The Triassic and Jurassic Sedimentary Cycles in Central Sardinia

Geological Field Trips

Società Geologica Italiana

2016 Vol. 8 (1.1) ISPRA Istituto Superiore per la Protezione e la Ricerca Ambientale

SERVIZIO GEOLOGICO D’ITALIA Organo Cartografico dello Stato (legge N°68 del 2-2-1960) Dipartimento Difesa del Suolo

ISSN: 2038-4947

DOI: 10.3301/GFT.2016.01 The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment and relationship between tectonics and sedimentation L. G. Costamagna - S. Barca GFT - Geological Field Trips geological fieldtrips2016-8(1.1) Periodico semestrale del Servizio Geologico d'Italia - ISPRA e della Società Geologica Italiana Geol.F.Trips, Vol.8 No.1.1 (2016), 78 pp., 54 figs. (DOI 10.3301/GFT.2016.01)

The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment and relationship between tectonics and sedimentation 85° Congresso Nazionale della Società Geologica Italiana, Sassari 6-8 settembre 2010 Luca G. Costamagna*, Sebastiano Barca** * Dipartimento di Scienze Chimiche e Geologiche, Via Trentino, 51 - 09127, Cagliari (Italy) ** Via P. Sarpi, 18 - 09131, Cagliari (Italy)

Corresponding Author e-mail address: [email protected]

Responsible Director Claudio Campobasso (ISPRA-Roma) Editorial Board Editor in Chief Gloria Ciarapica (SGI-Perugia) M. Balini, G. Barrocu, C. Bartolini, 2 Editorial Responsible D. Bernoulli, F. Calamita, B. Capaccioni, Maria Letizia Pampaloni (ISPRA-Roma) W. Cavazza, F.L. Chiocci, R. Compagnoni, D. Cosentino, Technical Editor S. Critelli, G.V. Dal Piaz, C. D'Ambrogi, Mauro Roma (ISPRA-Roma) P. Di Stefano, C. Doglioni, E. Erba, publishing group R. Fantoni, P. Gianolla, L. Guerrieri, Editorial Manager M. Mellini, S. Milli, M. Pantaloni, Maria Luisa Vatovec (ISPRA-Roma) V. Pascucci, L. Passeri, A. Peccerillo, Convention Responsible L. Pomar, P. Ronchi, B.C. Schreiber, Anna Rosa Scalise (ISPRA-Roma) L. Simone, I. Spalla, L.H. Tanner, Alessandro Zuccari (SGI-Roma) C. Venturini, G. Zuffa. ISSN: 2038-4947 [online]

http://www.isprambiente.gov.it/it/pubblicazioni/periodici-tecnici/geological-field-trips

The Geological Survey of Italy, the Società Geologica Italiana and the Editorial group are not responsible for the ideas, opinions and contents of the guides published; the Authors of each paper are responsible for the ideas, opinions and contents published. Il Servizio Geologico d’Italia, la Società Geologica Italiana e il Gruppo editoriale non sono responsabili delle opinioni espresse e delle affermazioni pubblicate nella guida; l’Autore/i è/sono il/i solo/i responsabile/i. DOI: 10.3301/GFT.2016.01 The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment and relationship between tectonics and sedimentation L. G. Costamagna - S. Barca geological fieldtrips2016-8(1.1)

INDEX

Information

Abstract ...... 5 2.2.2. Monte Maiore fm.: homoclinal ramp Riassunto ...... 6 sub-environments ...... 20 Safety/Hospitals ...... 8 2.3 First Mesozoic sedimentary cycle in Central Sardinia: Service stations/Accommodations ...... 8 some remarks ...... 22 General information about the Itinerary ...... 9 3. Post-variscan geological evolution: Jurassic ...... 24 Recommended cartography ...... 10 3.1. Jurassic successions: regional frame and stratigraphy ..24 3 3.1.1. Genna Selole fm...... 27 Excursion notes 3.1.2. Dorgali fm...... 32 3.1.3. Genna Silana fm...... 33 General framework ...... 12 3.1.4. Definition of the Baunei group ...... 33 The Tacchi area (Central Sardinia): geomorphological and 3.2 Depositional environment of the Jurassic units ...... 34 paleogeographical premise ...... 12 3.2.1. Baunei group, Genna Selole fm.: Geological setting ...... 14 alluvial to deltaic (?) system ...... 34 1. Variscan Paleozoic Basement and 3.2.2 Baunei group, Dorgali fm.: Permo-Carboniferous covers ...... 14 tidal flat and inner ramp lagoon ...... 36 2. Post-variscan geological evolution: Triassic ...... 15 3.2.3 Baunei group, Genna Silana fm.:

2.1. Triassic successions: regional frame and stratigraphy ..15 oolitic margin with patch-reefs ...... 36 index 2.1.1. Escalaplano Fm...... 16 3.2.4. Paleogeographic and geodynamic meaning of 2.1.2. Monte Maiore fm...... 18 the Baunei group ...... 37 2.2 Depositional environment of the Triassic succession .....20 3.3. The Jurassic succession: 2.2.1 Escalaplano Fm.: alluvial fans and mudflats .....20 second Mesozoic sedimentary cycle, conclusions ...... 38

Itinerary

Day 1 - From Cagliari to Jerzu (OG) ...... 41 Day 2: from Jerzu to Osini ...... 64 STOP 1 - Bruncu su Para (Orroli): general features of STOP 8 - Pitzu S. Antonio (Tertenia Tacco): the Escalaplano Fm. and Monte Maiore fm...... 44 sedimentological features of the Middle Jurassic STOP 2 - Bruncu Geroni (Orroli): algae in the yellow transgression over the Variscan basement ...... 64 dolostones member of the Monte Maiore fm. and Stop 8b - Ungul'e Ferru: accretion clinoforms in the passage to the Tertiary deposits ...... 46 Dorgali fm...... 67 STOP 3 - Piccheri (Orroli): Middle Triassic/ Middle Jurassic STOP 9 - Monte Lumburau (Jerzu Tacco): 4 unconformity and general features of the Genna Selole fm. ..48 laterites(“Ferro dei Tacchi”) at the base of the STOP 4 – Escalaplano (Escalaplano Tacco): type section and Middle Jurassic transgression ...... 68 sedimentological features of the Escalaplano Fm...... 51 STOP 10 - Bruncu Matzeu (Ulassai Tacco): synsedimentary Stop 4b - Ponte Tradala - Features of the transition from the extensional tectonics, transitional depositional environments and Genna Selole fm. to the Dorgali fm...... 55 early karstic cycles at the Genna Selole fm./Dorgali fm. STOP 5 - Arcu de Is Fronestas (Escalaplano Tacco): transition ...... 69 unconformity between the Escalaplano Fm. and STOP 11 - Grutta Orroli and Punta su Scrau (Osini Tacco): the Genna Selole fm...... 55 oolitic grainstones, patch reefs and oncoids of the STOP 6 - Sa Teria (Perdasdefogu Tacco): sedimentologica Genna Silana fm...... 71 l features of the upper Genna Selole fm. and Stop 11a - Osini Tacco: small patch reef in the Genna Silana fm. ..71 the lower Dorgali fm...... 59 Stop 11b - Punta Su Scrau: index STOP 7 - Serra Is Arangius (Perdasdefogu Tacco): oncolitic floatstones in the Genna Silana fm...... 71 parastratotype and sedimentological features of the Genna Selole fm...... 61 References ...... 75

Abstract geological fieldtrips2016-8(1.1)

This field trip presents a general overview of the stratigraphical, sedimentological and paleogeographic evolution of the Middle Triassic and Middle Jurassic successions in che Central Sardinia Tacchi area (Gerrei, Sarcidano, Barbagia, Ogliastra). These successions are divided by an unconformity and are both laid down under active extensional tectonics conditions. The Triassic Eastern Sardinia succession belongs to the Germanic Triassic Domain (Buntsandstein and Muschelkalk facies group), so showing strict affinites with the Iberian and Mid-European successions. It is featured by transgressive siliciclastic to carbonate deposits not more than few tens of meters thick: they represent the evolution from a continental, middle to low-energy environment to a restricted shallow marine one. This succession deposited along the stretching southern margin of the Paleo-European Plate under a hot- arid climate: it represents the last remain of the first Mesozoic depositional cycle in the area. The Middle Triassic deposits pass upward through an disconformity to the Middle Jurassic transgressive siliciclastic to carbonate succession that is some houndreds of meters thick. The represented depositional environments are all those comprised between high-energy fluvial deposits (fluvial fan) and carbonate shelf 5 margin ones. These sediments deposited under a hot-humid climate and correspond to the second Mesozoic depositional cycle of Central Sardinia. They are directly linked to the opening of the Alpine Tethys that triggered in the Eastern Sardinia area the uplift of a wide tectonic high leading to the dismantling of the main part of the previous Mesozoic (Triassic-lowermost Jurassic) to Permian successions.

Key-words: Alluvial depositional systems, Carbonate depositional systems, Triassic, Jurassic, Extensional information tectonics, Eastern Sardinia.

Riassunto geological fieldtrips2016-8(1.1)

In questa escursione viene presentata una panoramica generale dell’evoluzione stratigrafica, sedimentologica e paleogeografica delle successioni del Triassico Medio e Giurassico medio localizzate nel settore dei Tacchi (Gerrei, Sarcidano, Barbagia, Ogliastra), nella Sardegna centrale. Tali successioni sono separate da una disconformità e si sono deposte in condizioni di tettonica estensionale attiva. La successione medio-triassica è riferita al dominio triassico in facies germanica (gruppi di facies Buntsandstein e Muschelkalk), e mostra affinità con le successioni iberiche e dell’Europa centrale. Essa è caratterizzata da una successione trasgressiva, a litologia da silicoclastica a carbonatica, dello spessore di non più di poche decine di metri, e rappresenta l’evoluzione da un ambiente continentale di energia da media a bassa ad un ambiente marino ristretto di bassa profondità. Questa successione si è depositata lungo il margine meridionale in estensione della placca paleo-europea sotto un clima caldo-arido: essa rappresenta la sola testimonianza, lasciata dall’erosione medio-giurassica, del primo ciclo deposizionale Mesozoico nel settore. I depositi triassici passano verso l’alto, tramite una disconformity, alla successione trasgressiva, anch’essa da silicoclastica a carbonatica, del Giurassico medio, dello spessore di alcune centinaia di metri. Gli ambienti 6 deposizionali in essa rappresentati sono tutti quelli compresi fra il contesto fluviale di alta energia ed il margine di piattaforma carbonatica. Questi sedimenti si sono depositati sotto un clima caldo-umido e rappresentano il secondo ciclo deposizionale mesozoico della Sardegna Centrale. Essi sono direttamente legati all’apertura della Tetide alpina, apertura che ha attivato nella Sardegna orientale lo sviluppo di un esteso alto strutturale che ha portato allo smantellamento della parte principale delle precedenti successioni da mesozoiche (Triassico- Giurassico inferiore pp.) a permiane. information

Parole chiave: Sistema deposizionale alluvionale, Sistema deposizionale carbonatico, Triassico, Giurassico, Tettonica distensiva, Sardegna orientale.

7 information

Safety geological fieldtrips2016-8(1.1)

Every partecipant should wear a safety shiny jacket to be worn during the stops along the motorways. The best times to make the trip are from March to May and from September to November. In this case clothing should be light, with perhaps a raincoat to spare for possible rare drizzles. All participants require comfortable walking boots. A small rucksack is needed for daily use. This needs to be at least big enough to carry a spare T-shirt (and maybe a fleece/sweater), a bottle of water and small snacks. Sun protection is needed: hats are pretty useful. Short pants are not advisable: ticks, fleas and others annoying insects are still in the field. Mobile/cellular phone coverage is good although in same place it can be absent. The emergency telephone number for ambulance is 118. The emergency telephone numbers for police is 112 and 113.

Hospitals

CUP Ospedale San Giuseppe - 1, Via Emilia - Isili, CA 08033 – Tel. 070 474747 P.A Croce Verde Escalaplanese - Via Santa Barbara, Escalaplano, CA 08043 – Tel. 070 8001123 8 Clinica Tommasini S.p.A. Via Ospedale 08044 Jerzu OG – Tel. 0782 7616

Service stations

Loc. Siurgus, Orroli, Nurri, Escalaplano, Perdasdefogu, Jerzu. information Accommodations

Omu Axiu Hotel - Via Roma, 46, 08030 - Orroli NU Tel. 0782 845023 Albergo Su Tettioni - Loc. Su Tettioni 08046 - Perdasdefogu – Tel. 0782 94190 Rifugio d’Ogliastra - Spalto 13 Km. 5, 500 - 08044 Jerzu OG – Tel. 320 606 3728

General information about the itinerary geological fieldtrips2016-8(1.1)

The field trip develops only on paved roads. Long walks will be not needed: all the outcrops will be reached by bus, plus 5 minutes of walking at most. The risk level is very low. So, people can make this trip alone or accompanied by the authors of this guidebook. The complete itinerary needs 2 days. We may spend the night of rest in a welcoming agritourism located between Perdasdefogu and Jerzu in the hearth of the Southern Ogliastra, standing right on the Variscan peneplain, whose flat continuity is broken up by the sudden rise of Jurassic carbonate mesas and plateau. Cagliari Elmas is left behind and the motorway SS131 “Carlo Felice” running along the NW/SE oriented Plio- Quaternary Campidano graben is taken. At the Km 20 (Sardara exit) we turn to Northeast proceeding along the National Road SS128 to Senorbi. Along the travel we cross the Trexenta territory: here nearly horizontal miocenic deposits of the Tertiary Sardinian Rift crop out. We go through Senorbui, Suelli 9 and Siurgius Donigala and keep toward East to Orroli: a few Km before reaching this little village, in the Gerrei territory, we reach the Mesozoic outcrops representing the topics of our field trip (Fig. 1): here they cover unconformably the Variscan basement outcrops information pertaining to the “granitoid” batholith or to the metamorphics of the Variscan chain. The itinerary will take us in two days through the landscapes of the Fig. 1 - Stratigraphic and geographic location of the field trip stops: Gerrei and Ogliastra, with an overnight VB: Variscan Basement; EF: Escalaplano Fm.; MMF: Monte Maiore fm.; stay in a confy little residence close to GSF: Genna Selole fm.; DF: Dorgali fm.; GSilF: Genna Silana fm; T.B.H.: Jerzu (OG). Tectonic Barbagia High. DOI: 10.3301/GFT.2016.01 The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment and relationship between tectonics and sedimentation L. G. Costamagna - S. Barca

Recommended cartography geological fieldtrips2016-8(1.1)

Geological maps

Geologic Map of Sardinia, scale 1:200.000 (Carmignani et al., 2001); Sheet 218 “Isili”, scale 1:100.000 of the Carta Geologica d’Italia; Sheet 226 “Mandas”, scale 1:100.000 of the Carta Geologica d’Italia; Sheet 541 “Jerzu”, scale 1:50.000 of the Carta Geologica d’Italia (CARG Project);

Topographic maps

Topographic Regional Map; scale 1:25.000

Touristic maps 10 Sardegna Carta Stradale e Turistica Scala 1:200.000 – Touring Club Editore (Italiano) Sardinia Regional Map, Touring Club Italiano, Folded Map, Scale 1:200.000 (English) information

DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) excursion notes 11 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Nortward overview of the Tacchi di Jerzu, Ulassai and Osini The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) excursion notes 12 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation 2). from each other by deep are often separated These relieves The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 General framework The Tacchi area (Central Sardinia): geomorphological and paleogeographical premise Sarcidano), a peculiar scenery appears to the traveller: Sardinia (Gerrei, Barbagia, Ogliastra, In Central-Eastern landscape showing one of the most peculiar (Plateau) area is a natural or “Tacchi” “Tonneri” dubtless the Jurassic by flat-topped in the multifaceted Sardinian geological area. This landscape is marked morphological varieties carbonate Triassic) (and rarely, Jurassic highlands, plateau, mesas and buttes which top is built of horizontal metamorphics (Fig. Variscan rocks resting over gorges and they are located at different topographic levels rising gradually from 350 m (Tacco di Escalaplano) from 350 m (Tacco rising gradually levels gorges and they are located at different topographic of uplifting tectonic movements di Seui) to North. This is due the Tertiary in the South to 1300 m (Tacco erosion, determined the present Cenozoic-Quaternary the area. This tectonics, together with coeval outcrops. These outcrops represent the remnants of a former widespread scattered distribution of the Jurassic the whole Sardinia over which deposited most likely continental to marine cover, and uninterrupted Mesozoic of Eastern - Northeastern Island: this assumption is suggested by the correlatable, similar rocks of Jurassic succession of the Capo Figari), of the Mesozoic Golfo di Orosei, Isola Tavolara, Sardinia (Supramonte, S. Pino, rocks of the Sulcis area (Porto to Jurassic N and E of Alghero (NW Sardinia) the Triassic Nurra Antioco: SW Sardinia). geological field trips 2016 - 8(1.1) excursion notes 13 L. G. Costamagna - S. Barca L. G. Costamagna - S. = Triassic; = Triassic; TR en tectonics and sedimentation = Permian; = Permian; P = stratigraphic sections. = stratigraphic Red dots = Quaternary; Q = Paleozoic Variscan Basement; Variscan = Paleozoic PZ = Miocene; M = Eocene; E The Ferro dei Tacchi level and inactive and active quarries are also signed. and active and inactive level dei Tacchi The Ferro = Jurassic; = Jurassic; J Fig. 2 – Geological map of the Tacchi area; Fig. 2 – Geological map of the Tacchi The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) excursion notes 14 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 3 – Geological sketch of the Tacchi area with of the Tacchi Fig. 3 – Geological sketch (modified after Costamagna et al., 2007). (modified after Costamagna et al., evidenced the Mesozoic outcrops: the location of evidenced the Mesozoic tectonic Barbagia paleohigh is evidenced (M.B.H.) to the “Outer Nappe Zone” (Carmignani et al., to the “Outer Nappe Zone” before, the Variscan 1992; 1994). As sketched be locally covered metamorphics may unconformably also by little remains of molassic sediments belonging to the limnic (Late Carboniferous –sediments cycle Early and/or to the red beds sediments Permian) they reach a maximum (Permian): cycle thickness of 400 m (Cassinis et al., 2000). units are formed by The allochton Variscan metamorphics deriving to middle grade low- mainly from terrigenous deposits: volcanics and carbonates are subordinate protoliths. The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Geological setting 1. Variscan Paleozoic Basement and Permo-Carboniferous covers metamorphics through an angular mainly the Variscan deposits cover Sardinia (Fig. 3) the Mesozoic In Central post-Variscan Permo-Carboniferous they could be posed unconformably over More rarely, unconformity. molassic sediments. lithologies (Late Cambrian-Early Carboniferous) are assigned to different tectonic Sardinia the Variscan In Central Those tectonic units pertain to the “Inner Nappe Zone”units: their metamorphic degree grows up northward. and geological field trips 2016 - 8(1.1) excursion notes 15 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 4 – Olenekian (Lower Triassic): Dercourt et al., 2000). Dercourt et al., European paleogeography and Sardinia: the European paleogeography star marks the field trip area. (modified after The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 2. Post-variscan geological evolution: Triassic and stratigraphy successions: regional frame 2.1. Triassic chain times the Variscan During Late Carboniferous and Permian These molassic basins developed. collapses. Intra-chain gradually 2000; deposits (Cassinis et al., basins were filled by erosive the extensional tectonic 2002). Afterwards, Cassinis & Ronchi, 1990): the extension (Ziegler, break up the Pangea cycles spreads down to the southern subsiding border of Paleo- Europe where the Sardinia-Corsica block was located (Fig. 4). depositional cycleThus the first Mesozoic started: it is referable to the lower part of wider Alpine tectono-sedimentary cycle. located on the southern edge of The Sardinian area was by (Costamagna & Barca, 2002). It is characterized Paleo-Europe deposits belonging to the Germanic facies. Triassic starts with continental (red Sardinia the Middle Triassic In Central sediments belonging beds facies) to transitional-lagoonal–littoral to the Escalaplano Fm. (late Anisian – early Ladinian?) (Sardinian 2000; Costamagna & Buntsandstein group) (Costamagna et al., Barca, 2002). These sediments are the base of sedimentary induced by the and forecast the marine trasgression cycle of the Alpine tectonics. extensional movements the peneplaning and almost complete flooding of Following basement, the Escalaplano Fm. mainly siliciclastic the Variscan by the Monte Maiore fm. (Sardinian sediments are covered Muschelkalk group), built of carbonate shelf deposits aged late (Ladinian). Middle Triassic geological field trips 2016 - 8(1.1) excursion notes 16 2) Microbialitic 13) Sandstones and L. G. Costamagna - S. Barca L. G. Costamagna - S. 4) Palynomorphs-bearing en tectonics and sedimentation 9) Bioturbation; Carbonate sandstones and marls; 12) 6) Conglomerates; Conglomerates; Dolostones; 3) 8) Halite – casts; 11) Siltites and clayey siltites; Siltites and clayey Reddish to greenish metasandstones (Variscan basement; to greenish metasandstones (Variscan Reddish 5) 1) Mud-cracks; Mud-cracks; Plane-parallel laminations (mod. after Costamagna & Barca, 2002). Plane-parallel 10) 14) Siltites, clays and evaporites; and evaporites; Siltites, clays Fig. 5 - Escalaplano (Gerrei, Central Sardinia) type section of the Escalaplano Fig. 5 - Escalaplano (Gerrei, Central mats; conglomerates; conglomerates; Fm. Legend – 7) Basal pedogenization of the basement; horizons; horizons; 2.1.1. Escalaplano Fm. (Middle Triassic: late Anisian – early Ladinian?) The Escalaplano Fm. (Fig. 5), from 0 to 20 m thick, shows at (Gerrei) a well-exposed type section. This unit can be subdivided into 4 by the Italian Commission on is validated lithofacies. The Formation 2006a). (Delfrati, Stratigraphy Litofacies 1 rare The lithofacies 1, the thinnest one, is formed by conglomerates, the Variscan breccias and sandstones, lies unconformably over or clast-supported, can be matrix- basement. The conglomerates bedding. They are formed by with cross bedding or graded rarely Permian reworked pebbles made up by quartz, metamorphics and rare The sandstones are immature. volcanics. This lower lithofacies shows up evidently only in the southeasternmost thin and outcrops of the Escalaplano Fm.: elsewhere, it can be very discontinuous, or be no present at all. Litofacies 2 siltites and alternations of clays, The lithofacies 2 is built of rhythmic thin laminations and bedding. Rare, marls showing plane-parallel are also present. This lithofacies can be reddish to sandstone layers a rich palynological In the blackish levels blackish in colour. rarely grey, to the late Anisian is contained. In reddish association referable The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) excursion notes 17 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Antonescu 1969: Pittau Cristianisporites triangulatus The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 clay levels mud-cracks, bioturbation structures and halite-casts can be found. In the blackish to yellowish mud-cracks, levels clay wrinkled microbialitic mats and chaotic algal envelopesmarly levels, been observed have In the frequently. fade out and are replaced by sandstone layers easternmost outcrops of the lithofacies 2 marls gradually locally showing cross lamination structures. Litofacies 3 The lithofacies 3 is formed by alternations of fissile of pinkish and thin levels blackish and purplish clays The gypsum has a satin spar appearance connecting the different levels. gypsum locally filling late fractures that suggests it is now mainly due to ricirculation of sulphate solution. Litofacies 4 lithologies. In the Escalaplano area to marly-carbonate The lithofacies 4 is usually constituted by silty-marly thin fine Rarely, and silty clays. infrequently reddish, clays this lithofacies is made by grey-greenish, suddenly and pass to carbonate are present. In this lithofacies the gypsum beds vanish sandstones layers marls, to the dolostones clayey sediments. This change foretells the close passage, throughout green-yellowish of the Monte Maiore fm. only in the Escalaplano area. In The lithofacies 2 and 3 of the Escalaplano Fm. are clearly separated M. Maiore) they instead form a single unit made by silty clays westernmost areas (Orroli, Nurri, Escalaplano, in the upper part it changes to grey- siltites: while in its lower part the purplish colour prevails, and clayey and scattered. Nonetheless, mud cracks are very green. The blackish deposits, the marls and evaporites in the lithofacies 2 thin nodular calcrete Rarely, halite casts are still present in the reddish siltites and clays. been observed. have horizons take del Sarcidano) the passage to carbonate Monte Maiore fm. may In the northern areas (Orroli, Tacco lithofacies at most 1 m thick: here suddenly the carbonates appear and place throughout a dark grey-greenish came to be dominant. rapidly by microfloristic assemblages found in the lithofacies 2 The age of the base Escalaplano Fm. is marked –and referred to the Pelsonian Illirian (late Anisian: Demelia & Flaviani, 1983; Costamagna et al., 2000). Due to the missing of palaeontological reliable data, 1983; Costamagna et al., Demelia & Flaviani, referred to the early Ladinian. top of the unit is tentatively geological field trips 2016 - 8(1.1) excursion notes 18 , so dating L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Costatoria goldfussi Conglomerates; 3) Dolostones containing chert Fig. 6 – Lateral correlations of the Triassic succesions in correlations of the Triassic Fig. 6 – Lateral after Costamagna et al., 2000). after Costamagna et al., 8) Eastern Sardinia from NW (Monte Maiore) to SE (Escalaplano): thinning of the Escalaplano Fm. (mod. note the northwestward the marine transgression to the early late Ladinian. the marine transgression The Escalaplano Fm. thins out gradually towards NW (Fig. towards The Escalaplano Fm. thins out gradually 6): almost completely in the northern area of it vanishes Monte Maiore the Laconi and Monte Maiore (Nurecci). At start with sandy to pebbly even deposits may Mesozoic directly the dolostones of the Monte Maiore fm covering basement. Close to the base of unit, Variscan with basal lags bearing limestone beds contain storm layers marker the Germanic Triassic Late-Variscan granitoids; granitoids; Late-Variscan 2) Marly limestones; 7) Limestones; 6) Dolostones; 5) Variscan micaschists (Variscan basement); micaschists (Variscan Variscan 1) Silty clays; Silty clays; Fig. 7 - Monte Maiore (Sarcidano, Central Sardinia): Middle Triassic succession. Sardinia): Middle Triassic Central Fig. 7 - Monte Maiore (Sarcidano, nodules. The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe 4) Legend: DOI: 10.3301/GFT.2016.01 2.1.2. Monte Maiore fm. (Middle Triassic: early – late Ladinian) The Escalaplano Fm. is followed by the dolostones and limestones of Monte 2000; Sardinian Muschelkalk group, Maiore fm. (Fig. 7) (Costamagna et al., Costamagna & Barca, 2002). This unit is only informally defined for the lack of a well-exposed and continuous type section. The best outcrops are located at Monte Maiore. The Maiore fm. is constituted by two members: the yellow dolostones The yellow dolostones member and the blue limestones member. member differently depending to the location of outcrop. upwards developes geological field trips 2016 - 8(1.1) excursion notes 19 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : they suggest an early late Ladinian age. Otherwise, in the Costatoria goldfussi Usually the passage between the two members is gradual: it takes place through grey calcareous it takes Usually the passage between two members is gradual: The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Southwestward, where the Monte Maiore fm. rests over the Escalaplano Fm., the transition from the lower unit the transition the Escalaplano Fm., where the Monte Maiore fm. rests over Southwestward, dolostones the base of Monte Maiore fm. is built yellowish Lacking the Escalaplano Fm., is gradual. of quartzose angular pebbles of metamorphic rocks. Thin layers cm-sized containing scattered quartz and rare intercalate. matrix(dolomitic)-supported conglomerates to yellowish 0 to 25 m thick, is formed by grey-yellow dolostones member, Monte Maiore the yellow At dolostones. Where the Escalaplano Fm. misses, lower terrigenous-carbonate cobbly basal facies stratified 2) Halokinetic- by irregular alternations of dolomitic lithofacies as 1) Collapse breccias horizons; is covered molds, calcitic pseudomorphs after dolostones containing evaporitic 3) Thickly stratified featured levels; texture; 5) sulphates and scattered nodules of chert; 4) Laminated algal bindstones locally with fenestral intercalate: the basal lag is thin storm layers peloidal mudstones and fine mudstones. Rare Finely dolomitized and peloids. gastropods, ostracods) bivalves, formed by bioclasts (microbial mats and green algae fragments, In this member the fossil remains are rare. the blue limestones member appears dolostones member, and aside the upper part of yellowish Upwards (Fig. 7). dolostones (oolitic-bioclastic, rarely peloidal grainstones), followed by blue, well-stratified limestones rich of followed by blue, well-stratified peloidal grainstones), rarely dolostones (oolitic-bioclastic, The intermediate part of this ostracods. bioclasts and peloids. The fossil rests are crinoids, gastropods, bivalves, calcareous marls and marls. Frequently member contains bluish limestones with intercalations of grey-greenish of provided the limestone beds are built of alternations bioturbated calcarenites-calcilutites and storm layers followed by calcarenites with HCS structures of gastropods and bivalves, a coarse basal lag containing fragments are infrequently contained in the marly beds too. Thin calcareous storm layers (Hummocky Cross Stratification). of the marly intercalations, and The top of the blue limestones member is featured first by vanishing by pinkish dolostones with algaeafterwards c), containing nodules of chert. The (Damiani & Gandin 1973 a, b, the total thickness of formation in Monte Maiore area thickness of this member is estimated 35-40 m. So, reaches about 50 m. it becomes differ depending to the locality: as Escalaplano Fm., The age of the Monte Maiore fm. may the peneplaned progress over transgression following the Middle Triassic this way NW, towards younger by calcareous layers is marked continent. In the Monte Maiore area, age of transgression Variscan containing remains of Escalaplano area, the beginning of carbonatic sedimentation could be referred to early Ladinian. geological field trips 2016 - 8(1.1) excursion notes 20 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Smith (2000) (Fig. 8) run by stream sensu These higher energy depositional bodies withdraw gradually and gradually These higher energy depositional bodies withdraw lakes these, firstly a mudflat with scattered playa Over disappear. mirrors (lithofacies 2, 3 and 4 of the Escalaplano and slack water 2000), perhaps interested by weak tidal Costamagna et al., Fm., by is often characterized place. This environment processes, takes the deposition of dark muds rich organic matter intercalated episodes. Spotted bioturbations, mud- periodically by evaporitic of gypsum support this halite-casts and thin layers cracks, marly limestones with microbial mats reconstruction. Rare intercalate in the middle-upper part of unit: this suggests marine ingressions before the ultimate flooding. ephemeral 2.2.2. Monte Maiore fm.: homoclinal