Rivista Italiana di Paleontologia e Strarigrafia volume 101 numero I pagrne r,/-rb Maggio 1995

ANATOMY OF A SEMIARID COASTAL SYSTEM: THE UPPER CARNIAN OF (ITAIY)

EDUARDO GARZANTI, MARIO GNACCOLINI 8. FLAVIO JADOUL

Key-uords: Semi-arid Fan, Coxtal Plain, Sabkha,/Lagoon, part of the Breno Formation), generally 2OO to 3OO m thick, are Salina, Carbonate Platform, Sandstone Petrography, Climate, Late assigned to the Late Carnian. They respectively overlie lagoonal Carnian, Southern Alps. limestones ( Fm.) and peritidal carbonares (Annunciata Mem- ber of the Breno Fm.), and underlie intraformational breccias and Riassunto. II Carnico Superiore in Lombardia è rappresentato recrystallized limestones (Castro Fm.). Recognition of an unconfor- dalla Lingua di Campolungo (parte superiore della Fm. di Breno) e mity, ascribed to a relative fall of sea-level (sequence boundary), dalla Fm. di . Lo studio di detraglio di questa allowed us to subdivide rhe Upper Carnian succession into rwo successione, potente da 2O0 t 300 m, ha consenriro di identificare 10 p arrs. Iitosomi, car att erizzari da differente I itol ogia, súumure sedimentarie ln the huer part (SGBL), six lithosomes were recognized. e composizione mineralogica, e di ricostruirne la geometria e il si- Red to green alluvial clastics in the south-east and sourh-west pass gnificato ambientale. La Fm. di San Giovanni Bianco viene qui sud- northward to mixed terrigenous-carbonate coastal sediments and fi- divisa in due parti (SGB1 e SGB2), separate da una discontinuità nally to dolostones deposited in carbonate tidal flats. In rhe proxi- maggiore, interpretata come dovuta a un abbassamento relativo del mal sections of the Prealps, renewed north-westward pro- livello del mare (limite di sequenza). gradation of alluvial redbeds with intercalated calclirhite conglomer- Nella parte inferiore della Fm. di San Giovanni Bianco ates points to a stage of teconic uplift. A distinct increase in quartz, (SGBl) sono stati riconosciuti sei litosomi. Arenarie e peliti da verdi representing a regional petrographic marker followed all across a rosse, accumulatesi a sud-ovest e a sud-est, passtno verso nord a Lombardy, indicates deepening of erosion into the metamorphic sedimenti costieri misti rerrigeni-carbonatici e infine a dolomie de- wallrocks of rhe volcanic belt. A major hiatus at the top of the poste in piane carbonatiche peritidali. Una significativa attività retto- SGB1 is best documented in the northern Presolana area by a sil- nica è testimoniata, nelle sezioni più prossimali delle Prealpi brescia- crete crust directly overlying the Julian Annunciata Member of the ne, dalla progradazione verso nord-ovest di facies rosse continentali Breno Formation. In the Brembana Valley area, the discontinuity con intercalati Iivelli lentiformi di conglomerati ricchi di frammenti occurs within a greenish siliciclxtic coastal plain succession, and di rocce carbonatiche. Un netto aumento di quarzo derritico rappre- may be traced at the top of a marker interval of inrerbedded reddish senta un marker regionale, che può essere correlato attraverso le siltstones and sandstones. Prealpi lombarde e documenta I'approfondimento dell'erosione a in- The upper part (SGB2) consisrs of four lithosomes. Greenish taccare il basamento dell'arco magmatico posro a meridione. Una sandstones and siltstones, accumulating in coastal plains in the lacuna importante al tetto dell' SGBl è documentata, nell'area della south-west, passed northward to mudrocks and dolostones. In the Presolana, da un paleosuolo siliceo che ricopre direttamente il Mem- southernmosl Camonica Valley area, mudrocks are locally inter- bro dell'Annunciata della Formazione di Breno, di età Julica. In Val bedded with calcarenites containing bored or pedogenized lithoclasts Brembana, la discontinuità cade all'interno di una successione clasti- ripped from the underlying sequence and varied bioclasts, restifiying ca di piana costiera, e viene tracciata al tetto di un livello guida to relatively open shallow-marine conditions during rransgression. ceraflerrzzato da arenarie e siltiti rosse. Next, thick gypsum accumulated in coasral salinas barred by locally La parte superiore della Fm. di San Giovanni Bianco (SGB2) oolitic platform carbonates to the north. Rare sandstone lenses oc- comprende quattro litosomi. Arenarie e siltiti verdi, accumulatesi in curring in the Brembana Valley at the top of the unit conrain exclu- piane costiere a sud-ovest, fanno transizione verso nord a peliti e sive rhyolitic detritus, indicating either a terminal phase of explo- dolomie. In meridionale, alle peliti sono inrercalare sive volcanism or erosion of older felsic volcanic Droducrs. calcareniti fossilifere di mare aperto che contengono anche litoclasti perforati da organismi e pedogenizzati, strappati alla sequenza sot- tostante durante Ia rapida trasgressione. In seguito, notevoli spessori Introduction. di gesso si accumularono in saline costiere sbarrate a nord da piatta- forme carbonatiche spesso oolitiche. Alla sommità della formazione The Carnian Stage in the Lombardy Southern in Val Brembana, rare lenti di arenaria conrengono detrito riolitico Alps is represented by several terrigenous to carbonate esclusivo, documentando l'erosione di ignimbriti più antiche o, in units deposited in deltaic, lagoonal and carbonate pe- alternativa, una fase terminale di vulcanismo esplosivo. ritidal environments (Garzantí & Jadoul, 1985; Gnac- Absrract. The mixed terrigenous-carbonate-evaporitic S.Gio- colini, 7987; Gnaccolini & Jadoul, 1988). The upper vanni Bianco Formation and dolomitic Campolungo Tongue (upper part of the Carnian succession, underlain by lagoonal

Dipartimento di Scienze della Terra, Mangiagalli 34, 20133 Milano, . 18 E. Garzanti, M. Gnaccolini & F. Jadoul

limestones (Gorno Formation) or by peritidal car- uppermost Gorno Fm. - Campolungo Tongue; SGBI), bonates (Annunciata Member of the Breno Formation; and on sequence C4 (upper S. Giovanni Bianco Fm.; Gnaccolini & Jadoul, 1-99a) and overlain by the in- SGB2). The SGB1/SGB2 sequence boundary occurs rn traformational breccias and recrystallized iimestones the Camonica Yalley area at the top of the Cam- of the Castro Formation (iadoul et al., 1992b), is poiungo Tongue peritidal dolostones (Fig. t). In Val characterrzed by largely unfossiliferous, mixed ter- Supine (section 7 ìnFig. 1), it corresponds with sharp rigenous-carbonate deposits and iocally by evaporites. transition to richly fossiliferous calcarenites. In the These rocks, reaching a maximum thickness around southeast, the boundary is thought to occur at the top 350 m (average 170 m), and tentatively ascribed to the of the 150 to 2OO m thick lower part of the S. Late Carnian according to their stratigraphic position Giovanni Bianco Fm., charactertzed by red mudrocks (Allasinaz, 1968a), are known in the geologic literature (Zone; section 15 in Fig. 1) and sandstones with inter- as S. Giovanni Bianco Formation and Campolungo calated pebbly conglomerates (Val Nozza; section 16 Tongue of the Breno Formation after the work of in Fig. 1) and corresponds to a strong decrease in Assereto & Casati (1965). grain size of largely dolomitized sandstones inter- Only local sedimentological or petrographic fea- bedded with poorly exposed mudrocks. In the west, tures have been analyzed in these rocks (Assereto, in the Brembana Valley area, the discontinuity has 1965; Casati & Gnaccolint, 1967; Garzantr, 1985 a,b, been traced at the top of a reddish silty to sandy interval 1986, 1988). A detailed regional analysis has never in the middle part of the S. Giovanni Bianco Formation. been completed so far, also due to discontinuous out- This unconformity can be traced also north of crops and alpine deformations, which are concentrated the study area, in the Presolana thrust sheet (Fig. 1). in this incompetent décollement horizon (De Sitter & Here a carbonate platform succession corresponding to the Annunciata Member of the Breno Fm., contain- De Sitter Koomans, 1949; Gaetani & JadouI, 1979; Laubscher, 1985). ing several tepee horizons and yielding cephalopod The purpose of the present paper is to provide faunas ascribed to the Julian (Allasinaz, 1968a), is for the first time a detailed and up-to-date physical capped by a silcrete profile (Rodeghiero, 7977) docu- stratigraphic frarnework for the Upper Carnian succes- menting a prolonged hiatus. This emersion surface is sion, and to reconstruct the paleogeographic evolution overiain by dark pelites passing upward to alternating of Lombardy through facies and microfacies analysis. grey perrtidal dolostones and greenish peiites, con- sidered as Gorno Fm. by previous authors but here ascribed to the upper S. Giovanni Bianco Fm. (SGB2). Strati graphic f ramework The SGB2 sediments are overlain by a unit of thick recrystallized limestones and collapse breccias, pointing to carbonate deposition on a very unstable The 550 up to 900 m thick Carnian succession substratum (Castro Fm. of et al., 1992b), fi- of central Lombardy (Southern Alps), arranged in east- Jadoul nally transgressed by the Dolomia Principale car- west trending belts (Brusca et a1., tltz), has been re- bonate platform. cently subdivided into four depositional sequences (Gaetani et. al., 1995). The first sequence (C1), repre- sented by peritidal carbonates (Breno Fm. and Calcare Physical stratigraphy and lithofacies description. Metailifero Bergamasco; Assereto ef al., 1977), is overlain by the Gorno Fm. marly limestones, passing laterally to \fithin the two depositional sequences repre- the Val Sabbia deltaic sandstones in the south (Gnac- sented in the Upper Carnian succession of Lombardy, colini, 1983, 1986) and to the Breno Fm. peritidal car- 10 intertonguing lithosomes have been recognized and bonates in the north (second sequence, C2). After a bio- traced Iaterally, in order to reconstruct their geometri- oo-caicarenitic tongue documenting a major event of cal relationships. Lithosomes are physically expressed carbonate platform progradation in the middle part of by characteristic lrthofacies associations, which will be the Gorno Fm. (Gnaccolini & Jadoul, 1990), open described in detarl here below. Overall, 21 lithofacies lagoonal limestones to mixed terrigenous-carbonate have been recognized; their concise description and shallow-bay sediments continued to be deposited in sedimentological interpretation are given in Table 1. the third sequence (C:), which is capped by peritidal dolostones in the north-east (Campolungo Tongue at Lower S. Giovanni Bianco Fm.- Campo the top of the Breno Fm.), and by prograding alluvial lungo Tongue (SGB1). fan to coastal plain and lagoonal sedirnents in the south- east and south-west (lower S. Giovanni Bianco Fm.). Six lithosomes have been recognized within this In the present paper, we will focus on this upper interval (Fig. t). These are described below from bot- part of sequence C3 (lower S. Giovanni Bianco Fm. - tom to toD. UWr Carnian coastal system L9

