Alleghanian deformation in the eastern Gaspe Peninsula of Quebec, Canada

Pierre Jutras² Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada Gilbert Prichonnet GEOTERAP, DeÂpartement des Sciences de la Terre et de l'AtmospheÁre, Universite du Quebec aÁ MontreÂal, C.P. 8888, Succursale Centre-Ville, MontreÂal, Quebec H3C 3P8, Canada Steven McCutcheon New Brunswick Department of Natural Resources and Energy, P.O. Box 50, Bathurst, New Brunswick E2A 3Z1, Canada

ABSTRACT sin, Cannes-de-Roches Basin, Carbonifer- rocks of the Gaspe Peninsula. We argue herein ous, strike-slip faults. that these structures are related to the Allegh- Juxtaposition of the Mississippian Risti- anian orogeny and were responsible for the INTRODUCTION gouche and Cannes-de-Roches Basins, postsedimentary juxtaposition of two Missis- sippian depocenters, namely, the Ristigouche which are subbasins of the composite late Transpressive deformations associated with (van de Poll, 1995) and Cannes-de-Roches Paleozoic Maritimes Basin, occurred peripheral effects of the Carboniferous to (Jutras et al., 2001) Basins (Fig. 1). These de- through dextral movement along the north- Permian Alleghanian orogeny are well docu- pocenters are subbasins of the large late Pa- west-striking Perce Fault system in the east- mented in Atlantic Canada (Fralick and leozoic Maritimes Basin, which extends ern Gaspe Peninsula of Quebec. The north- Schenk, 1981; PiqueÂ, 1981; Bradley, 1982; throughout most of Atlantic Canada (Fig. 1A). west-striking faults are truncated by small Keppie, 1982; Ruitenberg and McCutcheon, Identi®cation of post-Acadian transpressive north-northwest±striking dextral strike-slip 1982; Nance and Warner, 1986; Gibling et al., faults, which probably developed as region- 1987, 2002; McCutcheon and Robinson, structures in the Gaspe Peninsula indicates al stress gradually rotated clockwise from 1987; Nance, 1987; Yeo and Ruixiang, 1987; that the tectonic impact of the Alleghanian north-northwest±south-southeast to north- Reed et al., 1993; Murphy et al., 1995; Pas- orogeny affected rocks much farther north east-southwest. This study provides the ®rst cucci et al., 2000). However, until now, it was than previously thought, thus adding signi®- evidence in eastern Quebec for signi®cant thought that the Alleghanian fault system that cantly to our understanding of late Paleozoic post-Acadian block displacement other affects Carboniferous rocks of the Maritime tectonics in the northern Appalachians. The than normal faulting and indicates that Al- Provinces did not extend as far north as the identi®cation also underlines a need to re- leghanian deformation extended much far- Gaspe Peninsula of Quebec (Fig. 1), a large evaluate the age attribution of all brittle strike- ther north than previously thought. Iden- segment of the Canadian Appalachians. Prior slip faults in the Gaspe Peninsula, which were ti®cation of these structures formed during to a study by Faure et al. (1996a), post-Acadian previously attributed to late stages of the Aca- the Alleghanian orogeny but more than deformation in the rocks of the Gaspe Penin- dian orogeny (Kirkwood et al., 1995; Malo 1000 km away from areas of peak Allegh- sula was thought to be limited to Carbonifer- and Kirkwood, 1995). anian metamorphism in the southeastern ous synsedimentary dip-slip faulting (Rust et United States underlines the far-reaching al., 1989) and to minor postsedimentary nor- POST-ACADIAN TECTONIC HISTORY effects of continental collisions. It also casts mal-fault readjustments (Alcock, 1935; St- OF SOUTHEASTERN CANADA doubt on the age attribution of brittle Julien and Hubert, 1975; Bernard and St- strike-slip faults elsewhere in the Gaspe Julien, 1986; Kirkwood, 1989; Bourque et al., The Middle Devonian Acadian orogeny Peninsula, away from Mississippian expo- 1993; Peulvast et al., 1996). Faure et al. brought together Laurentia, Baltica, and sures. Such brittle faults were previously (1996a) documented evidence for post- Gondwana, and during Late Devonian and associated with late stages of the Acadian Acadian compressive paleostresses from slick- Mississippian time, southeastern Canada orogeny but could in fact be considerably en®bers on mesoscopic brittle fault planes in mainly was subjected to extension and graben younger. southern Quebec, including the Gaspe Penin- formation (Howie and Barss, 1975; Arthaud sula, but no signi®cant displacement was and MatteÂ, 1977; Fralick and Schenk, 1981; noted. Bradley, 1982; Keppie, 1982, 1993; Ruiten- Keywords: Alleghanian orogeny, structural Described here are large transcurrent faults berg and McCutcheon, 1982; Fyffe and Barr, geology, Gaspe Peninsula, Ristigouche Ba- and associated compressive features, such as 1986; Gibling et al., 1987, 2002; McCutcheon reverse faults and drag folds, which were rec- and Robinson, 1987; Rust et al., 1989; Pe-Piper ²E-mail: [email protected]. ognized for the ®rst time in Mississippian et al., 1991; Durling and Marillier, 1993; Reed

GSA Bulletin; December 2003; v. 115; no. 12; p. 000±000; 13 ®gures; Data Repository item 2003xxx.