ramp sub-environments trend. The Monte Maiore fm. is initially featured by a transgressive of the terrigenous input and rise sea With the vanishing Fig. 8 – Depositional environments of the Fig. 8 – Depositional environments (mod. after Costamagna et al., 2009). (mod. after Costamagna et al., The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe Escalaplano Fm. (late Anisian – early Ladinian) DOI: 10.3301/GFT.2016.01 floods could be hypothesized. floods could be hypothesized. facies are replaced by sabkha supratidal Escalaplano Fm. environments the continental-transitional level, restricted lagoon environments. low-energy, (Costamagna & Barca, 2002), followed later by tidal flat / shallow, forming the yellowish and scattered evaporites down carbonatic muds, microbial mats, storm layers Here lay rising, the keeps the sea level 2000). Afterwards, dolostones member of the Monte Maiore fm. (Costamagna et al., outer shelf facies, formed initially by oolidal- by the deeper, covered carbonatic lagoon open up and is gradually oncoidal calcarenites representing an intermediate, bordering shallow bar dividing the inner from outer shelf. The outer shelf is featured by alternations of fine calcarenites, bioturbated calcilutites and marly limestones 2.2 Depositional environment of the Triassic succession of the Triassic 2.2 Depositional environment 2.2.1 Escalaplano Fm.: alluvial fans and mudflats alluvial fans with low relief (litofacies A). They are The Escalaplano Fm. begins with small, thin, short-lasting outlets located behind. built of scattered flood lobes deposited by streams flowing out from the valleys mild alluvial slopes tectonic activity, for the waning Alternatively, geological field trips 2016 - 8(1.1) excursion notes 21 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 10 – Transgressive evolution of evolution Fig. 10 – Transgressive facies of the yellow dolostones mb. facies of the yellow the carbonate ramp of Central Sardinia of Central the carbonate ramp during late Anisian to early Ladinian facies of the blue times. The outer ramp over gradually limestone member move facies – tidal flat the inner ramp-lagoon bioconstructions; absence of slope and high-energy deposits), the morphology of this carbonate shelf can be referred to an homoclinal (Figs 9, 10) (Costamagna & ramp Barca, 2002). Fig. 9 – Paleogeography of the carbonate ramp of Central- of the carbonate ramp Fig. 9 – Paleogeography facies. (mod. after Costamagna & Barca, 2002). The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe Southern Sardinia during early Ladinian times. The structural high of Southern Sardinia during early Ladinian times. The structural sea, will be Sardinia, entirely surrounded by the Triassic Central submerged during the maximum eustatic flooding of gradually shift of the outer ramp landward late Ladinian. Note the progressive DOI: 10.3301/GFT.2016.01 forming the blue limestones member. Here storm layers intercalate. Over those marly-calcareous alternations, the those marly-calcareous intercalate. Over Here storm layers forming the blue limestones member. by the coming back of blue limestones first, and later pinkish trend is marked renewing of the regressive and nodules of chert: this lithofacies forms the top succession. dolostones with algae, evaporites The orientation of the shelf in respect to eastern trade storms a prevailing 1988) makes & Tucker, winds (Calvet depositional mechanism. Besides, for the previously evidenced sedimentological features of the shelf (storm deposits abundance; lacking of lagoon-protecting geological field trips 2016 - 8(1.1) excursion notes 22 : this L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Costatoria goldfussi Busson, 1982) is marked in the Escalaplano area by a microfloristic assemblages found Busson, 1982) is marked sensu The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 bivalve is an index specimen of the late Ladinian in Catalonia (Sephardic Province of the Germanic Triassic is an index specimen of the late Ladinian in Catalonia (Sephardic Province bivalve close to the Sardinian area. very 1987; Hirsch, 1991), that at those times was Domain: Hirsch et al., terrigenous deposits at the base of this first In part of the Monte Maiore area, lacking prevalently the metamorphic Variscan thin lateritic deposits covering together with localized, cycle, depositional Mesozoic Sardinia basement (Damiani & Gandin, 1973b; Costamagna, 1998) suggest the complete flooding of central those times, perhaps, only the northeasternmost part sea at late Ladinian times. At by the carbonate Triassic area) emerged from the sea (Figs 11, 12). of the Island (Gallura On the whole, lower part of succession, comprised between continental Escalaplano Fm. and the middle part of upper member Monte Maiore fm. figuring out an outer ramp debuting in Sardinia megacycle, of the sedimentary Triassic event represents the transgressive environment, at late Anisian times and expressing during Ladinian its maximum flooding surface (Costamagna & Barca, is represented only by the topmost part of part of this megacycle Sardinia, the regressive 2002). In Central the blue limestones member of Monte Maiore fm. (Fig. 7). in the lower part of lithofacies 2 Escalaplano Fm. completed during the early late Ladinian, when Monte Maiore area, where The transgression flooded (Costamagna et al., basement, was direcly the Variscan carbonates cover 2000). Here calcareous dolostones and dolomitic limestones containing quartz angular pebbles represent the basal deposit of this first followed by limestones containing These deposits are rapidly sedimentary cycle. 2.3 First Mesozoic sedimentary cycle in Central Sardinia: some remarks in Central sedimentary cycle 2.3 First Mesozoic (Figs 6, 7): in fact, the Escalaplano Fm. and Monte Maiore fm. are partially coeval As mentioned above, basement of Central the peneplaned Variscan over transgression of the marine Triassic the rising branch the last to N towards Sardinia progresses gradually thinning the gradually highs and so covering Variscan is initially formed by this first sedimentary cycle deposits of the Escalaplano Fm. So, continental-transitional sediments, and then by marine carbonate deposits. The late Anisian sedimentary continental to transitional ( transgression geological field trips 2016 - 8(1.1) excursion notes 23 ======Aj 8) AM C B CPM B Ks PO SiB KRD KaP = Ebro = Central Ebr = Sardinia- = Lombardy; MC Exposed land; = Ebro Massif; = Burano; = Burano; L Margino-litoral to Margino-litoral 1) CSb = Australpine; = Australpine; L. G. Costamagna - S. Barca L. G. Costamagna - S. Ebr Terrigenous shallow Terrigenous 3) BuA = Sicilicum; = Meliata Zone; = Meliata Zone; = Budva Through; = Budva AuA = Australpine; = Australpine; Carbonate(?)-Evaporitic 6) en tectonics and sedimentation Si = Hallstatt Zone; = Hallstatt Zone; = Karst Platform; = Karst = Kabilia-Riff ridge; = Kabilia-Riff Bu Mel = Serbo-Pelagonian Massif. = Serbo-Pelagonian 4) = Drama; = Drama; = Sardinia. Slopes and deep basins; Aua Hst = Bosnia; KaP SP S KRD = Apennine Carbonate Platform; Marls and clayey carbonates. Marls and clayey Dr = Iberian Meseta; 7) Bo = Iberian Meseta; 9) = Apennine Carbonate Platform; ACP IM = Balaton; IM = Emma; ACP Bat = Calabria-Peloritain Massif; = Calabria-Peloritain Shallow shelves; Shallow shelves; = Meliata; = Hallstatt; = Armorican Massif; = Central Massif; = Central Fig. 12 – Late Norian paleogeography of Fig. 12 – Late Norian paleogeography 5) Sicanian Basin; Cpt Mel = Calabria-Peloritain Massif; = Calabria-Peloritain MC AM Brianconnais; Kirsheir; Pindos-Olonos Zone; Karst platform; Karst Corsica Massif; Western Tethys and Sardinia (mod. after Tethys Western Costamagna & Barca, 2002 and from Dercourt et 2000): al., Emm Hst Fluvio-lacustrine environments; Fluvio-lacustrine environments; Fig. 11 – Late Anisian paleogeographic setting of the Fig. 11 – Late Anisian paleogeographic Massif; Kabila-Riff Ridge; Kabila-Riff = Armorican Massif; Massif; Corsica; Brianconnais; = Alpujarride; 2) lacustrine environments; lacustrine environments; shelves; shelves and basins; shelves Shallow carbonates; Western Tethys and Sardinia. Legend: Tethys Western The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) excursion notes 24 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 13 - Stratigraphy and general Fig. 13 - Stratigraphy Costamagna et al., 2007). Costamagna et al., The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe framework of the Central-Eastern- framework (after Northeastern Sardinia Jurassic DOI: 10.3301/GFT.2016.01 Basing on several indirect leads found even at regional scale we suggest the first sedimentary Mesozoic cycle at regional scale we suggest the first sedimentary Mesozoic indirect leads found even Basing on several deposits, despite the fact they actually are to Early Jurassic Late Triassic Sardinia comprised even in Central not unconformably terrains continental deposits cover nowhere to be found: the well-dated Middle Jurassic – the erosion of Late Triassic than the Ladinian carbonates. So, younger deposits for the Early Jurassic Sardinia during these in Central developing to settle the environments extensional tectonics prevents Tethyan NW Sardinia: Cherchi & Schroeder, Sardinian areas (Nurra, similarly to the close Western times. Anyway, 1986; Sulcis, SW Sardinia: Costamagna, 2000; Costamagna & Barca, 2002), and by means of the reworked & Peybernés, in Southern Corsica (Durand-Delga pebbles sampled from the Eocene Chiappa conglomerates in almost all the at those times even 1986), a more or less restricted shallow carbonate shelf is hypotesizable eastern part of Sardinia. 3. Post-variscan geological evolution: Jurassic successions: regional 3.1. Jurassic and stratigraphy frame Eastern and Northeastern In Central, Sardinia the Middle-Late Jurassic down successions (Fig. 13) lay the Variscan unconformably over on more rarely, metamorphics, or, deposits, or Triassic the first cycle the older Permo-Carboniferous molassic deposits. geological field trips 2016 - 8(1.1) excursion notes 25 = TQ = Middle = Permian; J P L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation = Late Jurassic; = Late Jurassic; Js = Middle Triassic; = Middle Triassic; = Variscan basement; = Variscan Fig. 14 – Location of the tectonic Tertiary and Quaternary Tertiary Jurassic; Jurassic; TR Barbagia paleohigh in Central Sardinia. Barbagia paleohigh in Central PZ of the Variscan basement itself of the Variscan were dismantled. Otherwise, in the SW marginal, sloping parts of the paleohigh still the Middle Triassic Nurri, remained (Laconi, Nurallao, Escalaplano). Those mentioned localities are posed along a NW/SE belt possibly corresponding to a main extensional discontinuity main reviving a former Variscan thrust. The erosion and the the over pedogenesis developed Variscan surface of the discovered part of the basement in the central Barbagia paleohigh are evidenced The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Thus, these sediments cover usually a variously eroded, older substratum. In the Tacchi area the depth In the Tacchi eroded, older substratum. usually a variously Thus, these sediments cover reached by the erosion in different sectors is related to their location respect paleorelief (tectonic SardiniaBarbagia paleohigh) rised in Central (Figs 14, 15) (Costamagna & Barca, 2004; Costamagna et al., created by extensional tectonics connected with the opening of 2007). This articulated landscape was 1986). The more the areas were Bernoulli & Jenkyns, 1974; Abbate et al., Jurassic, (Early-Middle Alpine Tethys Esterzili, part of the paleohigh (Perdasdefogu, in the central uplifted, the deeper dug up erosion: so, and successions, most of the remaining part Permian and Triassic Ussassai, Seui) the Lower Jurassic 2000), and often also sectors erosional cyles (Cassinis et al., left by the former coeval Carboniferous covers geological field trips 2016 - 8(1.1) excursion notes 26 1) Genna Selole fm.: Dorgali fm. (mod. L. G. Costamagna - S. Barca L. G. Costamagna - S. “Lateritic paleosoils”; 5) 6) 2) en tectonics and sedimentation Genna Selole fm.: Nurri- 4) Genna Selole fm.: Laconi-Gadoni Fig. 15 - Sketch of the setting Fig. 15 - Sketch after Costamagna & Barca, 2004). Ussassai-Perdasdefogu lithofacies (a: NW Ussassai-Perdasdefogu facies: b: NE facies); Jurassic deposits in the Tacchi area. deposits in the Tacchi Jurassic basement; Variscan 3) lithofacies; Escalaplano lithofacies; by lateritic deposits (accumulated as fillings: “Ferro small lenses and vein Marini, 1984) located dei Tacchi”, The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 along the angular unconformity between the Middle Jurassic sediments and the Variscan basement. Those Fe sediments and the Variscan along the angular unconformity between Middle Jurassic stabilized Aalenian-Bajocian (Middle Jurassic) of the short-lasting deposits are the most significant marker on the paleohigh. peneplain developed Eastern and Northeastern Sardinia area initially rises the Central, during the early Middle Jurassic generally So, as an archipelago formed by the exposed juts of paleohigh: erosion wiped off almost entirely Permian drowned by rapidly basement. Still this archipelago was the Variscan deposits and discovered to Lower Jurassic Sardinia) in Central The slopes of the larger islands (located prevalently the extensional tectonics movements. by at most some tens of metres siliclastic deposits (Genna Selole fm.) deriving from the were first covered flooding of the paleohigh following the gradual Afterwards, erosion of the exposed parts paleohigh itself. of the terrigenous input, lagoonal to marginal carbonate sedimentation progressed (Dorgali and the vanishing at the end last emerged spots. In this latter case carbonate deposits and Genna Silana fms), covering basement, the Variscan rest directly over sediments. remains of Permo-Carboniferous over rarely, or, Sardinia are described in of Central-Eastern evolution paleogeographic Analogies with the Triassic-Jurassic 1973; Costamagna, 2013) 1981), in the Brianconnais Domain s.s. (Bourbon et al., & Rieuf, Corsica (Beauvais and the Ligurian-Brianconnais Domain (Lualdi, 1994; 2005). Those areas show interesting similarities: in and directed belt interested by the same tectonic evolution they formed a paleogeographic Tethys Western edge (Fig. 16), so forming a well-defined regional domain. along the North-Tethyan WSW-ENE geological field trips 2016 - 8(1.1) excursion notes 27 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation = H Nurra, Genna 1) 3) = Choc thrust. Cc S’Adde fm. Area, extra- S’Adde “Prepiemontese” Zone: 4) 8) = Licicum; Dorgali fm. area, extra-Alpine Lm 2) Possible feeding area of the carbonate Possible Balagne thrust: radiolarites area, extra- Balagne thrust: radiolarites 5) 9) Autochton: peritidal dolostones area, extra- Hypothesized Margin – Outer Shelf area, not Hypothesized 6) 7) = Krizna thrust; Kz Laconi-Gadoni conglomeratic-arenaceous lithofacies; Laconi-Gadoni conglomeratic-arenaceous lithofacies; Nurri-Escalaplano siltitic-arenaceous-clayey-lignitiferous Ussassai – lithofacies. siliciclastic-carbonatic mixed Perdasdefogu Fig. 16 - Paleogeographic reconstruction of the Sardinia- Fig. 16 - Paleogeographic The arrow shows the hypothesized shift of the coastline. The arrow shows the hypothesized The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe Corsica Tethyan margin during Callovian (Middle Jurassic) (mod. (Middle Jurassic) margin during Callovian Corsica Tethyan 2007). Legend: Sardinia: after Costamagna et al., Sardinia-Provence Domain; Sardinia-Provence Domain; Silana fm. Area, extra-Alpine Domain (according to Durand Delga & Peybernés); Delga & Peybernés); Domain (according to Durand Alpine Domain. Corsica: Sardinia- pebbles contained in the Eocene Chiappa Conglomerates, Domain; Provence Alpine Domain; outcropping, extra-Alpine Domain; outcropping, extra-Alpine Francardo breccias, nodular limestones and area, Francardo Domain; extra-Alpine Alpine Domain (according to Durand Delga & Peybernés). Delga & Peybernés). Alpine Domain (according to Durand Hochstegen; DOI: 10.3301/GFT.2016.01 3.1.1. Genna Selole fm. (Middle Jurassic: Bajocian - Bathonian) between 0 to 78 m. (Fig. 17). The thickest 1983) ranges area the Genna Selole fm. (Dieni et al., In the Tacchi Liana, in the northwestern sector. section has been measured at Perda stratigraphic The Genna Selole fm. is along a circular belt surrounding the tectonic Barbagia paleohigh. The Genna Selole fm. has been thicker subdivided into three lithofacies (Costamagna & Barca, 2004; Costamagna, 2015) (Fig.18), from the bottom: 1) 2) 3) sections stratigraphic investigated Sometimes the described lithofacies do not crop out together in diverse thickness, are frequently heteropical and reasons. Besides, they show extremely variable for paleogeographic Besides, in some localities alternations of the Laconi- locality. not