Dolomites Geology: a Key to All Major Rock Types.

The Dolomites Geology is quite a complicated matter. In other locations across the site I have (hopefully) devised pages that deal with this complex subject in an easy, down-to-earth, comprehensible way. The purpose of this page, however, is sligthly different, as it is aimed at those technically oriented readers who are searching for a more detailed description of all the rock types to be found in the Dolomites. The text of the current page uses as a basis the explanatory notes to the Geological Chart of Italy (Carta Geologica d’Italia), Sheet No. 29, Cortina d'Ampezzo, which is taken as representative of the Dolomites Geology as a whole. For those wishing a more gentle and easy-to-read introduction on the subject, please refer to the page Geology-of-the-Dolomites.

Quaternary Stratigraphic Units

Postglacial Alpine Synthem

Debris slope with large blocks in an actual and ancient debris slide. Sandy matrix with sandy-gravelly intercalations and plurimetric sub-angular blocks. Marsh, peat-bogs, and lacustrine (lake-originated) deposits; carbonated stratified concretions; sandy-gravelly sediments with pebbles and rounded/sub-rounded blocks, with sporadic intercalations of sandy-muddy levels, sometimes discontinuously terraced; debris-flow deposits (Holocene).

Amola Sub-synthem

Recent glacial deposits; chaotic accumulations of blocks with a partially open pockets texture; sandy-muddy matrix with angular and sub-angular clasts, undifferentiated. Sandy-gravelly intercalations (deposits of mixed origin); muddy gravel, pebbles and sands with rare sub-rounded and rounded blocks, moderately sorted, which form fluvio-glacial deposits (Holocene).

Piave Synthem

Massive rounded or sub-rounded clasts, polished and sometimes layered, dipped in an over-consolidated matrix of argillaceous mud; sandy-muddy matrix with clasts ranging from sub-angular to sub-rounded; moderately altered clasts with heterogeneous petrographic composition (Pleistocene).

Val Cernera Sub-synthem

Clast-supported, matrix-supported sub-synthem with sandy-muddy and coarse sand matrix, never argillaceous; heterometric angular/sub-angular lithologies that form moraine ramparts. Sandy gravels with sub-rounded pebbles and blocks, roughly stratified and moderately sorted; locally cemented and terraced fluvio-glacial deposits. Chaotic accumulations with calcareous-Dolomite angular, muddy matrix, organized in concave-convex layers; often cemented and sorted gravels (Late Pleistocene).

Cancia Sub-synthem

Matrix supported by mud and argillaceous (clayey), hazel-brown sands; accumulations of Dolomite sub-angular megablocks with a clast-supported structure organized in lateral and saddle moraine ramparts. Sandy-muddy gravels and pebbles with rare blocks; clast-supported texture, with well-cemented sorted horizons. Erosive surfaces and traces of channels. Sands and muds with gravel and pebbles, clast-supported; sorted horizons with iso-oriented pebbles (fluvio-glacial deposits). Sandy-muddy matrix-supported deposits with angular/sub-angular heterometric clasts, alternated with tabular bodies of sorted and cemented gravels, and lenses of laminated mud and sands; deposits of glacial contact (Late Pleistocene).

Monte Sorapis Sub-synthem

Clast-supported, matrix-supported sub-synthem with muddy and coarse sand; angular/sub-angular heterometric clasts with homogenous petrography (Grey Limestone, Main Dolomite, Dolomite Cassiana). Gravels with pebbles and medium to coarse sands, stratified, locally massive or clast-supported. Rounded/sub-rounded clasts, often tiled; lenses of laminated sands, terraced and not terraced; fluvio-glacial deposits. Matrix-supported with partially open pockets sometimes cemented; angular/sub-angular heterometric clasts; horizons with iso-oriented clasts; wavy, erosive boundaries are also recognizable. Deposits of mixed origin; glacial-lacustrine (lake-originated) deposits (Late Pleistocene).

