THE SILURIAN-DEVONIAN DISCONFORMITY IN SOUTHERN ...

BULLETIN OF CANADIAN PETROLEUM GEOLOGY VOL. 25, NO. 6 (DEC. 1977), P. 1157-1186

THE SILURIAN-DEVONIAN DISCONFORMITY IN SOUTHERN ONTARIO DAVID R. KOBLUK', S. GEORGE PEMBERTON ~, MARIKA KAROLYI' and MICHAEL J. RISK s ABSTRACT The sub-Devonian (Gedinnian) disconformity in southern Ontario is developed upon the Upper Silurian Bertie Formation. Two erosion surfaces are recognizable: pre- and post-Oriskany sandstone. An extensive system of Silurian joints and fractures is developed within the Bertie beds. A few of these are filled with Oriskany-type orthoquartzitic sand and conglomerate, and represent subaefial solution prior to Ofiskany deposition. The others are filled with Springvale sand and conglomerate and represent solution and widening during subaerial exposure following Oriskany deposition. Below the disconformity surface, a system of solution rugs and extensive leached patches stained with hydrocarbons is present in the uppermost Bertie dolomite. The rugs and leached patches are vadose and represent extensive freshwater solution during subaerial exposure. The mottling is not developed below the disconformity beneath the Oriskany, which suggests that leaching and rug porosity developed only during the second erosional period. The disconformity surface consists of a solution topography of rounded ridges, solution pits and other small-scale karren forms. Straight to gently curved borings of the morphological ichnogenus Trypanites are present on the disconformity surface and were established during the marine transgressions. The walls of the Trypanites borings are penetrated by silica-infilled algal microborings. No evidence for the presence of an encrusting epizoan fauna was found. Rounded solution pitting developed on the surface may be the result of an algal or moss cover. Dendritic, branching and single linear etchings developed on some parts of the disconformity greatly resemble the etchings produced by land-plant root or rhizome systems. Analysis of sedimentological and paleontological data leads to the recognition of a marine transgressive-regressive sequence in which two distinct subaerial disconformities are present. I NTRODUCTION The s u b - D e v o n i a n (Gedinnian) disconformity (angular u n c o n f o r m i t y at Port Colborne, Fig. 1) in southern Ontario is d e v e l o p e d upon the U p p e r Silurian Bertie F o r m a t i o n (formerly Bertie-Akron F o r m a t i o n ; Caley, 1940, 1941; Telford and Tarrant, 1975). In the study area, f r o m Hagersville in the west to Port C o l b o r n e in the east (Fig. 1), the lowest D e v o n i a n beds, the Oriskany sandstone and the Springvale Sandstone M e m b e r of the

~Department of Geology, Memorial University, St. John's, Nfld. Present address: Dept. Earth and Planetary Sciences, Erindale College, University of Toronto, Mississauga, Ontario, L5L 1C6. 2Department of Geology, McMaster University, Hamilton, Ontario. ~Department of Geography, McMaster University, Hamilton, Ontario, L8S 4M1. The authors thank the operators of the Law Quarry, Humberston Port Colborne Quarries Ltd., Port Colborne, and Haldimand Quarries Ltd. and Construction Ltd., Hagersville, for allowing access to their quarries. Dr. G. V. Middleton, McMaster University, provided helpful comment on the Hagersville locality. The manuscript was reviewed by Dr. C. F. Kahle (Bowling Green, Ohio), Dr. N. P. James, (Memorial, Newfoundland), Dr. R. S, Harrison (Manitoba, Winnipeg), Dr. B. A. Liberty (Brock University, St. Catharines), and Dr. P. G. Telford (Ontario Ministry of Natural Resources, Toronto). Dr. D. C. Ford, McMaster University, was helpful in interpreting karst processes and features, though any subsequent misinterpretations are solely the responsibility of the authors. Elizabeth Kobluk generously gave of her time to assist in the field. Jack Whorwood helped with photographic reproduction. Comparative work in the Caribbean by Kobluk was greatly aided by the co-operation of the Discovery Bay Marine Laboratory, Jamaica, and in particular Eileen Graham and Jeremy Woodley, and the Caribbean Marine Biological Institute (CARMABI) in Curacao and Bonaire, Dutch West Indies. 1157

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Bois Blanc Formation (Emsian), directly overlie the Silurian Bertie Formation (Fig. 2). Although the Springvale sandstone may possibly be an Oriskany equivalent, Caley (1941) stated that it may be Lower Onondaga, owing to the Onondaga fauna it contains in some areas. Much of the Springvale sand may, however, have been derived by erosion of the Oriskany. The orthoquartzitic Oriskany sands, derived from the Canadian Shield or the Appalachian highlands, are highly variable in thickness in the study area (absent or a few centimetres to over 1 metre). The Oriskany immediately overlies the Bertie Formation (Fig. 3) and is disconformably overlain by the Springvale Member. Where the Oriskany Sandstone is missing, the Bertie Formation is overlain directly by the Springvale Member. Some fossil joints are filled with Oriskany sand and conglomerate (see discussion below), indicating that it certainly covered the area originally. Details of the Lower Devonian and Upper Silurian stratigraphy, lithology and paleontology may be found in Middleton (1958), Telford and Tarrant (1975), Caley (1940, 1941), Stauffer (1915), Best (1953), Oliver (1967), Sanford (1964, 1968, 1969) and Douglas (1970). The Springvale Sandstone at both Port Colborne and Hagersville is a distinctive unit. It consists of green, fine to coarse grained, calcareous quartz and glauconite conglomerate, sandstone and siltstone. At the Haldimand quarry in Hagersville (Fig. 1), Caley (1941) views the very thin glauconitic sand overlying the disconformity as Oriskany equivalent, although this must be regarded as interpretative in the absence of fossils. At Port Colborne (Law and Port Colborne quarries; Fig. 1), the base of the Springvale consists of quartz-rich glauconitic sandstone and conglomerate. The conglomerate contains well-rounded to subrounded pebbles, up to 12 cm in diameter, of Salina and Bertie dolomites, Oriskany sandstone, and rare chert-beating limestone fragments resembling similar lithologies in the Bois Blanc Formation.

