The St. George Unconformity, northern Appalachians: The relationship of plate convergence at the St. Lawrence Promontory to the Sauk/Tippecanoe sequence boundary

I. KNIGHT Geological Survey Branch, Department of Mines and Energy, Government of Newfoundland and Labrador, P.O. 8700, St. John's, Newfoundland A IB 4J6 Canada N. P. JAMES Department of Geological Sciences, Queen's University, Kingston, Ontario K7L 3N6 Canada T. E. LANE* Department of Earth Sciences, Memorial University of Newfoundland, St John's, Newfoundland A IB 3X5 Canada

ABSTRACT foundland. This and changing rates of sub- lacks synchroneity within North America and sidence influenced not only the shape of the among continents. In the Appalachians, it is The Middle Ordovician St. George Uncon- unconformity, but also pre- and post-uncon- thought to mark the transition from a passive to formity is the Sauk/Tippecanoe sequence formity , that is, facies, thick- a convergent plate boundary (Rodgers and boundary in western Newfoundland. It is a ness, and cyclic sedimentation; the ordered Neale, 1963; Bird and Dewey, 1970; Williams karst unconformity to disconformity to para- timing of events upon the shelf and in coeval and Stevens, 1974; Williams, 1979; Mussman conformity. It formed by uplift and erosion slope ; and a diachronous event and Read, 1986) and reflect passage of the car- during lithospheric flexure as a forebulge stratigraphy from Newfoundland to Quebec. bonate platform across a forebulge (Chappie, passed across the apex of the St. Lawrence This indicates that (1) early Taconic orogene- 1973; Jacobi, 1981; Rowley and Kidd, 1981; Promontory of Laurentia's continental shelf sis rather than eustatic events fashioned the Shanmugam and Lash, 1982; Quinlan and in the initial stages of the Taconic . unconformity and associated stratigraphy Beaumont, 1984; Bradley and Kuski, 1986; Erosion was preceded by gentle uplift, and (2) the transformation from a passive to a Bradley, 1989). It has, however, been difficult to warping, and block faulting of platform convergent plate boundary began in the mid- separate the effects of eustasy and tectonics as a carbonates. Early faults directed ground- dle Ibexian, long before the unconformity cause of the unconformity (Mussmann and water flow and dissolution and locally re- developed. During the early stages of this Read, 1986; Knight and James, 1987). The de- sulted in subsidence dolines that were sites of transformation, imminent convergence of the velopment of the unconformity at the St. Law- anomalously thick pre-unconformity peri- margin caused the slowing to cessation of rence Promontory in western Newfoundland is tidal carbonates. Regional erosion that fol- subsidence. Consequently, there was abrupt reconstructed using recent detailed biostrati- lowed during Whiterockian time probably shallowing of the shelf reflected in the sudden graphic and lithostratigraphic studies of both lasted 1 to 3 m.y. and locally removed as change from open to restricted shelf facies platform (Knight and James, 1987; Williams much as SO m of stratigraphy on block- throughout western Newfoundland. The and others, 1987; James and others, 1989; Stait, faulted topographic highs. Surface karst model predicts that the timing and duration of 1988) and deep-water sediments (James and marked the unconformity with minor karren events, and the longevity of the unconformity Stevens, 1986; Williams and Stevens, 1988). and proto-soils. Subsurface karst as much as reflects the area's location at the St. Law- This has allowed a further assessment of the rela- 120 m below the unconformity was mani- rence Promontory. In this respect, western tive importance of tectonics and eustasy. Newfoundland will be different from other fested as near-surface porosity and - The purposes of this paper are to (1) docu- areas along the Appalachian system, espe- filled fissures, and deeper, structurally con- ment and interpret the nature of the unconform- cially reentrants. The broad scheme of events trolled, small and large caves filled by ity and related features which define the is consistent, however, from area to area dolomite muds, chert sands, and -matrix Sauk/Tippecanoe boundary in western New- along the length of the margin. breccias. Upward stoping during breccia foundland; (2) interpret the history of sedimen- formation finally produced marine and non- tation, erosion, and tectonics revealed by these marine, sediment-filled collapse dolines at the INTRODUCTION features; (3) assess the relative importance of unconformity. Chert-pebble conglomerate eustasy and tectonics; (4) assess the role of the lags rested upon the unconformity before it The unconformable nature of the Sauk/Tip- St. Lawrence Promontory; and (5) apply the was onlapped and buried by widespread per- pecanoe sequence boundary (Sloss, 1963) is model to other parts of the Laurentia's margin. itidal carbonates. well known, but only recently has it been stud- Faulting active throughout late Ibexian and ied in detail and integrated into a model of REGIONAL SETTING Whiterockian time is consistent with the pas- lithospheric dynamics (see review in Mussman sage of the forebulge through western New- and Read, 1986). Because of its extent, both in The northwestern margin of the northern Ap- North America and on other continents (Sloss, palachian Orogen (Humber Zone of Williams, 1972, 1988), the unconformity has long been 1979) is an early Paleozoic, low-latitude mio- *Present address: Teck Explorations Ltd., P.O. 14019, Station A, St. John's, Newfoundland A1B 4G8 viewed as a product of eustatic sea-level fall. The geocline that originally lay along the northern Canada. unconformity is not universal, however, and margin of the Proto-Atlantic or Iapetus Ocean.

Geological Society of America Bulletin, v. 103, p. 1200-1225, 20 figs., 1 table, September 1991.


Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDOVICIAN TO SEDIMENTARY & METAMORPHIC ROCKS TACONIC ALLOCHTHONS ¡^¡¡J ORDOVICIAN FLYSCH [ I ORDOVICIAN CARBONATES CAPE NORMAN A I'.:•:•;.CAMBRIAN PLATFORMAL ROCKS MM PRECAMBRIAN BASEMENT


PORT AU CHOIX Fault and Figure 1. Geologic map of western Joint Rlls-HAWKEI Newfoundland illustrating the main POINT/f geological elements and the location of BATEAU BARRENS stratigraphie sections of Figure 3. Inset map shows the location of the St. Law- TABLE rence Promontory, the Quebec Reen- POINT

trant, the Phillipsburg Group and Ordo- DANIELS HARBOUR vician platformal rocks at Mingan PORTLAND CREEK. Islands and the St. Lawrence Low- POND lands. The solid line is the approximate position of the present-day eastern limit of the carbonate shelf.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1202 KNIGHT AND OTHERS

The early Paleozoic passive margin miogeocline between the Humber Arm and Hare Bay alloch- Stenzel and others, 1990; L. Quinn, 1989, per- of what is now eastern North America was par- thons and a large Precambrian crystalline inlier sonal commun.). Westward transport of an ac- tially destroyed by closing of this ocean and ac- of the Long Range Mountains (Fig. 1). Utilizing cretionary wedge of oceanic lithosphere and cretion of outboard tenanes during Middle detailed litho- and biostratigraphy, excellent deep-water rift and continental-margin sedimen- Ordovician time. Similar miogeoclinal facies are coastal outcrops can be correlated with sections tary rocks in Early to Middle Ordovician time recognized along the western margin of most of along rivers and ponds and in widespread rocky caused flexure of the continental margin and the Appalachian-Caledonian Orogen (Williams and boggy barrens and with subsurface drilling formation of this foredeep prior to burial be- and Stevens, 1974; Williams, 1978,1979). Little over 300 sq. km at Daniel's Harbour Zinc Mine. neath Taconic allochthons. deformed autochthonous and parautochthonous The miogeocline begins with a basal succes- platform strata crop out over wide areas around sion (Fig. 1) of late Precambrian to early Middle St. George Group the St. Lawrence Promontory. Contemporane- Cambrian terrigenous clastic and minor carbon- ous deep-water sediments of the Cow Head ate sediments called the Labrador Group (Schu- The -500-m-thick package of and Group and Cooks Brook Formation lie within chert and Dunbar, 1934; James and others, dolomite is divided into four formations (Knight allochthonous thrust complexes that were trans- 1989). Most succeeding shallow-water carbon- and James, 1987, 1988), the depositional his- ported westward to their present position during ate rocks are encompassed by the Middle to tory of which can be resolved into two third- the . The of this suc- Upper Cambrian Port au Port Group (Chow, order sequences (sensu Vail and others, 1977) of cession has been documented by Rodgers 1986) and predominantly Lower Ordovician St. about equal thickness (Fig. 2). The common se- (1968), Stevens (1970), Williams and Stevens George Group (Knight and James, 1987). The quence boundary is the Boat Harbour discon- (1974), James and Stevens (1982, 1986), Bots- St. George Unconformity lies within the upper formity, a regional paleokarst surface which is ford (1987), and James and others (1988, part of the St. George Group or is the contact the topic of a separate study. The upper se- 1989). In Quebec, the miogeocline crops out in between the St. George Group and overlying quence comprises a basal unit of meter-scale, the Mingan Islands, St. Lawrence Lowlands, Table Head Group. The Table Head Group shallowing-upward, peritidal cycles (Barbace and the allochthonous Phillipsburg Group (Des- (Klappa and others, 1980), comprising carbon- Cove Member, Boat Harbour Formation); a rochers, 1985; Globensky, 1981,1987). ates and shales deposited during foundering and middle subtidal carbonate (Catoche Formation); collapse of the platform in early Middle Ordovi- and an upper sequence of peritidal dolostone SHALLOW-WATER PLATFORM cian time (Stenzel and James, 1987,1988; Sten- (Aguathuna Formation). SEDIMENTARY ROCKS zel and others, 1990), was buried by foreland Costa Bay Member, Catoche Formation. basin flysch and carbonate conglomerate of the This succession of peloidal grainstone and fenes- Goose Tickle Group (James and others, 1989; The rocks crop out in a sinuous belt along tral mudstone, 25 to 60 m thick, at the top of the western Newfoundland's coastal plain, winding formation has conspicuously fewer faunal ele- ments than does the subtidal limestone below, OF THE and it marks the increasing restriction of an UPPER ST. GEORGE AND open-marine shelf. It is thickest near Daniel's ORDOVICIAN LOWER TABLE HEAD Harbour (Fig. 1). Rhythmic, 2- to 3-m-thick, GROUPS CARBONATE locally deepening-upward sequences occur at LITHOSTRATIGRAPHY Daniel's Harbour and Port au Port Peninsula (Fig. 1) (Lane, 1990) but are absent north of Port au Choix. It is conformably overlain by the Aguathuna Formation. The upper part of the Catoche Formation is extensively altered by multistage dolomitization (Haywick and James, 1984; Haywick, 1985) MIDDLE (WHITEROCKIANl and hosts zinc mineralization at Daniel's Har- bour (Fig. 1) (Collins and Smith, 1975; Lane, 1984,1987,1990; Lane and James, 1987). Aguathuna Formation. This complex peri- tidal unit consists of buff-weathering, fine to mi- crocrystalline dolostone, dolomitic shale, and "jT * COSTA minor limestone. It is generally thickest (60-70 BAY m) south of Table Point (Figs. 3 and 4) but Ï /f\ MBR locally attains 100 m at Daniel's Harbour. Pre- TL * dominance of dolostone, abundance of desic- -p- fi cated, cryptmicrobial laminite and shale, scar- city of macrofauna, and the presence of silicified evaporites suggest restricted, hypersaline, deposi- tional environments. The Aguathuna Formation is informally divided into three members based upon detailed core logging at Daniel's Harbour CAMBRIAN Zinc Mine (Lane, 1990). - DISCONFORMITY The lower member, as much as 62 m thick, Figure 2. Stratigraphy of Ordovician carbonate rocks in western Newfoundland and de- comprises burrow-mottled to massive dolo- tailed stratigraphy of the St. George Unconformity. stone/limestone and desiccation-cracked dolo-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 S ALLOCHTHON










Figure 3. Schematic cross sections of the St. George Unconformity in western Newfoundland. Sections are located on Figure 1. Section A, Cape Norman to Pistolet Bay; section B, mainland and islands of Hare Bay; section C, Canada Bay area; section D, Port au Choix area south to Portland Creek Pond; section E, Aguathuna Quarry to Gravels, Port au Port Peninsula. Maps indicate localities of sections illustrated in cross sections. Each section is independently adjusted to reflect local correlations and geological setting. These relationships indicate a largely block-faulted terrane that was subdued by erosion before it was onlapped by upper Aguathuna Formation (Fig. 3D) and the Spring Inlet Member.

Figure 3. (Continued).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1204 KNIGHT AND OTHERS



Figure 3. (Continued).