simultaneously be present in every they may been noticed. Gadoni and Nurri-Escalaplano lithofacies have geological field trips 2016 - 8(1.1) excursion notes 28 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Nurri-Escalaplano lithofacies; C) ) Laconi-Gadoni lithofacies; B total thickness; A) Ussassai-Perdasdefogu lithofacies (after Costamagna & Barca, 2004). Ussassai-Perdasdefogu D) Fig. 17 - Genna Selole fm. isopachs The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) excursion notes 29 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 18 – Stratigraphy of the Genna Selole fm. in Tacchi Fig. 18 – Stratigraphy area (modified of the Tacchi stratigraphy Fig. 19 – Jurassic after Costamagna & Barca, 2004). (mod. after Costamagna & Barca, 2004). The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe area and relationships with the Permian and Triassic deposits and Triassic area and relationships with the Permian DOI: 10.3301/GFT.2016.01 The transgressed Variscan basement can be strongly Variscan The transgressed altered and weathered for the subaerial processes (Fig. 19). In occurred during the early Middle Jurassic fact, the alternations of erosion, biostasy and resistasy of more or less processes triggered the development surfaces. complete lateritic paleosoils or calicitized geological field trips 2016 - 8(1.1) excursion notes 30 ) can be found. L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Williamsonia The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Upwards, this lithofacies passes gradually either to the other Genna Selole lithofacies, or directly, with the either to the other Genna Selole lithofacies, or directly, this lithofacies passes gradually Upwards, increase of the carbonate matrix, to dolostones Dorgali fm. Nurri-Escalaplano lithofacies area investigated part of the Tacchi The Nurri-Escalaplano lithofacies is from 0 to 12 m thick. In the central coarser intercalation basement without any the Variscan rest unconformably directly over this lithofacies may and siltites, lignitiferous clays in-between. This lithofacies is built of alternations siltites, clayey The to thinly laminated, blackish whitish in colour. to fine sandstones, from well-stratified medium-grained be lens-shaped and cross-bedded, with evident epsilon-cross bedding. In the finer lithologies, sandstones may Load casts are present. Bioturbation is scattered. Besides, fossil wood lamination can be observed. convolute casts. In the blackish and branch as plants rests, formed by leaves can be found in the lignitiferous clays, lithologies the pyrite is often present, as well scatterd gypsum crystals. The macro- and microfloristic age (Del Rio, assemblages found in this lithofacies suggest a Bajocian to Bajocian-Bathonian (Middle Jurassic) 1976; 1984; Dieni et al., pass directly upwards area this lithofacies may part of the Tacchi 1983). In the central to the carbonate Dorgali fm. Laconi-Gadoni lithofacies to moderately The Laconi-Gadoni lithofacies, from 0 to 35 m thick, is built of usually mature, clast-supported, to quartzose-feldspatic containing lenses of quartzose well-sorted, monomictic to oligomictic conglomerates thus passing in the end to to fine sandstones. This lithofacies tends upwards, medium-grained a maximum lenses. The pebbles, angular to subrounded in shape, have conglomeratic sandstones with rare siltites and lignitiferous dark in and sheets of siltites, clayey of 15-20 cm. Still, scattered pockets size be be intercalated between coarser deposits or alternatively may colour with occasional wood fragments basement surface.disposed along limited shallow scours and lows the lower Variscan The pebbles of the are usually formed by quartz, but in limited areas the presence of metamorphics and late- conglomerates be also deposits may and Triassic dominant. Locally pebbles of Permian be even clasts may porphyds Variscan and tabular or through cross- Crude, parallel is usually sandy. present. The matrix of the conglomerates surfaces. Imbrications are bedding and erosive laminations, graded bedding are diffuse, as well convolute by a reddish lateritic crust. In some episodes is marked scattered. Sometimes the top of conglomeratic specimens (es. well-preserved macroflora whitish sandstone beds rare fine-sized, geological field trips 2016 - 8(1.1) excursion notes 31 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation (1989), in the grouping of , 1983; Dieni & Massari, 1986), . . (2013) question the pertinence of Ussassai – lithofacies to the Genna Selole fm.: Perdasdefogu . . (1983), the paleontological content allows attribution of this lithofacies to Bathonian. Close The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Ussassai-Perdasdefogu lithofacies area: mainly in the northern sector of Tacchi from 1 to about 35 m, and develops This lithofacies ranges thin (Fig.18). This lithofacies shows significant changes depending be very instead, in the other sectors it may from its location. In the NW area it is thinner (6 m at most) and formed by marly dolostones containing the lithofacies is higly scattered cm-thick siltitic and fine sandy terrigenous beds. Otherwise, in the NE sector, and thick (until 20 m): it is formed by alternations of limestones, dolomitic marls plant- variable cm-sized siliciclastics sometimes lens-shaped. Close to the passage Dorgali fm., rich, fine to medium-sized beds of black siltites with scattered plants rests are diffuse. The passage to the Dorgali fm. occurred of the terrigenous inputs in carbonate sediments. The carbonates this lithofacies are complete vanishing algae oogons; in the upper part characean ostracods, brachiopods, frequently fossiliferous (gastropods, bivalves, form dm- and sponge spicules still appear) cross-bedded: the fossiliferous beds may crinoids, foraminifers, as well fine and flaser bedding has been observed, wavy, thick coquinas due to the winnowing. Lenticular, intercalations of siliciclastic sediment between the carbonatic small-scale lens-shaped bodies. According to Dieni et al often level, been found. Besides, at this stratigraphic scattered little microbialitic mounds have upper boundary, crusts and early karstic firm- and hard ground surfaces partially bioturbated and/or bioeroded, thin oxidized blackish first by siltitic-clay the carbonates, presently covered over levels at several phenomena develops regressive sediments, and later sharply by carbonate deposit again. These data evidence limited short-lasting (Costamagna et al., trasgression Middle Jurassic during the evolving events 2007). Dieni et al for the lithological prevalence of carbonate deposits, they consider it a lower member the Dorgali fm. and for the lithological prevalence think that, disagree with this attribution made on a lithological basis. We We Liana mb. called it Perda criteria expressed by Bosellini et al according to the stratigraphic-depositional stratigraphic units the paleoenvironmental meaning of the lithofacies is significant as lithological features, units the paleoenvironmental stratigraphic as it will be explained better below. Dieni et al In addition to the Dispensa Selole type section (Baunei, Ogliastra: now almost totally buried by landslides and canceled road works, two further supporting parastratotypes will been proposed (Costamagna & Barca, 2004): one of them (Perdasdefogu) area have located in the Tacchi be showed during the field trip (Stop 7). geological field trips 2016 - 8(1.1) excursion notes 32 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Synsedimentary tectonics in the Genna Selole fm. all in the Genna Selole fm.: they are neptunian dykes, Evidences of synsedimentary tectonics can be observed brecciated sediments and rare laminations in the varved synsedimentary faults, slumps. Diffuse, thin convolute suggest that early deformations could be related to seismic shocks. Field observations carbonate layers be due to a sudden dump of the coarse bedload occurred before the lithification of sediment: they may slowing down of intense floods. The described features are related to the extensional tectonics during the rapid opening. connected with the Alpine Tethys 3.1.2. Dorgali fm. (Middle – Late Jurassic: Bathonian-Kimmeridgian) 1960; Dieni & Massari, 1986; Costamagna Barca, 2004; The carbonatic Dorgali fm. (Amadesi et al., Costamagna et al., area, reaching 250 m in its NE unit of the Tacchi Jurassic 2007) (Fig. 19) is the thickest sharply to the calcareous deposits of Genna Silana fm. (Costamagna et al., Here it passes upwards sector. of all the terrigenous input: this by the complete vanishing 2007). The base of the Dorgali fm. is marked The event. emersion, regressive continental influence and of any of any indicate clearly the disappearance (Dieni et al.,start of the Dorgali fm. is referred to Bathonian (Middle Jurassic) 1983). From that time on, became entirely marine with no turning back. the environment area the Dorgali fm.In the Tacchi fossils are present dolostones. Several to well-stratified is formed by massive totally the echinoderms). Usually the strong dolomitization processes erased corals, brachiopods, (bivalves, for original textures of the carbonate deposits: only few outcrops whose structures were valuable area a type section of the Dorgali fm. has in the Tacchi been found. So, have sedimentological investigations and lyditic basement, quartzose the Variscan When the Dorgali fm. rests directly over not established yet. are scattered in the lower carbonate beds. angular to subangular pebbles and quartz grains been evidenced. The main lithofacies association is represented by lithofacies have In the Dorgali fm. several calcarenites and bioturbated dolomitized to cross-laminated dolomitized irregular alternations of parallel- coarse lag formed by bioclasts, have an erosive calcilutites. The laminated calcarenites, locally resting over In the structure occur. Here and there microbial mats locally containing fenestral been related to storm layers. rip–up clasts, bioturbations, winnowed beds. In several structures can be observed: carbonate mud several of the Dorgali levels of polygenic carbonate breccias posed at different stratigraphic outcrops, metric horizons been found. fm. have geological field trips 2016 - 8(1.1) excursion notes 33 : these latter L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Ellipsactinia (Middle-Late Jurassic) The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 3.1.3. Genna Silana fm. In the Tacchi area the calcareous Genna Silana fm. (Costamagna et al.,In the Tacchi 2007) (Fig. 19) occurs only on the top of area Tacchi of the easternmost carbonate outcrops: it corresponds to top Jurassic the highest relieves abruptly the Dorgali fm. Nonetheless, it reaches its maximum thickness (150 m) northward, succession. It covers area of Eastern Sardinia: here is located its type section. In the NE sector Tacchi in the Baunei Supramonte 30 m and is arranged exceeds area the Genna Silana fm. succession never discontinuous belt running in a narrow, calcarenites, containing NW/SE (Fig. 14). The unit is here formed by cross-laminated oolitic to oolitic-bioclastic spongiomorph bivalves, bioclasts of corals, the unit includes bioclasts and green algae. Subordinately, hydrozoans specimens of and echinoid spines, together with rare of crinoids, gastropods, foraminifers allow to refer the age of the Genna Silana fm. in the Tacchi area to the Late Jurassic (Oxfordian). area to the Late Jurassic allow to refer the age of Genna Silana fm. in Tacchi base and formed by polygenic angular intraclasts with erosive Here and there, scattered carbonate layers been found. embedded in a muddy matrix have succession is formed by oncoidal floatstone beds made of cm- Jurassic The top of the unit and Tacchi around bioclastic nuclei. matrix. The oncoids start to develop oncoids embedded into a muddy-sandy sized 3.1.4. Definition of the Baunei group (Middle - Upper Jurassic: Bajocian – Kimmeridgian) area pertain to a carbonate shelf related the wider Central- units of the Tacchi stratigraphic The Jurassic Only in Eastern-Northeastern Sardinia carbonate environment. Eastern-Northeastern Sardinia Jurassic to the S’Adde and Baronie area: Fig. 3), those units partially are capped by coeval (Supramonte fm. (Dieni & Massari, 1986), figuring out an outer shelf – of the evolution that is the natural slope environment Middle –transgressive sequence. Upper Jurassic been All these formational units pertaining to this sequence have 2007). The Baunei group (Fig. 13), Bathonian to united to form the Baunei group (Costamagna et al., in age, is terminated at the top by Tithonian –Kimmeridgian (Middle - Upper Jurassic) Berriasian and to a sea level boundary), related to a sharp fall of the relative unconformity (Jurassic-Cretaceous of the Sardinian sector of the marine facies. The Baunei group represents subsiding evolution retrogradation meaning and strict for its features, paleogeographic margin. The Genna Selole fm., of the Alpine Northern Tethys connection with the Bajocian – can be included as base of the Baunei group. Kimmeridgian sedimentary cycle, from the upper carbonate the Genna Selole fm. depositional cycle Jadoul et al. (2010) propose to separate the authors infer this from units, suggesting these latter pertain to an independent sedimentary cycle: lithofacies. According to them, those presence of diffuse emersion evidences in the Ussassai-Perdasdefogu geological field trips 2016 - 8(1.1) excursion notes 34 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation alluvial fan and braided high: here, side by side, stream environments slopes of the tectonic system placed along the continental depositional represents a narrow passing rapidly to an passing rapidly drowning. Thus the unit alluvial-palustrine-littoral belt containing isolated brackish ponds, and perhaps brackish limited delta bodies are developed (Figs. 20, 21). The developed fans were placed at the outlet of the valleys, while the of the valleys, high and ending with its final with the rise of Barbagia tectonic extensional tectonics context, starting sedimentary response to an active Fig. 20 – The Genna Selole fm. was the The Genna Selole fm. was alluvial to deltaic (?) system 3.2.1. Baunei group, Genna Selole fm.: Isopachs of the terrigenous Laconi-Gadfoni and Nurri-Escalaplano lithofacies of the Genna Selole fm. in Tacchi area: they evidence the relief of tectonic Barbagia paleohigh. 3.2 Depositional environment of the Jurassic units of the Jurassic 3.2 Depositional environment The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 emersions could encompass significant stratigraphic gaps during Callovian times, so representing minor gaps during Callovian emersions could encompass significant stratigraphic simply as cycles irregular small regressive we consider these upper, Conversely, depositional cycles. due to the drowning of consequence of a diffuse microtectonic activity during the marine transgression tectonic Barbagia paleohigh, and not really related to the Middle – sedimentary main cycle. Upper Jurassic geological field trips 2016 - 8(1.1) excursion notes 35 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 21 – Paleogeographic sketch of the sketch Fig. 21 – Paleogeographic Selole fm. (mod. after Costamagna, 2013). alluvial to transitional environments of the Genna environments alluvial to transitional belt was posed along all the coastline: its width was limited in respect to the alluvial fans. posed along all the coastline: its width was belt was The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 alluvial-palustrine-littoral Sometimes the coarse fan / braided stream deposits passed quite sharply to marine carbonate deposits: that Sometimes the coarse fan / braided deltas (McPherson et al., of braid the development possibly, presence of little fan deltas, or, suggest the localized and the thicknesses of Genna Selole fm. are the depositional mechanisms, environments 1987). So, basement, at that time of the Variscan and by the arrangement by the local paleogeography constrained leading to the opening of Alpine-Tethys. by the Alpine extensional movements tectonically reactivated channels deposited in humid alluvial fan crossed by braided Thus, in detail, the Laconi-Gadoni lithofacies was deltas. The at their back and close to the coast: probably sometimes fan deltas passed braid with relieves from each are longitudinal bars separated events conglomeratic flood episodes. The surfaces due to diverse other by erosive discontinuous, lens-shaped sandstone intercalations located at sequences are related to sandy the top of conglomeratic deposition in minor channels crossing the bar surface during and clayey-silty floods. The limited scattered dark clayey waning to the settling of fine sediment and accumulations is linked organic matter in little, protected side areas piling of vegetable of abandoned channels: perhaps those areas were comparable lakes. to oxbow deposited into a low The