{"id":5209,"date":"2020-10-07T01:35:01","date_gmt":"2020-10-07T01:35:01","guid":{"rendered":"https:\/\/joycecountrygeoparkproject.ie\/?p=5209"},"modified":"2020-10-09T11:13:26","modified_gmt":"2020-10-09T11:13:26","slug":"the-end-of-an-ocean-ordovician-to-devonian-periods","status":"publish","type":"post","link":"https:\/\/joycecountrygeoparkproject.ie\/ga\/geological-stories\/the-end-of-an-ocean-ordovician-to-devonian-periods\/","title":{"rendered":"The end of an ocean \u2013 Ordovician to Devonian periods"},"content":{"rendered":"
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490-440 Million Years Ago<\/strong><\/span><\/h4>\n

Deireadh Aig\u00e9in \u2013 Na Tr\u00e9imhs\u00ed Ordaiv\u00edseach Go Dt\u00ed Dheav\u00f3nach<\/strong><\/h1>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div><\/div><\/div><\/section>
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Stua oile\u00e1n bolc\u00e1nach agus fodhucht\u00fa<\/h5>\n

Thart ar 100 milli\u00fan bliain i ndiaidh a chruthaithe ag t\u00fas na tr\u00e9imhse Ordaiv\u00eds\u00ed (490 go 440 milli\u00fan bliain \u00f3 shin)<\/strong>, thosaigh an tAig\u00e9an laip\u00e9iteas<\/strong> d\u00e1 dh\u00fanadh. Bh\u00ed fodhucht\u00fa<\/strong> screimhe aig\u00e9ana\u00ed ina ch\u00fais le cruth\u00fa stua oile\u00e1n bolc\u00e1nach<\/strong>. Le\u00e1dh an screamh aig\u00e9anach fodhuchtaithe i dteochta\u00ed an-ard agus crutha\u00edodh insn\u00ed magma go dt\u00ed an dromchla, a bh\u00ed ina ch\u00fais le cruth\u00fa bolc\u00e1n. Analach leis an bpr\u00f3iseas seo, t\u00e1 oile\u00e1in nua-aimseartha bholc\u00e1nacha na h\u00c1ise Thoir a chrutha\u00edtear mar gheall ar chriosanna fodhuchtaithe san Aig\u00e9an Ci\u00fain.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div>

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D\u2019\u00fasc laibhe bhasaltach, a bh\u00ed chomh te le 1200\u00b0C, amach go grinneall na farraige agus d\u2019fhuaraigh an t-uisce farraige go tapa \u00ed. Tugaimid laibhe adhartach<\/em> uirthi seo, mar nuair a bhreathna\u00edtear ar an trasghearradh, b\u00edonn na sreabha aonair laibhe cos\u00fail le hadhairteanna carntha. T\u00e1 seo le feice\u00e1il ar thaobh an bh\u00f3thair i bhFionnaithe, gar do Loch na Fuaiche. T\u00e1 adhairteanna aonair le feice\u00e1il, chomh maith le saic\u00edn\u00ed n\u00f3 bolg\u00e1in g\u00e1is. N\u00edos faide \u00f3 thuaidh i dTuar Mhic \u00c9adaigh, agus beag\u00e1n n\u00edos \u00f3ige in aois, t\u00e1 fianaise ann ar stua bolc\u00e1nach eile, a crutha\u00edodh an uair seo ag laibhe ina bhfuil n\u00edos m\u00f3 \u00e1bhair \u00f3 screamh ilchr\u00edochach, ar n\u00f3s mianra\u00ed silice, a bhfuil tuf<\/em>, ar cloch a dh\u00e9antar de luaithreamh\u00e1n bolc\u00e1nach \u00e9, mar fhianaise air.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div><\/div><\/div><\/section>

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Imbhualadh agus ions\u00e1 an stua mhagmataigh<\/h5>\n

