Role of the Sylvania Formation in Sinkhole Development, Essex County; Ontario Geological Survey, Open File Report 5861, 122P
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® Ontario
Ontario Geological Survey Open File Report 5861
Role of the Sylvania Formation in Sinkhole Development, Essex County
1993
Ministry of Northern Development and Mines Ontario
ONTARIO GEOLOGICAL SURVEY
Open File Report 5861
Role of the Sylvania Formation in Sinkhole Development, Essex County
By
D.J. Russell
1993
Parts of this publication may be quoted if credit is given. It is recommended that reference to this publication be made in the following form: Russell, D.J. 1993. Role of the Sylvania Formation in sinkhole development, Essex County; Ontario Geological Survey, Open File Report 5861, 122p.
© Queen's Printer for Ontario, 1993
Ontario Geological Survey
OPEN FILE REPORT
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iii
Contents page ABSTRACT xi
INTRODUCTION 1 Background and Purpose of Investigation 1 Acknowledgements 5 Geology of the Windsor Area 5 Salt Production in Windsor 9
ENGINEERING GEOLOGY OF SINKHOLE DEVELOPMENT 9 Previous Work 9 Review of Models 21
GEOLOGY AND ENGINEERING GEOLOGY OF SYLVANIA FORMATION 22 Stratigraphy 22 The Sylvania Formation in Essex County 27 TOPOGRAPHY OF THE SUB-SYLVANIA FORMATION DEPOSITIONAL SURFACE 30 THICKNESS OF THE SYLVANIA FORMATION SANDSTONE 30 Petrology of the Sylvania Formation 33 Drilling and Sampling 35 Lithology of Intervals Sampled 37 Wl 37 W2, W3- 37 Petrography: Purpose and Methods 40 Petrography: Results 42 Sedimentology 47 Engineering Properties 50 Test Methods 51 Results 52 UNCONFINED COMPRESSION TEST DATA 52 POINT LOAD TEST DATA 59 TRIAXIAL COMPRESSION TEST DATA 61 Summary 61
THE OPERATIONAL HISTORY OF THE SANDWICH BRINE FIELD 61
A MODEL FOR SINKHOLE FORMATION AT SANDWICH BRINE FIELD 79
SUMMARY 85
REFERENCES 90
APPENDIX 1 DRILL HOLE LOGS 95
APPENDIX 2: DESCRIPTIONS OF SYLVANIA SANDSTONE THIN SECTIONS 108
APPENDIX 3: POINT LOAD STRENGTH TEST RESULTS 118
v
List of Figures page Figure 1. Location maps of study area and approximate locations of boreholes Wl, W2 and W3 2 Figure 2. Plan of Sandwich site, with contours (in inches) of total subsidence, 1948-1954, and outline of eventual sinkhole 4 Figure 3. Paleozoic geology of southwestern Ontario, southeastern Michigan 7 Figure 4. Post-Middle Ordovician stratigraphy of southwestern Ontario 8 Figure 5. Subsidence curves for various observation points on the Sandwich site for 1948-1954, showing rapid subsidence in 1952 and 1953 11 Figure 6. Subsidence profiles along line A-A' {see Figure 2) from 1949 to 1953 12 Figure 7. Sinkhole formation mechanism, according to Terzaghi (1954) 14 Figure 8. Sinkhole formation mechanism, according to R. Terzaghi (1970) 16 Figure 9. Sinkhole formation mechanism according to Nieto-Pescetto and Hendron (1977) 17 Figure 10. Sinkhole formation mechanism, according to Stump (1980) 20 Figure 11. Isopach map for Sylvania Formation, southeastern Michigan and southwestern Ontario, after Brigham (1971) 26 Figure 12. Diagrammatic view of relationships between the Bois Blanc Formation, Sylvania Formation and Detroit River Group 28 Figure 13. Structure contour of base (of the upper, main sandstone interval) of the Sylvania Formation, Essex County based on data obtained from drilling records 31 Figure 14. Isopach map of the Sylvania Formation (upper, main sandstone interval only), Essex County based on data obtained from drilling records 32 Figure 15. General lithological logs of Borehole Wl, W2 and W3 36 Figure 16. Petrography results {see Appendix 2 for descriptions) determined from thin section analysis, borehole W3 39 Figure 17. Photomicrograph showing intergrowth of quartz grains 45 Figure 18. Photomicrograph showing well defined quartz overgrowths 46 Figure 19. Paleogeographic reconstruction of the Michigan Basin during the deposition of the Bois Blanc Formation, Sylvania Formation sandstone and carbonates of the Detroit River Group during the early Middle Devonian. 49 Figure 20. Unconfined compressive strengths for samples from W2, W3 53 Figure 21. Cartoon showing control of different grain/overgrowth boundary types on strength 54 Figure 22. Young's Moduli and Poisson's ratios for samples from W2, W3 55 Figure 23. Stress-strain curves for sample W3 340-341 58 Figure 24. Point Load Index results for samples from W3 60 Figure 25. Mohr's circles for triaxial tests on samples from W3 62 Figure 26. Stratigraphy of Sandwich brine field 64 Figure 27. Well histories for Sandwich brine field, 1902-1954 66 Figure 28. Single well injection method of brine extraction and resulting "momign glory" cavity 67 Figure 29a. Plan view of Sandwich site showing development of brine field, 1920 69 Figure 29b. Plan view of Sandwich site showing development of brine field, 1925-1930 70 Figure 29c. Plan view of Sandwich site showing development of brine field, 1935-1940 71 Figure 29d. Plan view of Sandwich site showing development of brine field, 1945-1954 72 Figure 30. Extent of interconnections in salt beds at various time intervals, 1925-1954 73 Figure 31. History of repairs, Sandwich brine field, 1902-1954 75 Figure 32. Model for sinkhole formation, early stages, pre-mid 1930s 83
vii
Figure 33. Model for sinkhole formation, 1930s and 1940s 84 Figure 34. Model for sinkhole formation, 1950-1952 86 Figure 35. Model for sinkhole formation, 1952-1954 87
List of Tables page
Table 1. Lower to Middle Devonian stratigraphy, extreme southern Ontario 23
ix
ABSTRACT
On February 19th, 1954, a large surface crater (or sinkhole) developed over some salt solution mining cavities (in the Silurian Salina Formation) at Sandwich, near Windsor, Ontario. Over a period of a few hours, a hole over 60 m across and up to 7.5 m deep had formed. This caused severe disruption to buildings and transport facilities; brine extraction was stopped on that site. After backfilling, the sinkhole stabilised. In 1970 a similar sinkhole developed over solution mining cavities on Grosse lie, Michigan, a few miles away.
This report presents the results of a comprehensive engineering geological study made of the 1954 sinkhole at Windsor, Ontario. The investigation involved a study of regional and local stratigraphy, a programme of sampling by diamond drilling, strength testing, petrographic examination and a detailed study of the production and well repair history of the brine field from 1902 to 1954. It is concluded that the presence of sandstones of the Middle Devonian Sylvania Formation (basal formation of the Detroit River Group), with its unusual geomechanical properties, was an important factor in the formation of the Windsor sinkhole.
Petrographic examination shows the Sylvania sandstone to be a variably dolomitic quartz arenite. The quartz grains are very well rounded and have undergone severe pressure solution, causing intense intergrowths of, and overgrowths on, the grains. The texture compels the grains to rotate during compressional failure, causing the sandstone to turn into running sand. The sandstone contains 3 zones of enhanced dolomite content, which give it greater strength. In general, the pure sandstone is very weak, has Poisson's ratios of up to 0.8 and exhibits the "liquefation" noted above.
Two specific questions related to the Windsor sinkhole are addressed. Firstly, the unit from which salt was assumed to be dissolving, the B Salt of the Salina Formation, lies between 420 and 490 m below ground; how did a void migrate upward from this depth without the rubble column generated bulking up to support the roof? Secondly, why did the sinkhole occur at that specific location? The combination of geological and geotechnical studies listed above have enabled a model of sinkhole formation to be proposed for the Windsor occurrence.
Although the unusual deformation characteristics of the Sylvania was important in promoting void migration, the history and techniques of salt production at Windsor were the initial factors causing the sinkhole. From the beginning of brine production at the Sandwich site in 1902, well completion practices allowed the development of an extensive system of solution connections in the salt beds above the B Salt. In addition, vertical communication resulted from the poor plugging of damaged wells. Two wells were drilled in 1923 and 1928 in the centre of the area which was to become the 1954 sinkhole. They both intercepted rubbly zones and consequently were plugged soon after drilling. These holes provided the first zone of vertical connection, by which unsaturated brine solution was allowed access to significant salt beds (the F Salt) only 305 m below the ground surface. These salt beds would be dissolved preferentially since the brine system would be gravity-stratified, being least saturated at the top. The dolostone overlying this salt bed would subside into the formed void, setting up stresses in the overlying Sylvania Formation causing failure within the sandstone and the formation of a mass of loose sand. This sand slurry would flow slowly through joints produced in the underlying failed dolostone unit If the void could migrate up through the dolostone unit to the base of the sandstone, the sand would flow away through rubble leaving a secondary void only 107 m from the surface. This void would then migrate by conventional stoping to the surface, forming a sinkhole.
xi
INTRODUCTION
Background and Purpose of Investigation
One of the most important mineral resources of southern Ontario is the salt of the Upper Silurian Salina
Formation. In 1981,4.9 million tonnes of salt were extracted from the Salina Formation from 2 locations
(Goderich and Windsor) at a value of $55 million. This represents over 60% of the value of all nonmetallic minerals extracted within Ontario (Minnes 1982). A significant amount of this salt is obtained by solution mining methods. Certain techniques involved in this procedure (which is necessary to provide high purity salt) involve the creation of large solution caverns. These caverns frequently have larger unsupported spans than those created by conventional rock salt mining, in which the extraction ratio is as low as 57%. The presence of such large unsupported spans in solution mining areas can cause varying degrees of ground subsidence, and, in extreme cases, rapid ground surface collapse to form sinkholes.
Ground subsidence and sinkhole development clearly affect the environment at the surface and may curtail salt production.
Salt has been extracted from the Salina Formation at several sites (Figure 1) in the area of
Windsor and Detroit for many decades. Brine production operations have been conducted at the Sandwich site, near Windsor, for over 75 years. Brine is created by the injection of fresh water into salt beds and the collection of brine through the same or adjacent wells.
In 1948, cracks became visible in some buildings on the property of the Canadian Salt Company
(CSC) and the adjoining property of Canadian Industries Limited (CIL). In response to this, a study of the subsidence of the area was started. Changes in elevation of 85 reference points from 1948 to 1954 showed the development of a bowl of subsidence with a maximum diameter of 610 m, and a maximum depth of 41 cm. On the 19th of February, 1954, low rumbling noises and vibrations were observed by both
CSC and CIL personnel early in the day. By 4:00 p.m. a sinkhole formed at the centre of the pre-existing
1 Figure 1. Location maps of study area and approximate locations of boreholes Wl, W2 and W3.
2 depression (Figure 2), had stabilized, and filled with water. The sinkhole had a maximum diameter of 152 m and a depth of about 7.64 m. This caused appreciable damage to some CSC buildings and brine production was temporarily halted. The purpose of this study is to investigate the occurrence of the 1954 sinkhole and to develop an explanation for its formation.