For permission to copy, contact [email protected] ᭧ 2003 Geological Society of America ALLEGHANIAN DEFORMATION IN EASTERN GASP͘a PENINSULA, QUEBEC

Figure 1. (A) Location of the study area within the late Paleozoic Maritimes Basin (light shading where its deposits are currently below sea level and dark shading where they are on land; modi®ed from Gibling et al., 1992). (B) Simpli®ed geology of the eastern Gaspe Peninsula (modi®ed from Brisebois et al., 1992), showing only post-Acadian (Middle Devonian) relationships. Box in the vicinity of Mal Bay shows map area of Figure 3. et al., 1993; Murphy et al., 1995; Pascucci et al., 2000). Onset of this extension was coeval with orogenic uplift in New England, source area of the uppermost Devonian Catskill clas- tic wedge (Rust et al., 1989). Within the Low- er to Middle Devonian clastic wedge of the eastern Gaspe Peninsula, observation of a gradual displacement of source areas from the southeast to the southwest led Rust et al. (1989) to propose a model that correlates this succession with the Upper Devonian Catskill clastic wedge within one continuous wrench tectonic event. This Devonian migration of stress and foreland-basin development toward the southwest was accommodated by the grad- ual closing of the Theic (or ``Rheic'', for some authors) Ocean (Fig. 2A), which culminated with the Pennsylvanian to Early Permian Al- leghanian orogeny and the formation of Pan- Figure 2. Tectonic model for the formation and deformation of the Maritimes Basin in gea (Fig. 2B) (Arthaud and MatteÂ, 1977; Pi- the context of Theic Ocean closure. Dotted line represents the contour of the Precambrian queÂ, 1981; Lefort and van der Voo, 1981; West African craton within Gondwana. Light wavy lines represent areas affected by pen- Russell and Smythe, 1983; Haszeldine, 1984; etrative early to middle Paleozoic (pre±Late Devonian) deformation. Thick wavy lines Kent and Opdyke, 1985; Lefort et al., 1988; represent areas that were then affected by penetrative deformation. Dark gray shading Kent and Keppie, 1988; Rodgers, 1988; Sacks represents areas of active continental clastic sedimentation; white arrows represent in- and Secor, 1990; Pique and Skehan, 1992; ferred paleocurrent trends. Keppie, 1993; Faure et al., 1996a). As the West African craton converged with southern North America (Lefort and van der have accommodated much of these plate re- Roches Basins of eastern Quebec are among Voo, 1981; Sacks and Secor, 1990; Pique and adjustments, generating pull-apart extension the grabens that developed in southeastern Skehan, 1992), Gondwana rotated counter- in most of southeastern Canada as the main Canada during the Late Devonian and the clockwise with respect to the assembled Eur- stress vectors migrated toward New England Mississippian; altogether the grabens formed american landmass (Laurussia), causing dex- (Fig. 2A). In favor of the pull-apart model, the composite Maritimes Basin (Fig. 2A). tral shear from central Europe to northeastern Late Devonian and Mississippian magmatism The Reguibat uplift, a well-de®ned prom- North America (Kent and Keppie, 1988) (Fig. along the Cobequid-Chedabucto Fault evolved ontory on the West African craton margin, act- 2A). Within this general context, the Cobequid- under a transpressive regime (Koukouvelas et ed as a rigid indenter when Gondwana and Chedabucto Fault, which separates a Gond- al., 2002), while the rest of southeastern Can- southeastern North America started colliding wanan terrane (Meguma) from Iapetan ter- ada was undergoing general extension. The in Pennsylvanian time, and much of the com- ranes in Nova Scotia (Keppie, 1982), may Mississippian Ristigouche and Cannes-de- pression concentrated around it (Lefort and

