rab rhy pul

(1)

2127

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2238

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Costa

Laus ea d`A

lpetto

degli dei

Cas tagni Serrera

del

del dell`Arp

dell`In fernetto della

della Desertetto

Punta Stramondin

Palanfré

Passo di Ciotto Mien Punta Balmarossa

PIAN

Pia nard

PIANODELLAREINA Poggio Pironetto

Prati Punta Baral

Punta Bussaia Punta del Van

Punta della Splaiera

Valle Rio Rocca

d`Orel

Rocca dell'Abisso Rocca della Bastera Rocca San Giovanni

Rocca Speron

Rocca Vanciampi

Rocce della Scregna

Sab bione San Bernardo

San Lorenzo

cry

Costa

1800

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Bec Baral

Bec Matlas

0 160 1109

1290 1292

1340 1371

1432 1459

1506

1564 1613

1667

1669

Gias della Culatta

Grande Il Cairas

LA

Laghi del Frisson

Lago degli Alberghi

Limonetto Liret

Monte Becco Rosso Monte Lausa

Monte Viver Madonna del Colletto

Monte Bussaia

Monte Ciotto Mien Monte Colombo

Monte Corno

Monte Creusa

Monte del Chiamossero

Monte Frisson Monte Garbella

Monte la Bastia

Monte la Croce Monte la Piastra

Monte Pianard Monte Servatun Monte Testa

Monte Testas

Valle Vallone

Valle Valletta

Vallone

Vallone Caire dell’Uglia

00 16

1600 1600

1600

0 160 21

00

2100

2100

0 210

00 21

2173

2251 2237

2278

2298 2305

2337

2374 2440

2451

2476

2629

2756 805

1835

ADREIT

Alberg hi Balmera

Bric Brusata Caire del Lupo

Caire di Porcera Cave di Marmo

Cima Pissousa Cima Saben

Colle dell'Arpione

Colle di Tenda Comba

Costa

Costa Sandri

Scom bes

Serra Colletta Soprana

Tetti Porcera Tetti Prer Tetti Rim

Tetti Violin

Torre nteBousset TorrenteGesso

Torrente Gesso

Torre nteG

esso

Trinita`

Tunnel del Colle di Tenda

Valdieri

VALERA

Valet Valle

Valle Valle

1673

1700 1712

1714 1721

1818

1830 1851

1880

1928 1951

1972

2036

2093

2126

di

DI

di

Entracque

Entracque

Forte Alto

Forte Margheria Forte Pernante

Fredda FUNS

Garb Gias d`Alpetto

1600

1600

Chiesa Cima Cialancia

Cima della Guglielma

Lago dell’Oro

1958 00 12

Vallo ne

Pioccia

Artesin

Costa degli

2261 S

.S. 20 S.P. 22

ITALIA FRANCIA

pul_s pul_s

pul_s

pul_s deb

deb deb

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deb deb

deb ans deb

ans ans

ans

cry

rab

gar

cry

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rab

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lau

lau mne

mne mne

pul

pul car

rhy

num

num num

num

agn mat

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ser

cbl mic

mic enm

enm enm

enm

gla

gla gla

all tes

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tes pul_d

pul_d

pul_d pul_s

gar

num

num num

num

num gla

gla

gla gla

car deb

deb

ans

ans all

all

all all

all

car car

car

car car

enm

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lau

gar

gar gar

gar

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gla gla

gla

gla all

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gla ans ans

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mic

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ans

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num

num tes

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ans gla deb

all

sba

gla gla

tes all

vsa

agn agn

agn

agn agn

mat mat

mat

ser ser

ser

cbl

mne num

ABF ABF

ABF

ABF ABF

SG T SG

T SGT

SGT

TTT LiVZ

o

LiVZo

LiVZo LiVZ

o 12

12

12 12

12

14

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17

18 18

18

18 18

20

20 20

20 22 22

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8

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9

16

20

22 28

30

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44 48

50 50

50

52

52 52

56

58 64

66

68 70

76 82

82 86

48 10

14

18

60

20 30

30

35

35 35 35

36

36 45

45

50 60

65 num 70

rha

rab rhy pul

_s

pul

_d

pul car

num ans

mic sba

C 1800 m 2000 m 2200 m

SSW

C’