TABLE POINT FM I * * I i . i zr 40


Figure 3. (Continued). 0 J

laminite and shale. Dolomite-chert breccia, shale to dololaminite to burrowed dolostone most cycles shallow upward. A regionally stromatolitic limestone/dolostone, and chert with erosional breccia caps that can be traced mapped, distinctive, 10-m-thick, burrowed unit occur throughout. In the Daniel's Harbour area, over 400 km2 (Lane, 1990). This rhythmic stra- caps the lower member south of River of Ponds. detailed logging shows that beds have subtle tigraphy can be tentatively correlated 200 km to The middle member is developed only locally thickness variations and are organized into Port au Port Peninsula. Such sequences are rare over structural depressions near Daniel's Har- deepening-upward sequences, 2 to 6 m thick, of to the north of the Daniel's Harbour area where bour where it is as much as 70 m thick. It com-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 1205


. COLLAPSE ® Figure 3. (Continued), BRECCIA




Figure 3. (Continued).

prises meter-scale, shallowing-upward sequences paleo-sinkhole deposits and onlap the uncon- and James, 1987), 1 to 80 m thick, is organized of typical Aguathuna lithologies. formity. Mudcracks and local tepee structures in classic, shallowing-upward sequences com- The upper member overlies the St. George point to continued deposition on muddy interti- prising basal, fossiliferous, burrowed, muddy Unconformity. Although mostly 5 to 15 m thick dal flats. limestone; intermediate sparsely fossiliferous, (section D, Fig. 3; Fig. 4), it reaches more than oncolitic, and fenestral limestone; and caps of 50 m thick locally in collapse dolines at Daniel's Table Head Group desiccation-cracked, laminated, dolomitic lime- Harbour. Basal quartz pebble and sand beds at stone with local tepee structures. Like similar most localities comprise reworked intraforma- The Table Head Group is a 100- to 300-m- basal Middle Ordovician carbonates in the tional chert with minor Precambrian basement thick, deepening-upward succession of mostly southern Appalachians (Graver and Read, detritus. Widely distributed, massive, finely crys- limestone and lesser shale (Klappa and others, 1978), the sediments are interpreted to represent talline, calcareous dolostone; green-gray dolo- 1980; Stenzel and others, 1990). The Table deposition on and adjacent to open, "humid," mitic shale; and minor nodular limestone with Point Formation is a fossiliferous, subtidal lime- muddy, peritidal flats (Ross and James, 1987; trilobites, ostracods, and conodonts cap the stone. The basal Spring Inlet Member (Ross Knight, in press a). The rest of the Table Point

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1206 KNIGHT AND OTHERS

Formation comprises subtidal that and 5) accumulated more outboard in the All or some of these features occur at many display slumped and brecciated horizons. reentrant. Deepening-upward carbonate to localities throughout western Newfoundland flysch sedimentation characterizes each Middle (Table 1), but in some exposures of the contact, DEEP-WATER SEDIMENTARY Ordovician sequence disconformably overlying there is no or very circumstantial evidence of ROCKS the Lower Ordovician strata. discontinuity. In such cases, the presence of the disconformity is based upon regional geology Allochthonous Cow Head Group (James and THE ST. GEORGE UNCONFORMITY and biostratigraphic evidence. Stevens, 1986), equivalent to the upper part of The link between the unconformity and pa- the St. George Group (Fig. 5), consists of prox- This break is a regional unconformity varia- leokarst is, however, not related to one specific imal, interbedded limestone and shale punctu- bly expressed as a paraconformity to disconform- event. Understanding the inter-relationship be- ated with limestone conglomerate. The largest ity to slight erosional unconformity within the tween synsedimentary faults, dolines, and matrix conglomerates which have been given bed Aguathuna Formation. Elsewhere, the Table breccias is fundamental to unraveling the evolu- numbers (Kindle and Whittington, 1958) in- Point Formation rests with angular, erosional tion of the St. George Unconformity and its as- clude Bed 14, a megaconglomerate of early unconformity upon either Aguathuna Forma- sociated features and stratigraphy. The uncon- Whiterockian age that correlates with the St. tion or Catoche Formation (Fig. 3). formity is but one of several events which began George Unconformity. The Cow Head is over- The unconformity is a faulted, karst-modified before actual exposure and included faulting and lain by flysch, equivalent in age to the Table surface. Erosional relief, scalloped surfaces, rub- subsurface diagenesis even while pre-uncon- Point Formation (Fig. 5). ble breccias (proto-soils), and locally dolines formity sedimentation was culminating. The typify the surface itself. Chert-sand- and dolo- products of these events in turn contributed to QUEBEC mite-mud-filled, solution-enlarged spaces along the local fashioning of the unconformity when faults and joints extend down at least 120 m uplift and exposure actually took place. Ibexian to Whiterockian subtidal to restricted below the unconformity. Subsurface paleo-karst peritidal dolostone, shale, and minor limestone is also expressed by (a) near-surface, vuggy po- Age of the Unconformity of the Beauharnois Formation, St. Lawrence rosity filled with dolomite mud; (b) small caves Lowlands (Globensky, 1987; Knight, in press b) filled with dolomitic shale; and (c) shallow to The St. George Unconformity was, until re- and Romaines Formation, Mingan Islands (Des- deep, stratabound, concordant and discordant cently, thought to separate Ibexian rocks of the rochers, 1985) compare closely to strata in west- bodies of rock-matrix collapse breccias, some of St. George Group from overlying Whiterockian ern Newfoundland. They lie along the inner which were open to the surface (collapse strata of the Table Head Group. Although this is margin of the Quebec Reentrant. Ibexian car- dolines). true locally, recent conodont studies at Daniel's bonates of the lower Phillipsburg Group (Figs. 1



Figure 4. Isopach maps of the lower and upper members of the Aguathuna Formation and Spring Inlet Member, Table Point Formation; thrusting has tightened the distribution of the Spring Inlet Member isopachs in the northeast. Synsedimentary faults occur near River of Ponds and Cape Norman (Figs. 3A, 3D).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 TABLE 1. DISTRIBUTION OF SURFACE AND SUBSURFACE FEATURES ASSOCIATED WITH DIFFERENT EXPOSURES OF THE ST. GEORGE UNCONFORMITY + j o f Roa d o f Min e Ba y Eas t Broo k Wes t Choi x Broo k Pon d Pon d Pon d Ba y arm . Poin t Pon d Island s Cov e odd Roc k Norma n Ba y Norma n Squar e Inle t Nea r Wes t R Burn t Islan d feede r Islan d a u Cook s Bridg e Vikin g gravel s Quarr y Anthon y Barren s gravel s Barren s Airpor t Spring s Rive r Rive r Daniel' s Portlan d Har e Bi g Schoone r Bellbum s Northeas t Southwes t Bac k Northwes t Highwa y Locality Pond s Bonn e Aguathun a Cole s Roddickto n Lane s Pond s Tabl e Cree k St . Lane s Mari a Beave r Cap e Beave r Cap e Por t Harbou r Hor n Harbou r Islan d

Solution sculpture X X L -

<§2 3£ Rubble breccias - X - - - L ------X X - L - X ------co <22 Local paleorelief 1-2 m 0.1 m X X 2m 8 m - 0.3 m 0.3-1.2 0-1 m 0.3-2.0 - 0.5 m - - - - - 0.3 m 0.2 m - - 0.3 m - 0.1 m - 0.15 m - - - m m

, .2 Silicification - X - - - X - X - - — — - X — - — — X X X - - X - X - X X X

3 £ Dolomitization X X X X X ------

Shallow fractures - — X X X L - — X — — — - X — — — — X X — X — X - X - - — —

Porosity - X - - X - - - X ------— ------

Geopetal sediment - X - X - - - X ------g - S Interstratal caves X

Oligomict X £1 Rock matrix g s breccia 3 Polymict L L X X a C/5 Dolines X X

™ Structurally controlled caves - X - - - X - - X ------X - - - X ------

Egg-carton caves X - - - - - X X X X X X

Basal/Pebble lag conglomerate X X — X X L X X L — L L X X X X X — L — L L —

Sinkhole fills X X X 1 £ g Local disconformity X X - g§ f6

o Cl. SI SI SI SI SI SI SI SI SI SI SI SI SI SI SI SI UA UA UA UA UA UA UA UA UA UA SI SI SI SI Stratigraphie relationship 'VA, 'VA, -VA, 'W -va, 'W "UV -va, 'VA, 'VA, "VA, -VA, "VA, "VA/ "VA, 'VA, "VA; "VA, "VA, 'VA, "VA/ *\A, 'VA/ "va, "VA, "va, 'VA, LA/CD LA LA/CD LA LA CB LA/CB LA LA LA LA CB CL LA LA LA CD CD CD LA M-LA LA MA/LA LA LA LA LA LA LA LA CL

CL = Catoche Limestone; CD = Catoche Dolostone; CB = Costa Bay Member; LA, MA, UA = Lower, Middle, Upper Aguathuna Formation; SI = Spring Inlet Member, X = Present; L = Local; — = Absent/no information. Note: Bonne Bay is interpreted from Levesque (1977).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1208 KNIGHT AND OTHERS

Figure 5. Chronostratigraphy of Ordovi-

cian carbonate sequences in western New- GRAPTOLITES foundland and Quebec and coeval slope COW HEAD, NORTH BRITISH AUSTRALIA deposits of the Huinber Arm Allochthon. Bio- (NFLD.) AMERICA ISLES stratigraphy utilizes schemes of Williams and -J Pleurograptus Climacograptus P.

IA N § linearis pygmaeus ASH - Stevens, 1988; Ross and others, 1982; GILL - linearis Barnes and others, 1981; Boyce, 1989; Stait, CC Q< c. LU Dicrano- spiniferus Dicrano- 1988; and Stouge, 1982,1984. Chronostratig- graptus Orthograptus graptus ruedemanni raphy: western Newfoundland (Knight and 111 z hians ^ Corynoides clingani James, 1987; Klappa and others, 1980; Sten- z z americanus < o zel and others, 1990; Lane, 1990); Humber i- z 1/1 Q_ z Climato- Arm Allochthon (James and Stevens, 1986; o 3 c. < 1- graptus Q_ barag- <0 Botsford, 1987); Quebec (Globensky, 1981, z c Iii wanathi Diplo- u wilsoni 1987; Desrochers, 1985; Knight, in press b). o CC H graptus BbC = Barbace Cove Member, Boat Harbour o E Formation; LA = Lower Aguathuna; MA = Q w < 3 ID a. Middle Aguathuna; UA = Upper Aguathuna; c Q TC = Table Cove Formation; BC = Black CC tr peltifer CTl < multidens O C. Cove Formation; CC = Cape Cormorant o D. ~ peltifer multidens Formation; GT = Goose Tickle Formation;

BLACKRIVE I o Yapeenian; BOL = Bolindian. m a LU N < gracilis + Nemagraptus graptus Harbour (Stait and Barnes, 1988; Stait, 1988) -« N — < bicornis indicate that the unconformity lies between Z

IA N o rocks of Whiterockian age, within the St. Glyptograptus G. Q G. cf. teretiusculus

LLANDEI L teretiusculus George Group. Trilobites (Fortey, 1979; Boyce, o teretiusculus 1983; Boyce and others, 1988), graptolites (Wil- Didymograptus liams and others, 1987), and conodonts (Stouge, Q murchisoni z 1 D. 9 1982; Kenna, 1985; Stait, 1988; Stait and 3 decoratus Para- < Barnes, 1988) show that regionally the upper — 1 glosso- z S G. — § 3 (-.a 3 or 4-B " D. deflexus CC CO liams and others, 1987) equivalent to the upper o LU 4 B T. fruticosus 4 OC < a 2 S " T. akzharensis Orthidiella to Anomalorthis zones and Midcon- o m 1 frut-/approx Tetragraptus approximatus tinent fauna 4. A nomalorthis-zone brachiopods LU < 3 T. approxim. T. approximatus (Ross and James, 1987), zone-M trilobites (Wil- r 2 A. victoriae A. victoriae Adelograptus liams and others, 1987), and Midcontinent 1 a 1 fauna 4 conodonts (Stouge, 1982, 1984; Stait, z< a Adelo- 1988) indicate a late Whiterockian age for the ¡¡j graptus

Spring Inlet Member, Table Head Group. < -IA N E 1.5 - Clono- o DEMIN G o Clono- graptus This evidence indicates that the St. George o \ graptus Unconformity lies within the earliest Whiterock- o o < ian Orthidiella zone, probably spanning much of 1 - < 5 Anisograptus- the time occupied by Midcontinent conodont < 1 s z Staurograptus fauna 3 (Stait, 1988) and Nevada-Utah trilobite LU Anisograptus zone L (W. D. Boyce, 1989, personal com- o WARENDIAN CC CO mun.). Both Williams ancl others (1987) and Stauro- b- (3 graptus Ross and James (1987) suggested that it occurs DATSONIAN

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 » o •o OD-oO a o o m M -O U O ai a> oo to o j] I I oz o i\i ui 3>"0 -O II o (A (0 D)

OD X - e- n-o CO X 3 O m o m S S —S 3 3 O 3 î J 23 o c 2. œ c » S ? S s UH' »rjr-n X £ m m m m mtflOnÇ C > z o 1 O z I- z S o g Cî o O DJ m ^ O m c>m5 X X 3J m> H > I I M • o X m 1,1 M i ' O 3D S Black + Gray • • Red SHALES


GROUP TABLE HEAD GP > •) * H O . " '1 T1 C coS S T C r= '/X / -< C H nJwo G T zO ' H5î3 689 • ALLOCHTHON EMPLACEMENT O X o z PHILLIPSBURG GROUP STANBRIDGE GROUP LOWER UPPER r I I s it I- * Q.-OÏL o;•O :» S5, i 11 ¡;; fSg BM 1.1 S —. ' «TO " y i o j- i •:• 3) c \ ' M> H m 81 DO m Î C/l o POTSDAM GROUP BEEKMANTOWN GROUP BEAUHARNOIS FORMATION O >

>IH m r1 z z o o en m

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1210 KNIGHT AND OTHERS


1 -


3 -








Figure 6. Sketch of the St. George Unconformity at Aguathuna Quarry, Port au Port Peninsula. The St. George Group is gently folded below the unconformity; small disconformities (2) occur in the overlying Table Point Formation.

in the lower Darriwilian. Subaerial exposure in variations in lithostratigraphic units bounding graphic relationships between Table Point and the region is therefore probably relatively short- the St. George Unconformity (Fig. 3) indicate Port au Choix indicate that major erosion oc- lived (perhaps less than 1 m.y. to a maximum of that there could have been as much as 50 m of curred northwest of the northeast-trending Tor- 3 m.y.), during which time considerable erosion paleo-relief and erosion on the unconformity. rent River fault (Knight and Boyce, 1984; occurred locally. Erosion soon reduced this relief that was con- Knight, in press a). A northeast-trending lin- trolled by synsedimentary faulting that delin- eament 8 km south of Cape Norman (Figs. 1, Paleo-relief and Pre-unconformity Tectonics eated large regional highs such as the Port au 3A) is a synsedimentary fault that placed Agua- Choix high (Figs. 3D, 4) and smaller highs, for thuna Formation against Catoche dolostone be- Although local paleo-relief in outcrop is usu- example, Burnt Island (Fig. 3A) and Canada fore erosion and subsequent deposition of the ally less than 10 m (Figs. 6 and 7), regional Bay (Fig. 3C) (Knight, 1986, 1987). The strati- Springs Inlet Member, Table Point Formation

Figure 7. A small channel infilled by dololaminite and a pebble lag at the St. George Unconformity (arrows) on Burnt Island. The uncon- Figure 8. Crudely stratified, chert- and dolostone-pebble conglom- formity surface is flat and featureless to the left of the channel, which erate of the upper Aguathuna Formation unconformably overlying a is cut in karst-fractured limestones of the Costa Bay Member, Catoche rubble breccia and fracture zone developed in extensively silicified Formation. The unconformity is overlain by fenestral limestones of the dolostones of the Lower Aguathuna Formation, Portland Creek Spring Inlet Member, Table Point Formation. Pond. Beds are overturned and young to the right.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 1211


Figure 9. Local erosional disconformities separating and cutting down into peritidal carbonates of the Spring Inlet Member, Table Head Group, Viking Highway, just west of St. Anthony airport. Beds are gently tilted below the scours.