Geological Society of America Bulletin, December 2003 JUTRAS et al. van der Voo, 1981; Sacks and Secor, 1990; Gaspe Peninsula, whether ductile or brittle, (Rust, 1981). These units are now absent from Pique and Skehan, 1992; Faure et al., 1996a) were assigned to late stages of the Acadian the inferred source area for the Bonaventure (Fig. 2B). Peripheral areas, such as the Mari- orogeny (Malo and BeÂland, 1989; Malo et al., Formation detritus in the Cannes-de-Roches times Basin, mainly were subjected to tran- 1992, 1995; Kirkwood et al., 1995; Malo and Cove section, which is to the southwest ac- spressive accommodation of this indentation, Kirkwood, 1995) and had not been recognized cording to paleocurrent vectors (Fig. 1) (Rust, while being simultaneously buried by sedi- within Mississippian rocks. 1981) and which is now in part underlain by ments coming from the Alleghanian orogen, Bonaventure beds of the Ristigouche Basin or which was being constructed to the southwest PROBLEMS RAISED BY THE by older basement rocks (Fig. 3). Likewise, (Thomas and Schenk, 1988; Gibling et al., REGIONAL STRATIGRAPHIC paleocurrent vectors measured in Bonaventure 1992; Keppie, 1993) (Fig. 2B). RECORD beds of the Ristigouche Basin in the Perce area indicate a source area to the north (Jutras POST-ACADIAN Paleocurrent, provenance, and facies- et al., 2001), where Bonaventure beds of the TECTONOSTRATIGRAPHY OF THE distribution data indicate that the Mississip- Cannes-de-Roches Basin are now located EASTERN GASPE PENINSULA pian successions of the Mal Bay and Chaleur (Fig. 1). In other words, the two basins had to Bay areas were deposited in two different ba- be separated by a source area during deposi- The pre-Carboniferous basement in the sins that are referred to as the Cannes-de- tion of the Bonaventure Formation, but that eastern Gaspe Peninsula comprises late Pre- Roches (Jutras et al., 2001) and Ristigouche source area is no longer present. cambrian to Ordovician rocks deformed by the (van de Poll, 1995) Basins, respectively (Fig. The present distribution of Mississippian Middle Ordovician Taconic orogeny and Late 1). In the Cannes-de-Roches Basin, red clastic rocks in the eastern Gaspe Peninsula implies Ordovician to Middle Devonian rocks de- rocks that were previously assigned to the that a signi®cant lateral displacement has oc- formed by the Middle Devonian Acadian lower and middle members of the abandoned curred between the two basins. The fault sys- orogeny (Kirkwood, 1989). The oldest post- Cannes-de-Roches Formation (Alcock, 1935) tem along which this took place is exposed in Acadian unit in the eastern Gaspe Peninsula are now included in the Bonaventure Forma- the Perce area (Figs. 3, 4). The main fault is is the undated La CouleÂe Formation, a gray tion (Jutras et al., 2001). Correlation of the here referred to as the ``Perce Fault'' (new clastic succession that unconformably under- Bonaventure and Cannes-de-Roches red beds name), although Kirkwood (1989) referred to lies the also-undated red clastic rocks of the is based on facies equivalence and stratigraph- the same fracture as the ``TroisieÁme-Lac Bonaventure Formation (Jutras et al., 1999) ic position, both successions being uncon- Fault.'' The new name is proposed because (Fig. 3). Thick and massive groundwater cal- formably underlain by the La CouleÂe Forma- this fracture zone is not coincident with the crete forms the base of the La CouleÂe For- tion and disconformably overlain by gray beds TroisieÁme-Lac Fault as de®ned by BeÂland mation and is often the only remnant of this of the Pointe Sawyer Formation. (1980) (Fig. 1). unit, which was uplifted and almost entirely The just-mentioned correlation raises a The Perce Fault and other faults of the east- eroded prior to sedimentation of the Bonaven- problem because the Bonaventure Formation ern Gaspe Peninsula are described in the fol- ture Formation. is less than 50 m thick in the Cannes-de-Roches lowing section. Structures within pre-Missis- The La CouleÂe (Jutras et al., 1999) and Cove section (Figs. 3, 4E) of the Cannes-de- sippian basement rocks were studied by Bonaventure (Rust et al., 1989) Formations Roches Basin, but at least 350 m thick in the Kirkwood (1989). The focus of this paper is are interpreted as fault-controlled sedimentary incomplete Perce section (Figs. 3, 4C, 4D) of on structures that affect Mississippian rocks, units. These two units are locally in fault con- the Ristigouche Basin, 500 m away. In fact, if which exhibit brittle fabrics of strongly cata- tact with one another, which implies that fault the subvertically tilted strata of the Cannes- clastic material but which contain only scarce activity also occurred after deposition of the de-Roches Cove section (Fig. 4E) were to be kinematic indicators. Subordinate Riedel Bonaventure Formation (Jutras et al., 1999). restored to horizontal, they would literally structures and reverse faults locally bear slick- Renewed fault activity is thought to have touch rocks of the much thicker Perce section ensided surfaces with calcite ®bers that pro- controlled sedimentation of the Pointe Sawyer (Fig. 4C, 4D), which only includes the coarse vide diagnostic kinematic indicators through Formation, which overlies the Bonaventure lithofacies that corresponds to the lower half their asymmetric shape. These data are com- Formation and was dated as late ViseÂan to ear- of the Bonaventure Formation (Jutras et al., piled in Table DR1.1 ly Namurian (Late Mississippian) (Jutras et 2001). The residual 350 m, which are seven al., 2001) from a spore assemblage (the SM times thicker than the full Cannes-de-Roches POST-MISSISSIPPIAN STRUCTURES Zone of Utting, 1987) that is now considered Cove section, may therefore represent less OF THE PERCE AREA (EASTERN to be exclusively Namurian (J. Utting, 2002, than half of the original thickness of the Bon- GASPE ) personal commun.). The conformably overly- aventure Formation in the Perce section. ing Chemin-des-PeÃcheurs Formation, consist- Moreover, paleocurrent indicators in the two The Perce Fault ing of undated sandstones, marks the onset of successions show opposing trends (Fig. 1), sedimentation from distal sources (Jutras et and clast compositions indicate that they were The Perce Fault system separates Mississip- al., 2001). not fed by the same local source area (Jutras pian rocks of the Ristigouche Basin from Faure et al. (1996a) recorded evidence with- et al., 2001). Clast compositions in Bonaven- those of the Cannes-de-Roches Basin. Along in Late Devonian plutons of southern Quebec ture Formation beds of the Cannes-de-Roches transect A±B, the Perce Fault separates the and within Mississippian rocks of the Gaspe Basin (Cannes-de-Roches Cove section) are Peninsula for three minor paleostress orienta- mainly characterized by Lower Devonian si- 1GSA Data Repository item 2003xxx, the numer- ical data used for plots in Figure 3, is available on tions involving no signi®cant displacement. liceous limestones of the Forillon, Shiphead, the Web at http://www.geosociety.org/pubs/ Prior to the present study, large strike-slip and Indian Cove Formations (encompassing ft2003.htm. Requests may also be sent to faults affecting Silurian±Devonian rocks in the the abandoned Grande-GreÁve Formation) [email protected].

Geological Society of America Bulletin, December 2003 ALLEGHANIAN DEFORMATION IN EASTERN GASP͘a PENINSULA, QUEBEC Â Fault terpretation Â-Beach, (4) the roadside outcrop near Âe Formation groundwater calcrete at Perce Âe Formation groundwater calcrete on the side of Murphy Creek. Geology of pre-Mississippian units is by Kirkwood (1989). Â area, with fault-plane (great circles) and slicken®ber (dots and dotted arrows) orientations in (1) the strike-slip duplex of the Perce the Ruisseau Blanc Fault, andComposite (5) columns the of La localities Coule of a±e the and three the groups cross of section secondary of structures transect recorded A±B in are the shown vicinity in of Figure the 4. Ruisseau The Blanc cross Fault section is of shown transect in C±D inset. is shown in Figure 9. In at Cannes-de-Roches Point, (2) the deformation corridor at Cap Blanc, (3) the La Coule Figure 3. Geology of the Perce

Geological Society of America Bulletin, December 2003 JUTRAS et al. Â area (legend, localities, and transect are Figure 4. Stratigraphic columns a to e and cross section A±B, showing the main structures and stratigraphic units of the Perce shown in Fig. 3). A sketch of the open drag fold adjacent to the Cap Blanc Fault is shown in inset. C.-d.-R BasinÐCannes-de-Roches Basin.

