P68 Copertina R OK C 27-05-2004, 15:16:24 the Scientific Content of This Guide Is Under the Total Responsibility of the Authors

Volume n° 6 - from P55 to PW06

32nd INTERNATIONAL GEOLOGICAL CONGRESS

THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND PALAEONTOLOGY

Leader: F. Jadoul Associate Leader: M.T. Galli, F. Berra, S. Cirilli, P. Ronchi, A. Paganoni Field Trip Guide Book - P68 Field Trip

Florence - Italy August 20-28, 2004 Post-Congress P68

P68 copertina_R_OK C 27-05-2004, 15:16:24 The scientific content of this guide is under the total responsibility of the Authors

Published by: APAT – Italian Agency for the Environmental Protection and Technical Services - Via Vitaliano Brancati, 48 - 00144 Roma - Italy

Series Editors: Luca Guerrieri, Irene Rischia and Leonello Serva (APAT, Roma)

English Desk-copy Editors: Paul Mazza (Università di Firenze), Jessica Ann Thonn (Università di Firenze), Nathalie Marléne Adams (Università di Firenze), Miriam Friedman (Università di Firenze), Kate Eadie (Freelance indipendent professional)

Field Trip Committee: Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia (Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and Riccardo Polino (CNR, Torino)

Acknowledgments: The 32nd IGC Organizing Committee is grateful to Roberto Pompili and Elisa Brustia (APAT, Roma) for their collaboration in editing.

Graphic project: Full snc - Firenze

Layout and press: Lito Terrazzi srl - Firenze

P68 copertina_R_OK D 27-05-2004, 15:15:08 Volume n° 6 - from P55 to PW06

32nd INTERNATIONAL GEOLOGICAL CONGRESS

THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND PALAEONTOLOGY

AUTHORS: F. Jadoul1, M.T. Galli1, F. Berra1, S. Cirilli 2, P. Ronchi3, A. Paganoni4

1 Dipt. Scienze della Terra,“A. Desio”, Università degli Studi di Milano - Italy 2 Dipt. Scienze della Terra, Università degli Studi di Perugia - Italy 3 ENI Exploration and Production Division, SPES Department, San Donato Milanese - Italy 4 E. Cafﬁ Natural History Museum, Bergamo - Italy

Florence - Italy August 20-28, 2004

Post-Congress P68

P68_R_OK A 27-05-2004, 15:19:43 Front Cover: Late Carnian-Hettangian stratigraphic setting of the Bergamasc Alps

P68_R_OK B 27-05-2004, 15:19:44 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY

AND PALAEONTOLOGY P68

Leader: F. Jadoul Associate Leaders: M.T. Galli, F. Berra, S. Cirilli, P. Ronchi, A. Paganoni

1. Introduction succession exhibits variable thickness (from 500 In the course of this three-day ﬁ eld trip you will to 4000 m; Assereto and Casati, 1965), related to become familiar with the main factors controlling sedimentation controlled by transtensive tectonics the stratigraphic, palaeoenvironmental and (Norian asymmetric rifting; Jadoul et al., 1992). palaeogeographic evolution of the Upper Triassic- The lower depositional system (uppermost Carnian lowest Jurassic succession in the Western Southern to middle Norian) lies on shallow water carbonates, Alps of Central Lombardy (Figure 1). evaporites and siliciclastics (sabkha facies) of the The sedimentary succession records the earliest stages S. Giovanni Bianco Fm. and is represented by the of the evolution of a passive margin, dominated by shallow water limestones and breccias of the Castro synsedimentary tectonic, that will lead to the Liassic Fm. covered by the thick carbonate platform of the opening of the Jurassic Alpine Tethys. The following Dolomia Principale (DP) and coeval basin facies (late Cretaceous-Tertiary) closure of this seaway led (Aralalta Group). The upper depositional system (Late to the folding and overthrusting of these successions, Norian-Hettangian) consists of subtidal mixed shale- that are now preserved in different tectonic units that carbonate units Riva di Solto Shale (ARS) and Zu can generally be restored in order to reconstruct their Limestone (Zu) passing to the Hettangian carbonate original palaeogeographic relationships. platform Conchodon Dolomite (CD). The boundary

Figure 1 - Structural Alpine Domains and geographical location of the Bergamasc Alps.

The successions that will be observed in the between the two systems is well-marked and denotes excursion belong to a slightly deformed portion of the a sharp change in the sedimentological regime. Alpine chain, and give the opportunity to study the Relationships and thickness of the whole Late Triassic syndepositional tectonics and the sedimentological succession are shown in Figure 2; the palynological and diagenetic processes that affected the Upper biostratigraphy is presented in Figure 3. Triassic-lowest Liassic rocks of this portion of the Lombardy Basin. 2.1. The upper Carnian-middle Norian dolomitized carbonate platform (Dolomia Principale) and the 2. Regional geologic setting: intraplatform basin carbonates (Aralalta Group). stratigraphy and palaeogeography The DP of the western Southern Alps is up to The upper Carnian to Rhaetian succession of the reaches its maximum thickness (about 2000 m) on P55 to PW06 n° 6 - from Volume Lombardian Southern Alps is organized in two the eastern side of Lake Iseo. In the visited area, superimposed depositional systems and outcrops the DP deposition started probably during the latest along the E-W. The thick Upper Triassic succession Carnian in restricted shallow water basins, lagoons of Lombardy is bordered by less subsiding structural and tidal ﬂ ats, as recorded by 200-300 m thick, dark highs to the S (subsurface data; Errico et al., 1979), bedded dolomites with intraformational breccias and the Trento Platform to the E and the Varese High to microbialites (Lower Member of DP; Stop1.1). the W (Figure 2). The uppermost Carnian-Rhaetian These subtidal facies are overlain by stacked

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Volume n° 6 - from P55 to PW06 P68 - P68 with thestratigraphiclocationofStops(b)(modiﬁ Figure 2-LateCarnian-Hettangianstratigraphicsettings ofthe Western Southern Alps (a)andoftheBergamasc Alps Leader: F. Jadoul 4 ed fromJadoul etal.,1994). 27-05-2004, 15:20:10 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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shallowing upward cycles (5 to 25 m thick) which the east in the Lake Idro area (Jadoul, 1985; Lualdi consist of several dm to m-thick peritidal cycles and Tannoia, 1985; Trombetta,1992). The depocenter with Dasycladales and locally tepees, pisoids and shifted from the Lake Idro area towards the Lake Iseo fl at-pebble breccias at the top. This middle part of area, where the Norian succession is about 3000 m the DP is cross-cut by sedimentary dikes, testifying thick (Assereto and Casati, 1965). syndepositional extensional tectonics that will lead to The complete development of the DP carbonate the development of small intraplatform basins. platform during the upper Norian records important The intraplatform basin successions (up to 1000 palaeoenvironmental and geodynamic changes m thick) consist of well bedded, fi ne crystalline, involving the whole western Tethys (Figure 5). The dark dolomites, limestones and rare organic-rich, upper DP in Lombardy exhibits margins colonized by laminated, marly limestones (Dolomie Zonate and peculiar serpulid patch reefs and microbial mounds Zorzino Limestone of the Aralalta Group; Jadoul, associated to thick carbonate breccia bodies (Cirilli 1985; Figure 2 and Stop 1.7). The depositional and Tannoia, 1985; Berra and Jadoul, 1996, Zamparelli processes are dominated by gravity fl ows and et al., 1999; Stops 1.5, 1.6; Figure 4), the development slumpings (Jadoul, 1985). The intraplatform basins of which was controlled by synsedimentary tectonic are interpreted as semigrabens (Picotti and Pini, and high subsidence rates. These peculiar buildups 1988; Jadoul et al., 1992; Trombetta, 1992) generally at the platform margins have been interpreted as exhibiting two margin types (Figure 4): one is an ecological adaptation to restricted and stressed tectonically controlled, the other is a fl exural margin. conditions of the intraplatform basins developed The tectonically controlled margins are located to the during the upper Norian rifting in the westernmost W of the basins in central-western Lombardy, and to Tethys (Cirilli et al., 1999; Fig.5). A relative sea level fall at the top of the DP depositional system is recorded by local carbonate platform progradation, meteoric diagenesis or erosional disconformity documented at the top of platform, together with the fi ndings of herbivorous terrestrial reptiles in the coeval uppermost Aralalta Group (Wild 1989; Stefani et al., 1991; Renesto S., pers. comm.). A change in circulation pattern and nutrient distribution in marine waters could be ascribed to this sea level fall.

2.2. The crisis of carbonate platform deposition and the drowning of the platforms (middle-late Norian). A sudden crisis of the carbonate production, recorded in both the platform and basin facies, characterized the top of the ﬁ rst depositional system. The uppermost Zorzino Limestone (Zo) consists of a few meters of thin bedded, micritic limestones, micro-turbidites with slumpings (Stop 1.7), and organic-rich layers yielding vertebrates (reptiles and ﬁ shes) and invertebrates (crustaceans, crinoids and rare haermatipic corals) (Tintori et al., 1985; Pinna, 1986). The high concentration of organic matter (OM) and well preserved fossils is probably related to low P55 to PW06 n° 6 - from Volume sedimentation rate and anoxic bottoms. Palynological assemblage documents the middle-late Norian Figure 3 - Chronostratigraphy of the Upper Triassic- boundary in this horizon (Figure 3). Lower Jurassic succession in Lombardy based on The carbonate platform succession of structural highs palynological assemblages. 1) Lithostratigraphic units; exhibits lenses of dolomitic breccias, marly dolomites 2) palynological assemblages with selected species; with wood and cuticle remains and locally, a thin 3) palynological phases according to Schuurman (1979) phosphatic hardground at the top. and 4) Morbey (1975).