1600 m 1800 m NNE

2000 m 2200 m

Monte del Chiamossero Monte Creusa

Bec Matlas

Costa degli Artesin

ans

gar gar gar

gar

num num

sba mat

rabnum car rab

ans

TTT TTT

LiVZ

o

B

pul B’

pul

cry enm

gar

gar gar

gar mne tes

ans

ser ser car

pul num

num

deb

all

Caire di Porcera

Torrente Bousset

Monte Servatun

1200 m 1400 m 1600 m 1800 m

SSW

1000 m 800 m

1200 m 1400 m 1600 m NNE

SGT 800 m

1000 m 1200 m 1400 m

1000 m 1200 m 1400 m 1600 m 1800 m SW

NE

A

A’

cry

mat mat

enm enm

enm

gar

gar car

mat

ans

Monte Lausa

Entracque

Rocce della Scregna

agn

ans

car

SGT

mne

lau tes

enm gar

ser

mat cbl

agn

vsa

cry

A

A’

32

38

a

b

a

b

Marne Nere

Dark shales and marls with echinoderm fragments.

Thickness: 70–80 m (northwestern part of the Entracque unit), 10–20 m or locally absent in other sectors.

Hemipelagic deposits. APTIAN–CENOMANIAN

MIDDLE JURASSIC–LOWER CRETACEOUS PROVENÇAL SUCCESSION

Testas Limestone

- Marly limestones, with abundant belemnites, and echinoderm fragments. Thickness: few metres (Punta Bussaia and Vallone del Sabbione).

- Crinoid-rich, bioturbated (Thalassinoides) wackestones and packstones, locally proper encrinites (Monte Testas), with dm-sized silicified nodules, abundant belemnites, planktonic foraminifera (Hedbergella sp.), fragments of large tube worms, and phosphate grains. At the top, thick conglom- erate bed with belemnites, reworked ammonite moulds (Melchiorites sp., Barremites sp.), solitary corals, and phosphatized lithoclasts. Thickness: 10–15 m (Roaschia unit).

Open-marine shelf deposits. HAUTERIVIAN P.P.?–BARREMIAN?

Garbella Limestone

Massive bioclastic packstones to rudstones and coral boundstones, containing corals, nerineid gas- tropods (e.g., Ptygmatis pseudobruntrutana), rudists (Diceratidae), stromatoporoids, and benthic foraminifera (Textularidae and Valvulinidae). In the upper part, mudstones–wackestones rich in Clypeina jurassica. In the Roaschia unit the lower part consists of bioclastic wackestones to packstones or floatstones, with abundant crinoid ossicles, along with rare gastropods, bivalves, cor- als, stromatoporids and red algae. At the top, m-thick interval of fenestral and laminated mudstones, with flat pebble breccias, oolitic grainstones, and nodular mudstones, locally containing beds of bioclastic wackestones with Porocharaceae (sp. aff. Porochara fusca), ostracods, and gastropods (Monte Colombo and Passo Ciotto Mien). Thickness: 200–300 m.

Carbonate platform deposits. MIDDLE? JURASSIC–BERRIASIAN?

MIDDLE JURASSIC–LOWER CRETACEOUS DAUPHINOIS SUCCESSION

Lausa Limestone

Fine-grained limestones, with abundant dm-thick beds of clast-supported polymictic breccias, with mm- to dm-sized clasts of mudstones, coarsely crystalline dolostones (dolomitized Garbella Limestone) and finely crystalline dolostones (Mont Agnelet Formation). Locally (Tetti Prer, Colletta Soprana, and San Lorenzo), m-sized blocks of dolomitized Garbella Limestone occur. In the upper part, grey mudstones and crinoid-rich wackestones, in cm- to dm-thick beds, with abundant silicified portions. Thickness: 60–70 m.