Geological Society of America Bulletin, December 2003 ALLEGHANIAN DEFORMATION IN EASTERN GASP͘a PENINSULA, QUEBEC

breccia is also observed on the southern ¯ank of Pic de l'Aurore, separating horizontal beds of the Bonaventure Formation from vertical beds of the Shiphead Formation, which con- stitute the fault slab (Fig. 7). Randomly ori- ented patches of ®ssile structures, absence of sedimentary structures, higher compaction, and more angular clasts clearly differentiate this breccia from the ¯at-lying sedimentary breccia of the Bonaventure Formation, which constitutes part of Pic de l'Aurore (Figs. 8A, 8B). The Perce Fault turns inland in an east strike at the westernmost end of Pic de l'Aurore (Fig. 3) and resumes a southeast strike ϳ2 km to the west. The sharp bend in the fault trajectory at Pic de l'Aurore may have caused the reverse fault to offset rocks of the Mississippian succession parallel to the bend, a few hundred meters to the north of the main fault near Cannes-de-Roches Point (tran- sect C±D in Figs. 3 and 9). Measured reverse- fault planes are oriented east-west on average, but can be subdivided in two groups, one striking east-northeast and the other striking east-southeast (Fig. 3, stereonet 1; Table DR1 [see footnote 1]). One of the east-northeast± Figure 5. Large limestone blocks of the Forillon Formation and red fault breccia in mul- striking fault planes shows slicken®bers tiepisodic, laminated calcite veins within the deformation corridor of the Perce Fault. Pen plunging 60Њ with a 218Њ trend, indicating is 15 cm long. thrusting toward 038Њ. The orientations of reverse-fault slicken®- bers, reported here and elsewhere in this paper, thin and steeply dipping Cannes-de-Roches sandstones (Early Devonian) (Kirkwood, are interpreted as re¯ecting the main principal ␴ Cove succession (Fig. 4E) from the thick ¯at- 1989), which are reddened and contain nu- stress ( 1) that controlled their formation, but lying Perce succession (Fig. 4C, 4D) to the merous laminated calcite veins and which are not necessarily that of the paleostress that con- south (Fig. 3). The fault corridor includes the oriented at high angle to the structural trend trolled formation of the fault itself (see sub- northernmost tip of Bonaventure Island of the pre-Carboniferous basement. sequent discussion). In some cases, the ob- (southeast corner in Fig. 3), which is charac- The Trois Soeurs and Pic de l'Aurore are served slicken®bers may only re¯ect the last terized by red fault breccia (Fig. 5) plastered separated from pre-Carboniferous basement movements in the history of a fault plane that against ¯at-lying Bonaventure Formation con- rocks by red fault breccia. This cataclastic ma- may have been subjected to paleostresses hav- glomerate and sandstone. The breccia com- terial can be best observed within large blocks ing different trends. In friable clastic rocks, prises a mixture of pulverized Bonaventure fallen on the beach from the 2±3-m-thick in kinematic indicators of early fault movement Formation detritus and angular limestone situ fault breccia that plasters the northern are unlikely to be preserved after reactivation clasts of the Devonian Forillon Formation. ¯ank of Pic de l'Aurore (Fig. 6). Red fault of the fault under a different trend. Only re- Large blocks (1 to 10 m3) of red fault breccia and limestone of the Forillon Formation are enclosed within laminated calcite veins. The blocks are also invaded by older but similar calcite veins, indicating that this section of the deformation corridor was affected by several hydrothermal episodes. The northwest-striking deformation corri- dor is exposed for several kilometers on the coastal cliffs of PerceÂ, where a series of 100- m-scale rock slabs can be observed, including Rocher PerceÂ, the Trois Soeurs, and Pic de l'Aurore (located in the eastern half of Fig. 3). The fault slabs stand in the local landscape as differential-erosion monoliths. All these slabs are composed of vertical beds of Forillon For- mation limestones and Shiphead Formation Figure 6. Fallen slab of compact red fault breccia near Pic de l'Aurore.

Geological Society of America Bulletin, December 2003 JUTRAS et al.

measurements made by Kirkwood (1989) on these thrusts, the average strike is 086Њ. From these structures and the conjugated secondary strike-slip faults affecting Matapedia Group rocks, movement along the TroisieÁme-Lac Fault (Perce Fault in this paper) was inter- preted as dextral by Kirkwood (1989), which corroborates with our data. Northwest of Mont Blanc, the Perce Fault resumes a northwest strike, with Mississippian beds of the Cannes-de-Roches Cove succes- sion tilting 70Њ perpendicular to the fault (cen- ter of Fig. 3). Farther to the northwest, the trace of the Perce Fault makes another bend Figure 7. View of ϳ200-m-high Pic de l'Aurore from the west with superimposed mapping into a west-northwest strike (west of the vil- data. A large fault slab of the Shiphead Formation (DSh) is caught between rocks of the lage of Coin-du-Banc in Fig. 3) and is adja- Matapedia Group (OSM) and subhorizontal beds of the Bonaventure Formation (CBo; cent to a tight anticlinal drag fold (plunge 30Њ, light dashed lines). Breccia is concentrated along heavy dashed lines. trend 105Њ) affecting strata of the La CouleÂe and Bonaventure Formations on the north side verse faults that strike approximately perpen- sures of the reverse fault, Matapedia Group of the fault (Fig. 10). This drag fold is the dicular to their slicken®bers are assumed in rocks (Ordovician to Silurian) thrust over Mis- northernmost evidence for compressive stress this study to have undergone a single defor- sissippian rocks of the Pointe Sawyer and affecting Mississippian rocks in this area, but mation event. Chemin-des-PeÃcheurs Formations (east of continuation of the Perce Fault farther north The thrust block near Cannes-de-Roches transect C±D in Fig. 3). These contractional is suggested by the sharp stratigraphic break Point is interpreted as a ``strike-slip duplex'' features associated with a left bend suggest between Matapedia Group rocks and Missis- (sensu Woodcock and Fischer, 1986) within a that movement of the Perce Fault was dextral sippian rocks (northwest quadrant of Fig. 3). positive ¯ower structure. The Mississippian (Woodcock and Fischer, 1986). The path of the Perce Fault is offset by two succession on the hanging wall of the reverse Although only fault planes directly involv- small north-northwest±striking dextral faults, fault is steeply dipping (Figs. 8A, 8B), where- ing Mississippian strata are represented on the near Coin-du-Banc and near Perce (Fig. 3), as the same units on the footwall of this fault, stereonets of Figure 3, east-striking reverse one of which is adjacent to the drag fold exposed at Cannes-de-Roches Point, are near- faults affecting pre-Carboniferous strata are shown in Figure 10. The west-northwest± ly horizontal (Fig. 9). In the western expo- also abundant near Pic de l'Aurore. Of 29 striking fold and the north-northwest±striking