With the continuous closure of the Iapetus Ocean through subduction, the two ancient continents of Laurentia and Gondwana, and the volcanic island arc in between them, got closer and finally collided<\/strong>. This took place 475 to 460 million years ago<\/strong> and resulted in an enormous amount of deformation to the rocks that had previously been deposited over 200 million years earlier in the Neoproterozoic Era. These originally sedimentary rocks were metamorphosed<\/strong> (i.e. transformed) under those extreme heat and pressure conditions at depth and became metamorphic rocks such as schist<\/em>, marble<\/em> and quartzite<\/em>. These metamorphic rocks are seen throughout north Connemara, e.g. the Maumturk Mountains and the area between Maam and Cornamona. Quartzite is made of a very high percentage of the mineral quartz, which is one of the more abundant but harder minerals found on Earth. This property gives quartzite a particularly strong resistance to erosion and the shape of the modern peaks of the 12 Bens or the Maumturks visible either side of Lough Inagh is a clear demonstration of this.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div>

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The townland of Cloghbrack got its name from the white speckles of quartz found in the local schist, <\/em>as it means \u201cthe speckled stone\u201d in the Irish language\u201d. The world-famous green Connemara Marble<\/em> is found to the south of the geopark region where it has been quarried for over 200 years. Further examples of other types of marble<\/em> can be seen at Cur hill or Corr na M\u00f3na <\/a>where their folded internal structure testifies to the enormous forces that created them. These metamorphic rocks are grouped under the term Dalradian, a rock group which extends to Co Donegal and Scotland and whose rocks have the same origin as those found in our geopark region.<\/p>\n

Ag an am c\u00e9anna, tharla d\u00edfhoirmi\u00fach\u00e1n ar sc\u00e1la i bhfad n\u00edos forleithne mar thoradh ag an bpr\u00f3iseas imbhualadh<\/strong>. Filleadh an bhuncharraig ina sliabhraon m\u00f3r ar a dtugtar na Calad\u00f3naigh<\/strong> (\u00f3n bhfocal Laidine ar an Albain), a d\u2019fh\u00e9adfadh a bheith chomh hard leis na Himil\u00e9ithe inniu. Thug geolaithe an tOraigineas Grampach<\/strong> ar fhoirmi\u00fa an sliabhraoin seo, a ritheann tr\u00edd an Albain agus tr\u00ed \u00c9irinn. Tharla an d\u00edfhoirmi\u00fach\u00e1n m\u00f3rsc\u00e1la seo go seicheamhach nuair a filleadh an bhuncharraig uair amh\u00e1in, agus ansin uair amh\u00e1in eile agus mar sin de. T\u00e1 cuid de na fillteacha le feice\u00e1il go soil\u00e9ir sa t\u00edrdhreach go f\u00f3ill agus is f\u00e9idir iad a fheice\u00e1il, mar a l\u00e9ir\u00edtear leis na radhairc iontacha ar na Beanna Beola \u00f3 ghleann Eidhneach n\u00f3 ar Shl\u00e9ibhte Mh\u00e1m Toirc \u00f3 ghleann an Mh\u00e1ma. T\u00e1 an doicim\u00e9ad\u00fa ioml\u00e1n ar an oraigineas seo ar cheann de na c\u00faiseanna a bhfuil geola\u00edocht a bhfuil t\u00e1bhacht idirn\u00e1isi\u00fanta ag baint l\u00e9i i r\u00e9igi\u00fan gheoph\u00e1irc Dh\u00faiche Sheoigheach & Lochanna an Iarthair; d\u2019fh\u00e9adfa\u00ed a mha\u00edomh gurb \u00e9 an sampla is fearr ar fud an domhain \u00e9 den Oraigineas Grampach-Tacanach.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div><\/div><\/div><\/section>

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Nuair a bhuail na pl\u00e1ta\u00ed ilchr\u00edochacha a ch\u00e9ile, le\u00e1dh clocha ar domhain agus ions\u00e1dh magma isteach sa bhuncharraig mar a bh\u00ed i seomra\u00ed ar a dtugtar pl\u00fat\u00f3in<\/strong>. Tharla na hions\u00e1nna bruthacha seo sa screamh ilchr\u00edochach, agus crutha\u00edodh rud ar a dtugtar stua magmatach<\/strong> d\u00e1 mbarr. Anseo, fuara\u00edonn magma thar thr\u00e9imhse fhada ama, agus mar gheall air sin, crutha\u00edtear criostail mhianracha n\u00edos m\u00f3. T\u00e1 na mianra\u00ed seo m\u00f3r go leor chun gur f\u00e9idir iad a fheice\u00e1il leis an s\u00fail f\u00e9in. Cuireadh na hions\u00e1nna bruthacha seo faoin meiteamorfacht freisin, mar a cuireadh na clocha ar ions\u00e1dh iad iontu. Seo mar at\u00e1 don mheiteagabr\u00f3<\/em> agus ortanaghas<\/em> a aims\u00edtear taobh \u00f3 dheas de Shraith Salach ag Cnoc Leitir Seanaidh agus taobh \u00f3 dheas den Teach D\u00f3ite ag Bh\u00f3thar Ghleann Trasna.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div>

