Trevor Faulkner: Tektonska incepcija v kaledonskih marmorjih V centralni Skandinaviji je več kot tisoč izdankov marmorja v katerih je znanih preko tisoč jam. Razlika med temi jamami in tistimi v apnencih, je pogojena s procesi metamorfoze in zanemarljivo primarno poroznostjo prvih. S tem je povezano drobno plastenje (foliacija) in posledična odsotnost lezik. Najgloblja jama je globoka 180 m, kljub temu, da vertikalni razpon izdankov znaša do 900 m. Jame največkrat najdemo v skupinah in so v vertikalnem merilu precej naključno porazdeljene, pri čemer jih redko najdemo več kot 50 m pod površjem. Kljub temu, da so nekateri izdanki pasastega krasa dolgi več deset kilometrov, zelo dolgih jam ne poznamo, kraški hidrološki sistemi pa ne presegajo dolžine 3.5 km. Ker so jame kratke in blizu površja, je kemijska incepcija manj verjetna. Zato predlagam model tektonske incepcije, ki predvideva, da so jame v kaledonskih marmorjih nastale zgolj vzdolž sistemov odprtih razpok, pri čemer je dimenzija in frekvenca teh razpok povezana z magnitude tektonskih premikov, ki so nastali kot posledica izostatičnega uravnoteženja ob umikih ledenikov po ledenih dobah. Sistemi takih razpok so nastajali vzdolž incepcijskih površin med marmorji in neprepustnimi plastmi in vzdolž incepcijskih razpok v marmorjih, ki so vzporedne ali pravokotne s plastenjem. Model gradim tudi na poročilih o delno odcepljenem tankem vrhnjem delu skorje v podobnih okoljih na Škotskem. Model podpirajo tudi opažanja kasnejših neotektonskih premikov, na katere kažejo ostri robovi in tektonska zrcala v jamah in na površju.

IzvlečekUDK 550.34 :551.44(234.652) Trevor Faulkner: Deglacialna seizmičnost in razvoj jam v kaledonskih marmorjih: razmerje ena proti osem Razvoj jam v kaledonskih marmorjih na periodično poledenelem 40000 km 2 velikem območju osrednje Skandinavije se je začel s tektonskim začetjem, procesom pri katerem so se prvotne prevodne razpoke ustvarile zaradi razbremenitev ob umikih ledenikov. Vzdolž teh prevodnih poti se v obdobju umikanja ledenikov in medledenih dobah razvijajo kraški kanali. Model tektonske incepcije, ki obravnava razvoj jam v "delno ločenem" vrhnjem delu skorje, temelji na opažanjih, da je največja globina jamskih rovov ( pri tem je mišljena razdalja med površino in rovom) manjša od osmine globine lokalne ledeniške doline. To nakazuje, da je nastanek prevodnih razpok povezan z izostatičnim dvigom in delno pogojen z velikostjo seizmičnosti, ki so jo povzročili diferencialni pritiski in dvigi, ki so nastali ob ledeniških dolinah med umikanjem ledeniških pokrovov v smeri od zahoda proti vzhodu. Razmerje ena proti osem je značilno tudi v drugih območjih kaledonskih marmorjev v Skandinaviji, na Škotskem in v Novi Angliji (ZDA), kar kaže, da so podobni procesi botrovali nastanku številnih jam na teh območjih. Ključne besede: Kaledonidi, deglacialna speleogeneza, podzemlje, rob ledu, incepcijske razpoke, marmor, neotektonika, razmerje ena proti osem, seizmičnost, kras v pasovih, razdalja površje-jama, tektonska incepcija, Weichselian, Skandinavija. 2 region in central Scandinavia was initiated by tectonic inception, a process in which open fracture routes, primarily created by deglacial seismicity, provided the opportunity for subsequent dissolution and enlargement into cave passages in both deglacial and interglacial environments. The tectonic inception model built on reports of a 'partially detached' thin upper crustal layer in similar settings in Scotland and this paper shows that the present maximum subsurface cave distance (i.e. the distance of a passage to the nearest land surface) is commonly less than one-eighth of the depth of the local glaciated valley. This suggests that fracture generation was related to the scale of isostatic uplift and was partly determined by the magnitude of seismicity caused by the differential pressure change and differential uplift that occurred along valley walls as the ice margin of each of the major Pleistocene icesheets receded from west to east. The maximum one-eighth relationship is also commonly maintained in other Caledonide marble terranes in Scandinavia, Scotland and New England (USA), suggesting that many of the caves in these areas were formed by similar processes.

Neptune's Cave in the Velfjord-Tosenfjord area of Nordland, Norway is described, together with its various organic deposits. Samples of attached barnacles, loose marine molluscs, animal bones and organic sediments were dated, with radiocarbon ages of 9840AE90 and 9570AE80 yr BP being derived for the barnacles and molluscs, based on the superseded but locally used marine reservoir age of 440 years. A growth temperature of c. 7.51C in undiluted seawater is deduced from the d C and d18 O values of both types of marine shell, which is consistent with their early Holocene age. From the dates, and an assessment of local Holocene uplift and Weichselian deglaciation, a scenario is constructed that could explain the situation and condition of the various deposits. The analysis uses assumed local isobases and sea-level curve to give results: that are consistent with previous data, that equate the demise of the barnacles to the collapse of a tidewater glacier in Tosenfjord, and that constrain the minimum extent of local Holocene uplift. An elk fell into the cave in the mid-Holocene at 5100AE70 yr BP, after which a much later single 'bog-burst' event at 1780AE70 yr BP could explain the transport of the various loose deposits further into the cave.

No abstract

After the work of Jean Corbel in the 1950s, who compared karstifi cation in the Scandinavian Caledonide marbles with that in sedimentary limestones in temperate and tropical regions, the understanding of underground limestone dissolution has developed considerably. Corbel concluded that 'karstifi cation proceeds much faster in a cold than in a warm climate', based on the knowledge that the solubilities of both CO 2 and CaCO 3 increase with lower temperature, without realizing that because cave streams in Scandinavia rarely reach saturation this fact is not directly relevant. We now know that the dissolutional enlargement of inception channels in limestones proceeds commonly via a slow initial 'pre-breakthrough' laminar fl ow stage before conduits can enlarge chemically at maximum rates under turbulent fl ow conditions. Recent research has shown that the pre-breakthrough stage is speeded up at low temperatures, as occurs in cold climates now, and as occurred during the deglaciation of the Weichselian ice sheet in Scandinavia, especially under steep hydraulic gradients and, in many cases, despite the lower partial pressure of CO 2 . Additionally, this whole stage might be bypassed if fractures created by deglacial seismicity were wide enough and short enough. After breakthrough, although limestone dissolution is slower in cold rather than warm climates, conduit enlargement still proceeds at a signifi cant rate, provided the water remains unsaturated, and especially if high fl ow rates promote mechanical erosion. The exploration of large numbers of (short) caves in central Scandinavia shows that Corbel's conclusion is partly true for the more recent geological past, because of the special conditions that apply during the Quaternary glacial cycles.