Pelagic sediments, with interbedded gravity flow deposits. VALANGINIAN?–EARLY APTIAN?

Entracque Marl

Dark marls, calcareous marls, and shales, in dm-thick beds, with rare bioclastic mudstones and wackestones. In the upper part cm- to dm-thick breccia beds, more and more abundant towards the top of the unit. Breccia clasts, mm- to cm-sized, are both extraformational (finely crystalline dolostones, ooidal–peloidal grainstones, bioclastic wackestones) and intraformational (greyish and pinkish mudstones). Estimated thickness: some hundred metres.

H e m i p e l a g i c s e d i m e n t s , w i t h i n t e r b e d d e d g r a v i t y f l o w d e p o s i t s . M I D D L E ? JURASSIC–BERRIASIAN?

PERMIAN–LOWER JURASSIC SUCCESSION

Costa Balmera Limestone

- Bioclastic packstones and wackestones with crinoid ossicles (Pentacrinites? sp.), bivalves, belemnites, and ammonite shell fragments, cropping out in hm-sized tectonic slices.

Open-marine shelf deposits.

- Carbonate breccias with clasts of fine-grained dolostones, limestones, and cherts. Thickness: few metres (Punta Bussaia).

SINEMURIAN

Monte Servatun Formation

Fine-grained limestones and dolomitic limestones, with algal lamination, flat-pebble breccias and bivalve-coquina levels, and dark shales with Cardita munita. This unit crops out only in tectonic slic- es and, therefore, it is not possible to evaluate its thickness.

Peritidal and lagoonal deposits. RHAETIAN–HETTANGIAN

Bec Matlas shales

Red and green shales showing a marked slaty cleavage, occurring as m- to dam-thick, strongly sheared tectonic slices (e.g. Bec Matlas, Palanfré, and Monte Servatun).

Continental deposits. LATE TRIASSIC

Mont Agnelet Formation

Finely crystalline dolostones, dolomitic limestones, and limestones, in dm-thick beds, with microbial/algal lamination, collapse breccias, and flat-pebble breccias, rare brachiopods and gastro- pods, cropping out in tectonic slices of limited extent and thickness (Monte del Chiamossero, Vallone del Sabbione, Gias d’Alpetto, and Colle di Tenda).

Peritidal deposits (under arid, sebkha-like conditions). MIDDLE TRIASSIC

Valette du Sabion quartzarenites

- Cross-bedded quartzarenites and pebbly quartzarenites, in dm-thick beds, locally followed by a few decimetres of dark-red pelites. Thickness: 5–8 m (Vallone del Sabbione, Monte del Chiamossero, and Forte Margheria).

- Greenish arenites and siltites, locally cemented by a brown, Fe-bearing carbonate. Thickness: 0–3 m (Vallone d’Alpetto).

Coastal deposits. EARLY TRIASSIC

Rocca dell'Abisso Formation

- Arenites and conglomerates, with minor pelite intercalations. Conglomerates are composed of clasts of volcanic rocks (mainly rhyolites), migmatites, gneiss, quartzites and granites (Rocca dell’Abisso and Vallone del Sabbione). Thickness: several hundred metres.

Continental deposits.

- Volcanic–subvolcanic rhyolitic rocks, cropping out in a tectonic slice (Colle dell’Arpione). (rhy) PERMIAN

ARGENTERA MASSIF CRYSTALLINE BASEMENT

Undifferentiated crystalline rocks

Migmatitic granitoid gneiss, with local masses of granitoids and migmatitic amphibolites (Vallone del Sabbione, Laghi del Frisson).

