Paleokarst in the Lower Ordovician Beekmantown Group, Ottawa Embayment: Structural Control Inboard of the Appalachian Orogen

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Paleokarst in the Lower Ordovician Beekmantown Group, Ottawa Embayment: Structural control inboard of the Appalachian orogen

George R. Dix* Ottawa-Carleton Geoscience Centre and Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada George W. Robinson Seaman Mineral Museum, Michigan Technological University, 1400 Townsend Drive, Houghton, Michigan 49931-1295 D. Colin McGregor Eastern Paleontology Section, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1N 0E8, Canada

ABSTRACT and porosity development well inboard of the Mountjoy, 1994; Palmer, 1995). In eastern On- Appalachian orogen. tario and southwestern Québec, mineralized Two paleokarsts, different in age, character, (sulfide, sulfate, carbonate, quartz, minor hydro- and origin, occur in dolostones of the Lower INTRODUCTION carbon) and nonmineralized paleokarsts occur Ordovician Beekmantown Group of eastern within dolostones of the Early to Middle Or- Ontario, well within the interior of the Lau- Types and patterns of porosity in carbonate dovician Beekmantown Group. This region rentian paleoplatform. Surficial to shallow platforms help to define the history of platform forms part of the Ottawa Embayment, an interior subsurface (<2 m) epikarst formed during the aggradation, and constrain interpretation of part of the Laurentian paleoplatform, positioned latter stage (late Arenig to Llanvirn) of Sauk paleogeographic distribution of potential petro- well inboard of the structural front, or Logan’s platform development in this region, resulting leum and mineralization occurrences (Qing and Line, of the Appalachian orogen (Fig. 1). The as- from local change to base level and patterns of meteoric circulation likely initiated by reactivation of shallowly buried Precambrian structures along a cratonic fault system, now defined by the Ottawa-Bonnechere Graben. Faulting was contemporaneous with initiation of the crustal forebulge within the distal, developing Taconic orogen. Mineralized, intrastratal, vuggy to local cavernous porosity composes a prominent second, more regional paleokarst. Dissolution followed burial chemical compaction, but predated a history of further burial and tectonism defined by stages of geopetal cavity-fill sedimentation, cavity-fill mineralization, calcite veining, and renewed stylolitization. Regional paleokarst is inter-

preted to have arisen from changes in pCO2 and H2S concentrations arising from mixing of continentally derived pore waters with brines derived from dissolution of Beekmantown evaporites. Compared to the region’s geologic history, a pre–late Paleozoic age for formation of the regional paleokarst and mineralization is likely. The two platform-interior paleokarsts demonstrate unexpected links between tectonism, changes in paleohydrological patterns, Figure 1. Location of the Ottawa Embayment and Beauharnois arch relative to the structural front (Logan’s Line) of the Appalachian orogen. Other patterned areas denote distribution of *E-mail: [email protected]. Precambrian rocks. Provincial boundaries of Québec (PQ) and Ontario (ON) are indicated.

GSA Bulletin; August 1998; v. 110; no. 8; p. 1046–1059; 10 figures; 2 tables.

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sociation of paleokarst, calcite veining, and regional metallogenic (including hydrocarbon) patterns within lower Paleozoic carbonate strata is well known along the length of the Appala- TABLE 1. LOCATIONS REFERRED TO IN THE TEXT Location* NTS map UTM coordinates† References chian orogen (e.g., Hoagland, 1976; Schrijver sheet Easting Northing et al., 1988; Kesler and van der Pluijm, 1990; 1 Kennedy’s Quarry (i) 31G 422800 5031500 Williams (1991) Knight et al., 1991; Gauthier et al., 1994; 2 Dunrobin (o/c) 31G 418000 5030000 This study Montañez, 1994; Dykstra and Longman, 1995; 3 GSC Lebreton (c) 31G 444900 5027500 Williams (1991) 4 Royel Quarry (i) 31F 410600 5001600 Forgrave (1995) Kesler et al., 1995; Paradis and Lavoie, 1996). 5 GSC Observatory Crescent (c) 31G 440470 5026700 Williams (1991) How mineralization in the platform-interior 6 Cumberland (o/c) 31G 463900 5040000 Williams (1991) strata in eastern Ontario is related in time and 7 Grant Quarry (a) 31G 459500 5014500 Derry et al. (1989) 8 Beaver Road Builders Quarry (a) 31G 456000 5016800 Williams (1991) space to orogen metallogenesis has received lit- 9 GSC Russell (c) 31G 469400 5017600 Bernstein (1991) tle attention (see Williams, 1991). 10 Maple Grove Quarry (a) 31G 452000 4986200 Derry et al. (1989) 11 Highways 16 and 44 intersection (o/c) 31B 451900 4981200 This study We first discuss the origin of the two paleo- 12 Groveton (o/c) 31B 455000 4970800 This study karsts within Beekmantown Group dolostones in 13 Williamsburg (c) 31G 474200 4984800 Williams (1991) eastern Ontario and southwestern Québec to bet- 15 McCrimmon’s Corners (c) 31G 520100 5029900 Bernstein (1991) 14 Imperial Oil Laggan #1 (c) 31G 521200 5026300 Bernstein (1991) ter define the origin and distribution of available 16 Carillon Dam (o/c) 31G 548000 5045600 Bernstein (1992) porosity at the time of mineralization. Develop- 17 St. Justine Quarry (A) 31G 544000 5026300 Avramtchev (1994) ment of porosity is evaluated relative to discor- 18 St. Eustache Quarry (A) 31H 588200 5048500 Avramtchev (1994) 19 St. Chlotilde Quarry (A) 31H 608200 5002800 Bernstein (1991) dant relationships with cavity-fill sediment, stylo- Notes: NTS—National Topographic System; UTM—Universal Transverse Mercator. lites, mineralization, faults, and calcite veins. *Inactive (i) and active (a) quarry; outcrop (o/c); core (c). Placed in context of the early Paleozoic tectono- †Measured at scale of 1:250 000. stratigraphic framework of eastern North Amer- ica, separate stages of shallow and deep-burial dissolution are interpreted to reflect reorganization of paleohydrology linked to, but well inboard of, early to middle Paleozoic orogenic activity. Residue was placed on coverslips in cellosize and Taconic foredeep; foundering of the platform is affixed to glass slides with Elvacite. defined by deposition of synorogenic mudrock METHODOLOGY (Fig. 3) derived from the Taconic highlands GEOLOGICAL SETTING (Williams, 1991; Sanford, 1993b). Data were collected over the period 1994 to The Sauk-Tippecanoe sequence boundary in 1996 from active and abandoned quarries, drill The Ottawa Embayment is an intracratonic ex- the Ottawa Embayment is Middle Ordovician in cores, and outcrops from 19 localities in eastern tension of the central St. Lawrence Platform age (Bernstein, 1992), slightly younger than its Ontario and western Québec (Table 1; Fig. 2). In (Fig. 1; Sanford, 1993a). Although only Cam- late Early Ordovician equivalent along more addition to field observations and examination of brian–Ordovician strata are preserved today, seaward positions of the paleoplatform (Knight polished slab samples, powder X-ray diffractom- Middle Devonian rock fragments in Cretaceous et al., 1991). Recent work in eastern Ontario and etry (XRD) and scanning electron microscopy diatremes in the Montreal region (Fig. 2; southern Québec suggests that erosion ranged (SEM) were used to examine mineralogy and tex- Sanford, 1993b) suggest that substantial erosion from minor to diastemic (Bernstein, 1991; Dix tural characteristics of cavity-fill sediment and may have occurred; estimates of missing post- and Molgat, 1997). paleokarst wall rock. Oriented XRD sections of Ordovician strata range from ~2 to 7 km (Héroux The regional structure of Paleozoic strata in the mud fraction of unlithified cavity-fill sediment and Tassé, 1990; Héroux and Bertrand, 1991; eastern Ontario defines a mosaic of fault blocks at location 7, and rock powder of other mudrocks, Sanford, 1993b). (Fig. 2), part of a relatively narrow (100 km) cra- were obtained by centrifuging mud-water solu- Two carbonate platform successions are pre- tonic fault system manifest today by the Ottawa- tions for 10 s at 10 000 revolutions per minute to served in the embayment. The Early to Middle Bonnechere Graben (Kay, 1942). A seismic re- deposit the >2 mm size fraction (see Laver, 1981). Ordovician Beauharnois and Carillon Forma- fraction profile across the Ottawa-Bonnechere Aliquots of the remaining solution were placed on tions (Bernstein, 1992) of the Beekmantown Graben northwest of Ottawa (Mereu et al., 1986) glass slides to air dry. An XRD scan rate of 1° 2- Group (Fig. 3) contain heterogeneous peritidal lends support to the interpretation that many Ot- θ/min was used over the range 4° to 60° 2-θ. Cav- facies assemblages of siliciclastic, carbonate, and tawa-Bonnechere Graben faults are surface ex- ity-fill sediment and mudrock from locations 7, evaporite lithologies. The formations contain pressions of reactivated, older structures associ- 10, and 19 were processed for potential fossil pa- platform-interior carbonate facies of the Sauk ated with a cratonic fault system of Precambrian lynomorphs. Bulk samples were immersed in passive-margin succession (Sloss, 1963), which age (see Kumarapeli, 1985). Initial work (e.g., HCl (50% by vol) and heated for 1 hr at 65 °C. extends along the eastern margin of the North Kay, 1942) emphasized a Mesozoic age for The residue was transferred to concentrated HF American craton (James et al., 1989; Read, 1989; graben development; an interpretation influ- for two days, then placed in 50% HCl at 95 °C for Sanford, 1993b). The overlying Middle to Upper enced, no doubt, by common east-west strikes for 6 hr. Residue from location 7 was cleaned ultra- Ordovician siliciclastic-to-carbonate succession some faults and local carbonatite dikes in eastern sonically for 10 s, then oxidized for 20 min in is part of the Tippecanoe Sequence (Sloss, 1963), Ontario. The dikes are of similar age, and along