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Volume n° 6 - from P55 to PW06 P68 - P68 2.4). Thin phosphatichardgroundswithsphalerite, (stratigraphic marker of Valle Imagna)(Stops2.3; (up to18mthick)thatintercalatewithintheshales portion containslenticularmicriticlimestonehorizons are commoninthewhole ARS1. The middle-upper Slumpings andlocally, fossil-richlayers(Stop2.4) marls, muddylimestonesandparaconglomerates. organic richshales,marlyshalesandminordarkgrey The unitmostlyconsistsofblack,thinlaminated present withinthemoresubsidingareas(Figure2). The lower partof ARS (ARS1,0to250mthick)is (middle-late Norian). 2.2.1. The lower Riva diSoltoShale (ARS1) (Jadoul etal,1994). Figure 4-Stratigraphic-palaeogeographicevolution oftheDolomiaPrincipale depositionalsysteminLombardy Leader: F. Jadoul 6 M. Zucco,Catramerio,S.Pellegrino) thatarelocally margins andextend onstructuralhighs(Albenza, Shales ﬁ upwards isdocumented. is quitesimilar:onlyaslightdecreasein AOM content content in ARS andinthelower memberofZu(Zu1) amorphous organic matter(AOM). Palynofacies as sporomorphs,cuticuleandwood remainsandof proportion ofallocthonouscontinentaldebris,such The palynofacies arecharacterizedbyahigh with anoxicbottomanddistallysteepenedramp. locally present. This unitdepositedinrestrictedbasins barite, ﬂ uorite andcelestinemineralizationsare lls thebasinsonlappingonbasin 27-05-2004, 15:20:16 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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characterized by stratigraphic gaps and thin (5 to 15 with oncoids and Megalodontids to well thin bedded cm thick) dark crusts of calcium phosphate, with calcilutites (Zu4 member). The palynological (Figure irregular botryoidal features or fi lling fractures and 3) and foraminiferal assemblages indicate a late cavities (Pizzo Formico). Small mounds composed Norian-Rhaetian age. of serpulids, cyanobacteria, encrusting foraminifers, Dasycladales and problematica document short 2.3.1. The upper Riva di Solto Shale. periods of recolonisation. This unit (ARS2, up to 350 m thick, Upper Norian), This particular lithofacies marks the platform has a greater extension than ARS1 (Figure 2). The fl ooding and may correspond to the basal argillaceous passage from ARS2 to the overlying Zu1 is marked sediments of the ARS1 deposited in the troughs by the increased occurrence of intercalated limestone. (Figure 4). Palynological assemblage refers the ARS1 This defi nition of the boundary (Gnaccolini, 1965) to the middle-late Norian (phase II of Schuurman implies a transitional zone up to 100 meters thick: (1979) and TR zone of Morbey (1975); Buratti et al., due to the general trend of the succession, we 2000). propose to set the boundary at the carbonate bank showing the fi rst evidences of a shallowing trend (rare 2.2.2. Palaeoenvironmental meaning of the ARS1. stromatolites and evaporitic lithofacies) just below a The argillaceous sedimentation of ARS1 marks the Gervilleia rich marker bed. sharp transition with the upper depositional system The ARS2 is characterized by Bactrillium bearing that was probably controlled by climatic changes, such laminated shales, marls, marly limestones and as increased rainfall that favored the fl uvial delivery calcilutites, locally bioturbated and fossiliferous, of fi ne siliciclastics from continental areas. Rivers- arranged in 6 to 30 m thick asymmetric cycles deposited estuaries probably run from Europe to the coast of the on a mid-outer ramp. The fi ne terrigenous sediments Tethyan gulf, where the argillaceous sediments were at the base of the cycle show well-developed parallel trapped in N-S depressions. Carbonate production lamination. Rare paraconglomerates are present at the decreased, as a consequence of the large siliciclastic base of the cycles. Thin bioclastic calcarenites, with infl ux and the decreased salinity, related to the input prevalent pelecypods, often micritised or affected by of large masses of fresh water. microborings commonly intercalate within marls and Deposition of laminated organic rich clays and shales. These layers may record storm wave episodes marls occurred in anoxic sea-fl oors as testifi ed by (Masetti et al., 1989). the abundance of preserved AOM. Sedimentologic The palynological assemblage is referred to the upper and paleontologic data suggest seafl oors located phase 2 of Schuurman (late Norian; Figure 3). below the photic zone in prevalent anaerobic-quasi anaerobic conditions. 2.3.2. The Lower Zu Limestone (Zu1 member) The local co-occurrence of marine and terrestrial (late Norian). fossils in several horizons of this lithozone (Stop The cyclic organization of this lithofacies is similar 2.4) indicates emerged areas (where fresh water to that of ARS2, but for less common black shale was available) close to this basin. Geometry and intercalation and slumpings. This unit (200 to 500 thickness variations of ARS1 inherited the previous m thick) is characterized by the upward increase palaeogeography. Slumpings and paraconglomerate of fossil content and limestone intercalations (7 bodies, with intraformational carbonate clasts, record to 20 m thick). Thin bioclastic lenses commonly bathimetric variations within the basins, presence of intercalate within laminated marls and marly slopes and persistence of synsedimentary tectonics. limestones: bivalves, echinoids and brachiopods are the most common fossils. The microfacies 2.3. The cyclic Upper-Norian-to-Rhaetian consist of bioturbated mudstones, wackestones and carbonate ramps with mixed sedimentation. rare intrabioclastic packstones with foraminifers P55 to PW06 n° 6 - from Volume ARS1 is overlain by 500 to 1500 m of limestone- (Aulotortus spp., Agathammina spp., Glomospirella marls asymmetric cycles showing upward gradual spp. and rare Triasina sp. (in V. Cavallina). In Zu1 carbonate enrichment. This succession is represented of V. Imagna at least two horizons, characterized by by the upper Riva di Solto Shale (ARS2) and the three vuggy carbonates, evaporite pseudomorphs (replaced members of Zu Lmst. (Zu1, Zu2 and Zu3). The lower by chalcedony, celestine and feldspar) and planar boundary with ARS1 is gradual. The upper boundary stromatolites are present. of the succession is sharp, from bioclastic limestones Asymmetric and subordinate symmetric cycles (3-

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Volume n° 6 - from P55 to PW06 P68 - P68 associations ofZu1identifyprevalent low-energy Lithofacies, microfacies andpalynofacies percentage of AOM. and palynomacerals)bymoderatetolow proportion ofcontinentalorganic matter(miospores Palynofacies are always characterizedbyhigh overlie theDP. possible todistinguishthetwo units,thatdirectly Zu1 isgenerallycondensedanditdifﬁ trend. Instructuralhighareasthesuccession ARS2- in carbonateandashallowing andshoalingupward cycles. The upperZu1documentsafurtherincrease and lesscommonbioturbationmarkthetopofsome energy, bio-intraclasticﬂ 4 mupto30thick),arewelldeveloped. High Leader: F. Jadoul 8 Figure 5-LateNorianpalaeogeographyofthe Western Tethys (fromCirillietal.,1999). oatstones withclaychips cult ornot Limestone, Zu2member)(Rhaetian 2.3.3. The middleZuLimestone(lower Coral regional carbonateplatformprogradations. carbonate rampandexported basinward duringthe was producedinsituthemiddle-outerpartof with periodicterrigenousinput.Carbonatemud and carbonatemuddepositionwas stillassociated subtidal environments. Seabottomswereoxygenated organization documentstheevolution ofaprograding In thewestern-centralLombardylithofacies stratigraphic marker 50to100mthick(Figure2). with different facies andthickness, representinga which spreadthroughouttheLombardyBasin Zu2 representsacarbonateplatformsuccession, pp .).

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carbonate ramp from mid to inner conditions. The within the middle part of cycles, and mammillary, stacking pattern of the facies identifi es some major iron-oxide thin crusts (hardgrounds) at top cycles cycles (15 to 20m thick), with shallowing-shoaling often characterize the facies association of the mid- upward trend, locally recorded by peritidal facies ramp in the less sudsiding areas (Albenza) (Stop 3.1). with fenestrae, dolomitized limestones, stromatolites -Zu3c corresponds to the upper (40-50 m thick) and/or oolitic grainstones (Stop 2.5). On structural calcareous part of the succession (second Coral highs carbonates are dominant, whereas in the more Limestone marker) and records the second regional subsiding areas thin marls intercalation persist. carbonate platform progradation (inner ramp facies The dominant subtidal carbonates consist of associations; Stop 3.2) with patch-reefs and local bioturbated mudstone-wackestones, with scattered evidences of meteoric diagenesis at the top (Lakew, coral framestones (mainly Retiophyllia spp.) 1990; 1994). and foraminiferal packstones, baffl estones with Palynofacies from Zu3 contain a high total amount calcisponge and porostromata (Lakew, 1990). of OM. The percentage of continental derived Bioclastic calcarenites locally rich in echinoids are organic debris (miospores and palynomacerals) common at the base of the cycles. is high. An increase in marine OM (dinofl agellate In the most subsiding areas (Val Taleggio and cysts, foraminifer linings and algal spores) is Val Cavallina-Iseo) muddy lithofacies prevail, recorded in the uppermost part of the Zu3c. The documenting the passage to deeper and outer AOM is generally from low preserved to absent. carbonate ramp environment. Both the facies and palynofacies arrangements The shallowing upward trend at the top of the Zu2 indicate general well oxygenated conditions of represents the fi nal progradation of the ramp system, the depositional environment. In such conditions characterized by local dolomitized facies and a the good preservation rate of particulate OM, is disconformity at the top (Stop 2.5). indicative of high sedimentation rate, denoting that The well preserved palynological assemblage the OM can quickly be buried beneath the oxidizing recorded in the marls at the base of Zu2, a few meters water-sediment interface and be preserved also in above a Homomia sp. and Cardita sp. bearing marly well oxygenated conditions. bed, indicate a late Norian-Rhaetian age (Figure 3; The quantitative analysis of palynological Stop 3.1). assemblages from ARS and Zu shows a progressive The two episodes of carbonate enrichment represented upwards increase of xerophytic elements which by the Zu 1 and 2 could be related both to a decreased become dominant in the Zu3. The rapid increase of terrigenous input and to an increased carbonate xerophytic sporomorphs and the decrease in AOM production, probably related to sea level fl uctuations. suggest a shifting towards warmer and probably dryer climate, during the deposition of the upper portion of Zu Limestone. 2.3.4. The upper Zu Limestone and the second The top of Zu3c is marked by a paraconformity (Stop Coral Limestone (Zu3 member, Rhaetian pp.). 3.2) interpreted as a regional drowning unconformity This unit, present in the whole Bergamasc Alps, at the top of the last Zu platform progradation. records a new transgressive-regressive third order cycle developed along a mid-inner carbonate ramp 2.4. The platform drowning at the T/J boundary with fi ne cyclic terrigenous input. Zu3 thickness (uppermost Zu Limestone -Zu4 member- outer ranges from 120 to over 200 m. ramp). Three lithozones have been recognized, each The thin bedded and not cyclic Zu4 member (Stops representing a different evolutive stage of the ramp 1.8; 3.3; 3.5) consists of 15 to 30 m thick prevalent depositional system: micritic limestones, poor in fossils. It represents -Zu3a consists of a 7.5 to 15 m thick marly limestones, a regional stratigraphic marker in the central P55 to PW06 n° 6 - from Volume shallowing and coarsening upward asymmetric cycles Lombardy developed between two shallow water that exhibit local iron-oxides crusts at top of the carbonates units (Zu3 member and CD). At the base carbonate banks and rare evaporitic facies within the bioturbations and slumpings are present, whereas at basal marly horizons. the top oolitic-bioclastic fi ne calcarenites alternate -Zu3b is represented by alternated grey to greenish with mudstones yielding sponge spiculae, rare marls and black marly shales grading to marly radiolaria and small chert nodules. The lithofacies limestones and micritic limestones. Evaporitic facies evolution documents a major transgression with