Ladiere Sub-synthem

Muddy-sandy matrix-supported with blocks of Dolomite Cassiana, sub-angular/angular, matrix- or clast-supported, normally consolidated, intercalated with levels of moderately sorted gravels and muddy sands with pebbles; blocks iso-oriented; widespread conglomerate lenses, clast-supported with sandy matrix alternated with well-sorted horizons and partially open sandy-gravelly texture, often cemented (deposits of glacial contact). Muddy sands slightly gravelly; pebbly and sandy gravels, coarsely stratified; sub-rounded clasts and, if tabular, tiled. Terraced and not terraced fluvio-glacial deposits. Lacustrine deposits (Late Pleistocene).

Santa Fosca Sub-synthem

Sandy-muddy matrix; heterometric clasts, from sub-angular to sub-rounded. Gravel and sandy gravels, sometimes well-sorted, with polygenic clasts, alternated with concave-convex bodies and angular/sub-angular clasts, with levels of accumulated sand and silt, and plane-parallel laminations with dropstones (fluvio-glacial deposits). Texture from partially open to open, made of blocks, mega-blocks, and subordinated fine gravel, angular and monogenetic (Dolomite Cassiana). Clast-supported, with large blocks of sandy-muddy matrix, concentrated in the deepeest parts (ancient debris slide, rock glacier; Late Pleistocene, Upper Late Glacial).

Malga Fiorentina Sub-synthem

Sandy-argillaceous, dark hazel-brown mud; heterometric clasts with some larger blocks, rounded to sub-angular. Later moraine ramparts which are now isolated shreds. Massive or coarsely stratified gravels, well-cemented, of braided marginal glacial environment with light hazel-brown muddy matrix; sorted bodies with iso-oriented pebbles and blocks. Deposits of glacial contact; terraced and not terraced fluvio-glacial deposits (Late Pleistocene).

Val d’Oten Unit and Col Vallon Unit

Glacial deposits (ablation till), fluvio-glacial terraced and not terraced deposits; mixed deposits related to the first phase of the glaciers’ retreat (Lower Late Glacial, Late Pleistocene).

Garda Synthem

Clast-supported with sandy matrix; grain size ranges from gravel to metric blocks, sub-angular, of exclusively local petrography. Matrix-supported, with polygenic sub-rounded clasts, often striated (i.e. layered; Pleistocene).

Podestagno Sub-synthem

Texture from clast-supported to matrix-supported, with muddy-sandy matrix, light grey-pinkish; huge heterometric clasts, sometimes sub-angular. The petrography of clasts and matrix is related to the lithologies outcropping in the area. Gravels with pebbles and sands from coarse to medium size, stratified – now and then well-cemented. Clasts are carbonate in nature, with some elements of marl. Tractive structures are frequent, also with bi-directional trend. Fluvio-glacial deposits terraced and not-terraced; glacial-lacustrine deposits (Late Pleistocene).

Monte Padeon Sub-synthem

Matrix- to clast-supported, with muddy-sandy light brown-pinkish matrix; heterometric clasts with blocks larger than one cubic metre, from sub-angular to sub-rounded, of local origin. Sandy-pebbly gravels with rare blocks, often cemented, in decimetric to metric thick bodies with tabular or lenticular geometry; frequently sorted horizons and alignments of pebbles and blocks; numerous erosive surfaces. Fluvio-glacial deposits; deposit of glacial contact (Late Pleistocene).

Monte Antelao Unit

Conglomerate with carbonate clasts including two facies: a) massive matrix-supported with sandy-muddy matrix and rare sub-angular clasts of metric size, not well stratified, and erosive boundaries (cemented deposits of mixed origin); b) body organized in strata and low-angle lamina (fluvial bars; braided type), of gravel and pebbles, well-rounded and sorted, with variable texture, from open- to clast-supported (cemented alluvial deposits; Pliocene and Middle Pleistocene).

Mesozoic Statigraphic Units

Deep Water Jurassic-Cretaceous Successions

Marne del Puez (Puez Marls)

Grey-green marls alternated with micritic limestone and calcarenitic turbidites, with frequent ammonioids; black shale, reddish calcareous marls with planktonic foraminifers (Thickness 0-70 metres; Hauterivian/Barremian).

Rosso Ammonitico Veronese (Ammonite Red)

Nodular reddish micritic limestones, moderately marly, rich in internal molds of ammonioids; at the base, thin shell bivalves horizons (Lumachella with Poseidonia alpina; thickness 35 metres; Dogger/Malm).