12 -fi2uatueno 4.1"\' .J .o$' N oPs' l -r' / F--t\ ,.q\' / qv'-1rè- / -2 I VIII ,/o 10 LC / a

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Conglomerate

Sandstone - --- Pelite - * Marl -7----7 Dolostone SGBl T*-tr Limestone

mA = Annunciata Member gr"no Pelitic interbed I>Eà LC = Campolungo Member.J ""' """..- Carbonate breccia FAult SGB : S. Giovanni B. Fm. Tepee structure * Sequence GO = Gorno Fm. ""'""' GYPsum boundary AVS = V. Sabbia Sandstono &ffi "Carnioulo" t-X Litlìosonìos AVS

Fig. 1 - Fence diagram showing vertical and lateral relationships between lithosomes recognized in the Upper Carnian succession (upper part of sequence C3: SGBl; sequence Ca: SGB2) of the Lombardy Southern Alps. Location of measured stratigraphic sections is shown in inset(1 :S.Pellegrino;2:;3:S.GiovanniBianco/ValTaleggio;4:Brembella;5:Valtorta;6:Val Riso;7:Val Supine; 8, 9 : Colle di Vareno; 10 : Castello Orseto; 11 : Rifugio Albani; 12 and 13 : inferiore; 14 : ; 15 : Zone/Casere;16 : Val Nozza). Lithofacies characterizing Lithosomes I to X are summarized in Tab. 1.

Lithosome | {transition with the underlying Gorno Fm.). most Gorno Fm. lagoonal deposits and is overlain by Alternating sandstones, mudrocks and subordi- terrigenous Lithosome II (Brembana Valley). nate dolostones represent the transition with the un- Lithofacies: derlying Gorno Fm (Fig. 2); thickness ranges from 25 53) up to upper fine-grained, grey-green, parallel to cross- m (Val Supine; section Z) about 36 m (Brembana to laminated sandstones locally with scoured base (up to 2 m thick

Valley; section 3). Lithosome I passes laterally to top- interv a1 s); 20 E. Garzanti, M. Gnarcolini G F. Iadoul

LITHOFACIES DESCRIPTION DEPOSITIONAL CODE SETTING

Channellized exraformational conglomerates. Channel deposits; ,:ximal fan. C2 Red to grey-greenish intraformational conglomerates, with rough cross-bedding. Channel, bank farlure; alluvial fan.

S1 Medium to coarse-grained red sandstones, mostly with scoured base and trough Channel; alluvial fan. crosslamination, locally with epsilon cross-stratification.

S2 Fine-grained reddish sandstones, locally channellized and with low-angle or par- Crevasse to levee; distal alluvial fan. allel lamination.

S3 Fine to medium-grained grey-green sandstones, with trough to low-angle or Channel; distal alluvial fan to coastal parallel lamination, locally with scoured base. plain.

S4 Thin-bedded, very fine-grained grey-green sandstones with parallel ro current Overbank, flash flood; coastal plain. ripple laminations.

S5 Greenish-grey, very fine to fine-grained sandsrones with wave ripples. \flave-reworked delta front.

P1 Reddish siltstones to shales, locally containing nodular caliches. Floodplain.

P2 Grey to bright green siltstones to shales, locally with parallel to ripple lamina- Interchannel; coastal plain. tion and dolomitic concretions.

P3 Dark grey mudrocks, locally with fine laminarions. Prodelta.

D1 Dark grey dolostones (dolomitized mudstone to intra-bioclastic packstone). Restricted shallow lagoon. D2 Light grey dolostones in rhin single beds intercalared in prwailing P2 lithofacies Ephemeral pond ro srorm layers; (dolomitized mudsrone ro oo-intra-bioclastic grainstone). coastal plain.

D3 Light grey dolostones and marly dolostones, locally fossiliferous andlor biotur- Shallow lagoon. bated, in thin to medium beds separated by peliric drapes (mudstone to bio-in- traclastic pachstone).

D4 Grey stromatolitic dolostones, locally displaying fenestrae andlor small tepees Carbonate tidal flat. (bindstone to intraclastic packstone).

D5 Grey dolostones with vugs locally filled by reddish internal sediment and white Shallow hypersaline lagoon, possible sparry dolomite (wackestone to intra-bioclastic packstone). local emersions.

D6 Grey, thick-bedded oolitic dolostones, locally with crosslamination (dolomitic Oolitic bars; shallow carbonate plat- to oo-intraclastic arainstone). form. D7 Thin-bedded, dark-grey dolostones with dark chert nodules (bindstone to fine Restricted shallow lagoon. packstone).

LDl Dark-grey biocalcarenites, locally with scoured base and containing pedogenized Shallow marine, transgressive. lithoclasts; locally dolomitized (mainly biolithoclastic packrone to rudstone). tnî Grey limestones, locally dolomitized (bio-intraclastic wackestone ro packstone). Subtidal carbonate platform.

G Laminated gypsum, with discontinuous dolosrone drapes, locally intercalated 5alrna. with stromatolitic dolostone. Frequently deformed and recrystallized.

Diagenetic and tectonic microbreccias, with dolomitic and subordinately pelitic clasts.

Tab. 1 Brief description and sedimentological diagnosis for the 21 lithofacies recognized in the LJpper Carnian succession of the Lombardy Southern Alos.

54) very fine to fine-grained, faintly laminated grey-green Depositional environments. sandstones in beds a few cm thick, intercalated with predominating Sedimentological features restify a deltaic en- siltstones; to 55) thin beds of very fine to fine-grained greenish-grey sand- vironment. Terrigenous lithofacies document deposi- stones, locally separated by drapes of dark mudrocks, displaying tion by fluvial currents (S3, 54) entering a lagoon and small symmetrical ripples and rarely dark mudclasts (intervals up to locally interacting with waves and tidal currents (S5). over 2 m thick); P2) grey to bright green silrstones ro shales, locally with Lagoonal lithofacies are represented by dark mudrocks faint lamination; and carbonates v/ith faunal assemblages typical of the P3) dark grey mudrocks (from a few cm to over 1 m thick), Gorno Fm. (P3, D1). locally laminated or containing plant material; D1) dark grey fossiliferous dolostones in 5 to 60 cm thick beds, commonly associated with lithofacies P3. \fholly dolomitized Lithosome ll (sandstones and mudrocks of the Brembana intrabiocl astic packstones, locally b ioturbated, showing prism crack Valley). and containing pelecypods (Myopboia sp.), crinoids, gastropods, os- This 100 best tracods, foraminifers, dasycladacean algae and coated grains, predom- up to m thick clastic wedge is inate. developed in the middle Brembana Valley (sections 1 Upper Carnian coastal systent 21

SECTION 3 SECTION 3 SECTION 15 SECTION 1ó LITHOSOME LITHOSOME LITHOSOME LITHOSOME I II m UI

Facies Faciss Facies Facies cod6 cod6 cod6 code P1 P3/S4 s2 P2t34 s3 P1 P3/S4 P2tg4 P2 s3. s5 P2tS4

P2 P1 P3tD2/54.