Nurri-Escalaplano lithofacies was (Fig. 21). This energy alluvial-palustrine-lacustrine environment crossed by migrating, was alluvial plain, often waterlogged, by sandy meandering sandy channels sometimes overtopped tropical climate by hot-humid, and colonized splays, crevasse 1976; 1984). With the smoothing of (Del Rio, vegetation this lithofacies started to and the rise of sea level, relieves the Laconi-Gadoni litofacies, following be deposited over high. A limited tidal the structural trend over transgressive influence is supposed at the outer rim of this lithofacies. geological field trips 2016 - 8(1.1) excursion notes 36 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 The Ussassai – lithofacies represents the passage to Dorgali fm. This facies is well developed Perdasdefogu area. In the NW sector it figures out a littoral-interdeltaic- mainly in the northern sectors of Tacchi environment: from the coast, carbonate sediments grew up until they dominated. Otherwise, away moving with limited environments the closeness of fluvial outlets, and consequently deltaic-lagoonal in the NE sector, figured by protected lagoons and interdistributary bays, saline marshes can be supposed. In this environment, carbonate muds settled. Tidal influence is clearly evident, as well sinsedimentary tectonics. before, Dieni et al. (2013) refer the Genna Selole fm. upper lithofacies as a lower member of As sketched pertains to an already well-established Dorgali fm. instead, claiming the member depositional environment disagree on this assumption because the and so more similar to the Dorgali fm. We marine environment, and microsequences driving to karst development lithofacies contain diffuse regressive Ussassai-Perdasdefogu deposition of dark, pyrite- and organich-rich intercalations with plant remains suggesting the persisting the unit more similar to continental - transitional this make onset of palustrine environments: ephemeral Genna Selole fm. than to the marine Dorgali 3.2.2 Baunei group, Dorgali fm.: tidal flat and inner ramp lagoon energy inner shelf lagoon and variable The Dorgali fm. is a monotonous unit (Fig. 22) that posed in shallow, locally showing the typical three- is featured mainly by alternations of bioturbated muds and storm layers Still are represent sectors of synsedimentary tectonic activity. may folded sequence. Brecciated layers and tepee structures, as bindstones containing mud cracks scatteredly present tidal flat areas with fenestral well as oncoidal restricted ponds and little oolitic bars. 3.2.3 Baunei group, Genna Silana fm.: oolitic margin with patch-reefs The lithologies of the Genna Silana fm. represent carbonate shelf margin, featured by high-energy patch reefs (Fig. 22). embedding scattered little coral conditions and built of oolitic bars (oolitic grainstones) episodical oncoidal facies embedded into an abundant micritic matrix (oncoidal floatstones) The upper, the optimum depth of patch suggests the beginning of a slightly deeper sedimentation, probably just over reefs development. geological field trips 2016 - 8(1.1) excursion notes 37 : SAF L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : Genna Silana fm.; : Laconi-Gadoni lithofacies; 1° intermediate stratigraphic gap intermediate stratigraphic GSLF G2: : Tithonian. Tit : Dorgali fm.; DF : Genna Selole fm. ( GSF : Kimmeridgian; Kim : upper stratigraphic gap (eustatic fall: type 2 discontinuity after Bosellini, : upper stratigraphic G3 : Oxfordian; : lower stratigraphic gap (shelf drowning); : lower stratigraphic Oxf G1 : Ussassai-Perdasdefogu lithofacies); : Ussassai-Perdasdefogu 3° : Bathonian; Bat : Monte Bardia fm.. MBF : Bajocian; Baj : Nurri-Escalaplano lithofacies; Fig. 22 – Schematic stratigraphic-sequential evolution of the Jurassic ramp of Central-Eastern-Northeastern Sardinia (after of Central-Eastern-Northeastern ramp of the Jurassic evolution Fig. 22 – Schematic stratigraphic-sequential 1991); The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe Costamagna et al., 2007 - scale and distance only indicative). Legend: 2007 - scale and distance only indicative). Costamagna et al., 2° S’Adde fm.; S’Adde point of the depositional system); (inversion DOI: 10.3301/GFT.2016.01 3.2.4. Paleogeographic and geodynamic meaning of the Baunei group thickness and Sardinia Baunei group is formed by an alluvial system of variable The Central-Eastern-Northeastern (Fig. homoclinal carbonate ramp to regressive and by a transgressive morphology, width according to the blanketed margin. The Baunei group drowning of the Northern Tethyan 22): both are related to the opening and gradual geological field trips 2016 - 8(1.1) excursion notes 38 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation = Ussassai – Perdasdefogu; U-P = Laconi-Gadoni; L-G = Nurri–Escalaplano; = area. = lithofacies; Fig. 23 - Paleogeographic sketch of the sketch alluvial system and the carbonate ramp of Central-Eastern- Northeastern Sardinia during Bathonian times (mod. after Costamagna et al., 2007): Costamagna et al., LT N-E AR The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 represents a Bajocian-Kimmeridgian transgressive- part transgressive Only the lower, cycle. regressive area is visible in the Tacchi of this cycle (LST and TST) part 2007): the upper regressive (Costamagna et al., (HST) can be seen just in Eastern and Northeastern area the Baunei group Sardinia (Fig. 23). In the Tacchi is formed by the Genna Selole fm. (from alluvial stream to deltaic system/tidal flat?) fan/braided the Dorgali fm. (tidal flat and open shelf (LST/TST), and the (TST), environments) lagoon: inner ramp The carbonate Genna Silana fm. (shelf margin) (TST). shelf of Central-Eastern-Northeastern Jurassic this is suggested configuration: Sardinia had a ramp by the significant amount of storm deposits into thickness and extent of lagoon, the scarce continuity, the bioconstructions, lacking of well-developed slope facies suggesting the absence of a strongly inclined slope. conclusions sedimentary cycle, succession: second Mesozoic 3.3. The Jurassic (Fig. 24), possibly during Due to the strong extensional tectonics leading opening of Alpine Tethys Central Sardinia area emerges: in particular, Aalenian-Early Bathonian (?) the whole Central-Eastern-Northeastern Sardinia area turned to be the wider emerged part of horst (tectonic Barbagia paleohigh) all. The entire Sardinia area perhaps resembled an archipelago disposed along the Northern margin Central-Eastern-Northeastern deposits are completely eroded, as well part of the Jurassic (Fig. 25). Here the Triassic-lowermost of the Tethys metamorphic basement too. molassic sediments and the Variscan Permo-Carboniferous Post-Variscan it starts to be buried just during the Bajocian-Bathonian, when Baunei Still the emerged horst is short-lasting: 2007). First, on the horst sides, Costamagna et al., group deposits begins to accumulate (Middle-Late Jurassic, place: they are feeded by the erosion of siliciclastic deposits (Genna Selole fm.) taken continental to transitional geological field trips 2016 - 8(1.1) excursion notes 39 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 24 – Regional and paleogeographic framing and paleogeographic Fig. 24 – Regional al., 2000). al., of Sardinia during the Middle Callovian: the star of Sardinia during the Middle Callovian: marks the field trip area. (modified after Dercourt et horst itself. Due to the gradual subsidence of the Due to the gradual horst itself. horst, correlated to the spreading Tethyan margin collapse and the eustatic rise, by deposits are covered continental-transitional marine carbonate shelf sediments (tidal flat, lagoon and margin: Dorgali Genna Silana area those formational units fms). In the Tacchi (Fig. 23) and system tract form the trasgressive the lower part of Bajocian-Kimmeridgian The complete marine tectono-sedimentary cycle. crops out in the of this cycle development Eastern-Northeastern Sardinia (NE Ogliastra, Baronie): here the marginal Genna Supramonte, figuring fm., by the S’Adde Silana fm. is covered out mild slopes and possibly shallow basin environments. setting, the Central In this paleogeographic more Sardinia area represents the inner, protected sector of the continental shelf and an important part of the SW margin Alpine Tethys. The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 40 Fig. 25 – field trip in Itinerary of the L. G. Costamagna - S. Barca L. G. Costamagna - S. Central Sardinia. en tectonics and sedimentation The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 41 . L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Luca G. Costamagna Day 1 - From Cagliari to Jerzu (OG). The Formation is validated by the Italian Commission on Stratigraphy (Delfrati, 2006b) (Delfrati, by the Italian Commission on Stratigraphy is validated The Formation The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 After overtaking the Mulargia Lake artificial basin, about 4 km SW to Orroli, the Mesozoic succession crops artificial basin, about 4 km SW to Orroli, the Mesozoic the Mulargia Lake After overtaking (Stop 1), Bruncu Geroni 2) and Piccheri 3). Along out along some road cuts at Bruncu Su Para stratigraphic a short distance (about 1.5 km), from Stop 1 to 3 (Figs 26, 27), the post-Variscan gaps located differently according to the stratigraphic significantly and shows several succession varies times. This in several location (Fig. 28). This is a plain indication of repeatedly tectonically disturbed zone erosional windows metamorphic rocks outcropping in rare assumption is further confirmed by the Variscan Just leaving the calcareous Late miocenic hills of Cagliari, itinerary proceeds along National Road 131 Carlo Felice headed to NNW and following the eastern rim of Plio-Quaternary Campidano graben (Fig. 25). Up to the km 20 of Cagliari-Sassari SS131 motorway, first Early-Middle Miocene carbonate-terrigenous deposits are crossed, and later, andesites pertaining to the calc-alkaline Oligo-Miocene volcanic cycle and sandstones/siltstones of the Eocene-Oligocene Cixerri fm. On our left is Plio-Quaternary NW/SE trending Campidano graben plain, resulting from the recent extensional tectonics leading to Southern Tyrrhenian sea opening and filled by the Pliocene Samassi fm. Quaternary alluvial deposits. Conversely, Oligo- Miocene sediments and volcanics (Pecorini & Pomesano Cherchi, 1969) fill the main, older N-S Sardinian rift crossing all the island. This former rift is related with opening of Algero-Provençal basin representing the back-arc basin of Apennine Orogeny. At the km 20 of 131 motorway, we leave Cagliari-Sassari motorway and take SS 128 road “Centrale sarda” leading to the Central Sardinia area, crossing towns of Senorbi and Suelli: here along road still Tertiary siliciclastic to carbonate deposits crop out. From Suelli, a secondary road the northeast take us Siurgus Donigala town. After we pass this last town leave behind the Tertiary sedimentary deposits of Sardinian Rift and we enter in the Variscan basement outcrop area. This area is here featured by low-grade metamorphics as phyllites, schists and rare marbles: the inferred age of their protolith is Cambrian to Carboniferous. The Variscan metamorphic rocks are here and there covered by Permian molassic, limic to red bed deposits of the Rio Su Luda Fm. geological field trips 2016 - 8(1.1) itinerary 42 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation = stay overnight. = stay Bed = Jurassic; = Jurassic; J = Triassic; = Triassic; TR Fig. 26 – Geological Map of the Tacchi area, itinerary of the field trip and location Stops; area, itinerary Fig. 26 – Geological Map of the Tacchi The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 43 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 28 - Permian, Mesozoic and Tertiary sedimentary cycles in the Gerrei – sedimentary cycles and Tertiary Mesozoic Fig. 28 - Permian, Ogliastra area and their relationships with the Variscan basement. area and their relationships with the Variscan Ogliastra underneath the post-Variscan cover. In fact they belong to several cover. underneath the post-Variscan superimposed tectonic units and pertain to the western part of 1992, 1994), a strongly “Flumendosa antiform” (Carmignani et al., structure. deformed Variscan outcrops located between the Sarcidano and The Triassic Sardinia (Fig. 25) (Costamagna et al., Northern Gerrei in Central 2000; Costamagna & Barca, 2002) form a short siliciclastic to succession whose thickness grows evaporites) carbonate (with rare up from NW to SE, being comprised between 2 and 35 – 40 m. They crop out along a narrow belt 40 Km long, oriented NW/SE and posed between the Laconi and Escalaplano villages. : (2) RLF : debris : Variscan QT VB : Escalaplano : Ussana fm. EF : Monte Maiore : Genna Selole fm. USF , Bruncu Geroni MMF : Monte Cardiga fm. (1) GSF MCF = Fault. areas. Legend; F (3) Fig. 27 - Stop 1, 2, 3: Geological sketch (Quaternary); The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe and Piccheri Rio Su Luda Fm. (Permian); Rio Su Luda Fm. (Permian); Basement (Cambrian-Carboniferous); of the Bruncu Su Para of the Bruncu Su Para Fm. (Middle Triassic); Fm. (Middle Triassic); fm. (Middle Triassic); (Middle Jurassic); Eocene); (Early-Middle (Late Oligocene – Early Miocene); DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 44 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 The Triassic succession rests unconformably over the Variscan metamorphics, and in its turn is covered by metamorphics, and in its turn is covered the Variscan succession rests unconformably over The Triassic Eocene or Miocene age. The complex relationships between all those sedimentary deposits of Jurassic, younger age (Barca & Costamagna, 1999). The main of variable superposed erosional cycles suggest several cycles carbonates that probably came the Triassic over are the intense pedogenetic alteration effects of these cycles carbonates may some of the dolomitization processes Triassic to be frequently exposed surfaces. Even be related with the same events. STOP 1 - Bruncu su Para (Orroli): general features of the Escalaplano Fm. and Monte Maiore fm. (Middle Triassic) attitude and rests succession shows an almost horizontal In this road-cut the Gerrei Middle Triassic tectonic of the Meana Sardo Variscan the metavolcanics unconformably over Vittoria fm., unit (Monte S. red bed remain (Rio Su Luda Fm., a thin Permian over 1992, 1994) and, locally, Carmignani et al., Ordovician: 2001). Here the Escalaplano Fm. (late Anisian–early Ladinian) siliciclastics of Sardinian Carmignani et al., to the well-bedded carbonates of Buntsandstein group passes sharply upwards dolostones member yellow to the Sardinian Muschelkalk group (Fig. 29 A). of the Monte Maiore fm. (Ladinian), referable Bruncu su Para succession succession (Fig. 30) is exposed along two road cuts: on the right, it rests Bruncu Su Para The Middle Triassic (Fig. 29 B), and, cycle schists pertaning to the Variscan red to dark brownish metavolcanic unconformably over calcrete nodules red arenaceous siltites and containing yellowish thickly stratified Permian over locally, basement. the Variscan in their turn laid down over and layers, Escalaplano Fm. starts with a thin 20 cm thick bed of polygenic (quartz, metamorphics) The Middle Triassic reddish to greenish to poorly stratified breccias, followed by massive conglomeratic clast-supported marly thin, irregular beds of yellowish argillaceous siltites and containing scattered cm-sized The argillaceous siltites may now calcitized. sandstones / sandy marls previously containing former evaporites, Often the lower surface of marly/sandy beds shows halite casts (Fig.contain mud cracks. 