(Knight, 1986). These relationships indicate that Conglomerates were locally washed into mudstone; and (3) thin-bedded and fossiliferous early Whiterockian block faulting took place be- lows during sea-level rise over the disconform- wackestone; fossiliferous, nodular, shaly wacke- tween deposition of the lower and upper ity where they were trapped beneath microbial stone; shaly, calcareous dolostone; and green- members of the Aguathuna Formation. mats (for example, Schooner Island, section A, gray shale. Fossils include ostracods, trilobites, Further evidence of tectonism is provided by Fig. 3). Thick, crudely stratified conglomer- gastropods, and cephalopods. truncation of gently folded St. George Group ates (Fig. 8) were probably fluvial sheetflood Sinkhole deposits are interpreted as both ma- strata by the unconformity on Burnt Island, at deposits reworked from residual soil veneers rine and lacustrine. Unfossiliferous, hackly Aguathuna Quarry (Fig. 6) and subsurface rela- and swept into lows or channels on the shales accumulated in shallow, nonmarine tionships at the Daniel's Harbour mine (Lane, unconformity. ponds. Sheetfloods from the surrounding flat to 1990). Sinkhole Deposits. These deposits are re- gently sloping karst surface deposited the cal- stricted to the Daniel's Harbour area and careous siltstones and thin beds of chert chips. Sediments Overlying the Unconformity possibly Big Cove, Port au Port Peninsula (Fig. Restricted, quiet, deep-water, marine sedimenta- 1). At Daniel's Harbour, dolines are filled by as tion containing a fauna tolerant of fluctuating Conglomerates. Basal conglomerates are lag much as 50 m of millimeter-scale, argillaceous salinity (Kaesler, 1987) filled the upper parts of deposits of limited areal distribution which ac- limestone rhythmites with bioclastic lamina- the holes when waters from the rising sea cumulated in lows and veneered slopes on the tions, no burrowing, and quartz sand layers. drowned the dolines. Present spatial relation- unconformity. Clasts were reworked from a pro- Strata near doline margins are disorganized by ships indicate that sinks were surrounded by tosoil/regolith or eroded from lithified carbon- slumping; ostracods and trilobites are abundant muddy tidal flats, but marine connection via ate. Quartz and chert pebbles, many of them in fossiliferous layers. At Big Cove, the succes- channels or caves is also likely. Slumped muds silicified evaporites (Pratt, 1979; Knight, in press sion comprises 18 m of (1) hackly weathering, in sinkholes may reflect tectonic instability of a), represent the insoluble residue of solution blue-gray shale; thin beds of massive to lami- the platform, continued collapse beneath the do- during prolonged exposure. Rounded carbonate nated, calcareous siltstone and angular chert line, or instability of the soft muds due to rapid, pebbles in some deposits suggest wave or stream pebbles and sand grains; (2) petroliferous, gray local deposition at the margins of the sinks. action. shale and lumpy, fossiliferous lime wackestone- Mussman and others (1988) reported soft-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1212 KNIGHT AND OTHERS

Figure 10. Southeast-trending rinnenkar- ren with pinnacles (arrows) on fallen block at Southwest Feeder, south of Portland Creek Pond. They are developed in dolostones of the lower Aguathuna and overlain discon- formably by dolostones of the upper Agua- thuna. Beds dip and young to the right. Open arrows indicate negative molds of pinnacles on the underside of the bedding plane. Block is 45 cm thick.

nected flutes and depressions up to 20 cm long with smooth crests between occur incised 4 to 6 cm into interbedded dololaminitc and chert at the crest of a paleohigh on the unconformity at Aguathuna Quarry (Fig. 6). Dissolution took place on a relatively flat surface that was cov- ered by sediment or proto-soil (compare with Desrochers and James, 1988). Larger rinnenkarren (Fig. 10) at Southwest Feeder, Portland Creek Pond (Fig. 1) are linear, sediment structures in similar muddy, fossilifer- ing cut bank that can be traced for more than 30 knife-edge sharp, southeast-trending, pinnacled ous carbonates from paleo-sink holes in north- m. An elevated, slightly undulating terrace with ridges, several centimeters high and up to 60 cm ern Virginia. a kaminitza, 50 cm deep and 2 m wide, is pres- long. They are separated by smooth, 10- to 30- Spatial, Thickness, and Facies Variations of ent east of the scarp. cm-wide troughs. Here, running water sculp- Overlying Sediments. Aguathuna Formation tured a gently inclined rock surface (Esteban carbonates form a thin, onlapping veneer on the SURFACE PALEOKARST and Klappa, 1983; James and Choquette, unconformity restricted to the Daniel's Har- 1984). bour-Port au Choix area (Figs. 3D, 4). In the Solution Sculpture Scarcity of karren on the unconformity sur- overlying Table Point Formation, there are large face may reflect the lack of any significant slope, thickness variations (Klappa and others, 1980; Few surface karren are present at the uncon- the microcrystalline, impervious nature of the Stenzel and others, 1990) and especially rapid formity surface, which is for the most part Aguathuna dolostones, or low precipitation (Es- lithofacies changes and thickness variations in smooth and planar. Small, irregular, uncon- teban and Klappa, 1983). A sediment lag over- the Spring Inlet Member (Ross and James, 1987; Knight, 1986, in press a; Stenzel and oth- ers, 1990). The member is thinnest (3 to 20 m) on top of, or flanking, paleo-highs (Port au Choix, Cape Norman, and Canada Bay west areas, sections A, C, and D, Fig. 3), where the lower Aguathuna was eroded. It is thickest (50 to 80 m) in the parautochthon at Big Spring Inlet and Maria Islands, Hare Bay (section B, Fig. 3), and southeast of Table Point, where it is underlain by the upper Aguathuna. Local Disconformities-Spring Inlet Mem- ber. Two small unconformities occur in separate depressions above, but merging with, the St. George Unconformity at Aguathuna Quarry (Fig. 6). In one depression, a 10- to 15-cm-thick, chert-pebble conglomerate was lithified and do- lomitized, then planed and eroded with small solution pits, indicating karstification. The sec- ond unconformity, 2 m above the St. George Unconformity, separates laminated, ostracod- rich, schizohaline (pond?) wackestone below from fossiliferous marine limestone above. Northwest of Hare Bay along the main highway (Fig. 9), surfaces with erosional relief of up to 3 Figure 11. Rubble breccia (proto-soil), River of Ponds lake, west section (Fig. 3). Dark m truncate slightly tilted beds. One surface de- fragments of chert and dolostone of the Catoche Formation are surrounded by fine dolostone veloped a steep, step-like, west- and north-fac- (white zones) of the upper Aguathuna.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 14

B Figure 12. A. Reticulate Assures (open arrows) and large mesopores (light speck- les near solid arrows) both occluded by buff-weathering, fine dolomite mud, within limestones of the Costa Bay Member, Catoche Formation, Burnt Island. The struc- tures lie only a few meters below the unconformity. B. Bedding-plane caves (known locally as "the cannonballs") developed in limestones of the Costa Bay Member, Catoche Formation on Burnt Island. They occur 32 m below the St. George Uncon- formity and were filled by shales and fine dolostone that have since been eroded away.

lying the surface may also have inhibited dissolution (see Desrochers and James, 1988). SUBSURFACE KARST truncates the network in the member on the Maria Islands (Fig. 1; section B, Fig. 3). Coastal Rubble Breccias (Proto-Soil) Subsurface dissolution is manifest by shallow erosion hides the relationship of the fissure to the fracture systems, shallow porosity and geopetal unconformity. Poorly sorted breccias of burrow-mottled, sediment, local removal of limestone beds, The widely developed fissure network con- dark gray Catoche dolostone, black chert, and bedding- and structurally controlled caves, and fined to the Costa Bay Member occurs beneath some white quartz set in a fine dolomite matrix rock-matrix breccias. Subsidence and collapse the St. George Unconformity only in the parau- occur just beneath the unconformity at River of dolines are commonly associated with the ma- tochthon of the Northern Peninsula (Fig. 3). It Ponds (Figs. 3D and 11) and Cape Norman trix breccias at the unconformity. formed a shallow maze of subsurface passages barrens (Fig. 3A). Rubble breccia at Cape Nor- connecting downward, at least locally, to man barrens occurs along the linear crest of a Reticulate Sediment-Filled Fissures and bedding-plane passages along which there were low paleo-cliff. At River of Ponds, breccia (up Associated Porosity small caves with phreatic cross sections (Bogli, to 30 cm thick; Fig. 11) overlies cherty Catoche An irregular network of hairline to 3-cm- 1980; Ford, 1988). These narrow fissures im- dolostones (Knight, in press a) and consists of 3 wide fractures penetrates the Costa Bay Member mediately beneath the St. George karst surface gradational zones: (1) a lower zone of thin veins in the Pistolet Bay and and Hare Bay areas (Figs. probably formed by corrosive ground waters or cracks, (2) an intermediate zone of in-place 1, 2; sections A and B, Fig. 3) but is absent in the that infiltrated a lithified but broken limestone. breccia, and (3) an upper zone of rubble clasts overlying lower Aguathuna Formation, where it Because some developed beneath unfractured up to 5 cm in size. Yellow- to buff-weathering, separates the member from the unconformity. Aguathuna dolostones, they were probably gray, very fine-grained dolostone (upper Agua- The fractures cross beds as random, anastomos- formed in a confined aquifer that was subse- thuna Formation) surrounds the clasts and lo- ing networks of straight, dog-leg to branching quently exposed by uplift and erosion. This is cally fills the cracks. Dolostone and chert-pebble cracks that are filled by yellow-weathering do- supported by the presence of fissures choked conglomerate pockets overlie the breccia (upper lomite silt and green, dolomitic shale. On Burnt with fine detrital dolomite and shale that likely Aguathuna Formation). Island (Fig. 1; section A, Fig. 3; Fig. 12A), frac- infiltrated the solution-enlarged maze from the Rubble breccias containing clasts of underly- tures extend down 32 m below the unconform- karst surface. Similar green-colored shales oc- ing lithologies are interpreted to be the remnants ity to a series of bedding-plane-controlled, clude a shallow subsurface (20 to 30 m) joint of a discontinuous protosoil (compare with meter-scale, spherical caves (Fig. 12B). Only system of a regional karst developed on top of Kerans, 1988). The zonation is similar to a poorly developed fissuresan d open spaces occur the Lockport dolomite in Ohio. Kahle weathering or soil profile present at the top of in the underlying limestone. (1988) suggested that the Silurian shales repre- karsted Mississippian carbonates in New Mex- A south-trending, vertical fissure, 50 cm wide, sent the infilling of solution-enlarged joints by ico (Meyers, 1988). filled by dolomite pebbles, sand, and matrix, soils infiltrated down from the karst surface.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1214 KNIGHT AND OTHERS

Figure 13. Cavernous porosity in Watts Bight Formation dolo- Figure 14. Egg-carton caves between two dolostone beds, lower stones filled by geopetal dolomite (arrows). The porosity was opened Aguathuna Formation, west Gravels section, Port au Port Peninsula. by vadose dissolution beneath the St. George Unconformity and Port The cave marks the site of an interbedded limestone, dissolved in the au Choix High near Cape Norman. subsurface beneath the St. George Unconformity.

Shallow Porosity and Geopetal Sediment neath the disconformity in Costa Bay Member geopetal fabrics in rotated dolomite blocks of limestones at Pistolet Bay and Hare Bay (Figs. 1 nearby matrix breccias confirm that the void Millimeter- to centimeter-scale, irregular, and 12A). Similar porosity occluded by black filling preceded dolomitization and brecciation. laminar, and fabric-selective porosity filled with geopetal dolomite occurs in upper Catoche Bedding-parallel, laminated, silt-sized geopetal fine dolomite silt is common immediately be- Formation dolostones near Table Point. Similar dolomite fills small cavernous porosity (Fig. 13) in the Watts Bight Formation near Watts Bight (Fig. 3, map). Association of porosity with the reticulate fis- sures in the Costa Bay Member suggests that it formed within the same vadose zone which pro- duced the fissures. Geopetal-filled cavities in the Watts Bight Formation occur beneath the Port au Choix high.