Encrinite di Fanes Piccola

Cross-laminated, dark encrinal calcarenites in discontinuous lenses, sometimes associated with sub-ordinated micrites, at the top of the Calcari Grigi. Fauna: brachiopods, bivelves, cephalopods (Thickness 0-20 metres; Pliensbachian/Domerian).

Late Triassic-Lower Jurassic Platform Succession

Calcari Grigi (Grey Limestone)

Prevailing light-grey micritic limestones and oolitic bioclastic calcarenites, densely stratified, sometimes with thin marly layers interbedded, organized in peritidal cycles. The lower part, which is not lithostratigraphically separable from the rest of the unit, is characterized by layers with corals, large Grey Megalodontacea and Dicerocardia, and it partly corresponds to the so-called ‘Calcare di Dachstein Auct’ (Norian-Rhaetian). The middle-upper part corresponds to the Liassic Calcari Grigi (Thickness 450-550 metres; Rhaetian/Pliensbachian).

Dolomia Principale (Main Dolomite)

Light-grey Dolomite, well-stratified, prevalently made by the cyclic alternation of bio-turbated units, locally fossiliferous, and inter-supratidal layers with stromatolitic laminites; locally (Monte Pelmetto), footprints of Dinosaurs and Tetrapods (Thickness 500-1000 metres; Carnian/Rhaetian).

Travenanzes Formation

Siltites of various colours (red, green, grey); argillites and marls alternated with fewer aphanitic white Dolomite and subordinated sanstones and conglomerates (in the lower part of the formation). Intervals of laminated gypsum and Dolomite layers are locally present. In the south-western areas, breccias and para-conglomerates are found at the contact with the Heiligenkreuz Formation. Fossils include megalodontes (Thickness 2-150 metres; Carnian/Tuvalian).

Heiligenkreuz Formation

In the area of Cortina, this unity presents a considerable lateral and vertical variability, which locally allows its subdivision in members, which are possible to map (Thickness 0-160 metres; Carnian/Julian/Tuvalian). It is divided into three members.

I) Lagazuoi Member

Arenitic Dolomite, dolo-arenites and oolitic-bioclastic grey and light-brown calcarenites, with bi-directional cross-lamination. Towards the east, it gradually passes to thin calcarenites and micrites, although – at the base, – high energy structures are still visible. In the upper part, a peritidal cycles organization with stromatolites is possible. In the north-western area (Falzarego Pass, Monte Nuvolau, Lastoni di Formin) there are grey bi-directional cross-laminated and hummocky sandstone outcrops, and these are assigned to the Arenarie del Falzarego ('Falzarego sandstones'), which are not distinguishable in a map (Carnian/Tuvalian).

II) “Areniti del Dibona” Member (Dibona Sandstones) 

Polygenic conglomerates; dark cross-laminated sandstones; light brown, grey or black pelites with frequently micritic to ruditic calcareous layers interbedded, progressively more frequent to the north and east. Vegetal remains are frequent, sometimes represented by centimetric coal horizons. Fossils: bivalves and rare ammonoids (Carnian/Julian/Tuvalian).

III) Borca Member

Dolomite limestone; arenitic Dolomite and well-stratified hybrid arenites with frequent peltic layers interbedded; sometimes a large scale cross-lamination is recognizable; at the base, dark coarse sandstones with frequent rests of plants, interbedded with calcarenites and sometimes bound-stones with stomato-poroids and colonial corals. At the top, a few metres interval of light Dolomite is present, well stratified, with centimetric grey or green-grey marly interstrata and stromatolitic levels. Fossils include bivalves, nautiloids and tetrapods’ footprints in the uppermost part (Carnian/Julian).

Post-volcanic and Cassian Succession

Dolomia Cassiana

Massive crystalline Dolomite, light brown and grey, dominated by slope deposits characterized by original cross-stratification, with angles reaching up to 30-35 degrees; locally, a mega-breccia texture is visible, while all the other structures and depositional textures are obliterated by ‘dolomitization’. Fossils: rare and not well preserved colonial coral heads. There is also a sub-type made of well-stratified crystalline Dolomite with stromatolites, pisolites and tepee, which represent the inner platform facies (Thickness 0 – 800 metres; Upper Ladinian-Lower Carnian/Langobardian/Julian).