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Volume n° 6 - from P55 to PW06 P68 - P68 10 packstones andooliticgrainstones. type carbonateplatformconsistsoffi Zu4 (Stop3.4). The upperpartofthisBahamian- the platformshoalsprogradingmargin ontopofthe micrite lithoclastsandbioclasts,whichrepresent of theCDconsistsgrey ooliticgrainstoneswith to over 250mintheLake Iseoarea. The lower part Hettangian. Itsthicknessrangesfromabout100m the LombardyBasin,occurredduringearly regional carbonateplatformprogradationin This unitdocumentsthelastandmostconspicuous 2.5. The earlyHettangianConchodonDolomite. Galli, 2002). at thelower partofthismember(Cirillietal.,2000; the T/J boundary(Figure3)inthemicriticlimestones carried outonseveral sectionsenabledthelocationof CD platformprogradation.Palynological studies created thenecessaryaccommodationspacefor sea level risethatcontrolledthedepositionofZu4 platform environments toward thetop. The relative at thebaseandagradualtransitiontoshallower monotonous outercarbonaterampfacies associations erosional surface separating ARS1 from ARS2 (Valle marker-bed locallycappedbyaparaconformityor boundary correspondstoathickdecametercarbonate overlying thebrecciasattopofDP. The upper boundary, identifyingthetransgressive event with phosphatecrustsmarkthelower sequence On structuralhighsandmargin areas,hardgrounds carbonate productivity (lower boundaryof ARS1). -The fi 80-100 m. frequency cycles, eachwithathickness thatexceed on thebasisoforganization ofIVorderhigh Upper Norian-Lower HettangianofBergamasc Alps Five thirdordercycles have beenrecognizedinthe Conchodon Dolomite(cyclesN3-H1)(Figs.2,15). The Riva diSoltoShale,ZuLimestoneand DP). respectively tothelower-middle DPand theupper of DP(Figure2),cycles N1andN2corresponding transgressive-regressive thirdordercycle atthetop point outapossibleexistence ofasecondregional recognized (Gaetanietal.,1998).Ouranalysis Within thisthickunitonlyonesequencehasbeen The DolomiaPrincipale 3.1. Third ordercycles-depositional sequences (with contributions byM.ClaspsandD. Masetti). 3. Sequenceandcyclostratigraphy Leader: F. Jadoul rst one(N3)begins withthecrisisofDP . n peloidal ne arrangement andawhollycarbonateunitthatmarks carbonate semicoupletsshow ageneralthickening-up composed oflimestone-marlcouplets,wherethe unit (blackshaleormarl);amiddle,rhythmic part thick, areformedbythreeparts:alower argillaceous thickness ofthisordercyclicity. Cycles,3to30m 1989). We willmainlyfocusonvertical patternand to berelatedfourthordercycles (Masettietal., cycles groupedin bundles; such bundles areassumed couplets arearrangedinmeter-scale asymmetric hierarchy (Figure6).Decimeterlimestone-marl upward, subtidalcycles organized inacomposite The ARS2 andZuLmst.consistofthickening- the UpperNorian-Rhaetian. 3.2. High-frequency cyclicity(IVand V order)in lithozones oftheSedrinaLimestone(Gaetani,1970). cycle (sequenceH2)isrepresentedbythethree overlying secondHettangiantransgressive-regressive tepee structureswithpisoids(McRoberts,1994). The carbonate breccias,peritidallimestonesandsmall depositional sequenceislocallycharacterizedby Stand progradation. The regression atthetopofthis lower shallow water CDcarbonatesrecordtheHigh micritic limestones(lower-middle Zu4),whilethe and theCD. The TST isrecognizedinthebasin - CycleH1(100-300mthick)isrepresentedbyZu4 sequence inLombardy. identify thiscycle asthelast Triassic depositional the regional transgressive-regressive trendallow to The welldefi same trendandfacies organization ofN5-R1cycle. - CycleR2(Zu3upto170mthick)presentsthe Hettangian sequencesofthe Western Southern Alps. et al.,1998)betweenthetwo majorRhaetian-Early has beeninterpretedasasequenceboundary(Gaetani capped byadisconformity(Stop3.1). This boundary characterized bytidalfacies andooliticshoals,locally whole Lombardybasin. The topofthecycle is carbonate rampprogradationoftheZu2over the ramp cycles (Zu1),followed bytheregional inner base exhibits thickening upward outercarbonate - CycleN5-R1(Zu1and2,upto350mthick). The type’ facies (Costa-RotaImagna). coarsening upward subtidalcarbonatesor‘evaporitic cycles withprevalent micriticlimestonesandlocally thickening upward shale-marlylimestoneasymmetric a renewed terrigenousinput,whereasthetopexhibits - The N4cycle (ARS2)ischaracterizedatthebaseby indistinguishable fromN4. and tectonicallycontrolled,infact, eastward itis Imagna). CycleN3isprobablyoflocalmeaning ned lower andupperboundary and 27-05-2004, 15:20:24 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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the upper part of each cycle. Cycle tops are usually as common background indicative of the proximity sharp, although they can be locally gradational, of source areas. Dark brownish AOM and large giving rise to a partially symmetric organization of fragments of poorly rounded and sorted inertinite, the cycle (more typical in the Lake Iseo successions). subordinate vitrinite and abundant pyrite dominate The fi fth order cycles (1 to 3 m thick) display an the palynofacies from argillaceous intervals. These inner arrangement similar to the described major palynofacies confi rm oxygen-depleted bottoms. In B- hierarchy. Variations in this general trend are shown type cycles the palynofacies is characterized by minor in Figure 6, according to the depth of the depositional amount of AOM and high proportion of sporomorphs environment. and poorly sorted rounded equidimensional inertinite. The A-type cycle characterizes the deepest portions of In the uppermost part of this cycle a blooming of fungi the basin, corresponding to ARS1 and 2. It is wholly is associated with small fragments of poorly sorted muddy, up to 30 m thick. The lower part consists of and rounded equidimensional inertinite, which reveal black claystones poor in fossils. The middle unit is more oxygenated sea fl oors. This cycle was deposited made by dm-scale laminated claystone/marl couplets, in a low-energy, outer deep ramp environment, where whereas dark micritic limestone with thin marly the shallower sea fl oor allowed the deposition of thin layers represents the cycle top. Occasionally slumps bioclastic storm-layer. and paraconglomerates occur. The depositional The C-type cycle, typical of Zu3b, exhibits a environment can be referred to relatively deep (below coarsening and shallowing-upward evolution. The storm wave’s base) and poorly oxygenated sea-fl oor lower portion of the cycle consists of bioturbated within intraplatform troughs and in the outer-slope marls bearing poor associations of small pelecypods ramp environments. in thin storm layers. The central part is composed The B-type cycle is entirely muddy and differs of an irregular alternation of black marls, yellow/ from A-type on the basis of a higher carbonate/ reddish dolostones with carniola-type breccias shale ratio and of the presence of thin bioclastic and fi ne grained storm layers showing swaley and storm layers. The faunal assemblage evolves hummocky cross-stratifi cation. The upper calcareous upcycle: the basal claystone/marl contains small unit consists of cross-bedded grainstones capped by endobiontic pelecypods, the upper part of the cycle peloidal limestone. These fi ne-grained beds could be is characterized by larger epibiontic pelecypods. interpreted as: 1) inner ramp facies overlying cross- The palynofacies from A and B-type cycles show a bedded sands during the progradational evolution of high percentage of terrestrial allochtonous material the cycle; 2) deeper ramp deposits corresponding to Volume n° 6 - from P55 to PW06 n° 6 - from Volume

Figure 6 - Different 4th order asymmetric cycles of the Norian-Rhaetian succession. Numbers in vertical columns refer to higher frequency cycles.