PALAEOZOIC

Stratigraphic scheme of the Provençal and Dauphinois Mesozoic successions and of the Alpine Foreland Basin succession

Breccia beds (Entracque Marl, Lausa Lst.) Dolostone clasts (Nummulitic Limestone)

San Lorenzo quarry

(2)

Monte Corno (3)

Punta Stramondin

(4)

Colletta Soprana

(5)

Tetti Prer (6)

Caire di Porcera (7)

Monte Garbella

(8)

Monte del Chiamossero

(9)

? ? Valdieri

Valle di Desertetto

(1)

4 Km

100 m pul

enm

cry gar num

mne

lau rab

mic

tes lau

mne

vsa

ser Ba

Fe

0 1 2 3 Km

Scale 1: 25,000

Geological sections (scale 1:25,000)

all deb

gla

LITHOSTRATIGRAPHIC UNITS

QUATERNARY DEPOSITS Slope and talus debris

Undifferentiated alluvial deposits

Undifferentiated glacial deposits

FAULT ROCKS

Carnieules

Vacuolar carbonates and polymictic or monomictic carbonate-cemented tectonic breccias, occur- ring as irregular bodies along tectonic contacts, up to several tens of metres large and more than 1 km long. Locally they include m-sized blocks of green and red pelites, coarsely-crystalline gypsum, and fine-grained dolostones (Gias della Culatta).

The main masses of carnieules crop out in correspondence with the tectonic boundary between the Argentera basement and the adjoining sedimentary successions (Valle Desertetto, Vallone d’Alpetto, and Vallone del Sabbione).

WESTERN LIGURIAN HELMINTHOIDES FLYSCH

San Bartolomeo Formation

Thin-bedded varicolored pelites alternating with cm-thick carbonate levels, cropping out as dam- to hm-thick sheared tectonic slices involved in the Limone–Viozene Zone (Costa degli Artesin).

Basin plain deposits. LATE HAUTERIVIAN–LATE CAMPANIAN

ALPINE FORELAND BASIN SUCCESSION

Annot Sandstone

Alternation of dm- to m-thick sandstones beds, with erosional base, normal grading, and parallel laminations at the top, and dark shales. Thickness: some hundred metres.

Deep-sea fan turbidite deposits. LATE PRIABONIAN–EARLY RUPELIAN

Nummulitic Limestone

- Planktonic foraminifera-rich marls and calcareous marls (Globigerina Marl Auct.), in cm-thick beds, affected by a marked slaty cleavage. Thickness: 0 to few metres due to intense tectonic lamination.

Slope deposits.

- Conglomerates, pebbly sandstones, and sandy limestones with abundant clasts of dolomitized Garbella Limestone, rare quartz grains and bioclasts (nummulitids, echinoderms, bivalves, gastro- pods, and red algae). Thickness: 20–25 m (Refrey Zone and southern part of the Entracque unit).

- Dark limestones with echinoderm fragments, small nummulitids and bivalves. Thickness: 5–10 m (northern part of the Entracque unit).

- Sandy limestones with quartz, mica, lithic clasts, and bioclasts (Nummulites, Dyscocyclina). Thick- ness: 15–20 m (Roaschia unit and Limone–Viozene Zone).

Carbonate and mixed carbonate–siliciclastic ramp.

BARTONIAN–EARLY PRIABONIAN

Microcodium Formation

Lenticular bodies of clast-supported conglomerates, with cm- to dm-sized clasts consisting of: lime- stones and marly limestones, locally encrusted by Microcodium (Entracque unit: Caire di Porcera);

more or less dolomitized Garbella Limestone (central part of the Refrey Zone: Passo Ciotto Mien and Punta Bussaia); and mainly volcanic (rhyolites and dacites) and metamorphic rocks (Roaschia unit: Cima Saben; Limone–Viozene Zone: Bec Baral; and eastern part of Refrey Zone: Colle di Tenda). Thickness: max. 20–25 m (Cima Saben).