Salt production on the Michigan side of the Detroit River started in the late 19th century, and on
Grosse He (about 16 km south of the Sandwich brine field) in the Detroit River, in 1943. Operation on
Grosse He was by single well injection and by other more advanced techniques such as undercutting. The elevations of a network of reference points established on Grosse lie were monitored on a regular basis.
According to Landes and Piper (1972), the results of observations in the late 1960s indicated a "maturing situation" and it was planned to abandon certain operations by mid 1971. However, in late 1969 cracks were observed at the surface and on January 9th and April 28th, 1970, 2 separate sinkholes developed.
The history of research into the sinkhole phenomenon will be described in some detail below. It is useful, however, to mention that early observers, such as Terzaghi (1954), attributed the sinkhole at the
Sandwich brine field to upward migration of a void from cavities in the B Salt (the supposed producing horizon in the Salina Formation, 427 m below the surface) to the rock/overburden interface. More recently, in a study of the Michigan collapses, Stump (1980) has proposed, in an alternative hypothesis, that a void is generated closer to the surface due to horizontal stresses (induced by subsidence into salt cavities), causing explosive failure of the Sylvania Formation sandstone, about 91m below the surface. Sand from this failure would then be removed by eluviation, creating a cavity closer to the surface.
The objective of this present study is to determine the mechanism of surface collapse at Windsor.
From the work of Stump (1980) and discussions with A. Robinson and T. Piper, the Sylvania sandstone is assumed to have played a significant role in the development of the sinkhole. Thus, the sandstone was
3 Figure 2. Plan of Sandwich site, with contours (in inches) of total subsidence, 1948-1954, and outline of
eventual sinkhole. Location of borehole Wl is shown. See Section on Engineering Geology for reference
to line A-A' and observation points #71, 99, 88 and 44.
4 extensively sampled (by diamond drilling) and subjected to petrographic examination and various strength
tests (unconflned uniaxial compression, triaxial compression and point load tests). Additional subsurface
data was obtained from drilling records and samples stored at the Petroleum Resources Laboratory,
London, Ontario. In addition, a detailed analysis of the company production and repair records was made
so that the occurrence of the 1954 sinkhole at that location could be explained. Although this is a local
case study, the implications for void migration in solution mining and in other contexts may be significant.
Acknowledgements
This work would not have been possible without the great help and forebearance of the Canadian Salt
Company. In particular, A. Letts and A. Robinson provided information and suggestions which were
extremely useful. T. Piper, of BASF Wyandotte, Michigan, made several helpful suggestions by
commenting on a preliminary version of Chapters 1, 2 and 3; A. Robinson also reviewed that material.
James Eckert supervised the drilling program, made a preliminary log of the borehole samples and
did most of the work in preparing the structure contour and isopach maps. Other forms of assistance were
provided by Rainer Wolf, Ann Murphy, and David Bree. Early versions of the text were reviewed by staff
of the Ontario Geological Survey: D.K. Armstrong, R.K. Bezys, M.D. Johnson, and D.C. Roumbanis.
Final review, editing and compilation of the report were completed by M.A. Rutka.
Geology of the Windsor Area
Between the Cambrian and early Jurassic Periods, there was a large intracratonic depression in northcentral
North America, centred on what is now the State of Michigan. Great thicknesses of sediments accumulated
in this, the Michigan Basin. The Windsor-Detroit area is located close to the southeastern edge of the basin. Sediment thickness around the southern edge is controlled, to some extent, by the presence of the northeast-trending Algonquin and Findlay Arches. Essex County, in the extreme southwest of the Province
5 of Ontario, is located on top of the northeastern extremity of the Findlay Arch, which is separated from
the Algonquin Arch farther to the northeast by the Chatham Sag. These major regional structures had
varying influences on the distribution and nature of sediments in the area throughout Paleozoic time.
Today they control the outcrop patterns of the Paleozoic strata (Brigham 1971; Figure 3). Only the
post-Middle Silurian rocks of the Windsor-Detroit area are relevant in this study and are described briefly
below.
The Upper Silurian rocks of the Michigan Basin comprise the Salina and the Bass Islands
Formations (Figure 4). The Salina Formation overlies the Middle Silurian Guelph Formation, which
consists of various types of dolostone, the most economically important of which are the hydrocarbon
producing pinnacle reefs. The Salina Formation, which consists of evaporites, carbonates and shales, was
initially divided into 8 units (labelled A to H by Landes (1945), but the H unit, a grey-buff dense
•dolostone, is now known as the Bass Islands Formation {see Figure 4). The salt beds now exploited in the
Windsor and Goderich areas are the units of most economic significance. Salt is the main constituent of
the B and D units and is a significant part of the F unit. Salt has been removed by natural dissolution in
some areas, causing collapse breccias and thickening of overlying units (Hutt et al. 1973; Sanford 1975).
Disconformably overlying the Bass Islands Formation in the Windsor area is the Lower Devonian
Bois Blanc Formation which is usually a cherty dolostone or limestone (Telford and Russell 1981). In the
southwestern part of Lake Erie, the Bois Blanc Formation is directly overlain by the carbonate strata of
the Detroit River Group. North of Lake Erie, the Sylvania Formation, which forms the base of the Detroit
River Group in this area (Uyeno et al. 1982), marks a clastic break between the 2 essentially carbonate
units. The stratigraphy and formational status of the Sylvania Formation are discussed in detail in the
Stratigraphy Section below. The Detroit River Group, a predominantly carbonate group of units, consists of the basal Sylvania Formation sandstone, the middle Amherstburg Formation, characteristically a brown
6 Figure 3. Paleozoic geology of southwestern Ontario, southeastern Michigan, after Brigham (1971). (Refer to Figure 4 for rock types and ages of units exposed.) PORT LAM8TON GP. DEVONIAN AND KETTLE POINT MISSISSIPPIAN
HAMILTON GP. LEGEND
DUNDEE Limestone COLUMBUS
> . > Shaly limestone DETROIT RIVER GP. • I. • • .SYLVANIA Sandy limestone
BOIS BLANC =4= Dolomite as ORISKANY BASS ISLANDS Shaly dolomite / - /
Sandy dolomite
Shale
SAUNA Sandy shale or shaly sandstone
ZL 1. ZL\ Calcareous shale A-2
_t ^] Dolomitic shale A-i
GUELPH, LOCKPORT-AMABEL Sandstone
CUNTON GP. "H Sandstone, limestone, A and dolomite
CATARACT GP. Evaporites
QUEENSTON ORDOVICIAN Chert
Figure 4. Post-Middle Ordovician stratigraphy of southwestern Ontario.
8 dolostone with bituminous partings, and the upper Lucas Formation, which is lighter coloured and contains interbedded anhydrite in the subsurface.
Salt Production in Windsor
A detailed history of brine production at the Sandwich brine field site is given in in the Operational
History of the Sandwich Brine Field below. Hewitt (1962) gives an account of the development of salt production in the Windsor area. Salt was first discovered at Windsor during the drilling of a well near the
Canadian Pacific Railway station in 1891. Production started there 2 years later. In 1902, brining operations began at Sandwich for the production of caustic soda, chlorine and other chemicals. In 1955, a rock salt mine was opened 3.2 km south of the brine workings. A section of salt, 8.2 m thick, in the F unit of the Salina Formation (well above the supposed target unit for brining operations) was mined by room and pillar methods. The brine operation affected by the 1954 event closed down shortly after the collapse but a new solution mining operation was opened at a nearby site in 1958 (Mair 1963). Eighteen wells were drilled at the new site to the B-Salt level, and connections between various combinations of wells was made by hydrofracing. This system of brine extraction continues at present.
ENGINEERING GEOLOGY OF SINKHOLE DEVELOPMENT
Previous Work
In this section, engineering geological data on the Sylvania Formation sandstone that is available at the time of writing will be reviewed, and the various mechanisms proposed for sinkhole development will be outlined. These models are summarized in diagrams that have been either taken from publications or have been constructed from written (e.g., Terzaghi 1970) or verbal descriptions.
Following the events of February 19th, 1954, a group of consultants, led by Professor Karl
9 Terzaghi, were engaged to investigate the cause and consequences of the collapse. Reports by R. B. Peck
(1954) and C. A. Bays were submitted to Terzaghi concerning surface and subsurface evidence, respectively. Three wash borings were made and a seismic refraction survey was carried out by Bays to determine bedrock topography. Terzaghi submitted his report on October 27th, 1954, with a comment that not enough borehole data was available to establish firm conclusions concerning mechanisms of subsidence around the sinkhole. The following section is largely extracted from that report In addition, the report by Peck is available and has been used in this discussion. However, the information and opinions attributed to Bays' report are as reported by Terzaghi, for no copy of Bays' report has been located.
Peck's analysis of surface settlement included elevation information from over 100 reference points on, and cracks observed in, permanent man-made structures. It showed that the rate of subsidence of the ground over what was to become the sinkhole increased from 38 mm/yr (1.5 inches/yr) in 1950 to 64 mm/yr (2.5 inches/yr) in 1951, and up to 229 mm/yr (9 inches/yr) between October, 1952 and October,
1953 (Figures 5 and 6). This settlement formed a bowl-shaped depression of radius greater than 305 m
(see Figure 2). Cracks in 1 building were of such magnitude that Peck concluded they had been formed
"several years before the sinkhole was formed" (Terzaghi 1954: p. 8), implying that settlement had probably commenced even before 1948, when measurements were started.
Analysis of production records and well connections by Bays led him to postulate the existence of an extensive solution cavity 183 m wide, with its top 290 m below the surface. Bays considered most of the brine to have been produced from the F-Salt horizon rather than the B-Salt, to which all wells were drilled and from which the brine was presumed to originate. He concluded that the location of the sinkhole was controlled by an anticlinal flexure in which air, exsolved from water pumped in, was trapped.
10 1948 1949 1950 1951 1952 1953 1948 1949 1950 1951 1952 1953
Figure 5. Subsidence curves for various observation points on the Sandwich site for 1948-1954, showing rapid subsidence in 1952 and 1953. Location of observation points shown on Figure 2.
11 A' 24 25 90 uu 0
10 w o - 20 w Q CO PQ & - 30 CO
- 40
SUBSIDENCE PROFILES 1948-53 Figure 6. Subsidence profiles along line A-A' (see Figure 2) from 1949 to 1953. Elevation data of observation points (#88, 44, 45, 14, 15, 23,
24, 25 and 90) from Peck (1954).
12 According to Terzaghi (1954), the cause of the collapse was the result of a simple upward migration of a void created by salt extraction. Air probably accumulated in the crest of an anticline, causing the effective density of blocks isolated by joints to double, helping to initiate the stoping process.