Intrastratal Solution and Formation of Caves

Shallow, undulating topography at the uncon- formity on Maria Island (section B, Fig. 3) is due to preferential dissolution of several limestone beds, 10 to 40 cm thick, in the underlying lower Aguathuna Formation. On Port au Port Penin- sula (section E, Fig. 3; Fig. 14), similar preferen- tial dissolution of limestone beds produced tabular caves that are locally filled with green, dolomitic shale. They resemble an "egg carton" because the dolostone protrusions and pendants on cave floors and roofs that support the cave meet irregularly. Figure 15A. Stratified chert fill- ing a narrow, vertical cave developed along a Solution-Enlarged, Sediment-Filled northeast-trending, early Whiterockian fault Joints and Faults that displaced Catoche limestones 120 m Figure 15B. Dolomite-mud-fiMed joints below the unconformity. The sandstone is lith- cutting the middle of the Catoche Formation Sand- and mud-filled open spaces along faults ologically similar to chert sands in the upper east of Hawke Point. The joints trend 035° and joints penetrate strata beneath the uncon- Aguathuna Formation. Note the inclined and dip 62° southeast. The muds petrograph- formity to a depth of 120 m (Knight and Boyce, stratification cut by the synsedimentary fault. ically show fine lamination that is locally 1984; Knight, in press a). At Hawke Point (Fig. Location, Hawke Point. convoluted. 1), a cave 30 cm wide and several meters long

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 1215

Figure 16A. Polymictic breccia consisting of light colored dololami- Figure 16B. Polished section of an oligomictic breccia, Daniel's nites and dark, burrow-mottled dolostones set in a dark, vitreous Harbour Zinc Mine. Dolomite fragments formed mostly during early, dolomite matrix. Bateau Barrens. shallow-subsurface, burial diagenesis of limestones of the Catoche Formation. Bar is 1 cm long.

formed along a fault that trends 040° and dis- Rock-Matrix Brecc&s Contacts between the discordant matrix breccia places flat-lying Catoche limestone a few tens of and the country rock are either sharp and gener- centimeters. It is filled with poorly sorted, Carbonate rock^breccias are common in the ally smooth or slightly uneven or transitional matrix-supported, coarse-grained sandstone with upper St. George Group from Daniel's Harbour into halos of oligomictic breccias. Wedges of rare dolostone intraclasts and well-sorted, fine- to Port au Choix. They are characterized by a dolomite-chert sand locally intervene between grained sandstone. Sand grains consist of chert, matrix of fine- to medium-crystalline gray do- the matrix breccia and the contact (Fig. 17). chalcedonic quartz, oolitic chert, silicified fossil lomite crystals and predate epigenetic breccias Stratabound oligomictic breccias (Fig. 16B) fragments, clear quartz with dusty inclusions with saddle dolomite cement (Lane, 1984, comprise local fragments of burrow-mottled, that mimic earlier evaporitic fabrics, calcareous 1990). They are mostly all dolomite. The brec- dark gray dolostone, dolomitized burrow-mot- grains (ooids, pelmatozoan parts, and indeter- cias (Figs. 16,17, and 18) that are related to the tles, and chert. They occur in a 100-m interval of minate calcareous and chitinous skeletal parts), unconformity occur as (1) stratabound bodies Catoche limestone which was reduced up to pyrite, mica, detrital quartz, and zircon. Curved that lie parallel to bedding, commonly involve 30% in thickness due to dissolution (lane, to inclined planar stratification, local disconti- several beds, and can be traced for hundreds of 1990). nuity surfaces, and small syndepositional faults meters along strike; and (2) vertical, discordant, Extensively dolomite-veined country rock typify the cave sediments (Fig. 15A). meter-wide veins to 150-m-wide bodies along with small to locally significant block displace- Nearby at Hawke Flats and Port au Choix, faults and fractures that crosscut tens to hun- ment forms spar breccia halos around the upper solution-widened, steeply dipping joints trending dreds of meters of stratigraphy. A third type of levels of matrix breccias. They resemble crackle 035° cut the Catoche limestones. They are filled body that is not related to the unconformity oc- breccias (Ohle, 1985) and fitted fabric (Muss- with dolomite mudstone (Fig. 15B) consisting of curs as breccia pipes which are subcircular in man and others, 1988). 20- to 50-/xm, broken rhombic dolomite crystals; plan, cut the unconformity, and penetrate the The breccias formed in caves by partial disso rare quartz and mica silt; and a few skeletal and lower Table Point Formation. lution of limestone and collapse in the subsur- dolomite grains derived from the wall rocks. The breccias are classified according to face. Concordant types formed along beds; Dolomitization halos up to 60 cm wide pene- their clast composition. Discordant, rubble- to discordant types, by upward stoping (Ford, trate from the joints into the limestones at Port matrix-rich polymictic breccias (Fig. 16A) con- 1988) along joints and faults intersecting bed au Choix. Similar, northeast-trending dolostone- sist of granule- to block-sized clasts of light gray, ding. Limestone below, or intercalated with, the filled joints occur at the top of the Costa Bay massive, and burrowed dolostone; light gray dolostones in the upper Catoche Formation Member at Hare Bay (section B, Fig. 3). dololaminite; and dark gray, massive, and probably dissolved first, followed by local dolo- The open-space fillings along these northeast- burrow-mottled dolostone and variably abun- stone dissolution. It is unlikely that breccias trending faults and joints indicate penetration of dant chert set in dark, vitreous, fine-grained formed by dissolution of evaporites because evi- meteoric waters to a considerable depth. These dolomite or unsorted sandy and granulose do- dence of their presence is confined to minor narrow passageways clogged with chert sand lomite matrices. Some clasts are displaced more chert nodules in the Aguathuna Formation. and detrital dolomite mud from the upper Agua- than 50 m below their original stratigraphic po- Sharp cave walk and lack of cave precipitates thuna Formation confirm that they were con- sition. Clasts are jumbled chaotically, locally suggest corrosional regimes (Mussman and nected to the unconformity. Synsedimentary fractured in situ, and never show evidence Read, 1986). Dolomite-chert-sand wedges be- deformation and faulting of the fills may imply of soft-sediment deformation. Some breccias tween breccia and cave walls are preserved in settling or small-scale movements as the sedi- coarsen upward. Upper parts of some breccias corrosion notches in the cave walls (Ford, ments were deposited. show less disorganization and rotation of blocks. 1988).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1216 KNIGHT AND OTHERS

Figure 17. Sketch map and cross section of O: MATRIX BRECCIA the Bateau Barrens breccia body. The upper CLIFF part of the breccia consists of a spar breccia SPAR BRECCIA that developed by ceiling stoping and fractur- u, FAULT, DIP, THROW ing, only incipient collapse, and later dolomite BEDDING cementation. JOINT


In the Daniel's Harbour area, several north- east-trending, elongate, pear-shaped to approx- imately spherical breccia bodies (Fig. 18A) up to 3,000 m long and 300 m wide are distributed along early faults (Collins and Smith, 1975; Crossley and Lane, 1984; Lane, 1984, 1990; Lane and James, 1987). These complex breccia bodies terminate at the unconformity and are interpreted as largely subsidence dolines cut by narrow collapse dolines along the faults (Fig. 18B). Subsidence Dolines. Deposition of the anom- alously thick (10 to 70 m), middle member of the Aguathuna Formation occurred in solution- and tectonically controlled subsidence dolines. The dolines formed mostly above oligomictic breccias and before the formation of the uncon- formity (Fig. 18B). Later brecciation of the mid- dle member suggests that the depressions had a protracted geological history (Lane, 1984, 1990). The middle member thickens into the depressions, and some subtidal burrowed beds pass into laminites as they emerge from the cen- ter of the lows. Subsurface collapse was gradual enough that peritidal sedimentation of the thick- ened middle member kept pace with subsidence. Nevertheless, there is insufficient limestone dis- solution to account for the large (up to 70 m) thickness of the middle member in the dolines. This indicates that tectonic warping of the plat- form was significant and may have controlled the location of early subsurface dissolution. Collapse Dolines. Northeast-trending, high- ZONE OF DOLOMITE- angle faults displace the oligomictic breccias and CEMENTED FRACTURED COARSE TO FINE AND BRECCIATED SPAR BRECCIA are the loci of vertical, polymictic, matrix brec- DOLOSTONE cias that penetrate the Catoche Formation and the lower Aguathuna Formation. Where the breccias stoped to the unconformity, they created collapse dolines (sinkholes) as much as WELL-SORTED 50 m deep. MATRIX BRECCIA GRANULAR PROMINENT DOLOMITE Formation of Rock Matrix Breccias and FRACTURES SAND Dolines. A sequence of events associated with the dolines is as follows (Lane, 1990): (1) depo- PSEUDOBRECCIA sition of the lower member of the Aguathuna BED Formation; (2) partial subsurface dissolution of Catoche limestone and stratabound collapse of interbedded dolomites to form oligomictic brec- cias; (3) subsurface dissolution concomitantly with tectonically enhanced sagging of strata to create broad subsidence dolines (Bogli, 1980)

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 1217




Figure 18A. Schematic cross section of oligomictic and polymictic breccias, and subsidence and collapse dolines near Daniel's Harbour to illustrate the relationship of faults, dolines, and stratigraphy associated with the St. George Unconformity (based on drill-hole data of Lane and Newfoundland Zinc Mine's at Daniel's Harbour).

during deposition of the middle Aguathuna; sed- imentation generally kept pace with subsidence; (4) faults crosscut and displaced oligomictic breccias and localized upward stoping into the lower Aguathuna to form narrow polymictic breccias; and (5) lower and middle Aguathuna collapsed into the solution cavities in the Catoche Formation, forming collapse dolines (Bogli, 1980) up to 50 m deep at the unconformity. The isolated and clustered dolines were the culmination of many events begun at least 100 m below the eventual unconformity and long before the unconformity actually formed. Facies and thickness variations of subunconformity sediments indicate (1) synsedimentary collapse and (2) that subsurface waters derived from out- side the immediate geographic area initiated the synsedimentary collapse. The Costa Bay Mem- ber and/or early, partial dolomitization of the upper Catoche (indicated by rubble breccias at Figure 18B. Structural contour map of the Lower Aguathuna Formation, showing the the unconformity and Catoche dolomite clasts in relationship of northeast-trending faults to the location of rock matrix breccias in the Daniel's matrix breccias) probably provided local aqui- Harbour mine area (Lane, 1990). Line of cross section (Fig. 18A) is shown. fers, because underlying fine-grained Catoche limestones lack good porosity and permeability. In addition, northeast-trending faults probably structural conduits to the area of dolines, which surface fluids of varying salinities and/or mete- served to locally enhance fluid movement and generally flank the high. It is therefore reason- oric composition (James and Choquette, 1984; dissolution, and elevated fault blocks such as the able to conclude that early dolomitization of the Lohmann, 1988). Kerans (1988) has explained Port au Choix high later provided a zone of upper Catoche and later limestone dissolution dissolution in contemporaneous Ellenberger infiltration. Fluids then readily moved along occurred in a hydrological mixing zone of sub- karst in Texas in a similar way.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 CRATON 250 km WEST NEWFOUNDLAND PLATFORM » DEPOSITIONAL SITE OF GAP COW HEAD GROUP QUEBEC AUTOCHTHON THRUST NO AND ASSOCIATED ROCKS (50 KM WIDE) ALICES'" RECORD



BED 10





Figure 19. Schematic diagram illustrating the middle Ibexian to late Whiterockian stages of sedimentation and Hthospheric adjustment to the cratonward migration of the peripheral bulge through Ordovician slope and platform of western Newfoundland and Quebec during the initial stages of the Taconic Orogeny.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 1219