San Cassiano Formation

Alternation of grey and black pelites and marls with micritic limestone and turbiditic oolitic-bioclastic calcarenites; in the middle-lower part of the formation, volcano-detritic litharenites are frequent. Calcareous olistoliths (‘Calcari di Cipit’ Auct.), of metric to decimetric size, are present; those derive from the Cassian platforms and are made of micro-bialitic boundstones with subordinated metazoan builders (corals, stromato-poroids, sphnctozoa). Fossils: ammonoids, bivalves, gastropods, echinoids, crinoids (Thickness 60 – 500 metres; Upper Ladinian-Lower Carnian/Langobardian/Julian).

Wengen – La Valle Formation

Dark grey or black turbiditic sandstone – deriving mainly from the erosion of the vulcanites – are present, alternated with black marly siltites and pelites. In the south-western sector, levels of volcano-clastic para-conglomerates. Carbonatic olistoliths are also locally present (‘Calcari di Cipit’  Auct.). Fossils: bivalves, ammonoids, rests of continental plants (Thickness 50 – 200 metres; Upper Ladinian-Langobardian).

Pre- and Syn-volcanic Ladinian Succession

Monte Fernazza Formation

Mainly volcano-clastic black sandstone, sometimes with subordinated fine intercalations (calcisiltites and calcilutites with Daonella sp. and ammonoids); they correspond to ‘Ialoclastiti’  Auct. In the higher part of the Cordevole valley, submarine basaltic lava flows and pillow-breccias are also present. There is a sub-formation with chaotic mega-breccia and graded breccia with polygenic clasts deriving from the pre- and syn-volcanic formations. Fossils: pelagic bivalves and ammonoids (Thickness 40 – 400 metres; Upper Ladinian/Langobardian).

Acquatona Formation

Dark grey colour siliceous calcisiltites and micrites, with plane-parallel lamination and intercalations of tufites like ‘Pietra Verde’ (Green Stone), and subordinated horizons of grey sandstone in the upper part. Fossils: pelagic bivalves (Daonella, Poseidonia) and ammonoids (Thickness 10 – 30 metres; Upper Ladinian/Langobardian).

Arenarie di Zoppé

Grey and dark-grey turbiditic sandstone, with quartz of both magmatic and metamorphic derivation and lithic fragments derived from metamorphites; intervals of arkosic arenites in plurimetric and amalgamated banks alternate with levels dominated by dark grey pelites with plant remains. Fossils: pelagic bivalves (Daonella, Posidonia sp.) and ammonoids (Protrachyceras spp) (Thickness 20 – 500 metres; Upper Ladinian/Langobardian).

Sciliar Formation

Prevailing massive Dolomite and/or Dolomite limestone with coarse inclined stratification (margin and slope facies) which laterally pass to Dolomites and subordinated limestone with horizontal stratification (inner platform facies). Locally (Gruppo del Cernera), at the top of the formation, drowning facies are also present; those are made of micritic limestones with pelagic bivalves and ammonoids (Thickness 0 – 800 metres; Anisian/Ladinian – Illyrian/Langobardian).

Livinallongo Formation (Buchenstein)

From the base to the top it consists of: i) black siliceous limestone in centimetric tabular strata with millimetric plane-parallel lamination, with thin peltic interstata (Plattenkalke); ii) nodular siliceous limestone in decimetric and amalgamated strata (Knollenkalke); iii) dark siliceous limestone with parallel lamina and current ripples, sometimes in centimetric strata (Baenderkalke). Intercalations of green coloured acid tufites (‘Pietra Verde’ Auct.) are distributed in the whole formation. Fossils: ammonoids, Daonella sp. (Thickness 0 – 200 metres; Anisian/Ladinian – Illyrian/Langobardian).

Anisian Succession

Ambata Formation

Calcisiltites with thin shell lamellibranchs and nodular limestone alternated with grey silty marls; towards the top, siltites and dark silty marls, in lamina and thin layers (from millimetric to centimetric size), separated by films of argillites (‘Marne a Daonella’, Auct.), follow. Fossils include rests of plants; Daonella sp., and ammonioids (Thickness 20 – 50 metres; Anisian/Illyrian).