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Ions\u00e1 eibhear Uachtar Ard<\/h5>\n

I dtreo dheireadh an phr\u00f3isis imbhualadh thart ar 462 milli\u00fan bliain \u00f3 shin, chruthaigh an chuid dheireanach den ions\u00e1 magmatach isteach sa stua magmatach a luadh thuas an t-eibhear<\/em> thart ar Uachtar Ard. Cos\u00fail leis an gcuid n\u00ed ba luaithe d\u2019ions\u00e1 an stua mhagmataigh, bh\u00ed d\u00e1t\u00fa beacht na n-ions\u00e1nna leis na d\u00faile radaighn\u00edomhacha i l\u00e1thair sna mianra\u00ed an-\u00fas\u00e1ideach ar fad do gheolaithe. Go deimhin, chabhraigh ions\u00e1 eibhear Uachtar Ard leis na clocha D\u00e1lriadacha ar ions\u00e1igh \u00e9 isteach iontu a dh\u00e1t\u00fa, toisc gur tharla an t-ions\u00e1 idir imeachta\u00ed fillte ar leith.<\/p>\n

Nascadh Chonamara<\/h5>\n

An aspect of the geological history of the Joyce Country and Western Lakes geopark region that is particularly interesting is the fact that the entire region that comprises the Connemara Dalradian rock and its magmatic arc has moved in its entirety in relation to south Co Mayo. As discussed previously, these rocks are comparable to those found in north Co Mayo or Co Donegal. Our understanding of these rocks requires for their formation to have occurred when it was part of the Laurentian landmass located north west of what is now south Co Mayo. The whole block was detached from the rest of Laurentia around 468 million years ago and was subsequently thrusted<\/strong> (i.e. pushed laterally above other rocks) around 464 million years ago to finally dock itself in its modern position. This movement has been called the Mannin Thrust, as remnants of the underlying rock over which Connemara was thrusted outcrop in the area of Mannin Bay, south of Clifden.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div><\/div><\/div><\/section>

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Dr\u00edodr\u00fach\u00e1n Ordaiv\u00edseach i gCo Mhaigh Eo<\/h5>\n

Nocht forbairt an stua oile\u00e1n bolc\u00e1nach, a imbhualadh leis an ilchr\u00edoch Labhr\u00e1sach agus cruth\u00fa an sliabhraoin Chalad\u00f3naigh m\u00e9id suntasach buncharraige a ndeachaigh an s\u00edonchaitheamh i bhfeidhm uirthi; agus is pr\u00f3iseas \u00e9 at\u00e1 ar bun go f\u00f3ill f\u00e9in. Sil-leagadh r\u00e9imse leathan dr\u00edodair chreimthe i gCo. Mhaigh Eo theas, idir Cuan M\u00f3 agus an Caolaire Rua agus \u00f3n gc\u00f3sta go Sliabh Phartra\u00ed. Ar na dr\u00edodair chreimthe bh\u00ed gaineamh n\u00f3 gairbh\u00e9il a sil-leagadh ansin i leapacha abhann, inbhir, uisc\u00ed c\u00f3sta agus uisc\u00ed n\u00edos doimhne. I ndiaidh an sil-leagain, forshreathna\u00edodh tuilleadh dr\u00edodar os cionn na leapacha dr\u00edodair agus th\u00e1thaigh an br\u00fa forshrathnaithe na dr\u00edodair lena ch\u00e9ile chun clocha comhdhl\u00faite a chruth\u00fa. Tugtar gaineamhchloch<\/em> agus comhcheirtle\u00e1n<\/em> faoi seach ar na clocha a chrutha\u00edtear \u00f3 leapacha gainimh agus gairbh\u00e9il. Gaineamhchlocha<\/em> agus comhcheirtle\u00e1in<\/em> at\u00e1 sna sl\u00e9ibhte Cho. Mhaigh Eo theas de Chnoic Sh\u00edofra agus Maol R\u00e9idh, sliabhraon Partra\u00ed agus M\u00e1m Trasna mar at\u00e1 le feice\u00e1il ag na D\u00e9irceanna<\/a> agus timpeall ar Loch na Fuaiche<\/a>.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div><\/div><\/div><\/section>

