Interna! characteristics of sandbodies of the Ordovician Tourelle Formation, Quebec, Canada R.N. Hiscott1 and M. DeVries2

1Department of Earth Sciences, Memorial University of Newfoundland, St John's, Newfoundland, Canada AlB 3XS 2EXXON Corporation, Houston, Texas, USA

The Tourelle Formation of the Quebec Appalachians was deposited during the latest Arenig in one or more slope-basins situated on a migrating thrust stack (Hiscott et al. 1986). The thrust slices formed an accretionary prism that developed during subduction of the passive margin of Laurentia beneath an offshore volcanic arc (Hiscott 1978). The ultimate collision of this arc with Laurentia produced the Middle to Late Ordovidan Taconic Orogeny. The sedimentary rocks in the thrust slices were first deposited on the passive­margin continental slope and continental rise of Laurentia, and subsequently scraped off the subducting plate and transferred to the accretionary prism. The prism loaded the edge of the Laurentian plate to produce an elongate foreland basin (Quinlan and Beaumont 1984; Hiscott et al. 1986).

The source area for the Tourelle Formation consisted mainly of uplifted passive-margin sediments, but also included mafic to felsic volcanic rocks of the volcanic arc and obducted ophiolites (Hiscott 1978, 1984). The mean palaeocurrent direction is to the west-north-west, oblique to the north-north-east tectonic strike of the local front of the Appalachian orogenic belt. At some outcrop localities, however, palaeocurrents are bimodal or polymodal as a result of switching of the local distributary system (see below).

The Tourelle Formation is believed to have had a depositional thickness of 500--lOOOm (Hiscott 1980), although its top is truncated everywhere by either modern erosion or thrust faults (Biron 1972, 1974). The base of the formation, where exposed, is characterized by a zone, tens of metres thick, of spectacular clastic dikes and sills (Hiscott 1979). The rest of the

formation, at many localities, consists of an alternation of clusters of sandstone beds 10-40m thick (called 'sandstone packets'; these contain very little mudstone or siltstone), and intervals of about the same thickness that consist mainly of Iaminated mudstone (mud turbidites) and thin-bedded siltstone or fine sandstone turbidites. At other localities, sections more than 100m thick contain very little mudstone or siltstone. Sections through the Tourelle Formation, whether or not they contain clearly defined sandstone packets, show few convincing upward thinning or upward thickening cycles (Hiscott 1980, 1981).

Some deposits of single sediment gravity flows within the sandstone packets are as thick as c. 20m; mean deposit thickness is c. 4m. These beds contain a variety of features indicative of rapid deposition from high-concentration density currents, including disorganized grain fabric, fluid-escape pillars, slabs of chert and siliceous mudstone up to 16m long suspended within depositional units, and inversely graded traction-carpet stratification (Hiscott and Middleton 1979, 1980). The first detailed description and interpretation of the latter structure, subsequently designated as 'division S2' by Lowe (1982), was based on beds in the Tourelle Formation (Hiscott and Middleton 1979, 1980). The characteristics of very thick sandstone beds of the Tourelle Formation fit those predicted for the deposits of high-concentration turbidity currents and sandy debris flows (Pickering et al. 1989). The thinner bedded sandstone and siltstone fades within the more mud-rich parts of the succession are dassie turbidites (Hiscott 1980).

The Tourelle Formation has been interpreted by Hiscott 0980) as the record of deposition on small, radial to somewhat elongate, mixed sand-mud submarine fans with a scale similar to the California borderland submarine fans described by Normark 0970). Features critical to the fan interpretation are: (1) abundance of deposits from high-concentration sediment gravity flows that could not have travelled very far away from feeder channels; (2) presence of five small channel cuts with depths of 7 m, > 13m, 9 m, 10m and > 50 m; and locally dramatic differences in the palaeoflow direction for successive sandstone packets at single localities, suggesting periodic major

Atlas of Deep Water Environments: Architectural style in turbidite systems. Edited by K.T. Pickering, R.N. Hiscott, N.H. Kenyon, F. Ried Lucchi and R.D.A. Smith. Published in 1995 by Chapman & Hall, London. ISBN 0 412 56110 7.

swings in local dispersal direction (Hiscott 1980). The erosional cuts can only be examined in two­dimensional outcrops, so that they could be large scours like those described recently from modern fans (Mutti and Normark 1987; Normark and Piper 1991). Nevertheless, the presence of either small channels or large scours favours a fan interpretation. The swings in palaeoflow are consistent with lobe switching on a submarine fan. Hiscott's 0980) estimate of the size of the fans is based on an inferred 15-45 km spadng between feeder channels; this spadng is similar to that of multiple channels of the San Lucas Fan off Baja California (Normark 1970).