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Fig. 3. Orthoquartzitic Colborne (Law quarry).

D. R. KOBLUK et al.

Oriskany Formation sandstone overlying the disconformity at Port

NATURE OF THE DISCONFORMITY The Disconformity Surface

In several places at the Haldimand quarry in Hagersville, and in the Law quarry at Port Colborne, operations have exposed the horizontal plane of the Silurian disconformity (Fig. 8). Many blocks blasted from the walls are found separated along thin shale or silt seams at the disconformity, and provide spectacular direct views of the erosional surface (Figs. 9, 11, 12, 13, 14). The surface is undulatory on a large scale, with local topography of up to 1 m (Fig. 8a). Rounded knobs and prominences are common on the disconformity surface at Port Colborne, as are small vertical ledges. Joints and Fractures

At all three localities studied (Figs. 1, 4), an extensive system of Silurian joints and fractures is developed within the Bertie beds, which does not extend upward into the overlying Bois Blanc beds. Presumably these Silurian joints and fractures are present throughout the rest of the southern Ontario subsurface wherever the disconformity is developed. These features were noted previously (Caley, 1940, 1941; Telford and Tarrant, 1975), but were not described in detail. These solution-widened joints may be called klufkarren, or grikes, and commonly are found developed in massively bedded limestones. The selective weathering of these joints takes place mainly under subaerial conditions (Williams, 1966). These karren forms may vary from several centimetres to a metre in width and centimetres to several metres in depth: they are rounded and wider at the top and taper towards the base. Examples are described from numerous areas such as the Dinaric Karst area, Ireland, England etc. (Cvijic, 1924; WilliamS, 1966; Sweeting, 1973).


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Fig. 4. A) A joint, widened by solution, developed within the Bertie Formation and filled with Springvaie sand and conglomerate. The post-Silurian disconformity is at the top; the joint does not go through the Springvale Member Height of the exposure is 3 m. B) A solution-widened joint similar in size, form and origin to that in (A) above. First Pleistocene reef terrace at Discovery Bay, Jamaica. Hammer for scale. C) Solution and bio-erosion-widened joints in the coastal environment at Discovery Bay, Jamaica. The exposure here, 0.5 m above sea level, is very similar to the supratidal and subtidal exposures interpreted to have developed at the Silurian disconformity. Compare with Figure 23. These joints are filled by carbonate sand and rubble below sea level.

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All of the joints and fractures are pre - Bois Blanc Formation (presumably pre-Devonian). At Port Colborne (rarely at Hagersville) a few of the joints are filled with Oriskany-type orthoquartzitic sand and conglomerate (containing cobbles and pebbles of Oriskany orthoquartzite), and represent later solution and widening of joints during subaerial exposure and erosion following Oriskany deposition (Fig. 4a). Infilling of the earlier joint sets by Ofiskany sand prevented subsequent solution and widening of those joints during the post-Oriskany subaerial erosion. Both types of infilled joints and fractures vary from small-scale features a few centimetres deep and a fraction of a centimetre wide to widely spaced (several metres or more) parallel joint sets at least 10 m deep (they disappear into the quarry floors). In most cases, the joints are wide (up to 0.5 m), taper downward, and have nonplanar, irregular, or smooth surfaces. The lips of the joints at the disconformity are rounded and weathered (and often quite heavily bored; see discussion below), and definitely underwent extensive subaerial solution and widening. The penetration and erosion of the lips of both pre- and post-Oriskany joints by boring marine organisms indicate that in both cases the joints were not completely filled by detritus during subaerial exposure and probably were widened further at the aperture following, or immediately preceding, marine submergence; similar features can be seen today on tropical limestone coasts (Figs. 4b,c). Whether the boring and associated widening took place in the intertidal or shallow subtidal is unknown. The lithified remnants of the Oriskany sandstone not removed during post-Oriskany erosion served very effectively to preserve the pre-Oriskany disconformity surface (Fig. 3). Borings developed in the sub-Oriskany disconformity remain pristine and were never infilled by Springvale silts and sands (Fig. 5). Sub-Disconformity Leaching and Porosity

The Bertie dolomite shows a pronounced mottling from 10 cm to 0.5 m, (very rarely to 1 m) below most of the disconformity (Fig. 6). The only place where mottling is not generally developed is below the disconformity underlying Oriskany sandstone remnants. The mottling consists of a vertically trending system of brown to tan or white interconnected irregular patches (0.5 to 4 cm across) which is most intensive immediately below the disconformity, and gradually disappears downward. The patches are original solution vugs completely or partially infilled with mixtures of calcite-cemented quartz, glauconite, or carbonate sand and silt, or areas of extensive leaching of the original rock. The leached patches retain up to an estimated 50 per cent porosity which in some places is partially infilled with precipitated coarse white euhedral dolomite. Hydrocarbons commonly stain the leached patches. Up to 10 cm below the disconformity, most of the infilled vugs and leached patches are lined with diffuse hematite, as are many of the infilled microfractures projecting down from the disconformity. Some of the vugs did not fill completely with washed-in detritus and were subsequently filled, or nearly filled, with precipitated calcite spar or coarse white dolomite. The vugs and leached patches are vadose and represent extensive freshwater solution during subaerial exposure. Some of the detrital infill is vadose silt and sand but some, notably the glauconitic and quartz silt and sand, was introduced later, probably during the post-Oriskany transgression, or by being windblown from elsewhere and washed into the pore system. Dunham (1969) discusses the characteristics and origin of vadose sediments. Subaerial solution is a characteristic feature of exposed carbonate rocks; pore systems ranging from microscopic to cavernous are represented at Port Colborne and Hagersville (Choquette and Pray, 1970, discuss porosity in carbonate rocks). The original cavernous porosity, represented by poorly preserved, rubble-infilled structures from 1 to 2 m in diameter, is developed well below the disconformity, within the Bertie Formation (Fig. 7). Gill (1973), Huh (1973) and Kahle (1974) describe similar fracture, vug, and cavern porosity at Maumee, Ohio and elsewhere in the Michigan Basin within the Salina and Niagara groups, which probably represent vadose and phreatic diagenesis. A similar vug porosity developed below a disconformity containing macroborings similar to those