DISCUSSION OF THE and lower Aguathuna Formation (Lane, 1990) in press a) in the middle of a wide, passive- UNCONFORMITY AND THE ROLE and also controlled pre-unconformity doline lo- margin platform. Post-unconformity peritidal OF TECTONISM cation and sedimentation. Strata beneath the sediments of the Spring Inlet Member are unconformity were gently folded, and relief on shallowing-upward sequences of fossiliferous The St. George Unconformity is the most ob- the unconformity was structurally controlled. and fenestral limestone with some dolostone vious manifestation of serial events which ter- Above the unconformity, local disconformities that were deposited on unrestricted "humid" minated widespread, uniform deposition on a truncate tilted peritidal sediments in the Spring tidal flats at the edge of a-foreland-basin sea carbonate platform and initiated local, irregular Inlet Member, and slump folds and breccias are (Ross and James, 1987; Knight, in press a and in sedimentation along a convergent continental common in overlying Table Point Formation press b). Both sequences, however, suggest dep- margin. The unconformity and associated sedi- subtidal sediments. Profound facies and thick- osition under open-ocean, nonrestrictive, humid mentation were the product of tectonics, sea- ness variations in the Table Point Formation settings. level fluctuations, regional climate, subsurface were also controlled by block faulting. The shelf The Aguathuna Formation, however, is diagenesis, and fluid migration. We interpret the itself ultimately foundered and was buried by typified by dolostones with minor limestone foregoing data, however, as indicating an over- synorogenic flysch. arranged in both deepening and shallow- riding tectonic control, contrary to previous ing-upward cycles. The dolostones contain an conclusions (Knight and James, 1987). Influence on Late Ibexian Sedimentation extremely restricted and sparse macrofauna, The relationship of the St George Uncon- evidence of evaporites, and numerous exposure formity to the regional stratigraphy of western Ibexian sedimentation (top of the upper meg- surfaces which indicate a peritidal setting with Newfoundland and the northern Appalachians acycle of the St. George Group) was influenced restricted water circulation. This common style indicates that it is one aspect of a whole series of in two notable ways. First, rapid regional shal- of deposition at this time along the Appala- diachronous, tectonically controlled events. In lowing is marked by the abrupt passage from chians is generally attributed to a short period of the past, the unconformity has been seen as the open subtidal shelf limestone (lower Catoche arid climate and gradual eustatic sea-level fall. end product of sea-level lowering related to glob- Formation) to more restricted peloidal lime- We believe, however, that the obvious influence al sea-level fall (Fortey, 1984), although others stone (Costa Bay Member) to restricted peritidal of tectonics synchronous with this change in (Williams and Stevens, 1974) have implied that dolostone (lower Aguathuna Formation). Sec- Newfoundland reflects the plate dynamics af- it is the first intimations of Taconic orogenesis. ond, the character of the peritidal sediments of fecting the margin at this time, namely slowed or More recently, Knight and James (1987) noted the Aguathuna Formation is markedly different arrested subsidence and passage of the shelf edge that tectonism affected the Newfoundland shelf from other peritidal deposits of the Ordovician over a forebulge. Tectonism, principally the in- at this time; Mussman and Read (1986) con- shelf. teraction of the forebulge with the shelf margin, cluded that in the Appalachians tectonism was Shallowing of Shelf Sediments. The shal- fundamentally controlled paleogeography, pro- influential in shaping the Knox Unconformity lowing-upward transition from Catoche to ducing an uplifted and faulted, rimmed margin during a period of sea-level fall and rise. The Aguathuna Formations is a rapid to abrupt that isolated the platform and restricted circula- chronostratigraphy of coeval Ordovician slope event throughout the Newfoundland platform. tion during deposition of the Aguathuna Forma- and shelf sediments in Newfoundland and com- Consistent regional stratigraphy across this con- tion. Behind this marginal barrier of archipel- parison of these events and stratigraphy with formable contact reflects the slowing to perhaps agos or low ridges (upfaulted highs) separated those in Quebec (Figs. 5,19, and 20) have led us cessation of platform subsidence as imminent by broad channels (downfaulted lows, Fig. 20), to conclude that Taconic tectonics, not eustasy, convergence of the continental margin termi- circulation was obstructed, and restricted, hy- was the fundamental driving force that con- nated thermal subsidence, and it accounts for persaline sedimentation prevailed. More normal trolled sedimentation and erosion on the shelf craton-wide shoaling in Ibexian time. It is possi- marine conditions existed near the shallow during much of Early and Middle Ordovician ble that contemporaneous eustatic sea-level rise channels. time in western Newfoundland. (documented in Nevada, Ross and others, 1989) Several lines of evidence support this conten- facilitated continued sedimentation on the shal- Coupled Response of Shelf and tion: (1) the longevity of tectonism on the Ordo- low platform and prevented early exposure and Slope Environments vician shelf of Newfoundland through late erosion of the platform. Ibexian and Whiterockian time; (2) the effect of Influence on Peritidal Sedimentation. Peri- Review of timing of events in coeval shelf and tectonism upon shelf sedimentation; (3) the rela- tidal sediments directly beneath, and locally slope sequences in western Newfoundland re- tive timing of events in Newfoundland slope and above, the unconformity (Aguathuna Forma- veals a distinct, ordered pattern that suggests shelf sediments; and (4) the diachronous chrono- tion) are unlike any others in the platform more than a coincidental linkage between slope stratigraphic events from Newfoundland to succession. and shelf sedimentation (Figs. 15, 19). We in- Quebec. Older peritidal sediments in the St. George terpret this to reflect changing lithospheric plate Group, even those beneath regional disconform- dynamics as convergence approached the con- Longevity of Tectonism ities (for example, Boat Harbour Formation), tinental margin and a forebulge affected in turn are limestone with dolostone, fossiliferous, nor- the shelf slope, shelf margin, and the shelf. Al- There is abundant evidence of faulting and mally arranged in shallowing-upward sequences, though this migrating sequence of events has seismicity on the Newfoundland shelf through- and poor in evaporites. They were deposited on, been postulated for foreland basins in the south- out late Ibexian and Whiterockian time. Late and adjacent to, relatively unrestricted muddy ern, central, and northern Appalachians (Brad- Ibexian synsedimentary faults generated subtle tidal flats under a humid climate (Pratt and ley and Kusky, 1986; Bradley, 1989) and in thickness variations in the Costa Bay Member James, 1986; Knight and James, 1987; Knight, geodynamic models of arc-passive margin colli-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 w. QUEBEC POSITION TIMING AND DURATION OF ORDOVICIAN ST. OF EVENTS EFFECTING MIOGEOCLINE NFLD PHILLIPS ANTICOSTI- LAWRENCE BURG MINGAN LOWLANDS BULGE AND FORELAND BASIN

I «



tona. OCEAN ü s'T FLOOR & tí) s ARC >- 111 FORMATION UJ < PASSIVE SHELF OC o 3 o Z tí) UJ O O X


Figure 20. Diagrammatic summary of the relationship between diachronous sedimentation and event stratigraphy on the Ordovician platform and foreland basin and the position of the migrating peripheral bulge through western Newfoundland and Quebec.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 1221

sions (Stockmal and others, 1986), nowhere In the following history (Fig. 19), the stage (3) Terminal Ibexian-Early Whiterockian does the stratigraphy of the Ordovician conti- names currently employed for the biostrati- (Late Arenigian) nental margin prove it more clearly than in graphic subdivision of Ordovician platform and Newfoundland (see History of the Ordovician basin strata (Barnes and others, 1981; Ross and By late Ibexian time, tectonism significantly Platform below). others, 1982) are used to frame our discussion. affected both the slope and platform as the fore- Central to this interpretation is the location of bulge moved across the slope to the platform Diachroneity of Events the western Newfoundland platform sequence margin and elevated the platform edge. relative to the platform margin. Recently, James Platform. Fades. Uplift of the platform mar- Figure 20 illustrates the stratigraphy and tim- and others (1989) calculated that this part of the gin profoundly impeded the open-marine circu- ing of events on the outboard Newfoundland platform lay at or just inboard of the hingeline, lation that had previously characterized the shelf and inboard Quebec platform during Or- on the outer part of the platform but well in- passive margin. Peritidal carbonates (Aguathuna dovician time. It shows that both the timing of board of the edge. In addition, the area lay at the Formation) deposited under conditions of re- the unconformity and the style, order, and tim- apex of the SL Lawrence Promontory, and this stricted circulation in the lee of this barrier of ing of sedimentation before and after the uncon- forward geographic position fundamentally con- semi-continuous islands were dolomitized early. formity are consistent, yet diachronous. This is trolled the relative rapidity with which the se- Nodular sulfate evaporites, precipitated locally compatible with cratonward migration of a quence of events was completed compared to beneath sabkha-like flats, were quickly altered forebulge and foreland basin, but contrary to other places along the Appalachians. to chert (compare with Chowns and Elkins, what would be expected if events were related to 1974). Chert was also precipitated in saline eustasy. The unconformity in Quebec, because it (1) Middle Ibexian (Tremadocian-Arenigian pools (compare with Muir and others, 1980). lies inboard of Newfoundland, should have evi- Boundary) Chert clasts, liberated by weathering, were re- dence of regression and unconformity before deposited on deflation surfaces between meter- that in Newfoundland; the opposite is true. Par- Several coeval events point to the initiation of scale cycles. ticularly telling are the restricted peritidal fades convergent plate dynamics in the form of litho- Cycles. Small-scale sequences in the lower of the upper Beauharnois Formation that be- spheric loading east (paleosouth) of the margin Aguathuna Formation and the Costa Bay come younger as they onlap Precambrian base- during the middle part of Early Ordovician Member may indicate the operation of high- ment (L. Bernstein, 1990, personal commun.) time. Oceanic lithosphere which cooled at 495 frequency, high-amplitude, sea-level oscillations and the significantly earlier timing of events in to 490 Ma (Dunning and Krogh, 1985) as- suggestive of climate-controlled eustatic cycles the co-eval Phillipsburg Group. sembled in a thrust stack (Williams, 1975; (compare with Hardie and Shinn, 1986; Hardie Recent analyses of Ordovician foreland ba- Dallmeyer and Williams, 1975; Dallmeyer, and others, 1986; Grotzinger, 1986). Alterna- sins of the Appalachians confirm a diachronous 1977; Dunning and Krogh, 1985) well outboard tively, these cycles associated with regional vari- westward progression of an assemblage of car- of the continental margin soon after formation. ations in stratigraphic thickness, poor correlation bonate shelf, deep-water shale basin, and east- Associated volcanism affected the geochemistry between north and south, and local differences erly derived flysch basin (Bradley and Kusky, of deep-water shales in the Cow Head Group in the style of sedimentation may reflect 1986; Bradley, 1989). Comparable scenarios are (middle Bed 8) (Suchecki and others, 1977). On subdued seismicity and block faulting. Regional present along Mesozoic margins in Oman the platform, a pronounced disconformity and subtidal emersions and repeated exposure of (Searle and others, 1983; Robertson, 1987a, initiation of transgression in the upper Boat Aguathuna sediments can be interpreted as 1987b) and Guatemala and Honduras (Home Harbour Formation (upper megacycle of Knight seismic aberrations of normal sedimentation and others, 1974; Wilson, 1974). A Cenozoic and James, 1987) approximately coincides with processes. counterpart occurs where collision of the Banda this distant tectonism and changing ocean-basin Faults. Northeast-trending faults subtly con- Arc and the New Guinea Orogen with the geometry. trolled penecontemporaneous sedimentation northern margin of Australia has created fore- and subsurface diagenesis at this time. Partial land basins (Hamilton, 1979; Karig and others, (2) Late Ibexian (Early Arenigian) dolomitization of the Catoche Formation oc- 1987; Charlton, 1989; Pigram and others, curred as the lower Aguathuna Formation ac- 1989). In any model of convergence, the forebulge cumulated. Dolomitization resulted possibly must first pass beneath the deep-water, slope- from reaction of downward-seeping, shallow- HISTORY OF THE ORDOVICIAN and-rise deposits of the ancient continental mar- subsurface brines with the limestones (Patterson, PLATFORM: RESPONSE OF gin. In Newfoundland, numerous sediment 1972), subsurface saline fluids (Sass and Katz, SEDIMENTATION TO TECTONISM gravity flows which originated on the slope (Bed 1982; Simms, 1984), or from dissolution- 10 complex, Cow Head Group; James and precipitation in a mixing zone (Haywick, 1985) Convergence of the Iapetus plate with Lau- Stevens, 1986) were likely triggered by seismic- between near- and sub-surface ground waters. rentia during Middle Ordovician time resulted ity at this time. The style of deep-water sedimen- Breccias. Oligomictic breccias developed lo- in a progressive chain of events which culmi- tation in the Northern Head Group changed at cally along incipient faults 60 to 100 m beneath nated in the development of the St. George Un- this point from carbonate dominant to shale the platform surface by dissolution of partially conformity and subsequent collapse of the dominant (Botsford, 1987). On the shelf, follow- dolomitized upper Catoche limestone. Disso- platform. The following reconstruction of events ing prolonged sea-level rise and subtidal shelf lution was probably accomplished by the same interrelates sedimentation on the platform, its sedimentation (lower Catoche Formation), rela- extrabasinal fluids that caused partial dolomit- margin, and slope with the evolving deformation tive subsidence slowed to initiate widespread ization. Penetrative northeast-trending fractures of the lithosphere as the Taconic accretionary deposition of peloidal sand shoals (Costa Bay aided the access of these fluids through the prism migrated westward (paleo-north). Member). platform. Subsurface dissolution and local down-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1.222 KNIGHT AND OTHERS