An interface between broken rock and overlying void moved toward the surface, eventually causing collapse at the rockhead and ground surface (Figure 7, taken from Terzaghi 1954). Terazaghi, however, did not take into account bulking, that is the expansion in volume caused by the change from intact rock to a pile of rubble. His main concern was to determine whether the widespread gradual ground subsidence around the sinkhole was due to the flow of glacial clay into a depression formed by collapsing bedrock immediately underlying the sinkhole site (i.e., localized subsidence), or due to subsidence of bedrock underlying the entire subsidence area (i.e., general bedrock subsidence). He remained noncommittal on this point, but tended to favour the former.
Since no further drastic subsidence occurred after backfilling the sinkhole, the urgency of the original situation diminished. Salt production operations of the brine company were transferred a few hundred yards to the northeast and resumed soon thereafter (Mair 1963).
In 1970, Dr. Ruth Terzaghi published an account of the Windsor sinkhole, incorporating some new data and a reappraisal of the subsidence mechanism. The following new evidence was presented:
1. During the drilling of some wells, cavities, most of natural origin, with of heights up to
6 m were found in the salt beds between 335 and 381 m above the B-Salt, which was
supposedly the main producer.
2. Applying figures from production records to the assumption that a single, inverted cone-
shaped cavity had been produced by salt extraction, a maximum cavity height of 46 m
was derived.
3. Subsidence after 1954 was at a rapidly decreasing rate and did not follow the pattern
13 Figure 7. Sinkhole formation mechanism, according to Terzaghi (1954). A simple chimney of stoped rock migrates to the surface. Flow of clay into depression caused by localized rock subsidence produces widespread ground subsidence.
14 established before collapse.
Since the surface gradient towards the centre of the depression was similar to pre-collapse times and subsidence rates after the collapse were appreciably lower, it is unlikely that pre-collapse settlement of the ground surface outside the area of the sinkhole was due to the lateral migration of surficial clay toward the area of collapsed bedrock. Thus R. Terzaghi (1970) discounted the theory of subsidence due to localized collapse, accepting that the rock subsided regionally (i.e., general subsidence). Results from a program of drilling in the area of the sinkhole carried out in 1971 also tended to support the theory of generalized subsidence. To account for the fact that bulking of debris had not filled the cavity prior to major subsidence, she postulated a gradual slumping of more or less intact layers into the solution cavity until a point had been reached where, due to failure of supporting salt pillars in cavities at lower levels, violent collapse of the top layers occurred (Figure 8).
Following the sinkhole collapses on Grosse lie in 1970 and 1971, the Solution Mining Research
Institute sponsored a program of research which resulted in 2 publications. Landes and Piper (1972) gave an account of the development of the sinkholes but were mainly concerned with the environmental impact of the sinkholes. A detailed examination of production records and subsidence measurements for the
Grosse He brine field was made by Nieto and Hendron (1977). Calculations were also made investigating the ability of a void to migrate to the surface from a given depth, taking the bulking factor into account.
Assuming a value of 0.43 for the bulking factor (i.e., the volume of rock increases by 43% upon forming a rubble pile), the calculations showed that the Windsor sinkhole could have been developed in this way.
These authors postulated that the beds overlying the brine cavity sagged into the void, creating large tensile strains at the base of the roof stratum in the centre of the span. This caused fracturing to occur and upward stoping of the rock to commence (Figure 9). As the authors admit, however, the investigation produced contradictory evidence—despite the presence of a sinkhole at the surface, their exploratory
15 Glacial Drift Glacial Drift
Devonian Carbonates Devonian Carbonates
Salina Formation
CAVITY REDRAWN FROM TERZAGHI, 1970
Figure 8. Sinkhole formation mechanism, according to R. Terzaghi (1970). (a) After dissolution of main salt bed, load on remaining salt is increased and these pillars deform viscously allowing little bulking of overlying beds during their subsidence, (b) Further stoping above these beds allows void to migrate towards the surface.
16 Figure 9. Sinkhole formation mechanism according to Nieto-Pescetto and Hendron (1977). Strains are concentrated at the edges of the cavern and in the centre, allowing relatively efficient stoping with a low bulking factor. boreholes were unable to locate an open cavity in the salt—and their conclusions about mechanisms of sinkhole formation were very tentative.
One of the recommendations made by Nieto-Pescetto and Hendron (1977), drawn from observations that surface gradients over incipient sinkholes were about 64 mm/30 m, was that surface surveys could be used to detect potential problem areas. Surveys of the "Southwest Gallery" workings on
Grosse lie showed accelerated rates of subsidence for 1975. A borehole was drilled in the centre of the bowl of subsidence to investigate the phenomenon (Dowhan 1976). Several, apparently relevant, but inconclusive pieces of information were obtained. Extracts from the borehole log are as follows:
DEPTH REMARKS (feet) (mi 224-225 68.3-68.6 lost water circulation 267-273 81.4-83.2 6 foot (1.8 m) break in Sylvania; sonar log ran on this section 287-317 87.5-96.6 broken rock (sandstone) 757-867 230.7-264.3 broken rock, lost circulation 903 ' 275.3 drill became stuck 957 291.7 drill stuck again 967-1007 294.7-306.9 broken rock, lost circulation 1017-1127 310-343.5 rock solid to top of B Salt, apart from a 1 foot (30.5 cm) break at 1087 feet (331.4 m) level 1127-1237 343.5-377.0 B Salt, undisturbed - the supposed target for dissolution
Salt dissolution above the B Salt was regarded as the cause of the broken rock between 750 feet
(230 m) and 1020 feet (310 m). The sonar log at the 6 foot (1.8 m) break in the Sylvania Formation showed a cavity extending at least 60 m to the north and 21 m to the east, with a very restricted extent to the south and west. Those apparent restrictions were discounted as minor obstructions from which the reflection of the sonar wave had been interpreted as the cavity boundary. Dowhan (1976) concluded that the cavity in the Sylvania Formation interval extends beneath the entire area of subsidence. No definite proposals were made to explain its existence.
The most recent work (at the time of writing) on the sinkhole development mechanism is by
18 Stump (1980). This work, a MSc thesis, was in response to suggestions by T. Piper (BASF Wyandotte,
Michigan) and A. Robinson (Windsor Salt Company). These operators, with their considerable knowledge of brining methods and experience of well development, were skeptical of whether a deep cavern could stope all the way to the surface in the manner Terzaghi (1954) suggested. They suggested (Stump 1980;
A. Robinson, personal communication, 1981) that broken casings at the level of the Sylvania Formation sandstone would allow relatively dense water/sand slurries to enter the wells and be transmitted downwards into solution cavities. This would create, much nearer to the surface, a void which could migrate the much smaller distance to the rockhead. Data which may substantiate this theory is reviewed the Operational History Section, below.
Stump (1980) does not, however, concur with the suggestion given above. The first strictly geotechnical data concerning the problem were generated in Stump's study. Uniaxial compressive strength testing showed the Sylvania Formation sandstone to have special engineering properties which likely were important in the process of sinkhole formation. Strengths measured by Stump (1980) were variable, from
2000 to 7000 p.s.i. (14 to 50 MPa), the lowest strength zone occurring about 11m from the upper contact.
However, a more important finding was that the weaker sandstone specimens failed explosively under uniaxial compression, generating loose sand. Pre-failure behaviour of these specimens was also unusual in that the Poisson's ratios of the pure sandstone samples were rather high, over 0.5. Petrographic analysis of the rock fabric showed an intense pressure solution effect, causing intergrowth of grains. This feature was interpreted to be the cause of the unusual geomechanical properties (high Poisson's ratios and explosive failure), since the grains were constrained to rotate relative to each other, causing dilation and disaggregation (discussed further in the Section on Engineering Properties).
The sinkhole formation mechanism model described by Stump (1980), based on his findings of the geotechnical properties of the Sylvania sandstone, is shown in Figure 10. Subsidence of strata into the
19 a b c
Figure 10. Sinkhole formation mechanism, according to Stump (1980). (a) Subsidence due to salt extraction increases horizontal compressive stresses on Sylvania Formation causing it to shear, forming loose sand, which runs down through joints, (b) Large secondary void is created by migration of sand downwards, (c) This void then migrates to surface by normal stoping.
20 cavern left by salt solution sets up shear stresses in the overlying Sylvania Formation, causing failure and the generation of loose sand. Analysis by linear arch theory shows that failure in compression would occur extensively throughout the sandstone where it is thick-bedded, which Stump claims is the case in the
Windsor-Detroit area. These stresses also cause fracturing in the underlying Bois Blanc Formation, allowing the loose sand of the Sylvania Formation to flow as a slurry down through it, thereby creating a shallow void at the level of the Sylvania Formation. This void then migrates to the surface by mass slumping of the overlying material (see Figure 10).
Review of Models
Until the current, more sophisticated techniques of solution mining were introduced, surface sinkholes associated with solution mining operations were not uncommon in many parts of the world. Upward migration of the original void created by salt extraction appears to be a satisfactory explanation for most pther sinkhole occurrences (e.g., Walters 1979). However, with respect to the Windsor case, the models of Terzaghi (1954) and Nieto-Pescetto and Hendron (1977) must be regarded as unlikely since the bulking factor is ignored in the former case and is probably underestimated in the latter. The model proposed by
Terzaghi (1970), whereby individual beds slump into a solution cavity without fracturing, still allows for effective bulking-up since voids will inevitably be formed between each layer. In addition, this theory requires that all the tensile stresses are concentrated in the overlying strata at the point above the margin of the solution cavity, which is unlikely. The proposal of Robinson and Piper (discussed above) is also not supported by pertinent data.
The work of Stump (1980) showed that the Sylvania sandstone was probably the vital factor in allowing the upward transmission of a void from many hundreds of metres in depth to the surface.
However, the present author considers it is unlikely that a sufficient volume of sand would be able to pass through the underlying Bois Blanc Formation as depicted in Figure 10. Unless significant new voids are
21 created in the underlying dolostone, it is unlikely that the dolostone would be able to transmit the many thousands of cubic metres of sand required to create such a void in the Sylvania Formation.
The aim of this study is, therefore, to collect and examine new information concerning the sinkhole formed at Windsor to enable a reinterpretation of its causes in light of the work performed by
Stump (1980). In particular, consideration is made of the mechanisms of void migration and of controls on the eventual sinkhole location.
GEOLOGY AND ENGINEERING GEOLOGY OF SYLVANIA FORMATION
The Middle Devonian of southern Ontario consists of a thick sequence of limestones and dolostones with some thin beds of sandstone. One of these sandstones, the Sylvania Formation, constitutes the lower most unit of the predominantly carbonate Detroit River Group (Table 1). The Sylvania Formation is a well sorted quartzose rock with a variable proportion of dolomite cement. The Sylvania Formation has been studied as part of the entire Middle Devonian sequence of the Michigan Basin (e.g., Landes 1951); in its capacity as a source of high purity silica sand (Heinrich 1979); and as a factor in contributing to the formation of sinkholes over the solution mines in Michigan (Stump 1980). In this section, the geology and engineering properties of the sandstone will be described using information from the literature and from work carried out as part of this study this study.