Figure 8. (A) View from the southeast side of the 200-m-high Pic de l'Aurore. The thick, ¯at-lying succession of Bonaventure Formation beds within the Ristigouche Basin contrasts with that succession's thin and steeply dipping equivalent within the Cannes-de-Roches Cove succession, in the background. (B) Opposite view. A major post-Acadian strike-slip fault separates the Cannes-de-Roches Basin succession from the Ristigouche Basin succession. The heavy dashed lines are fault contacts, thin full lines are interformational strati- graphic contacts, and thin dashed lines are intraformational contacts. OHoÐHonorat Group; OSM (Pa)ÐPabos Formation (lower Matapedia Group); OSM (WH)ÐWhite Head Formation (upper Matapedia Group); DFoÐForillon Formation; DShÐShiphead For- mation; CLCÐLa CouleÂe Formation; and CBoÐBonaventure Formation (refer to legend in Fig. 3). The pre-Carboniferous geology is by Kirkwood (1989).

Geological Society of America Bulletin, December 2003 ALLEGHANIAN DEFORMATION IN EASTERN GASP͘a PENINSULA, QUEBEC

away from the fault, below ¯at-lying Bona- venture beds (between km 2 and km 3 on cross section A±B of Fig. 4). However, this pre-Bonaventure normal movement is oppo- site to the present stratigraphic offset observed along that fault. Basement rocks are vertically offset by at least 200 m at the level of the Cap Blanc Fault, according to thickness extrapolations for the Bonaventure Formation on the coast- line. Along the 15 km of coastline southwest of PerceÂ, several normal faults parallel to the Cap Blanc Fault have offset the Bonaventure Figure 9. Unnamed reverse fault creating an offset within the Cannes-de-Roches Point Formation by tens of meters. The largest nor- succession (from transect C±D of Fig. 3; the legend is also in Fig. 3). mal fault is designated the PerceÂ-Sud Fault (Fig. 4 and southeast quadrant in Fig. 3). The 25-m-wide deformation corridor of the Cap Blanc Fault (Figs. 11A, 11B) includes a 2-m-thick slab of vertically dipping Matapedia Group limestone and a 20-m-wide anticlinal drag fold (plunge ϳ45Њ, trend 330Њ) developed within the Bonaventure Formation (Fig. 4, in- set). To be compatible with the observed drag- fold geometry, normal or reverse movement would imply that the northeast block collapsed with respect to the southwest block, which is contrary to the observed stratigraphic dis- placement. The fold is open and plunging to- ward the north-northwest, suggesting that it may be related to lateral dragging from dextral strike-slip motion along the 115Њ-striking Cap Blanc Fault (cf. Biddle and Christie-Blick, 1985). Rocks in the deformation corridor are also cut by minor reverse faults with slickensided Figure 10. Drag fold in the La CouleÂe Formation groundwater calcrete (CLC) and Bon- surfaces bearing calcite ®bers indicating aventure Formation (CBo) near the village of Coin-du-Banc (location shown in Fig. 3). thrusting toward the north-northeast (ϳ021Њ) The photograph is oriented toward the southeast. and the south-southwest (ϳ201Њ) (Fig. 3, ster- eonet 2; Table DR1 [see footnote 1]). On the northeast side of the Cap Blanc fault, in the fault are compatible with a north-northeast± Jutras et al. (1999) to coincide with a line of groundwater calcrete of the La CouleÂe For- south-southwest main principal stress (Wilcox abrupt stratigraphic breaks, is clearly observ- mation at PerceÂ-Beach, three low-dipping et al., 1973). North-northwest±striking faults, able on aerial photographs but is not exposed. thrusts (Ͻ10Њ) with slicken®bers indicating with usually Ͻ1 km offset, are found through- Although kinematic indicators are lacking, it thrusting toward the north-northeast (ϳ032Њ) out the eastern Gaspe Peninsula (Fig. 1) and is postulated that this fault is part of the ¯ower are truncated by steeper (ϳ35Њ) reverse faults were considered to be late Acadian structures structure associated with the left bend in the with slicken®bers indicating thrusting toward by Kirkwood (1989), who also included larger Perce Fault system at Pic de l'Aurore. the northeast (ϳ047Њ) and the southwest northwest-striking faults within the same sys- (ϳ227Њ) (Fig. 3, stereonet 3; Table DR1 [see tem. From the observed offset of stratigraphic The Cap Blanc Fault footnote 1]). breaks, it is here concluded that the northwest- The orientation of slicken®bers on these striking fault system is truncated by the north- The Cap Blanc Fault parallels the Perce subsidiary reverse faults is interpreted to re- ␴ northwest±striking fault system and that both Fault and separates the Matapedia Group from ¯ect the main principal stress vector ( 1) that systems produced lateral offsets in Mississip- the Bonaventure Formation on the south side led to their formation, which seemingly rotat- pian rocks. of Cap Blanc (southeast quadrant in Fig. 3). ed clockwise from north-northeast to north- It was interpreted as a normal fault by Alcock east. On both sides of the Cap Blanc Fault, The Mont-Sainte-Anne Fault (1935) and Kirkwood (1989). According to these slicken®bers are nearly perpendicular to Jutras et al. (1999), the Cap Blanc Fault may the main fault trace, which precludes their be- The Mont-Sainte-Anne Fault (southeast have acted as a normal fault prior to Bona- ing related to strike-slip movement on that quadrant of Fig. 3), which merges with the venture Formation deposition to account for fault. The slicken®bers are oblique to the Perce Fault at both ends and was inferred by the 20Њ tilting of La CouleÂe Formation beds hinge line of the drag fold, which makes them

Geological Society of America Bulletin, December 2003 JUTRAS et al.

