Val Gardena formation

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The Val Gardena Formation is a red to gray colored lithostratigraphic formation of the Upper Permian , which occurs in both the Southern Alps and the Eastern Alps . Above the paleo-relief of the Etschtal volcanic group , it initiates the second tectono-sedimentary cycle in the Southern Alps. The predominantly continental sediments were deposited in an intramontane basin that opened into a sea bay. A flooding by the Tethys , which progressed from east to west , also interlocked with a shallow marine facies. The paleoclimate at that time was warm and semi-arid .

Val Gardena formation in the Seceda area in Ortisei in Val Gardena

designation

The Val Gardena formation, also called Grödner Sandstone or Grödner layers ( Italian Arenaria di Val Gardena ), is named after the Val Gardena valley in South Tyrol . The formation is different in the Southern and Eastern Alps. Therefore there is no uniform, cross-national definition and several type localities , as well as various synonymous names. What they have in common is that they are upper Permian, predominantly clastic sediments with a predominantly reddish color, which were mainly formed on the mainland. The name Gardena Sandstone comes from the German geographer and geologist Ferdinand von Richthofen , who described the formation as early as 1860.

Italy

The Bletterbach gorge, a fossil find point in the Val Gardena formation. The resistant cephalopod bank is in the middle of the wall above the violet color.

In the Southern Alps, an upper Permian terrigenous rock body moves relatively constantly from Lombardy to the Karawanken . In Lombardy, these layers, which were deposited in a separate area, are separated from the Val Gardena formation as Verrucano Lombardo .

Especially in the western Dolomites, the Val Gardena formation is separated from the stratigraphically deeper volcanic-sedimentary succession of the Etschtal volcanic group by a layer gap . It is also underlain by Variscan metamorphic rocks such as the Brixen phyllite - for example in the Pustertal , in Val Sugana or in the central and eastern part of the Dolomites. In the Carnic Alps , it follows the Permian-Carboniferous sediments. The Val Gardena Formation is overlaid by the evaporitic- carbonatic Bellerophon Formation , with which it also interlocks and which it completely replaces west of the Adige Valley. There the Val Gardena formation is directly replaced by the Werfen formation . The thickness of the Val Gardena formation fluctuates between zero and 600 meters on Italian territory .

Lithologically, it is mostly sandstones and pelite with a reddish or gray color. Conglomerate layers often occur in the lying area, which in the past also received their own names, such as Sexten conglomerate , Val Gardena conglomerate or Tarvisian breccia . In the transition to the Bellerophon layers, different colored marls and occasionally carbonates can also appear. Flow ripples often occur in sandstone, which can be layered crosswise or parallel . The rock fragments in the sandstone consist of volcanic rocks ( ignimbrites and andesitic to rhyolite lavas), plutonites (granitoids) and metamorphic rocks of low to medium metamorphosis. In particular, they come from the Eschtal volcanic group, which was exposed to intense erosion for 27 to 14 million years. Mineralogically, the sandstones have quartz as the main component; the most common feldspar is plagioclase .

Austria

Eastern Alps

In Austria , the Val Gardena formation is defined for the Upper Eastern Alpine area in the Riedgraben , which is located in western Carinthia in the Drauzug north of Kötschach and southwest of Paternion . Synonymous names are Val Gardena layers , Griffen layers , Permoskyth sandstone and East Alpine Verrucano . The sediments are alluvial rubble fans . In the sediments also can mineralization found, for example, in the Kalkkögel mountains in the Stubai Valley were also dismantled.

Southern Alps

The Val Gardena formation in the southern Alpine region of Austria (Carnic Alps) is formed at its base as a Tarvisio breccia and is separated from the Trogkofel formation ( Trogkofel group ) and also from the Treßdorfer Kalk and Goggau formation by a layer gap . It is overlaid by the Bellerophon formation.

Facies

The Val Gardena formation, which is 210 meters thick at the Italian type locality, is predominantly built up by continental siliciclastic sediments, which facially reflect the proximal and distal deposit environment of an alluvial alluvial plain. Their red coloration of the recumbent, caused by hematite pigments, gradually merges with the gray tones of the Redukionsmilieus towards the hanging wall. An analysis of the paleo-currents shows that the sediments in rivers were poured from high areas in the north and west.

The fluvial regime was exposed to rapid and erratic changes in the volume of currents. At the same time, the flow width decreased downstream and with it the average flow rate. At the end of the flood plain, the main streams split into a ramified network of innumerable tributaries, which led into the clay plain of a coastal sabcha.