faulting resulted in subsiding depressions Absence of cave precipitates suggests that In Newfoundland, rising sea-level waters (dolines) characterized by increased thickness these caves were phreatic during their early flooded an unevenly eroded, block-faulted land- and deeper-water facies of middle Aguathuna stages. Organic-poor protosoils on the uncon- scape of low denuded arches (for example, Port sediments. formity giving low pC02 of ground waters, and au Choix high); low-lying, rolling corrosion Slope. The irregularly elevated platform rim caves clogged with rubble and matrix (matrix plains with clustered open dolines (near Daniel's cut off sediment supply to deep water, and the breccias) preventing free air circulation in the Harbour); and ?fluviokarst valleys (for example, resultant starved slope sedimentation produced cave system probably contributed to lack of Burnt Island and Aguathuna quarry). This siliceous muds, phosphates, and dolomitization cave precipitates (James and Choquette, 1984; landscape, slowly drowned by rising seas, pro- (lower Bed 11, Cow Head Group; James and Choquette and James, 1988). Flat-lying, lithi- duced a marine vista of peninsulas, archipelagos, Stevens, 1986). A narrow platform later devel- fied Aguathuna dolostones at the unconformity and islands that continued to undergo dissolu- oped seaward of the elevated rim because were probably mostly impervious as suggested tion while the always shallow sea floor between carbonate slope sedimentation resumed. Ongo- by smooth surfaces and karren (Choquette and was periodically exposed. Nonmarine to fossilif- ing, irregular seismicity of varying intensity as- James, 1988). Input points, presumably local- erous marine muddy sediments in dolines sug- sociated with down faulting, however, produced ized to narrow zones associated with faults and gest that they were either fresh-water lakes or massive, debris-flow megabreccias in some areas collapse dolines, limited ground-water entry to "blue holes," depending on their position rela- (Bed 12, Cow Head Group) and almost com- the subterranean cave system. tive to sea level. Because tidal flats surrounded plete cessation of carbonate slope deposition in Weathering at the unconformity likely broke the collapse dolines, open-marine sea water was others where there was wholesale margin col- the dolostones down to a fine dolomite silt probably recharged from interconnected caves lapse (James and others, 1987). or sand. Much of this sediment was then blown (compare with Logan, 1987) or tidal channels. away (Dalrymple and others, 1985; Coniglio, Continued karst erosion on the "hills" resulted 1985), but some was washed into solution- in soil stripping and chert conglomerate veneers, (4) Early Whiterockian (Terminal Arenigian) enlarged cracks and sinks; infiltrated shallow as well as multiphase solution sculpture. Re- vuggy porosity developed where folding and stricted, tidal-flat sediments (shale, fine dolo- stone, and chert-quartz-carbonate sand and Migration of the forebulge to the area of erosion exposed the underlying Catoche conglomerate, upper Aguathuna Formation) western Newfoundland by the early Whiterock- Formation. gradually filled hollows and onlapped the low ian resulted in faulting, uplift, and karst erosion Faulting, Folding, and Collapse Dolines. karst hills. of the outer shelf (St. George Unconformity) but Continuing subsurface dissolution was synchro- subsidence of the shelf edge and slope. The nous with the propagation of faults that cut and Overlying limestones, unlike the underlying, unconformity in the Pbillipsburg Group of displaced the oligomictic breccias and gently restricted dolostones, accumulated under open southern Quebec (Globensky, 1981; Knight, warped the platform. Dissolution along faults tidal-flat conditions on a narrow ramp shelf in- in press b) coincides approximately with this and at joint intersections opened cave passages. itiated adjacent to the oceanward foreland basin. event (Figs. 1, 5). Collapse probably ensued immediately, produc- "Hills" were buried by peritidal, shallowing- Platform-St. George Unconformity. Sub- ing chaotic, polymictic breccia composed of upward cycles, whereas deposition in lows was aerial Exposure, Karstification, and Erosion. Al- Aguathuna dolostone. Collapse dolines as much generally subtidal with local basal conglomerate though subsequently relief at the unconformity as 60 m deep formed at the unconformity above layers and peritidal caps. Considerable thicken- was attenuated by erosion, stratigraphy indicates some of these breccias. ing of these largely peritidal carbonates (as much that maximum demonstrable relief between Slope. A narrow platform developed out- as 3x) in eastern facies (Fig. 4) indicates that fault blocks was at least 50 m. Internal stratig- board of the uplifted shelf but was subject to peritidal sedimentation was able to keep pace raphy within blocks shows that individual horsts continuing seismicity, resulting in spectacular with rapid subsidence in outboard areas. In- were gently tilted, but not in any obvious con- sediment gravity flows (Bed 14, James and board, thin peritidal sediments veneered highs sistent fashion. Extensive karstification of the en- Stevens, 1986). These deep-water sediments and accumulated briefly in fault-controlled lows. tire terrane eroded horsts (for example, Port au were eventually covered by foreland basin Erosional disconformities truncating tilted bed- Choix, where all of the lower Aguathuna For- flysch. ding indicate continuing local seismicity. Mete- mation [40 m] and possibly as much as 30 m of oric water migration through the subsurface the underlying Catoche Formation was re- (5) Mid-Late Whiterockian (Early Llanvirn) during Spring Inlet Member deposition locally moved). Small-scale, rounded, surface sculpture formed solution chimneys of breccia (Fig. 18 A) attests to corrosion locally beneath a thin surface The penultimate stage began when rapid sub- that locally extended down into the Catoche veneer or protosoil with abundant chert clasts. sidence followed passage of the forebulge across Formation (Lane, 1990). Shallow subsurface karst, as intrastratal solu- western Newfoundland at a time when uplift The rest of the Table Point Formation was tion (egg-carton caves, bedding-parallel, water- was just beginning on the inner platform in deposited subtidally as topographic relief was table passages, and small caves), vuggy porosity, Quebec in the late Whiterockian. The "plat- buried and relative subsidence increased. Slump and solution-enlarged reticulate fissures devel- form" was a site of rapid carbonate sedimenta- folds and breccias, irregular thickness, a broken oped in outboard limestones of the Costa Bay tion over a series of fault blocks subsiding at and cemented upper contact locally, and rapid Member. Inboard, meteoric dissolution extend- different rates (Table Head Group). Flysch de- drowning of the subtidal Table Point limestones ed as much as 120 m below the unconformity rived from allochthonous terranes to the east beneath slope and basinal shales, limestones, and and enlarged northeast-trending joints and (paleosouth) buried slope sediments. In Quebec, erosive megabreccias (Stenzel and James, 1987; faults. In the Daniel's Harbour region, dissolu- karsted unconformities were initiated at different Stenzel and others, 1990) testify to the increas- tion and perhaps later removal of water support times on the Mingan Islands (Desrochers and ing tectonic control during this culminating (Ford, 1988) led to cave-roof collapse and de- James, 1988) and in the St. Lawrence Lowlands phase of deepening-upward carbonate sedimen- velopment of collapse dolines. (Harland and Pickerill, 1982; Globensky, 1987). tation in western Newfoundland.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 1223

(6) Late Whiterockian (Late Llanvirn) 1988; Read, 1980, 1989; Shanmugam and flexure. Greater wavelength to the forebulge Walker, 1980; Walker and others, 1983; Ruppel may also account for longer-lived unconform- In western Newfoundland by late Whiterock- and Walker, 1984; Harland and Pickerell, 1982; ities and the thin, foreland basin carbonate ian time, rapid subsidence was followed by ex- Mussman and Read, 1986; James and others, shelves in these areas (S. Colman-Sadd, 1989, tensive tectonism, manifested by thrusting and 1989; Knight, in press b) show the contrasts personal commun.). folding. The forebulge was by then moving between promontories and reentrants during across what is now the area of Middle Ordovi- passage of a peripheral forebulge and foreland Reentrants cian sedimentation in southern Quebec. Sedi- basin. mentation in western Newfoundland culminated Reentrants, in contrast, have minor hiatuses with burial of the carbonate sequence by fore- Promontories (Lash, 1988), thick platformal sequences, and land basin flysch as thrust complexes en- long-lived flysch basins. They were depocenters croached into the area. Cratonward in Quebec, Promontories are characterized by pro- during both passive-margin and foreland-basin protracted uplift and erosion was followed by nounced and complex unconformities (Lash, stages of the tectono-sedimentary cycle, imply- gradual subsidence and deposition of shallow- 1988), thin carbonate platform sequences, gen- ing that the rifted-margin geometry exerted a water carbonates. erally short-lived flysch sedimentation, and long-lived influence upon subsequent sedimenta- uplift of adjacent cratons, which shed siliciclastic tion. This may be due to thinning of continental Summary of Events detritus onto the platform. crust by horizontal extension during rifting Unconformities. Faulting and uplift induced (Dunbar and Sawyer, 1989), thermal variations The sequence of events outlined above fall deep erosion at the Virginia Promontory (Muss- within crust of uneven thickness, local tectonic into a simple pattern. man and Read, 1986) and complex stratigraphic control, and/or load-induced subsidence. Trans- (1) Global sea-level rise following subaerial relationships between pre- and post-unconform- form margins, which originally may have exposure coincided with the first evidence of ity sediments at the New York Promontory formed one side of the promontories in the early active plate motions, that is, distant plate con- (Fisher, 1977). Migration of the bulge into cra- stages of rifting (see Stockmal and others, 1987; vergence, island-arc generation, and possible in- tonic areas behind promontories produced uplift Mascle and Blarez, 1987), may have influenced creased sea-floor spreading (Colman-Sadd, adjacent to reentrants. This probably explains subsequent development of reentrants. 1982; Fortey, 1984) (Event 1). local unconformities and siliciclastic detritus Unconformities. Unconformities are of short (2) Convergence caused cessation of platform present in areas marginal to reentrants (for ex- duration. Mussman and Read (1986) and Read subsidence and rapid shallowing of the platform ample, the unconformity and of (1989) have emphasized the insignificant time (Events 2-3). Shelf sedimentation was main- Blackriverian age along the St. Lawrence Low- break associated with the Knox Unconformity tained by continued eustatic sea-level rise; uplift lands and within the Anticosti Basin (Harland in the Pennsylvania Reentrant. In the St. Law- of the shelf edge controlled peritidal sedimenta- and Pickerill, 1982; Roliff, 1968). rence Lowlands, Quebec Reentrant (Fig. 1), tion on the shallow shelf, and seismicity on the Sedimentation. In Newfoundland, evidence conodonts and shelly faunas indicate a short slope marked the impingement of the forebulge indicates that the passage of the shelf edge across time gap (possibly less than 1 m.y.) between at the shelf edge. the forebulge effected penecontemporaneous dolostones of the upper Beauharnois Formation (3) Active faulting, folding, and subaerial ex- pre-unconformity shelf sedimentation. Post- and the unconformably overlying Chazy Group posure of the platform marked the passage of the unconformity sediments at promontories are (Knight, in press b; L. Bernstein, 1989, personal peripheral bulge across the shelf (Events 4-6). characterized by deepening-upward sequences commun.). (4) Renewed carbonate sedimentation syn- (James and others, 1989; Stenzel and others, Sedimentation. Thick, shallow cyclic, pre- chronous with deposition of flyschoccurre d in a 1990; Bradley, 1989). The thin New York se- unconformity sediments in the reentrants of the foreland basin as thrust loading caused rapid quence, however, spans considerably more time United States Appalachians (Read, 1989) indi- subsidence (Events 4-€). (Fisher, 1977; Ross and others, 1982) than that cate that eustatic sea-level rise as seen in con- in Newfoundland. At the Virginia Promontory, temporary sediments of the Great Basin (Ross VARIATIONS ALONG THE post-unconformity stratigraphy is an onlap- and others, 1989) must have counterbalanced APPALACHIAN SYSTEM DUE TO offlap sequence that shallowed in the later stages the effect of slowed subsidence and forebulge PLATE-MARGIN CONFIGURATIONS of the foreland basin cycle (Read, 1989). Signif- uplift. Read (1989) preferred the idea of uplift The diachronous nature of the events between icantly, peritidal carbonates dominate the onlap due to incipient collision. This enabled the shelf Newfoundland and Quebec (Figs. 5,20) reflects sequence (Read, 1980), suggesting that in spite to remain below sea level and the reentrants the position of Newfoundland at the St. Law- of sea-level rise associated with flexural down- open to the influence of the shrinking Iapetus. rence Promontory relative to the Mingan Islands warping, the promontory remained a positive Sufficient shallowing of the pre-unconformity and St. Lawrence Lowlands, inboard, in the area where sedimentation kept pace with sea- shelf, however, restricted circulation and pro- Quebec Reentrant. The stratigraphy of the al- level rise. These relationships imply that the duced dolostone facies such as those in the lochthonous Phillipsburg Group (Figs. 1, 5) of New York and Virginia promontories behaved Aguathuna Formation in Newfoundland. southern Quebec suggests that its depositional differently than the one in Newfoundland, in Post-unconformity sedimentation in reen- position lay more outboard in the reentrant than spite of the fact that global sea-level rise in trants typically progressed from shallow- to did the autochthonous successions. the Middle Ordovician (Ross and others, 1982), deep-water carbonate ramp to flysch basin, re- Sequences at the Virginia, New York, and coupled with load-induced subsidence, should flecting the drowning of the shelf as the margin Newfoundland Promontories and in the Tennes- have drowned the promontories. In addition to flexed downward under Taconic loading. The see, Pennsylvania, and Quebec-Vermont Reen- their more inboard position, the thickness and foreland basin of the Pennsylvania Reentrant trants (Belt and others, 1979; Bussieres and buoyancy of the crust beneath these two had a protracted history, however, with evi- others, 1977; Globensky, 1981, 1987; Lash, promontories may have resisted downward dence for at least two shale-flysch sequences

