shoreline, then a unique origin for a kame terrace in the north is unlikely, but does not rule it out completely.

Also relevant to the formation of the Hutton Buscel terrace is its northern boundary, which abuts against a steeply inclined face of Corallian Group limestone. This cliff, of about 10 m elevation, is exposed near its termination above Ruston and in the East Field gully (an informal name) [SE 9900 8567] east of Forge Valley due to fluvial incision (Fig. 6b). The surface trace of the cliff (Fig. 6b), which appears to truncate the interfluvial ridges of Jurassic bedrock, could therefore preclude the formation of a kame terrace to the south. That there could have been considerable erosion of the Jurassic dip slope prior to the deposition of the terrace is also indicated by much of the Hutton Buscel terrace lying in an embayment on the northern margin of the Vale of Pickering (Figs 3 and 6b). That there could have been glacial erosion in the Vale of Pickering from an advance of the North Sea ice lobe to deposit the Wykeham Moraine is indicated by Eddey et al. (2017) and Evans et al. (2016). Such an advance was also suggested by Kendall & Wroot (1924).

The East Field gully

This steep-sided gully, which joins Forge Valley north of East Ayton (Fig. 3), forms an erosional boundary between a cliff of bedded Jurassic strata in the north and a diamicton to the south. The Jurassic cliff (Fig. 7m) rises over 20 m from near the base of the gully at 50 m O.D. to over 70 m O.D. On the south side, an eroded Jurassic platform (Fig. 7n), at about 55 m O.D., is overlain by the diamicton (Fig. 7o). Because the outcrop is poor, improved access to the site is required to allow a shallow excavation to determine if the diamicton is a glacial till.

While there has been recent fluvial erosion, it is thought that the gully is a continuation of the buried cliff under much of the Hutton Buscel terrace.