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P1 P2 D,I/P3 <. s3/s2 s3 P3/S4 P2

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P3/S4 S2

P1

P3/D 1 P1 q2 P3 s2 S3 P2 s2tP1 ,.,<. P1 P2 P2 ^^ o2 P1

S2 Pl

P1 P1

I ostracods P hydrozoans o ooids q dasyclad algae .'. forams a fenesîrae P pofostromata \l bioturbations T dessication cracks s spongiostromata parallel lamination A:47 water escape strucÎures stromatolites /K. cross lamination O vugs - O oncolites à Currenl rlpples @ dolomiticconcretions b gastropods .& wave ripples @ white sparry dolomite Fig. 2 - Key sedimentologic logs / pelecypods decreaslnggrain-size (ò caliches show typical lithofacies asso- I ciations for Lithosomes I, II Ò crinoids v groove casts , \ tepee sîructures and III. For location of sec- I brachiopods - - clay inîraclasts ,,w erosional surface tions 3, 15 and 16 see Fig. 1. O corals large carbonate diagenetic/tectonic microbreccias ^a. intraclasîs Ò&Òtr and 3). It gradually thins to 40 m towards the north Lithofacies: and north-east, where finer-grained lithofacies prevail C2) grey-greenish intraformational microrudites with rough cross-bedding and oversized mudclasts, associated with up to coarse (upper Brembana Valley: section 4; Yal Riso: section sand-sized siliciclasts (up to 1 m thick lenses). Reworked caliche 6). Some 80 m of alternating sandstones and mu- nodules are locally abundanr; drocks, passing rapidiy to 0 northward, also occur in 53) fine to rarely medium-grained grey-green sandstones with Val Supine, where they represent the distal part of faint trough to subordinately low-angle and parallel lamination (up to 3 m lenses, locally with scoured base). One bed intercalated Lithosome III (Fig. 1). Lithosome II is bracketed be- within mudrocks shows flute casts. Carbonaceous fragments, leaves tween the underlying Lithosome I and the and up to decimetric plant logs are locally found associated with SGB1/SGB2 sequence boundary at the top, and is clay chips. Paleocurrents are mostly towards the ESE (100 to 1300N) in the Brembana Valley (Fig. 3C). Pelitic or rarely Iaterally replaced north-eastward by dolostones and dolomitic intraclasts up to 10 cm in size were locally observed; mudrocks of Lithosomes IV and V. dolomitic concretions up to some dm in size occur; 22 E. Garzanti, M, Gnaccolini G F. Iadoul

:'$,,,

,'ijj;"r:',1 f

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Fig. 3 Proximal to distal lithofacies associations in the Upper Carnian. Phoros arranged from SGB1 alluvial redbeds (A,B), to SGB1 - lower SGB2 sabkha,/lagoons (C to F), to upper SGB2 salinas (G,H) and oolitic shoals (I). A) Lenticular channellized conglomerares and cross-bedded sandstones (arrows; Lithosome III, section 16; L. Crepaldi srands by Cl bed in Fig. 2); B) red overbank mudrocks with thin crevasse-splay) sandstones (Lith. IIi, sect. 15; black arrow points to scoured base of thick S1 interval in Fig. 2); C) sharp-based green sandstone with sole casts (arrow; base of Lith. II, sect. 3; rule for scale); D) green siltstones cyclically alternating with grey dolostones (Lith. VII, sect. 12; rucksack for scale); E) septaria-like dolomitic concrerions within green siltstones (Lith. IV, sect. 5; lens cap for scale); F) stromatolitic dolostones with centimetric embryo tepees (Lith. V, sect. 8); G) deformed whire gypsum layers interbedded with dark grey stromatolitic bindstones. Boundary between D4 and G lithofacies in lower right corner enlarged in H) (Lith. [X; quarry; hammer for scale); I) sharp boundary between Lith. VIII and thickening-upward carbonate rycles of Lith. X (sect. 14 in Fig. 1). Upper Carnian coastal system ZJ

54) mainly fine-grained grey-green sandstones, with parallel in the south when deposition of the S. Giovanni Bian- (1 10 to current ripple lamination and local groove casts, in thin to co Fm. began. Rare and thin cherty dolostone interca- cm) beds intercalated with predominating siltstones; lations (Dz) point temporary tidal sabkha P1) reddish silrstones to shales (top SGB1 marker interval to flat to increasing westward in thickness from 9-i13 m between S. Pelle- sedimentation on the coastal plain. grino and S. Giovanni Bianco to over 30 m in Vai Taleggio; sections In the middle ?art of the lithosome between 1 and 3), with rarely interbedded fine-grained sandstones and abun- S. Pellegrino and S. Giovanni Bianco (Fig. 4), large- dant dolomitic concretions up to 40 cm in diameter; scale, wedge-shaped and up to lower medium- P2) grey to bright green siltstones to shales, locally with faint laminations or plant material (intervals from a few cm to 15 grained channel-fills are ascribed to scouring of the m). Coalescent dolomitic concretions up to 40 cm in size are com- coastal plain by ephemeral streams. Intraformational mon, as well as authigenic pyrite; caliche-arenite lenses are particularly abundant at S. D2) light grey dolostones in thin to medium beds (a few to Pellegrino. Reddish lithofacies P1 found at the top 30 cm) intercalated within lithofacies P2, locally with well- of the lithosome was seemingly the result of pro- developed mudcracks or chert nodules. Oo-intraclastic packstones with rare pellets, foraminifers (lagenids), ostracods and relatively longed subaerial exposure. common siliciclasts prevaii over rarely bioturbated mudstones. Authigenic bipyramidal quartz or feldspars grew in small cavities or Lithosome lll (redbeds of Val Nozza). replaced carbonate to evaporitic minerals. About 180 m thick reddish sandstones and mud- rocks yielding caliche and/or dolomitic concretions Depositional environments. with intercalated conglomerates crop out in the east- Most common in the Brembana Valley are ern part of the study area (Zone to Sabbia Valley). lithofacies 53 and P2, which alternate in 1 to 5 m The base of Lithosome III lies in Val Nozza (section thick fining-upward cyclotems, locally with sharp 16; Fig. 3A) within a thick wedge of continental base (Fig. 2). Mudrocks prevail several sec- scoured in redbeds, and can be detected mostly on petrographic tions. Lithofacies distribution points to semi-arid grounds (see paragraph on sandstone petrography); at coastal plain environments, representing the distal toe Casere (section 15; Fig. 38) the lithosome follows of alluvial fans passing northward to paralic and (stratigraphically?) 30 m thick dacitic pyroclastics and marginal-marine tidal settings. Channel areas are docu- extraformational microbreccias with angular dolomitic mented by fining-upward (S3 +P2) cyclothems, pebbles, in turn overlying, with faulted and covered whereas mudrocks are Dredominant to exclusive in in- contact, the karstified top of Ladrnian Esino dolo- terchannel areas. stones. The top of Lithosome III, poorly exposed or In the lower part of the lithosome, thin-bedded somewhat faulted, would correspond with the and up to lower fine-grained sandstones intercalated SGB1/SGB2 sequence boundary overlain by widely with mudrocks and locally displaying flute or groove dolomitized siltstones and very fine-grained sand- casts are interpreted as flash floods in coastal plain to stones (Lithosome VID. North-eastward of Zone, paralic environments (Fig. 3C; these structures were Lithosome III interfingers with the top of the Gorno ascribed to turbiditic flows by Assereto, 1965). Abun- Fm. and with greenish sandstones and mudrocks alter- dant plant material (Equisetaceae and conifers; A. Pa- nating with yellow dolostones on both sides of the ganoni, pers. comm. 1994), found both in the Brem- Camonica Valley (Toline and Vai Supine; Lithosome II). bana Valley (between S. Pellegrino and S. Giovanni Bianco; Asscreto, 1965) and in Val Supine (north of Lithofacies: Lovcrc), indicatc that vcgctarcd cmcrgcd lands existed Cl) channellized extraformational conglomerates containìng light to dark grey subrounded carbonate cobbles (median diameter 3 cm; maximum diameter up to 13 cm) and subordinate red chert and green volcanic pebbles (0.4 to 1 m thick; Fig. 3A); C2) lenticular intraformational microrudites with reworked caliche and red to greenish mudclasts up to 20 cm in size (thickness 0.2 to 1.3 m); S1) medium to coarse-grained red sandstones, mostly with base and trough cross-lamination indicating \lN\l-ward E:4 cz + s3 Liîhoracios . - Pàlitic intrsclasts scoured paleocurrents in the Nozza section, commonly containing dolomitic t--.-ll:l S3 Lithofaci€s a € Dolomitic concretions clasts, reworked caliche and red to greenish mudclasts up to 9 cm in size (thickness from A.7 to 3.5 m, exceptionally reaching 6 to 10 m); t- P2 Litholacies -'I 52) commonly dolomitized fine-grained reddish sandstones, locally channellized and with Iow-angle to parallel Iamination, in Fig. 4 - Channel-fiìl deposits ascribed to wadi-type ephemeral medium beds (5 to 25 cm) intercalated with reddish siltstones (P1) streams migrating periodically on a coastal plain (coarser (intervals up to 3.3 m thick); middle part of Lithosome II; SGB1 in type section 3 at S. 53) grey-green sandslones with grey mudclasts; Giovanni Bianco). Direction of sediment transport is away 54) thin-bedded very fine-grained greenish sandstones, locally from the observer. Drawing from photo. with concretions, interbedded with greyish pelites (P2); 24 E. Garzanti, M. Gnmcolini G F. Jadoul