concentrated HNO3. Samples from the other two and records the establishment of a foreland-basin strike of, prominent Early Cretaceous (Monte- localities were oxidized for 30 min in Schultze’s carbonate platform (Ottawa Group; Fig. 3). A regian) intrusive rocks in the Montreal region

reagent (concentrated HNO3 saturated with general deepening-upward succession of carbon- (Hogarth et al., 1988). More recent work indi- KClO3), then ultrasonically cleaned for 10 s. ate facies coincides with development of the cates that many graben faults in Ontario and

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Figure 2. Bedrock and structural geology of the Ottawa Embayment; locations of study sites of paleokarst (circles) and other localities (squares) mentioned in the text are listed in Table 1. The geological map is based on Ontario Geological Survey (1991) and Ministère de l’Énergie et des Ressources due Québec (1991).

southern Québec have pre-Cretaceous histories paleokarst extends up to 1–2 m beneath a discon- jor northwest-southeast–oriented faults (Fig. 2) (Rimando, 1994; Faure, 1996). In addition, nor- formity that forms locally along the Beauharnois- that offset Upper Ordovician strata within the city mal faulting and possible uplift along the axis of Carillon formation contact (Fig. 4, A and B). The of Ottawa. Differential Sauk erosion across any the Beauharnois Arch (Fig. 1), defining the east- disconformity truncates a 2 m shallowing-upward one of these fault traces is not confirmed. ern structural boundary of the Ottawa Embay- succession; from burrowed dolostone, through At location 2 (Fig. 2), vertical solution- ment (Sanford, 1993a), illustrate that a phase of stromatolitic mudstone, up into a thick (60 cm) enhanced fractures (<1 m deep), or grikes (Ford tectonism began as early as Late Ordovician time bed of gastropod rudstone. The gastropod rud- and Williams, 1989), compose part of an exposed (Globenksy, 1987; Bernstein, 1991). stone contains intergranular meniscus (vadose) karst pavement developed on Beauharnois dolo- dolomite cement. The disconformity is generally stone. The pavement forms part of a dissected DISTRIBUTION AND smooth but preserves local erosional remnants of Quaternary upland plain (Wilson, 1946), and lies CHARACTERISTICS OF PALEOKARST a spongiform dissolutional fabric developed in the along the northeastern margin of a northwest- Beauharnois dolostone. Across the trace of a re- southeast–oriented fault-bound upland of Pre- Paleokarst within Beekmantown Group dolo- gional northwest-southeast–oriented fault (Fig. 2) cambrian rock (Fig. 2). Whether the plain is an stones in the Ottawa Embayment are placed into tens of meters north of this outcrop, the Carillon exhumed Ordovician paleosurface is unknown. two groups: group I displays obvious connec- Formation disconformably overlies the biomot- 2. The second type of group I paleokarst is rep- tions to the present or paleoerosional surfaces; tled dolostone; the contact displays a sharply de- resented by a tabular-shaped (approximately 0.5 m group II dissolution patterns display no such link, fined irregular paleotopographic relief of as much thick and 10 m long) sediment-filled paleocavern and paleocavities are mineralized. as 5 cm. The abrupt lateral stratigraphic variation exposed along the inaccessible part of a cliff at lo- suggests that there was either about 2 m of differ- cation 16 (Fig. 2). The paleocavern is positioned Group I ential pre-Carillon erosion or that minor erosion about 10 m above the base of the Carillon Forma- enhanced an abrupt lateral facies change. tion (Bernstein, 1991), and is oriented parallel to Distribution and Morphology. Two general In a core at location 3 (Fig. 2), a 1-m-deep sub- bedding. The site is located adjacent to a north- geometries are recognized. vertical cavern (width unknown) occurs within the west-southeast–oriented fault (Fig. 2). 1. Vertical to subvertical, sediment-filled chan- Carillon Formation, and displays an obvious con- Previously workers (e.g., Wilson, 1946) sug- nels, solution-enhanced fractures and associated nection to a paleoerosional surface (Fig. 4C). Lo- gested that small (centimeter ]high) rounded, ero- vuggy porosity occur at location 11 (Fig. 2). The cation 3 is also located adjacent to one of three ma- sional wave-form ridges and mounds found lo-

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Figure 3. Paleozoic stratigraphy of eastern Ontario compiled from Wilson (1946), Williams (1991), Bernstein (1992), and Salad Hersi and Dix (1997). The approximate preserved thickness of strata for Geological Survey of Canada Russell Well (location 9) is from Williams (1991); Carillon thickness is from Bernstein (1991).