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Fig. 5. Plan view (A) and vertical section (B) through a sample block showing the disconformity developed on Bertie dolomite. Scales are in millimetres. The surface is heavily bored and very irregular. Well-rounded quartz grains are adhering to the surface and are lodged in some of the apertures of borings Many of the borings are still empty, having been kept from being filled in by grains lodged near the apertures: others are filled with quartz silt and sand

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Fig. 6. Specimen of Bertie dolomite cut perpendicular to the disconformity ~n contact with Springvale glauconitic sands. The mottling consists of leached patches retaining up to 50% porosity; original vugs are now filled with fine quartz and glauconitic silt. The darkest patches are stained brown by hydrocarbons, Scale bar is 1 cm.

Fig. 7. At the centre of the photo is an infilled cavernous pore, filled with fallen (and cemented) disoriented blocks of Bertie dolomite. The beds above the feature and below the disconformity have all sagged downward; the disconformity, however, is flat and horizontal, and is overlain by Springvale sands. This indicates that this cavernous porosity developed during subaerial exposure, certainly prior to Springvale deposition. The relationship with the Oriskany is unknown. On what was once the floor of these caverns are found Springvale sands, in some cases, which were washed in from the surface during Springvale deposition. Section from top to bottom is 2.5 m.

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Fig. 8. A) Detail of the Silurian-Devonian disconformity at Port Colborne Quarries Ltd, Port Colborne. The piJes of rubble at the top are due to quarry excavation The Springvale Member is here in contact with the Bertie dolomite Note the irregularity of the topography, consisting of sharp prominences, and shallow depressions. Exposure is 3 m high B) The exposure at Haldimand quarry, Hagersville The car is on thedisconformity, which was exposed during quarrying. TheBertie Formation is below. Remnants of the Oriskany sandstone are preserved here, but the disconformity ~s generally overlain by Springvale sands.

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described below is also present within the Devonian Snipe Lake reef complex (Havard and Oldershaw, 1976). The general absence of leaching, vug, and fracture porosity at the disconformity below the Oriskany suggests different environmental conditions in the pre-Oriskany erosion from those present during post-Oriskany erosion. Although many of the same karst features are present on both disconformity surfaces, leaching and vug-porosity development took place only during the second erosional (post-Oriskany) period. This would suggest that conditions during pre-Oriskany erosion were wet enough to permit dissolution of joints but that extensive rug solution and leaching in the Bertie Formation did not develop, perhaps for lack of sufficient water circulation. Very extensive solution along joints without the development of associated vug porosity is common in many areas, particularly where the rocks are tightly cemented. The pre-Oriskany surface may not have been exposed long enough under the appropriate conditions to allow the rug development and leaching that took place during the later erosion.

Fig. 9. Specimen of the disconformity surface, showing the base of a small, shallow depression and one side of a small prominence. The surface has undergone extensive erosion similar to that in Figure 14, possibly by etching and solution under an algal or moss cover. Such topography and surface erosion is common today (see Fig. 14B). Scale bar 0.5 cm.

Karren Development on the Disconformity Surface

Karren forms are solution features developed on either bare or covered limestone surfaces; they vary in size from millimetres to metres, but rarely exceed 100 m in greatest dimension. The various karren forms found on the disconformity surface (rarely exceeding 1 m in size) consist of solution pits of varying shapes and sizes, micropitted (or pinhole) solution surfaces, solution hollows or irregular solution-enlarged depressions, small solution runnels, and kluftkarren (solution-widened joints).


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Fig. 10. A) Contact between the Bertie dolomite (below) and the Springvale sandstone-conglomerate. Contact is at end of hammer. The Bertie dolomite is strongly mottled (see Fig. 6, and discussion on leaching) below the disconformity. The base of the Springvale, here at the Law quarry, is a breccia-conglomerate, made up of fragments of the Bertie. B) Gently curved disconformity surface showing macroborir~gs at Hagersville The surface is identical to that in Figure

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D. R. K O B L U K et al.

14 and probably represents solution under a soil or algae cover. Only a few centimetres remain of the Oriskany, which is overlain by the Springvale. Note the absence of mottling below the disconformity. C) Springvale Member overlying a very irregular disconformity surface. The hammer handle rests in a glauconite-sand - filled joint developed in the Bertie dolomite. Only the very top of the joint is seen here, which has rounded to subrounded lips. D) "Pleistocene-Recent disconformity" developed along the north coasl first reef terrace at Rio Bueno, Jamaica. The surface *s irregular, and is pitted; in profile it is very similar to that in (A) and (C) above. Surface textures are identical to that in Figure 12A. Patches of white sand filling in some of the pits are wave- and wind-carried