P1) red siltstones, commonly containing caliche nodules thin dolostone intercalation (D:) was observed at Mal- (paleosoil profiles may be up to 1 m thick) or dolomitic concretions paga. Much coarser-grained deposits with respect to up to 60 cm in size (intervals,0.15 to 2 m thick in Val Nozza, reach Lithosome II, abundant red colours ,nd widespread up to 6 m and may be burrowed at the top at Casere; Fig. 3B); caliche nodules deposition in semi-arid allu- P2) grey to greenish pelites; testify to D3) impure grey calcareous dolostone (0.15 cm). vial fan settings.

Depositional environments. Lithosome lV (mudrocks and dolostones of the Camonica Main lithofacies are 52 and P1 (Fig. 2). Com- Valley). monly channellized lithofacies S1 (replaced or under- Lithosome IV, characterized by greenish mud- lain by C1 or C2) marks the base of poorly-defined rocks (P2) with intercalated grey dolostones (D3) and fining-upward cyclothems, mostly 4 to 6 m thick (bet- thin layers of (tectonic?) carbonate microbreccias with ter defined and reaching 12 m at Casere). Only one pseudomorphs of evaporites ("carnieules"; Ca), is

SECTION 7 SECTION 9 SECTION T4 Facies code D6/D1

F.82 (t) Facies 6 cods F. J

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Key sedimentologic logs P3. show typical lithofacies asso- Lithosomes IV, D3/D5 ciations for 9a VI, VIII and X. For location D 1 /D3/P3 of sections 7, 9 and 74 see [.' F8; Fig. 1. J P2 Upper Carnian coastal systent 25 poorly exposed from Val Riso (Z m; secrion 6) to Vai Lithosome Vl (dolostones). Supine (:O m; section Z) (Fig. 5). In Valtorta (about 60 Lithosome VI (Campolungo dolomitic Tongue m; section 5), thin sandstones (S3, 54) and greenish of the Breno Fm.; sections 8 to 14) decreases in thick- mudrocks (Pz) with septaria-like dolomitic nodules ness along the middle Camonica Valley from a maxi- (Fig. :E) are intercalated with vuggy or concretionary mum of about 90 m in the north, where it overlies grey dolostones (D5) rn 2 to 6 m thick cyclothems. the calcareous Annunciata Member of the Breno Fm.. Lithosome IV, which is capped by the to 0 in the south, where it both overlies and passes SGBl/SGB2 sequence boundary, was probably laterally to the more pelitic Lithosomes IV and V deposited in coastal sabkha/lagoons interfingering (Fig. t). Lithosome VI is capped by the SGB1/SGB2 with aliuvial fans (Lithosomes II and III) to the south, sequence boundary. and with the Campolungo Tongue peritidal dolostones (Lithosome VI) to the north. Lithofacies: P3) dark grey dolomitic mudrocks mainly in up to 15 cm Lithosome V (dolostones with thin mudrock intercalations). thick beds: Dl/D3/D4) grey Lithosome V, reaching a maximum thickness in to locally dark grey dolostones, in up to 1 m thick beds. \fholly dolomitized intrabioclastic packstones yield- Val Riso (70 m; section 6) and at Colle di Vareno (40 ing ostracods, Porostromata, Spongiostromata, dasycladacean algae m; sections 8 and 9), consists of thin-bedded (a few to and subordinately foraminifers, prevail over locally intercalated 20 cm) dolostones cyclically alternating with greenish- fenestral stromatolitic bindstones. Authigenic quartz occurs in both grey to dark grey siltstones and shales in generally early and late cavities and fractures. thin (but exceptionally up to Z0 cm) intervals. It over- Depositionai environments. lies Lithosome I and is replaced laterally by Litho- Dominating lithofacies D3 (Fig. 5) indicates the somes II and iV p.p.; it underlies arenaceous Litho- seaward part of the shallow lagoons to tidal flats also some II to the south and dolomitic Lithosome VI in represented by Lithosome V. the north (Fig. t).

Lithofacies: Upper S.Giovanni Bianco Fm. (SGB2). P2) light srev ro ereen siltstones and shales in a few mm to 70 cm thick beds, locally laminated or containing dolomitic concre- Four lithosomes have been recognized (Fig. 1). tronst This sequence can be in turn subdivided in a basal P3) dark grey to black mudrocks in a few mm ro 20 cm part char acterìzed mixed thick bedsr by carbonate-terrigenous sed- D3) mainly light grey dolosrones in thin to medium beds (a imentation (Lithosomes VIi and VIII) and a carbonate- few to 30 cm) separated by mudrock drapes. \lholly dolomitized evaporite upper part (Lithosomes IX and X), which packstones with intraciasts, bioclasts and pellets prevail; Porostro- marks a sharp reduction in terrigenous detritus re- mata, Spongiostromara, ostracods, rare dasycladacean algae and lo- corded Lombardv Prealps. cally foraminifers are common. Bioturbation is frequent. Authigenic all over the quartz and feldspars grew in fractures and cavities, possibly ar the expense of carbonate to evaporitic minerals; Lithosome Vll (mudrocks and sandstones of the Bremba- D4) grey stromatolitic dolostones in medium beds (15 25 to na Valley). cm), locally displaying centimetric embryo-tepees (Fig. 3F). Bind- stones alternate with burrowed inrraclastic packstones, rarely yield- In the Brembana Valley (sections 3 and 4), ing ostracods and Porostromata. Borh early and late Èactures are Lithosome VII mainly consists of green to greenish- commonly filled by authigenic quartz and felspars; grey mudrocks (P2). Up to lower medium-grained D5) grey dolostones in up to 30 cm thick beds with abun- dant vugs, locally filled by reddish internal sediments and white greenish grey sandstones with oblique to parallel lami- coarse dolomite spars. Microfacies are similar to D3. nation and pelitic to dolomitic intraclasts (S:, S+; up to 50 cm thick intervals, exceptionally reaching 3 m) Depositional environments. locally occur at the base of frning-upward cyclothems. Dolostones prevail (mainly D3), with greenish Dolomitic concretions up to 35 cm in size grew in mudrocks (P2) rhythmically intercalated. Up to 90 cm greenish siltstones (P2) full of pyrite in well-deveioped thick lenticular intervals containing gypsum and pentagonal dodecahedrons. In Val Nozza (section 16), dolomitic or pelitic ciasts (Ca) may be interpreted as at least 40 m thick altered reddish dolomitized sand- early diagenetic evaporitic-collapse breccias, even stones (S2), alternating with reddish to grey-greenish though they are commonly associated with along-bed siltstones with yellowish concretions (P1, P2), impure tectonic deformation. Lithofacies associations point to dolostones (D:) and intraformational conglomerates a sabkha/shallow iagoon, passing laterally ro car- (C2), pass upward to poorly exposed weathered mud- bonate supratidal-intertidal flats only episodically rocks and finally to the evaporites of Lithosome IX. reached by fine-grained terrigenous detritus from the Lithosome VII, about 50 m thick, occurs only in south. iouthernmost sections. where it overlies reddish clas- 10 E. Garzanti, M, Gnarcolini & F. Jadoul tics capping the SGB1 (Lithosomes II and III); laterally it passes to mudrocks and dolostones (Lithosome VIII). The upper boundary is never well exposed. Lithofacies are, in order of decreasing abun- dance, P2, 53, 54, P1, 52 and C2, suggesting deposi- tion on an arid coastal plain passing northwards to marginal marine environments.