In detail, the facies encountered vary from alluvial cone , plait stream and meander deposits to sand bodies at the end of the alluvial cone. But Sabchas sediments of the coastal area were also deposited. The sandstones formed can be referred to as feldspar-rich litharenites and lithic arcs . Various sedimentary structures such as ripple marks , surcharge marks , cross and oblique stratification can be observed. Based on these structures, Conti and colleagues (1986) interpret the sandstones as typical point-bar sequences, ie as deposits of sandbanks on the river bank. Also present are drought cracks , prints of rock salt cubes , layers of caliche and gypsisol with associated Gilgai and thin coal seams . Limestone and gypsum- bearing horizons correspond to paleo soils of a salt marsh (former calcareous soils and vertisoles ), which indicate a warm to hot, subhumid to semi-arid climate with pronounced seasonality.

Against the hanging wall, the Val Gardena Formation is increasingly being replaced by marine carbonates, shale clays and evaporites of the Bellerophon Formation, which correspond to the environment of coastal Sabchas, salt lagoons and flat shelf areas. A large number of sedimentary structures can now be observed, such as inclined stratification, sandstone bodies typically arranged in a lens-shaped manner (flasher stratification), dry cracks (which indicate that the shallow beach area has occasionally fallen dry), traces of grave and digging through soil-living organisms, current marks (as an indicator of moving water) as well as plant residues washed in . The gradual transgression of the Bellerophon Sea from the east resulted in an interlocking of river and coastal deposits.

Sequence stratigraphy

In the Bletterbach Gorge, three transgression / regression cycles (low-high-low) can be distinguished using sequence stratigraphy , whereby only the transgression part of the first cycle is preserved. The fourth cycle then leads with a transgression into the marine Bellerophon formation. Generally, a decrease in the grain size and the individual thickness of the individual layer packages from one another by boundary faces ( English bounding surfaces are separated) from each other, are observed to slope ends. It is quite possible that these second order cycles are tectonically conditioned.

The 25-meter-thick first half cycle consists of deposits of a meandering river system in a coastal plain - gritty, sandy mudstones, breccias, sandstones and siltstones. The second cycle , 65 meters thick, is fully developed and also fluvial. The sea ​​level is at 75 meters - there was an ingression of the sea from the east, which left the cephalopod bank. Silky marls were now deposited in a sea bay. The second cycle ends with a return to fluvial sediments with a low of 85 meters. The 90-meter-thick third cycle - also predominantly fluvial - is complete. The second high level has been reached at 150 meters and through the Nautiloidenhorizont A marked. The sediments of the second plateau are partially dolomitic and testify to the change from a sabcha to restrictive marine conditions. A low point with a return to fluvial conditions is then 180 meters. In the fourth cycle that followed, the sea level rose again, so that with the onset of the Bellerophon Formation at almost 200 meters, now partially dolomitic Sabcha and lagoon sediments were deposited.

Fossil guide

In the Val Gardena Museum in Ortisei in Val Gardena , numerous fossils from the Val Gardena formation of the Seceda mountain are exhibited.

Trace fossils

Ferry from Chelichnus tazelwurmi
Dicynodontipus geinitzi

The Val Gardena formation is known for its very rich creeping and walking tracks of a diversified Ichnofauna . In the Butterloch , a section of the Bletterbach Gorge near Aldein in South Tyrol, there are occurrences of quadrupedal tracks . Up to sixteen Ichnotaxa have so far been recovered from several horizons, including the groups Cynodontia , Gorgonopsia , Lepidosauromorpha , Pareiasauridae and Rhynchosauria . However, there are no fossils from the polluters.

In addition to typical Permian ichnotaxa such as chelichnus tazelwurmi ( Therapsida ) Ganasauripus ladinus ( younginiformer Archosauria ) Ichniotherium accordii , I. cottae , I. Trent , ( diadectomorpha ) Janusichnus bifrons , Hyloidichnus Tirolensis ( Captorhinida ) Paradoxichnium radeinensis (lepidosauromorpha) Protochirotherium (Archosauria) and Synaptichnium (Archosauria) are found Rhynchosauroides pallini , R. palmatus , R. schochardti (younginiform Neodiapsida ) and Dicynodontipus geinitzi (Therapsida) with Triassic affinity.