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The formation of karren is the result of various chemical reactions, precipitation, and other climatic factors; it is influenced by the lithology and texture of the rock, the slope of the limestone surface, and the presence or absence of vegetation and/or till cover. Chemical weathering of the limestone by carbonic acid is the main process responsible for karren formation; chemical aggressivity of the water flowing over the surface may be increased by the influence of a vegetation or a soil cover. The resulting karren forms, such as solution pits, may show smooth and rounded sides when developed under cover, whereas uncovered areas tend to show rough, sharp edges (Bogli, 1960; Pluhar and Ford, 1970). The erosion surface underwent small-scale solution represented by solution pits of several millimetres to a centimetre in diameter and up to several millimetres deep. Some of these pits show rounded, smooth edges, whereas others have irregular and sharp edges (Figs. 12, 13, 14). These solution pits are termed " k a m e n i t z a s " and in modern environments generally range from millimetres to several decimetres or even metres in diameter, and from millimetres to tens of centimetres in depth. Development of modern kamenitzas (and presumably those developed on the disconformity surface as well) is restricted largely to surfaces that are horizontal or slightly inclined (3-5 °) (Sweeting, 1973). Their formation is attributed to water collecting in tiny, previously existing hollows (due to slight irregularities of the surface), and enlargement of these hollows by solution. They are round to oval with flat bottoms and commonly have steep sides: the edges may be sharp because of solution by free-flowing water (Sweeting, 1973). They are known from all climatic regions (Sweeting, 1973; Jennings, 1971; Bogli, 1960; Lowry and Jennings, 1974; Wall and Wilford, 1966). The size of these features depends on a number of factors such as vegetation cover, slope of the surface, climate, different chemical reactions, lithology and texture of the rock, and the availability of water. On the disconformity surface only microkamenitzas are found, developed on both partly covered and bare surfaces as indicated by both rounded and sharp edges. These may owe their origin to solution by either fresh or salt water, or both. The development of these microkamenitzas on the Silurian disconformity surface may have been aided by the organic debris accumulating in the pits, increasing the acidity of the water and thereby increasing solution. Solution pits (microkamenitzas) are found together with scattered small areas of micropitting (or pinholes) due probably to a patchy moss or lichen cover (Figs. 13, 14). Very similar micropitting is described by Jones (1965) on modern lichen-covered limestone surfaces. Numerous irregular depressions existed previous to solutional enlargement on the disconformity surface. These hollows served to collect water and allowed solution to enlarge and smooth out the interiors. The resulting solution hollows are several centimetres in diameter and a few centimetres deep. Once water started to collect in them their development was probably similar to that of kamenitzas. Subsurface solution took place below the disconformity, as evidenced by small-scale runnels with smooth sides and smooth interfluves (Fig. 16A). These runnels formed by solution between limestone beds where water was under hydrostatic pressure. Water flowing between limestone and an insoluble and semipermeable cover, such as clay, may also produce similar features. Similar solution runnels in various stages of development may be observed forming today in many karst areas such as parts of Kentucky (Ewers, 1972) and England (Ford, 1971). The disconformity surface is relatively free of large-scale runnels and pits, but on a small scale (millimetres to metres) the surface is etched and pitted in places by solution hollows and grooves. Microsolutional features such as etched surfaces, pinholes and small solution-pit development may represent a primary stage in the karst cycle (Clark et al., 1974). The patchy development of microsolutional features on the disconformity

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B Fig. 11. A) Sample from the disconformity surface at the Law quarry. Note the pitted, irregular surface. The sharp-edged, more or less circular pits are characteristic of karst solution. The linear and branching depressions are solution features, not burrows or fractures. By direct analogy wit'l (B) they may represent etching produced by land-plant rhizomes or root systems. Scale bar 0.9 cm. B) Pitted, irregular surface on Pleistocene limestone from Port Rhodes, Jamaica. When found the surface was covered in moss and lichen; the dendritic features contained vascular plant roots which etched impressions into the surface. Scale bar 0.8 cm.

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Fig. 13. Plan view of a sample showing the disconformity surface at Hagersville. This surface, which shows pitting very similar to that in Figure 12 above, is much the same as karst surfaces developed around modern tropical limestone coasts (see Fig. 10D). Scale bar 1 cm.

SILURIAN-DEVONIAN D1SCONFORMITY

Fig. 14. A) Surface of the disconformity characteristic of solution beneath an algal or surface of Holocene limestone from the south producing the irregular surface is still present.

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at Hagersville. This form of round-edged pitting is soil cover. Scale bar 1 c m B) Modern pitting on the coast of Bonaire, Dutch West Indies. The algal cover Similarity with (A) above is striking. Scale bar 1 cm.

Fig. 15. Parts of the disconformity surface at both Hagersville and Port Colborne are brecciated in this jigsaw-puzzle fashion The areas between the clasts are filled with micritic carbonate, not glauconitic sand or orthoquartzitic sand. Springvale caps the breccia. Although there is no proof for it here, such breccias are commonty produced subaenaNy; another possibility involves the formation of caliche or calcrete crusts.

D. R. KOBLUKet al.

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surface tends to indicate either limited availability of fresh water (climatic conditions were dry, or water was channeled away by the joints) or salt water interaction, in which only small amounts of meteoric water acted on the surface. BORINGS MACROBORINGS The macroborings found on the disconformity surface are defined according to the classification system proposed by Bromley (1970), as single-entrance, pouch-like borings. In contrast to other trace fossils originating in soft sediment, borings of this type have been recorded from a variety of substrates including penecontemporaneously cemented sediment, igneous rocks, pebbles, and carbonate skeletons. Recently Bromley (1970, 1972) and Hantzschel (1975) pointed out the confusion that arises when fossil borings are given the names of modern boring organisms. They have suggested general ichnological names for groups of borings, such as Entobia Bronn, for all borings produced by sponges (Bromley, 1970), and Trypanites Magdefrau for all single-entrance pouch-shaped borings (Bromley, 1972).

Systematic Paleontology Ichnogenus Trypanites Magdefrau 1932, p. 151 Teredolites Leymerie 1842, p. 2, pl. 2, figs. 4-5 Gastrochaenolites Leymerie 1842, p. 3, pl. 3, fig. 1 Trypanites Magdefrau 1932, p. 151 Nyginites Magdefrau 1937, p. 56 Specus Stephenson 1952, 1.51, pl. 8, figs. 4-5 Martesites Vitalis 1961, p. 124, pl. 1-2 Vermiforichnus Cameron 1967, p. 190, figs. 1-2 Conchifora Muller 1968, p. 68, figs. 3-7. Type Ichnospecies Trypanites weisei Magdefrau 1932 Diagnosis: Simple, unbranched borings in hard substrate with a single opening to the surface. Discussion: Pouch-borings excluding those of acrothorecican cirfipeds. From a single entrance, the boring may extend as a long cyclindrical tube or a flattened U-shaped chamber with a figure-eight entrance. Borings in all substrates are included, with no restriction to geological age.