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Volume n° 6 - from P55 to PW06 P68 - P68 12 suggested approximately10 the uppermostportionoframps. A roughestimate generate coarsening-andshallowing-up cycles in to thebasins. The sameeustaticfl factory andfi exposure oflarge platformareas‘killed’ thecarbonate in accommodationattheplatformtop. A subaerial shallowing evolution andtheconsequentdecreasing in thedeepeningphaseandincreasedduring basinward exportation ofcarbonatemudwas negligible represent carbonatemudproductivity areas. The accommodation atthetopofplatforms,which to eustaticfl Authors, theasymmetriccarbonatesignalwas linked succession previously described. According tothese and Burchelletal.(1990),appliedtothesame B, Figure6)was publishedinMasettietal.(1989) without any coarsening-upward trend(cycles A and The onlyinterpretationofmuddyasymmetriccycles D-type cycles, have beendescribedinseveral papers. composed ofsubtidalcarbonatessimilartoCand Meter-scale, coarsening-andshallowing-up cycles, portion ofthecarbonateramp. and Zu3cdepositedinthemoreproximal,inner This cyclic organization istypicaloftheZu2,Zu3a terrestrial fractionincreases. of marineelementsdecreasesupward cycle, while relative percentagesvary acrossthecycle: theamount amounts ofbothmarineandterrestrialOMwhose intercalated. Palynofacies arecharacterizedbyhigh packstones andcoral-richboundstonesmaybe and locallygrainstones.Intheupperpart,bioclastic entirely characterizedbyfi fi thin marlyinterlayersandbioturbatedorlaminated type, but thelower marlyfacies arereplacedby The D-typecycle the mid-innersectorsoframp. analysis. The depositionalenvironment isreferredto shallowing upward trendasevidenced byfacies preservation rate,whichpointtoananalogous abundance of theorganic constituentsandtheir the cycle. These differences concerntherelative show thatvarious signaturescanberecordedacross up evolution ofthesecycles. Palynofacies parameters coarsening-up trendcanbereferredtoashallowing- cycles. The increasingtempestiteproximality, andthe to anon-depositionalhiatusbetweentwo adjacent and marked byametallicoxidecrustprobablyrelated a retrogradationalphase. The topofthecycle issharp the mentionedmodel,objectives ofthisstudyare magnitude foreachcycle duration.Startingfrom Leader: F. Jadoul ne wackestones\packstones. The cycle isalmost uctuations controllingproductivity and nallystoppedthecarbonatemudsupply shows thesametrendasC- ne tocoarsepackstones 5 yearsastheorderof utain could uctuations DESCRIPTION OF THE OUTCROPS of cycles. of frequenciesratiosbetweenthedifferent hierarchies displayed inapower spectrum,andaregiven interms contribution ofeachsinglesignal. The resultsare several elementaryconstituents,estimatingthe analysis istodecomposetheinputtimeseriesinto thickness timeseries. The mainobjective ofspectral history’. The sequencesofdataheretreatedare axis itispossibletoreconstructtheir‘variance plotting thesevarious data-setsalongthestratigraphic by several parameterscontinuouslyfl et al.,1994).Eachcyclic sequenceischaracterized of spectralanalysismethodologies(ClapsinJadoul periodicities istheapplicationofacompositesystem The mostreliablestrategy inhuntingforMilankovitch stratigraphic sequences. at aglobalscale. Therefore they couldberecordedin in theinsulationpatternandtoinfl perturbations have thepotentialtoproducechanges eccentricity (19-23,41-54,95-123,413ka.). These are theprecession,obliquity, short- andlong-term theory theperturbationsaffecting theEarth’s orbit type ofcyclicity. As illustratedintheMilankovitch eustasy) couldbethedriving forceproducingthis glacio-eustatic variation (like Milankovitch-driven a numberofevidences supportstheideathatperiodic recorded mustbecorrectlyconsidered.Collectively unequivocal deterministiclaw intheway they are frequency cycles. Inparticularthepresenceofan hierarchic patternoftheLateNorian-Rhaetianhigh- the onlymechanismabletogeneratemulti- Composite glacio-eustaticfl tectonic processes,3)Milankovitch glacio-eustasy. includes: 1)autocyclic processes,2)allocyclic The possibleoriginofhighfrequency cyclicity periodicities. (IV and V order):huntingfor Milankovitch 3.3. The originofhigh-frequency carbonatecycles fl the correlationwithfourthorderglacio-eustatic producing thehigh-frequency cycles andtoestimate to evaluate theforcingmechanismresponsiblefor succession. Morning: theshallow-water Corna Trentapassi the DolomiaPrincipale(DP)depositionalsystem. The stratigraphicevolution andfaciesanalysisof uctuations previously proposed. DAY 1 uctuation seemstobe uence theclimate utaig By uctuating. 27-05-2004, 15:20:28 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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About 4 km of walking, with ﬁ ve stops, along the Stop 1.1: abandoned road on the eastern side of the lake. Pleistocene dedolomitization along fractures. This thick succession (about 2 km, Figure 7A, B ) On both sides of Iseo Lake, in correspondence to represents most of the Norian, because intraplatform the valley narrowing between Monte Clemo and basin facies (Zo Limestone) are not developed in the Corna Trentapassi, the DP shows dedolomitized this area. The whole DP outcrops with sub vertical patches. attitude and is interested by pervasive dolomitization, The dedolomitization is interpreted forming in often with late diagenetic recrystallization (sparry different setting: from subsurface-deep burial to white dolomite), Quaternary karstiﬁ cation and subaerial environments (Nader et al., 2003 with dedolomitization phenomena. Slope gravitational wherein references); the proposed model for the deformations and landslides, linked to the retreat of Iseo case points out that dedolomitization process is glacial bodies, are also present (Figure 7). a surface one, that occurred in presence of meteoric derived waters and strictly associated to the advancing Volume n° 6 - from P55 to PW06 n° 6 - from Volume

Figure 7 - The Dolomia Principale of the Corna Trentapassi section (east L. Iseo) with the location of the Stops.

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Volume n° 6 - from P55 to PW06 P68 - P68 14 tectonic have beenre-openedafterwards, allowing the some ofthesefractures,formedduringthelate Alpine group hasa45-50°strike and40°dip.Itislikely that group hasthesamestrike anda45°dip,thethird has 110-120°strike withsubvertical dip;thesecond fractures belongtothefollowing threesets:thefi Both thededolomitizedandnon-dedolomitized on bothsidesofthefracturewalls (Figure8A). width rangesfromfew centimetersuptofew meters color, arestrictlyrelatedtofracturenetworks andtheir The calcitizedpatches,characterizedbyawhite-gray Corbari andBini,2001). to 650-700ms.l.(Pleistoceneglacialterraces, area widespreadfromthelake level (185msl)upward The dedolomitizationisshown alongfracturesinan the valley. and retreatofthePleistoceneglacieronslopes Leader: F. Jadoul Figure 8-Macro(A,B),microfacies(D,E)andgeochemical features ofthe dedolomitizationintheLDP. rst The dedolomitizedfabrics show alteredisotopic (Figure 8D,E). the dolomitedissolutionandcalciteprecipitation boundaries. The processiscomposedoftwo steps: fractures, smallmicrofracturesandcrystal the rockalongpermeableways representedbylarge micro scale:thefl acted inthesameway bothatthelarge andthe observations demonstratedthatthededolomitization sediments withraresmallostracods. The petrographic laminated internalfi cavities, by‘pseudobreccias’ orochre-reddish texture (Figure8B)and,locallyinlarger fractures- and honey/orange calcitecement,aspeleothem-like still beopenorsealedbyathick(upto5cm)withish The fracturesassociatedtodedolomitizationmay dedolomitizing fl uids fl uids percolatedandpermeated ne grainedcalcsiltites-lutites ow in. 27-05-2004, 15:20:32 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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signatures with a shift of the δ13C and δ18O toward produced by the growth of microbial communities more and more depleted values (Figure 8C) in relation which trapped and bound the sediment. The top of to the increase of calcitization (from fabric A to B). the DP Lower Member may consist of transgressive, The presented isotopic values suggest that dolomite intraclastic packstones with rare pelecypods and maintains its DP original signature, while calcite intraformational breccias associated with strata records the signature of the dedolomitizing fl uids deformation. Borings and bioturbations can be locally (typical of a carbonate which underwent a subaerial observed at the top of the mudstone beds. Rhythmic diagenesis). and, locally, cyclic facies arrangement indicate a Radiometric absolute age determination (230U/234Th) shallowing upward trend, with cycle thickness ranging indicates that calcite cements precipitated in the last from several decimeters up to a few meters (Figure 9). 100000 years: age during which the area was subject The depositional environment was prevalent subtidal to several advances and retreats of glacial tongues. with bottoms frequently characterized by anaerobic The fi eld mapping, analytical data and the conditions that were unfavorable to sustain a rich geomorphology of the area, allow us to propose a benthic fauna: only bacterial or algal mounds are peculiar genetic model that involves the presence of present (TOC up to 0,1%). the multiphase advances and retreats of the Pleistocene The observed facies associations, characterizing the Camuno glacier in the area. The morphology of the fi rst development of the DP platform all over the valley is the main cause that allowed the glacier western Southern Alps, document at the Carnian/ to be one of the triggering factors of the extensive Norian boundary environments with anomalous dedolomitization. During glacial periods the presence salinity, probably adjacent to emerged lands, and of the Monte Clemo-Corna Trentapassi straight humid climate. forced the glacier into a gorge causing strong pressure The gradual passage to the DP (the transition zone is along the slopes. This pressure contributed to enlarge about 100 m thick) is marked by the intercalations of some of the fractures in the DP and provided the huge grey-dark grey thick bedded dolomites (prograding quantity of dolomite-undersaturated melting waters. facies of the DP) and the fi ne bioclastic packstones, The pressure fl ux of these waters caused the starting with small thin shell bivalves of the Lower Member. of dolomite matrix dissolution along the fractures and the calcite precipitation. During the interglacial Stop 1.3: periods, the lack of the ice pressure along the slopes The shallow subtidal carbonates of the Middle DP of Iseo Lake caused the opening of the preexisting (Figure 7). fractures, joints and faults. The humid and warm This succession is very thick (over 1 km) climate gave rise to the soils coverings and karst and represented by light grey thick bedded or processes caused the extensive calcite precipitation amalgamated beds of mainly shallow subtidal- along the joints. The glacial and interglacial lagoonal recrystallised dolomites. Beds and lenses environments alternated few times during the of packstones-grainstones with reworked and sorted Quaternary: the restoration of the glacier compression Dasycladales and small bivalves are frequently in the gorge area (last Quaternary glacial stages) may intercalated as well as small Megalodont rich beds has been responsible of the compaction observed on and fenestral, planar stromatolite horizons. some dedolomitized breccia. The bulk of dolomitization of the DP occurred in the early stages of diagenesis and at superfi cial setting. Stop 1.2: In the inter-supratidal facies, dolomitization is related The Lower Member of DP (250-300 m thick) to capillary evaporation and refl ux of marine-derived (Figure 9). fl uids, evaporated on the platform (Frisia, 1991). This dark grey and bedded unit exhibits algal and Most of the subtidal facies dolomitization is also microbial laminites (Figure 9A, C), intercalated with early diagenetic. However, its completion occurred P55 to PW06 n° 6 - from Volume intraclastic packstones and intraformational breccias through several stages, up to burial temperatures over often recrystallised and mudstones (Figure 9A, B) 60°C. Dolomitization of intraplatform basin facies that increase towards the upper part of this Member. occurred by marine-derived fl uids and seems related These dark laminated facies form both laterally-linked to platform-derived, density-driven fl uids. hemispheroids and plane mats several decimeters thick. Microfacies show rhythmic alternation of dense micrite with fi ne fenestral fabric. These crusts are

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Volume n° 6 - from P55 to PW06 P68 - P68 16 (‘pseudo tepee’)affecting bioclastic packstones Zonate), characterizedbyinternalstratadeformations grey intercalation ofwellbeddeddolomites(Dolomie DP). These dikes predatestheﬁ peritidal dolomites(transitionfacies totheUpper dark grey internal sediments(Figure10)cutthe large Medalodonts,smallsedimentarydikes with dolomites richinDasycladalesandlocallywith Above thethreetunnelsand the massive grey (Figure 10). intercalation and thesyndepositionaltectonics facies totheplatform margin, theﬁ The upperDolomiaPrincipale:thetransition Stop. 1.4: Leader: F. Jadoul

Figure 9-StratigraphicsectionwithdetailsoftheLower DP(Stop1.2). rst meterthick dark rst basinfacies sediments becamemorefrequents(Fig.10C). and subvertical sedimentarydikes ﬁ rich inDasycladales.Upward, tensionalfractures Stop 1.5: Within thesefacies, irregular, metersize intraformational brecciasoccuratthetop. geometries. Deformations(slumpings)andchaotic arenite-siltites, locallylaminated,withlenticular intercalation ofdarkgrey, wellbeddeddolomitic massive tothickbeddeddarkgrey dolomiteswith The topoftheCorna Trentapassi sectionshows Principale platform margin (Figure 11). Microbialites and slopebreccias oftheDolomia

lled byinternal 27-05-2004, 15:20:37 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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Figure 10 - Sedimentary dikes and breccias in the Upper DP (Stop 1.4).

bioconstructions are present (Figure 11A, B). They pelecypods) prograding horizon up to few decameters consist of dark, homogeneous microbialitic patches, thick are intercalate. The upper part of the platform often reworked, associated with encrusted breccia margin complex is composed of partially colonized blocks; upward domal, laminated microbialites, few breccias, associated with intra-bioclastic packstones- meters in size, can be observed. The microfacies rudstones and semilithiﬁ ed clasts of Dolomie Zonate of this platform margin succession, interpreted as (Figure 11). The upper DP continues in the Vello area the outer-upper slope portion, are dominated by with the similar margin-slope facies associated to a Spongiostromata bindstones and bioclastic intraclastic thick succession (up to 100 m) of Dolomie Zonate packstones-rudstones to ﬂ oatstones with pelecypods with at the top a new platform margin progradation (mainly Modiolus sp.) (Figure 11C), Dasycladales and represented by microbialitic and serpulid patch reefs, rare benthic, sessil foraminifers (Glomospirella spp., (Berra & Jadoul, 1996), also present on Stop 1.6. Agathammina spp., Tolypammina gregaria). Locally, The stratigraphic evolution of the Upper DP thick grey subtidal bioclastic (manly Dasycladales and corresponds to repeated phases of growth and Volume n° 6 - from P55 to PW06 n° 6 - from Volume

Figure 11 - Details of microbialites and breccias of Upper DP (Stop 1.5).