Stratigraphy
The Sylvania Formation was first differentiated from the enclosing carbonates in the northern Ohio area by Newberry (1873); he termed it the Oriskany Sandstone, after a unit of similar lithologic character found in New York. Orton (1888) showed that the "Oriskany" of Ohio is distinct from the genuine Oriskany
Sandstone, but gave its age as Upper Silurian. Further work by Grabau and Sherzer (1910) and Prosser
(1903) established subdivisions of the overlying and underlying carbonate sequence, respectively named
22 DUNDEE FORMATION
ANDERDON Q. MEMBER D LU o Q LUCAS rr 111 FORMATION o LU LL J -J LU rr O LU Q AMHERSTBURG > rr t FORMATION O rr LU SYLVANIA FM. a
O BOIS BLANC > LU < a CO FORMATION ill 111
o
Table 1. Lower to Middle Devonian stratigraphy, extreme southern Ontario
23 the Detroit River and Bass Islands Series (Lane et al. 1909). They persisted in assigning the Detroit River
Series to the Upper Silurian because of faunal misinterpretations (Briggs 1959).
The next phase of study was by Carman (1936) in northwestern Ohio. He observed a disconformity between the Sylvania and Bass Islands formations. The upper boundary of the Sylvania
Formation, on the other hand, was observed to be gradational, with the dolomite content increasing and the quantity of sand grains decreasing gradually upward into the pure dolostone of the Amherstburg
Formation; as a result, the contact was arbitrarily defined. It was also noted that the contact was gradational regardless of the age of the overlying unit The age of the overlying units increased to the south, suggesting a diachronous relationship. Fauna of the Sylvania Formation suggested an association with the Middle Devonian Detroit River Group. The practice of including the Sylvania Formation within this group has continued to this day. The stratigraphy of the lower Middle Devonian was formalized by
Ehlers (1950). Fagerstrom (1967) places the Sylvania Formation within the Lower Eifelian.
The status of the Sylvania Formation has been the subject of dispute. Landes (1951) considered the Sylvania to be a member of the Amherstburg Formation, because of the perceived gradational nature of the upper contact. Sanford (1968), too, adopted this designation. However, the view of Ehlers (1950) has generally prevailed, regarding the Sylvania to have formational status within the Detroit River Group
(e.g., Fagerstrom 1966; Winder 1961; Hatfield et al. 1968; Lilenthal 1978).
Since the Sylvania Formation does not outcrop in Ontario, studies of the unit in Essex. County have been restricted to samples recovered from boreholes and borehole logs. Cole (1923) was the first to mention the unit but apparently confused it with many subsurface occurrences of other Devonian sandstones. Dyer (1931) reviewed existing borehole data in the Amherstburg area and the scant literature on the geochemistry of the Sylvania Formation. Caley (1945) and Sanford and Brady (1955) recognized
24 it as a clastic sequence distinguishable from the carbonates in the Detroit River Group. They showed the eastern limit of the sandstone to be about 16 km east of Amherstburg. However, Reavely and Winder
(1961) were the first to examine the Sylvania Formation of southwestern Ontario in any detail. They described the lower contact of the Sylvania Formation with the Bois Blanc Formation as sharp, but did not discuss further the nature of this contact (Landes (1951) and Reavely and Winder (1961) describe it as a disconformable contact). Reavely and Winder (1961) pointed out the analogous position of the
Sylvania Formation with the Oriskany and Columbus sandstones, which underlie the Bois Blanc and
Delaware (Dundee) formation carbonate units, respectively. They concluded from drilling records that the
Sylvania Formation thins northwards and postulated that the unit pinches out north of Amherstburg.
A regional stratigraphic analysis of the Detroit River Group in the Michigan Basin using oil well records was presented by Landes (1951). He produced an isopach map of the Sylvania Formation showing an elongate body trending northwest, with a maximum thickness of over 90 m. Briggs (1959) reviewed the stratigraphy, described the geological history and sedimentary framework and, using over 100 well logs, examined subsurface relationships of the lower Middle Devonian in the Michigan Basin. For purposes of his study, he divided the strata into 2 units: (a) the Bois Blanc and Sylvania formations; and
(b) the overlying remainder of the Detroit River Group.
Sanford (1968) synthesized data for the Devonian of the Michigan Basin in Michigan and Ontario.
He regarded the Sylvania Formation as a minor facies variation of the Amherstburg Formation. Brigham
(1971) used a computer-aided method to analyze many thousands of well records from southeastern
Michigan and southwestern Ontario. The resulting isopach map (Figure 11) was similar to that of Landes
(1951), showing the Sylvania Formation to be absent east of a line passing through east Windsor and
Colchester in Essex county.
25 Figure 11. Isopach map for Sylvania Formation, southeastern Michigan and southwestern Ontario, after
Brigham (1971).
26 An extensive study of Lower and Middle Devonian sandy units of the North American craton was made by Summerson and Swann (1970). Similar composition and other features were used to correlate many discontinuous sand bodies at or near the Kaskaskia erosion surface (late Early Devonian) across the area from southern Illinois to the Niagara Peninsula. They correlated the Sylvania Formation with sandstone lenses and sandy carbonate beds in the Ingersoll area.
In summary, the Sylvania Formation is an elongate, northwest trending, diachronous sandstone body of early Middle Devonian (early Eifelian) age forming the base of the Detroit River Group in southwestern Ontario, southeastern Michigan and northwestern Ohio. It disconformably overlies the Bois
Blanc Formation in southwestern Ontario and southeastern Michigan, and the Bass Islands Formation farther to the southwest, in Ohio. It is overlain by the carbonates of the Detroit River Group, usually with a gradational contact. Figure 12 summarizes these relationships.
The Sylvania Formation in Essex County
The bedrock geology of Essex County has been determined almost entirely by drilling (Telford and
Russell 1981). Because the Sylvania Formation does not outcrop in Ontario information regarding the lithic characteristics, geometry and distribution of the unit can only be derived from oil well records and samples. However, various problems arise when using well records for subsurface interpretation of the
Sylvania Formation. One of the major problems concerns the accurate determination of lithologic contacts, a problem, of course, not unique to the Sylvania Formation, but other factors complicate the situation in this case. First, the main sandstone bed varies in dolomite content from 0% to over 50%. Cross-sections presented by Sanford and Brady (1955) clearly show that significant changes in vertical variation of lithology occur from west to east. Descriptions of the unit in Ohio (Carman 1936) and Essex County
(Reavely and Winder 1961) state that the upper contact of the sandstone is gradational into the overlying
Detroit River Group dolostones. However, observations in this study of the sandstone in the Windsor area
27 Northern Ohio Essex Co. Southeastern Michigan Ontario
Bass Islands Formation
Figure 12. Diagrammatic view of relationships between the Bois Blanc Formation, Sylvania Formation and Detroit River Group.
28 reveal a sharp upper contact It is therefore possible that inconsistent interpretations of the upper contact of the unit have been made.
A second source of complication is similar to that described above, but potentially more drastic.
There is a zone of interbedded sandy and cherty dolostone beds at the base of the Sylvania Formation, apparently increasing in significance to the west. Some of the extremely rapid changes in elevation of the base of the unit may therefore be due to inconsistent placement of the lower contact of the Sylvania
Formation. As it is common stratigraphic practice to place a formation boundary at a point where significant changes in lithology occur (inferring significant changes in depositional conditions), it is proposed here that the base of the Sylvania Formation be placed at the first appearance of a dominantly sandy interval above the Bois Blanc or Bass Islands formations.
The third possibility of confusion is in mistaking the Springvale Member (Bois Blanc Formation) or Oriskany Formation sandstones for the Sylvania Formation sandstone. Descriptions of these units by
Cowan (1977) to the east of Essex County show that they are very similar in lithology, and potentially easily confused in well cuttings. Where the Sylvania Formation sandstone is absent, the contact between the Bois Blanc Formation and the Detroit River Group is very difficult to place. If this contact is missed, the first white sandstone encountered down the hole may be called the Sylvania Formation in error.
Subsurface data for this study have been derived primarily from drilling records and samples stored at the Petroleum Resources Laboratory in London, Ontario. Additional information was obtained from the records of the Canadian Salt Company, Windsor, and by drilling carried out for this study (drill logs presented in Appendix 1). Since exploration for hydrocarbons has been concentrated almost entirely in the southern part of Essex County, there is very little control on structure contours and isopachs in the northern part.
29 TOPOGRAPHY OF THE SUB-SYLVANIA FORMATION DEPOSITIONAL SURFACE
A structure contour of the base (of the upper, main sandstone interval) of the Sylvania Formation (Figure
13) indicates a dip to the north of about 8 m/km (0.5°). In the area of good control, there are significant irregularities superimposed on this pattern (not shown on diagram). In all probability, these occur throughout the area but are not revealed because of lack of data. Detailed interpretation of these irregular ities is unwarranted, given, as discussed above, the difficulties in picking the Sylvania-Bois Blanc formation contacts. However, they may reflect channelling into the erosion surface during the Middle
Devonian transgression, as postulated by Fagerstrom (1967). Assuming the sand was a nearshore deposit
(see discussion in Sedimentology section below) and Essex County was at the edge of the area of deposition, channelling into the Bois Blanc Formation would not have been unlikely. Closed depressions in the Bois Blanc Formation surface due to dissolution of underlying evaporites of the Salina Formation cannot be identified with confidence. However, the dome structure in the Guelph Formation which forms the Maiden Gas Pool (Sanford and Brady 1955), about 5 km southeast of Amherstburg, appears to continue into the Bois Blanc Formation. The relief of the dome on the Bois Blanc Formation upper surface is about 24 m.
THICKNESS OF THE SYLVANIA FORMATION SANDSTONE
Figure 14 shows the isopach map for the Sylvania Formation. In the Windsor area, the thickness of the upper sandy bed alone was used in constructing this map. If the total thickness of the Sylvania Formation in this area (up to 55 m) had been used (i.e., including the dolostone beds at the base, as discussed above), the resulting pattern in that area would have conflicted wildly with the broader regional picture (i.e., with maps produce by Brigham (1971), for example). This illustrates the need for a more comprehensive study of the stratigraphy of the Devonian sandstones in southwestern Ontario. The eastern edge of the unit approximates that determined by Brigham (1971). The edge is drawn as a smooth line, but in reality it is probably a complex zone of salients. The eastern edge of Sylvania Formation occurrence runs just west
30 Lakm J Sandwich site St. Clair
INSAL MAP \ /
\ Huron 1 V'^ .
V/^ ONTARIO \C
'•**• f \) ^ ~Y^C^ s / St (Mr/
1 ' s1^^ / \. CL—-^y u 3 A
• drill sites
Lake Erie
Figure 13. Structure contour of base (of the upper, main sandstone interval) of the Sylvania Formation,
Essex County based on data obtained from drilling records. Contours are shown with respect to sea level.
31 Figure 14. Isopach map of the Sylvania Formation (upper, main sandstone interval only), Essex County based on data obtained from drilling records.
32 of Colchester in the south (possibly controlled by a Bois Blanc Formation or Bass Islands Formation high), northward to a point 4 km east of McGregor in Colchester North Township. North of this point, control is absent The most northeasterly drill site gives a thickness of 17 m at the old Canadian Pacific Railway station in downtown Windsor. If the rate of thinning is uniform from west to east, the eastern edge of the sand probably lies somewhere between Windsor and Tecumseh.