Description of the Borings Trypanites occurs not only along the horizontal surface of the disconformity (Fig. 5a) but also on rounded knobs, prominences, and vertical ledges (Fig. 17b). Apertural diameter ranges from 2 to 3 mm; borings are usually circular to subcircular in transverse section. In longitudinal section the borings are subparallel-sided (Fig. 18), and taper toward the base. The borings are generally straight, though gently curved holes are found, and are usually oriented normal to the surface (Fig. 19). Length of borings is variable and ranges from 1 to 3 cm, with a mean of 2.4 cm. X-ray radiographs (Fig. 17c) and acid-dissolution techniques show that the borings rarely interconnect or branch, and are not U-shaped. The borings are not lined and the walls appear ragged (Fig. 20). Some of this raggedness is due to the late growth of dolomite rhombs peripheral to the borings during a late but minor episode of dolomitization. The majority of the borings appear as sediment-filled holes. The basal section is composed of fine-grained orthoquartzitic or glauconitic sand and silt, and scattered euhedral dolomite rhombs (Fig. 21a). The main section of the boring is generally filled with coarser grains (Fig. 2 lc). The aperture is filled by glauconitic or orthoquartzitic sand or silt of the Oriskany or Springvale (Fig. 21b).


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Fig. 16. A) Solution runnels apparently formed under hydrostatic pressure at the surface bounding two differing rock lithologies, or under a soil or clay cover. Scale bar 1 cm. B) Very similar though larger-scale features developed on the subaerial surface at Pierrefonds, Montreal Island, Quebec. These features appear to be due to rainwater runoff and solution under a semipermeable clay-rich soil. Developed upon Middle Ordovician Trenton limestone.

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Fig. 17. A) Borings of Trypanites weisei Magdefrau developed in Bertie dolomite at the disconformity. Note that most of the borings are empty, and that borings are present on the horizontal and vertical surfaces. Scale bar 1.2 cm. B) Same specimen as in (A) above, but cut. Note that the bedding, which is vertical in the photo, is truncated by erosion and borings..This structure is one part of a lip from a solution-widened joint beneath the Oriskany. Millimetre scale. C) X-ray radiograph of the same specimen as in (A, B) above. Note that none of the borings are U-shaped, branch, or interconnect. Same scale as in (B).


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Fig. 18. Longitudinal section of Trypanites weisei, showing subparallel sides, and the glauconitic Springvale sand infill. The disconformity is developed below the dark sediment above the boring, and filling the small, fracture Scale bar 26 cm

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D. R. KOBLUK et al,

Fig. 19. Scanning-electron micrograph mosaic of a gently curved Trypanites weisei boring projecting into the Bertie dolomite from the disconformity. Scale bar 500/~m: x 20,

Many samples show open borings (Fig. 17b). These open holes contain no fill except for minor amounts of quartz sand in some of them, and are presumed to have been open since their construction, as there is no evidence to suggest internal solution or disturbance of any kind. They appear to have been plugged with coarse quartz sand which prevented infilling by finer sand and silt. Borings of a similar morphology and size have been reported from the Silurian of Wales (Newell, 1970, pl. 2, p. 341); the Devonian of Alberta (Havard and Oldershaw, 1976, fig. 9, p. 39); the Jurassic of England (Hallam, 1969, fig. 3, p. 234); the Cretaceous of Texas (Perkins and Stewart, 1971, fig. 43, p. 63). These include a variety of forms from subaerial paleocaliche cobbles (Perkins and Stewart, 1971), subaerially exposed backreef deposits (Havard and Oldershaw, 1976), cavities in the coral Heliolites interstinctus (Newell, 1970) and coinstone formed in a supratidal environment (Hallam, 1969). In addition, numerous investigations of ancient hardground deposits have figured forms similar to the To,panites borings described here (see Bromley, 1975, for a review). The nature of the organisms responsible for the borings is problematical. Little is known about rock-boring organisms in the Paleozoic and very few studies have attempted to associate specific borings with a particular group of organisms. Cameron (1969) reviewed the evidence for Paleozoic shell-boring polychaetes, and also described an occurrence of soft-part preservation of a Devonian spionid (Cameron, 1967). Studies of

SILURIA N-DEVONIA N DISCONFORMITY

I 179

modern rock borers suggest that borings similar to Trypanites could have been produced by polychaetes (Perkins, 1971; Warme, 1975), sipunculids (Rice, 1969) or cirripeds (Warme, 1975). MICROBORINGS