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cally along the post-Sauk erosional surface (Fig. 4D; locations 1, 3, and 6) are examples of paleokarst. Minor surficial paleokarst is present in the form of small (centimeter high) mushroom-like pinnacles that have angular, serrated margins. Evidence of differential lithification along the contact (Dix and Molgat, 1997) indicates that the paleotopography (Fig. 4D) may have a greater association with mechanical erosion. At location 13 (Fig. 2), the contact is reported to be burrowed (Bond and Greggs, 1976). Sediment Fill. Paleokarst at location 11 is filled by a light yellow– to orange-brown–weathering unfossiliferous dolomudstone (Fig. 4, A and B). Fractures crosscut both the sediment fill and adjacent Beauharnois strata, and predate Car- illon deposition (Fig. 4A). An angular (fracture- defined) block of the Beauharnois gastropod rudstone appears to have been uplifted a few inches relative to the surrounding erosional surface (Fig. 4A). Dolomudstone also fills paleokarst at location 3, and is traced upsection directly into similar lithology above the paleoerosional surface (Fig. 4C). At location 16, fallen rocks along the cliff base suggest that the initial stage of cavern fill is represented by erosional remnants of laminated dolomudstone that weathers to dark red to orange-brown. Fractures through both the mudstone and adjacent cavern walls predate deposition of a poorly sorted, orange-brown–weathering, polymict pebble to cobble conglomerate and breccia. Well-rounded clasts of Precambrian rock types, angular clasts of cavity-fill mudstone, and host Carillon dolostone are contained within a feldspathic arenite matrix. No erosional remnants

Figure 4. Group I paleokarst. (A) Solution- enhanced fractures (arrows) define a block of gastropod rudstone (b) of the Beauharnois For- mation that has been raised slightly relative to surrounding paleo-erosion surface. Paleokarst is filled with dolomudstone that is fractured and disconformably overlain by basal Carillon dolostone (c). Outcrop, location 11. Pen is 17 cm in length. (B) Vertical section through gastropod rudstone (b) at same locality as in (A), showing dolomudstone (s) within subhorizontal paleokarst cavities. Visible length of pen is 16 cm. (C) Downward-tapering epikarst (out- lined by black dashed line) in drill core through the Carillon Formation (c). The sediment fill (s) is a dolomudstone, similar in lithology to the Carillon strata overlying the cavern roof (arrow). Top of the core is to the upper right. Lo- cation 3; scale bar = 10 cm. (D) Post-Sauk erosional bedforms developed within dolostone of the Carillon Formation, and buried by Tippecanoe (Rockcliffe Formation) siliciclastic rocks. Location 1; scale bar = 5 cm.

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of cavities at location 19. Here, cavities are as much as 1 to 2 m in height, and crosscut relatively thick (to 1 m) bedding. In thin-bedded dolostone (e.g., location 4), vuggy porosity and elongate cavities of as much as a few centimeters in height extend discontinu- ously along several bedding planes. At locations 7 and 10, paleocavities as high as 30 cm are laterally linked by partially collapsed lenticular cavities less than 10 cm high (Fig. 5B). Angular fragments of host dolostone lie on the floors of the cavities. Locally, cavity ceilings preserve dila- tional bedding-plane fractures now filled with calcite and associated mineralization. Some strata above partially collapsed cavities are silicified, and show structural sagging. South of location 11 and at location 12 (Fig. 2), paleocavities occur within brecciated upper parts of thrombolitic and stromatolitic mounds (Fig. 6). Breccia and solution and fracture porosity networks crosscut the mound-intermound contact. However, the majority of group II paleokarst shows no spatial association with an obvious skeletal or nonskeletal host framework. In- stead, preserved stromatolites and paleocavities occupy separate stratigraphic levels at several localities (e.g., locations 7 and 10). Sediment Fill. Three generations (types 1 to 3) of geopetal sediment are recognized. Type 1 is a chemical “sediment,” represented by laminated chert or microquartz (Fig. 7A). Preliminary pet- rography of type 1 sediment shows there to be no obvious replacement of a precursor sediment. This sediment is found at most localities in the western portion of the embayment, with exception of location 4 and in brecciated cavities asso- Figure 5. Group II paleokarst, location 7. (A) Dome-shaped cavity with horizontal floor; min- ciated with organic frameworks (Fig. 6). Type 1 eralization has been mostly excavated. Hammer is 30 cm in length. (B) Laterally linked polygo- sediment has not been found in cavities in central nal cavities (arrow), separated by partially collapsed lenticular cavities, are filled with predom- or more eastern parts of the study area. The chert inantly calcite (white). Hammer is 30 cm in length. weathers black to dark brown, but a speckled light brown color is locally present due to dis- persed crystals of silicified authigenic dolomite. of a pre-Quaternary sediment have been found in majority of cavities are exposed in the western At location 7, silicification of host dolomite oc- grikes at location 2; modern leaves and humic part of the embayment where the Beauharnois curs preferentially beneath some cavities that con- material compose the sediment fill. Formation lies directly beneath Quaternary cover tain type 1 sediment (Fig. 7B). There is little uni- (Fig. 2). However, cavities also occur in the cen- formity in distribution and abundance of Group II tral and eastern parts of the embayment (loca- silicification at location 7 or type 1 sediment at this tions 9, 14, and 15), where post-Beekmantown and other localities. West of location 7, silicified Distribution and Morphology. This paleo- strata are preserved (Fig. 2). dolomite forms alteration haloes around fractures karst consists exclusively of paleocaverns. Cavi- Many group II paleocavities display horizon- that crosscut thrombolitic mounds. Fractures are ties are mineralized, are typically oriented paral- tal, planar floors and domed ceilings, but irregu- incompletely filled with euhedral crystals of lel to bedding, and display no obvious conduits lar cross-sectional geometries are also common quartz, part of an early stage of mineralization (see connected to the present or an ancient erosional (Figs. 5–7). Cavity margins crosscut crystalline following). Silicification of Beauharnois dolo- surface. The geographic and intraformational dis- fabric of the host rock, and narrow (few cen- mudstone is recognized above collapsed cavities tribution of these paleocavities is not well known timeters), local dedolomization haloes occur at location 7, and has replaced Carillon dolomud- due to limited outcrop and quarry exposures. around cavity margins. Cavities are as much as stone at location 15, where there is no obvious spa- However, cavities appear to be restricted to the several tens of centimeters in diameter, and cav- tial association with paleocavity distribution. Beauharnois Formation, possibly preferentially ity heights match or slightly exceed bedding Type 2 sediment (Fig. 7B) is a finely laminated, positioned toward the formation’s base (location thickness. One exception to the above parallel- dolosiltstone that weathers to a light beige. Scan- 4) and top (e.g., locations 7, 10, 11, and 12). The to-bedding relationship is the vertical orientation ning electron microscope (SEM) analysis indi-