The Ichnofossils of the Bletterbach can be divided into three groups: In traces of large herbivores, such as Diadectamorpha or Pachypes dolomiticus , a Pareiasauridae up to 3 meters in size and weighing 600 kg. In the tracks of predatory gorgonopsids and archosaurids that hunted herbivores. And finally in the tracks of small lizard-like dinosaurs such as captorhinids and therapsids, which can be described as omnivores. This also includes the neodiapsids, which were specialized in insects .

The Ichnofauna of the Val Gardena Formation thus contains, in addition to the Pareiasaurid Pachypes dolomiticus , one of the largest known dinosaurs of the Permian, with Protochirotherium , one of the oldest Archosaurids. Their specialty lies in their very modern appearing wealth of shapes.

flora

Ortiseia leonardii , fossil of a conifer of the Val Gardena sandstone, kept in the Museum Val Gardena in Ortisei in Val Gardena

Macroflora

The continental flora of the Val Gardena formation, which includes more than 500 plant fossils, is also known. Leaves, shoots, trunks and fruit clusters were found which can be assigned to ferns , horsetail (Sphenophyta), scale trees ( Lepidodendraceen), seed ferns (Pteridospermae), cycads (Cycadales), ginkgoales and conifers . Charred remains refer to the bushfires of the time.

Particularly noteworthy among the ferns are Pecopteris miltoni , among the scale trees Lepidodendron , among the Sphenophyta the genus Equisetites , among the Pteridospermae the Taxa Germaropteris martinsii , Lepidopteris martinsii , Peltaspermum martinsii , Sphenopteris sp. , S. pinnae and S.suessii , among the cycadales the genus Taeniopteris , among the ginkgoales the genera Baiera digitata and Sphenobaiera and among the predominant conifers the taxa Dolomitia cittertiae , Lebachia laxifolia , Majonica alpina , Ortiseia leonardii , O. jonkeri and O. jonkeri and O. jonkeri . visscheri , Pagiophyllum , Pseudovoltzia liebeana , P. sjerpii , Quadrocladus , Ullmannia bronnii , U. geinitzii , Voltzia hungarica and Walchia florini . The genus Dicranophyllum cannot be assigned to any group (incertae sedis).

Microflora

As microflora 97 previously recognized taxa of find pollen (mainly disaccat - alet, monolet, taeniat and multitaeniat) and 27 taxa of spores , including Alisporites nuthallensis , Circumstriatites , Cyclogranosporites varius , Densoisporites holospangia , Endosporites hexareticulatus , zapfei Falcisporites , Gardenasporites heisseli , G . oberrauchi , Gigantosporites hallstattensis , Guttulapollenites , Inaperturopollenites dolomiticus , Jugasporites delasaucei , Klausipollenites schaubergeri , Limitosporites , Lueckisporites granulatus , L. parvus , L. virkkiae ( Lueckisporites are pollen from Majonica ) Lunatisporites alatus , L. labdacus , L. noviaulensis , Nuskoisporites dulhuntyi , N. klausi ( Nuskoisporites are pollen from Ortiseia ) Paravesicaspora splendens , Perisaccus granulosus , Platysaccus papilionis , Playfordiaspora crenulata , Protohaploxypinus angulistriatus , P. limpidus , P. micro corpus , P. minor , Scheuringipollenites tentulus , jacobi Striatites , vesica spora and Vestigisporites minutus .

Also represented are Leiosphaerida , the spores of freshwater algae ( Planctonites ) and the fungal cell Tympanicysta stoschiana .

From the Drauzug, silicified wooden trunk fragments of Dadoxylon schrollianum and spores of Vittatina costabilis are known. Among the green algae are Dasycladaceen to mention.

Other

In marine sections, invertebrates such as mussels or nautiloids occur, for example the nautiloids Lopingoceras , Nautilus , Mojsvaroceras , Pleuronautilus , Pseudoorthoceras , Stearoceras and Tainoceras .

In the Julian Alps near Bled even smaller sponge-algae reefs can be found. Stromatolites , smaller foraminifera , ostracods and brachiopods occasionally appear in the eastern part of the Carnic Alps .

Volcanism

The breccia slot in the butter hole

In the Butterloch there is a volcanic vent that penetrated the sediments of the Val Gardena formation in the Ladinium 235 million years ago. It consists of a breccia of dark brown basalt matrix mixed with basalt and secondary rock fragments (porphyry, sandstone, limestone and dolomite). The volcanic eruption, which was related to the volcanism of the Alpe di Siusi , was explosive because the eruption column had fallen back into the chimney (recognizable by fragments from the hanging wall).