The walls of the macroborings are penetrated by silica-infilled microborings up to 100 /zm long and 10 /.zm to 30 /zm in diameter (Fig. 22). These borings are slightly curved, pinch and swell, and generally are subnormal to the boring wall. Filamentous endolithic (boring) algae commonly are found infesting marine carbonate substrates, and have an extensive record ranging from Cambrian to Recent (Pia, 1937; Hessland, 1949; Golubic et al., 1975). These borings are algal, and are similar in form to borings produced by the chlorophytic alga Ostreobium. Endolithic algae are often found infesting the walls of larger borings and cavities in modern carbonates. For example, algal borings are commonly found in the walls of t h e borings produced by Cliona in coral heads, and living within and penetrating the walls of cavities deep within Bermuda reefs (Schroeder, 1972). The walls of the Trypanites borings are not heavily infested by algal borings; none of the phenomena commonly associated with repeated or long-term algal infestation, such as micritization, are present (Bathurst, 1966, 1971). The very low density of borings in the walls suggests that the Trypanites borings were open for a time after being vacated by the organism and before being infilled or covered. Work by Kobluk and Risk (1977) suggests that initial shallow endolithic algal infestation is very rapid, occurring within days to weeks. If these results can be applied here, the borings were vacated and open, and algal infestation active, for only a relatively short period, perhaps in the order of weeks. EPIZOANS Epizoans are a common and dominant component of hardground biota (Bromley, 1975), yet there is no evidence for the presence of encrusting organisms on the disconformity surface. Encrusting organisms are known from Silurian hardground surfaces, and include tabulate corals and auloporid corals, circular attachments of craniid brachiopods, crinoid holdfasts and root systems (Halleck, 1973). Encrusters are also known from an Ordovician hardground surface (Brett and Liddell, 1976). None of these were found on the disconformity surface, even though submergence followed subaerial exposure. The absence of an encrusting fauna may have several explanations. The environment may have been too rigorous to allow settlement and colonization of the surface; the intertidal zone in the tropics is subject to extreme environmental fluctuations and contains, in modern examples, relatively few species (Hallam, 1969). The encrusting fauna, if present, perhaps was abraded and eroded off the submerged surface by the abrasive action of Oriskany and Springvale sands. Middleton (1958), did in fact note the presence of unidentified fragments of tabulate corals and brachiopods in the Spfingvale sandstone at Hagersville.

EPIPHYTES There is some evidence, in the form of rounded solution pitting on the disconformity surface, that at least during the shoreline phases of the Devonian transgression there was an algal or moss cover. Figure 14 shows the most commonly preserved expression of the algal cover (produced by carbonic-acid solution of the carbonate below the cover). Whether the cover was supratidal, intertidal or subtidal, or all of these, is unknown. Identical features are produced today on limestone coasts in the supratidal-intertidal zones in many areas (Fig. 14b). Algae, along with rain water or salt-water spray, are also capable of producing jagged, sharp or irregular " p h y t o k a r s t " surfaces which may, under exceptional conditions, result in extreme topography (Folk et al., 1973). Many areas on

1180


the disconformity surface show the rough, sharp surface produced by modern phytokarst. It is, however, often difficult, on a purely textural basis, to distinguish some types of phytokarst from small-scale solution karst produced solely by rain or salt-water spray solution. The dendritic, branching and single linear etchings developed on some parts of the disconformity (Fig. l la) greatly resemble the etchings produced by land-plant root systems (Fig. 1 lb) in pattern, size, branching and cross section. The existence of Silurian vascular land plants has been known for some time, and there is no reason to expect that they would not have left traces on subaerial surfaces as modern plants do. Lycopods and psilophytes having horizontal rhizomes are known from the Upper Silurian of Australia and New York (Cookson, 1935; Lang and Cookson, 1935; Andrews, 1961).

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Fig. 20. Scanning-electron micrograph of the wall of the same Trypanites boring shown in Figure 18 above. Note the raggedness, which is probably due to the late growth of dolomite rhombs during a minor episode of dolomitization following boring and infilling. Scale bar 50 tim; x 200.


1181

Fig. 21. A) Basal filling of a Trypanites boring, made up of gtauconitic, quartz and carbonate siltand clay-sized sediment. Note the euhedral dolomite rhombs. Scale bar 50 p.m; x 200. B) SEM of the infill near the aperture of a boring made up of euhedral dolomite rhombs, quartz, carbonate, and glauconite silt, sand and clay. Scale bar 50 /zm; x 200. C) SEM of the infill near the centre of the boring shown in Figure 18 above. The infill consists of rounded limestone and dolomite quartz, and glauconitic sand grains. Scale bar 200/zm; x 50.

SUMMARYANDCONCLUSIONS The Upper Silurian Bertie Formation is representative of the final stages of a marine regression in southern Ontario. The disconformity at the top of the Bertie Formation (Fig. 23) represents extreme shallowing and subaerial exposure. The transgression that covered the area in Oriskany orthoquartzitic sands was followed by a second regression and period of subaerial exposure before the influx of Springvale (Bois Blanc Formation) glauconitic and quartzitic sands. The post-Oriskany erosion removed much of the Oriskany orthoquartzite, so that the Springvale Member is commonly found in contact with the Upper Silurian Bertie Formation. Solution-widened joints developed during the pre-Oriskany exposure are filled with orthoquartzitic sands and conglomerates, whereas solution-widened joints developed during the post-Oriskany erosion are filled with Springvale sand and conglomerate.

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Fig. 22. A silicified endolithic algal boring projecting from a glauconite sand filled macroboring at the disconformity below the Springvale Member, from Port Colborne. The carbonate of the host Bertie dolomite was dissolved away in hydrochloric acid, leaving three-dimensional casts of the resistant sand-filled macroborings and silica-filled algal microborings. Scale bar 40 p.m.

Leaching, rug and cavern porosity are commonly developed in the uppermost Bertie dolomite where the post-Oriskany erosion removed the Oriskany orthoquartzite. Hydrocarbons commonly stain the leached patches. Both disconformity surfaces developed on the Bertie dolomite show pronounced small-scale karst features, including an irregular to undulatory solution topography, ridges, protruberances, and solution holes, as well as outcrop ledges up to 1 m high. Solution runnels are developed, as are two kinds of pitted surface, indicative of moss or algae cover, and rainwater or salt-spray dissolution. Soil is absent and may not have developed or, if it was present, was removed subaerially or during the marine transgression. Macroborings (I-2 cm long and 2-3 mm wide) are commonly developed on the lips of joints along ridges and ledges, and along the surface of both pre- and post-Oriskany disconformities. Borings underlying the Oriskany are filled with orthoquartzitic sand and silt, or are empty; those under the Springvale Member are all filled with glauconitic and quartz-rich silt and sand. The borings belong to the morphological ichnogenus Tr).panites," the nature of the actual organisms responsible is problematical, but they may have been polychaetes or sipunculids, on the basis of comparison with modern borings. Low densities of silica-infilled microborings produced by boring (endolithic) algae are found penetrating the walls of the Trypanites borings.