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T\u00e1 baili\u00fach\u00e1in agus cluichre\u00e1in shuimi\u00fala iontais\u00ed<\/strong> i roinnt de na clocha seo. T\u00e1 iontais\u00ed t\u00e1bhachtach chun sc\u00e9al na beatha ar Domhan a insint d\u00fainn, ach anuas air sin, cuireann siad ar \u00e1r gcumas d\u00e1t\u00fa coibhneasta a dh\u00e9anamh ar chlocha tr\u00ed iad a chur i gcompar\u00e1id le clocha in \u00e1iteanna eile. Go deimhin, t\u00e1 iontais\u00ed i lom\u00e1n neamhghn\u00e1ch scealla<\/em> (cine\u00e1l sonrach l\u00e1ibchloiche<\/em>) a sil-leagadh idir dh\u00e1 shreabhadh laibhe i bhFionnaithe a chuireann ar \u00e1r gcumas an stua bolc\u00e1nach a luadh thuas a dh\u00e1t\u00fa. Thug an fhaisn\u00e9is phail\u00e9-ointeola\u00edoch<\/strong> (na cine\u00e1lacha iontais\u00ed a shainaithn\u00edodh i ngach sraith cloiche ar leith) na ch\u00e9ad leideanna do gheolaithe maidir leis an gcaidreamh idir na clocha in iarthuaisceart na h\u00c9ireann agus clocha eile de chuid ilchr\u00edoch na Labhr\u00e1ise in Albain agus Meirice\u00e1 Thuaidh.<\/p>\n

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Neamh-chomhfhoirmeacht Siol\u00farach<\/h5>\n

I ndiaidh a gcruthaithe, filleadh clocha dr\u00edodracha Ordaiv\u00edseacha Cho. Mhaigh Eo theas freisin ag an imbhualadh lean\u00fanach teicteonach a d\u2019fhill na clocha i gConamara. T\u00e1 an filleadh soil\u00e9ir san uillinn a chrutha\u00edonn na sraitheanna \u00e9ags\u00fala dr\u00edodar at\u00e1 le feice\u00e1il go f\u00f3ill sa bhunchloch ar an d\u00e1 thaobh de Mh\u00e1m Trasna; n\u00edl an uillinn seo mar an gc\u00e9anna nuair a bhreathna\u00edonn t\u00fa ar an Sliabh \u00f3n oirthear n\u00f3 \u00f3n iarthar. N\u00edlimid cinnte go f\u00f3ill c\u00e1 huair go d\u00edreach a th\u00e1inig deireadh leis an bpr\u00f3iseas fillidh seo ach t\u00e1 a fhios againn gur tharla s\u00e9 sular crutha\u00edodh na ch\u00e9ad chlocha dr\u00edodracha eile in\u00e1r sc\u00e9al gheola\u00edoch, le linn tr\u00e9imhse ama ar a dtugtar an Siol\u00farach (440 go 420 milli\u00fan bliain \u00f3 shin)<\/strong>. T\u00e1 seo ar eolas againn toisc gur sil-leagadh clocha Siol\u00faracha a raibh teagmh\u00e1il dh\u00edreach acu le clocha Ordaiv\u00edseacha ar uillinn ingearach lena ch\u00e9ile; cialla\u00edonn s\u00e9 seo gur bhog an t-imeacht fillte ar a nd\u00e9antar cur s\u00edos thuas na bunchlocha n\u00edos sine sular sil-leagadh dr\u00edodair na gcloch n\u00edos \u00f3ige os a gcionn. Nuair a thagann geola\u00ed ar fhianaise den chine\u00e1l seo allamuigh, tugann siad neamh-chomhfhoirmeacht<\/strong> uirthi agus sainmh\u00edni\u00fa ginear\u00e1lta ar an t\u00e9arma sin n\u00e1 bearna sa taifead dr\u00edodrach. Is \u00e9 sin le r\u00e1, cialla\u00edonn neamh-chomhfhoirmeacht go bhfuil fianaise ann gur creimeadh na clocha n\u00edos sine roimh shil-leagan na gceann n\u00edos \u00f3ige. An \u00e1it is fearr chun seo a fheice\u00e1il in\u00e1r r\u00e9igi\u00fan geoph\u00e1irce n\u00e1 idir mulla\u00ed Bhinn U\u00ed Chuinne\u00e1in agus na Binne Bige.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div><\/div><\/div><\/section>