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 1224 KNIGHT AND OTHERS

REFERENCES CITED Ford, D., 1988, Characteristics of dissolutional cave systems in carbonate rocks, (Ross and others, 1982; Read, 1989), the second in James, N. P., and Choquette, P. W., eds., Paleokarst: New York, sequence corresponding to the passage from Barnes, C. R., Norford, B. S., and Skevington, D., 1981, The Ordovician Springer-Verlag, p. 25-57. System in Canada: International Union of Geological Sciences Publica- Fortey, R. A., 1979, Early Ordovician trilobites from the Catoche Formation shelf to flysch in the Quebtic Reentrant (Bradley, tion 8,27 p. (St. George Group), western Newfoundland, in Griffin, P. T., éd., Con- Belt, E. S., Riva, J., and Bussiferes, L., 1979, Revision and correlation of late tributions to Canadian paleontology: Geological Survey of Canada Bul- 1989; Knight, in press b). Middle Ordovician stratigraphy northeast of Quebec City: Canadian letin 321, p. 61-114. Foreland-basin carbona te shelf to flysch sed- Journal of Earth Sciences, v. 16, p. 1467-1483. 1984, Global Early Ordovician transgression and regressions and their Bird, J. M., and Dewey, J. F., 1970, Lithospheric plate-continental margin biological implications, in Bruton, D. L., ed., Aspects of the Ordovician imentation in the Quebec: Reentrant began al- tectonics and the evolution of the Appalachian orogen: Geological So- System: Paleontological Contributions from the University of Oslo, ciety of America Bulletin, v. 81, p. 1031-1060. Universitetsforlaget, No. 295, p. 37-50. most 10 m.y. later than in Newfoundland and Bogli, J., 1980, Karst hydrology and physicat speleology: Berlin, Heidelberg, Globensky, Y., 1981, Regions de Lacolle Saint-Jean(s): Quebec Minestère de lasted -20 m.y., twice as long as in Newfound- Springer-Verlag, 285 p. l'Energie et des Ressources de Quebec, Rapport Géologique 197,197 p. Botsford, J. W., 1987, Depositional history of Middle Cambrian to Lower 1987, Géologie des Basses-Terres du Saint-Laurent: Quebec Ministère land. This significant time difference may reflect Ordovician deep-water sediments [Ph.D. thesis]: St. John's, Newfound- de l'Energie et des Ressources de Quebec. MM85-02,63 p. land, Memorial University of Newfoundland, 534 p. Grotzinger, J. D., 1986, Upward shallowing platform cycles: A response to 2.2 (1) the geographic positions of the two areas as Boyce, W. D., 1983, Preliminary Ordovician trilobite stratigraphy of the Eddies billion years of low-amplitude, high-frequency (Milankovitch band) sea outlined in the diachronous collision model of Cove West-Port au Choix area, western Newfoundland, in Current level oscillations: Paleoceanology, v. 1, p. 403-416. research: Newfoundland Department of Mines and Energy, Mineral Grover, G., Jr., and Read, J. F., 1978, Fenestral and associated vadose diage- Bradley (1989), (2) the time required to develop Development Division, Report 83-1, p. 11-15. netic fabrics of tidal flat carbonates, Middle Ordovician New Market 1989, Early Ordovician trilobite faunas of the Boat Harbour and Ca- Limestone, southwestern Virginia: Journal of Sedimentary Petrology, a transform fault between the St. Lawrence toche Formations (St. George Group) in the Boat Harbour-Cape Nor- v. 48, p. 453-473. Promontory and the reentrant and to resume man area, Great Northern Peninsula, western Newfoundland: New- Hamilton, W., 1979, Tectonics of the Indonesian region: U.S. Geological Sur- foundland Department of Mines and Energy, Geological Survey vey Professional Paper 1078, 345 p. westward motion of allochthons and volcanic Branch, Report 89-2,169 p. Hardie, L. A., and Shinn, E. A., 1986, Carbonate depositional environments, Boyce, W. D., Ash, J. S., and Knight, I, 1988, Biostrattgraphic studies of modern and ancient; 3, Tidal flats: Colorado School of Mines Quar- arc into the reentrant following the collision of Ordovician carbonate rocks in western Newfoundland, 1987, in Hyde, terly , v. 81(1), 74 p. the arc with the promontory, and (3) the slow R. S., Walsh, D. G., and Blackwood, R. F., eds., Current research: Hardie, L. A., Bosellini, A., and Goldhammer, R. K., 1986, Repeated subaerial Newfoundland Department of Mines and Energy, Mineral Develop- exposure of subtidal carbonate platforms, , northern Italy: Evi- migration of the foreland basin in the Quebec ment Division, Report 88-1, p. 75-83. dence for high frequency sea level oscillations on a 104 year scale: Bradley, D. C., 1989, Taconic plate kinematics as revealed by foredeep stratig- Paleoceanography, v. 1, p. 447-457. Reentrant as the Laurentian plate gradually raphy, Appalachian Orogen: Tectonics, v. 8, p. 1037-1049. Harland, T. L., and Pickerill, R. K., 1982, A review of Middle Ordovician resisted the effects of accretionary loading dur- Bradley, D. C., and Kuski, T. M., 1986, Geologic evidence for rate of plate sedimentation in the St. Lawrence Lowland, eastern Canada: Geologi- convergence during Taconic arc-continent collision: Journal of Geol- cal Journal, v. 17, p. 135-156. ing the final stages of Taconic orogenesis. ogy, v. 94, p. 667-681. Haywick, D. W., 1985, Dolomites within the St. George Group (Lower Ordo- Bussiferes, L., Mehrtens, C. J., Belt, E. S., and Riva, J., 1977, Late Middle vician), western Newfoundland [M.Sc. thesis]: St. John's, Newfound- Ordovician shelf, slope and flysch fades between Baie-St-Paul and La land, Memorial University of Newfoundland, 281 p. Malbaie, in New England Intercollegiate Geological Congress, 69th Haywick, D. W., and James, N. P., 1984, Dolomites and dolomitization of the CONCLUSIONS Annual Meeting, Laval University, Quebec, excursion B9, p. 1-26. St. George Group (Lower Ordovician) of western Newfoundland, in Chappie, W. M., 1973, Taconic orogeny: Abortive subduction of the North Current research, part A: Geological Survey of Canada, Paper 84-1A, American continental plate?: Geological Society of America Abstracts p. 531-S36. The St. George Unconformity is the boundary with Programs, v. 11, p. 7. Home, G. S., Atwood, M. G., and King, A. P., 1974, Stratigraphy, sedimentol- Charlton, T. R., 1989, Stratigraphic correlation across an arc-continental colli- ogy, and paleoenvironment of Esquias Formation, Honduras: American between the Sauk and Tippecanoe sequences in sion zone: Timor and the Australian northwest shelf: Australian Journal Association of Petroleum Geologists Bulletin, v. 58, no. 2, p. 176-188. western Newfoundland. Detailed analysis of the of Earth Sciences, v. 36, p. 263-274. Jacobi, R. D., 1981, Peripheral bulge—A casual mechanism for the Lower/ Choquette, P. A., and James, N. P., 1988, Introduction, in James, N. P., and Middle Ordovician unconformity along the western margin of the unconformity itself, together with the packages Choquette, P. W., eds., Paleokarst: New York, Springer-Verlag, Northern Appalachians: Earth and Planetary Science Letters, v. 56, p. 1-21. p. 245-251. of sediment above and below, indicates that the Chow, N., 1986, Sedimentology and diagenesis of Middle and Upper Cam- James, N. P., and Choquette, P. W., 1984, Diagenesis 9—Limestone— feature is tectonic in origin and does not reflect brian platform carbonates and siliciclastics, Port-au-Port Peninsula, The meteoric diagenetic environment: Geoscience Canada, v. 11, western Newfoundland [Ph.D. thesis]: St. John's, Newfoundland, p. 161-194. eustatic sea-level lowering. The whole complex Memorial University of Newfoundland, 458 p. James, N. P., and Stevens, R. K., 1982, Anatomy and evolution of a lower Chowns, T. M., and Elkins, J. E., 1974, The origin of quartz geodes and Paleozoic continental margin, western Newfoundland: International As- of sediments, faults, and erosion surfaces is best cauliflower cherts through the silicification of anhydrite nodules: Jour- sociation of Sedimentologists Congress, Field excursion no. 2B, 75 p. explained by slowing to cessation of subsidence nal of Sedimentary Petrology, v. 44, p. 885-903. 1986, Stratigraphy and correlation of the Cambro-Ordovician Cow Collins, J. A., and Smith, L., 1975, Zinc deposits related to diagenesis and Head Group, western Newfoundland: Geological Survey of Canada and gradual passage of a forebulge across the intrakarstic sedimentation in the Lower Ordovician St. George Forma- Bulletin 366, 143 p. tion, western Newfoundland: Bulletin of Canadian Petroleum Geology, James, N. P., Botsford, J., and Williams, S. H., 1987, Allochthonous slope paleocontinental margin. The model developed v. 23, p. 393-427. sequence at Lobster Cove Head: Evidence for a complex Middle Ordo- from these rocks is applicable to other promon- Colman-Sadd, S. P., 1982, Two stage continental collision and plate driving vician platform margin in western Newfoundland: Canadian Journal of forces: Tectonophysics, v. 90, p. 263-282. Earth Sciences, v. 24, p. 1199-1211. tories and reentrants along the length of the Ap- Coniglio, M., 1985, Origin and diagenesis of fine grained slope sediments: Cow James, N. P., Knight, I., Stevens, R. K., and Barnes, C. R., 1988, Sedimentology Head Group (Cambro-Ordovician), western Newfoundland [Ph.D. the- and paleontology of our early Paleozoic continental margin, western palachian orogen. Such an interpretation implies sis]: St. John's, Newfoundland, Memorial University of Newfoundland, Newfoundland: Geological Association of Canada, Mineralogical Asso- that this boundary, that lacks true synchroneity 684 p. ciation of Canada, Canadian Sodety of Petroleum Geologists, Field trip Crossley, R. V., and Lane, T., 1984, A guide to the Newfoundland Zinc Mines guidebook Bl, 121 p. between different plate margins, including Lau- Limited ore bodies, Daniel's Harbour, in Swinden, S. S., ed., Mineral James, N. P., Barnes, C. R., Stevens, R. K., and Knight, I., 1989, A lower deposits of Newfoundland—A 1984 perspective: Newfoundland De- Paleozoic continental margin carbonate platform, northern Canadian rentia's, but long interpreted as a global sea-level partment of Mines and Energy Report 84-3, p. 45-51. Appalachians, in Crevello, T., Sarg, R., Read, J. F., and Wilson, J. L., fall, is due to global tectonic rearrangements. Dallmeyer, R. D., 1977, Diachronous ophiolite obduction in western New- eds., Controls on carbonate platforms and basin development: Society foundland: Evidence from 40Ar/39Ar ages of the Hare Bay metaraor- of Economic Paleontologists and Mineralogists Special Publication 44, phic aureole: American Journal of Science, v. 277, p. 61-72. p. 123-146. Dallmeyer, R. D., and Williams, H., 1975, ^Ar/^Ar ages for the Bay of Kaesler, R. L., 1987, Superclass crustacea, class Ostracoda, in Boardman, R. S., ACKNOWLEDGMENTS Islands metamorphic aureole: Their bearing on the timing of Ordovi- Cheetham, A. H., and Rowell, A. J., eds., Fossil invertebrates: Palo cian ophiolite obduction: Canadian Journal of Earth Sciences, v. 12, Alto, Oxford, London, Blackwell Scientific Publications, p. 241-254. p. 1685-1690. Kahle, C. F., 1988, Surface and subsurface paleokarst, Silurian Lockport and Dalrymple, R. W., Narbonne, G. M., and Smith, L., 1985, Eolian action and Peebles Dolomites, western Ohio, in James, N. P., and Choquette, We thank D. Boyce, S. Colman-Sadd, the distribution of Cambrian shales in North America: Geology, v. 13, P. W., eds., Paleokarst: New York, Springer-Verlag, p. 229-255. S. Stenzel, R. K. Stevens, and S. H. Williams for p. 607-610. Karig, D. E., Barber, A. J., Charlton, T. R., Klemperer, S., and Hussong, D. M., Desrocheis, A., 1985, The Lower and Middle Ordovician platform carbonates 1987, Nature and distribution of deformation across the Banda Arc- field assistance and provocative discussion. Lane of the Mingan Islands, Quebec: Stratigraphy, sedimentology, paleokarst Australian collision zone at Timor: Geological Society of America and limestone diagenesis [Ph.D. thesis]: St John's, Newfoundland, Bulletin, v. 98, p. 18-32. thanks Newfoundland Zinc Mines and Teck Memorial University of Newfoundland, 454 p. Kenna, K„ 1985, Upper Canadian to Whiterock conodonts of the upper St. Corporation for access to drilling information Desrochers, A., and James, N. P., 1988, Early Paleozoic surface and subsurface George Group, western Newfoundland [abs.]: Geological Association of karst: Middle Ordovician carbonates, Mingan Islands, Quebec, in Canada, Canadian Paleontology and Biostratigraphy, Seminar, Quebec and permission to publish . Research by James is James, N. P., and Choquette, P. W., eds., Paleokarst: New York, City, Quebec, Program with Abstracts, p. 45. Springer-Verlag, p. 183-210. Kerans, C., 1988, Karst-controlled reservoir heterogeneity in Ellenburger funded by the Natural Sciences and Engineering Dunbar, J. A., and Sawyer, D. S., 1989, Patterns of continental extension along Group carbonates of west Texas: American Association of Petroleum Council of Canada. Knight was funded by joint the conjugate margins of the central and north Atlantic Oceans and Geologists Bulletin, v. 72, p. 1160-1183. Labrador Sea: Tectonics, v. 8, p. 1059-1077. Kindle, C. H., and Whittington, H. B., 1958, Stratigraphy of the Cow Head Canada-Newfoundland Mineral Development Dunning, G. R., and Krogh, T. E., 1985, Geocbronology of ophiolite of the region, western Newfoundland: Geological Society of America Bulletin, Newfoundland Appalachians: Canadian Journal of Earth Sciences, v. 69, p. 315-342. Subsidiary Agreements from 1980 to 1989 and v. 22, p. 1659-1670. Klappa, C. F., Opalinski, P. R., and James, N. P., 1980, Middle Ordovician publishes with permission of the Geological Esteban, M., and Klappa, C. F., 1983, Subaerial exposure environment, in Table Head Group of western Newfoundland: A revised stratigraphy: Scholle, P. A., Bebout, D. G., and Moore, C. M., eds., Carbonate Canadian Journal of Earth Sciences, v. 17, p. 1007-1019. Survey Branch, Newfoundland Department of depositional environments: American Association of Petroleum Geolo- Knight, I., 1986, Ordovician sedimentary strata of the Pistolet Bay and Hare gists Memoir 33, p. 1-54. Bay area. Great Northern Peninsula, Newfoundland, in Blackwood, Mines and Energy. D. C. Bradley, J. J. Packard, Fisher, D. M., 1977, Correlation of Hadrynian, Cambrian and Ordovician R. F., Walsh, D. G., and Gibbons, R. V., eds., Current research: and R. J. Ross critically read the manuscript. rocks of New York State: New York State Museum Map and Chart Newfoundland Department of Mines and Energy, Mineral Develop- Series, folio 25,75 p. ment Division, Report 86-1, p. 147-160.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021 ORDO VICIAN ST. GEORGE UNCONFORMITY, NEWFOUNDLAND 1225