Moena Formation

Bituminous dark micritic limestone, frequently laminated and deformed by slumps; breccias with flattened clasts derived from the laminites cited above; carbonatic breccia and mega-breccia with decimetric to metric clasts, deriving from the surrounding carbonate platforms (Thickness 0 – 60 metres; Anisian/Illyrian).

Contrin Formation

Prevailing light Dolomites with plane-parallel stratification, which is thin at the base, and with thick banks in the middle-upper part. Locally it is represented by strongly re-crystallized limestone made of grainstones and calcareous algae thalli (margin facies), and of subordinated boundstones with Tolypammina and Tubiphytes. Fossils: Dasycladacea (Thickness 0 – 150 metres; Anisian/Illyrian).

Morbiac Limestone

Nodular, grey, marly, silty and arenaceous limestone, intensely bio-turbated, with thin marly-pelitic lenses. The terrigenous content decreases upwards. Fossils: bivalves. At the base, reddish and yellowish polygenic conglomerates are present (Richthofen Conglomerate), with generally reworked clasts derived from the underlying formations. Towards the top, it passes from red and grey lithic sandstone to siltites with tetrapods’ footprints: Rhynchosauroides tirolicus, Chirotherium sp., Brachychirotherium sp. (Thickness 0 – 50 metres; Anisian/Illyrian).

Monte Bivera Formation

Nodular mictritic limestone with silty marls of varying colours, with pelagic Lamellibranchia and ammonoids. Possible intercalations of thin to coarse bio-clastic calcarenites and grey tufites (Thickness 0 – 20 metres; Anisian/Illyrian).

Dont Formation

Grey, medium-thin micaceous sandstone and silty limestone in centimetric to decimetric strata with wavy joints; towards the top, it passes from pure to marly, nodular, brown micritic limestone alternated with marls. In the upper part, alternation of grey calcisiltites and marls. Locally, olistolithic clusters fed by a carbonate platform are present. Fossils: brachiopods, bivalves, ammonoids, crinoids (Thickness 20 – 160 metres; Anisian/Pelsonian-Illyrian).

Serla Superiore Formation

Dolomites; Dolomite limestone and light grey limestone, massive to coarsely stratified; the prevalent calcareous litho-facies are made of micro-bialitic bounstones, associated to bio-clastic calcarenites with calcareous algae and skeletal remains of invertebrated (bivalves, brachiopods, crinoids), and fossiliferous micrites (Thickness 40 metres; Anisian/Pelsonian).

Recoaro Limestone

Nodular, dark bioclastic and micritic limestone with thin marly lenses; thin to coarse sandstone, in centimetric to pluri-decimetric strata; bio-calcarenites with crinoids are frequent, calcareous algae, brachiopods. Patch-reef of metric size are also locally present (Thickness 20 – 50 metres; Anisian/Pelsonian).

Voltago Conglomerate

Conglomerates with sub-angular and rounded clasts deriving from the Serla Inferiore Dolomite, from the Gracilis Formation, from the Monte Rite Formation and from the upper terms of the Werfen Formation; towards the top, it passes to sandstone and red-grey bio-turbated siltites; siltites with carbonaceous fragments are also present, and tetrapods’ footprints (Thickness 0 – 70 metres; Anisian/Bithynian-Pelsonian).

Monte Rite Formation

Dolomitic limestone and light coloured Dolomites in tabular strata of decimetric to metric thickness; among the prevailing litho-facies: micro-bialitic boundstones and bio-clastic horizons with algae and crinoids. (Thickness 0 – 100 metres; Anisian/Bithynian).

Calcari Scuri del Coll’Alto (Coll’Alto Dark Limestone)

Limestone and sub-orinated dark, nodular Dolomites in centimetric to decimetric strata, with minor marly inter-strata, alternated with sandstone and bio-clastic calcarenites with foraminifers, dasycladacean, crinoids, bivalves and gastropods (Thickness 40 – 80 metres; Anisian/Bithynian).

Piz da Peres Conglomerate

Conglomerates sometimes in lenses and pockets, with pebbles of Dolomite, light Dolomite limestone (Serla Inferiore Dolomites) and subordinated pebbles of micritic limestone, calcarenites and oolitic-bioclastic dolo-arenites; siltites and sandstone deriving from the Werfen Formation; sometimes reddish sandstone and argillaceous siltites are also present (Thickness 0 – 20 metres; Lower Anisian/Aegean-Bithynian).