Note: Gerhard Niedermayer (2007) has recently viewed the vent formation as intrapermic.

Minerals and Natural Resources

In connection with plant-rich sandstone layers, the Val Gardena formation contains silvery pale ores , especially disseminated tennantite . Early to syndiagenetic lead - zinc mineralization with galena and sphalerite also occurs at higher elevations . Already in the 16th century was the Taubenleck (in two tunnels Knapp holes ) with only moderate success after copper ( azurite , bornite , malachite ) mined, therefore, stirred and the old expression Kupferschiefer . The occurrence had been known since 1483. Malachite and azurite are secondary formations of pale ore. Other minerals that occur are chalcopyrite , chalcosine , covelline , dolomite , magnesite , mimetite , partzite and pyrite . Among the heavy minerals, rutile , zircon , tourmaline and barite dominate . The formation also shows diagenetic enrichment of uranium .

According to Wopfner (1984), the early diagenetic Pb, Zn, Cu- and U-mineralization as well as the formation of dolomite, magnesite and barite indicate aggressive groundwater conditions in a seasonally arid sedimentation environment. The author sees this as a sign of intracontinental rifting in the early stages of the second Alpidian cycle.

Age

The age of the Val Gardena formation has so far only been determined imprecisely. Age was determined on the basis of paleontological and paleomagnetic criteria; absolute radiometric ages are missing. Mauritsch and Becke (1983) and Dachroth (1988) found the Illawarra field reversal magnetostratigraphically at 265 million years BP, which corresponds to the uppermost wordium . Massari and colleagues (1988) and Pittau and colleagues (2005) were able to assign the Val Gardena Formation and the subsequent Bellerophon Formation to the latest Capitanium to Changhsingium on the basis of spores , footprints, foraminifera and algae communities in the Bletterbach Gorge . Typical elements of the Capitanium such as Crucisaccites are missing, however. Schönlaub and Forke (2007) therefore assume the interval Wordium including Wuchiapingium as the age of the Val Gardena formation. This roughly corresponds to the period 267 to 253 million years BP . The tetrapod traces of the Val Gardena formation speak for the Wuchiapingium. Ceoloni and colleagues (1988) date the Bellerophon formation in turn to the upper Wuchiapingium. As a result, the Val Gardena formation is only limited to the lower Wuchiapingium, ie to an age of around 260 to 257 million years BP.