Lithosome Vlll (mudrocks and dolostones of the Seriana- Camonica Valleys). Grey-greenish to locally dark grey siltstones and shales (a few cm to 9 m thick intervals) alternate with thin beds of light to dark grey dolostones, locally amalgamated in up to 8 m thick intervals (sections Z to 14; Fig. 3D). Locally bioclastic dolostones gradually become prevalent northward (Val Supine: section Z), Fig. 6 - Coarse bioclastic packstone with scattered radial to con- whereas they are replaced by the terrigenous Litho- centric ooids (o) and coated grains. Open marine fossils some VII in Val Nozza and Brembana Valley (Fig. 1). include abundant echinoderms (e), sponges (s), brachiopods Bioturbated marls and dolostones are dominant in (b), pelerypods (p), sessile and benthic foraminifers (f) (lithofacies LD1; base of Lithosome VIII at Valle Valtorta, where rare beds of very fine-grained carbo- dell'Orso, Val Riso area). natic sandstones display north-dipping crossJaminae. Along the Camonica Valley, Lithosome VIiI Layers rich in varied bioclasts occurring at its base in overlies Lithosome IV in the south (Val Supine) and Val Supine and Valle de1l' Orso (Val Riso area; LD1) Lithosome VI in the north; where the upper boundary locally document storm events in more open and rela- is exposed, it is overlain by evaporitic Lithosome IX tively deeper environments with normal salinity (Fig. or calcareous Lithosome X. Maximum thickness is 6). Even a few halobids were observed at Dossena about 35 m (Colle di Vareno; sections 8 and 9). and, further to the west, nautiloids ("Nautilus" brem- banus; identification by M. Balini, 1993) were found Lithofacies: in at , in beds presumably belonging P2) grey to green siltstones and shales, locally with large dolomitic concretionsr to Lithosome VIIL P3) dark grey marls and siltstones with ripples or parallel lamination; Lithosome lX (evaporites). DL/D3/D4/D5) dark to light grey dolostones. Vholly dolomitized, burrowed intraclastic packstones, rarely containing Up to 100-200 m thick evaporitic successions ooids and bioclasts, prevail over stromatolitic bindstones locally crop out from the sourheastern (Auro: section 16; with tepees; small Lovere and Toline: between sections 7 and 15) to the Dz) dark grey dolostones in thin (2 r.o 20 cm) beds separated by black clay drapes and clayey micritic dolostones locally with up northwestern (Dossena: section 2; S. Brigida: section to 30 cm thick bands and nodules of black chertl small concordant 5) parts of the study area. In the rare relatively con- sedimentary dykes with brownish internal sediments occur. Typical tinuous exposures, Lithosome IX is seen to overlie microfacies are bindstones with Spongiostromata and fine-grained Lithosome and pass lateraliy carbonatic burrowed packstones with ostracods. Lithofacies D7 occurs only in VIII to to the northern part of the Camonica Valley (and further to the north- Lithosome X. Post-depositional deformation, due not east in the Brenta Dolomites); only to alpine tectonics but probably also to dehydra- LD1) locally dolomitized bioclastic calcarenites in lenticular tion during burial, is cxtensive. beds with scoured base, locally showing fining-upward grain size and parallel to ripple lamination. Bio-intraclastic packstones and wackestones yielding crinoids, brachiopods, foraminifers (Auhtortus Lithofacies: praroide, Aulotortus gr. sinuosus; determinations by R. Rettori, i994; D3/D4) light to dark grey dolostones in up to 1 m thick Involutinidae), corals (Isastrea), sponges, hydrozoans?, dasycladacean beds. \flhoily dolomitized packstones with ostracods and Porostro- aigae and ostracods predominate; bioclastic rudstones with locally mata, locally thin laminae of burrowed mudstones and bacterial pedogenized or bored lithoclasts, mudclasts, phosphates, quartz and stromatolitic bindstones occur (Fig. 3G); micas occur in Val Supine (section 7); G) evosum in mm-thick deformed micronodular laminae al- Ca) up to 50 cm thick carbonate microbreccias are locally ternating with discontinuous dark grey limestone to dolostone even metric horizons con- intercalated. Several of these, occurring in drapes (Fig. 3H); anydrite was observed in a core drilled by ANAS taining iarge clasts and associated with thrust surfaces, are tectonic ar S. Pe)legrino (and as reìict in the Lovere quarry). in origin.

Depositional environments. Depositional environments. Lithosome VIII represents the distal part of the Thick gypsum was deposrted in a strongly subsi- Va1 Nozza and Brembana Valley coastal plain (Fig. 5). dent evaporitic lagoon, extending from east to west Upper Carnian coastal system 27

across the study area and barred to the north by the above an about 20 m thick interval of olivine basalts, locally oolitic carbonates of Lithosome X. in red sandstones and siltstones with interbedded channellized caiclithitic conglomerates and thick Lilhosome X (limestones and calcareous dolostones of paleosoils with caliche to ferriferous nodules (30 to 45 the Camonica Valley). m). A much sharper break occurs in the overlying Lithosome X widely crops out in the north- dolomitized redbeds, about 180 m thick, where con- eastern part of the study area (sections 7 to 14), where sistently more quartzose compositions are recorded it overlies Lithosome VIII (Fig. 3I) and passes upward (proximal part of Lithosome III: Q15 F23 L62).If the to the commonly tectonized intraformational lime- latter of these two petrologic intervals (both mapped stone breccias of the Castro Fm. (]adoul et al., tltzb). as Val Sabbia Sandstone in the Foglio "Breno" of the Due to extensive cover, lateral transition to Litho- geologic map of ltaly) can be ascribed safely to the S. some IX can only be hypothesized according ro srrari- Giovanni Bianco Fm. (SGB1) on both sedimentologic graphic position. and petrographic grounds, correlation of the former Lithosome X consists of irregularly alternating with the Gorno Fm. remains rentative. Iimestones to dolomitic limestones, in a few cm to The over 100 m thick redbed succession exposed about 2 m thick beds locally separated by thin pelitic at Casere/Croce di is similarly ascribed to the intercalations. Dolomitization is more extensive in the S. Giovanni Bianco Fm. (distal part of Lithosome III: north-east (northern Camonica Vailey to Adamello Q13 F3Z L50). To the west, a similar trend is docu- Group; Gaetani, 1986). Maximum observable thick- mented in Val Supine, where the Gorno Fm. (Qto ness is about 30 m. F59 L31 n= 1) passes gradually upward to the S. Giovanni Bianco Fm. (distal part of Lithosome II: Lithofacies: Q1s F43 L42). P2/P3) dark to greenish-grey dolomitic mudrocks, locally In the western part of the study area (Brembana with parallel lamination or pyrite, in a few to 60 cm thick beds Valley; Bergamo intercalated with carbonate lithofacies; alluviai fan), detrital quarfz increases D3/D4/D5) light grey, locally stromatolitic dolostones (simi- from the Val Sabbia Sandstone (Q6 F36 L59 n: 39; lar to those of Lithosome V); sequence C2) to the Gorno Fm. (Q10 F44 L45 n: 3). D6) grey dolostones (oolitic to oo-intraclastic grainstones) in These sandstones are already markedly enriched in up ro 2 m thick beds, locally displaying megaripple cross-lamina- pumiceous lithics and in basement-derived qlJartz tlon i grains (Garzanti, 1985b, rncreases LD2) grey recrystallized limestones and dolomitic limestones fig. 6, 7). Quartz in dm- to m-thick beds. Bioclastic wackestones yielding ostracods, further from the transition with the S. Giovanni Bian- foraminifers, Spongiostromata and dasycladacean algae are locally as- co Fm. (Lithosome I: Q11 F36 L53) to rhe prograding sociated with intraclastic to bioclastic (pelecypod) packstones. coastal plain green sandsrones of the SGBl (proximal part of Lithosome II: Q15 F32 L53), and reaches a Depositional environments. maximum in green sandstones interbedded up to rhe Lithofacies D3 and D5 prevail at the base of top of the SGB2 (Lithosome ViI: Q18 F25 L57; Litho- Lithosome X, whereas lithofacies LD2 e D6 gradually some VIII: Q22F50 L27). Petrographic data for the S. become predominant parr; dolostones in the upper Giovanni Bianco Fm. are resumed in Table 2. prevail in the northern part of the study area (Fig. 5). Tectonized breccias containing large clasts of various underlying lithofacies are associated with thrust sur- Depositional setting faces at the top of the S. Giovanni Bianco Formation. Lithosome X is inferred to represenr a mainly subtidal Detailed three-dimensional reconstruction of carbonate platform. previously described lithosomes, their lateral relation- ships and environmental significance, allowed us to envisage a sequence of varied depositional scenarios. Sandstone petrography

Lower S. Giovanni Bianco Fm. - Campolungo Tongue In the eastern part of the study area (Sabbia Val- (sGB1). ley to Zone; Brescia alluvial fan), the Carnian succes- sion is mostly represented by continental redbeds. At The proximal southern areas of the Lombardy about 5OO+550 m from the base of the Val Sabbia Prealps were characterized by alluvial fans, prograding Sandstone, detrital modes show a subtle change, with towards the ESE in the west and towards the \lN'Sl transition to slightly more quartzose compositions in the east. They are best documented in the Brescia (from Q6 F33 L62 n= 76 in sequence C2, to Q9 F31 area, where continental redbeds, up to conglomeratic L60 n= 7). In Val Nozza this change is recorded at Nozza, extend f.or 20 km toward the north-west 28 E. Garzanti, M. Gnaccolini & F. Jadoul