Figure 11. The Cap-Blanc Fault. (A) Coastal outcrop of the fault zone, with an over 10 m long fault slab containing Matapedia Group limestone (OSM) and highly deformed Bonaventure Formation sandstone (CBo). The photograph is oriented toward the northwest. (B) View of the northeast limb of a 20-m-wide drag fold and of the undeformed Bonaventure Formation beds that extend away from it. The photograph is oriented toward the west.

incompatible with that structure as well. As The Ruisseau Blanc Fault gest that they are respectively R, RЈ, and P the reverse faults are overprinted in the fold, structures of a main dextral fault with an they are interpreted as being related to a sub- In a roadside outcrop of Bonaventure For- ϳ320Њ strike (Fig. 3; inset). The main princi- ␴ sequent north-northeast± to northeast-trending mation conglomerate (Fig. 3, locality 4), mi- pal stress ( 1) responsible for motion along compression event, which may be responsible nor subvertical fault planes forming a conju- these structures is inferred to bisect the aver- for the 15Њ tilting of Mississippian strata away gate set are plastered with thick calcite age R and R' structures, giving a north-north- from the fault on the northeast block. This 15Њ slicken®bers that cumulatively indicate sev- east (005Њ) strike (Fig. 3; inset). dip of Mississippian beds, away from the Cap eral meters of displacement (Fig. 12). Dextral The fault orientations and proposed kine- Blanc Fault, is also observed at the southern faults striking north-northwest are conjugate matics can be attributed to the nearby Ruisseau end of Bonaventure Island (southeast corner to sinistral faults striking north-northeast (Fig. Blanc Fault, one of several north-northwest± in Fig. 3). The Cap Blanc Fault may have 3, stereonet 4; Table DR1 [see footnote 1]). striking dextral fractures truncating the east- been the site of minor reverse movement in Less than 1 km to the northwest, on a brook- striking Grande-RivieÁre Fault (Kirkwood, the process, but the dominant vertical dis- side exposure (Murphy Creek), subvertical 1989) (Fig. 1). Although the Ruisseau Blanc placement along that fault is normal, as older northwest-striking fault planes cut the basal Fault on Kirkwood's map is shown as buried rocks compose the footwall (Fig. 4). In con- calcrete of the La CouleÂe Formation and bear under the Bonaventure Formation to the south, clusion, although secondary structures mainly dextral slicken®bers (Fig. 3, stereonet 5; Table lineaments on aerial photographs indicate that indicate reverse movement along the Cap DR1 [see footnote 1]). The average 53Њ angle the fault cuts this poorly exposed unit. Blanc Fault, such kinematics can only repre- that separates the strikes of dextral faults from The Ruisseau Blanc Fault apparently trun- sent a minor reactivation of a fault that mainly those of sinistral faults on stereonet 5 and the cates the Cap Blanc Fault (western half of Fig. supported normal and transcurrent movement average 86Њ angle that separates the latter from 3), whose location can be approximately de- earlier in its history. the strikes of dextral faults on stereonet 4 sug- duced from stratigraphic breaks and scarp de-

Geological Society of America Bulletin, December 2003 ALLEGHANIAN DEFORMATION IN EASTERN GASP͘a PENINSULA, QUEBEC

thickness, opposite paleocurrent trends, and nonmatching provenance. At the time of deposition, the petromict fan- glomerates of the Bonaventure Formation that are now near Pic de l'Aurore in the Cannes- de-Roches Basin are interpreted to have been located north of the Grande-RivieÁre Fault (Fig. 3), which forms the northern boundary of the Ristigouche Basin (Jutras et al., 2001), to al- low the presence of an intervening source area between the two basins at the time of depo- sition. In support of this interpretation, pre- Carboniferous rocks exposed north of the Grande-RivieÁre Fault (Fig. 3) correspond well with the clast compositions of Bonaventure Figure 12. Thick dextral slicken®bers plastered on Bonaventure Formation conglomerates beds in the Cannes-de-Roches Cove section, in the area of the Ruisseau Blanc Fault (Fig. 3, locality 4). The photograph is oriented which are dominated by Lower Devonian si- toward the east. liceous limestones of the Forillon, Shiphead, and Indian Cove Formations (Rust, 1981). These units are only present in the form of velopment from the coast to the inferred in- Peninsula area is further complicated by the fault slabs in the source area indicated by pa- tersection with the Ruisseau-Blanc Fault. scarcity of inland exposures and by the cha- leocurrent vectors determined from alluvial- However, scarcity of exposure on land makes otic, cataclastic nature of the main faults. fan deposits in the Cannes-de-Roches Cove it dif®cult to trace faults accurately. Moreover, the ¯at-lying Mississippian conti- section (Rust, 1981) (Fig. 3). nental clastic rocks, which are characterized At least 10 km of lateral displacement along DISCUSSION by high lateral variability, do not provide tight the Perce Fault, away from contemporaneous constraints on stratigraphic displacements. Ristigouche Basin rocks, is necessary to re- Synopsis and interpretation of The main structure affecting Mississippian turn these northeast-trending alluvial-fan de- Alleghanian structures in the eastern rocks in the Perce area is the northwest- posits to the outcrop area of basement rock Gaspe Peninsula striking Perce Fault, but kinematic indicators corresponding to the clast compositions in the from secondary structures along this fault are alluvial-fan deposits and to reconstruct a plau- The absence of observed paleostress indi- especially limited within these rocks, as op- sible pre-displacement paleogeography (Fig. cators within Mississippian units of the Gaspe posed to those provided by the local basement 13). Even more displacement is necessary to Peninsula led many authors to conclude that rocks (Kirkwood, 1989). The overall orienta- allow space for the signi®cant source area that these rocks were not affected by the brittle tion of reverse faults cutting Mississippian would have been needed to provide the south- strike-slip motion that affected older rocks rocks near Cannes-de-Roches Point (Fig. 3, ward-trending coarse-grained alluvial-fan de- (Alcock, 1935; St-Julien and Hubert, 1975; stereonet 1) is compatible with dextral move- posits of the Ristigouche Basin in the Perce area, away from contemporaneous Cannes-de- Bernard and St-Julien, 1986; Kirkwood, 1989; ment along the northwest-striking Perce Fault, Bourque et al., 1993; Malo and Kirkwood, Roches Basin rocks (Fig. 13). Hence, although which would imply a north-northwest±south- 1995; Kirkwood et al., 1995). Subsequently, displacement values based solely on basin re- southeast to north-south main principal stress. however, Faure et al. (1996a) demonstrated construction cannot be precise, a post-Missis- However, the only observed slicken®bers on that such indicators exist, although they are sippian displacement in the order of 10 to 20 these reverse-fault planes are oriented at a 90Њ scarce. km along the Perce Fault is considered angle with the main fault trace, which casts The paucity of paleostress indicators within probable. doubt on this inferred north-northwest±south- Mississippian rocks of the Gaspe Peninsula As the Cap Blanc Fault is parallel and ad- area can be explained by the nature of the ma- southeast to north-south stress direction and jacent to the Perce Fault, it probably has a terial, which is dominated by poorly consoli- instead indicates a north-northeast±south- similar tectonic history. The Cap Blanc Fault dated coarse-grained clastic rocks. Such rocks southwest main principal stress. Moreover, provides evidence for successive normal, dex- are not good materials for recording paleos- structural data presented by Kirkwood (1989) tral strike-slip, and reverse motion. The dex- tress indicators compared to more massive and for this fault collectively indicate a north- tral strike-slip component, which would indi- competent rocks. For example, subordinate northeast±south-southwest main principal cate a north-northwest±south-southeast to structures in Mississippian rocks of the Perce stress, which is nearly perpendicular to the ob- north-south main principal stress, is suggested area are best recorded in the massive and com- served fault trace, thereby raising questions by the presence of an open drag fold plunging petent La CouleÂe Formation groundwater cal- about the dextral strike-slip interpretation pre- ϳ45Њ on the southwest block of the Cap Blanc crete (drag fold in Fig. 10, and slicken®ber- sented in that paper as well. However, such Fault (Fig. 4, inset). bearing fault planes plotted in stereonets 3 and movement is necessary to explain the present In summary, the Perce Fault system struc- 5 of Fig. 3), although this lithology has very distribution of Mississippian strata in the area. turally bounded the Cannes-de-Roches Basin limited exposure. Neither normal nor reverse movement can ex- during deposition of the Bonaventure Forma- Interpretation of structures affecting the plain the juxtaposition of time-equivalent tion (Fig. 13A), in accordance with the paleo- Mississippian clastic succession of the Gaspe units with such a signi®cant difference in geography proposed by Rust (1981), and was