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cates the presence of rounded, abraded dolomite and quartz crystals, detrital clay (illite, muscovite, kaolinite), and some euhedral dolomite. Type 2 sediment is abundant only in a few cavities at location 10, and occurs sporadically throughout the western part of the embayment, forming thin lam- inae along paleocavity floors. It postdates type 1 sediment. Type 3 sediment is an unlithified, laminated to thinly bedded, organic-bearing clay to sandy clay. It is lithified only where silicified along its upper contact with overlying mineralization (Fig. 7C). Type 3 sediment has been found only at location 7, in about 10 cavities along one stratigraphic level. Constituent clay minerals include illite, kaolinite, and prominent chlorite, and SEM analysis suggests that the clay is detrital. Sand- to gravel-size detritus makes up <5% of the bulk sediment, and includes fragments to rare whole crystals of mi- Figure 6. Secondary porosity filled by calcite and sulfate mineralization is restricted to stro- croquartz and calcite, rounded particles of cream- matolites (above arrow) south of location 11. Visible length of hammer is 20 cm. colored, microcrystalline kaolinite, and angular to rounded fragments of the dolomite host rock. Where found beneath subsequent cavity-fill mineralization, type 3 sediment is dry and grayish cation 19. Similar films separate two stages of cal- along the base of the paleocavity, overlain by sub- brown. In three cavities, however, type 3 sediment cite precipitation at locations 7, 10, and 19 (Dix sequent mineralization. is water saturated, greenish, and contains platelets and Robinson, unpub. data). Moving southeast from locations 9 and 13, of framboidal pyrite oriented parallel to bedding. Mineralization. Details of the geochem- and in equivalent strata intersected in core along In two of these cavities, type 3 sediment has oc- istry and history of cavity-fill mineralization the St. Lawrence River (Guillet, 1964; Giles, cluded remaining available cavity space, and over- (Fig. 8) have been compiled elsewhere (Dix 1976), Beekmantown dolostone contains nodules lies an early stage of sulfide mineralization (see and Robinson, unpub. data). Here we note that of gypsum and rarely calcite. The nodules are following). Water saturation appears to occur due the mineralization succession can be divided similar in size to those already described herein. to ground-water flow along present-day fractures into three groups (Fig. 8). The first stage con- Farther east, in southern Québec, evaporite nod- that intersect paleocavities. The fractures and wa- tains minor sulfide. The second stage is char- ules, some later silicified and showing chicken- ter flow can be traced up to the present erosional acterized by euhedral quartz, similar to wire fabric, also occur in equivalent Lower Or- surface. At location 19, water-saturated detrital Herkimer “diamonds” (Ulrich, 1989), and by dovician strata (Tassé and Schrijver, 1989; mud postdates mineralization. The mud has a calcite, saddle dolomite, and hydrocarbon, Lavoie, 1992; Paradis and Lavoie, 1996). In the chloritic composition similar to type 3 sediment, both as intercrystalline films between stages of western and northwestern parts of the embay- but shows no obvious lamination. Angular frag- calcite and as liquid and gas inclusions in ment, evidence for likely differential collapse of ments of minerals similar to in situ mineralization quartz. The third stage has a mineral assem- carbonate strata through removal of evaporites beneath the mud occur disseminated throughout blage similar to that found in calcite veins that was reported by Dix (1997), and includes in- the mud. crosscut cavity margins in Beauharnois rocks, traformational low-angle bedding discordance Fossil Organic Material. A Middle to Late Carillon dolostones, and younger Ottawa Group within Beauharnois strata (e.g., at location 8); lat- Ordovician palynomorph assemblage (Table 2) carbonates. In several exposures, contiguity eral pinchout of bedding into amalgamated gyp- was recovered at location 7 from a paleocavity of stage 3 cavity and vein mineralization is siferous shale; and contorted, in places wave- containing water-saturated type 3 sediment and demonstrable. form, bedding within Carillon strata overlying no postsediment mineralization. Gloeocapsomor- In the western part of the embayment, small pinch-and-swell stratigraphy of gypsiferous pha prisca Zelessky is a species related to either (<3 cm) nodules of white and pink calcite are com- shale-carbonate interbeds (location 11). Residual cyanobacteria or green algae, and is commonly mon to locally abundant within the Beauharnois shale in the Carillon and Beauharnois Formations found in, but not restricted to, Upper Ordovician Formation, less common in the Carillon Forma- contains local calcitized chickenwire fabric (lo- strata. Striatotheca tenuata (Burmann) Fensome tion, and locally abundant within dolostone beds cation 11). In the central and southeastern part of et al. is considered equivalent to Arkonia tenuata of the Pamelia Formation of the lower Ottawa the embayment, in contrast, Beauharnois and of Burmann (1970), an Ordovician species that, in Group (Fig. 3). Calcite nodules also occur locally Carillon strata preserve thin (<5–10 cm) in- western Europe, has not been found in strata in the lower part of some stromatolites at location terbeds of gypsum and subhorizontal gypsum- older than Llanvirn age (Middle Ordovician) 8. Sedimentary lamination is often deformed filled fractures a few centimeters thick (Guillet, (Molyneux, 1990). In type 2 sediment, and in pa- around a given nodule, and angular fragments of 1964; Giles, 1976). leocavities where mineralization overlies type 3 surrounding host rock can be found encased by the sediment, fossil organic material includes only calcite. Some nodules in the Beauharnois Forma- STRUCTURAL RELATIONSHIPS rounded fragments of indeterminate origin. Frag- tion contain calcite, saddle dolomite, and barite ments of reddish-brown solid petroleum films similar to cavity-fill mineralization. One cavity For locations 3, 11, and 16, there appears to be a were found within the water-saturated mud at lo- contains a thin lamina of chert (type 1 sediment) spatial association between locations of northwest-

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southeast–oriented faults, or their traces, and group I paleokarst, differential paleoerosion, and fracture development. Similar relationships occur at other sites. (1) At location 15, a post- Beauharnois disconformity without obvious paleokarst caps a 5-cm-thick skeletal carbonate with meniscus (vadose) intergranular cement. At location 14, a few kilometers to the south and across a post-Ottawa Group, northwest-southeast–oriented fault (Fig. 2), there is no evidence for either erosion or the thin skeletal carbonate. (2) At location 1, the spatial density of pre-Tippecanoe fractures that crosscut the post-Sauk paleosurface appears to increase toward the margins of a minihorst defined by a northwest-southeast–oriented fault and local drag fold that disrupt lithified Rockcliffe and Car- illon strata (Dix and Molgat, 1997). Fracture strikes are oriented parallel to the axes of these later developed structures. Margins of many group II paleocavities truncate wispy, discontinuous, bedding-parallel stylolites, or solution seams (Wanless, 1979). The paleohorizontal of each stage of geopetal sediment is roughly parallel to host-rock bedding. This relationship is maintained in dipping strata (<20°; location 11); i.e., sediment deposition occurred prior to structural displacement. At location 7, local flame structures (Fig. 9A) and lumps of type 3 sediment are incorporated into overlying mineralization. Other cavities at this location display a gentle concave-up surface geometry beneath mineralization. Calcite veins and veinlets are locally common throughout Lower to Upper Ordovician strata in the embayment (Williams, 1991). Locally, dedolomitization haloes extend as much as 10 cm from margins of veins. The strike of veins is often parallel to local faults (Williams, 1991; For- grave, 1995). Veins dip steeply (>70°), and range in width from a typical few centimeters to 10 cm.