The rate of thinning between the Detroit River and Colchester is about 2 m/km to the east. The thickness of the upper sandstone bed in the area underlying the Sandwich salt works varies considerably.
In one instance, it thins from 32 m to 21 m over a distance of about 300 m. The effect of the Maiden Gas
Field dome is also apparent the sandstone being thinner as it drapes over this positive feature.
Petrology of the Sylvania Formation
The lithology of the Sylvania sandstone is distinctive: "the sand rock is a remarkably pure, sparkling, snow white aggregation of incoherent quartz grains... Lumps of it may be crumbled in the hands" (Grabau and
Sherzer 1910, p.71). Although variation in lithology exists, involving varying amounts of dolomite cement, it is the quartz-rich zones which have attracted most attention. The purity of some sections of the unit is illustrated by analyses given by Dyer (1931), which show silica contents of over 98%. However, another analysis gave a silica content of 45%, indicating significant variation.
Carman (1936), working in northwestern Ohio, made the first detailed petrographic examination of the Sylvania sandstone, and noted the following features:
1. High purity, almost entirely quartz;
2. Grains are very rounded; maximum deviation from sphericity was a radii ratio of 3:2;
3. Grain surfaces are pitted or frosted;
33 4. Grains are very uniform in size (well sorted) at a given locality, however, a distinct
decrease in grain size from Michigan to Ohio was noted, with modes decreasing from
0.25 to 0.5 mm to 0.125 to 0.25 mm;
5. Many grains show secondary enlargement by optically continuous quartz overgrowths,
occasionally featuring doubly terminated crystals enclosing grains.
Information on minerals other than quartz is given by Enyert (1949) who studied the unit in both outcrop and the subsurface. Zircon and tourmaline were detected as detrital accessory minerals, and celestite, anhydrite, pyrite, anatase and fluorite, as authigenic accessories. The total amount of these minerals is very small. Dolomite contents ranged from 1 to 58% in the outcrop samples studied. Reavely and Winder
(1961) noted variations in colour from brownish grey to pure white in the Sylvania Formation sandstone in cores from Essex County. Their petrographic study showed the white sandstone to have less than 5% carbonate content and the grey up to 40%. They measured the maximum average grain diameter to be 0.4 mm (similar to that noted for the sandstone in Michigan) and observed the grains to be extremely well sorted and rounded. They reported up to 10% authigenic silica; a later diagenetic phase has calcite replacing silica.
Briggs (1959) observed the polished surfaces of previously frosted grains indicating the originally wind-transported quartz grains to have been modified by wave action. Petrographic analysis by Hatfield et al. (1968) determined the sandstone to be an orthoquartzite (or quartz arenite of Dott, 1964) and confirmed the finer grain size in Ohio, the mean grain size being close to 0.25 mm. Although a major part of their study involved measurements of sand grain orientation, these authors do not mention quartz overgrowths; cementation is supposedly up to 15% dolomite. They also observed polishing of previously frosted sand grains.
34 Stump (1980) examined vertically- and horizontally-oriented thin sections of the Sylvania
Formation sandstone. He observed a high degree of pressure solution and silica overgrowth with little carbonate cement. He estimated porosity to be about 10%.
Regional variation in the subsurface lithology of the Sylvania Formation sandstone in the Michigan
Basin is described by Gardner (1974). In general, lithology is similar to outcrop but there is a silty and cherty facies which is restricted to the northwestern of the depositional area.
Drilling and Sampling
Very little information is available concerning the detailed stratigraphy, lithology and engineering properties of the Sylvania Formation in the Windsor area. Therefore, a limited program of drilling and sampling was carried out at the sinkhole site and at the Canadian Rock Salt Company, 3.2 km south of the brine field. Three boreholes (Wl, W2, W3; see Figures 1 and 2 for location) were drilled using a triple tube NQ-3 core barrel, giving 45.2 mm diameter core. No samples of overburden were taken. Full lithological descriptions of the cores are given in Appendix 1. Generalized lithological logs are shown for all three boreholes in Figure 15.
The complete sequence of the Sylvania Formation was intersected in only 1 borehole, W3. At Wl, on the brine field site, the borehole was aborted at 79.2, about 61 m above the top of the Sylvania
Formation. Borehole W2, at the rock salt mine, was abandoned at 118 m, 12.5 m into the Sylvania
Formation, because the drill rods became stuck in the sandstone which was extremely soft and disaggregating easily. Borehole W3 is located 4.7 m east of W2 and provides a full section from rockhead
(22.6 m below ground level) to below the Sylvania Formation (total depth: 143.3 m), with virtually 100% recovery in the Detroit River Group carbonates, reducing to 91% in the pure silica facies of the Sylvania
Formation sandstone.
35 BOREHOLE W1 BOREHOLE W2 BOREHOLE W3
DESCRIPTION DEPTH DESCRIPTION DESCRIPTION m«tr«a
mo 29 57m. Glacial Drift Oto22.56m.Glacial Drift. 0 to 22.56m. CUoaJ drift, no aampWi
20 - 20 - 22.S6to33.76m Dotroit Rr*« Group DokKont. ftvmd brown 22 56 to 30 73m. Dttroit Ri««r Group DoioHona ortv buff and brown (odauinad).oooinflnaUvuu»4w** and nodular baddnd, f of to wry fma cryawUma
30 29 57 to 43 13m. Dttroii Rivar Group Lmmmom- fray and biuaaray 3073 to 35.13m. DatroitRivar Group Dotoatona: cryctauoM intarnui Foajuiftrout. n T and buff, fma to **ry fa
35 13 to 51.64m, DavntRitar Uro.mo.dK arav. buff and brown, with btrw pora. attar bracbopoda (33 53 to 34 Oumj • crwuta (J472 lithoaraphic. fraquandy to 3541«> and biaboy form toward* baar Umaaioa*. 41 40 u 56.77m. Drvoit Rim Croup 43.13to4707m.DatfoitRnarGrou» I, imaatoni: lNHWd«n uthouraohie 45.49 to 47.65m
145*0,49 99 to 412\m
50 48.23 to S«.92m. Dwai Rwar Group Liwiupi and d
56 92(oo«76m.O«rottRt*jrGroup DotoMMM W< dotenutw Immhvw 5* 77 to 63.20m. Dttroit Rjwtr Group and Mir f»a crytuUint, wit* rwy bah mtipAMM Rare buununoui ia»mnir»n
63.20 to 78 05m. Dttroit Rmr Group iimMton* uauauy laminated am buff 60.76(0 76,33m. DatrW Riaar Group OoWrtonaandd 6 78to7B2I>n.D»troitRiwOt>ur DotoatoM momh'Ununatad « and ahalv Umuva* (ma to w
'4 19m Lanunaa of ton o 68.86m t*uojy-> and 7] 3S to ?2 75m Imatru) Aocuiar oynaum ('
76,33 io 62.02m. DatroM Rwar Group Lmimmoiw' ueht any and aty 80 - oolitic and paolioc with tlucft bituminous parunaa, with buff, vary fma m bmatUM, with many anbury and branehina corals
82 02 to 87,07m. Datroic Rivar Group Doiowona: ar«yandba>wn id and lamiaatad with buununoui partinga. fin«
90
4 31 to 102.62m.Detroit RrvarGroup Dokmona- brawn and ouff try fina cryaulunt. with oypawn maam. no chart Calcua-unad vuo a-. oitomHAmm
6 02 to 114 43m. Synwua fm 114.66 to 117.04m. Sylvan* F 111 79m 117Q4to 117 35m.laa 114 43 to 125.02m. Sylvania Formation Sandaton* at 102.62 u
129.39 to 135 89m. SylwrnFonaatum. Dotaatona. mm bvcomuif pun, oraybhia ana am. fina cryauUina. vnth m and atylolitaa wary (in* oryuuluna to uthoaraphic at baaa, i
Dolostone Limestone [ | Sandstone
Figure 15. General lithological logs of Borehole Wl, W2 and W3. (See Figures 1 and 2 for location of
drill sites).
36 Litkology of Intervals Sampled
Wl
Borehole Wl is located about 9 m from the edge of the original sinkhole. The interval penetrated by Wl
(Figure 15, Appendix 1) consists of the carbonates of the Detroit River Group. Under the 29.6 m of glaciolacustrine clay, the first 21.3 m of bedrock is predominantly grey, buff-grey or blue-grey, very fine- to medium-crystalline limestone with some zones of high moldic porosity. From 50.9 m to the base of the hole at 78.46 m, there is an interval of brown and grey, mainly very fine-crystalline dolostone. Bituminous laminae, sulphates and moldic porosity occur in this dolostone at various levels. Although borehole Wl did not penetrate the Sylvania Formation, as intended, the fact that intact rock was encountered for the entire 78.46 m of the hole is significant. With precise knowledge of rockhead topography, a better limiting value can be approximated for the slope of the surface dividing intact rock from rubble.
W2, W3
The Detroit River Group interval intersected by boreholes W2 and W3 (see Figure 15) consists of a wide variety of dolostones. The basic rock type is a brown or buff-grey, fine- to very fine-crystalline dolostone; however, bituminous laminae, oil staining, moldic porosity, oolitic facies and chert nodules occur locally in this unit. These features are consistent between boreholes W2 and W3, but correlation with borehole
Wl is less definite.
A significant feature relating the 2 boreholes, W2 and W3, is the offset and apparent dip of the top of the sandstone and of distinctive units within the Sylvania Formation. The offset of the Sylvania
Formation's upper surface is 3.6 m over the 4.6 m separating the 2 holes, an apparent dip, therefore, of
38°. Stump (1980) analyzed stresses set up in the sandstone assuming that they act on a horizontal tabular body. The information from these 2 boreholes suggests, therefore, that this assumption may be a significant oversimplification.
37 Because borehole W3 intersects the entire Sylvania Formation interval and because borehole W2, which intersects only the upper half of the Sylvania Formation, has similar lithological characteristics and unit thicknesses as borehole W3, reference is made here to only borehole W3 for the following lithological and sedimentological descriptions.
Three cycles of upward decreasing carbonate content (Figure 16) are present in the dominantly sandy interval of the Sylvania Formation. The first cycle occurs near the base of the formation. The basal contact of the dolomitic quartz arenite of the Sylvania Formation, at 140.8 m below ground level, with the underlying cherty grey-blue dolostone of the Bois Blanc Formation is sharp. Just above the base there are significant occurrences of dark bands, which are typically 12 mm thick and richer in dolomite than the white, purer sandstone host. The frequency of these dark bands decreases upwards, until they become relatively rare at about 137.2 m level.
The lower sandstone bed is sharply overlain by a bed of grey-blue, cherty dolostone, 5.2 m thick.
The presence of this dolostone, which is similar to that of the Bois Blanc Formation, introduces the possibility that the lower sandstone bed may be, infact, the Springvale Formation sandstone. However, thin section examination (see below) rules this out. The dolostone bed becomes sandy at 130.4 and remains so until the 125 m level, which marks the base of the second upward decreasing carbonate cycle (see
Figure 16). The 2.4 m above this point are characterized by rapid alternations of quartz- and dolomite-rich bands, each typically 25 mm thick, causing recovery in thick discs. Above this, the typical slightly dolomitic quartz sandstone extends for over 9.1 m. Dolomite in this sandstone is concentrated in thin bands as in the lower sandstone bed, again decreasing in frequency upwards. Between 115.8 and 118.9 m core recovery in borehole W3 dropped to 60%. This zone corresponds stratigraphically with that at which W2 was aborted. There is clearly a zone of very poor quality rock at this depth.