Tab.2 - Sandstone petrography for Lithosome Environment Locality F/F +L the clastic lithosomes recog- ntzed rn rhe 5. Giovanni Bian- SGB2 co Formation (methods and parameters afrer Dickinson, VIII Prodelta/Lagoon Valtorta 2 22 50 27 0.65 1970, and Zul[a,1985; data VII Coastal plaìn S. Pellegrino 2 18 37 45 0.45 after Garzanti, 1985a; Cre- V[ toe of Alluvial fan Val Taleggio 5 18 27 62 0.25 pa)di, l99O; Tosoni, pers. comm., 1994), Detrital quartz SGBl increases primarily with time, from : 11 at the base of IV Prodelta Val Supine 4 75 43 42 0.51 Q the SGBI to Q : 22 in rhe II Alluvial fan San Pellegrino 7 74 37 54 0.36 SGB2. F,/F+L ratio is instead (green beds) S. Giovanni 15 JI JJ 0.38 II Bianco 11 largely controlled by deposi- n distal Alluvial fan Casere 1 13 37 50 0.42 tional environments, increas- n proximal (redbeds) Val Nozza 7 75 23 62 0.27 ing laterally both in the SGBl I Coasta) plain S. Giovanni Bianco 7 11 36 53 0.40 and SGB2 from proximal to distal settings.

(Lithosome III). The eastern toe of a second fan, prob- north (Valtorta; section 5). Deposition of coarsening- ably represented by redbeds poorly exposed around and then fining-upward regressive alluvial facies Lecco, is recognized in the middle Brembana Valley {Garzanti, 1.986, ftg. 3) took place landward of the (Lithosome II), where it rapidly passes eastward to bayline during the late highstand stage, when the rate paralic and shailow iagoonal settings (Fig. Z). of accomodation deveiopment decreased and the equi- These semi-arid fans reached a coastal plain epi- librium point moved seaward (Posamentier & Vail, sodically scoured by ephemeral streams, forming an at 1988). Prolonged subaerial exposure eventually charac- Ieast 7 km (Camonica Valley) to about 10 km (Brem- terized the coastal plain at the top of the SGB1 bana Valley) wide belt extending from east to west (marker horrzon of red mudrocks in the Brembana across the Bergamasc and Brescian Prealps. Dolostone Valley). Local emergence is indicated even in areas beds document local deposition in sabkha-type where lagoonal sediments were previously accumu- ephemeral ponds. iated (extrasequential clasts with borings or pedo- The coastal plain passed northward to marginal genrzed in the biocalcarenites at the base of the SGB2 marine environments $/ith mixed terrigenous-carbona- in Val Supine; section 7), and is particularly well- te sedimentation, including shallow sabkha/lagoons documented in less subsiding northern carbonate plat- (Lithosomes IV and V p.p.) and tidal flats (Lithosome form areas (silcretes of the Presolana; Rodeghiero, V p.p.). This facies belt extended southvrard to form 1e77). an at least 10 km wide embayment centered along the present Seriana Valley and separating the Bergamasc Upper S. Giovanni Bianco Fm. (SGB2). from the Brescian clastic wedges. The microtidal coast was protected from waves by a carbonate platform Poorer exposures and widespread alpine tectonic characterized by continuous peritidal sedimentation in deformation hamper accurate reconstruction of the the north (Lithosome Vi). iess competent uppermost part of the Carnran succes- These facies belts evolved in time. During sion. deposition of the SGB1, lagoonal environments were Sedimentation resumed in coastal piains (Litho- gradually confined by progradation of both alluvial some VII), which passed northward to cyclic car- fans (towards the east, west and north) and peritidal bonate-siliciclastic shallow lagoonal environments carbonate platforms (towards the south). The SGBl in (Lithosome VIII). The latter facies belt was at least 8 the Brembana Valley in fact displays an overall regres- km wide and extended north of Vai Supine. Biocal- sive trend, indicated by vertical transition from very carenites rich in open marine fossils (Fig. 0) form a frne-grained paralic clastics with sole marks and inter- distinct horizon at the base of the SGB2 from Val calated dolostones to up to medium-grained cross- Supine to Val Riso (possibly represented by beds bear- laminated alluvial sandstones, capped in turn by finer- ing thin-shelled pelecypods at Dossena and Nautilus in grained subaerial redbeds. Paleocurrent directions as Valsassina); these document the persistence of a shal- well as decreasing thickness and maximum grain size low trough connected with the open sea in the north consistently document lateral transition from proxi- during the basal transgression (Fig. a). mal environments in the west (Val Taleggio to S. Next, terrigenous detritus from the almost pene- Giovanni Bianco; section 3) to distal settings in the planed emerged lands to the south was drastically re- east (S. Peilegrino to Dossena; sections 1 and 2) and duced, probably also due to progressively dryer cli- Upper Carnizn coastal systern 29

Fig.7 - Paleogeographic sketch map of the Lombardy Southern Alps during SGB1 time. Loca- tion of srratigraphic secrions 1 to 16 is shown. Nore that a shallowJagoon centered along the Seriana Valley still sepa rates, as earlier in Val Sabbia Sandstone times, the Berga- masc from the Brescian clastic system.

R. 4:!da /' voLrrtìtii

ffi siticictastic coastat ptain

É-.:-j e ' .:-'é M: ino T\ 7' l:,/ -: Fig. 8 - Paleogeographic sketch map H^t*' of the Lombardy Southern Alps during early SGB2 time. f Location of stratigraphic sec- ,rooo"oo/ I tions X to 16 is shown. Note persistence of a shallow trough, still centered along the Seriana Valley and con- nected with the open sea 0 lorm tJ during ransgression.

matic conditions. Thick evaporitic successions (Litho- tropical zone of the northern emisphere. Similar dis- sorne IX) in fact rapidly accumulated in salt pans tribution of siliciclastic to carbonate-evaporite facies characterized by strong subsidence, through repeated belts, with alluvial fans passing laterally to outwash cycles of surface evaporation and flood recharge plains crossed by wadis, in turn grading seaward ro supply of marine waters. These salinas were delimited coastal sabkhas, lagoons, algal flats and biogenic reefs to the north-east by mainly subtidal carbonate plat- or oolitic shoals, is observed around the Arabian Plate forms (l.ithosome X), which developed in shallow- margins north of the Tropic of Cancer, from the Per- marine environments where mixed terrigenous-car- sian Gulf (Purser, 1973) to the gulfs of the northern bonate deposits had previously accumulated (Fig. 9). Red Sea (Roberts Er Murray, 1988). More significant discrepancies are accounted for by differences in geodynamic (estimated Modern analogues. setting and topographic relief as 500 m at mosr for the SGBI; Garzanti, 1986, tab. 4) Actualistic models for the depositional setring of and in climatic conditions. Salina evaporites (\Tarren the S. Giovanni Bianco Fm. may be found in the & Kendall, 1985; \Varren, 199I) were in fac accumu- 30 E. Garzanri, M. Gnaccolini G F. Jaàoul

{,.,v! cvapofilc ragoons /t VALTELLINA /Qrz E csrbonate otatform IO / |€ l\lb J ,ù/\

\---f i;É::T^" \ ,/^"s \ \ c/ae,a setr. \ Y_-- ".^ )L r îí=Lé'oP'eì"',"ib\"- F"u'"ono d -/l \\) \ \colr&rore -Q--**?<€\i_, -- \\^ / SOV.,/ \--a--rf PotaM. --T- \$.r", -1 \ì--È l - -_L A - r?-un^ \\\ /-- Efu(- : I ftrc. t ,"r"J /r ( ('.f {zm" () ) Fig. 9 - Paleogeographic sketch map \*Y"""'-' ) tt\ta / ,,' I (Rì rtor.t 1 of the Lombardy Southern ou rs ,/ \o/ a /toúl,:!j:-\N Alps during late SGB2 time. r _-/ I ;\ " , , ?\ ú-"e)L Location of stratigraphic sec- ;t 'L tions 1 16 is shown. Clas- /s\r to tf tic influx has ceased and \ coastal salinas are barred by BREscrA / oolitic shoals in the north. lated extensively only in the SGB2, whereas sporadic probably correlates instead with the terrigenous hori- coastal sabkha deposits (sensu Purser, 1985) suggest zon in the lower part of the overlying Tor Fm. (Al- more humid conditions for the SGB1. lasioaz & Assereto, 1963). The latter includes volcani- clastic sandstones derived from the south (Fella Valley, Dogna), and a thin carbonate platform at the top ("Oriz- Sequence stratigraphy and regional correlations zonte di Mestri e Dordolla" of Bianchrn et al., tl79).