Geological Society of America Bulletin, December 2003 JUTRAS et al.

Figure 13. (A) Paleogeography of the Bonaventure Formation in the Cannes-de-Roches Basin (Rust, 1981) and Ristigouche Basin (Jutras et al., 2001). The thin Cannes-de-Roches succession of Bonaventure Formation beds (lower and middle members of the abandoned Cannes-de-Roches Formation) is characterized by fanglomerates and alluvial plain deposits only (Rust (1981), whereas alluvial fans in the Ristigouche Basin connected with west- to west-southwest±¯owing trunk rivers (Jutras et al., 2001). (B) Model for the juxtaposition of the two basins by strike-slip faulting.

subsequently involved in juxtaposing the array of main principal stress vectors deter- and are possibly not indicative of the cumu- Cannes-de-Roches and Ristigouche Basins mined in Mississippian rocks of the Perce lative history of that fault. (Fig. 13B). Most of this displacement oc- area. In their study of post-Acadian paleostresses curred along the Perce and Cap Blanc fault Further evidence in support of this stress- in southern Quebec, Faure et al. (1996a) also ␴ system, whereas only minor displacement rotation hypothesis is the attitude of reverse inferred a gradual clockwise rotation of 1 seems to have occurred along the north-north- faults in the Cap Blanc Fault corridor, which from north-northwest±south-southeast to west±striking fault system that truncates this does not correspond well with the orientation north-northeast±south-southwest, although ␴ system, even though secondary structures as- of their slicken®bers (Fig. 3, stereonet 2). none of their estimated 1 vectors are as clear- sociated with the latter are best represented. None of these reverse faults strike east-north- ly northeast-southwest as that suggested by According to the observed displacement of east, which would be expected under a north- the youngest reverse faults at PerceÂ-Beach. ϳ Ordovician and Silurian units, only 1kmof northeast±south-southwest ␴1, but three re- These authors tentatively associated this pa- dextral displacement occurred on the Ruisseau verse faults out of eight strike east-southeast leostress rotation with the gradual indentation Blanc Fault (Kirkwood, 1989), the main and are therefore compatible with north-north- of Gondwana's Reguibat uplift into Laurentia north-northwest±striking fault in the Perce west±south-southeast compression. The slick- during the Carboniferous (Fig. 2) (Lefort et area. al., 1988; Vauchez et al., 1987; Pique and Ske- en®bers may correspond to late movement on It is here argued that clockwise rotation of han, 1992). the fault planes and possibly formed under a ␴ Ðevolving from north-northwest±south- In most cases, objectively dividing struc- 1 slightly different stress regime than that pre- southeast to northeast-southwestÐand gradual tures related to one trend from those of the vailing when the fracture was originally reduction of its intensity may have occurred other can be a dif®cult task, as structures re- formed. in the eastern Gaspe Peninsula during post- lated to different episodes of deformation may Mississippian time. Evidence for this clock- Similarly, the only slicken®bers that were intermingle. Because Kirkwood (1989) consid- wise rotation of paleostress is given by the measured on reverse-fault planes associated ered northwest- and north-northwest±striking truncation of thrust planes that indicate an with the Perce Fault are oblique to the strike fault planes to lie within the same fault sys- ϳ Њ Њ␴ of the one fault plane that hosts them (Fig. 3, 032 ±212 1 orientation by reverse-fault tem, contrasting paleostress trends presented ϳ Њ Њ␴ stereonet 1; Table DR1 [see footnote 1]). Al- planes that indicate an 047 ±227 1 orien- by Kirkwood average out to north-northeast, tation in the calcrete of PerceÂ-Beach (Fig. 3, though orientation of this particular fault plane but may in fact re¯ect this clockwise rotation Њ Њ␴ would indicate a stress regime involving stereonet 3). The 005 ±185 1 orientation es- of paleostresses from north-northwest±south- timated from Riedel structures of the Ruisseau north-northwest±south-southeast compression, southeast to northeast-southwest. Blanc Fault (Fig. 3, stereonets 4 and 5) and the fault plane's slicken®bers indicate a north- The proposed scenario to explain the array Њ Њ␴ the 021 ±201 1 orientation estimated from northeast±south-southwest main principal of structural data collected in Mississippian reverse-fault slicken®bers in the Cap Blanc stress. Here again, the slicken®bers may only rocks of the Gaspe Peninsula is as follows: Fault corridor (Fig. 3, stereonet 2) add to this re¯ect the last movement on that fault plane 1. Dextral motion along the northwest-