Figure 7. Geopetal sediment in group II paleokarst. (A) Type 1 sediment consists of laminated chert deposited on the floor of a paleocavity. Location 7; scale bar = 1 cm. (B) Type 2 sediment (arrow) forms a thin cover over type 1 sediment, which overlies silicified host dolomite (s). Note the irregular but dome- shaped ceiling of unaltered dolomite (d). Re- maining porosity is filled with calcite (c). Lo- cation 7; scale bar is 5 cm. (C) A cavity at location 7 that has a double domed ceiling. The cavity floor (open arrow) is underlain by silicified host dolostone and overlain by type 1 sediment, type 3 sediment (s), a silicified crust of type 3 sediment (arrow), and void-fill calcite and sulfate mineralization (c). Dolomite immediately overlying the sulfate is dedolomi- tized. Location 7; penny (2 cm) for scale.

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TABLE 2. FOSSIL ORGANIC MATERIAL IN PALEOKARST SEDIMENT Age Preservation and color Organic type after oxidation Location 7. Grant Quarry Holocene Very good; yellow Bisaccate pollen: Pinus sp., Picea sp. Very good; yellow Angiosperm pollen: Alnus sp., Betula sp. Very good; yellow Trilete and monolete spores: Sphagnum sp.; ferns Ordovician–Devonian Moderate; yellow-brown Cyanobacteria or green algae: Gloeocapsomorpha prisca Zalessky Moderate; light brown Acritarch: Veryhachium spp. Ordovician (post-Arenig) Good; medium brown Acritarch: Striatotheca tenuata (Burmann) Fensome et al. Indeterminate Black, gray-brown Angular fragments and amorphous clumps Location 10. Maple Grove Quarry Holocene Very good; yellow Angiosperm and gymnosperm pollen (see above) Indeterminate Black, dark brown Unidentifiable angular fragments and amorphous organic clumps Location 18. St. Chlotilde Quarry Indeterminate Moderate to poor; brown Sheet-like organic fragments with linear to reticulate and imperfectly reticulate, cell-, suture- and rosette- like fabrics

In Beekmantown strata, veins cut across wispy and James, 1988; Ford and Williams, 1989; paleokarst and pre-Carillon faulting underscores solution seams, group II cavity margins, silicified Palmer, 1995). These features are distinct from a possible temporal link with onset of more dra- dolostone, and type 1 sediment (Fig. 9B) in both paleokarst horizons (Desrochers and James, 1988) matic block faulting, differential platform tilting, horizontal and dipping strata. Many veins pre- or diastemic surfaces that cap common to locally and formation of more extensive epikarst along serve stages of vein reactivation as suggested by abundant shallowing-upward rhythmites in Beek- the outer portions of the Laurentian paleoplat- corroded calcite along discordant contacts sepa- mantown and equivalent carbonates in the St. form in the Canadian Appalachians, interpreted rating stages of calcite fill (Forgrave, 1995). Lawrence platform (Desrochers and James, 1988; to be related to initiation and development of the Veins are discontinuous over tens of centimeters Bernstein, 1991; Lavoie, 1992; Friedman, 1994; Taconic peripheral bulge (James et al., 1989; to tens of meters along strike. Calcite veinlets oc- Dix, 1997). Desrochers and James, 1989; Knight et al., cur between shale interbeds or thickened solution The local distribution of sub-Carillon epikarst 1991). Transmission of in-plane stress toward the seams in thin-bedded dolostone. Bedding-paral- compared to apparent conformable Beauharnois- platform interior, resulting from developing lel stylolites crosscut cavity-fill mineralization Carillon contacts elsewhere in the embayment Taconic convergence (cf. Cloethingh, 1988) may (Fig. 10A) and vein calcite (Fig. 10, B and C). In (Bernstein, 1991, 1992; this study) requires have reactivated preexisting shallowly buried horizontal and dipping Beekmantown strata, ver- prominent but local lowering of base level, e.g., Precambrian structures along the interpreted cra- tical stylolites “neck-down” and truncate veins to 2 m, in order to produce vadose paleokarst at tonic fault system beneath the Ottawa Embay- (Fig. 10, D and E). location 11. Minor normal faulting is interpreted ment (Kumarapeli, 1985; Mereu et al., 1986; to have initiated local change in surface hydrol- Faure, 1996). Such tectonism, although far-flung DISCUSSION ogy on the basis of the spatial association among from the developing Taconic orogen, would have epikarst, pre-Carillon fracturing, and differential initiated subtle platform instability during the The morphology and stratigraphic relation- erosion adjacent to or across traces of northwest- waning stages of platform-interior deposition on ships of paleokarst within platform-interior facies southeast–oriented faults. These latter structures the Sauk platform. Tectonic instability may ac- of the Beekmantown Group in the Ottawa Em- may represent sites of reactivated older (e.g., count for the local intraformational (Carillon) pa- bayment provide a basis for identifying local and Middle Ordovician) structural lineaments (see leokarst at location 3 (Fig. 4C), and the heteroge- regional tectonic controls on changing patterns of following). Although the age of the paleocavern neous vertical and lateral facies assemblages in local and regional paleohydrology. at location 16 is currently unknown, deposition the Carillon Formation (Bernstein, 1991, 1992; of a poorly sorted cavity-fill sediment following Dix, 1997). Our interpretation supports previous Epikarst and Middle Ordovician Tectonism a period of fracturing also suggests an association work that found tectonism, and block faulting between paleokarst development and tectonically specifically, to have influenced latest Sauk and Characteristics of group I paleokarst are diag- controlled base-level change. Sources of Pre- earliest Tippecanoe facies patterns elsewhere nostic of epikarst (Palmer, 1995). Vertical epikarst cambrian rock lie adjacent to or on prominent along the western margin of the Taconic orogen (locations 3 and 11) and pavement grikes (loca- structural features proximal to location 16: to the in the United States (e.g., Cable and Beardsley, tion 2) identify surface to vadose-zone dissolu- east, the Beauharnois Arch (Fig. 2); and to the 1984; Lesser and Coogan, 1993; Holland and tion, whereas the parallel-to-bedding orientation north, the Precambrian-Paleozoic contact. Patzkowsky, 1997). of the paleocavern at location 16 may indicate dis- The approximate age of the Beauharnois-Car- The slightly younger age of the Sauk-Tippeca- solution along a paleo-ground-water table due to illon boundary in the embayment is late Arenig noe boundary within the platform interior relative mixing of vadose and phreatic waters (Choquette (Bernstein, 1992). Our suggested link between to outer regions of the paleoplatform in the Cana-