38 PRESSURE SOLUTION MEAN (#U SORTING (#) SKEWNESS KURTOSIS ROUNDNESS MgCO, % VOID <%) INDEX («) i J t.« it n • J« «.>• a*• on • • it *.» • M •*• I.* II t» *• M • I* M 100-i 1 T—I—r- I—i—r i—i—r ~j—i—i—r n—i—i—i—r~ i—I—r i—r •2
110- •3
-4
z • 5 g 120- •e z •7 •a g 130 H
.9
140-H Ir •10 \ \
Figure 16. Petrography results (see Appendix 2 for descriptions) determined from thin section analysis, borehole W3. Location of samples
examined shown along litholog.
39 Between 112.8 and 114.3 m there is a markedly dolomitic zone, the rock type becoming a dirty grey, highly dolomitic quartz sandstone or very sandy dolostone. This marks the base of the third cycle of upward decreasing carbonate content (see Figure 16). It is overlain by a zone of interbedded dolomite-rich and dolomite-poor quartz arenite, the frequency of dolomite-rich bands decreasing upwards.
In the zones characterised by interbedded dolomite-rich layers, some sedimentary structures are visible. Typically, the dark bands are distorted into U-shaped convolutions, or exhibit low angle dips of the order of 5°. These dips are restricted tosingle dark laminations. No unequivocal examples of ripple cross-laminations were observed, but this may be due to the small diameter core samples. A small scale feature associated with the dark bands appears to be the result of vigorous syn- or post-depositional disturbance of the bands, giving small 3 to 6 mm diameter mottlings of darker material enveloped by the usual sandstone. Heinrich (1979) shows photographs of burrows in the Sylvania Formation sandstone quarried at Rockwood, Michigan. None of the features in the drill core resemble those burrows. It is prob able, however, that the mottling is related to biogenic activity of some type since the mottles are richer in dolomite than the surrounding sand, similar to the burrows described by Heinrich (1979). The angle of cross-bedding recorded by Heinrich in the Rockwood Quarry (up to 30°) is significantly higher than any similar feature observed in the Windsor drill holes. The differences between the sedimentary structures at the 2 sites demonstrates the futility of attempting detailed environmental reconstruction for the Sylvania
Formation from the data obtained in this study alone. A complete sedimentological study of the formation is outside the scope of this project.
Petrography: Purpose and Methods
The texture of sandstones, specifically th degree and type of grain interaction, control the physical properties of quartz-rich rocks (Fahy and Guccione 1979). From hand specimen inspection, 2 types of
40 quartz arenite were identified in the Sylvania Formation with continuous variation between them: (a) dolomite-rich, the carbonate presumably acting as a cement; and (b) dolomite-poor, the sandstone presumably owing its coherence to direct interaction of the quartz grains. Stump (1980) showed that adjacent quartz grains were frequently intergrown and concluded that this resulted in the explosive failure and generation of running sand during compressive strength tests. Hatfield et al. (1968) observed dolomite contents of 4 to 15% cementing Sylvania Formation sandstone in Ohio. A study of the petrography of the
Sylvania Formation at Windsor was carried out primarily to identify lithologic controls over the physical properties of the sandstone and also to aid in the interpretation of the depositions conditions and diagenetic processes which formed this unit.
Thin sections of samples representative of all the sandstone intervals and relevant carbonate units identified in boreholes W2 and W3 (see Figure 15) were studied. Both vertically- and horizontally-oriented thin sections were made, but the former were generally used for detailed description so that a full inspection of the dolomitic laminations could be made. No differences in any of the grain size parameters were observed for the horizontally oriented sections. Mineralogical composition and porosity were determined by point counts of 300 grains or voids. Grain size parameters (i.e., mean, sorting, skewness, kurtosis) were determined by visual measurement of the first 100 quartz grains counted, using a calibrated eyepiece. The data generated in this manner was plotted on probability graph paper and parameters used to describe grain size distribution were converted to equivalent sieve data by the regression technique of
Friedman (1958). Elongation was measured on the first 20 grains. Roundness was estimated visually on the measured grains. To quantify the extent of intergrown quartz grain boundaries, an estimate was made of the proportion of the perimeter of the measured grains that was in direct linear contact with another quartz grain.
41 Petrography: Results
Since the properties of the sandstone of the Sylvania Formation were considered to be of importance and
relevence to this study, detailed observations of the highly dolomitic intervals were not made. Sample locations an the quantitative results of the thin section analyses are shown in Figure 16. Detailed petrographic descriptions are given in Appendix 2. The point count-derived dolomite content reflects, to
some degree, the cyclical nature of the Sylvania Formation sandstone. The cyclicity, as defined in previously, is based on the frequency of dolomitic bands. Dolomite contents of single samples from 1 point in a zone of higher or lower dolomitic layer frequency will not reliably reflect this frequency. Thus, sample #5 at 117.3 m although from a zone of low dolomite layer frequency, clearly intersected a dolomitic horizon, giving a high dolomite content.
The grain size parameters shown in Figure 16 refer only to detrital components of the sandstone; therefore, to use these parameters alone (and ignoring the presence of dolomite cement) to interpret the hydrodynamic conditions of sedimentation is probably erroneous. There is good evidence that the quartz grains were deposited at the same time as the carbonate material. Firstly, quartz grains are frequently seen floating in a matrix of dolomite. Secondly, the change from dolomite-poor to dolomite-rich bands in samples #3, 5 and 7 (at 110.3, 117.0 and 123.1 m, respectively) is gradual. Thirdly, there is evidence in sample #8 at 125.9 m for "primary carbonate grains" (homocrystalline grains showing some abrasion and usually of the same size as accompanying quartz grains (Sabins 1962)). Dolomite occurs primarily in rhombohedral form, typically 0.03 mm across. According to Folk (1968), the occurrence of dolomite in this form indicates replacement of primary calcite by dolomite. This primary carbonate may have been of similar size to the quartz grains, as noted in one sample (#8, at 125.9 m), but very little other indication, (i.e., "ghost" structures) of the primary carbonate grain size is discernible. It is quite likely that the carbonate was in the form of calcite mud or micrite. Thus, to treat the dolomitic quartz arenite as a well sorted sandstone (as the figures in Figure 16 show), cemented by secondary dolomite, may be
42 erroneous. If the dolomite were silt or clay size, then the dolomitic bands would be extremely bimodal, fine-skewed and poorly sorted. This concept is supported by the correspondence between increased dolomite content and poorer sorting of the quartz grains in the lower 2 cycles. However, in the uppermost cycle, the size distribution is fine-skewed and platykurtic (i.e., flatter grain size distribution) suggesting that quartz grains from another source may be present. Thus, the correspondence noted in the lower cycles does not exist.
The following statements apply to the quartz grains alone. The quartz fraction of the Sylvania
Formation ranges from very fine- to medium-grained sand. It is moderately to well sorted, with the sorting being better in the lower part of the unit. In this lower part the size distribution is nearly symmetrical
(skewness values of about 0). In the upper part, however, the distribution is bimodal (causing skewness values of above +0.15) and platykurtic (kurtosis values of less than 1.0). Grain shape of the quartz particles does not vary significantly throughout the unit. All samples, except for the sandy dolostone of sample #8 at 125.9 m which has subangular grains, have mean rounding of between 3 and 4 and fall in the subrounded range. Elongation ranges from subequant to subelongate, with no systematic variation with depth being apparent.
The parameter describing the degree of quartz-quartz interlocking sutured boundaries (whether by mutural interference of overgrowths or by pressure solution along grain contacts), PSI, varies inversely with dolomite content (see Figure 16). As with the dolomite-sorting relationship, this relationship (lower
PSI values with increasing dolomite content) does not hold in the uppermost cycle. This may be due to the greater number of fine quartz grains relative to the majority of grains (reflected in its fine-skewed size distribution). Since the surface area of contacts between adjacent grains will increase, the stress at each point will decrease, reducing the driving force for pressure solution.
43 The character of the sutured boundaries varies significantly. In the upper 2 cycles, clear evidence of quartz overgrowth (i.e., vacuoles, or "dust rims", defining the original grain shape) is extremely rare.
However, careful examination reveals that very small quartz crystal terminations in void spaces bounded on one side by a quartz grain are common. In many cases the neighbouring quartz-quartz contact is heavily intergrown. This is regarded as immediate reprecipitation of silica dissolved at a contact point in a nearby void (Siever 1962). Such overgrowths that were defined by a line of vacuoles may have been inherited from the source rock, since thin, obviously heavily abraded, overgrowths were seen on grains floating in the dolostone immediately above the sandstone. The major cause of quartz contact suturing in the 2 upper cycles would appear, at this level of investigation, to be due to pressure solution (Figure 17) rather than overgrowth interference. Since some overgrowths, albeit a very small number, have been observed, it may be that all suturing is due to precipitated quartz which has not completely filled the surrounding voids (Sippel 1968). Further work using cathodoluminescence is required to determine unequivocally the nature of the suturing in the upper 2 cycles. Also present in this interval is evidence for carbonate replacement of quartz, but determining the exact timing of this process relative to silica mobility is not possible.
In the lowermost cycle, quartz overgrowths are beautifully clear (Figure 18), separated from the original rounded grains by a layer of vacuoles. Distinct crystal terminations give some originally elliptical, rounded quartz grains the external morphology of quartz crystals. However, single examples of crystal terminations on 1 grain with another contact appearing to be due to pressure solution is more common.
Grains with no evidence of overgrowth are also present. The degree of quartz overgrowth decreases in the lower part of the lower sandstone bed probably because of higher initial carbonate content inhibiting quartz grain-to-grain contacts. This would limit the amount of dissolved silica generated.
44 Figure 17. Photomicrograph showing intergrowth of quartz grains.
45 Figure 18. Photomicrograph showing well defined quartz overgrowths. Note the "dust rims" outling the original shape of quartz grains.
46 Sedimentology
Sedimentological analysis of the Sylvania Formation has been aided by observations of the limited outcrops in Michigan and Ohio. Early workers observed large-scale cross-bedding and, supported by the presence of frosted grain surfaces, concluded that the Sylvania Formation sandstone was eolian in origin
(Grabau and Sherzer 1909). However, the collection of many marine fossils and more detailed observations of the sedimentary structures suggested to others (e.g., Carman 1936; Briggs 1959) that the unit consists of originally wind-transported grains which were subsequently reworked in a shallow marine, more specifically a beach, environment Gardner (1974) lists the following as evidence of a marine depositional environment for the sandstone: 1) facies gradation between the Sylvania Formation sandstone and the overlying fossiliferous carbonates of the Amherstburg Formation; 2) interbedding of the two rock types; and 3) brachiopods occurring "intact, as if buried by a sudden shift of beach and bar deposition".