1987, Geology of the Roddickton (121/16) map area, in Blackwood, Pratt, B. R., 1979, Sedimentology, diagenesis and cryptalgal structures, the St. 1988, Forty years of : Geological Society of Amer- R. F., Walsh, D. G., and Gibbons, R. V., eds., Current research: George Group (Lower Ordovician), western Newfoundland [M.Sc. the- ica Butletin, v. 100, p. 1661-1665. Newfoundland Department of Mines and Energy, Mineral Develop- sis]: St. John's, Newfoundland, Memorial University of Newfoundland, Stait K., 1988, Upper Canadian to Whiterockian (Ordovician) conodonts ment Division, Report 87-1, p. 343-357. 231 p. biostratigraphy of the upper St George Group, western Newfoundland —in press a, Geology of the Carobro-Ordovician rocks in the Port Saun- Pratt, B. R„ and James, N. P., 1986, The tidal flat island model for peritidal [M.Sc. thesis]: St. John's, Newfoundland, Memorial University of New- ders, Castors River, St John Island and Torrent River map sheets: New- shallow-upward sequences: St George Group, western Newfoundland: foundland, 494 p. foundland Department of Mines and Energy, Mineral Development Sedimentology, v. 33, p. 313-344. Stait K., and Barnes, C. R., 1988, Conodont biostratigraphy of the upper St. Division, Report. Quinlan, G., and Beaumont, C., 1984, Appalachian thrusting, lithospheric flex- George Group (Canadian-Whiterock), western Newfoundland [abs.]: in press b, Cambrian-Ordovician carbonate rocks of the Humber Zone, ure, and the Paleozoic stratigraphy of the eastern interior of North 5th International Ordovician Symposium, Memorial University of in Williams, H., coordinator, Geology of the Appalachian/Caledonian America: Canadian Journal of Earth Sciences, v. 21, p. 973-996. Newfoundland, Newfoundland, Canada, p. 98. Orogen in Canada and Greenland: Geological Survey of Canada, Read, J. F., 1980, Carbonate ramp-to-basin transitions and foreland basin Stenzel, S. R., and James, N. P., 1987, Death and destruction of an early Geology of Canada, no. 6 (also Geological Society of America, Vol- evolution. Middle Ordovician, Virginia Appalachians: American Asso- Paleozoic carbonate platform, western Newfoundland [abs.]: Society of ume F-l). ciation of Petroleum Geologists Bulletin, v. 64, p. 1575-1612. Economic Paleontologists and Mineralogists Annual Meeting, Austin, Knight, I., and Boyce, W. D., 1984, Geological mapping of the Port Saunders 1989, Controls on evolution of Cambrian-Ordovician passive margins, Texas, p. 80. (121/11) and the St. John Island (121/14) and parts of the Torrent U.S. Appalachians, in Crevello, P. D., Wilson, J. L., Sarg, J. F., and 1988, Foundering and burial of an early Paleozoic carbonate platform, River (121/10) and Bellbums (121/6) map sheets, northwestern New- Read, J. F., eds., Controls on carbonate platform and basin develop- western Newfoundland [abs.]: Geological Association of Canada, Min- foundland, in Murray, M. J., Whelan, J. G., and Gibbons, R. V., eds., ment: Society of Economic Paleontologists and Mineralogists Special eralogical Association of Canada, Canadian Society of Petroleum Current research: Newfoundland Department of Mines and Energy, Publication 44, p. 147-166. Geologists, Joint Annual Meeting, St. John's, Newfoundland, p. A117. Mineral Development Division, Report 84-1, p. 114-123. Robertson, A., 1987a, The transition from a passive margin to an Upper Stenzel, S. R., Knight I-. and James, N. P., 1990, Carbonate platform to Knight, I., and James, N. P., 1987, Stratigraphy of the St. George Group foreland basin related to ophiolite emplacement in the foreland basin; revised stratigraphy of the Table Head Group (Middle (Lower Ordovician), western Newfoundland; the interaction between Oman Mountains: Geological Society of America Bulletin, v. 99, Ordovician), western Newfoundland: Canadian Journal of Earth Sci- eustasy and tectonics: Canadian Journal of Earth Sciences, v. 24, p. 633-653. ences, v. 27 (in press). p. 1927-1952. 1987b, Upper Cretaceous Muti Formation: Transition of a Mesozoic Stevens, R. K., 1970, Cambro-Ordovician flysch sedimentation and tectonics in 1988, Stratigraphy of the Lower to lower Middle Ordovician St. carbonate platform to a foreland basin in the Oman Mountains: Sedi- west Newfoundland and their possible bearing on a proto-Atlantic George Group, western Newfoundland: Newfoundland Department of mentology, v. 34, p. 1123-1142. Ocean, in Lajoie, J., ed., Flysch sedimentology in North America: Geo- Mines, Report 88-4,48 p. Rodgers, J., 1968, The eastern edge of the North American continent during logical Association of Canada Special Paper 7, p. 165-177. Lane, T. E., 1984, Preliminary classification of carbonate breccias, Newfound- the Cambrian and Early Ordovician, in Zen, E., White, W. S., Hadley, Stockmal, G. S., Beaumont C., and Boutilier, R., 1986, Geodynamic models of land Zinc Mines, Daniel's Harbour, Newfoundland, in Current research, J. B., and Thompson, J. B., eds., Studies of Appalachian geology, north- convergent margin tectonics: Transition from rifted margin to overthrust Part A: Geological Survey of Canada, Paper 84-1A, p. 505-512. em and maritime: New York, Interscience Publications, p. 141-149. belt and consequences for foreland-basin development: American Asso- 1987, Setting and origin of shoestring sphalerite deposits. Lower Ordo- Rodgers, J., and Neale, E.R.W., 1963, Possible "Taconic" klippen in western ciation of Petroleum Geologists, v. 70, p. 181-190. vician St. George Group, Daniel's Harbour, western Newfoundland Newfoundland: American Journal of Science, v. 261, p. 713-730. Stockmal, G. S., Colman-Sadd, S. P., Keen, C. E., O'Brien, S. J., and Quinlan, [abs.]: Society of Economic Paleontologists and Mineralogists Annual Roliff, W. A., 1968, Oil and gas exploration—Anticosti Island, Quebec Geo- G., 1987, Collision along an irregular margin: A regional plate tectonic Meeting, Austin, Texas, p. 47. logical Association of Canada, Proceedings, v. 19, p. 31-36. interpretation of the Canadian Appalachians: Canadian Journal of 1990, Dolomitization, brecciation and zinc mineralization and their Ross. R. J., Jr., and James, N. P., 1987, Brachiopod biostratigraphy of the Earth Sciences, v. 24, p. 1098-1107. paragenetic, stratigraphic and structural relationships, Upper St. George Middle Ordovician Cow Head and Table Head Groups, western New- Stouge, S. S., 1982, Preliminary conodont biostratigraphy and correlation of Group—Ordovician—Daniel's Harbour, western Newfoundland foundland: Canadian Journal of Earth Sciences, v. 24, p. 70-95. Lower and Middle Ordovician carbonates of the St. George Group, [Ph.D. thesis]: St. John's, Newfoundland, Memorial University of New- Ross, R. J., Jr., Adier, F. J., Amsden, T. W., Bergstrom, D., Bergstrom, S. M., Great Northern Peninsula, Newfoundland: Newfoundland Department foundland, 565 p. Carter, C., Churkin, M., Cressman, E. A., Derby, J. R., Dutro, J. T., Jr., of Mines and Energy, Mineral Development Division, Report 82-3, Lane, T. E., and James, N. P., 1987, Coarse dolostone/sphalerite complexes, Ethington, R. L., Finney, S. G, Fisher, D. W., Fisher, J. H., Harris, p. 1-59. Lower Ordovician St. George Group, Daniel's Harbour, western New- A. G., Hintze, L. F., Ketner, K. B., Kotlata, D. L., Landing, E., Neuman, 1984, Conodonts of the Middle Ordovician Table Head Formation, foundland [abs.]: Society of Economic Paleontologists and Mineralo- R. B., Sweet, W. C., Pojeta, J., Jr., Potter, A. W., Rader, E. K., Re- western Newfoundland: Fossils and Strata, v. 16, 145 p. gists Annual Meeting, Austin, Texas, p. 47. petski, J. E., Shaver, R. H., Thompson, T. L., and Webers, G. F., 1982, Suchecki, R. K., Perry, E. A., and Hubert, J. F„ 1977, Clay petrology of Lash, G. G . 1988, Along strike variations in foreland basin evolution; possible The Ordovician System in the United States: International Union of Cambro-Ordovician continental margin, Cow Head Klippe, western evidence for continental collision along an irregular margin: Basin Re- Geological Sciences, Publication 12,71 p. Newfoundland: Clay and Clay Minerals, v. 25, p. 163-170. search, v. 1, p. 71-83. Ross, R. J., James, N. P., Hintze, L. F., and Poole, F. G., 1989, Architecture Vail, P. R., Mitchum, R. M., Jr., and Thompson, S., Ill, 1977, Seismic stratig- Levesque, R. J., 1977, Stratigraphy andsedimentology of Middle Cambrian to and evolution of a Whiterockian (early Middle Ordovician) carbonate raphy and global changes of sea level, in Payton, C. E., ed., Seismic Lower Ordovician shallow water carbonate rocks, western Newfound- platform, Basin Ranges of western U.S.A., in Crevello, P. D., Wilson, stratigraphy—Applications to hydrocarbon exploration: American As- land [M.Sc. thesis]: St. John's, Newfoundland, Memorial University of J. L,, Sarg, J. F., and Read, J. F., eds.. Controls on platform and basin sociation of Petroleum Geologists Memoir 26, p. 83- 97. Newfoundland, 276 p. development: Society of Economic Paleontologists and Mineralogists Walker, K. R., Shanmugam, G., and Ruppel, S. C., 1983, A model for carbon- Logan, B. W„ 1987, The Macleod Evaporite Basin, western Australia: Ameri- Special Publication 44, p. 167-186. ate to terrigenous clastic sequences: Geological Society of America can Association of Petroleum Penologists Memoir 44, 140 p. Rowley, D. B., and Kidd, W.S.F., 1981, Stratigraphic relationships and detrital Bulletin, v. 94, p. 700-712. Lohmann, K. C., 1988, Geochemical patterns of diagenetic systems and their composition of the medial Ordovician flysch of western New England: Williams, H., 1975, Structural succession, nomenclature and interpretation of application to studies of paleokarst in James, N. P., and Choquette, Implications for the tectonic evolution of the Taconic Orogeny: Journal transported rocks in western Newfoundland: Canadian Journal of Earth P. W., eds., Paleokarst: New York, Springer-Verlag, p. 58-80. of Geology, v. 89, p. 199-218. Sciences, v. 12, p. 1874-1894. Mascal, J., and Blarez, E., 1987, Evidence for transform margin evolution from Ruppel, S. C., and Walker, K. R., 1984, Petrology and depositional history of a 1978, Geological development of the northern Appalachians; its bearing the Ivory Coast-Ghana continental margin: Nature, v. 326, p. 378-381. Middle Ordovician carbonate platform: Chickamauga Group, north- on the evolution of the British Isles, in Bowes, D. R., and Leake, B. E., Meyers, W. J., 1988, Paleokarstic features on Mississippian limestones, New eastern Tennessee: Geological Society of America Bulletin, v. 95, eds., Crustal evolution in northwestern Britain and adjacent regions: Mexico, in James, N. P., and Choquette, P. W., eds., Paleokarst: New p. 568-583. Liverpool, England, Seal House Press, p. 1-22. York, Springer-Verlag, p. 306-328. Sass, E., and Katz, A., 1982, The origin of platform dolomites: New evidence: 1979, Appalachian Orogen in Canada: Canadian Journal of Earth Muir, M., Lock, D., and van der Borch, C., 1980, The Coorong model for American Journal of Science, v. 282, p. 1184 1213. Sciences, v. 16, p. 792-807. penecontemporaneous dolomite formation in the middle Proterozoic Schuchert, C., and Dunbar, C. O., 1934, Stratigraphy of western Newfound- Williams, H., and Stevens, R. K., 1974, The ancient continental margin McArthur Group, Northern Territory, Australia, in Zenger, D. H., land: Geological Society of America Memoir 1, 123 p. of eastern North America, in Burke, C. A., and Drake, C. L., eds., Dunham, J. B., and Ethington, R. L., eds., Concepts and models of Searle, M. P., James, N. P., Calón, T. J., and Smewing, J. D., 1983, Sedimento- The geology of continental margins: New York, Springer-Verlag, dolomitization: Society of Economic Paleontologists and Mineralogists logical and structural evolution of the Arabian continental margin in the p. 781-796. Special Publication No. 28, p. 51-68. Musandam Mountains and Dibba zone, United Arab Emirates: Geolog- Williams, S. H., and Stevens, R. K., 1988, Early Ordovician (Arenig) grapto- Mussman, W. J., and Read, J. F. 1986, Sedimentology and development of a ical Society of America Bulletin, v. 94, p. 1381-1400. lites from the Cow Head Group, western Newfoundland: Palaeontogra- passive to convergent margin unconformity: Middle Ordovician Knox Shanmugam, G., and Lash, G. G., 1982, Analogous tectonic evolution of the phica Canadiana, v. 5, 167 p. unconformity, Virginia Appalachians: Geological Society of America Ordovician foredeeps, southern and central Appalachians: Geology, Williams, S. H., Boyce, W. D., and James, N. P., 1987, Graptolites from the Bulletin, v. 97, p. 282-295. v. 10, p. 562 566. Middle Ordovician St. George and Table Head Groups, western New- Mussman, W. J., Montanez, 1. P., and Read, J. F„ 1988, Ordovician Knox Shanmugam, G., and Walker, K. R., 1980, Sedimentation, subsidence, and foundland, and implications for the correlation of trilobite, brachiopod paleokarst unconformity, Appalachians, in James. N. P., and Cho- evolution of a foredeep basin in the Middle Ordovician, southern Ap- and conodont zones: Canadian Journal of Earth Sciences, v. 24, quette, P. W., eds„ Paleokarst: New York, Springer-Verlag, p, 211 -228. palachians: American Journal of Science, v. 280, p. 479-496. p. 456-470. Oh!e, E. L., 1985, Breccias in Mississippi Valley-type deposits: Economic Simms, M., 1984, Dolomitization by groundwater-flow systems in carbonate Wilson, H. H,, 1974, Cretaceous sedimentation and orogeny in nuclear Central Geology, v. 80, p. 1736-1752. platforms: Gulf Coast Association of Geological Societies, Transactions, America: American Association of Petroleum Geologists Bulletin, v. 58, Patterson, R. J., 1972, Hydrology and carbonate diagenesis of a coastal sabkha v. 34, p. 411-420. p. 1348 1396. in the Persian Gulf [Ph.D. dissert]: Princeton, New Jersey, Princeton Sloss, L. L., 1963, Sequences in the Craton Interiors of North America: Geolog- University, 498 p. ical Society of America Bulletin, v. 74, p. 93-114. Pigram, C. J., Davies, P. J., Feary, P. A., and Symonds, P. A,, 1989, Tectonic 1972, Synchrony of Phanerozoic sedimentary-tectonic events of the MANUSCRIPT RECEIVED BY THE SOCIETY MARCH 16,1990 controls on carbonate platform evolution in southern Papua New Guin- North American craton and the Russian platform: International Geolog- REVISED MANUSCRIPT RECEIVED FEBRUARY 11,1991 ea: Passive margin to foreland basin; Geology, v. 17, p. 199-202. ical Congress, 24th, Montreal, section 6, p. 24- 32. MANUSCRIPT ACCEPTED FEBRUARY 13, 1991

Printed in U.S.A.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/9/1200/3381328/i0016-7606-103-9-1200.pdf by guest on 01 October 2021