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data). These paleotemperatures are similar to those documented from similar quartz crystals or Herkimer “diamonds” in equivalent cavities in Beekmantown strata in upstate New York (Ulrich, 1989). Organic acids can become more chemi- cally erosive at temperatures of >80 °C (Kharaka et al., 1983, 1986). Migration of hydrothermal fluids and resulting thermal maturation of local elevated abundances of organic matter associated with the organic frameworks may explain the location and style of this type of paleocavity. Most group II cavities display no obvious spatial association with organic frameworks. Without connection to any obvious paleoerosional surface, pore waters moving through the relatively thick carbonate succession in the Ottawa Embayment would quickly equilibrate to carbonate saturation. We suggest, therefore, that the regional distribution of intrastratal karst is linked instead to regional mixing of pore waters coincident with dissolution of evaporites (Palmer, 1995). Similar conclusions have been reached for solution-collapse features in equivalent Beekmantown strata in adjoining regions, in southern Québec (Lavoie, 1992; Paradis and Lavoie, 1992) and northern Figure 8. A general paragenetic succession of group II paleokarst, sediment fill, and New York State (Friedman, 1994, 1996). mineralization. Whereas undersaturation of waters relative to dolomite may be influenced by dedolomitization related to dissolution of evaporites (Raines and

dian Appalachians has been interpreted to reflect Within the burial realm, increased solubility of Dewers, 1997), contrast in H2S concentrations of diachronous erosion associated with migration of carbonate may occur due to (1) elevated CO2 de- two mixed waters can also enhance solutional ca- the Taconic forebulge away from the Taconic oro- rived from bacterially controlled oxidation or pacity (Hill, 1987; Palmer, 1995). Increased gen (e.g., Quinlan and Beaumont, 1984; Knight thermal maturation of organic matter (Machel, preservation of evaporites in the Ottawa Embay- et al., 1991). We suggest that dampening of fore- 1989); and (2) mixing of fluids of contrasting ment toward more “seaward” positions of the pa-

bulge uplift toward the craton interior (Quinlan dolomite saturation with respect to pCO2 leoplatform suggests the presence of a diagenetic and Beaumont, 1984) provides a structural frame- (Thrailkill, 1968), and both dissolved H2S con- gradient extending northwest to southeast across work in which to predict dramatic epikarst along centrations and dedolomization related to dissolu- the basin, possibly created by a southeastward outer platform sites, as found locally in the Appa- tion of sedimentary evaporites (Palmer, 1995; paleoflow of continentally derived waters under- lachian orogen (e.g., Mussman et al., 1988; Raines and Dewers, 1997). Mixing of fluids saturated with sulfate but not carbonate. Fluid Palmer and Palmer, 1989; Knight et al., 1991), within the subsurface of a carbonate platform may flow may have been preferential along potential and little if any epikarst within the platform inte- arise from (1) a drop in sea level, which estab- sandstone aquifers that bracket the Carillon and rior (see Bernstein, 1991; Lavoie, 1992; Dykstra lishes a seaward-migrating regional front of con- Beauharnois Formations (e.g., Nepean, Theresa, and Longman, 1995; Paradis and Lavoie, 1996; tinentally derived meteoric water; (2) topography- and Rockcliffe Formations; Fig. 3), and possibly Dix and Molgat, 1997). This model, however, driven flow along rising mountains (Garven and along thin sandstone interbeds within the Beek- must be amended to accommodate local base- Freeze, 1984) and/or orogenic tectonism (Oliver, mantown Group (Dix, 1997). Cross-stratal flow level change due to differential block faulting 1986) may create a landward-migrating front of along existing faults or fractures or during their (Mussman and Read, 1986; Knight et al., 1991; basin-derived brines; and (3) tectonism, which reactivation may have enhanced local fluid mix- this study). can establish cross-stratal flow along fractures ing. Present outcrop and core exposures preclude and faults, and local mixing of pore waters con- a definite spatial link between faults and in- Origin of Intrastratal Paleokarst trasting in saturation with respect to dolomite. trastratal karst, but fracturing obviously helped Group II cavities spatially associated with brec- cross-stratal flow of mineralizing fluids after Characteristics of group II paleokarst suggest ciated stromatolitic and thrombolitic mounds deposition of type 1 sediment (Fig. 9B), and frac- that dissolution occurred within the burial (Fig. 6) may identify dissolution related to local turing locally predates silicification through phreatic realm, forming intrastratal karst (Ford organic diagenesis. The absence of geopetal sedi- thrombolite mounds west of location 7. and Williams, 1989; Palmer and Palmer, 1989; ment in these cavities may indicate overlapping of Dedolomitization along margins of veins and Palmer, 1995). Dissolution postdates initial a common period of brecciation, dissolution, and some intrastratal paleokarst, and later sulfate stages of chemical compaction, and the forma- mineralization. Homogenization temperatures of mineralization in these cavities, illustrates migration of wispy solution seams likely represents a fluid inclusions in early quartz crystals in paleo- tion of sulfate-rich water. minimum burial depth of a few hundred meters cavities indicate mineralization temperatures Vertical intrastratal karst at location 19 may (Choquette and James, 1987). ranged up to 150+ °C (Dix and Robinson, unpub. represent a type of karst entrenchment (Ford and

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Williams, 1989), dissolution occurring concur- rently during base-level change created by either uplift of the Beauharnois Arch or along the adjacent north-south–oriented normal fault (Fig. 2; Globensky, 1987). Chemical evolution of continentally derived waters may also explain precipitation of silica as the initial stage of cavity-fill sediment. Conti- nental weathering of Precambrian strata adds silica to ground water following chemical weathering (hydrolysis) of feldspars (Nahon, 1991). Silica, as chert, is stable under acidic conditions that otherwise promote carbonate dissolution (Friedman et al., 1992, p. 106), and may precip- itate upon reaching supersaturation during mixing (Knauth, 1979). Contiguity of vein mineralization and the third stage of cavity-fill mineralization (Figs. 8 and 9B) suggests that later stages of mineralizing brines were flushed along fractures, then into paleokarst. Under these conditions, fluid flow was likely ag- gressive hydrodynamically, as suggested by cavity brecciation, rip-up clasts of type 3 sediment, and locally collapsed cavity ceilings. Type 3 sediment is also interpreted to represent fault-controlled transport of a mud slurry. Using chlorite as an indicator mineral, a cursory examination of clay composition of lower Paleozoic mudrocks in the Ottawa region (see stratigraphic locations in Fig. 3) identifies only two prominent stratigraphic units in which the mud fraction is chloritic: the Rockcliffe Formation, which overlies the post- Sauk erosional surface, and at least some of the synorogenic mudrock (e.g., Billings Formation) that buried the Ottawa Group carbonate platform. To the northeast of location 7, there is about 300 m of stratigraphic offset across the trace of the Gloucester Fault, and synorogenic mudrock is locally juxtaposed against Beekmantown strata (Fig. 2). On the basis of palynomorph assemblages (Table 2), type 3 sediment is derived from either the Rockcliffe Formation or younger synorogenic mudrock; sediment moved along the Figure 9. Structural relationships relative to geopetal sediment. (A) Flame structure (arrow) fault, then into intrastratal paleokarst during fault- of type 3 sediment (s) in cavity-fill calcite. Type 1 sediment (c) remains horizontal. Location 7; ing. Type 3 sediment was most likely deposited hammer head is 15 cm long. (B) Type 1 sediment (open arrow) and host dolomite are cut by cal- under anoxic, variably saturated conditions as cite-filled veinlets (solid arrow) that are contiguous with cavity-fill calcite and other mineraliza- suggested by (1) its darker color compared to ox- tion. Location 11; scale bar = 1 cm. idized sediment fill in epikarst (see previous discussion); (2) its stratigraphic position between two periods of mineralization that include sulfide meters of burial (see previous discussion), an in- foredeep with concurrent uplift of the hinterland precipitation (Fig. 8); (3) deposition in paleocavi- teresting coincidence exists between this depth (Quinlan and Beaumont, 1984). This structural re- ties without any obvious direct connection with a and that (~300 m) of the Beauharnois-Carillon organization may have allowed sufficient regional paleosurface; and (4) flame structures of type 3 contact at the time the Tippecanoe carbonate plat- seaward migration of continental-derived waters sediment in mineralization (Fig. 9A). form foundered, during developing Taconic con- with initiation of evaporite dissolution and sub- vergence (Fig. 3). Regional tectonism, affecting surface fluid mixing. With platform foundering, Timing of Intrastratal Paleokarst the entire paleoplatform, is considered to have ini- there was also likely high-angle block faulting and Mineralization tiated the series of events associated with forma- and local cross-stratal flow, especially linked to tion and occlusion of intrastratal paleokarst. With potential reactivation of buried Precambrian If formation of wispy stylolites in the Beau- platform foundering, there was likely an increase structures in the embayment. Such block faulting harnois Formation requires only several hundred in dip of the buried platform strata toward the is documented in southern Québec and New York