The beach environment hypothesis was supported by Hatfield et al. (1968), who associated it with a southward marine transgression. They summarize the evidence for this view as follows:
1. The Sylvania Formation sandstone rests unconformably on both Silurian and Devonian
rocks and was thus the initial deposit of a transgressing sea;
2. The strata it overlies are progressively older toward the south;
3. To the south, stratigraphically higher units of the Detroit River Group are the lateral
equivalents of the Sylvania Formation;
4. The distinctive petrology of the unit: well rounded, very well sorted, orthoquartzite with
frosted and polished, fine- to medium-grained quartz sand.
From outcrop sections examined in their study area (Michigan and Ohio), Hatfield et al. (1968) determined that the beach was probably aligned northeast, with a local source for the sand from the southeast
47 In their synthesis of well data Briggs (1959) and Gardner (1974) differ slightly in their conclusions regarding the depositional environment of the Sylvania Formation sandstone. According to Briggs, the sand was laid down on the beach of a transgressive sea that successively deposited sediments of the Bois
Blanc, Amherstburg and Lucas formations. Gardner, however, states that "because the sandstone generally overlies the Bois Blanc Formation in the basin, it represents, in part, a regressive phase within the overall transgression...". That the latter was his actual meaning is suggested by Briggs' diagrammatic representation of the evolution of the Michigan basin in early Middle Devonian times (Figure 19). From this it appears that the shoreline orientation in Essex County was north-northeast perhaps controlled by the Findlay Arch (Hatfield et al. 1968).
Landes (1951) disagrees with the beach depositional environment (particularly the role of ocean currents acting along the beach) proposed for the Sylvania Formation sandstone. He argues against the accumulation of the sediment as beaches and bars on the grounds of: (a) the large size of the deposit (402 km by 120 km and reaching a maximum thickness in Michigan of about 91 m); (b) isolation from source of supply; and (c) lack of finer grain sizes. He suggests that the sand was derived from weathering of
Cambrian and Lower Ordovician sandstones to the west, transported by prevailing westerly winds and fell directly into the early Amherstburg sea.
But these arguments are discounted by later workers. A "persistent shoreline environment along a shelf hingebelt", perhaps controlled by basement features reflected by the mid-Michigan gravity-magnetic high, is postulated by Gardner (1974) to explain the size, thickness, and distribution of the Sylvania
Formation sandstone. That the Sylvania Formation sandstone may represent marine reworking of an eolian deposit answers the second and third objections of Landes. Abundant evidence of the relatively shallow water origin of the deposit is given by Heinrich (1979) including widespread burrowing, low angle cross- bedding and features commonly associated with rapid deposition.
48 — ~" — 2 - ' — -• •" VRI; boreal.seavvay ,*
- / • . / • _
~-/±L - fir' ->:tt»':-^/.:'.T--ii? ^ / SUNC'SEAl 111- f BOIS •2 i \ : \ ; »\ 1 1 J » _ 1 1 "t. 11 •'»! ' "W '
~zSTONONDAGA - J..-^? SEA • I
A B
71/1
1 Saginaw
•' h-M Inlet AMHERSTBURG ^>?? > MICHIGAN •"^ / evapor/te , •R.R / SEA?'' r'"\ '^Mj basin {_/
"?Wf\ LUCAS SEA
carbonate deposition 'Sz^y-
Benson Harbor Inlet
"1 ~ ^^vonia I 5aN4.S-~ -"V^i Columbus "~ ** Co/umbus
" ~~'•^-f-r Sea • "••fi Sea
Figure 19. Paleogeographic reconstruction of the Michigan Basin during the deposition of the Bois Blanc
Formation, Sylvania Formation sandstone and carbonates of the Detroit River Group during the early
Middle Devonian. From Briggs (1959).
49 The source of sand grains in the Devonian strata of central North America was investigated by
Potter and Pryor (1961) and Summerson and Swann (1970). The quartz grains have similar size, shape,
surface characteristics and inclusions as the Cambro-Ordovician St. Peters Sandstone of the Ozark Dome
and Wisconsin area and were probably derived from the erosion of this and other Paleozoic rocks from
this area. The multicyclic nature of the sands accounts for its extreme purity and rounding. Summerson
and Swann (1970) suggest that the sand was concentrated on the western side of the Findlay and
Cincinnati arches and was reworked by subsequent transgressions. The exact nature of the depositional
processes may never be definitely established due to the inability to determine the exact 3 dimensional
geometry of and lithological variations within the sand body. Also, the diagenetic history of the sediment
must be unravelled to enable interpretation of the origin and original grain size of the dolomite cementing parts of the quartz sandstone. If the carbonate originated as micrite, then the conditions of deposition may have been quite different from those generally proposed.
Engineering Properties
Very little quantitative information is available concerning the geotechnical properties of the Sylvania
Formation sandstone. Stump (1980) determined that a zone about 10.7 m below the top contact has very low strength, a high Poisson's ratio and exhibits explosive compressive failure, generating loose sand.
However, few samples were tested by Stump and properties of the associated carbonates were not determined. Testing carried out in this present study was designed to provide a detailed profile of strength and deformation properties of the sandstone, thereby enabling a more exact delineation of zones significant in the subsidence mechanism. The data also provide general information on the behaviour of this type of sandstone.
50 Test Methods
Three series of tests were performed on samples of the Sylvania Formation sandstone: unconfined compressive strength tests, point load tests and triaxial compression tests. The work was done at the
Department of Earth Sciences, University of Waterloo, under the supervision of Dr. J.E. Gale. For labelling purposes, the borehole cores were divided into units of about 30 cm (1 foot) and were labelled according to the nearest footage (e.g., a core sample from 445'2" to 446'3" was labelled as 445-446).
Sections of core were selected from the lower parts of boreholes W2 and W3, concentrating on the sandstone, but including samples of the dolostones.
For the unconfined compressive strength tests, samples were cut and their ends ground to conditions as close as possible to those specified by the International Society for Rock Mechanics
(Anonymous 1979) for uniaxial testing. Because of the friable nature of some samples the conditions were less than ideal in these cases. Strain gauges were cemented to the surface of the cores using epoxy resin.
Cores were tested in a 375 tonne loading press with a Viceroy activator and three 200 000 lb (91 tonnes)
BLH load cells, controlled by MTS hydraulic and servo control units. Output was recorded both manually and on an x-y plotter. Strain rates were such that failure occurred after about 10 minutes test duration.
Typically, these rates were 4 x 104 mm/sec. Unconfined compressive strengths (Cp) were normalized using the length of samples according to the formula of Obert and Duvall (1967):
0.78+0.22D/L
where Co = normalized compressive strength, D = diameter, L = length of sample. Poisson's ratio (v) and Young's Modulus (E) values are calculated from stress-strain curves at 50% of the ultimate strength
(Cp). Some samples exhibited erratic strain behaviour, probably due to the sensitivity of strain gauges to
51 localized strain events (e.g., a single sand grain popping out); Poisson's ratio were not determined in these cases. Tangential and secant Young's Moduli were calculated for all samples.
Point load testing (which indirectly measures tensile strength) was carried out according to the method of Broch and Franklin (1972). The aim of this series of tests was: (a) to determine strength parameters for zones where poor core recovery prevented unconfined compression testing; (b) to gain an impression of any anisotropy in shear strength of the sandstone; and (c) to examine the variability in strength of the sandstone over a short vertical range (i.e., within samples). Most of the tests were performed loading the core diametrically (loaded parallel to bedding) with fewer samples loaded axially.
The point load index calculated for each sample was normalized using the sample length.
Triaxial compression testing was performed using the same press as for the unconfined series but incorporating-a triaxial cell. Confining stresses used were 3.98, 7.80, 11.69 and 15.58 M?a simulating insitu stresses.
Results
The results of the three series of tests are tabulated in Appendix 3 and summarized in Figures 20 and 21 to 22.
UNCONFINED COMPRESSION TEST DATA
The unconfined compressive strength of the samples tested (see Figure 20) ranged from very low to high
(according to the classification of Deere, 1968). The overall pattern of variation in strength in samples from W3 shows that there are 3 weak zones enclosed by stronger layers. These zones correspond, to some degree, with tops of the three stratigraphic (upward decreasing carbonate) cycles described earlier.
However, there are some significant diversions from the pattern anticipated from visual inspection of the
52 UNCONFINED COMPRESSIVE STRENGTH (MPa)
Figure 20. Unconfined compressive strengths for samples from W2, W3. Inter grown, concave • convex contacts Straight - edge contacts
failure by failure by sliding rotation of grains along planar contacts
resistance to shear « tensile strength resistance to shear, r = c + a tan tf> of qtz-qtz contact / cohesion of qtz-qtz contact angle of friction of qtz
Figure 21. Cartoon showing control of different grain/overgrowth boundary types on strength.
54 YOUNG'S MODULUS (GPA) POISSON'S RATIO
0 2 4 6 8 10 12 14 16 18 20 CI 0.2 0.4 0.6 0.8 100-N I I I 1 1 1 I I I I | I I 1 1 • • • • • • A • A 110- • • • • • • • m • O> % 120- • E • • • A
Z • •• fc • A ai • • °130- • • • • A • • A A 140- • • A • • •
Figure 22. Young's Moduli and Poisson's ratios for samples from W2, W3. core.
The associated carbonate rocks generally have strengths of about 100 MPa. An exception to this is the dolostone directly underlying the base of the Sylvania Formation sandstone (sample 462-463, at about 141 m) which has a strength of 62 MPa. This relatively low strength may be due to the presence of large amounts of porous chert. In general, however, the dolostones can be characterized as strong units.
There is a broad trend of increasing strength with depth in each stratigraphic cycle. This is most pronounced in the middle cycle where strength increases from under 10 MPa to over 100 MPa in less than
6 m. The trend is not seen, however, in the lower cycle, where the topmost sample has the highest strength of all in that cycle (see Figure 20). Thin sections of samples from this zone showed the most quartz overgrowth-affected grain boundaries and the highest percentage of sutured contacts of all samples inspected. Thus, it would appear that straight edge quartz-quartz overgrowth contacts may result in relatively high strengths whereas curved contacts, caused by pressure solution along grain boundaries probably result in lower strengths. Fahy and Guccione (1979) observed a significant positive correlation between strength and "percent straight contacts" in test results for a Utah sandstone. In contrast, a significant negative correlation exists between strength and "percent intergrown contacts" for the same sandstone. There therefore appears to be a correlation between grain/overgrowth boundary type and strength but further work is required to evaluate the exact relationship. The overgrowth-generated straight contacts appear to generate a fabric which constrains failure surfaces to traverse intact grains or, more likely, to be along flat contact surfaces which provide frictional resistance. Concave-convex boundaries, on the other hand, cause relative rotation of the grains, permitting failure planes to propagate between grains (see Figure 21). Although the Poisson's ratios are not totally reliable, the contrast in values of this parameter in the lower stratigraphic cycle confirms this hypothesis (Appendix 3). In general, since most of the quartz-quartz contacts are of the concave-convex type strengths of high purity sandstone (displaying
56 this intact to condensed framework relationship) are low. The rotation of grains causes high Poisson's ratios (see below) and, in turn, mass disaggregation of the rock, generating large volumes of loose sand.