For this contribution, three displays of field data that are too large for journal reproduction have been chosen. The first is an aerial photograph of the type locality of the Tourelle Formation at Cap Ste-Anne (Fig. 29.1). The second is a set of field gamma-ray profiles from the Cap Ste-Anne locality (Fig. 29.2), from which the log signature of sandstone packets with different bed thicknesses and sand to mudstone ratios can be determined. The third contribution (Fig. 29.3) is a set of correlated bed-by-bed sections (vertical exaggeration c. 5: 1) through a 60 m thick sandstone packet, extending 900 m in an approximately flow­parallel direction. Details of each contribution are described in the figure captions.

Heferences Biron, S. 1972. Geologie de Ia region de Ste-Anne des Monts.

Ministere des Richesses Naturelles de Quebec, Seroice de Ia Cartographie, open file rep.

Biron, S. 1974. Geologie de Ia regiondes Mechins. Ministere des Richesses Naturelles de Quebec, Seroice de Ia Cartographie, open file rep.

Hiscott, R.N. 1978. Provenance of Ordovician deep-water sandstones, Tourelle Formation, Quebec, and implications for initiation of the Taconic Orogeny. CanadianJournal ofEarth Sciences, 15, 1579-1597.

Hiscott, R.N. 1979. Clastic sills and dikes associated with deep-water sandstones, Tourelle Formation, Ordovician, Quebec. Journal ofSedimentary Petrology, 49, 1-10.

Hiscott, R.N. 1980. Depositional framework of sandy mid-fan complexes of Tourelle Formation, Ordovician, Quebec. Bulletin of the American Association of Petroleum Geologists, 64, 1052-1077.

Hiscott, R.N. 1981. Deep-sea fan deposits in the Macigno Formation (middle-upper Oligocene) of the Gordana Valley, northern Apennines, Italy-Discussion. Journal of Sedimentary Petrology, 51, 1015-1021.

Hiscott, R.N. 1984. Ophiolitic source rocks for Taconic-age flysch: trace-element evidence. Bulletin ofthe Geological Society of America, 95, 1261-1267.

Hiscott, R.N. and Middleton, G.V. 1979. Depositional mechanics of thick-bedded sandstones at the base of a submarine slope, Tourelle Formation (Lower Ordovician) Quebec, Canada. In: Doyle, L.J. and Pilkey, O.H. (eds) Geology of Continental Slopes. Society of Economic Paleontologists and Mineralogists, Tulsa, Special Publication, 27, 307-326.

Hiscott, R.N. and Middleton, G.V. 1980. Fabric of coarse deep-water sandstones, Tourelle Formation, Quebec, Canada. Journal of Sedimentary Petrology, 50, 703-722.

Hiscott, R.N., Pickering, K.T. and Beeden, D.R. 1986. Progressive filling of a confined Middle Ordovician foreland basin associated with the Taconic Orogeny, Quebec, Canada. In: Allen, P.A. and Homewood, P. (eds) Foreland Basins. International Association of Sedimentologists, Special Publication, 8, 309-325.

Lowe, D.R. 1982. Sediment gravity flows: II. Depositional models with special reference to the deposits of high­density turbidity currents. Journal of Sedimentary Petrology, 52, 279-297.

Mutti, E. and Normark, W.R. 1987. Comparing examples of modern and ancient turbidite systems: problems and concepts. In: Leggett, J.K. and Zuffa, G.G. (eds) Marine Clastic Sedimentology. Graham and Trotman, London, pp. 1-38.

Normark, W.R. 1970. Growth patterns of deep-sea fans. Bulletin ofthe American Association of Petroleum Geologists, 54, 2170-2195.

Normark, W.R. and Piper, D.].W. 1991. Initiation processes and flow evolution of turbidity currents: implications for the depositional record. In: Osborne, R.H. (ed.) From Shoreline to Abyss. Society of Economic Paleontologists and Mineralogists, Tulsa, Special Publication, 46, 207-230.

Pickering, K.T., Hiscott, R.N. and Hein, F.]. 1989. Deep Marine Environments: Clastic sedimentation and tectonics. Unwin Hyman, London, 416 pp.

Quinlan, G. and Beaumont, C. 1984. Appalachian overthrusting, lithospheric flexure and the development of Paleozoic stratigraphy in the eastern interior region, U.S.A. Canadian Journal of Earth Sciences, 21, 973-996.

•

Fig. 29.1. Aerialphotograph of the type section of the Tourelle Formation, Cap Ste-Anne, Quebec. The base of the formation here is a sandstone injection complex, 58m thick, that invades rocks of the underlying Cap des Rosiers Group (Hiscott 1979). The segregation of the thicker sandstone beds into clusters of beds ('packets') is pronounced at this locality. These are interpreted as the deposits of single Iobes on the surface of a small submarine fan. Packet 5 has an erosional base (channel depth • 9 m) that may indicate erosion at the distal end of a mid-fan channel; the

erosional reliefwas quickly buried by a very thick sandy debris flow (Hiscott 1980). The most coarse grained and sand-rich packets are Packets 1 and 5. Segregation of sandstones (in packets) from siltstones/mudstones is greatest in the upper part of the section, above Packet 4. The thinly bedded sequence between Packets 5 and 6 may be interchannel or levee deposits, based both on the strong fades segregation and abundant climbing ripple Iamination in the siltstones.