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Figure 10. Postmineralization stylolitization in Beekmantown strata. (A) Stylolite (at pen nib) cuts across cavity-fill mineralization at location 11. (B) Vertical section parallel to a subvertical calcite vein in tilted Beauharnois strata at location 11 shows a stylolite (at pen nib) that cuts across calcite vein. (C) Stylolite truncates calcite vein (arrow) in core from location 3. Scale bar = 1 cm. (D) Subvertical stylolite creates local “necking” of subvertical calcite vein at location 11. (E) Two parts of a once-subvertical calcite vein that have been partially “necked” down by stylolitization. Location 11; scale bar = 15 cm.

State during periods leading up to and during plat- tawa Embayment, the second and third stages of dle Paleozoic strata is a conservative estimate for form foundering (Globensky, 1987; Bradley and mineralization (Fig. 8) likely represent two dis- eroded strata in this region. In New York State and Kidd, 1991; Lavoie, 1994). tinct regional flow regimes. Further work will southern Québec, as much as 7 km of eroded strata Thus, the geologic elements required for in- compare metallogenic patterns and geochemistry has been interpreted on the basis of thermal matu- trastratal paleokarst formation, mineralization, in the embayment with those in the Appalachian ration indices (Friedman, 1987; Héroux and Tassé, and petroleum migration within the Ottawa Em- orogen (e.g., Schrijver et al., 1988; Kesler et al., 1990; Héroux and Bertrand, 1991). Friedman bayment appear to have been in place leading up 1995; Paradis and Lavoie, 1996). (1987) suggested that a maximum burial depth to and during the culmination of the Taconic A minimum age for paleokarst mineralization was achieved in the northern U.S. Appalachians orogeny (see also Dykstra and Longman, 1995; in the Ottawa Embayment is defined by postmin- during late Paleozoic time. In the Ottawa Embay- Paradis and Lavoie, 1996). Metal- and petro- eralization stylolitization (Fig. 10). This stage of ment, postvein stylolitization requires that the leum-bearing basin brines may have been tecton- chemical compaction cannot be accommodated by main flux of mineralizing fluids predates this his- ically flushed toward the platform interior during the relatively minor thickness of post-Beekman- tory, and may prove to be better represented as a Taconian orogenesis (cf. Oliver, 1986) and into town strata preserved in the Ottawa Embayment continuum with Taconic and Acadian mineraliza- newly formed intrastratal porosity and structural (Fig. 3). According to Sanford (1993b), erosion of tion events in southern Québec (Schrijver et al., traps (Dykstra and Longman, 1995). In the Ot- at least 1 to 2 km of latest Ordovician through mid- 1988; Paradis and Lavoie, 1996).