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No epizoan fauna has been preserved, nor has it left any traces if it was present at all. Epiphytes were present at or near the migrating shoreline in the form of a moss, algal or lichen flora. Impressions in the disconformity surface left by structures greatly resembling rhizomes or root systems of land plants suggests that a land flora, known from the Silurian and earlier in other areas, may have been present in southern Ontario during subaerial exposure phases in the Upper Silurian and lowermost Devonian.

REFERENCES Andrews, H. N., 1961, Studies in Paleobotany: New York, John Wiley and Sons, Inc., 487p. Bathurst, R. G. C., 1966, Boring algae, micrite envelopes, and lithification of molluscan biosparites: Geol. J., v. 5, p. 15-32. , 1971, Carbonate Sediments and their Diagenesis: Developments in Sedimentology 12, Amsterdam, Elsevier Pub. Co., 620p. Best, E. W., 1953, Pre-Hamilton Devonian stratigraphy of southwestern Ontario: Ph.D. thesis, Univ. of Wisconsin, Madison, Wisconsin. Bogli, A., 1960, Kalklosung and karrenbildung: Z. Geomorph., supp. 2, Internationale Beitrage zur karstmorphologie, p. 4-21. Brett, C. E. and Liddell, W. D., 1976, Middle Ordovician hardgrounds from Kirkfield, Ontario: Geol. Soc. America, Abstracts/Progs., v. 8/6, p. 790. Bromley, R. G., 1970, Borings as trace fossils and Entobia cretacea Portlock, as an example, in Crimes, T. P. and Harper, J. C., eds., Trace Fossils: Geol. J., Spec. Issue, no. 3, p. 49-90, , 1972• On some ichnotaxa in hard substrates, with a re-definition of Trypanites Magdefrau: Palaont. Zeitschr., v. 46, p. 93-98. , 1975, Trace fossil at omission surfaces, in Frey, R. W., ed., The Study of Trace Fossils: New York, Springer-Verlag, p. 399-428. Caley, J. F., 1940, Paleozoic geology of the Toronto-Hamilton area, Ontario: Geol. Surv. Canada, Mere. 224, p. 284. , 1941, Paleozoic geology of the Brantford area, Ontario: Geol. Surv. Canada, Mem. 226, p. 176. Cameron, B. 1967, New name for Palaeosabella prisca (McCoy) a Devonian worm-boring and its preserved probable borer: J. Paleontology, v. 43, p. 189-192. • 1969, Paleozoic shell-boring Annelids and their Trace Fossils, in Carriker, M. R., Smith, E. G. and Wiles, R. T., eds., Penetration of Calcium Carbonate Substrates by Lower Plants and Invertebrates: Am. Zoologist, v. 9, p. 689-703. Choquette, P. W. and Pray, L. C., 1970, Geologic nomenclature and classification of porosity in sedimentary carbonates: Am. Assoc. Petroleum Geologists Bull., v. 54, p. 207-250. Clark, D. M., Mitchell, C. W. and Varley, J. A., 1974, Geomorphic evolution of sediment filled solution hollows in some arid regions (Northwestern Sahara): Z. Geomorph. Suppl., Bd. 20, p. 130-139. Cookson, I. C., 1935, On plant remains from the Silurian of Victoria, Australia, that extend and connect floras hitherto described: Phil. Trans. Roy. Soc. London, v. 2253, p. 127-148. Cvijic, J., 1924• The evolution of Lapies: a study of karst physiography: Geog. J., v. 14, p. 26-49. Douglas, R. J. W., 1970, Geology and Economic Minerals of Canada: Geol. Surv. Canada, Econ. Geology Rept. 1,838p. Dunham• R. J., 1969, Early vadose silt in Townsend Mound (Reef), New Mexico: in Friedman, G. M., ed., Depositional Environments in Carbonate Rocks: Soc. Econ. Paleontologists, Mineralogists, Spec. Pub. 14, p. 139-181. Ewers, R. O., 1972, A model for the development of subsurface drainage routes along bedding planes: Unpubl. M.Sc. Thesis, Univ. of Cincinnati. Folk, R. L., Roberts, H. H. and Moore, C. H., 1973, Black phytokarst from Hell, Cayman Islands, British West Indies: Geol. Soc. America Bull., v. 84, p. 2351-2360.