Occurrence

See also

Individual evidence

  1. ↑ Cassinis, G., Nicosia, U., Lozovsky, VR and Gubin, YM: A view on the Permian continental stratigraphy of the Southern Alps, Italy, and general correlation with the Permian of Russia. In: Permophiles . tape 40 , 2002, p. 4-16 .
  2. ↑ Werner Buggisch: The Val Gardena layers (Perm, Southern Alps). Sedimentological and geochemical investigations to differentiate between marine and continental sediments. doi: 10.1007 / BF01803260 ; Retrieved November 11, 2009
  3. ↑ a b c Commissione Italiana di Stratigrafia: Arenaria di Val Gardena PDF file
  4. ↑ Neri, C .: Arenaria di Val Gardena. In Cita, MB et al., The nature of Permian rivers in Southern Alps. In: Cassinis, G., Permian and Permian-Triassic boundary in the South-alpine segment of the western Tethys and additional regional reports. (Ed.): Mem. Soc. Geol. It. Band 34 , 2007, p. 155-160 .
  5. ↑ Cassinis, G., Cortesogno, L., Gaggero, L., Massari, F., Neri, C., Nicosia, U. and Pittau, P .: Stratigraphy and facies of the Permian deposits between Eastern Lombardy and the Western Dolomites . In: Field Trip Guidebook, International Field Conference of “The Continental Permian of the Southern Alps and Sardinia (Italy). Regional Reports and General Correlations ” . 1999, p. 157 .
  6. ^ Federal Geological Institute : Treatises Volume 66 , p. 89.
  7. ↑ Stratigraphic table of Austria ( Memento of the original from February 3, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.77 MB) @1@ 2Template: Webachiv / IABot / geologie.univie.ac.at
  8. ↑ Ori, GC: The nature of Permian rivers in Southern Alps . In: Cassinis, G., Permian and Permian-Triassic boundary in the south alpine segment of the Western Tethys and additional regional reports (Ed.): Mem. Soc. Geol. Ital. tape 34 , 1988, pp. 155-160 .
  9. ^ Conti, MA et al .: Field Guide-Book, Field Conference Permian and Permian-Triassic Boundary in the South Alpine Segment of the Western Tethys . Soc.Geol.Italiana, Brescia 1986, p. 99-119 .
  10. ^ Wopfner, H. and Farrokh, F .: Palaeosols and heavy mineral distribution in the Groeden Sandstone of the Dolomites . In: Cassinis, G., Permian and Permian-Triassic boundary in the south alpine segment of the Western Tethys and additional regional reports (Ed.): Mem. Soc. Geol. Ital. tape 34 , 1988, pp. 161-173 .
  11. ^ Massari, F. et al.: The Bletterbach section (Val Gardena Sandstone and Bellerophon Formation) . In: Cassinis, G. ua, Stratigraphy and facies of the Permian deposits between eastern Lombardy and the Western Dolomites (Ed.): Field Trip Guidebook . Earth Science Department, Pavia 1999.
  12. ↑ Evelyn Kustatscher et al .: Sea-level changes in the Lopingian (late Permian) of the northwestern Tethys and their effects on the terrestrial palaeoenvironments, biota and fossil preservation . In: Global and Planetary Change . tape 148 , 2017, p. 166–180 , doi : 10.1016 / j.gloplacha.2016.12.006 .
  13. ↑ Wopfner, H .: About tetrapod tracks, coal and petrified wood from the Grödner sandstone (Perm) near Nova Ponente . In: The Sciliar . tape 73 (1) , 1999, pp. 23-32 .
  14. ↑ a b Avanzani, M., Bernardi, M. and Nicosia, U .: The Permo-Triassic tetrapod faunal diversity in the Italian Southern Alps . Ed .: Dar, IA and Dar, MA, Earth and Environmental Sciences. Tech, Rijeka 2011, p. 591-608 .
  15. ↑ Uhl, D., Butzmann, R., Fischer, TC, Meller, B. and Kustatscher, E .: Wildfires in the Late Palaeozoic and Mesozoic of the Southern Alps - The Late Permian of the Bletterbach – Butterloch area (Northern Italy) . In: Riv, Ital. Paleont. Strat. Band 118 (2) , 2012, p. 223-233 .
  16. ^ Evelyn Kustatscher et al.: A new flora from the Upper Permian of Bletterbach (Dolomites, N-Italy) . In: Review of Paleobotany and Palynology . tape 182 , 2012, p. 1–13 , doi : 10.1016 / j.revpalbo.2012.06.001 .
  17. ↑ Niedermayer, G .: The Bletterbach Gorge near Radein (Redagno) - a hike through 50 million years of geological history . In: Communications from the Austrian Mineralogical Society . tape 153 , 2007, p. 181-193 .
  18. ^ Wopfner, H .: Permian deposits of the Southern Alps as product of initial alpidic taphrogenesis . In: Geologische Rundschau . tape 73 , 1984, pp. 259-277 .
  19. ↑ Posenato, R .: Marine biotic events in the Lopingian succession and latest Permian extinction in the Southern Alps (Italy) . In: Geol. J. Band 45 , 2010, p. 195-215 .
  20. ↑ Massari, F. et al .: The Val Gardena Sandstone and Bellerophon Formation in the Bletterbach Gorge (Alto Adige, Italy) . In: Biostratigraphy and Sedimentology Mem. Sci. Geol. Band 11 , 1988, pp. 229-273 .
  21. ↑ Pittau, P., Kemp, H. and Kustatscher, E .: The Bletterbach Canyon. "Let us meet across the P / T boundary" - Workshop on Permian and Triassic Paleobotany and Palynology - June 16-18, 2005 . In: Excursion guide . Bozen / Bolzano, Italy 2005.
  22. ↑ Schönlaub, HP and Forke, HC: The post-Variscan sequence of layers of the Carnic Alps - Explanations of the geological map of the Young Paleozoic of the Carnic Alps 1: 12500. In: Abhandlungen Geologische Bundes-Anstalt . tape 61 , 2007, p. 3-157 .
  23. ↑ Ceoloni, P. et al .: Tetrapod footprint faunas from Southern and Central Europe . In: Z. Geol. Wiss. tape 16 , 1988, pp. 895-906 .