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turelles, Secteur des mines, MB 94-13, 17 p. 1992, Principles of sedimentary deposits: New York, CONCLUSIONS Bernstein, L. M., 1991, Lower Ordovician Beekmantown Macmillan, 717 p. Group, Québec and Ontario [Ph.D. dissert.]: Montréal, Garven, G., and Freeze, R. A., 1984, Theoretical analysis of the In the Ottawa Embayment, two types of paleo- Québec, Canada, Université de Montréal, 330 p. role of groundwater flow in the genesis of stratabound ore Bernstein, L. M., 1992, A revised lithostratigraphy of the Lower- deposits I. Mathematical and numerical model: American karst occur in platform-interior carbonates of Middle Ordovician Beekmantown Group, St. Lawrence Journal of Science, v. 284, p. 1085–1124. the Lower Ordovician Beekmantown Group. Lowlands, Québec and Ontario: Canadian Journal of Earth Gauthier, M., Chartrand, F., and Trottier, J., 1994, Metallogenic Epikarst represents shallow (<2 m) subsurface Sciences, v. 29, p. 2677- 2694. epochs and metallogenic provinces of the Estire-Beauce Bond, I. J., and Greggs, R. G., 1976, Revision of the Oxford regions, southern Québec Appalachians: Economic Geol- meteoric dissolution beneath paleoerosional sur- Formation (Arenig) of southeastern Ontario and northern ogy, v. 89, p. 1322–1360. faces created during waning stages of the Lau- New York State: Canadian Journal of Earth Sciences, Giles, P. S., 1976, Stratigraphy, petrology and diagenesis of v. 13, p. 19–26. Beekmantown carbonate rocks in eastern Ontario [Ph.D. rentian (Sauk) platform. The distribution of the Bradley, D. C., and Kidd, W. S. F., 1991, Flexural extension of dissert.]: London, University of Western Ontario, 328 p. epikarst is interpreted to reflect local structural the upper continental crust in collisional foredeeps: Geo- Globensky, Y., 1987, Géologie des Basses-Terres du Saint-Lau- control of base level via reactivation of underly- logical Society of America Bulletin, v. 103, p. 1416–1438. rent: Ministrère de l’Energie et des Ressources du Burmann, G., 1970, Weitere organische Mikrofossilien aus Québec, MM 85-02, 63 p. ing structure during the initiation and dampened dem unteren Ordovizium: Paläontologische Abhandlun- Guillet, G. R., 1964, Gypsum in Ontario: Ontario Department interior migration of the Taconic peripheral fore- gen, Abteilung B, Paläobotanik, v. 3, p. 289–332. of Mines Industrial Mineral Report 18, 71 p. bulge. Intrastratal karst is of deep-burial phreatic Cable, M., and Beardsley, R. W., 1984, Structural controls on Héroux, Y., and Bertrand, R., 1991, Maturation thermique de la Late Cambrian and Early Ordovician carbonate sedimen- matière organique dans un bassin du Paléozoïque in- origin and followed incipient chemical com- tation in eastern Kentucky: American Journal of Science, férieur, basses-terres du Saint-Laurent, Québec, Canada: paction. Dissolution probably resulted from mix- v. 284, p. 797–823. Canadian Journal of Earth Sciences, v. 28, p. 1019–1030. Choquette, P. W., and James, N. P., 1987, Limestones—3. The Héroux, Y., and Tassé, N., 1990, Organic-matter alteration in an ing of subsurface waters that contrasted in pCO2 deep burial environment: Geoscience Canada, v. 14, early Paleozoic basin: Zonation around mineral showings and H2S, the H2S being controlled by burial dis- p. 3–35. compared to that around intrusions, St. Lawrence Low- solution of sedimentary evaporites. Fluid mixing Choquette, P. W., and James, N. P., 1988, Introduction, in lands, Québec, Canada: Geological Society of America James, N. P., and Choquette, P. W., eds., Paleokarst: New Bulletin, v. 102, p. 877–888. was promoted by regional migration of continen- York, Springer-Verlag, p. 1–21. Hill, C., 1987, Geology of Carlsbad Cavern and other caves in tal-derived waters, likely augmented locally by Cloethingh, S., 1988, Intraplate stresses: A new element in the Guadalupe Mountains, New Mexico and Texas: New cross-stratal flow along faults or fractures. Two basin analysis, in Kleinspehn, K. L., and Paola, C., eds., Mexico Bureau of Mines and Mineral Resources Bulletin New perspectives in basin analysis: New York, Springer- 117, 150 p. stages of cavity-fill geopetal sediment (chert and Verlag, p. 205–230. Hoagland, A. D., 1976, Appalachian zinc-lead deposits, in kaolinite-bearing claystone) are considered to be Derry, Michner, Booth, and Wahl, and the Ontario Geological Wolfe, K. H., ed., Handbook of stratabound and strati- Survey, 1989, Limestone industries of Ontario, Vol. II— form ore deposits, Volume 6: Amsterdam, Elsevier, byproducts of weathering and regional subsurface Limestone industries and resources of eastern and north- p. 495–534. movement of diagenetic waters. A third stage, ern Ontario: Ontario Ministry of Natural Resources, Land Hogarth, D. D., Rushforth, P., and McCorkell, 1988, The sandy chloritic mud, occurs adjacent to a regional Management Branch, 196 p. Blackburn carbonatite, near Ottawa, Ontario: Dykes with Desrochers, A., and James, N. P., 1988, Early Paleozoic surface fluidized emplacement: Canadian Mineralogist, v. 26, fault, and contains a Middle or Upper Ordovician and subsurface paleokarst: Middle Ordovician carbon- p. 377–390. palynomorph assemblage. Local deposition is in- ates, Mingan Islands, Québec, in James, N. P., and Cho- Holland, S. M., and Patzkowsky, M. E., 1997, Distal orogenic terpreted to record movement of a mud slurry into quette, P. W., eds., Paleokarst: New York, Springer-Ver- effects on peripheral bulge sedimentation: Middle and lag, p. 183–210. Upper Ordovician of the Nashville Dome: Journal of Sed- paleokarst during downfaulting of Tippecanoe Dix, G. R., 1997, Tectonism and brackish to hypersaline, mixed imentary Research, v. 67, section B, p. 250–263. siliciclastic rocks. Paleokarst mineralization post- siliciclastic-carbonate facies patterns within the Middle James, N. P., Stevens, R. K., Barnes, C. R., and Knight, I., 1989, Ordovician Carillon Formation, Ottawa Embayment: Evolution of a lower Paleozoic continental-margin car- dates cavity-fill sedimentation and is, in part, con- Waning stages and demise of the Beekmantown platform bonate platform, northern Canadian Appalachians, in tiguous with later vein mineralization that cross- [abs.]: Geological Association of Canada–Mineralogical Crevello, P. D., Wilson, J. L., Sarg, J. F., and Read, J. F., cuts Sauk and Tippecanoe strata. A renewed Association of Canada Annual Meeting, Ottawa 1997, eds., Controls on carbonate platform and basin develop- p. A39. ment: Society of Economic Paleontologists and Mineral- phase of stylolitization identifies a subsequent Dix, G. R., and Molgat, M., 1997, Compaction and fracturing ogists Special Publication 44, p. 123–146. history of burial. Dolomite dissolution and move- across the Sauk-Tippecanoe (Middle Ordovician) se- Kay, M., 1942, Ottawa-Bonnechere graben and Lake Ontario ment of mineralizing brines are interpreted to be quence boundary, eastern Ontario: The effect of tectonism homocline: Geological Society of America Bulletin, on stratigraphic patterns inboard of the Appalachian oro- v. 53, p. 585–646. related to tectonic reorganization of fluid-flow gen: Calgary, Alberta, Canadian Society of Petroleum Kesler, S. E., and van der Pluijm, B. A., 1990, Timing of Mis- patterns well inboard of, but related to, Taconic Geology–Society for Sedimentary Geology (SEPM) sissippi Valley–type mineralization: Relationship to Appa- Joint Convention Program with Abstracts, p. 81. lachian orogenic events: Geology, v. 18, p. 1115–1118. and possibly Acadian orogenesis. Dykstra, J. C. F., and Longman, M. W., 1995, Gas reservoir po- Kesler, S. E., Appold, M. S., Martini, A. M., Walter, L. M., tential of the Lower Ordovician Beekmantown Group, Huston, T. J., and Kyle, J. R., 1995, Na-Cl-Br systematics ACKNOWLEDGMENTS Québec Lowlands, Canada: American Association of Pe- of mineralizing brines in Mississippi Valley–type depos- troleum Geologists, v. 79, p. 513–530. its: Geology, v. 23, p. 641–644. Faure, S., 1996, State of intraplate stress and tectonism of Kharaka, Y. K, Carothers, W. W., and Rosenbauer, R. J., 1983, We thank quarry owners for access to their northeastern America since Cretaceous times, with par- Thermal decarboxylation of acetic acid—Implications for properties; Craig Gillgrass, Marianne Molgat, and ticular emphasis on the New England–Québec igneous origin of natural gas: Geochimica et Cosmochimica Acta, province: Tectonophysics, 255, p. 111–134. v. 47, p. 397–402. Michel Picard for field assistance; Jan Jansonius Ford, D., and Williams, P., 1989, Karst geomorphology and hy- Kharaka, Y. K., Leroy, M. L., Carothers, W. W., and Goerlitz, (Geological Survey of Canada, Ottawa) for his drology: London, Unwin-Hyman, 601 p. D. F., 1986, Role of organic species dissolved in forma- Forgrave, J. R., 1995, The nature and distribution of vein min- tions waters from sedimentary basins in mineral diagene- suggestion that organic sheets at location 19 may eralization in Paleozoic rocks in the Ottawa Lowland re- sis, in Gautier, D. 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