The S. Giovanni Bianco Fm. documents two Upper S. Giovanni Bianco Fm. (SGB2). third-order depositional sequences (upper part of C3 and C4 of Gaetani et al., 1995), which can be tenta- Sequence C4 is characterized by more homo- tively traced eastward across the Southern Alps, geneous facies associations. In the Dolomites it is re- through the Dolomites (sequences Car3 and Car4 of presented by mixed siliciclastic-Carbonate-evaporite De Zanche et al., 1993) to Carnia and the Julian Alps. deposits (Raibl Fm.); at places, localized coastal sand- Due to lack of age-diagnostic fossils, correlations with stones probably equivaient to , Lithosomes VII and sequences recognized in other sedimentary basins (i.e. VIII p.p. (Falzarego fm.; Bosellini et al., 1928) pass up- Canadian Arctic: Skiold et al., 7992; Barents Sea: ward to multicoloured mudrocks with intercalated Embry, 1988, 1993) or with the globai eustatic chart shallow-water carbonates and local gypsum lenses (Haq et al., 1988) are unfortunately very poorly con- (equrvalent to Lithosomes VIII p.p., IX and X of strained. SGB2). In eastern Carnta, the SGB2 would correlate with the Monticello Fm. and the underlying gypsum ienses occurring in the west and south (Bianchin et Lower S. Giovanni Bianco Fm. - Campolungo Tongue a|., 7979).In the Alps, green to black mudrocks (sGB1). Julian are intercalated within dolomitized peritidai platform In the upper part of sequence C3, highstand pro- deposits in the Carnizza Fm. (Lieberman, 1928a, b; gradation of peritidal carbonate platforms is observed upper part of the Tor Fm. of Allasinaz & Assereto, from the Lombardy Preaips (Campolungo Tongue of 1e68). the Breno Fm.; Lithosome VI) to the Brenta Group in Trentino ("tepee"-bearing topmost part of the Upper Carnian successions in other nearby areas. "Dolomia Ladino-Carnica") and the Dolomites (upper part of the Dúrrenstein peritidal platform). In Carnia, Upper Carnian successions are only a few to the Dúrrenstein Fm. contains siliciclastic intercala- several tens of metres thick in western Lombardy, tions ("Violet Sandstone Member" of Pisa et al., tlll). south-eastern Switzerland and north-western Slovenia. In the Julian Alps, the Conzen carbonate platform In the Varese area, the highly lacunose Carnian may belong to the underlying sequence, and the SGB1 succession is capped by reddish-greenish dolomitic UWr Carnian coastal system JI

mudrocks, overlain in turn by marls, micritic su- interbedded evaporite lenses, but locally also caliche- pratidal dolostones and local gypsum lenses (Pizzella hematite to ferriferous pedogenic concrerions and he- Fm., 40 to 60 m thick; Allasinaz,7968b). matitized quartz grains. Marure lateritic-type soils In the Austroalpine domain, a 5 to 10 m thick developed during prolonged exposure, along with horizon at the base of the Fanez Fm. (Cluozza Mem- iron-manganese concretions formed on wood particles, ber of S. Frank, in Furrer, 1985, pp. 58-60) consists of document a warm humid stage at the top of the Val impure dolostones containing mid?-Carnian pelecy- Sabbia Sandstone in the Brescia Prealps (M. pods and locally very abundant ganoid fish scales, Cremaschi, pers. comm, 1991). Also, terra rossd paleo- passing upward to reddish arkosic sandstones with soils with iron pisoids are observed at the rop of the plant remains (Q25+a5 F35+50 L2O+30; samples Conzen platform in the Julian Alps (fadoul & Nicora, kindly provided by S. Frank, ETH Zurich, 1985). At 1e 86). this stage, which probably corresponds to rhe SGB1, The mid-Carnian sedimentary succession of the exclusively very fine-grained detritus, including abun- Southern Alps thus seemingly records a climatic epi- K-feldspar, dant some felsitic and very few microlitic sode such as that hypothesrzed for the whole Europe volcanic rock fragments, u/as largely derived from and North America (Simms & Ruffell, 199p); exist- Hercynian Europe in the north, possibly with sub- ence of such Carnian "pluvial events" has however ordinate suppiy from the Southern Lombardy volcanic been recently challenged (Visscher et al., Igg4). (Garzanti, 1988). belt The overlying stromatolitic About at the time the main body of the Gorno dolostones, possibly correlatable wrth the Cam- Fm. was deposited, southern landmasses were mantled polungo Tongue of the Lombardy Southern Alps, pass at least in part by forests with Equisetaceae and con- upward and laterally to lagoonal mudrocks containing ifers, remains of which are locally found in abundance interbedded siltstones, dolostones and oolitic fossilifer- in the lower part of the prograding SGB1 clastic ous limestones with abundant echinoderms (Mezdi wedge (Lithosome I to II). Semiarid tropical condi- Member). The latter unit, along with the overlying tions resumed in the upper parr of the SGB1, as docu- polymict dolostone breccias and "carnieules", would mented by widespread caliche paleosoils. Next, cli- represent the SGB2 sequence. Reddening of siliciclas- mates became progressiv ely dryer, until salina eva- tics in the Engadine Dolomites and local lateritic hori- porites were deposited in the upper part of the SGB2. zons in the Ducan Chain (Furrer, 1985, p. 23) might After a relatively humid event represented by be correlative with the SGBl/SGB2 unconformity. the Casrro Fm. (see et al., Ig92b), climate In northern Slovenia, sedimentary facies similar Jadoui turned again to arid in the Early Norian, during to the Julian Alps are srill found in the Meztca area deposition of the Dolomia Principale (]adoul er al., (|urkovsek, 1928), where shales and marls (about 15 m 1992a). Finally, palynological data document another thick) pass upward to thick-bedded unfossiliferous more humid episode in the Late Norian (Riva di Solto limestones with marly intercalations (40 to 60 m Shale), gradually followed by warmer semiarid cli- thick). A facies change is observed along the upper mates in the Rhaetian (Zu Limestone; et al., Sava Valley towards the south-east, where Jadoul cherty lime- tee4). stones with pelagic faunas (ammonoids, conodonts, This cyclic climatic evolution is consistent with fishes) become progressively more abundant tropical position of the Lombardy Southern Alps in throughout the Upper Carnian, documenting progres- the Late Triassic. Preliminary paleomagnetic analysis srvely deeper-water (Kolar-Jurkovsek, conditions of the S. Giovanni Bianco Fm. in the Brembana Val- Ieel). ley type-area suggests in fact paleolatitudes of about 15'N (Muttont,1994). Paleogeographic evolution Subsidence and paleogeographic belts. Climatic framework. In the Upper Carnian, volcanic-derived clastic The wide range of climatic indicators found at wedges followed by mixed siliciclastic-carbonate-eva- successive stratigraphic intervals within the Carnian porite sequences reach up to 400 m in thickness both succession of the Lombardy Southern Alps docurnents in the western (Lombardy) and eastern (Carnia) South- overall warm tropical conditions. In the lower part of ern Alps. The largely carbonatic successions deposited the Carnian climates were semiarid, probably with a in the central part (Brenta Group to Dolomites) are wet monsoonal season characterrzed by significant instead only 150 to 2QO m thick. rainfall (Garzanti,1986; Parrish, 1993), as suggested by Geometry and lateral relationships of lithosomes continental redbeds containing widespread caliche and recognized in the study area document remarkable J/ E. Garzanti, M. Gnarcolini & F. Jadoul persistence of paleogeographic belts through time. Neovolcanic origin of rhyolitic detrirus at the Both in the lower and upper parts of the Carnian (Val close of the Carnian cannot be ruled out. Although it Sabbia Sandstone to S. Giovanni Bianco Fm.), two is widely held that mid-Triassic magmatism evolved major prograding clastic wedges in the east (Brescia) from rhyolitic to latitic-andesitic and eventually basal- and west (Bergamo) show a marked increase in thick- tic products during its terminal phase, and ended ness in southern proximal sectors, whereas carbonate generally by the mid-Carnian (Bosellini et al., 1982), platform deposits document limited subsidence in in the Giudicarie area to the east rhyolitic pyroclastic northern sectors. layers are interbedded within the lower part of the Such paleogeographic scenario was inherited upper member of the Benna Fm., possibly Late Car- from the mid-Triassic, when volcaniclastics accumu- nian in age (Castellarin et a|., 1982). lated closer to the Southern Mobile belt (Brusca et al., In the studied area, the youngest volcanic rocks 1982, fig. 1), whereas carbonate buildups preferentially are vesicular lava flows of olivine basalts interbedded grew in cleaner waters to the north. Differential com- east of Malpaga in the uppermost Val Sabbia Sand- paction during subsequent burial may explain the stone. Clasts from these basalts are found in the over- much greater subsidence of southern sectors during lying redbeds (possibly lateral equivalent to the main the Carnian. body of the Gorno Fm., which is absent in Vai Nozza), and microlitic lithics derived from similar mafic volcanic products reach a relative rnaximum at Provenance of siliciclastícs and geodynamic setting. the top of the SGB1 to decline rapidly in the SGB2. The source area of. terrigenous detritus was the Circumstantiai evidence favouring a paleovol- Southern Mobile Belt (Brusca et al., Llsz). Detailed canic origin of rhyolitic detritus in the S. Giovanni quantitative petrographic analysis allowed recognition Bianco Fm. includes the appearance of vitric rock of five petrologic intervals withrn the Carnian silici- fragments along with hypabissal grains at the top of clastic succession of Central Lombardy, documenting the Val Sabbia Sandstone. This fact suggests that the progressive stepwise increase in detrital quartz from latitic to dacitic volcanic pile was already dissected the base ro the top (Garzanri, 1985a, b, 1986, 1988; before the mid-Carnian transgression of the main Crepaldi, 1990; Garzanti et al., 1995). body of the Gorno Fm. (Garzanti & Jadoul, 1985, fig. Although volcanic rock fragments and feldspars 7) Chessboard-albite, a typical component of the still predominate (Garzanti, 1985b, fig. 5), detrital Upper Anisian to Ladinian "Pietra Verde" rhyolrtic quartz neaily doubles at the base of the S. Giovanni tuffs (Callegari Er De Piert, 1966), is particularly abun- Bianco Formation. This significant change represents a dant in the SGBz (Garzantì 1985a, fig. 4b). Also, a regional petrographic marker which can be followed few chert grains locally bearing radiolarians and pre- across the Bergamasc and Brescian Prealps, and there- sumably derived from the mid-Triassic Buchenstein fore cannot be ascribed to local factors such as shifting Fm. occur in the Val Sabbia and Gorno Fms. of the drainage patterns. Since polycrystalline and monocrys- Lierna area (Garzanti & Pagni Frette, 1991, fig. 5d) talline qvartz with undulose extinction both increase, and sporadically also in the Bergamasc and Brescian and a few metamorphic lithics (phyllite to paragneiss) Prealps. Paleovolcanic origin could thus be claimed are recorded, deepening of erosion into the metamor- even for the Val Sabbia Sandstone, which might have phic wallrocks and basement of the volcanic belt is been fed by erosion of andesitic to latitic and dacitic indicated. Much greater abundance in quartz and oc- volcanic rocks largely erupted during the Ladinian currence of perthitic K-feldspar are recorded akeady (Barbieri et al., tltz). This hypothesis would explain in the Val Sabbia and Gorno Formations of the Lake why interbedded pyroclastic layers are present only in Como area ("Lierna lobe" of Garzanti & Pagni Frette, the basal part of the Gorno Fm., correlative with the 1991), reflecting local provenance from Hercynian Val Sabbia Sandstone. crystalline rocks and sedimentary cover exposed on In the Brescian Prealps (e,g., Sabbia Valley), the basement highs to the west. fluvio-deltaic Val Sabbia Sandstone locally overlies Abundance of monocrystalline qtJartz with directly Ladinian volcaniclastic turbidrtes (Wengen straight extinction, bipyramidal outlines or embay- Fm.; Brusca et al., 1982, fig. 1), documenting a malor ments due to magmatic resorption, along with tectonically-enhanced regression probably associated spheruiitic to axiolitic vitric rock fragments, increases wrth uplift and basin inversion around the Ladin- throughout the S. Giovanni Bianco Fm. and reaches a ian/Carnian boundary. On local structural highs (Re- maxirnum at the top of the unit. Either a terminal coaro: De Tanche & Mietto, 1977; Croce di Marone: phase of explosive activity or erosion of older felsic Cassinis &, Zezza, 1982; : Picotti, 1991),largely volcanic products is thus indicated. Middle Triassic sedimentary rocks were eroded, thus Upper Carnian coastal system JJ