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Volume n° 6 - from P55 to PW06 P68 - P68 18 of theLake Iseooverlain byavery thickZoLmst.(1 (about 1kmthick)outcroppingonthewesternside succession andcompareitwiththemorereducedDP to observe thepanoramaofCorna Trentapassi Marone toCastro.Duringthenavigation itispossible In theafternoonbyboatwecrossLake Iseofrom succession ofwestern Lake Iseo. Afternoon: The middleNorian-Hettangian related toatectoniccontrolledmargin. biogenic margins, but fortheupperpartthatcouldbe The brecciabodiescouldrepresentthetalusof energy bordersoftheintraplatformbasins. where thebiogenicmargins developed onthelow- whole upperDPdepositionalsysteminLombardy, and associatedpatch-reefsarecharacteristicofthe on theIseobasinalarea. The litho-bioclasticbreccias dismantling oftheDPmargin facies whichprograded Leader: F. Jadoul Figure 12-Mainfeatures oftheDolomiaPrincipalebuildups oftheEasternLake Iseo(Stop1.6). of thelake. setting ofthesedimentarysuccessionontwo side the cruise,itwillbepossibletodiscussstructural km) and ARS (upto1km)(Figure7,12A).During Stop 1.6: The nucleusofsomerecrystallisedoncoidsis features ofDPreefal facies (Figure12B,C,D). decimeter sub-roundedoncoidsarethedominant microbial coatingsandamalgamatedcentimeter- globular, mammillarymicrobiallaminations, thick), concretionary, large (uptometerindiameter) well preserved. Inthisoutcrop(afew tensofmeter dolomitized platformmargin oftheDPisthickand the topofmassive DP(Figure12A)thetypical Along theroadfromCastrotoRiva diSolto,at margin onwestern Lake Iseo(Figure 12). Buildups oftheDolomiaPrincipaleplatform

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represented by small serpulid tubes. mudstones. Upward, two chaotic breccia lenses with Same microbial inter-lamina and the scarce matrix dolomitization phenomena and platform-derived and consist of fi ne to coarse bioclastic packstones basinal clasts record a platform progradation episode with foraminifers, microbial bindstones, serpulids or tectonic instability of the platform margin-slope. and small pelecypods. Late diagenetic silicization Breccias are composed of intraformational and platform phenomena, dissolution cavities and sedimentary margin facies with Porostromata, Spongiostromata and dikes are also present. serpulids. The recovering of the fi ne grained, micritic sedimentation follows. Stop 1.7: The common micritic Zo facies and the adjacent east The basin intraplatform succession (Zorzino Iseo DP margin (Stops 1.5; 1.6) indicate that the eastern Limestone) of western Lake Iseo (Figure 13). slope of the Iseo-Cavallina basin was a prevalent Close to Stop 1.6, above the topmost DP, in a highly fl exure without a huge tectonic escarpment and that the subsiding area, we observe the typical Zo facies fi ne-grained carbonate of the Zo derived mainly from association consisting of fi ne grained well bedded the winnowing of the DP platform. These periplatform (15 to 40 cm thick in average) diluted and mud- muds were exported to the deeper basinal areas along dominated turbidites (Figure 13A) deposited in a this slope. Only locally, coarser deposits derived from basin palaeoenvironment. Only rarely, graded thin the margin were able to reach the deeper part of the calcarenites with small current ripples and laminated basin. marly limestones (up to 15 cm thick) intercalate within

Figure 13 - Stratigraphic section of the Lower Zorzino Lmst. (Stop 1.7) with large problematic structures (A) and dark organic rich laminites (B). Volume n° 6 - from P55 to PW06 n° 6 - from Volume

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Volume n° 6 - from P55 to PW06 P68 - P68 20 Stop 1.8: lamination richinquartsandmicaextraclasts. transgressive marly-siltylevel withparallel Zu4 member(about25mthick)startswitha wackestones intercalate. the base,thinmarlylayers.Bioclasticpackstones- bedded grey micriticbioturbatedlimestoneswith,at The topofZu3memberconsistscycles ofprevalent (Iseo sectionFigure14). cropping outinthewesterncoastofLake Iseo In thisstopyoucanobserve theupperZuandCD Lake Iseo(Figure 14). The Rhaetian-Hettangiansuccessioninwestern Leader: F. Jadoul

Figure 14-StratigraphicsectionoftheT/Jboundary thewestern L.Iseo(Stop1.8). preserved inanhistoricpark. prehistoric artwork (UnescoHeritagesite)are Capo diPonte(Val Camonica)whereimportant After thelaststopinlateafternoon,wewillreach upward trend. calcarenites, withbioturbationandathickening The lower CDischaracterizedbyprevalent oolitic upward limestoneswithbioclasticooliticgrainstones. carbonates (CD)andconsistsofdarkgrey thickening a transitionwiththeoverlying shallow water intraformational breccias. The upperpartrepresent well beddedmicriticlimestoneswithslumpingsand The lower partofthememberconsistsdarkgrey 27-05-2004, 15:20:48 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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DAY 2 fi shes, reptiles and arthropods (crustaceans, insects) The Upper Norian-Lower Rhaetian fi ne siliciclastic of the Zorzino Lmst. and of Riva di Solto Shale and to carbonate high-frequency cycles of the western corals of the Zu Limestone are in the Natural History Bergamasc Alps (Valle Imagna) (Fig.15). Museum exhibit. You can fi nd more details in www. apt.bergamo.it From Lovere to Valle Imagna with the fi rst Stop in the Lunch and a short visit of ‘Bergamo Alta’. old town ‘Bergamo Alta’. Stop 2.2: Stop 2.1: The ARS cycles of the lower Valle Imagna The Norian-Rhaetian collection at the E. Caffi (Figure 16). Museum of Bergamo. Along the Valle Imagna road, near Caschiettino-Ponte During the visit we have the occasion to observe a della Grata, one of the best exposed and complete rich fossil collection, coming from several localities section of the ARS2 crops out. The uppermost DP of the Bergamasc Alps. Wonderful and well-preserved represents the base of the section. Since the deposition Volume n° 6 - from P55 to PW06 n° 6 - from Volume

Figure 15 - Late Norian-Hettangian stratigraphic sketch of the Albenza-V. Imagna ramp depositional system.

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Volume n° 6 - from P55 to PW06 P68 - P68 22 conditions. (Figure 16C),indicative ofrestrictedenvironmental in monospeciﬁ consisting ofdarkshalescontainingthinlayersrich The typicalcycle ischaracterizedbyalower portion depositional environment. clearly referabletoashoaling-upevolution ofthe and donotexhibit anevident coarsening-uptrend The ARS2 fourthordercycles aremainlymuddy in smaller-scale ﬁ 6). Eachfourthordercycle canbefurthersubdivided of 13fourthorderasymmetriccycles (B-type;Figure deposit. The wholesection(about60mthick)consists occurs atthetopofastructuralhigh, ARS1 didnot Leader: F. Jadoul Bactrillium c assemblagesofsmallpelecypods Figure 16- Asymmetric cycles intheRivadiSoltoShaleof V. Imagna(Stop2.2). fth ordercycles (Figure16B). arealsocommon. Toward the associated withlow tomoderatepercentageof Palynofacies aredominatedbybrownish AOM events. some casesthey arecomposedofmany amalgamated often bioturbatedandconsequentlymassive, but in do notshow erosionalfeatures. These layersare in particularthelower contactsofcalcareouslayers boundaries betweenbedsareusuallytransitional,and structures suchasslumpingandloading. The and vice-versa anddeformedbysynsedimentary Thalassinoides) introducinglimestoneintomarls Bedding issometimesreworked byburrows (mainly marls andlimestonesprevail withrespecttoshales. top ofthecycle, limestonesbecomemoreabundant: 27-05-2004, 15:20:54 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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sporomorphs, equidimensional inertinite, dispersed productivity of limestones. During the arid portion spheroidal and angular crystals of pyrite. Diagenetic of the cycle, shales were trapped on the European and weathering pattern are indicative of a primary continent, whereas the normal marine conditions nature of the lithological alternations in the central in the Lombardy Basin favored the production and part of the cycle. accumulation of limestones. The time series (Claps, The palynofacies study of similar cycles in other in Jadoul et al., 1994) show that all the overimposed sections (Laxolo, Valle Imagna) shows a rapid fl uctuations (lithologic couplets, basic fi fth order and decrease in palynomorphs specimen and a blooming fourth order cycles) exhibit a thickening-up tendency, fungal fi laments associated to poorly sorted and which is refl ected in an asymmetric trend. The spectral rounded equidimensional inertinite. The palynofacies analysis permits to discard a stochastic mechanism in variation across the cycle shows a trend from producing the described cyclicity. The studied section disoxic-anoxic conditions in the lower part (testifi ed represents the fi rst case where obliquity is identifi ed by preserved AOM and pyrite) to more oxygenated as dominant over the precession cycle, which so conditions at the top, where the OM is degraded by far has been recognized as the common expression fungi, bacteria and burrowers. of Milankovitch periodicity recorded in supplier Cyclicity seems related to the amount of shale vs. platforms. Considering that the obliquity control is limestones, documenting both an intrabasinal and stronger at the middle latitude and that the Tethyan extrabasinal source of the sediments. According to the gulf was placed more southward, it is possible to fact that limestones are almost absent at the base of suggest that cyclic climatic changes on the European the cycle and shales are absent at the top, it is possible continent (passage from arid to humid conditions) are to recognize that the mechanisms that controlled the refl ected in the Tethys gulf due to the periodic input of cyclicity was able to control both the extrabasinal shales and fresh waters. input and the intrabasinal carbonate production. It is therefore possible to suggest that the delivery of shales Stop 2.3: was probably related to humid conditions which The upper ARS1 of the Ponte Giurino quarry favored the transport of fi ne-grained terrigenous (Figure 17). material from the European continent to the Tethyan Along the Valle Imagna road, close to Stop 2.2, we gulf via fresh water. This was able to lower the can observe a different ARS succession, separated by salinity in the Lombardy Basin preventing a large a fault from the previous one. Volume n° 6 - from P55 to PW06 n° 6 - from Volume

Figure 17 - The ARS1/AR2 boundary at Ponte Giurino (Stop 2.3).