29 C) due to the crystals. The Escalaplano Fm. is here 8.5 m thick. On the left road cut early dissolution of evaporitic but sharply with the sudden growth of carbonate content (Fig. 29 A) to Escalaplano Fm. passes gradually marly dolostones member of the Monte Maiore fm. This unit begins with yellowish the dolostones of yellow geological field trips 2016 - 8(1.1) itinerary 45 L. G. Costamagna - S. Barca L. G. Costamagna - S. : Monte Maiore fm. en tectonics and sedimentation MMF = Escalaplano Fm.; ) halite cast at the bottom of a sandy bed in EF C ) Collapse breccias in the yellow dolostones mb of the Monte Maiore fm. ) Collapse breccias in the yellow D ) Overview of the intermediate part of the Bruncu Su Para section. of the intermediate part Bruncu Su Para ) Overview A Fig. 29 - ) Unconformity of the Escalaplano Fm. (EF) over the Variscan basement (VB). the Variscan ) Unconformity of the Escalaplano Fm. (EF) over lithofacies 2 of the Escalaplano Fm.; The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe B DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 46 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : here the continental to transitional mudflat : here the continental to transitional Orroli road, the next stop is about 500 m ahead. Keeping going on along the Siurgus-Donigala – of the Middle Triassic Monte Maiore fm. of the Middle Triassic STOP 2 - Bruncu Geroni (Orroli): algae in the pass upwards to the restricted carbonate shelf ouctrops pass upwards deposits of the Middle Triassic Escalaplano Fm. sharply deposits of the Middle Triassic Summary of the unit here is less than 25 m. collapse breccias (Fig. 29 D). The supposed thickness late dolomitization process (Fig. 31 C). The upper part of this outcrop is deeply altered by later pedogenization processes. The dolostones are irregularly changed to Tertiary carbonatic calicitized “Pseudobreccias” carbonatic calicitized changed to Tertiary yellow dolostones member of the Monte Maiore fm. marks, tepees, evaporitic molds (gypsum and halite), marks, tepees, evaporitic identifiable in small isolated areas left untouched by the and passage to the Tertiary deposits This outcrop shows better on the left road cut. It is costituted by 2 to 3 m of Middle Triassic poorly stratified costituted by 2 to 3 m of Middle Triassic yellowish to grey dolostones bearing an almost horizontal yellowish attitude (Fig. 31 A). They contain abundant remains of Dasycladacean algae (Fig. 31 B). These remains are better Dasycladacean sedimentary structures, as cross bedding (HCS), ondulate bedding, ripple Collapse breccias; 2) present. The dolostone beds may be massive or alternatively may show several may or alternatively be massive present. The dolostone beds may laminated to thinly stratified bedding. Thin intercalation of yellowish marls are also bedding. Thin intercalation of yellowish laminated to thinly stratified Evaportic molds: Evaportic 1) Cross bedding. Fig. 30 – Bruncu su Para (Orroli) lower to intermediate Fig. 30 – Bruncu su Para 3) The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe part of the Middle Triassic Bruncu Su Para stratigraphic Bruncu Su Para part of the Middle Triassic section. Legend: DOI: 10.3301/GFT.2016.01 dolostones and dolomitic marls passing quickly upwards to grey to grey-yellowish dolostones showing a to grey grey-yellowish dolostones and dolomitic marls passing quickly upwards geological field trips 2016 - 8(1.1) itinerary 47 , that are L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Macroporella spectabilis and Diplopora annulata debilis PIA, Smit, 1979; Cherchi & Schröeder, 1988), described by Murru (1990) (Fig. 31 A). Monte Maiore fm. dolostones (MMF) passing upwards to the “Pseudobreccias” of Monte Cardiga Monte Maiore fm. dolostones (MMF) passing upwards A) Diplopora annulata Microcodium: Dasycladacean algae in the dolostones of the Middle Triassic Monte Maiore fm. algae in the dolostones of Middle Triassic Dasycladacean (ex- B, C) the algae-rich dolostones of the Monte Maiore fm. pass upward to the Paleogene pedogenetic to the Paleogene the algae-rich dolostones of Monte Maiore fm. pass upward Paronipora Fig. 31 - Bruncu Geroni: fm. (MCF); The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 with carbonate “Pseudobreccias”, and later to the fluvial Eocene deposits. carbonate “Pseudobreccias”, The next stop is located about 500 m northward. These “Pseudobreccias” mark locally the upward passage to the fluvial sandstones of Monte Cardiga fm. (Early These “Pseudobreccias” mark locally the upward be evidenced sharply by thin quartzose 2001). Otherwise, this passage may Eocene) (Carmignani et al., hematite pebbles. In the sandstones, locally channel rich of mm-sized or by subtle levels microconglomerates, The Monte Cardiga fm. is followed upwards be observed. even dolostones may the Triassic structures cut directly over Cherchi, 1969). & Pomesano by the reddish deposits of Upper Oligocene - Lower Miocene Ussana fm. (Pecorini dolostones is complicated: they algae contained in the Middle Triassic The classification of the Dasycladacean could be referred to Middle Triassic species described at Monte Maiore byMiddle Triassic Damiani & Gandin (1973a). Despite the complication of sedimentogical analysis this outcrop due to its deep dolomitization and nature suggest of the algae specimens and their fragmented nonetheless the chaotic arrangement plant cover, and a reworking of the bioclastic debris on shelf. a storm transport Summary: geological field trips 2016 - 8(1.1) itinerary 48 Pocket filled by Pocket L. G. Costamagna - S. Barca L. G. Costamagna - S. B) en tectonics and sedimentation Unconformity between the dolostones of the Middle Triassic Monte Maiore fm. (MMF) and the terrigenous Unconformity between the dolostones of Middle Triassic A) Fig. 32 – Piccheri: pedogenetic material between the Middle Jurassic Genna Selole fm. (GSF) and the Middle Triassic Monte Maiore fm. (MMF). Genna Selole fm. (GSF) and the Middle Triassic pedogenetic material between the Middle Jurassic The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe deposits of the Middle Jurassic Genna Selole fm. (GSF): the circle marks location of close-up B; deposits of the Middle Jurassic DOI: 10.3301/GFT.2016.01 STOP 3 - Piccheri (Orroli): Middle Triassic/ Jurassic unconformity and general features of the Genna Selole fm. (Bajocian-Bathonian alternations of the Middle Jurassic Here, on the right road cut, conglomeratic-sandy an irregular karstified surface 1983) Genna Selole fm. rest unconformably with a low angle over in Dieni et al., with evident relief (Fig. 32 A) Monte Maiore fm. dolostones of the Middle Triassic cut on the yellowish-grey in the coarse debris of the upper Genna Selole fm. fills karstic fractures Frequently, Monte Maiore fm. Both attitude of few degrees. the units show a northward geological field trips 2016 - 8(1.1) itinerary 49 Collapse breccias; = Monte Maiore Graded bedding. Graded L. G. Costamagna - S. Barca L. G. Costamagna - S. 2) 5) MMF en tectonics and sedimentation Evaporitic molds; Evaporitic Parallel laminations; Parallel 1) 4) = Fault. = Fault. F Cross bedding; Fig. 33 – Piccheri stratigraphic section. Fig. 33 – Piccheri stratigraphic 3) fm. Legend: The Monte Maiore fm. (Fig. 33) has a short thickness of no more than 5 m and is here constituted by thick-bedded mold-rich dolostones locally showing evaporitic yellowish The Genna Selole fm. and collapse-breccias horizons. levels is nearly 15 m thick and it made up by two fining upward one of them formed by the lower Laconi every (FU) cycles, to the intermediate - Gadoni lithofacies passing upward Nurri-Escalaplano lithofacies: whitish and well-sorted bedded conglomerates cross- to plane-parallel quartzose (made of subangular to subrounded pebbles quartz and fine up passing in the end to grey- lydites) gradually rare is posed sharply brown quartzsiltites. The upper FU cycle the lower one, whose topmost deposits are probably over surfaces rubefied oxidized Localized weakly pedogenized. with faint and discontinuous hematitic beds thin purple usually made of pebbly sandstone deposits to violet layers, periods, are scattered and possibly deriving from starvation in fact, the covering along the lower part of cycles: Rare coarser. is always above layer whitish quartzose In their turn these two hematitic pebbles are present too. minor siliciclastic FU sequences are formed by several representing scale, pebbly to sandy FU depositional events CU sequences are of fluvial bars. Rare building events superposition probably due to the progressive visibile too, the bar tail during normal flood events. of the bar head over The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 50 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : in this location the restricted carbonate shelf ouctrops of the Middle Triassic Monte Maiore fm. are : in this location the restricted carbonate shelf ouctrops of Middle Triassic The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Along the unconformity between the Triassic and the Jurassic rocks a fine siliciclastic brown fissile and the Jurassic Along the unconformity between Triassic and karstified Triassic the oxidized over down. It is confined in small pockets lay (pedogenetic?) deposit may dolomitic irregular surface (Fig. 32 B). unconformably by sandy cerithides-rich limestones In its turn, the Genna Selole fm. is covered pertaining to the Monte Cardiga fm. (Early Eocene). fault. This fault poses the unit in contact with Monte cut by a reverse The Genna Selole fm. is laterally This fault is sealed by the Lower Eocene deposits of Monte Maiore fm. dolostones acting as a hanging wall. be related to the so suggesting a pre-Eocene age of the fault itself: thus this discontinuity may Cardiga fm., 1984; Barca & Costamagna, 1997; 1999; 2000), up to now tectonic phase (Cherchi & Tremolières, Laramic part of the Island. signaled only in the Western Summary unconformably covered by the fluvial deposits of variable energy (channel and interchannel areas) of the by the fluvial deposits of variable unconformably covered Genna Selole fm. Middle Jurassic Still running along the road to Orroli, Eocene deposits of Monte Cardiga fm. pass abruptly fluvial located at the base of Upper Oligocene-Miocene depositional cycle. of the Ussana fm., conglomerates Nonetheless, the boundary is not directly visibile. The road reaches the Orroli village, and turn towards SE. Close to are noteworthy Nuraghe Arrubiu and another important archeological site: the “Domus de Janas” of Parco Su Motti. The itinerary goes surrounded by a landscape of highplains and smooth hills. While the slopes hills are formed by Variscan metamorphics, conversely their flat top may be covered unconformably sedimentary deposits of Mesozoic to Tertiary age or by Pliocene basaltic flows. Finally, passing through the Santo Stefano Gate, you reach the edge of deep gorge Flumendosa river. During Quaternary times the river escavated a valley, so cutting entirely the basaltic flows and Variscan metavolcanics of Santa Vittoria fm. (Ordovician). geological field trips 2016 - 8(1.1) itinerary 51 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Fig. 34 - Geological sketch of the Fig. 34 - Geological sketch marked. Escalaplano Stop (8) (Escalaplano Fm. type section). Legend; VB: Variscan Escalaplano Fm. (Middle basement; ESF: Monte Maiore fm. (Middle MMF: Triassic); Monte Cardiga fm. (Early MCF: Triassic); of the type section is Eocene). The trace Escalaplano (Escalaplano Tacco): type section and The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Now the itinerary proceeds down western slopes of Flumendosa valley, while to South on background stands the volcano-sedimentary Escalaplano Permian succession. In bottom of valley road turns sharply to East, crossing the Flumendosa river and climbing opposite slope. Along cuts may be observed the whole Permian red bed succession of post-Variscan molassic Escalaplano basin. At the end of rise, on top ridge Permian deposits are unconformably capped by terrigenous Early Eocene lower M. Cardiga fm. deposits. Then, you move down to the Escalaplano village (Fig. 34). The itinerary now runs again over the Variscan metamorphics, before to cross scattered Triassic outcrops resting unconformably above them. The Stop 8 is located close to the southern outskirts of Escalaplano village. STOP – 4 Here, on the road cuts of southern periphery Escalaplano unconformably sedimentary cycle village, the base of first Mesozoic basement. The Escalaplano Fm. (late the Variscan overlies Anisian/early Ladinian) (Fig. 5), here 16 m thick, is formed by 4 metasandstones and metasiltites Variscan lithofacies: it rests above Meana Late Cambrian - Early Ordovician: (San Vito sandstones fm., and Sardo tectonic unit) showing in their upper part alterations basement surface and the reworked carbonate pedogenesis. Over going uphill along the road cuts, follow: lithofacies 1, formed by 1 metamorphics, m of alternations reddish polygenic (quartz, Variscan breccias and and sandstones) conglomerates, volcanics Permian by the lithofacies 2 built sandstones (Fig. 35 A). It is sharply covered siltites and silty alternations of siltites, clayey of 7.20 m cyclical and decimetric beds of dolomitic marls reddish-purplish to grey-greenish from fissile to thinly stratified, clays are also present load casts and calcrete layers Localized in colour. and sandy dolomitic marls orange-yellowish sedimentological features of the Escalaplano Fm. (Middle Triassic) geological field trips 2016 - 8(1.1) itinerary 52 = MCF L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation = Escalaplano Fm.; EF : lithofacies 2; B : lithofacies 1; A ards, the lithofacies 3 gradually appears. It is built of 3 m thin, regular alternations clayey ards, the lithofacies 3 gradually Fig. 35 (p.1) – Escalaplano: the Escalaplano Fm. lithofacies ( Fig. 35 (p.1) Monte Cardiga fm. In the picture B circle marks hammer for scale. The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 (Fig. 35 B). Upw siltites, siltitic clays and subordinated siltites from greysh-blackish to reddish in colour, in their turn alternated and subordinated siltites from greysh-blackish to reddish in colour, siltites, siltitic clays (satin spar), probably precipitated from sulphate solutions inside the with thin pink crystalline gypsum veins crossing the rock (Fig. 35 bedding surfaces during late diagenesis. The same gypsum is present also in veins and the turning of colour to a grey- of the gypsum beds and veins, with the disappearance C). Finally, place. Especially in its upper part, scattered beds of carbonate greenish tone, the 4 m thick lithofacies takes sandstones and marly foretell the passage to dolostones of Monte Maiore fm. (Fig. 35 D). dolostones member: here it is formed by 1.2 m of yellowish The Monte Maiore fm. is represented by the yellow dolostones (Fig. 36 A). micritic levels. thin microbialitic laminae intercalated by thicker built of faintly wavy, geological field trips 2016 - 8(1.1) itinerary 53 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : lithofacies 4). D : lithofacies 3; C : during Middle Triassic over the smoothed Variscan basement mild alluvial slopes representing the the smoothed Variscan over : during Middle Triassic Fig. 35 (p.2) – Escalaplano: the Escalaplano Fm. lithofacies ( Fig. 35 (p.2) The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 The Triassic units are unconformably followed by the polygenic, chaotic conglomerates of the Monte Cardiga units are unconformably followed by the polygenic, chaotic conglomerates The Triassic carbonates contain also rounded pebbles and cobbles of the Triassic fm. (Early Eocene): these conglomerates (Fig. 36 B) posed underneath. Summary base of the Escalaplano Fm. took place: they were followed by an alternatively emerged and flooded, base of the Escalaplano Fm. took place: they were followed by an alternatively with the stop of terrigenous finally covered, sometimes restricted mudflat of the upper Escalaplano Fm., of the Monte Maiore fm. restricted ramp inputs, by the carbonate sediments of Middle Triassic geological field trips 2016 - 8(1.1) itinerary 54 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : Escalaplano Fm. (Middle : Genna Selole fm. (Middle EF : Monte Cardiga fm. (Early GSF MCF : Variscan basement; : Variscan VB Basal conglomerate of the Monte Cardiga fm. (Early Basal conglomerate B) : Monte Maiore fm. (Middle Triassic); : Monte Maiore fm. (Middle Triassic); : Dorgali fm. (Middle Jurassic); : Dorgali fm. (Middle Jurassic); : Fault. The trace of the stratigraphic section is marked. of the stratigraphic The trace : Fault. DF F MMF . This road runs bordering the edge of Escalaplano Tacco, Fig. 37 - Geological sketch of the Arcu de Is Fronestas Stop (9) and Fig. 37 - Geological sketch Eocene); surrounding areas. Legend: Jurassic); Triassic); Triassic); The road moves northward, turning back and crossing the Escalaplano village again. A secondary road to Perdasdefogu is picked: 1 km past, a right turn is chosen on the old road (a dirt track) to Perdasdefogu (Fig. 37) Microbialitic dolostones of the Monte Maiore fm.; A) Fig. 36 – Eocene) unconformably posed over the carbonate Monte Maiore fm.: light Triassic carbonate pebbes are clearly visible. the carbonate Monte Maiore fm.: light Triassic Eocene) unconformably posed over The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 55 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation , 2000) has been found. Above, . . The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 the Escalaplano Fm. is in its turn unconformably covered by the cross-bedded and locally graded quartzose by the cross-bedded and locally graded the Escalaplano Fm. is in its turn unconformably covered moving up and down along its edges, so allowing observation of the several stratigraphic unconformities among the Variscan basement and Triassic, Jurassic Eocene covers. Some interesting outcrops of Escalaplano, Monte Maiore, Genna Selole and Dorgali fms can be noticed from the Genna Selole fm. to Dorgali of the transition - Features Tradala Stop 4b - Ponte lithofacies of the (Stop 4b) the passage from upper Ussassai-Perdasdefogu