Ei? conr'n"ntal block

@ Intraplate volcano lliil:l vob"ni"t".ti""

Fî- votcanic arc

u"'in" sediments ili'..,'.ii 1

)/ subduction zone

Fig. 1O - Differences and similarities bet*een modern and ancient small-sized volcanic arcs formed due to confined subduction: a Provocatlve comparison between the present day Calabrian accretionary prism and the Triassic Southern Mobile Belt (mod. after Brusca et al., 1982; De Zanche k Mietto, 1985), where volcanisrn was actíve at least until the mid-Carnian. Reduced mid-Triassic sedimentary successions from the Varese area ro rhe Po Plain (Turbigo and Battuda \fells: Brugora,7977) may have been deposited in "forearc" serrings, with the Punta Bianca alkalic volcanics (Lucchini et al., 19SZ) possibly representing a Triassic analogous of Mt. Etna today

providing throughout the Carnian carbonate pebbles, Conclusions paleosoil clasts and other sedimentary and volcanic detritus to the Vai Sabbia and S. Giovanni Bianco allu- Integrated stratigraphic, sedimentologic and vial redbeds. Tectonic uplift associated with emer- petrographic analysis of the Upper Carnian succession gence took piace locally even in the north (Brenta exposed in the Lombardy Southern Alps allowed us to Group; Peloso & Vercesi, 1985). reconstruct the evolution in time of a mixed ter- To the south, a southward-convex arcuate base- rigenous-carbonate-evaporitic coastal depositional sys- can be prolonged from the Lake Como area ment-high tem (Fig. 11). (Garzanti Pagni Frette, 1991) to the south-east & During deposition of the lower part of the S. Po Plain (as documented by subsurface beneath the Giovanni Bianco Fm. (SGB1), two alluvial fan systems Monza, Malossa and Rodigo Vells: data from the progradrng towards the east in the Brembana Valley Brugora, 1977; Mattavelli & Margarucci, 1992) and as and towards the north-west in the Brescia area passed far as the Adriatic Sea (Villaveria, Legnaro and As- northwards to a siliciclastic coastal plain. They were sunta \lells: Brugora, 1977). According to the model separated and delimited seaward by a mixed siliciclas- of Marinelli et al. (1980; Garzantt, 1985b), the South- tic-carbonate lagoon, which formed an embayment ern Aipine and Austroalpine domains in the mid-Tri- centered in the Seriana Valley and was protected from assic may be envisaged as a retroarc basin on thinned waves by a mainly peritidal carbonate platform in the continental crust, dominated by transtensional to lo- north (Campolungo Tongue of the Breno Fm.). Major cally transpressional tectonics (Doglioni, 1984; Castel- paleogeographic features, such as the Bergamasc and larin et al., 1988; Garzanri,1988). If a back-arc rifting Brescian clastic wedges or the Breno carbonate plat- interpretation is accepted (".g., Stampfli et al., 1991, form, thus persisted throughout most of the Carnian fig. 2 and 3), the mid-Triassic geodynamic scenario (depositional sequences C1 to C4 of Gaetani et a1., might be compared with that of southern Italy today lees). (Fig. 1o), where the Thyrrhenian back-arc basin (i.e. Southern Alpine-Austroalpine) is bordered to the The regressive trend at the top of the SGB1 is local south by the Eolian volcanic arc and by the south- capped by an unconformity associated with profiles. ward-convex Calabria basement arc (i.e. Southern Mo- emergence and development of soil SGB2, sedi- bile Belt of Brusca et ai., 1982). During deposition of the overlying A major change in paleogeography is docu- mentation resumed in coastal plains, which passed mented in the Norian by widespread transgression of northward to mixed carbonate-siliciclastic shallow la- the Dolomia Principale, which onlapped paraconform- goonal environrnents. A distinct horizon of calcareni- ably the underlying succession and disconformably to tes rich in open marine fossils locally marks the tran- non conformably the Southern Mobile Belt. This new sgressive surface (Fig. 0). Next, terrigenous detritus tectono-sedimentary cycle, triggered by renewed tec- from emerged lands in the south was drastically redu- tonic extension, will lead to rifting and spreading of ced, and gypsum accumulated in subsident coastal sali- subtidal carbo- the Piedmont-Ligurian Ocean in the Jurassic (|adoul et nas barred to the north-east by mainly aI., I992a; Bertotti et al., 1993; Gaetani et al., t9l5). nate Dlatforms. 34 E. Garzanti, M. Gnaccolini & F, Jadoul

SW NE cUtATE RETATIVE SEA.LEVEI, HSAA +- Fig. 11 - Simplified stratigraphic frame- work for Carnian a the Upper -l a ,.> CastroFm. A ^ a ^A a of Lombardy (profile from ^ ^ ^ 4r.:!{vvr.vlt4)-_ )tJÈtZ @.v,rvvvr,,v., ,> / sE0uEt{ct the Brembana Valley in the c4 S\l to the Camonica Valley in the NE; Fig. 1). Long-term scsr l sE0uEf{cr eustatic and climatic changes . GO_- c3 are schematically shown. H _----: : humid; SA : semiarid; A / : arid. GO : Gorno Fm.; LC : Campolungo Tongue.

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