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Volume n° 6 - from P55 to PW06 P68 - P68 24 remains andinertinite. pyrite and,inthelightones,anincreaseoffungal which oftenmasksthesporomorphs,associatedwith the darklaminaeanenrichmentin AOM (upto60%), each of7-9laminae.Eachlight-darkcoupletshows in palynofacies fromthisinterval show cyclic pattern, are describedin A-type cycle (chapter3.2). The thick) (Figure17D). The organic matteranalysis and planararrangementofthelaminae(1to20mm limestone successionischaracterizedbyrhythmic angle unconformity. The overlying marlyand Imagna Valley thisboundaryisalsomarked byalow (boundary ARS1/ARS2). Inotheroutcropsofthe exhibiting smallintraformationalbreccialenses is characterizedbyaparaconformity(Figure17C) paraconglomerates arepresent. The topofthecycle marly interlayers.Nearthetopfi by monotonousdarkgrey mudstoneswiththin marker in Valle Imagna)(Figure17A)represented m thickmicriticcarbonatehorizon(stratigraphic The topofthecycle ischaracterizedbya17to20 covered bylaminatedmarlsandmarlylimestones. slumpings (Figure17B)andlarge claychips, out. The baseconsistsofblackshales,marlswith ARS1 andtheboundarywith ARS2 arecropping A thick A- typecycle (Figure6)atthetopof Stop 2.4: of insects( fi and gliding fi the mostcommonfi and Pholidophopleuriformes(Zambelli,1986)are 1993), rarepelecypods andisopods.Pholidophoridae Brasca, 1984),decapods(Garassinoand Teruzzi, a richfauna consistingofcrustaceans(Arduiniand dark mudstonesatthetop.Shalesandmarlsexhibit structures (Figure18B),andtobedded,laminate marly, laminatedlimestones withlarge slumping and marls(Figure18A)whichpassupwards to base weobserve fossiliferous,laminatedshales association ofan A-type cycle (Figure6). At the exhibits well-beddedandlaminatedlithofacies m above theboundarywith DP. The outcrop sulphurous spring(few minuteswalking), about60 This StopisintheBrunonelateral Valley nearthe (Figure 18). The fossiliferous ARS1 atPonte Giurino the E.Caffi emerged lands.Fossil collection hasbeenvisitedin and lepidosaursindicatethepresenceofadjacent Leader: F. Jadoul shes have beenrecovered (Tintori, 1982).Findings Birgeria shes (Tintori andSassi,1992), Museum(Stop2.1). Italophlebia gervasuttii)

are lesscommon.Raredurophagous shes, whereas predators,suchas ne matrix-supported ne , afl yn reptile ying Saurichthys , southwards. carbonate sourcewas probablylocatedwestwards or the questionabouttheirsourcearea. We inferthatthe in thestudiedareas. The presenceofmudstonesposes to amid-innercarbonateramphave notbeen recorded on adistalcarbonateramp,althoughtransitionalfacies deposition onagentleslope. They couldbedeposited trends. The structuresfromthebaseofcycles indicate evidences ofshallowing orcoarseningupward The whole ARS successionlackssedimentologic carbonate productivity. environment, whichledtoaregional crisisin c1ay (‘argillaceous event’) inthedepositional of the ARS1 andbythepresenceofabundant high sedimentationratedocumentedbythethickness supported bysedimentologicalevidence suchasthe can berelatedtoaclimatehumidifi the signifi (Buratti etal.,2000). The freshwater infl conditions forthedepositionoforganic richshales to anoxicenvironments, providing thenecessary to anintensifi particles andlow-density freshwater. These factors led continental runoff bringinglarge amountsofterrestrial This event was probablyrelatedtoaperiodofhigher by thepresenceoffresh-water alga with aconsistentfreshwater contribute, asconfi lands provided agreatnutrientsupplyassociated emerged areas adjacenttothebasins. The emerged The localpresenceofterrestrialfossilsindicates the fl water columnmusthave hadoxygenenoughtosustain fl 1992). Despitethecompleteanoxiarecordedatsea anaerobic toquasi-anaerobic;BottjerandSavrda, bottom conditions(oxygen-relatedbiofacies from surfaces recordingshortperiodsofpoorlyoxygenated rare anellidsandbioturbationcharacterizeafew bed with afaint slopeandanoxicbottoms.However, and palynofacies associationsarethereforeconsistent rate andtoanoxicbottoms. The biofacies, lithofacies amount ofOMcouldberelatedtohighsedimentation depositional environments thepresenceofgreat of relative proximityofthesourcearea.Insuch sporomorphs, cuticleandwood remains,indicative proportion ofcontinentalderived fragments,suchas Palynofacies aredominatedby AOM andbyahigh Buratti, 2002). Zone, 1975,mid-lateNorian)(Burattietal.,2000; upper partofSchuurman’s phaseII(Morbey’s TR assemblage (Figure3)whichreferredtothemiddle- The upperpartof ARS1 yieldedapalynological oor, theperipheralpartsofbasinandupper ourishing benthonicandnektoniccommunity. cantpresenceofhygrophiticpalynomorphs ed water stratifi cation andlow disoxic cation. This is also Pediastrum une and uence 27-05-2004, 15:21:01 rmed . THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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Figure 18 - The ARS1 section of Ponte Giurino ( Stop 2.4).

Stop 2.5: association which records the Norian-Rhaetian The Norian-Rhaetian transition and the fi rst transition (Figure 3). The overlying bioturbated Rhaetian carbonate platform (Zu2) of Brumano limestones at the top of the cycles yield corals, (higher Valle Imagna) (Figure 19). brachiopods, crinoids and foraminifers, phosphate P55 to PW06 n° 6 - from Volume Along the Rota Imagna-Brumano road the whole Zu clasts and quartz grains. Limestone succession crops out. The visit focuses on The Zu2 is characterized by a sharp decrease of the the fi rst, thick Rhaetian carbonate platform (Zu2). fi ne siliciclastic content (Figure 19). Three minor The Zu1-Zu2 transition (Stop a, Figure 19) consists subdivisions can be recognized within the Zu2 of meter to decameter marl-limestones cycles. Marls carbonates. contain large pelecypods (Homomia sp., Cardita a) Lower Zu2: the platform succession is characterized sp., Trigonia sp.) (Figure 19A) and a palynologic by a 18 m thick, shallowing upward and, in part,

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Volume n° 6 - from P55 to PW06 P68 - P68 26 Leader: F. Jadoul Figure 19-TheNorian-Rhaetiantransitionandtheplatform progradation(Zu2)oftheBrumanosection(Stop2.5). 27-05-2004, 15:21:05 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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coarsening upward carbonate cycle (D-type cycle) DAY 3 consisting of mudstones-wackestones and associated The upper Rhaetian carbonate ramp cycles, the Retiophyllia spp. patch reefs at the base. Bioclastic Triassic-Jurassic transgression and the Hettangian packstones with sponge, echinoids, Microtubus carbonate platform (Mt. Albenza). sp., Porostromata and foraminifers (among which Triasina hantkeni; Figure 22) and mudstones On the private road of the Italcementi Quarry (Stops overlying fi ne breccias are more common at the top 3.1; 3.4) and on the Valcava-Torre dei Busi road (Stop b, Fig 19). (Stop 3.5) in the Mt. Albenza (from 1000 to 1115 m) b) Middle Zu2: it is characterized by intra-bioclastic it is possible to observe in two different sections the packstones with fenestrae, covering marly limestones uppermost Triassic-lowermost Jurassic succession with chert nodules and interspersed corals. Towards of the Bergamasc Alps, represented by the upper the top of this part of the succession, the trend is still Zu (Zu3 and Zu4 members, about 150 m thick) and shallowing and coarsening upward and the facies the lower Hettangian CD. The Rhaetian/Hettangian commonly consist of intra-bioclastic, foraminiferal boundary, still matter of a controversial debate, is packstones, bioclastic storm-layers and oolitic here documented in a marine succession. grainstones. Cross laminations and wave ripples are A clear assessment of the Triassic/Jurassic (T/ quite common. J) system has been hindered by the scarcity of c) The upper Zu2 (Stop c, Figure 19): it consists of continuous marine sections spanning the Rhaetian/ two major shallowing and coarsening upward cycles Hettangian (Hallam and Wignall, 1997). This is (D-type) with bioturbated mudstones and wackestones why the T/J boundary is better defi ned in continental at the base and, upward, bioclastic packstones, oolitic settings (Kent and Olsen, 1999) but remains a matter grainstones and rare stromatolitic bindstones. Small of debate in marine sections (i.e. Hesselbo et al., 2002 Porostromata colonies and associated bioclastic lenses and references therein). with brachiopods (Rhaetina gregaria) characterize the base of the prograding oolitic shoals. Erosional Stop 3.1: surface (Figure 19B), cross bedded calcarenites and The Rhaetian marly-carbonate cycles of the upper small sedimentary dikes are also present near the Zu Limestone (Zu3 member) (Figure 20). top of this unit that is partially dolomitized (last 6-7 Along the private road of the Italcementi quarry the m) and show a regressive trend responsible for the Zu3-CD Albenza succession is well cropping out. development of a discontinuity with fi ne, bioclastic The cyclic Zu3 member consists of three different breccia pockets and oolitic grainstones at the top lithofacies associations: Zu3a, mainly represented by (Figure 19C). D-type cycles, Zu3b exclusively with C-type cycles The overlying Zu3 records the recovery of marl- and Zu3c characterized by D-type cycles (Stop 3.2). limestone cycles (Zu3a) (Figure 19D). The fi rst cycle The lower succession (Zu3a) is composed of 7.5 to 15 is still transitional, with prograding oolitic shoals at m thick marly limestone asymmetric cycles (IV order) the top. The arrangement of the overlying asymmetric exhibiting bioturbations and local iron-oxides crusts cycle differs in the minor fossil content and for the at top of the carbonate banks. predominant laminated mudstones, dolomitized marls In the middle part of the succession (Zu3b; and ochre, vuggy marly limestones (C-type cycles). Figure 20) cycles are thinner (2.5 to 8 m thick) These represent the lower Zu3 facies which will be with fi ner siliciclastics and lacking evidences of observed in detail on Stop 3.1 shallowing or coarsening upward trend. At the The facies evolution of Zu2 illustrates a general base they are characterized by grey and dark grey shallowing trend related to the prograding carbonate marls with pelecypods (i.e. Rhaetavicula contorta) ramp system on the Imagna-Taleggio depression and Bactrillium. Laminated or bioturbated marly Volume n° 6 - from P55 to PW06 n° 6 - from Volume (Figure 15). The eustasy-controlled shallowing trend bioclastic limestones (echinoids, ostracods, crinoids, also allowed the development of inner-middle ramp brachiopods) containing phosphatic and quartz grains facies on the Albenza-Imagna sector (top of the intercalate within the marls. Bioclastic and oolitic succession) and local subaerial exposures. thin storm layers (Figure 20C) characterize the lower- The overlying, cyclic lower Zu3 facies record a middle part of the carbonate intercalations. Oolites progressive crisis of carbonate production in the ramp exhibit iron oxide rims. A few cycles at the middle system polluted by terrigenous input (Figure 15). part of the succession are characterized by carniole-

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Volume n° 6 - from P55 to PW06 P68 - P68 28 Leader: F. Jadoul Figure 20-Italcementisectionwithcyclicityandmacrofacies ofLower-Middle Zu3(Stop 3.1). 27-05-2004, 15:21:10 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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Figure 21 - Italcementi section and macrofacies of the upper Zu3 (Stop 3.2).