Packers Packet4

P Packet 3 P acket2

acket 7

SOm

A APIGR

50

10

Cap Ste-Anne F= Packet6

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; ; ...

150

Packet 3

Packet2

100

Packet 1

Clastic injections

50

B APIGR

0 & (fj -

c APIGR

D APIGR

100

E APIGR

& f5 -

Packet 4

Packet 6 100

50

Packet 5

0

APIGR

F

Fig. 29.2. Hand-h ld gamma-ray profile ·, paced c. -om apan, through the Tourelle Formation at

Cap te- nne ( ompare inset map with Fig. 29.1 . ertical cal ary. mewhat b au ction E

and F \l ere ·lretched 10 b ner r n ct the geom try f Pack r - whi h ~ a mi r pre m d in th

original dara due 10 measurem n1 acro. minor normal fault . nit. of mea ur are merican P rroleum

In rirute amma ray ( PIGR). a ·ur ment were made with a cintrex GR --oo intillom ter that had

been calil rat d to PIGR value u in mea urernent n 1e 1 pad at the nited tat D partm m of

Energy radiation te r facility at ~ alk r Airfi ld, Grand Jun tion, C lorado. Lm t garnrna-ray readin

(c. -o API R unir-) come from coar e-grained andstone b d in th main and. ton pa k t . E en in

ingle ma i and t ne beds ucce ive reading nucruat by c. 5-10 PIGR unit . Re olution ofthin

mudstone bed. is limited b the rratigraphic ampling interval of 12 inche (c. 30cm . Thinly bedded

dep it b rween ·and. tone packet have a ragged gamma-ra re pon with a m an alue of c.

100 PI R unit . anclstone inje ti n anno1 be cli ringui h d from other and t ne bed u ing only

gamma-ra I

50

-----;;;;UZP

. 40 ·.--------= ===-------= 40 111 =-------

----

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=

0 L- 14

0 ... L - 15

0 Distance along strike of outcrop

100

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0 .. L · 12

200

Upper Datum

]

40

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----?

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Large fault offset here

30

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L- 11 L- 10

300

Large fault offsets

between sections

prevent bed tracing

Lower Datum

400 500

60

Upper Datum

50

40

Downcurrent direction

30

30 --

20

50

L- 5

500 600

Fig. 29.3. orrelation of individual and ton b d for 900 m do"' ncurr nt wirhin a 60 m thick and ton p·Kket at n -ä- arl r ( e Hi on 19 0 for I ati n), Queb . There are a number of -reep fault that off er I ed along thi outcrop; in place where l ed coul I not be walked out and traced in the field, da hed lin are u d to hm inferr d corr lation . The b d at th ba · f thi pack t thi k n up\ ard, but the internal ariation in bed thi kne i e ntially random becau e of bot11 original variation in d po it thickne and ·trong localized couring (e.g. at section height of c. LO m in ection L-6 to L- ). Berwe n e rion L- and L-2 ther i a ugge tion thar, in a c. 10m int rval b dding plan dip g ml down urr m. u h a d wncurrent dip would be n istent with minor progradation of th

growing andbody and a di tal thinning of the pack t. nforrunately thickn variati n f the entire pack t i unknown be au e rh lo r and upp r darum Je el can onl be ompar d at adja em ection L- / L-8. Al o, bedding lo all dip up-y tem that a g neralization r garding apparent progradati n cannot b mad .

Key

Texw r in th lower part of th pack t i nerall coar er toward ction L-15 how er, on i r nr wirh th po ibility of rapid down urr nr fining and thinnin , and mall lob dimen ion , perhap lik the mall andy lob of th Hueneme Fan (Pip r et al. Ch. 2 ). The 31 x 6mblock between ection L-13 and L-1 appear to ha b n tran port d wirh in a mud/ and debri flow rhar depo ited a lurry and tone bed (Hi con and Middleton 1979) I than 150cm thi karound the block 3-4 m at ecrion L-1 ; r.~ -1 m at ection L-13 · ith canered !arge block

roward ection L-12). Th block i lithologically imilar to unit in the underlying Cap d Ro i r Group implying cl rivation b ero ional undercuuing of an up lop canyon wall. Th !arg t bio k may ha e be n d po it d by 'grounding' a a andy d bri flow ten of metr rhick pa , ed over thi ite. The pre ent-day thinne of th lurry ·and ron b d can be explained by clraining of mo t of the fluid debri further down the fan urface.

fluid·escap!! pilla.rs stratification loaded base

slurry sandstone

111 granule sandstone = & conglomerate

20 --- ---

-------- ---- --- .. --- --- ---

0 L- 4

700

50

----------- 40

30 L -3

-------

sheet structure scoured base

------

Lower Datum

800

coarse sandstone "" medium sandstone

tine sandstone & siltstone shale

\ lhickness in metras

L - 2

50

L ·1

900