Alluvial-fan and fluvial deposits. LUTETIAN?–EARLY BARTONIAN

APTIAN–UPPER CRETACEOUS SUCCESSION

Puriac Limestone

Alternation of limestones (bioclastic mudstones and wackestones) and marly limestones in cm- to dm-thick beds.

- Siliciclastic lithozone: limestones and marly limestones interbedded with medium to very coarse, locally microconglomeratic lithoarenites and sandy limestones, in cm- to dm-thick beds with an ero- sional base. Grains are composed of mono- and polycrystalline quartz, volcanic rocks, granitoids, and recrystallized carbonate rocks. Lithoarenites show normal grading, plane parallel lamination and, locally, cross-lamination at the top.

Cm- to dm-thick beds of matrix-supported conglomerates with sandy limestone or lithoarenite matrix and clasts, up to 15 cm in diameter, of granitoids, migmatites, rhyolites, and limestones (lower Comba dell’Infernetto valley). (pul

_s

)

- Reworked dolomite lithozone: cm- to dm-thick beds of packstones, containing reworked submillimetric dolomite grains and mm- to cm-sized dolostone clasts (deriving from dolomitized Garbella Limestone), mudstone clasts and echinoderm fragments. Beds show erosional base, nor- mal grading, plane parallel and cross-lamination. (pul

_d

)

Thickness: several hundred metres in the northwestern part of the Entracque unit, 100 m in the Roaschia unit; absent in the southeastern sector of the map.

Hemipelagic sediments, with interbedded gravity flow deposits. TURONIAN P.P.–CAMPANIAN?

Topographic base derived from the CTRN (Vector Regional Technical Map) of Piedmont, vector_10 series, edi- tion 1991-2005, sections 225120, 226090, 226100, 226130, 226140, 226150, 243020, 243030, 243040, 243060, 243070). A small area in French territory (south of Colle di Tenda), not covered by the CTRN, was completely redrawn on the raster version of the Regional Technical Map of Piedmont at 1:10.000 (sections 243060 and 243070), which extends for a little portion beyond the Italy-France border.

Coordinate System: UTM WGS 1984, Zone 32 Nord

G G E E O O L L O O G G I I C C A A L L M M A A P P O O F F T T H H E E E E N N T T R R A A C C Q Q U U E E - - C C O O L L L L E E D D I I T T E E N N D D A A A A R R E E A A ( ( M M A A R R I I T T I I M M E E A A L L P P S S , , N N W W I I T T A A L L Y Y ) )

Luca Barale (a)

, Carlo Bertok (a)

, Anna d’Atri (a)

, Luca Martire (a)

, Fabrizio Piana (b)

, Gabriele Domini (c)

(a) Dipartimento di Scienze della Terra, Università degli Studi di Torino, Via Valperga Caluso 35 – 10125 Torino, Italy. Email: [email protected] (b) Istituto di Geoscienze e Georisorse, Consiglio Nazionale delle Ricerche, Via Valperga Caluso 35 – 10125 Torino, Italy.

(c) Via degli Olmi 4 – 10023 Chieri (TO), Italy.

N

S W E

A

A’

B

B’

7° 25'0" E 7° 20'0" E

7° 30'0" E

44° 10'0" N

44° 15'0" N 7° 20'0" E

7° 25'0" E

7° 30'0" E

44° 10'0" N

7° 35'0" E 44° 15'0" N

7° 35'0" E

C

C’

Geological setting

Torino

D DM M

Cuneo

40 km

Asti

Lig uri an Se a

ITALY

FRANCE CH

DP: Dauphinois and Provençal domains; EM: External Crystalline Massifs; WL: Western Ligurian Helminthoides Flysch; BR: Briançonnais domain; P: Piemonte–Ligurian domain; IM: Internal Crystal- line Massifs TPB: Tertiary Piedmont Basin; QD: Quaternary deposits

DP

EM

QD

TPB P IM

WL BR

TPB

P EM

WL STUDY AREA

Abstract

The 1:25,000 geological map of the Entracque – Colle di Tenda area covers an area of about 130 km

