THE LANGHOLM & NEWCASTLETON
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The Langholm and Newcastleton Hills lie on the southern margin of the Southern Uplands Terrane, a rocky massif, which has been an area of general lypositive relief for at least 420 million years (Ma). The ‘basement’ rocks of the terrane are the greywacke sandstones and siltstones of the Riccarton Group seen at Peden’s View and Monument View quarries (localities 1 and 2). These are deposits in which the original sand and mud sediment was transported by high-energy turbulent sediment/water slurries (turbidity currents) from continental shelf areas, via submarine canyons, onto large deep-water submarine fans in the Iapetus Ocean. Evidence for this origin can be seen on bedding planes, many of which show examples of characteristic sedimentary structures known as flute-, groove– or prod- casts. These are a common feature of such turbidite deposits and were formed when either spinning vortices or ‘tools’ (rock fragments carried along in the current) eroded or cut down into the underlying mud on the sea floor. Differential loading at the soft sand/mud interface tended to emphasise the depth profiles of these marks. The Iapetus Ocean lay between Scotland and England during Ordovician and Silurian times, some 470-420 Ma ago and closed due to the movement of huge crustal plates. The greywacke sandstones laid down in the ocean were squeezed up and intensely folded to give the steeply dipping beds we see today. WELCOME TO THE LANGHOLM AND NEWCASTLETON HILLS The rocks and landscape of the Langholm and Newcastleton Hills can be used to demonstrate many aspects of the geological history of southern Scotland during the last 430 million years. Over this period, the basement of older rocks, laid down in an ocean separating Scotland and England, were thrust up into a mountain chain. This was then eroded down and the sediment deposited in deserts, river valleys, deltas and shallow seas. During early Carboniferous times, volcanic activity led to the outpouring of the Birrenswark Lavas in the area. The most recent geological event, the Devensian glaciation, and its subsequent retreat, has had a profound influence in eroding and smoothing the underlying rock and depositing boulder clay, sand and gravel in the valleys. By visiting the localities described overleaf, you can explore and study the landforms and the natural and man- made exposures in the area to understand the geology and discover how it influences the landscape all around us. The importance of this geology, landscape and natural heritage is formally recognised in the designation of the Langholm and Newcastleton Hills as a Site of Special Scientific Interest (SSSI) and Special Protection Area (SPA). Find further information about many other attractions in the surrounding area at www.langholm-online.co.uk or by contacting the Langholm Initiative at Ashley Bank House, Langholm, DG13 0DJ. Tel: (013873) 80914. Email: [email protected] Please respect the country code, wear appropriate clothing and footwear and park in designated areas. Enjoy your visit! The Moorland Project is a partnership between The Langholm Initiative and The Buccleuch Estates Ltd. The generous support of all involved with the Moorland Project is gratefully acknowledged. Project Manager Emma-Jane Ahart. Text by Dr. James D. Floyd. Photographs by Dr. James D. Floyd, Andrew McMillan and courtesy of the British Geological Survey. Artwork and design by John Hills. GEOLOGY OF THE LANGHOLM & NEWCASTLETON HILLS A SPECIAL PLACE Above: Permian red sandstones forming cliff on south bank of the River Esk at Canonbie. These rocks were laid down in a desert and show traces of dune-bedding. Left: Modern alluvium next to the River Esk at Canonbie. At least three higher terraces can be seen in the background, each representing older and higher river levels since the Pleistocene glaciation. Above: Small flute casts on base of a greywacke bed, Peden’s View Quarry. Right: Cross section through a Siphonodendron colony in Carboniferous limestone at Penton Linns. These were colonial corals which helped to build large reefs in shallow tropical seas. The white rings to the right of the coin are disarticulated crinoid (Sea Lily) columnals. After closure of Iapetus, the Southern Uplands formed a mountain range, which was gradually eroded over the next 70 Ma. By early Carboniferous times (c. 350 Ma), the relief was almost similar to today though the conditions were hot and initially arid. However, a shallow marine basin, known as the Northumberland Trough, lay roughly along the Solway. Volcanic activity at that time led to the outpouring of basaltic lavas, examples of which can be seen at Skipper’s Bridge (locality 4). Over time, the lavas were covered by thick river sandstones (such as the Whita Sandstone at locality 3) and lagoonal limestones and mudstones, which were laid down as the climate gradually became more moist and tropical. As the Northumberland Trough gradually subsided, the sea extended farther northwards and the shallow marine limestones, sandstones and mudstones of the Penton Linns section (locality 6) were deposited. These have marine brachiopod fossils and both solitary and colonial corals such as Siphonodendron. As the basin filled and conditions became more deltaic, sandstone such as at Gilnockie Bridge (locality 5) and coals were deposited. By Permian times (c. 290 Ma), desert-like conditions had returned and the red sandstones of Canonbie were laid down (locality 7). After the Permian, there is almost no geological record preserved in the area until the evidence of glaciation during the Pleistocene Ice Ages of the Quaternary. When the glaciers finally retreated about 13,000 years ago, rapidly-released meltwater laid down huge spreads of alluvium, which, since then, have been gradually eroded into terrace ’staircases’ such as those seen in the River Esk at Canonbie. Large pothole c. 1m across, cut in sandstone, Liddel Water, Penton Linns. The boulder trapped inside must weigh several hundred kilograms but has been transported by the river. Geologists’ Association Curry Fund
Transcript of THE LANGHOLM & NEWCASTLETON
TheLangholmandNewcastletonHillslieonthesouthernmarginoftheSouthernUplandsTerrane,arockymassif,whichhasbeenanareaofgenerallypositivereliefforatleast420millionyears(Ma).