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The Silurian rocks come from sediments that were deposited in coastal to shallow sea conditions. The sea-level locally was getting higher and the sea inundated previously exposed sediments, a process geologists call \u2018marine transgression\u2019<\/strong>. The Silurian sedimentary rock succession that outcrops along the Finny to Kilbride road shows this change in sea-level. Sandstone <\/em>appears first corresponding to coastal areas with high energy environments, where wave and tidal processes dominate. Then it is followed by shelly sandstone<\/em> indicating shallow marine conditions where molluscs lived. As the sea got deeper, the conditions changed to lower energy environments and was characterised with the deposition of finer sediments like silt and mud, eventually becoming siltstone<\/em> and mudstone<\/em>. The fossil assemblages preserved in the local rocks from the Silurian Period are evidence of the rich biodiversity that existed around at the time. This was the subject of recent coverage by national media following the discovery of a new species of starfish from that era called Crepidosoma doylei<\/em> in T\u00f3in na L\u00ed south of Leenane which was named after its discoverer Dr Eamonn Doyle, the current geologist for the Burren and Cliffs of Moher UNESCO Global Geopark.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div>

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Eibhear Deav\u00f3nach na Gaillimhe<\/h5>\n

Nuair a d\u00fanadh an tAig\u00e9an laip\u00e9iteas faoi dheireadh ag deireadh an Siol\u00faraigh, nascadh an d\u00e1 chuid d\u2019\u00c9irinn a crutha\u00edodh ar dt\u00fas ar ilchr\u00edocha difri\u00fala lena ch\u00e9ile mar aon aonad amh\u00e1in. Le linn tr\u00e9imhse ar a dtugtar an Deav\u00f3nach (420 go 360 milli\u00fan bliain \u00f3 shin)<\/strong>, tharla an-chuid le\u00e1 go h\u00e1iti\u00fail a bh\u00ed ina ch\u00fais le hions\u00e1 suntasach magma (dar d\u00e1ta thart ar 400 milli\u00fan bliain \u00f3 shin) a fhuaraigh faoin talamh agus a chruthaigh Eibhear na Gaillimhe<\/em>, at\u00e1 le f\u00e1il ar fud Chonamara theas. T\u00e1 s\u00e9 le feice\u00e1il i dteagmh\u00e1il le clocha n\u00edos sine stua mhagmataigh Chonamara ag B\u00f3thar Ghleann Trasna, taobh \u00f3 dheas den Teach D\u00f3ite.<\/p>\n

Chruthaigh an pr\u00f3iseas t\u00f3g\u00e1la sl\u00e9ibhe a thosaigh san Ordaiv\u00edseach thart ar 460 milli\u00fan bliain \u00f3 shin sliabhraon suntasach. In imeacht 100 milli\u00fan bliain, \u00e1fach, chuaigh f\u00f3rsa\u00ed creimtheacha i bhfeidhm ar an sliabhraon, mar is f\u00e9idir a fheice\u00e1il sa l\u00e1 at\u00e1 inniu ann ag ardchl\u00e1r Mh\u00e1m Trasna<\/a>. D\u00e9anta na f\u00edrinne, n\u00edl i gclocha meiteamorfacha Chonamara agus na clocha D\u00e1lriadach ach fr\u00e9amhacha an tsliabhraoin seo at\u00e1 imithe as radharc \u00f3 shin.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div><\/div><\/div><\/section><\/section>\n<\/div>","protected":false},"excerpt":{"rendered":"490-440 Million Years Ago The End of an Ocean \u2013 Ordovician to Devonian Periods Volcanic...","protected":false},"author":1,"featured_media":5207,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[27],"tags":[],"class_list":["post-5209","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-geological-stories"],"yoast_head":"\nThe end of an ocean \u2013 Ordovician to Devonian periods — Joyce Country & Western Lakes Geopark Project<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, 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