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Volume n° 6 - from P55 to PW06 P68 - P68 30 Zu3b). at thetopofseveral asymmetriccycles (Zu3aand hypersaline andrestrictedconditionshiatuses terrigenous-carbonate sedimentationrecordsalso as amidrampenvironment. Inthe Albenza areathis Facies associationofthissuccessionisinterpreted type horizons. xerophytic sporomorphsisrecordedinthecarniole- (tracheids, cuticuleandwood remains). A peakof status, associatedwithotherterrestrialphytoclasts species diversity ofsporomorphsoftenintetrad Palynofacies containhighpercentageand terrigenous sedimentation. crisis ofcarbonateproductivity andtheabruptshiftto surfaces (hardgrounds). These horizonsrecordthe (Figure 20A,B),interpretedasnon-depositional bioturbations andbyiron-oxidemicrobialcrusts the topofthesebeds. Top cycles areoutlinedby with fecalpellets( (Figure 20D,E).Bioturbatedwackestones-packstones rare crosslaminations,ripplesanderosionalsurfaces with fi and inthemiddlepartthey areoccasionallyintercalated Carbonates oftheuppercycles aremainlyfi black shalyintercalations. type marlylimestones,withevaporite molds,and The uppermostZu3member(Figure21A) (Figure 21). progradational carbonatecycles(lithozoneZu3c) The shallow-water, uppermostRhaetian, Stop 3.2: sp.) (Figure21D) (Lakew, 1990). A few coralpatch-reefs( sponges, problematicaandencrustingorganisms (Figure 21E) or bioturbated(Figure21B) packstones-grainstones intercalatedwithlaminated characterized byanincreaseofbiogenicandoolitic progradation incentralLombardytestifi documents thelastRhaetiancarbonateinnerramp the carbonateplatform.Facies organization ofZu3c Zu3c identifi marine conditions. terrigenous pollutionandshallow water normal which banks (Figure21):foraminifers(Aulotortidaeamong The fossilassemblagesarericherinthelastcarbonate spores), refl dinofl Palynofacies show anincreaseinmarineOM(i.e. last cycle (Figure21). Leader: F. Jadoul agellate cysts, foraminiferliningsandalgal ne ooliticandintra-bioclastic packstoneswith Triasina hantkeni ecting highproductivity, low rateof es thesecond,regional progradationof

and oncoidscharacterizethetopof

are presentandlarge Megalodontids Parafavreina ) (Figs.21C,

mudstones-wackestones. sp.) arefrequentat

Thecosmilia 22), corals, ed alsoby ne grained

sulawesiana. sinuosus, D: Auloconus permodiscoides,E:Pilammina hantkeni, B:GandinellafalsofriedliC: Aulotortus gr. Figure 22-Foraminiferal assemblagesofZu. A: Triasina Stop 3.3: western Albenza. succession intheeasternBergamasc areathentothe indicate thepresenceofamorecompletestratigraphic in theeasternarea(Iseosection,Figure14).Itcould marly horizonpresentinthelowermost Zu4member Albenza structuralhigh.Itmaybecorrelatedwitha sedimentation gapatthebaseofZu4memberin by aFe-richhardgroundwhichmayrepresent boundary (Figure23)isoutlinedbyahiatus,marked In thewestern Albenza area,thesharpZu3/Zu4 Italcementi quarry(Figure 23). member) andthe T/J boundaryinthe inactive The transgressive micritic limestones(Zu4 at theendof Triassic. regression couldberelatedtoarelative sealevel fall its shallowing andshoalingupward trend. This

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Figure 23 - Zu4-Lower Conchodon Dolomite in the Italcementi quarry (Stops 3.3; 3.4).

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Volume n° 6 - from P55 to PW06 P68 - P68 32 (3) Malanotteand(4)Iseosection. Figure 25-ChemostratigraphicdatafromMt. Albenza sections:(1) Valcava-Torre deiBusiroad,(2)Italcementi, Limestone (simpliﬁ Figure 24-Foraminiferal distribution intheupperZu Leader: F. Jadoul ed fromLakew, 1990). member didnotreveal any fossilsusefulfor Macrofacies andmicrofacies analysisfromZu4 bryozoans. gastropods, Dasycladales,crinoidsandrare mostly representedbybivalves, brachiopods, reworked ooids,peloids,intraclastsandbioclasts to mudstonespassinggrainstones,containing ostracods andgastropods. They areintercalated packstones withthin-shelledbivalves, crinoids, calcarenites consistingofbioclasticwackestones- underlying intheprogressive upward increaseof 2) The upperpart(Figure23B,C)differs fromthe 23A). Slumping phenomenaarefrequentlypresent(Figure thin intercalationsofintraclastic-peloidalpackstones. crinoids. Bedsurfaces areoftenbioturbatedwith wackestones, withrarethin-shelledbivalves and 1) The lower partconsistsofprevalent mudstones- associations: Zu4 maybesubdivided intwo different lithofacies intercalations decreasingupward (Figure23). scale) grey–dark grey micriticlimestones,withmarly It consistsofthinlybedded(centimetertodecimeter carbonates. Rhaetian fromthelower Hettangianshallow-water marker horizon,upto30mthick,separatingtheupper any evidence ofcyclicity. Itrepresentsastratigraphic Zu4 differs fromtheotherZumembersinlacking 27-05-2004, 15:21:22 THE LATE TRIASSIC-EARLY JURASSIC OF THE LOMBARDY BASIN: STRATIGRAPHY, PALAEOGEOGRAPHY AND

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biostratigraphic correlation. The rich micro- and (Galli et al. submitted) that the C-isotope anomaly macrofaunal assemblages, characterizing the coincides with the end-Triassic biotic crisis and underlying strata abruptly disappear at the top of Zu3 with a widespread carbonate-platform drowning. member (Figure 24). Palynological studies carried out Galli et al. (submitted) argue that a sudden increase

on numerous sections have enabled the location of the in atmospheric CO2 was responsible for the C-cycle T/J boundary in the micritic limestones of the lower perturbation and, consequently, for the marine biotic Zu4 member. crisis at the end of the Triassic. Based on the palynological composition from Zu3 to Lithological features and facies analysis of Zu4 Zu4 and on the fi rst occurrence of Cerebropollenites underline an important relative sea-level rise that macroverrucosus, Cirilli et al. (2000) and Galli (2002) controlled the deposition of micritic limestones all propose to locate the palynological T/J boundary in over the inner-outer Rhaetian ramp system, leading to the Zu4 mudstone succession (Figure 3). a more uniform outer ramp depositional environment. A detailed stable isotope study of the Zu4 document The transgressive event of the Zu4 may be related that this unit exhibits an excellent preservation of the to the well known transgression recognized in the isotopic signal as testifi ed by the reproducibility of data lower Hettangian of the Western Europe (Hallam and in all the investigated sections (Figure 25). A marked Wignall, 1999). negative anomaly at the base of a positive excursion The abundant ooid facies of the lower CD present in has been identifi ed in the Eastern sections (Figure 25). all the Albenza area seems to represent the proximal- Although the sampling density was very high, in the high energy margin of the rimmed carbonate ramp more proximal area (Albenza) the negative excursion that separates the peloidal lagoon facies from the is absent, possibly due to condensation/sedimentary more open subtidal environment. gap and iron mineralization at the top of the drowned carbonate ramp (Lakew, 1990; Jadoul et al., 1994). Stop 3.4: The detailed C-isotope records across the marine T/J The Early Hettangian Bahamian-type platform boundary interval in the Lombardy Basin document (Conchodon Dolomite) (Figure 23). Volume n° 6 - from P55 to PW06 n° 6 - from Volume

Figure 26 - Details of the Zu Limestone-Conchodon Dolomite transition along the Valcava-Torre dei Busi road.