Tradala at Ponte In particular, brownish marly dolostones with lenticular to wavy Genna Selole fm. to the Dorgali is exposed. Well-stratified and intercalated thin beds of dark siltites with plant remains are bedding, bioturbation and bioclasts (bivalves) thin-bedded dolostones C, D). The last, upper dark siltite bed mark the passage to grey, visible (Fig. 38 B, decrease of the terrigenous content passing from brownish upper of the Dorgali fm.: here upwards lithofacies of the Genna Selole fm. to grey Dorgali carbonate deposits is clearly visible. (Fig. 38 A) of the lansdscape is visible, overview a panoramic valley across the Rio Tradala Looking northward lower lithofacies of the Genna Selole fm. and dolostones conglomeratic showing as ledges the quartzose deposits. and Paleozoic Triassic of the Dorgali fm. overlaying STOP 5 - Arcu de Is Fronestas (Escalaplano Tacco): unconformity between the Escalaplano Fm. (Middle Triassic) and the Genna Selole fm. Jurassic) (Fig. On the road cut at Km 10 of secondary connecting villages Escalaplano and Perdasdefogu section 2000), a well-exposed stratigraphic 1974; Costamagna et al., et al., 38), at Arcu de Is Fronestas (Fazzini deposits) on the dirt to Triassic about 25 m thick crops out (Fig. 39). This section is exposed partially (Paleozoic to Jurassic (Triassic secondary road located nearly 10 m above and partially on the paved followed thus far, track Late Cambrian - metamorphics (San Vito Sandstones fm., deposits). It is formed, from the bottom, by Variscan (Fig. 40 reddish conglomerates Meana Sardo tectonic unit) followed unconformably by stratified Early Ordovician: siltites ofA), sandstones and purple to blackish siltites clayey here 7-8 the Escalaplano Fm. (Middle Triassic), in the road m thick: cross laminations in the sandstone beds and halite-casts at their bottom are visible. Upwards, dm-thick marly-dolomitic- rare road, the blackish pelites of Escalaplano Fm. have cut located along the paved age sandy beds with scattered microbialitic mats. In the pelites a microfloristic assemblage of Pelsonian-Illyrian 1983; Costamagna et al Pittau Demelia & Flaviani, (late Anisian, Middle Triassic: geological field trips 2016 - 8(1.1) itinerary 56 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : Escalaplano Fm. (Middle EF Passage from the UP lithofacies of Passage B, C, D) : Variscan basement; : Variscan VB : Dorgali fm. (Middle Jurassic); : Dorgali fm. (Middle Jurassic); DF ): the upmost dark clayey siltites level separating the units is evidenced by separating siltites level ): the upmost dark clayey DF . Front height in (B) = 2.5 m. (D) Overview of the Rio Tradala left slope. Legend; of the Rio Tradala Overview ) to the Dorgali fm. ( A) GSF : Genna Selole fm. (Middle Jurassic); : Genna Selole fm. (Middle Jurassic); GSF and the bioturbation in (C) Fig. 38 - Ponte Tradala Tradala Fig. 38 - Ponte in The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe Triassic); Triassic); the Genna Selole fm. ( bedding change of colour and bedding from the lower to upper unit is evident, as well wavy The sudden upward arrow. DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 57 2) 7) 11) 14) L. G. Costamagna - S. Barca L. G. Costamagna - S. Marls, sandy marls, Graded bedding; Graded Microbialitic mats; Variscan basement; Variscan 5) en tectonics and sedimentation 13) 10) 1) Dorgali fm. Sandstones; 4) DF: Cross laminations; Parallel laminations; Parallel 12) Pelites; Pelites; 9) 3) Variscan basement; Variscan Coarse quartzose conglomerates containing sandstone lenses; conglomerates Coarse quartzose Halite-casts; VB: 6) 8) : the restricted mudflat of upper Escalaplano Fm. is Fig. 39 - Arcu de Is Fronestas (Escalaplano); stratigraphic section of the Fig. 39 - Arcu de Is Fronestas (Escalaplano); stratigraphic Imbrications; Palynomorphs-bearing horizons; horizons; Palynomorphs-bearing Oligomictic conglomerates; Oligomictic conglomerates; Dolostones; Escalaplano Fm. and Genna Selole fm. Legend – marls; clayey conglomerates of the lower Laconi-Gadoni litofacies Genna Selole conglomerates fm. are subdivided C). The conglomerates (Figs 40 B, (Middle Jurassic) by depositional FU sequences (Fig. 40 C) separated in meter-thick (CU) coarsening-upward erosional surfaces and containing rare and discontinuous rare sequences. In the middle of conglomerates are present. thin intercalations of dark siltites and clays blackish Imbricated pebbles are common. In the conglomerates, limestones are Permian pebbles from the dismantling of silicized by are suddenly covered scattered (Fig. 40 D). The conglomerates to flaser bedding (Fig. 40 C). Over whitish quartzarenites with wavy lithofacies this coarse lithofacies, the finer Nurri-Escalaplano darker sharply occur. Summary unconformably covered by the fluvial braided bars of the lower by the fluvial braided unconformably covered by in turn covered Laconi-Gadoni lithofacies of the Genna Selole fm., sandstones. The road descends from the northern slopes of Escalaplano Tacco and then climbs the next slopes of Perdasdefogu Tacco, once more on Variscan metamorphics the Jurassic succession follows. The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 58 nes; L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation ) Unconformity between the Genna Selole fm. (GSF) (Middle Jurassic) and the Escalaplano Fm. (EF) (Middle ) Unconformity between the Genna Selole fm. (GSF) (Middle Jurassic) B ) Conglomeratic base of the Escalaplano Fm. (EF) (Middle Triassic): a frontally-accreted pebbly bar prograding a frontally-accreted base of the Escalaplano Fm. (EF) (Middle Triassic): ) Conglomeratic A ) Cross bedding in the conglomerates of the Genna Selole fm.: the conglomerates are covered at the top by flaser–bedded sandsto at the top by flaser–bedded are covered of the Genna Selole fm.: conglomerates ) Cross bedding in the conglomerates C ) Close up of the Genna Selole fm. conglomerates: a black silicized Permian carbonate pebble 8 cm large (Middle Jurassic). Permian a black silicized ) Close up of the Genna Selole fm. conglomerates: Fig. 40 – Arcu de Is Fronestas: D The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe Triassic); Triassic); over the Variscan basement (VB); the Variscan over DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 59 DF: QT: GSF: Fault. The trace of The trace Fault. L. G. Costamagna - S. Barca L. G. Costamagna - S. F: en tectonics and sedimentation Variscan basement; Variscan VB: Fig. 41 – Geological sketch of the Sa Fig. 41 – Geological sketch the stratigraphic section is marked. the stratigraphic Teria Stop (10) and surrounding areas. Teria Legend; Genna Selole fm. (Middle Jurassic); Dorgali fm. (Middle Jurassic); Quaternary debris; The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 STOP 6 - Sa Teria (Perdasdefogu Tacco): sedimentological features of the upper Genna Selole fm. and lower Dorgali fm. (Middle Jurassic) (Fig. 41), the Jurassic 4 Km SW to Perdasdefogu Sa Teria, At the secondary road section is located below and above stratigraphic The upper Genna Selole fm. and the lower Escalaplano-Perdasdefogu. Dorgali fm. still running about 5 crop out along the old dirt track the new road. metres above starts with Tacco succession of the Perdasdefogu The Middle Jurassic the Genna Selole fm., Variscan about 30 m thick: it rests over Meana Sardo Ordovician: (Monte Santa Vittoria fm., metavolcanics tectonic unit). The lower part of this unit is reachable with difficulty The Genna below the secondary road Escalaplano-Perdasdefogu. passing quickly to Selole fm. is initially built of quartz conglomerates, whitish sandstones (Laconi-Gadoni lithofacies, about 15 m). The The intermediate lithofacies S or SW. pebbles are imbricated towards is formed by alternations of frequently cross-laminated to grey-whitish siltites and silty clays quartzarenites, siltites, clayey green in colour with load casts (Nurri-Escalaplano lithofacies, about 8 the carbonate m). In the upper part (along old dirty track), well-bedded dolomitic sandstone, grey-green whitish quartzarenites, rare sedimentation begins suddenly: over lithofacies, about 4 m). intercalate (Ussassai-Perdasdefogu sandstones and blackish lignitiferous siltitic clays the last terrigenous, blackish silty bed. The Dorgali fm. rests over There about 12 m thick, is built of well-bedded dolostones, white-grey to bluish in colour. Here the Dorgali fm., and cross laminations, rip- are rich in sedimentary structures and textures: bioturbations, load-casts, parallel irregular with coarse basal lags, erosive up and flame structures, algal bindstones (Fig. 42), storm layers and bioclasts are still evident. The most surfaces often rubified (Fig. 43). Oncoids, flat pebbles, intraclasts and bioturbated muds. frequent lithofacies association is formed by alternations of storm layers geological field trips 2016 - 8(1.1) itinerary 60 bioturbated A) L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation oncoidal basal lag of a storm layer covering laminated covering oncoidal basal lag of a storm layer C) bioclastic molds in a storm basal lag covering an erosive surface. an erosive bioclastic molds in a storm basal lag covering D) wave cross laminations; wave B) Fig. 43 – Sa Teria (Perdasdefogu): sedimentary structures in the Dorgali fm. (Perdasdefogu): Fig. 43 – Sa Teria microbialites; muds; : over a fluvial to palustrine sedimentation, following the progressive vanishing of the vanishing a fluvial to palustrine sedimentation, following the progressive : over the primary deposits and the deposition of storm layers (Dorgali fm.) dominated. the primary deposits and deposition of storm layers prevalently subtidal-lagoonal low energy environment frequently interested by reworking of subtidal-lagoonal low energy environment prevalently terrigenous input (Genna Selole fm.), a pure carbonate sedimentation took place: here a Summary Fig. 42 – Sa Teria dolostone. (Perdasdefogu): Stromatolitic (Perdasdefogu): bindstone with wrinkled mats (dark) and micritic beds (light) to bioclastic passing upward Dorgali fm. grainstones. The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 61 : BPZ : Dorgali fm. : Quaternary : Genna Selole FDO L. G. Costamagna - S. Barca L. G. Costamagna - S. QT FGS en tectonics and sedimentation : Fault. The trace of the The trace : Fault. F Fig. 44 - Geological sketch of the Fig. 44 - Geological sketch stratigraphic section is marked. stratigraphic Serra Is Arangius Stop (11) and Is Arangius Serra surrounding areas. Legend; basement; Variscan fm. (Middle Jurassic); (Middle Jurassic); debris; The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 The road moves on to the Perdasdefogu village: here it turns right and take a secondary towards Tertenia leading to the Serra Is Arangius stratigraphic section designated as parastratotype of the Genna Selole fm. STOP 7 - Serra Is Arangius (Perdasdefogu Tacco): parastratotype and sedimentological features of the Genna Selole fm. (Middle Jurassic) (Fig. 44) a splendid Genna Selole fm. section (Figs Is Arangius Serra At the base, of the unit crops out. At 45, 46 A), chosen as parastratotype metamorphics (San Vito sandstones fm. and Santa Vittoria Variscan Meana Sardo tectonic unit) Late Cambrian to Middle Ordovician: fm., first by the whitish crop out. They are unconformably covered Laconi-Gadoni FU lithofacies: at its monomictic conglomeratic-sandy be materials may of black silty-clayey base, scattered pockets very present. Cross-bedding is diffuse (Fig. 46 B), as well lens-shaped representing minor fluvial channels, and rubified oxidized horizons surfaces suggesting breaks in sedimentation. This lithofacies is 9.4 m siltites thick and it is sharply followed by the blackish siltites - clayey thin whitish sandstone beds of the Nurri-Escalaplano with rare pockets, lithofacies. Here rootlets (Fig. 46 C), plant remains, black clay laminations and load casts are visible. Thickness is about 6 convolute by the well-stratified m. In its turn this lithofacies is suddenly covered alternations of the Ussassai-Perdasdefogu carbonate-sandy-silty lithofacies, 11 m thick through a weak angular unconformity (?) cross bedding, surface. Rarely, perhaps related to a ravinement in the carbonate lenticular and flaser bedding are present. Frequently, surfaces erosive and gastropods-rich horizons, lithofacies brachiopods of the terrigenous inputs and bioturbation are visible. The vanishing marks the passage to Dorgali fm. The total thickness of the Genna Selole fm. is here 26.4 meters. geological field trips 2016 - 8(1.1) itinerary 62 5) : VB : Dorgali fm. DF Root-cast into a Root-cast Imbrications. L. G. Costamagna - S. Barca L. G. Costamagna - S. 7) C) Cross laminations; en tectonics and sedimentation 4) Plant rests; 3) Normal graded bedding; Normal graded : Genna Selole fm.); Stratigraphic section overview: Legend; section overview: Stratigraphic 6) GSF A) : Genna Selole fm. (Middle Jurassic); : Genna Selole fm. (Middle Jurassic); Bioturbation; Variscan basement / Genna Selole fm. unconformity: close Variscan GSF 2) B) : Variscan basement; : Variscan VB Fig. 46 – Serra Is Arangius. Is Arangius. Fig. 46 – Serra sandstone layer of the Nurri-Escalaplano lithofacies (Genna Selole fm.). sandstone layer (Middle Jurassic); (Middle Jurassic); up ( Variscan basement; Variscan Parallel laminations; Parallel Fig. 45 – Serra Is Arangius (Perdasdefogu): Genna Selole fm. parastratotype. Legend: Genna Selole fm. parastratotype. (Perdasdefogu): Is Arangius Fig. 45 – Serra Convolute laminations and load-casts; Convolute 1) The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 63 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : the deposition of the Genna Selole fm. occurred first into a braided stream context passing rapidly : the deposition of Genna Selole fm. occurred first into a braided The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Summary to a palustrine-alluvial environment and later to a lagoonal, tide-influenced one with various (carbonate and and later to a lagoonal, tide-influenced one with various environment to a palustrine-alluvial away. closed and moved terrigenous) sedimentary contributions: a fluvial outlet cyclically disappeared, giving place to the Dorgali fm. carbonate shelf. Here, in times the terrigenous inputs gradually On the western side of valley along an abandoned track, another good section Genna Selole fm. crops out. This is especially true for the upper Ussassai-Perdasdefogu lithofacies: here sedimentary structures suggesting tidal processes and fossils are abundant. The road turns back to Perdasdefogu and moves North, towards the Jerzu village. Along just out Perdasdfefogu, for about a couple of km are visible on the left road cuts Jurassic deposits unconformably overlapping the Permian late-Variscan volcanics. Here the Genna Selole fm. thins out dramatically, reaching at best not more than 3-4 m of thickness. It is formed only by fine terrigenous deposits and few carbonate beds. This stratigrapic arrangement the result of the paleogeographic setting area at early Middle Jurassic times: here watcher stands over former Barbagia paleohigh, where the Jurassic deposits often may even start directly with carbonate Dorgali fm. containing only scattered centimetric quartz pebbles close to its base. Our itinerary heads to the overnight stay place at “Rifugio di Ogliastra” and develops exclusively over low- to medium grade Variscan metamorphics. Overnight stay at “Rifugio d’Ogliastra”, 4 km SW to Jerzu. geological field trips 2016 - 8(1.1) itinerary 64 : QT : Fault. L. G. Costamagna - S. Barca L. G. Costamagna - S. F? : Variscan basement; : Variscan VB en tectonics and sedimentation : Genna Selole fm. (Middle Jurassic); : Dorgali fm. (Middle Jurassic); : Dorgali fm. (Middle Jurassic); Fig. 47 - Geological sketch of the Pitzu Fig. 47 - Geological sketch Quaternary debris. S. Antonio Gate Stop (12) and surrounding S. areas. Legend; GSF FD Luca G. Costamagna Day 2: from Jerzu to Osini The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 The itinerary moves back to SW for nearly 1 Km, reaching the Pitzu S. Antonio Gate (Fig. 47). Here Middle Jurassic transgressive deposits are strongly reduced in thickness. The features of the Pitzu S. Antonio stratigraphic section are connected to the peculiar Middle Jurassic paleogeographic and paleostructural configuration of the area. The tectonic Barbagia paleohigh for its raised topographic position was last area the Variscan basement reached by Middle Jurassic transgression (Costamagna & Barca, 2004; Costamagna et al., 2007). So, weathering and alteration phenomena worked hardly over the exposed paleohigh, activating pedogenesis and preventing deposition of the Genna Selole fm. but on its slopes. In some areas, those processes induced laterization over the Variscan basement and, consequently, the development of lateritic paleosoils along the unconformity between Variscan basement and Jurassic deposits (“Ferro dei Tacchi”: Marini, 1984). STOP 8 – Pitzu S. Antonio (Tertenia Tacco): sedimentological features of the Middle Jurassic transgression over Variscan basement Antonio Gate (Fig. 48), at the base of road cut the Pitzu S. At basement reddish schists crop out (Gennargentu grey phyllites Variscan Late Cambrian –fm., Barbagia tectonic unit); their Early Ordovician: passing in only 1 meter and almost the top, grow up towards alteration with quartz cobbles (weak reddish clays first to pedogenized sharply, with laterization - Fig. 49 A) followed quickly by greyish silty clays In their turn these gray quartz cobbles and finally by sticky grey clays. that terminate by 20 cm of black, fissile clays are covered clays the coal, carbonate coal bed. Over with a thin, locally shiny upwards geological field trips 2016 - 8(1.1) itinerary 65 : Variscan BPZ L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : Dorgali fm. (Middle Jurassic). FDO ) are also present. Often, in the carbonates erosional surfaces Nerinella bathonica : Genna Selole fm. (Middle Jurassic); : Genna Selole fm. (Middle Jurassic); FGS Fig. 48 – Overview of the Pitzu S. Antonio Gate stratigraphic section. The front is about 7 m high. Legend; Antonio Gate stratigraphic of the Pitzu S. Fig. 48 – Overview basement; The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 sedimentation starts suddenly. It is formed by bedded dolostones (bioclastic-intraclastic grainstones) with a grainstones) It is formed by bedded dolostones (bioclastic-intraclastic sedimentation starts suddenly. Here bioturbation (Fig. 49 B), irregular fading upwards. gradually terrigenous content (quartz pebbles and clays) and ripple cross laminations bedding are plane-parallel surfaces with significant relief, and erosive abundant. Gastropods ( are covered by thin oxidized, reddish coatings or by an intraclastic breccia containing also angular quartz reddish coatings or by an intraclastic by thin oxidized, are covered sharp transition that make pebbles. In their turn these deposits are followed by cm-thick blackish siltitic clays and siltitic coatings, conglomerates back to the carbonates. Sometimes a complete sequence made of oxidized it represents the start again of sedimentation following emersion and before develops: clays from the intercalation marks the transition of the carbonates. The topmost blackish siltitic-clayey recovery section is about 8 meters. Genna Selole fm. to the Dorgali The thickness of investigated geological field trips 2016 - 8(1.1) itinerary 66 L. G. Costamagna - S. Barca L. G. Costamagna - S. : Genna Selole fm., en tectonics and sedimentation FGSUP : weakly altered Variscan basement; : weakly altered Variscan VBa : Genna Selole fm., lithofacies NE (Middle Jurassic); lithofacies NE (Middle Jurassic); : Genna Selole fm., FGSNE Bioturbations in the UP lithofacies of Genna Selole fm. B) – Close-up of the Pitzu S. Antonio Gate stratigraphic section. Legend; Antonio Gate stratigraphic – Close-up of the Pitzu S. : this succession represents the development of an erosive-pedogenetic profile over the Variscan profile over of an erosive-pedogenetic : this succession represents the development A) : pedogenized Variscan basement; Variscan : pedogenized Fig. 49 lithofacies UP (Middle Jurassic); lithofacies UP (Middle Jurassic); The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe VBb DOI: 10.3301/GFT.2016.01 Summary basement, rapidly followed by a brief palustrine-littoral episode immediately preceeding the setting of a followed by a brief palustrine-littoral basement, rapidly (tectonic? eustatic?) some ephemeral carbonate-terrigenous sedimentation. Nevertheless, lagoonal mixed restarts of the continental- mild regressions and several determinate short-lived, drops of the sea level palustrine conditions before the ultimate setting of carbonate open shelf sedimentation. geological field trips 2016 - 8(1.1) itinerary 67 ) DF L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation the Dorgali fm. (Middle Jurassic). ) Genna Selole fm. (Middle Jurassic); ) Genna Selole fm. (Middle Jurassic); GSF ) Genna Silana fm. (Late Jurassic). The trace of The trace ) Genna Silana fm. (Late Jurassic). GSilF Fig. 50 - Ungul’E’Ferru (Stop 8b): progradation clinoforms in ) Variscan basement; ) Variscan VB Fig. 51 - Geological sketch map of the M. Lumburau (Jerzu) (9), Buncu Matzeu map of the M. Lumburau Fig. 51 - Geological sketch the stratigraphic section is marked close to the edge of Ulassai Tacco. section is marked the stratigraphic (Ulassai) (10) and Grutta Orroli (Osini) (11a, 11b) Stops surrounding areas. Legenda: Dorgali fm. (Middle Jurassic); Dorgali fm. (Middle Jurassic); Stop 8b - Ungul'e Ferru: accretion clinoforms in the Dorgali fm. Stop 8b - Ungul'e Ferru: locality turns Now the road leads to Jerzu, and close Ungul’E Ferru (Fig. 47): after some hundred of metres (Stop 8b), right on a small track of the whole hill is visible (Fig. 50). The stacking pattern a wide overview dolostones belonging to the Dorgali fm. is of about 80 m well-stratified a flat clinoforms unconformably overlying evident: there are prograding they are related to the N. Most likely basal surface and directed towards sand bar. shift of a little, intra-lagoon The road moves back to the secondary towards Jerzu (Fig. 51), and after 2 Km you take on the left a dirt track that go around Monte Limbarau (Jerzu Tacco): this hill is made up of Jurassic deposits unconformably posed over the Variscan metamorphics. The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 68 : VB : Genna GSF L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Unaltered zone; Unaltered zone; C) Fe precipitation zone; precipitation zone; Fe B) Lisciviation zone; Lisciviation zone; A) : Dorgali fm. (Middle Jurassic). The double arrow marks the ore level, nearly 1.2 m thick. The double arrow marks the ore level, : Dorgali fm. (Middle Jurassic). DF Fig. 52 – Monte Lumburau (Jerzu Tacco) abandoned Fe mine. Quarry front showing the main mineralized level. Legend: level. mine. Quarry front showing the main mineralized abandoned Fe (Jerzu Tacco) Fig. 52 – Monte Lumburau Selole fm. (Middle Jurassic) Selole fm. (Middle Jurassic) The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe Variscan basement, Gennargentu Grey Phyllites; basement, Gennargentu Grey Phyllites; Variscan DOI: 10.3301/GFT.2016.01 STOP 9 - Monte Lumburau (Jerzu Tacco): laterites (“Ferro dei Tacchi”) at the base of Middle Jurassic transgression II War exploited during the World iron mine (Jerzu) was The Su Lumburau (Fig. 52). In the trench leading to to thin-bedded; B) thin, laterally the front shows, from top: A) dolostones thick- the main gallery, dolostones; C) massive and conglomeratic conglomerates matrix-supported discontinuous lenses of quartzose E) material unconformably overlies of greyish to whitish silty-clayey to bedded dolostones; D) a thin interval whitish fissile, weathered basement ; F) sharp passage to violet fissile which colour passes gradually and in the fractures of iron oxides basement with high concentrations hard laterized to reddish; G) massive, Late schists (Gennargentu grey phillytes fm., H) sharp passage to unaltered blackish-bluish Variscan cavities. Cambrian – Barbagia tectonic unit). Early Ordovician: geological field trips 2016 - 8(1.1) itinerary 69 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation Bruncu Matzeu (Ulassai Tacco): synsedimentary extensional tectonics, transitional : in this locality, a thin lower Genna Selole fm. less than 2 metres thick (considering only the Laconi : in this locality, The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Summary STOP - 10 outcrop pertaining to the Laconi-Gadoni lithofacies of Genna Rising to the cliff a conglomerate-sandstone Selole fm. is visible. The outcrop (Fig. 53 A) and conglomerates quartzose is built of clast-supported part cross bedding as well In the lower conglomeratic depositional events. quartzarenites formed by several bedding: erosional together with the parallel the sandstones prevail surfaces are visible: upwards, as erosive building and eroding pebbly to sandy bars is flood events surfaces are also here. The occurring of several energy decreased and sandy bars with intercalation of possible the transport the top, clearly evident. Towards place. Besides, a reddish, rubified surfaces (suggesting periodic stops of the sedimentation) take poorly outcropping sinsedimentary tectonic discontinuity cutting the outcrop is clearly visible. Upwards, siltites and sandstones pertaining to the Nurri Escalaplano to blackish siltites, clayey alternations of gray sharply the coarser lithologies of lower cover lithofacies and related to an alluvial-palustrine environment lithofacies of the Genna Selole fm. depositional environments and early karstic cycles at the Genna Selole fm. / Dorgali transition (Middle Jurassic) Gadoni and Nurri Escalaplano lithofacies) and formed by fine terrigenous and rare thin conglomerate lenses thin conglomerate Gadoni and Nurri Escalaplano lithofacies) formed by fine terrigenous rare the upper part of Gennargentu grey phillytes fm. tectonic unit. During early covered exposing the were removed, covers the Barbagia paleohigh emerged and Early Mesozoic Middle Jurassic, position of the paleohigh, only a limited and upper the topographic basement underneath. For Variscan climate, the under a hot-humid deposited here. So, was siliciclastic part of the Genna Selole fm. cover first triggered a strong laterization of the metamorphics underneath, creating thick Fe- percolating waters were protected, remaining rich paleosoil. The metamorphic rocks below the base of groundwater unaltered. The secondary road to Jerzu leads towards Ulassai. Here you take a left reaches the cliff of Ulassai Tacco (Fig. 51). At its base the passage from the Genna Selole fm. to Dorgali fm is visible. A brief and easy walk is necessary to reach the carbonate cliffs of Bruncu Matzeu. geological field trips 2016 - 8(1.1) itinerary 70 : : : : F IC CH GB A) : cross- : tabular St SL : overbank fines; : overbank : plane-parallel : massive silt and : massive Vertically-restricted L. G. Costamagna - S. Barca L. G. Costamagna - S. OF Sh Fsm C) en tectonics and sedimentation : sandy bars; Braided multi-storey channel fill Braided SB A) Dolomitic limestones cut by rubified B) : cross-bedded conglomerates; : cross-bedded conglomerates; Fig. 53 – Bruncu Matzeu (Ulassai) Fig. 53 – Bruncu Matzeu are visible. Depositional architecture of the Laconi-Gadoni lithofacies: pebbly bars overlapping built of several (incomplete fluvial sequences) passing upwards to sandy tide-influenced bars. Synsedimentary Legend; tectonics features are clear. elements; architectural Channelized elements; interchannel architectural pebbly bars; bodies of laminated sand; Gt bedded sandstones; laminated sandstones; mud. Numbers: Bounding surfaces rank; fault. emersion surfaces; (arrow) evidencing ephemeral karstic events episodes in the upper part of regressive Genna Selole fm. Little angular quartz pebbles at the restart of carbonate sedimentation The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) itinerary 71 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation : in this Stop the complete evolution of the Genna Selole fm. continental to transitional system can of the Genna Selole fm. continental to transitional : in this Stop the complete evolution The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe DOI: 10.3301/GFT.2016.01 Still upwards, alternations of thick beds of grey to bluish limestones, dolostones and thinner layers of blackish alternations of thick beds grey to bluish limestones, dolostones and thinner layers Still upwards, place. lithofacies suddenly take lignitiferous pelites belonging to the Ussassai-Perdasdefogu and little angular pebbles are rich of bioclastic debris and sometimes quartz grains Here limestone layers and rubified surfaces with relief (Fig. 53 B), sometimes karst erosive also intercalated. Irregular, transgression emersion episodes during the Middle Jurassic the carbonates indicate ephemeral evidences over limited terrigenous inputs (early karstic phenomena: Fig. 53 C). and localized, Summary STOP 11 - Grutta Orroli and Punta su Scrau (Osini Tacco): oolitic grainstones, patch reefs and oncoids of the Genna Silana fm. (Late Jurassic) small patch reef in the Genna Silana fm. Stop 11a - Osini Tacco: top surface (Fig. 51): the Dorgali fm. dolostones crop out all road runs on the Osini Tacco A narrow paved oolitic and/or bioclastic North, at Grutta Orroli the dolomitization fades sharply: thick-bedded around. Towards follow on the right a narrow trail Here you cropout just along the sides of dirt track. calcareous grainstones lens- are sharply intercalated by a little massive in the wood (Stop 11a). After nearly 100 m grainstones C). This patch reef is in its turn about 20 m wide and 60-70 cm thick (Fig. 54 A, B, patch reef, shaped coral again by bioclastic/oolitic grainstones.covered Genna Silana fm. These limestones pertain to the Late Jurassic and represent the sharp passage to shelf margin sedimentation. oncolitic floatstones in the Genna Silana fm. Stop 11b - Punta Su Scrau: in the wood a to North, after 1 km close another trail on along the dirt track Coming back to the bus and moving the patch reef there is local (1000 m). Here (Stop 11b), over allows to reach Punta Su Scrau 10 minutes walk be seen, up to the passage marine sedimentation, as well early karst phenomena due ephemeral regressions and the sinsedimentary tectonics influence on unit. The road moves back and proceed to Ulassai: here, 1 km to NW, is the beautiful karstic Su Murmuri cave km long, a famous tourist attraction. In the Osini village local road climb to top of Tacco, passing all the way through S. Giorgio Gorge, a splendid natural monument due to karstic processes. geological field trips 2016 - 8(1.1) itinerary 72 Punta su D) L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation D C Overview of the patch reef: arrow points to massive Overview A) Close-ups of the patch reef evidencing the coral specimens; Close-ups of the patch reef evidencing coral B, C) : over the lagoonal deposits of the Dorgali fm., the Genna Silana fm. marginal unit is here formed the lagoonal deposits of Dorgali fm., : over Fig. 54 – Grutta Orroli (Tacco di Osini): Genna Silana fm. Fig. 54 – Grutta Orroli (Tacco Scrau: oncoids of the top Genna Silana fm. Scrau: The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe bed above the bioclastic/oolitic grainstones; the bioclastic/oolitic grainstones; bed above DOI: 10.3301/GFT.2016.01 A B upper level of the Late Jurassic Genna Silana fm., the topmost unit of the Tacchi succession: oncolitic floatstones (Fig. the topmost unit of Tacchi Genna Silana fm., of the Late Jurassic upper level are evident as well the subtle a diameter of 3 cm at most. The thin algal envelopes 54 D) where the oncoids have little rarely, or, fragments wrinkling between the different algal coatings. The nuclei are formed frequently by coral The matrix surrrounding the oncoids is formed by bioclastic grains,quartz grains. and peloids. possible intraclasts Summary first by oolitic/bioclastic deposits embedding little patch reefs. These latter are followed mudstones (floatstones). The patch reefs mark a containing oncoids and coarse bioclastic fragments and wackestones from a discontinuous belt constituing the rim of shallow carbonate domain and dividing inner ramp The superposition of the finer floatstones suggests deepening smoothly deepening outer ramp. gradually, and the passage to outer ramp. of the environment geological field trips 2016 - 8(1.1) itinerary 73 L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment relationship betwe Tacco di Tertenia: Punta Corongiu in the background DOI: 10.3301/GFT.2016.01 The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment and relationship between tectonics and sedimentation L. G. Costamagna - S. Barca g e o l o g i c a l

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DOI: 10.3301/GFT.2016.01 geological field trips 2016 - 8(1.1) references 75 l. a. nd ion iorn. L. G. Costamagna - S. Barca L. G. Costamagna - S. en tectonics and sedimentation the evolution of the Western Tethys. Mem. Soc. Geol. It., 31, 23-44. Mem. Soc. Geol. It., Tethys. of the Western the evolution 2, 28, 59-87. Geol., 325, 791-797. Acad. Sci. Paris, della Terra, Italiano di Scienze nella Sardegna centro-meridionale. Geoitalia 1999, 2° Forum sedimentari meso-cenozoici Riassunti, 1, Bellaria 1999, 309-311. 119, 497-515. per un modello geodinamico nell’ambito dell’orogenesi pirenaica. Boll. Soc. Geol. It., strutturali Fr., 23, 353-359. Fr., of the Tethys. In R.H. Dott Jr and R.H. Shaver (Eds), Repr. from “Modern and ancient geosinclinal sedimentation”, Soc. Econ. from “Modern and ancient geosinclinal sedimentation”, (Eds), Repr. In R.H. Dott Jr and Shaver of the Tethys. 19, 129-160. Spec. 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