Permian-Scitian Succession

Dolomia del Serla Inferiore (Serla Inferiore Dolomite)

Fine-grained Dolomites, light grey or whitish in colour, well stratified, with subordinated grey or greenish marly layers in the lower part and horizons, with tepee and stromatolitic lamina. Fossils are rare, limited to foraminifers of the Glomospira-Glomospirella group and some bivalves (Thickness 50 – 100 metres; Upper Olenkian/Lower Anisian-Spathian/Aegean).

Werfen Formation

It comprises a wide range of carbonate and terrigenous lithotypes, and they all present peritidal to shallow marine water facies associations. The formation has been divided into nine lower rank units, partly combined in the following legend, which provides five main units. Within this formation, the lower rank units have not yet been recognized (Changhsingian-Olenkian).

I) Cencenighe Member and San Lucano Member

The San Lucano Member is comprised of red cross laminated sandstone: red siltites with mud cracks; more or less marly limestone, red and purple, with little tepee; Dolomites and grey-green Dolomite marls, bio-turbated and fossiliferous, with Costatoria costata.

The Cencenighe Member is composed of limestone and oolitic/bio-clastic Dolomites, yellow and red coloured; grey and red fossiliferous marls with Dinarites sp., Eumorphis telleri, Turbo sp., Natiria sp., Neoschidozus sp., and red siltites with mud-cracks (Olenkian-Spathian).

II) Val Badia Member

Nodular, grey, micritic limestone, bio-turbated, with large burrows like Planolites and Thalassinoides, frequently marly; centimetric to decimetric scale alterations of oolitic-bioclastic calcarenites. Fossils: Tirolites cassianus, Natiria costata and Turbo rectecostatus (Olenkian-Spathian).

III) Oolitic-with-Gastropods Member and Campil Member

The Campil Member is composed of red-quarzose micaceous sandstone with strata of a few centimeters’ thickness and parallel lamination; hummocky and wave ripples, alternated with red siltites and pelites. Load cast structures like ball-and-pillow are frequent. Fossils: Eumorphotis hinnitidea; at the top, Costatoria subrotunda and Asteriacites are also present.

The Oolitic-with-Gastropods Member is mostly composed of grey arenaceous limestone and sandstone with calcitic cements, with hummocky and wave ripples; also reddish oolitic-bioclastic calcarenites with micro-gastropods, interclastic breccia with flat muddy clasts (Koken Conglomerate Auct.). Fossils: Eumorphotis hinnitidea (Induan-Olenkian/Dinerian-Smithian).

IV) Andraz Member and Siusi Member

The Siusi Member is composed of grey marly micritic limestone, grey-reddish marls, bioclastic and oolitic calcarenites; in the upper part, red and grey sandstone with Diplocraterion, red siltites with mud cracks; fossils: Claraia clarai, C. aurita.

The Andraz Member is a massive yellowish Dolomite, generally sterile, alternated with silty-marly Dolomite of varying colours, and with a small tepee (Induan-Olenkian/Greisbachian-Dinerian).

V) Tesero Member and Mazzin Member

The Mazzin Member is made of grey marly and silty limestone, intensely bio-turbated, micro-nodular; micrites and dark-laminated marls with pyrites; bio-clastic calcarenites with ostracods and bivalves in centimetric strata. Fossils: ostracods, Lingula sp. and, in the upper part, Claraia wangi.

The Tesero Member presents at the base a thin layer of oolitic calcarenites, sometimes with micro-fauna and Permian brachiopods. Light grey micrites follow, with minor intercalations of bio-clastic calcarenites, small oolites and peltoids (Changhsingian-Induan/Greisbachian).

Bellerophon Formation

Dark fossiliferous limestone, with algae, formaninfers, nautiloids, bivalves, gastropods (Bellerophon sp.) in decimetric, bio-turbated strata with marly intercalations. Possible intercalations of light coloured Dolomites with roots’ traces and fenestrae are also possible. At the top, dark limestone with fusulinids (Nankinella) and large brachiopods (Comelicania) (Thickness 150 metres; Changhsingian).

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