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Volume n° 6 - from P55 to PW06 P68 - P68 34 maintains aproximalramp-typephysiography. carbonate platform(CD)that,inthelower partstill ramp (Zu)was fi fi sequences. The of carbonateproductivity withrespecttotheRhaetian the depositionalenvironment withamajorcontribute sequence) andasignifi 15) (interpretedasthefi new transgressive-regressive thirdordercycle (Figure bryozoans. The Zu4-CDsuccessiondocumentsa Lithocodium fragments,echinoidsandrare are mostlybivalves, brachiopods,Dasycladales, are intercalatedwithpeloidalpackstones.Bioclasts 23D), areprevalent atthebase,whileupwards they ooids, grapestones,lumpsandcoatedgrains(Figure laminations. Grainstonesoftencontainingmicritised intraclast pockets andfrequentcrossherringbone grainstones, withselective dolomitizationandbio- oolitic grainstonespassingupward tofi The lower partoftheCDismainlyrepresentedby 25-30°) cross-beddedooliticbarsofthebasalCD. overlain bytheevident downlapping (withangleof In the Albenza area(Figs.23D,26),theZu4is References cited their stimulatingcollaboration. wish tothankH. Weissert andS.M.Bernasconifor well asProgettoGiovani Ricercatori(M.T. Galli). We IDPA (Milano)andProgettodi Ateneo (S.Cirilli)as Projects ofUniversity ofMilano(ex 60%F. Jadoul), Financial supportwas provided bytheResearch Acknowledgments section have beensummarizedonStop3.3. (Figure 3)andstableisotoperesults (Figure 26B)observed onStop3.4.Palynological transition characterizedbythesamedownlap (25-30°) micritic limestone(Zu4member)andtheZu–CD sharp Zu3-Zu4contact(Figure26A),thetransgressive Jurassic successioniswellcroppingout,showing the altitude) (Figure26)theuppermost Triassic-lowermost On the Valcava-Torre deiBusiroad(about1000min Torre deiBusisection(Figure 26). The Triassic-Jurassic boundaryonthe Valcava- Stop 3.5: meridionale (Lombardia). stratigrafi Assereto, R.andCasati,P. (1965).Revisione della Nat. MuseoMilano genere dellaclasse Thylacocephala. Arduini, P. andBrasca, A. (1984). Leader: F. Jadoul a permo-triassicadella V. Camonica nally replacedbyaBahamiantype ne mixed siliciclastic-carbonate 125,159-163. cant physiographicchangeof rst Hettangiandepositional Riv. It.Paleont. Strat. Atropicaris (Figure 25)ofthis Atti Soc.It.Sci. ne to coarse to ne nuovo 83, (1979). Malossafi Errico, G.Groppi,Savelli, S.and Vaghi, C.G. d’Iseo, BS).PosterFist,Geoitalia2001. Lombardia: ilcasodell’Anfi depositi quaternarinelprogettoCARGdellaRegione Corbari, D.andBini, A. (2001).Lacartografi 21, 79-85. giugno 2000”. delle piattaformecarbonatiche.Modena,13-14 “Crisi biologiche,radiazioniadattative edinamica Bergamasche). Retico-Hettangiano delM. Albenza (Prealpi ed evoluzione paleogeografi A. (2000).Implicazionistratigrafi Cirilli, S.Galli,M.T. Jadoul,F. Rettori,R.andSpina, environments. response ofshelfmargin communities tostressed Rhaetian of Western Mediterraneanarea:ecological (1999). Microbial-serpulidbuildups intheNorian- Cirilli, S.Iannace, A. Jadoul,F. andZamparelli, V. 313-326. platform-basin interactions. the importanceofclimateandeustasyincontrolling Cyclic SedimentationintheSouthern Alpine Rhaetic: Burchell, M.T. Stefani, M.andMasetti,D.(1990). Modena 13-14 giugno2000”. dinamica dellepiattaformecarbonatiche,Modena, (Eds), “Crisibiologiche,radiazioniadattative e di Menaggio(LagoComo). margine ebacino nellaDolomiaPrincipaledell’area e sedimentologicodiunparticolaresistema Cirilli, S.and Tannoia, G.(1985).Studiostratigrafi 816. paleoclimatologiche. occidentale): considerazionibiostratigrafi di Riva diSolto(BacinoLombardo,Sudalpino (2000). Analisi dellefacies organiche nell’Argillite Buratti, N.Cirilli,S.Jadoul,F. Paganoni, A. di Scienzedella Terra, University ofPerugia,187pp. implications. UnpublishedPhDthesis,Dipartimento in theNorthernHemisphereandpalaeogeographic paleoclimatology fromLate Triassic toEarlyJurassic Buratti, N.(2002).Palynostratigraphy and mudrock biofacies. Bottjer, D.andSavrda, C.(1992).Oxigen-related Alps, Italy). Platform Evolution intheLombardyBasin(Southern and MicrobialBioconstructions:Implicationsforthe Berra, F. andJadoul,F. (1996).NorianSerpulids 999-1097. 21,51-56. Facies Terra Nova In Acc. Naz.Sci.Lett. Arti diModena eld, deepdiscovery inPo Valley. A. CherchiandC.Corradini(Eds), 35,143-162. Sedim. Review In Acc. Naz.Sci.Lett. Arti di A. CherchiandC.Corradini 11,195-202. Sedimentology ca dellasuccessione Mem. Soc.Geol.It. teatro Sebino(Lago co-paleoclimatiche 1 , 92-102. 37, 795- ce e che 27-05-2004, 15:21:30 a dei a 30, co In

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“Giant Oil and Gas Field of the decade 1968-1978”. Triassic. J. Geophys. Res. 104, 12,831-12,841. AAPG Mem. 30, 525-538. Lakew, T. (1990). Microfacies and cyclic Frisia, S. (1991). Caratteristiche sedimentologiche sedimentation of the Upper Triassic (Rhaetian) Zu ed evoluzione diagenetica della Dolomia Principale Limestone (Southern Alps). Facies 22, 187-232. (Norico) del Lago d’Idro e delle Dolomiti di Brenta. Lakew, T. (1994). Diagenesis of a Rhaetian reef patch PhD Thesis Dip. Sc.Terra, Milano, 156 pp. (Lombardian Basin, Southern Alps). Riv. It. Paleont. Gaetani, M. (1970). Faune hettangiane della parte Strat. 100, 9-32. orientale della provincia di Bergamo. Riv. It. Paleont. Lualdi, A. and Tannoia, G. (1985). Evidenze di un Strat. 76, 355-442. bacino norico eteropico alla Dolomia Principale in Gaetani, M. Gnaccolini, M. Jadoul, F. and Garzanti, Val Menaggio (Co). Rend. Soc. Geol. It. 8, 37-42. E. (1998). Multiorder Sequence Stratigraphy in Masetti D., Stefani, M. and Burchell, M. (1989). the Triassic system of Western Southern Alps. In Asymmetric cycles in the Rhaetic facies of Southern “Mesozoic and Cenozoic Sequence Stratigraphy of Alps: platform-basin interactions governed by European Basins”, SEPM Sp. Publ. 60, 701-717. eustatic and climatic oscillations. Riv. It. Paleont. Galli, M.T. (2002). Il limite Triassico-Giurassico Strat. 94, 401-424. nelle Prealpi Bergamasche: un approccio stratigrafi co McRoberts, C.A. (1994). The Triassic-Jurassic integrato. Unpublished Ph. D. Thesis, Milano, 99.pp. ecostratigraphic transition in the Lombardian Alps, Galli, M.T. Jadoul, F. Bernasconi, S.M. Weissert, H., Italy. Paleogeo. Paleocl. Paleoecol. 110, 145-166. Anomalies in global carbon cycling and extinction Morbey, S.J. (1975). The palynostratigraphy at the Triassic/Jurassic boundary: evidence from a of the Rhaetian Stage, Upper Triassic in the marine C-isotope record, Palaeo, Palaeo, Palaeo, Kendelbachgraben, Austria: Palaeontographica 152, submitted. 1-75. Garassino A. and Teruzzi G. (1993). A new decapod Nader, F.H., Swennwn, R. and Ottenburgs, R. crustacean assemblage from the Upper Triassic of (2003). Karst-meteoric dedolomitization in Jurassic Lombardy (N.Italy) Paleontologica Lombarda 1, carbonates, Lebanon. Geologica Belgica 6, 3-23. 3-37. Picotti, P. and Pini, G. (1988). Tettonica Gnaccolini, M. (1965). Calcare di Zu e Argilliti di sinsedimentaria norica nel settore compreso tra il Riva di Solto: due formazioni del Retico Lombardo. Lago d’Idro e il Lago di Garda. Rend. Soc. Geol. It. Riv. It. Paleont. Strat. 71,1099-1121. 11, 225-230. Hallam, A. and Wignall, P.B. (1999). Mass extinction Pinna, G. (1986). On Drepanosaurus unguicaudatus and sea level-change. Earth science reviews 48, 217- an Upper Triassic Lepidosausian from the Italian 258. Alps. J. Pal. 60, 1127-1132. Hesselbo, S.P. Robinson, S.A. Surlyk, F. and Piasecki, Schuurman, W.M.L. (1979). Aspects of Late Triassic S. (2002). Terrestrial and marine extinction at the palynology. 3. Palynology of latest Triassic and Triassic-Jurassic boundary synchronized with major earliest Jurassic deposits of the Northern Limestone carbon-cycle perturbation: a link to initiation of Alps in Austria and southern Germany, with special massive volcanism?. Geology 30, 251-254. reference to a palynological characterization of the Jadoul, F. (1985). Stratigrafi a e paleogeografi a del Rhaetian Stage in Europe. Rev. Paleobot. Palynol. Norico nelle Prealpi Bergamasche occidentali. Riv. It. 27, 53-75. Paleont. Strat. 91, 479-512. Stefani, M. Arduini, P. Garassino, A. Pinna, G. Teruzzi, Jadoul, F. Berra, F. and Frisia, S. (1992). Stratigraphic G. and Trombetta, G.L. (1991). Palaeoenvironmental and paleogeography evolution of a carbonate platform of extraordinary fossil biotas from the Upper Triassic in an extensional tectonic regime: the example of the of Italy. Soc. Ital. Sci. Nat. Museo Civ. Storia Nat. Dolomia Principale in Lombardy (Italy). Riv. It. 132, 309-335. Paleont. Strat. 98, 29-44. Tintori, A. Muscio, G. and Nardon, S. (1985). The P55 to PW06 n° 6 - from Volume Jadoul, F. Masetti, D. Cirilli, S. Berra, F. Claps, M. triassic fossil fi shes localities in Italy. Riv. It. Paleont. and Frisia, S. (1994). Norian-Rhaetian stratigraphy Strat. 91, 197-210. and paleogeographic evolution of the Lombardy Tintori, A. and Sassi, D. (1992). Thoracopterus Bronni Basin (Bergamasc Alps): Excursion B1, 15th IAS (Osteichthyes: Actinopterygi): a gliding fi sh from the Regional Meeting, 5-38. Upper Triassic of Europe. Journ. Vert. Paleont. 12, Kent, D.V. and Olsen, P.E. (1999). Astronomically 265-283. tuned geomagnetic polarity time scale for the Late Tintori, A. (1982). Hypsisomatic Semionotidae

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Volume n° 6 - from P55 to PW06 P68 - P68 36 Italy), withrevision ofthegenus. from theUpper Triassic (Norian)ofCene(Bergamo, Wild, R.(1989). Bresciane. di pull-apartesedimentazionenelNoricodellePrealpi Trombetta Lombardy. (Pisces, Actinoptergii) fromtheUpper Triassic of Leader: F. Jadoul , G.L.(1992). Tettonica transtensiva, bacini Atti Tic.Sc.Terra Riv. It.Paleont. Strat. Aëtosaurus 35, 127-137. (Reptilia:Thecodontia) 88,417-442. Riv. Mus.Civ. Sc. Italy: asynthesis. communities intheNorian-Rhaetiancarbonatesof paleoceanographic controlsonmicrobial-serpulids Zamparelli etal.(1999).Paleotectonic and Superiore Pholidophorinae subfamilia nuova del Triassico Zambelli, R.(1986).NotesuiPholidophoriformes. Nat. Caffi Riv. Mus.Cic.Sc.Nat.Caffi 14, 1-24. Palaeopelagos, Sp.Publ. 10,1-32. 3, 1-83. 27-05-2004, 15:21:34 Back Cover: fi eld trip itinerary

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