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Ford, D. C., 1971, Geologic structure and a new explanation of limestone cavern genesis: Trans. Cave Res. Group Gt. Britain, v. 13, no. 2, p. 81-94. Gill, D., 1973, Stratigraphy, evolution and diagenesis of productive Niagaran Guelph reefs and Cayugan sabkha deposits, the Belle River Mills gas field, Michigan Basin: Unpubl. thesis, Univ. of Michigan. Golubic, S., Perkins, R. F. and Lukas, K. J., 1975, Boring micro-organisms and microborings in carbonate substrates, in Frey, R. W., ed., The Study of Trace Fossils: New York, Springer-Verlag Inc., p. 229-260. Hallam, A., 1969, A pyritized limestone hardground in the Lower Jurassic of Dorset (England): Sedimentology, v. 12, p. 231-240. Halleck, M. S., 1973, Crinoids, hardgrounds, and community succession: The Silurian Laurel-Waldron contact in southern Indiana: Lethaia, v. 6, p. 239-252. Hantzschel, W., 1975, Trace fossils and problematica, in Teichert, C., ed., Treatise on invertebrate paleontology, Pt. W.; Miscellanea Supplement 1: Lawrence, Kan., Geol. Soc. America and Univ. Kansas Press, p. 269. Havard, C. and Oldershaw, A., 1976, Early diagenesis in back-reef sedimentary cycles, Snipe Lake reef complex, Alberta: Bull. Can. Petroleum Geology, v. 24, p. 47-69. Hessland, I., 1949, Investigation of the Lower Ordovician of the Siljan district, Sweden. II. Lower Ordovician penetrative and enveloping algae from the Siljan district: Bull. Geol. Inst. Univ. Uppsala, v. 3, p. 40%424. Huh, J. M. S., 1973, Geology and diagenesis of the Salina-Niagaran Pinnacle reefs in the northern shelf of the Michigan basin: Unpubl. Ph.D. thesis, Univ. of Michigan. Jennings, J. N., 1971, Karst: London, M.I.T. Press. Jones, R. J., 1965, Aspects of the biological weathering of limestones: Proc. Geol. Assoc. London, v. 76, p. 421. Kahle, C. F., 1974, Nature and significance of Silurian rocks at Maumee Quarry, Ohio, in Guidebook for Eastern Section: Ann. Mtg., Am. Assoc. Petroleum Geologists, 91p. Kobluk, D. R. and Risk, M. J., 1977, Rate and nature of infestation of a carbonate substratum by a boring alga: J. Exp. Mar. Biol. Ecol., v. 27, p. 107-115. Lang, W. H. and Cookson, E. C., 1935, On a flora including vascular land plants associated with Monograptus in rocks of Silurian age from Victoria, Australia: Phil. Trans. Roy. Soc. London, v. 224B, p. 421-449. Leymerie, A., 1842, Suite du mrmoire sur le terrain Crrtace du Departement de l'Aube. Second partie: Mem. Soc. Geol. France, v. 5, p. 1-34. Lowry, P. and Jennings, J. N., 1974, The Nullarbor karst, Australia: Z. Geomorph., v. 14, p. 392-410. Magdefrau, K., 1932, Uber einige Bohrgange aus dem Unteren Muschalkalk von Jena: Palaont. Z., v. 14, p. 150-160. Middleton, G. V., 1958, Diagenesis of lowermost Devonian beds at Hagersville, Ontario, Canada: Proc. Geog. Assoc. Canada, v. 10, p. 95-107. Muller, A. M., 1968, Weitere Beitrage zur Ichnologie, Stratinomie und Okologie der gerinanischen Trias: Geologie, v. 5, p. 405-423. Newell, G., 1970, A symbiotic relationship between Lingula and the coral Heliolites in the Silurian, in Crimes, T. P. and Harper, J. C., eds., Trace Fossils: Geol. J., Spec. Issue no. 3, p. 335-344. Oliver, W. A. Jr., 1967, Stratigraphy of the Bois Blanc Formation in New York: U.S. Geol. Surv., Prof. Paper 584-A, p. 8. Perkins, B. F., 1971, Traces of rock-boring organisms in the Comanche Cretaceous of Texas, in Perkins, B. F., ed., A Field Guide to Selected Localities in Pennsylvanian, Permian, Cretaceous and Tertiary Rocks of Texas and Related Papers: Louisiana State Univ., Misc. Pub. 71-1, p. 137-148. - and Stewart, C. L., 1971, Stope 8: Lake Granbury, in Perkins, B. F., ed., A Field Guide to Selected Localities in Pennsylvanian, Permian, Cretaceous and Tertiary Rocks of Texas and Related Papers: Louisiana State Univ., Misc. Pub., p. 60-65. Pia, J., 1937, Die kalklosenden thallophyten: Arch Hydrobiol., v. 31, p. 264-328, p. 341-398.

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D. R. KOBLUK et al.

Pluhar, A. and Ford, D. C., 1970, Dolomitic karren of the Niagara escarpment, Ontario, Canada: Z. Geomorph., v. 14, p. 392"410. Rice, M. E., 1969, Possible boring structures of sipunculids, in Carricker, M. R., Smith, E. G. and Wiles, R. T., eds., Penetration of Calcium Carbonate Substrates by Lower Plants and Invertebrates: Am. Zoologist, v. 9, p. 803-812. Sanford, B. V., 1964, Subsurface stratigraphy of Silurian rocks in southwestern Ontario: Geol. Surv. Canada, Paper 64-2, p. 14-19. - - , 1968, Devonian of Ontario and Michigan: Proc. Internat. Devonian Symp., Calgary, 1967, v. 2, p. 973-999. - - , 1969, Geology Toronto-Windsor area, Ontario: Geol. Surv. Canada, Map 1263A, scale

1:250,000. Schroeder, J. H., 1972, Calcified filaments of an endolithic alga in Recent Bermuda reefs: N.Jb. Geol. Palaont. Mh., v. 1, p. 16-33. Stauffer, C. R., 1915, The Devonian of southwestern Ontario: Geol. Surv. Canada, Mem. 34,314p. Stephenson, L. W., 1952, Larger invertebrate fossils of the Woodbine Formation (Cenomanian) of Texas: U.S. Geol. Surv., Prof. Pap. 242,226p. Sweeting, M. M., 1966, The weathering of limestones, with particular reference to the Carboniferous limestones of northern England, in Dury, G. H., ed., Essays in Geomorphology: London, Heinemann, p. 177-210. - - , 1973, Karst Landforms: London, MacMillan Press Ltd., p. 362. Telford, P. G. and Tarrant, G. A., 1975, Paleozoic geology of Welland - Fort Erie area, southern Ontario: Ontario Div. Mines, Prelim. Map, p. 989, Geol. Ser., scale 1:50,000. Vitalis, S., 1961, Lebensspuren in Salgotarjaner Braunkohlenbecken: Ann. Univ. Sci. Budapest. Rolando Eotovos Nominatae, Sect. Geol., 4, p. 121-132. Wall, J. R. D. and Wilford, G. E., 1966, A comparison of small-scale solution features on microgranodiorite and limestone in West Sarawak, Malaysia: Z. Geomorph., v, 10, p. 462-468. Warme, J. E., 1975, Borings as trace fossils and the processes of marine bioerosion, in Frey, R. W., ed., The Study of Trace Fossils: New York, Springer-Verlag, p. 181-227. Williams, P. W., 1966, Limestone pavements with special reference to West Ireland: Trans. Inst. Brit. Geogr., v. 40, p. 155-172.