Geology Reference
In-Depth Information
Basics: Neptunian dikes and fissure fills
Cozzi, A. (2000): Synsedimentary tensional features in Up-
per-Triassic shallow-water carbonates of the Carnian
Prealpes (northern Italy) and their importance as paleo-
stress indicators. - Basin Research, 12 , 133-146
Fischer, A.G. (1964): The Lofer cyclothems of the Alpine
Triassic. - In: Merriam, D.F. (ed.): Symposium on cyclic
sedimentation. - Kansas Geol. Surv. Bull., 169 , 107-149
Füchtbauer, H., Richter, D.K. (1983): Relations between sub-
marine fissures, internal breccias and mass flow during
Triassic and earlier rifting periods. - Geologische Rund-
schau, 72 , 53-66
Garcia-Hernandez, M., Rey, J., Vera, J.A. (1989): Disques
neptunicos de edad Cretacica en la Sierra de Quipar (Sub-
betico externo, Prov. Murcia). - Rev. Soc. Geol. España,
2 , 85-93
Krystyn, L., Schäffer, G., Schlager, W. (1971): Über Fossil-
lagerstätten in den triadischen Hallstätter Kalken der Ost-
alpen. - Neues Jahrbuch für Geologie und Paläontologie,
Abhandlungen, 117 , 284-304
Lehner, B.L. (1991): Neptunian dykes along a drowned car-
bonate platform margin: an indication for recurrent ex-
tensional tectonic activity? - Terra Nova, 3 , 593-606
Martire, L. (1996): Stratigraphy, facies and synsedimentary
tectonics in the Jurassic Rosso Ammonitico Veronese
(Altopiano di Asiago, NE Italy). - Facies, 35 , 209-236
Playford, P.E., Kerans, C., Hurley, N.F. (1984): Neptunian
dikes and sills in Devonian reef complexes of the Can-
ning Basin, Western Australia. - Amer. Ass. Petrol. Geol.
Bull., 68 , p. 517
Schöll, W.U., Wendt, J. (1971): Obertriadische und jurassi-
sche Spaltenfüllungen im Steinernen Meer (Nördliche
Kalkalpen). - Neues Jahrbuch für Geologie und Paläonto-
logie, Abhandlungen, 139 , 82-98
Smart, P.L., Palmer, R.J., Whitaker, F., Wright, V.P. (1988):
Neptunian dikes and fissure fills: an overview of some
modern examples. - In: James, N.P., Choquette, P.W.
(eds.): Paleokarst. - 149-163, Berlin (Springer)
Vera, J.A., Ruiz-Ortiz, P.A., Garcia-Hernandez, M., Molina,
J.M. (1988): Paleokarst and related pelagic sediments in
the Jurassic of the Subbetic zone, southern Spain. - In:
James, N.P., Choquette, P.W. (eds.): Paleokarst. - 364-
384, Berlin (Springer)
Wendt, J. (1971): Genese und Fauna submariner sedimentärer
Spaltenfüllungen im mediterranen Jura. - Palaeonto-
graphica, Abteilung A, 136 , 122-192, Stuttgart
Winterer, E.L., Sarti, M. (1994): Neptunian dykes and associ-
ated features in southern Spain: mechanics of formation and
tectonic implications. - Sedimentology, 41 , 1109-1132
Further reading : K103
internal sediment in fossil-rich dikes suggests little free
mud on the sea floor, bolstering the cemented seafloor
concept of the Capitan limestone.
Tectonic Jurassic dikes in Triassic limestones of the
Northern Calcareous Alps, Austria
The Sonnwend Mountains in Tyrol represent an ex-
cellent example of Jurassic fissure infillings of differ-
ent stratigraphic age in Late Triassic reef limestones
(Fabricius 1962; Wendt 1969; Pl. 24/4, Figs. 5.12 and
5.13). The reef limestones are overlain by a condensed
Jurassic sequence of red bedded limestones. Identical
lithofacies types occur in vertical and oblique fissures
starting at the Triassic/Jurassic boundary and tran-
secting the upper part of the reef limestone. In con-
trast, lithofacies types and fossils in the sedimentary
infillings of the horizontal 'S-dikes' within the reef
limestones, running parallel to bedding planes, differ
strongly from that of the Q-dikes. These conspicuous
differences have caused considerable problems in de-
ciphering the structure of the mountains prior to the
recognition of the red apparent intercalations as sedi-
mentary fissures.
5.3.1.4 Significance of SedimentFilled
Fissures
Fissures and neptunian dikes are of major importance
in basin analysis:
• Internal sediments can preserve biota and sediment
for periods where other records are lacking. Low sedi-
mentation rates within fissures lead to condensed se-
quences covering substantial time periods.
• If sediments are not recognized as the internal sedi-
ments of neptunian dikes severe stratigraphical and
structural misinterpretations may be the result.
• Neptunian dikes and fissure fills are sensitive sea-
level indicators. Changes in the composition of inter-
nal sediments in dikes and fissures can reflect changes
between marine nd subaerial settings, e.g. the begin-
ning of transgressions or long-lasting karstification
phases (Gonzalez-Donoso et al. 1983).
• The existence of multiple crosscutting neptunian
dikes can be used to reconstruct recurrent syndepos-
itional extensional tectonic activities along drowned
platform margins and as paleostress indicators (Lehner
1991, Cozzi 2000).
Indications of tensional disruption other than nep-
tunian dikes are fractures, normal faults, shatter brec-
cias and laterally discordant intraformational breccias
dissecting platform-margin carbonates.
5.3.2 Microfractures and Veins (Calcite
Veins)
Many carbonate rocks display millimeter- to centime-
ter-sized, mineral-filled (often calcite-filled) microfrac-
tures (veins and veinlets, Box 5.8). Fractures are dis-
crete breaks within a rock mass and comprise micro-
fractures, joints and faults. The existence of ductile
shear zones, brittle shear zones and brittle-ductile shear
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