The‘basement’rocksoftheterranearethegreywackesandstonesandsiltstonesoftheRiccartonGroupseenatPeden’sViewandMonumentViewquarries(localities1and2).Thesearedepositsinwhichtheoriginalsandandmudsedimentwastransportedbyhigh-energyturbulentsediment/waterslurries(turbiditycurrents)fromcontinentalshelfareas,viasubmarinecanyons,ontolargedeep-watersubmarinefansintheIapetusOcean.Evidenceforthisorigincanbeseenonbeddingplanes,manyofwhichshowexamplesofcharacteristicsedimentarystructuresknownasflute-,groove–orprod-casts.Theseareacommonfeatureofsuchturbiditedepositsandwereformedwheneitherspinningvorticesor‘tools’(rockfragmentscarriedalonginthecurrent)erodedorcutdownintotheunderlyingmudontheseafloor.Differentialloadingatthesoftsand/mudinterfacetendedtoemphasisethedepthprofilesofthesemarks.
TheIapetusOceanlaybetweenScotlandandEnglandduringOrdovicianandSiluriantimes,some470-420Ma
agoandclosedduetothemovementofhugecrustalplates.Thegreywackesandstoneslaiddownintheoceanweresqueezedupandintenselyfoldedtogivethesteeplydippingbedsweseetoday.
WELCOME TO THE LANGHOLM AND NEWCASTLETON HILLSThe rocks and landscape of the Langholm andNewcastleton Hills can be used to demonstrate manyaspects of the geological history of southern Scotlandduring the last430millionyears. Over thisperiod, thebasementofolderrocks,laiddowninanoceanseparatingScotland and England, were thrust up into a mountainchain. This was then eroded down and the sedimentdeposited in deserts, river valleys, deltas and shallowseas.
DuringearlyCarboniferoustimes,volcanicactivityledtotheoutpouringoftheBirrenswarkLavasinthearea.Themostrecentgeologicalevent,theDevensianglaciation,anditssubsequentretreat,hashadaprofoundinfluenceinerodingandsmoothingtheunderlyingrockanddepositingboulderclay,sandandgravelinthevalleys.
By visiting the localities described overleaf, you canexploreandstudythelandformsandthenaturalandman-madeexposuresintheareatounderstandthegeologyanddiscoverhowitinfluencesthelandscapeallaroundus.
The importance of this geology, landscape and naturalheritage is formally recognised in thedesignationof theLangholm and Newcastleton Hills as a Site of SpecialScientificInterest(SSSI)andSpecialProtectionArea(SPA).
Findfurtherinformationaboutmanyotherattractionsinthesurroundingareaatwww.langholm-online.co.ukorbycontactingtheLangholmInitiativeatAshleyBankHouse,Langholm,DG130DJ.Tel:(013873)80914.Email:[email protected]
Please respect the country code,wear appropriate clothing andfootwear and park in designatedareas.Enjoyyourvisit!
TheMoorlandProjectisapartnershipbetweenTheLangholmInitiativeandTheBuccleuchEstatesLtd.
Thegeneroussupportofall involvedwith theMoorlandProjectisgratefullyacknowledged.ProjectManagerEmma-JaneAhart.
TextbyDr.JamesD.Floyd.Photographs by Dr. James D. Floyd, Andrew McMillan
andcourtesyoftheBritishGeologicalSurvey.ArtworkanddesignbyJohnHills.
GEOLOGY OF
THE LANGHOLM & NEWCASTLETON
HILLS
A SPECIAL PLACE
Above:PermianredsandstonesformingcliffonsouthbankoftheRiverEskatCanonbie.Theserockswerelaiddowninadesertandshowtracesofdune-bedding.
Left:ModernalluviumnexttotheRiverEskatCanonbie.Atleastthreehigherterracescanbeseeninthebackground,eachrepresentingolderandhigherriverlevelssincethePleistoceneglaciation.
Above:Smallflutecastsonbaseofagreywackebed,Peden’sViewQuarry.