Geological Society of America Bulletin, December 2003 ALLEGHANIAN DEFORMATION IN EASTERN GASP͘a PENINSULA, QUEBEC

striking Perce and Cap Blanc Faults occurred Acadian structures, giving a very poorly con- grain and into passive basins that are located in response to a strong initial north-northwest± strained upper age limit for them, whereas laterally behind the main orogenic front. How- south-southeast paleostress, resulting in the their lower age limit is constrained to the Na- ever, whereas the Himalayan orogeny involves displacement of Carboniferous units by more murian, which is the age of the Pointe Sawyer the collision of a small continent with a large than 10 km. Subordinate structures associated Formation. It is postulated that all deforma- one, the Alleghanian orogeny involved the with those faults are the Cap Blanc drag fold tions affecting Mississippian rocks of the Gas- collision of two major continental masses, (Fig. 4; inset) and the east-northeast± to east- pe Peninsula are distal manifestations of the which restrained the indentation to some striking reverse faults at Cannes-de-Roches Hercynian-Alleghanian orogeny, which ended degree. Point (Fig. 3, stereonet 1) and Cap Blanc (Fig. in the Permian, although later compressive 3, stereonet 2). features related to oceanic plate readjustments CONCLUSION ␴ 2. As 1 gradually rotated clockwise and as were also registered within Cretaceous rocks ␴ compressive stress diminished in intensity, the of southern Quebec, but indicate that 1 was Post-Acadian deformation involving signif- drag fold at Cap Blanc and the preexisting northeast-southwest (Saull and Williams, icant lateral displacement is demonstrated for subsidiary reverse faults were reactivated ac- 1974; GeÂlard et al., 1992; Faure et al., 1996b). the ®rst time in the Gaspe Peninsula along the cordingly, new ones were formed, and the As post-Acadian structures in the Gaspe Perce Fault system, which has juxtaposed the main faults were eventually truncated by new- Peninsula affect rocks that are as young as Na- Mississippian Cannes-de-Roches and Ristigo- ly developed north-northwest±striking dextral murian, they are possibly related to the defor- uche Basins in post±early Namurian time un- faults. Associated with this north-northeast± mation event that took place during the West- der a transpressive regime. Although the ¯at- south-southwest to northeast-southwest com- phalian B, which corresponds to the most lying Carboniferous succession does not pression are the drag fold near the village of important Alleghanian phase to have affected provide precise stratigraphic markers, signi®- Coin-du-Banc (Figs. 3, 10), the 70Њ tilting of the Maritimes (PiqueÂ, 1981; Ruitenberg and cant lateral displacement on the Perce Fault is Mississippian strata perpendicular to the Perce McCutcheon, 1982; Nance, 1987; Nance and necessary to justify the absence of a source- Fault in the Cannes-de-Roches Cove (center Warner, 1986; Gibling et al., 1987; Yeo and rock area between the juxtaposed strata of the of Fig. 3), the 15Њ tilting of Mississippian stra- Ruixiang, 1987; Ryan et al., 1988; Thomas Cannes-de-Roches and Ristigouche Basins in ta on the northeast block of the Cap Blanc and Schenk, 1988; Keppie, 1993; Reed et al., the Perce area. From these new data, age de- Fault (southeast quadrant in Fig. 3), the slick- 1993). The presence of seemingly undisturbed termination should be reconsidered for the en®bers and west-northwest± to northwest- Westphalian C to Stephanian beds of the Clif- strictly brittle strike slips of the peninsula, striking reverse faults at Cannes-de-Roches ton Formation on the south shore of Chaleur many of which could be post-Acadian and re- Point (Fig. 3, stereonet 1), Cap Blanc (Fig. 3, Bay, unconformably overlying Mississippian lated to phases of the Alleghanian deformation stereonet 2), and PerceÂ-Beach (Fig. 3, stereo- rocks, supports this hypothesis (Alcock, 1935; in Carboniferous to Permian time. net 3), and various Riedel structures associ- Ball et al., 1981; Legun and Rust, 1982). ated with the Ruisseau Blanc Fault (Fig. 3, Transpressive deformations in the Mari- ACKNOWLEDGMENTS stereonets 4 and 5). times Basin are also reported for the end of We thank S. Faure, M. Bardoux, N. Goulet, J. the Namurian (PiqueÂ, 1981; Waldron et al., Waldron, D. Roy, P. Cousineau, M. Gibling, and S. Regional perspective and timing 1989; Pe-Piper et al., 1991; St. Peter, 1993) Lin for supportive comments and discussions during constraints and for the Pennsylvanian-Permian boundary this project, as well as B. Murphy, H. Maher, and (Donkin episode; Pascucci et al., 2000; Gi- D. Moecher for constructive formal reviews. This Details on the post-Acadian tectonic history bling et al., 2002), but are less widespread. To project was supported by a doctoral fellowship of the Natural Sciences and Engineering Council of of the Gaspe Peninsula remain elusive on ac- conclude on the subject of potential timing, it Canada (NSERC) to P. Jutras. count of the complexity of paleostress trends, should be noted that some faults in the Mar- as de®ned by Faure et al. 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Geological Society of America Bulletin, December 2003