²

in the Ital- ian Maritime Alps, between the Gesso and Vermenagna valleys. The map area is of great relevance since the Alpine units of this region sampled a geological nodal point in the Mesozoic, at the transition between two differ- ent sedimentation domains of the Alpine Tethys European palaeomargin (the Dauphinois basin to the NW and the Provençal platform to the SE). During the Cenozoic, this palaeogeographic hinge was progressively incorpo- rated along multiple shear zone systems developed at the southern termination of the Western Alps arc.

HYDROTHERMAL PHENOMENA

Valdieri and Sabbione Marbles

Discrete, hm-sized masses of Dauphinois and Provençal Mesozoic carbonates, characterized by a high recrystallization and by the growth of new silicate minerals (Valle Desertetto, San Lorenzo, and Vallone del Sabbione).

Authigenic albite

Intense hydrothermal dolomitization

Partial dolomitization of the host rocks, with common dolomite vein frameworks and dolomite- cemented breccias. Metre-sized masses of completely-dolomitized rocks.

EARLY CRETACEOUS

Moderate hydrothermal dolomitization

Partial dolomitization of the host rocks, with rare dolomite vein frameworks.

EARLY CRETACEOUS

SYMBOLS

strike and dip line of bedding (dip value in degrees)

strike and dip line of overturned bedding (dip value in degrees)

faults (a), and their concealed or inferred prosecution (b)

main thrusts (a), and their concealed or inferred prosecution (b)

axial surface line of the Monte La Piastra–Monte Lausa anticline

traces of geological sections

Valdieri Marble quarries

Monte La Piastra

Monte Servatun Cima Saben

Entracque unit

Roaschia unit Mesozoic

succession

Alpine Foreland Basin succession Entracque

S SGGTT

ENE WSW

Panoramic view of the Serra Garb Thrust (SGT), causing the superposition of the Mesozoic succession of the Roaschia unit on the Alpine Foreland Basin succession of the Entracque unit.

Image taken from Monte Pianard.

ENTRACQUE VALDIERI

PALANFRÉ

ROCCA DELL’ABISSO COLLE DELL’ARPIONE

MONTE BUSSAIA AM

AM ENU

REZ LiVZ

DAZ

RYU ELB

ILB

2 Km

ELB

COLLE DI TENDA VERNANTE

LIMONE PIEMONTE ROASCHIA

TO RR

VERMENTE

AG NA EN

TOR R

BOU EN

TE ET SS TORR

TEGESSO EN

LiVZ ABF

ABF

ABF SGT

LiVZ_i LiVZ

o

LiV

oZ

LiVZ

o

LiV

oZ DAZs

TTT EBF

IBF

IBF

Structural scheme (scale 1:150,000)

Tectonic units:

AM, Argentera Massif; ENU, Entracque unit;

DAZ, Demonte–Aisone Zone; RYU, Upper Roya unit; REZ, Refrey Deformation Zone; ROU, Roaschia unit; LiVZ, Limone–Viozene Zone;

ELB, External Ligurian Briançonnais; ILB Inter- nal Ligurian Briançonnais.

Main tectonic boundaries:

ABF, Argentera Boundary Fault System;SGT, S e r r a G a r b T h r u s t ; L i V Z_i, L i V Z_o, Limone–Viozene Zone inner and outer boundaries;DAZ_s, DAZ Southern boundary;EBF, Exter- n a l B r i a n ç o n n a i s F r o n t ; I B F, I n t e r n a l Briançonnais Front;TTT, Tenda-Tunnel Thrust.

The dashed line indicates the area represented in the geological map.

ROU

Hillshade: Sfumo_Europa_WM, Arpa Piemonte

(http://webgis.arpa.piemonte.it/ags101free/rest/services/topografia_dati_di_base/Sfumo_Europa_WM/MapServer)