Right:CrosssectionthroughaSiphonodendroncolonyinCarboniferouslimestoneatPentonLinns.Thesewerecolonialcoralswhichhelpedtobuildlargereefsinshallowtropicalseas.Thewhiteringstotherightofthecoinaredisarticulatedcrinoid(SeaLily)columnals.
AfterclosureofIapetus,theSouthernUplandsformedamountainrange,whichwasgraduallyerodedoverthenext70Ma.
ByearlyCarboniferoustimes(c.350Ma),thereliefwasalmostsimilartotodaythoughtheconditionswerehotandinitiallyarid.However,ashallowmarinebasin,knownastheNorthumberlandTrough,layroughlyalongtheSolway.Volcanicactivityatthattimeledtotheoutpouringofbasalticlavas,examplesofwhichcanbeseenatSkipper’sBridge(locality4).
Overtime,thelavaswerecoveredbythickriversandstones(suchastheWhitaSandstoneatlocality3)andlagoonallimestonesandmudstones,whichwerelaiddownastheclimategraduallybecamemoremoistandtropical.
AstheNorthumberlandTroughgraduallysubsided,theseaextendedfarthernorthwardsandtheshallowmarinelimestones,sandstonesandmudstonesofthePentonLinnssection(locality6)weredeposited.ThesehavemarinebrachiopodfossilsandbothsolitaryandcolonialcoralssuchasSiphonodendron.Asthebasinfilledandconditionsbecamemoredeltaic,sandstonesuchasatGilnockieBridge(locality5)andcoalsweredeposited.
ByPermiantimes(c.290Ma),desert-likeconditionshadreturnedandtheredsandstonesofCanonbiewerelaiddown(locality7).
AfterthePermian,thereisalmostnogeologicalrecordpreservedintheareauntiltheevidenceofglaciationduringthePleistoceneIceAgesoftheQuaternary.Whentheglaciersfinallyretreatedabout13,000yearsago,rapidly-releasedmeltwaterlaiddownhugespreadsofalluvium,which,sincethen,havebeengraduallyerodedintoterrace’staircases’suchasthoseseenintheRiverEskatCanonbie.
Large pothole c. 1m across, cut insandstone,LiddelWater,PentonLinns.The boulder trapped inside mustweigh several hundred kilogramsbuthasbeentransportedbytheriver.
Geologists’AssociationCurryFund
Explore the geology of
THE LANGHOLM & NEWCASTLETON HILLS
A SPECIAL PLACE
2MonumentViewQuarry(NY374851)QuarrybesideminorroadtoMacDiarmidMemorial.Below: Thin-bedded greywacke sandstonesdip south but are overturned. A small faultcutsthefacefrombottomlefttotopright.
Left:Thesetoolmarkson the underside ofbeds were producedby small rockfragments carried inthe turbidity current.They sometimesprovide, as in thisexample, evidenceof different currentdirections.
7Canonbie(NY395765)Walk downstream from road bridge(B6357)invillage.Above: River alluvium lying onCarboniferoussiltstone.Below: Beds of Permian conglomeratedippingdownstreaminRiverEsk.
3WhitaHill(NY379847)Walk from car park at MacDiarmidMemorial.Above:TheMalcolmMonument on top ofthehillisbuiltoflocalWhitaSandstone.Below:View toeast fromWhitaHill. Thedark foreground isWhita Sandstone, withthe more distant ground underlain byyounger sandstones of the Border Group.The prominent hill in the centre distanceisTinnisHill, an agglomerate-filledventofLowerCarboniferousage.
1Peden’sViewQuarry(NY344862)Roadsideexposure(B709).Below:Thin- and medium-bedded greywackesandstones, which dip southwards but areoverturned.Right: The original ‘way-up’ of beds can bedetermined usingsmall-scalesedimentarystructuressuchastheseflute casts, whichcan be seen on theundersides of many ofthe sandstone beds inthequarry.
5GilnockieBridge(NY385781)Roadsideexposuresbelowbridge(oldA7).Above: Gently-dipping limestones in thebedoftheRiverEsk.Below:LargefallenblocksofcoarseCoalMeasuressandstoneonthenorthbank.Thebridge’s central pillar is founded on thissandstone.
6PentonLinns(NY432774)Walkdownstreamonnorthbankalongroughnarrowtrackfrombridge.Above left: Eroded blocky joints in limestone pavement, Liddel Water. This isreminiscentofkarstweatheringinuplandareas.Aboveright:Coreofanticlineinfoldedlimestonebeds.
4Skipper’sBridge(NY372833)Path to river below bridge from roadside(A7-B6318).Above:Thebridgeisbuiltonbasaltlavas.Below:Thesesmallholesinthelavawereoriginally gas bubbles. They are calledamygdaleswhenlaterinfilledwithcalcite.
