Jurassic neptunian dikes at Mt Mangart (Julian Alps, NW Slovenia)

Abstract

Jurassic neptunian dikes are common within Upper Triassic to Lower Jurassic platform limestone of the Julian Alps. At Mt Mangart, the following geometries were observed: irregular dissolution cavities, thin penetrative fractures, larger fractures with sharp sidewalls, and laterally conWned breccia bodies. Inside a complex neptunian dike system two main generations of inWllings were diVerentiated. The Wrst generation is heterogeneous and consists of bioclastic limestones, representing uniquely preserved sediments subdivided into Wve diVerent microfacies. The second generation is more common and typically consists of coarse-grained breccias with host-rock clasts and marly limestone matrix containing echinoderms. Fracture formation and void Wlling of the Wrst generation of neptunian dikes is dated as Pliensbachian and is interpreted to be caused by the Julian carbonate platform dissection due to widely recognized Lower Jurassic Tethyan rifting. The timing of formation for the second generation is only broadly constrained, ranging from the Pliensbachian to the Late Cretaceous.

Microfacies of Mesozoic Carbonate

“…V njih se menjavajo biosparitni, oolitni in mikritni apnenci, mestoma pa so prisotne tudi stromatolitne in loferitne plasti. Na kontaktu z zgornjetriasnimi karbonati so ponekod emerzijske bre~e in neptunski dajki, oboji zapolnjeni z rde~kastim glinastim vezivom (BaBi}, 1980/81;jurkov{ek et al, 1990;^rne et al, 2007).…”

“…Fig (turn{ek, 1966, 1969, 1972, 1997; turn{ek et al, 1981), , 1996; jurkov{ek, 2008, 2010), 42 -Komen (oGorelec et al, 1987a(oGorelec et al, , 1996bjurkov{ek et al, 1996;jurkov{ek & kolar-jurkov{ek, 2007), 43 -Senože~e (Pleni~ar & jurkov{ek, 1996;Pleni~ar, 2005), , 1995, 2007hansen et al, 1995;PuGliese et al, 1995;riccaMBoni, 2005), 47 -Dolenja vas (droBne et al, 1988, 1995), 48 -Gori{ka Brda (šriBar, 1965, 49 -Bohor, Kr{ko (Buser et al, 1982a 1969, 1972, 1997; turn{ek et al, 1981). Med grebeni, ki so se s prekinitvami vlekli {e v Suho Krajino in preko Gorjancev v Liko na Hrva{ko (veli} et al, 2002) so se odlagale medgrebenske bre~e ter plastoviti apnenci s hidrozojem Cladocoropsic mirabilis.…”

“…Na Krasu te vrzeli ne opazujemo. Druga emerzijska faza je imela ve~ji ~asovni razpon, ponekod na Krasu precej manj{i obseg med campanijem in maastrichtijem, proti jugu (Matarsko podolje, Istra) pa je okopnitev obstajala že od santonija pa vse do eocena (droBne, 1979;Buser, 1980;jurkov{ek et al,1996;otoni~ar, 2006, 2007jež, 2011). Rezultat emerzijskih faz in zakrasevanja so žepi boksitne gline.…”

“…Mikrofosilna združba je skromna in nezna~ilna (foraminifere, ostrakodi, alge -predvsem Thaumatoporella parvovesiculifera), na ob~asno povezavo lagun z odprtim morjem pa sklepamo po prisotnosti pelagi~nih fosilov. Poleg rib so v apnencu prisotni {e drugi makrofosili, kot so kopenske rastline, sakokome, amoniti in drugi (jurkov{ek & kolar-jurkov{ek, 1995, 2007doBruskina et al, 1999;suMMesBerGer et al, 1996suMMesBerGer et al, , 1999. Tomajski apnenec vsebuje tudi plasti biokalkarenita, ki kažejo ve~krat postopno zrnavost.…”

“…V njih se menjavajo biosparitni, oolitni in mikritni apnenci, mestoma pa so prisotne tudi stromatolitne in loferitne plasti. Na kontaktu z zgornjetriasnimi karbonati so ponekod emerzijske bre~e in neptunski dajki, oboji zapolnjeni z rde~kastim glinastim vezivom (BaBi}, 1980/81;jurkov{ek et al, 1990;^rne et al, 2007).V zgornjem liasu je bila Julijska karbonatna plo{~a razkosana na ve~ blokov, ki so bili razli~no poglobljeni. Na njih se je pri~ela pelagi~na sedimentacija ter kondenzacija sedimentov (Buser, 1986a;jurkov{ek et al, 1990;šMuc, 2005).…”