The position of the main zone of low strength in W3 can be correlated with other features. It corresponds with the horizon at which W2 was aborted due to caving and clogging of the bit Also, the weakest zone detected by Stump (1980), 10.7 m from the top of the 30.5 m thick unit at the Michigan location sampled) is equivalent to the position of the weakest rock at Windsor. Intervals at 103.6 to 105.2 m, 106.7 to 109.7 m, and 137.2 to 138.7 m in W3 also have very low or low strength. Most of the samples from these depths exhibit explosive failure. It is likely, therefore, that there is not a single zone of loose sand generation but 4, sandwiched between units with more conventional failure characteristics.
These units may contain the failed sandstone until undermined whereupon the sand may flow out unhindered.
The limited strength data for the upper part of the sandstone sampled at W2 do not allow detailed interpretation. There is a slight rise in strength at the base of this sampled interval.
The Young's Moduli calculated from the stress-strain curves (Appendix 3, see Figure 22) reflect the variation in strength from sample to sample. Values of tangential modulus, Et, range from 1.56 GPa to 13.46 GPa. Poisson's ratios, for those samples for which measurement of this parameter was possible at 50% of failure stress, are also plotted in Figure 22. Most samples have a Poisson's ratio of less than
0.3, which is typical for sandstones. However* some have ratios of over 0.4, and these samples have a greater tendency to produce free sand (e.g., W3 344-345; Poisson's ratio = 0.86, 40 to 50% of sample reduced to sand). Among the samples for which calculation of the ratio proved difficult, W3 340-341 provides an example of the complications (Figure 23). The axial stress-strain curve appears normal. How ever, Poisson's ratios increase markedly according to stress level. In other cases, popping of sand grains
57 22
20
60% OF PEAK STRESS 18
^ 16 • 0. 2 A'
CO 14 CO IU AC r- CO 33.3% OF PEAK STRESS 12 < < b~ 10
A' 25% OF PEAK STRESS '
W3 340-341
0.5 1.5 2.5
£,%STRAIN (xlO*-3.)
Figure 23. Stress-strain curves for sample W3 340-341.
58 and poor strain gauge bonding caused difficulties. However, this example shows the effect of the prefailure
rotational motion of sand grains, which causes the eventual mode of failure.
POINT LOAD TEST DATA
Data provided by point load testing is tabulated in Appendix 3 and shown in Figure 24. It confirms trends
shown by unconfined compressive strength and provides strength data for intervals recovered in core
lengths that were too short for more involved testing. The interval between 122.5 and 125 m was
recovered in thin discs, giving a Rock Quality Designation (R.Q.D.) of zero. This is reflected in low point
load strengths. However, the low strength of these samples is caused by fine laminations of alternating
dolomite-rich and dolomite-poor sandstones presenting small planes of weakness. Generation of loose sand
is not likely in this zone. Axial and diametral testing of cores by the point load method is not a precise method of determining strength anisotropy since the different attitudes of the cylinder to the
applied load generate slightly different stress magnitudes at the points. However, in 85% of the cases
strengths measured axially were appreciably higher than those determined diametrically. If, as seems likely, high horizontal stresses exist in the bedrock of the Windsor area, the operational limiting strength for the Sylvania Formation sandstone may be significantly lower than that determined by testing vertically oriented cores.
Since there were relatively few replicates of point load tests only a general statement concerning variability within samples can be made. Over three-quarters of the samples which had been tested more than once had ranges of strength of more than 40% of the mean strength (i.e., ± 20% of the mean). The samples with large ranges were those of low strength where operator and machine error have a proportionately greater effect.
59 POINT LOAD INDEX ( megapascals ) 2 3 4 5 6 100 J I I L • • LEGEND • • •i AXIAL TEST • 110-| . D • • • DIAMETRAL TEST • • • •
CO i • J © 120 E z |8 % • »- CL • • LU O - • 130-
140-
Figure 24. Point Load Index results for samples from W3.
60 TRIAXIAL COMPRESSION TEST DATA
The Sylvania Formation sandstone probably fails in an unconfined state in the manner described above.
Nevertheless, to determine the full range of strength parametres for the unit, a series of triaxial
compression tests were carried out. A typical value of unconfined strength was also used to delineate the
failure envelope at zero confining stress. The data are tabulated, Mohr's circles plotted and failure
envelope drawn in Figure 25. The envelope is based on tests 1, 2, 3 and the unconfined test. A cohesion
of 6.2 MPa and angle of friction ranging from 60° at o3 =0 MPa to 45° at a3 = 20 MPa best fits the data.
Summary
The poor and rather unique engineering properties of the Sylvania Formation sandstone have been
confirmed by this study. The more extensive testing described here has shown that the system is more complex than that determined by Stump (1980). There are at least 3 zones liable to produce loose sand upon unconfined compressive failure. These zones are separated by more robust units which, although still of rather low strength, will fail in a more conventional fashion. The failure strains are similar for all
Sylvania Formation sandstone rock types (Appendix 3). Therefore, assuming initial failure to be due to subsidence over the salt workings, all units would fail when the same level of deformation had occurred.
This would occur sequentially, as support for one unit after another disappeared. The method of failure, however, would vary according to rock type: the carbonate units would produce extra fractures or, in extreme cases, rubble; whereas the sandstone units would be reduced to sand grains which would then escape, via cracks, in the underlying carbonate (failed) units to lower levels.
THE OPERATIONAL HISTORY OF THE SANDWICH BRINE FIELD
Salt was produced from the Sandwich site for over 50 years using a number of techniques and at varying rates. The 1954 collapse was caused by the interaction of past and current extraction processes as well as
61 120 Test no.
100 R—
80
(MPa) MOHR-COULOMB FAILURE CRITERIA 60
40
20 h-
120 140 160 180 P = — (MPa)
Figure 25. Mohr's circles for triaxial tests on samples from W3.
62 the geological conditions. To analyze the cause of sinkhole formation an examination of the production history at the site is necessary.
According to Cole (1915) the Canadian Salt Company (CSC) was incorporated in 1901 and built a processing plant at Sandwich in 1911. Piper (1954) states that the Saginaw Salt and Lumber Company produced salt from wells of unknown location in the Sandwich area until 1909. CSC then took over these operations. Information concerning operations in the first 2 decades of salt manufacture at the site is not clear as to whether new wells were drilled or previously existing wells were used. Records of CSC suggest the latter.
The stratigraphy underlying the Sandwich site is shown in Figure 26. There are three main salt beds, at 427 to 488, 366 to 372, and 314 to 341 m below the surface. These are known as the Lower,
Middle and Upper Salts and are ascribed to the B, D and F units, respectively, of the Salina Formation.
The first few wells extracted brine mainly from the D and F Salts. The remaining wells were directed at the B Salt but it is likely that considerable quantities of salt were also extracted from the overlying salt horizons due to leakage of water through faulty packers.
The following history of production is derived from study of CSC records which consist of a collation of well records made in 1946 followed by monthly reports up to the collapse in early 1954.
Recorded in the reports are descriptions of repairs to well casings made necessary by rockfalls and corrosion. Production volumes are also recorded. The wells had a finite life span controlled by the extent of rockfalls experienced. When it became uneconomical to re-drill and repair a well it was plugged. Thus, in effect, a data point was lost; only 3 wells were operating on the site at the time of collapse. A great deal of extrapolation is therefore involved in the interpretation of the brine cavern development process from these records.
63 METRES
0- Glacial Deposits Quaternary
Detroit River Group 100 Devonian
Sylvania Formation
200 Bois Blanc Formation
Bass Islands Formation
300
Silurian Units of Salina Formation BSE 400-
B
500-
Figure 26. Stratigraphy of Sandwich brine field.
64 The development of the Sandwich brine field from 1902 to 1954 is summarized in Figure 27. As production proceeded, the character of the brine field changed as did the type of well used to extract the brine. This evolution is best exemplified by the well history of well number 4. Drilled in 1921, the well encountered what was thought to be natural solution cavities in the F Salt. These may have been caused by leaching of salt at that level by fluids injected through other wells. However, company records state unequivocally that no connections existed between well 4 and the earlier wells.
The base of well 4 was at 488 m. It was cased to 349 m, just above the D Salt. It was operated as a water forcing well until 1935. In this system, water is injected down the casing annulus between casing and a central pipe. It dissolves salt and becomes denser as the saturation level increases, and sinks to the base of the well. If the solution cavity is pressure-tight, the brine is forced by the incoming fresh water through the smaller diameter pipe in the centre of the well to the surface. The cavity so formed tends to be of the so-called "morning glory" shape because the injected water is lighter than the brine, so it tends to move horizontally across the salt roof until it has dissolved some salt and increased in density, whereupon it moves downwards (Saberian 1977; Ege 1979; Figure 28). Because the first salt encountered by water injected down the casing of well 4 was the D Salt, this was preferentially dissolved leaving the
B Salt intact. This process caused rapid undermining of the overlying E unit (primarily dolostone) causing rockfalls which damaged the casing and tubing, thus interrupting production. To stop this process the casing was lowered in 1929, to 384 m (i.e., below the D Salt).
Single water force well operation continued until 1935 with occasional rockfalls occurring at the
D Salt level. Presumably, the packers securing the casing were leaky so that they allowed unsaturated brine access to the D Salt. During this period many other wells had been drilled nearby. In My 1935 it was discovered that well 4 was connected with one of these wells (number 17). The connection may have been through the thin D Salt or at the top of the B Salt because of the morning glory shape of the cavity.
65 1902 1910 1915 1920 1925 1930 1935 1940 1945 1950 1954 I I I I I I I I I I I
3 — 4 •••••••••••••••••••••••••••••••••• • • • •
6 —— 7 •••^•••i • • • 8 9 < WELL NUMBER 10 11 • 12- 13" LEGEND n 15 Water forcing well j7 ».»»...... Deep pump well 18 Air lift well 19——————— 20 Not completed Water injection well 21 22 »
Figure 27. Well histories for Sandwich brine field, 1902-1954.
66 BRINE OUT WATER IN
TOP INJECTION :=
'iinriiMTiiiiiiiriiifiT \
SALT
fi /111111 ii I
Figure 28. Single well injection method of brine extraction and resulting "mornign glory" cavity (modified from Quiero 1977).
67 This interconnection was symptomatic of a widespread episode of well connections in the mid-1930's.
Since individual well cavities were not pressure-tight, new methods of brine recovery were required.
From 1935 to 1940, well 4 was available for use as an air-lift well although it is not possible to say if it was used in this mode. In this system, air, introduced into the central tubing, lifted the dense brine to the surface. This method, not widely used at Sandwich, was abandoned in 1940.
By the early 1940s a large cavity or gallery had been formed (the "general cavity" or "main gallery" of company records and this report), connecting all of the wells on the main site. A system of water injection down 1 well and brine pumping from others was instituted. Thus, well 4 was used to inject water into the general cavity from 1940 to 1942. In 1942 it was converted to a deep well pump in which a submersible pump was placed in the well just below the static brine level. Brine was pumped from the base of the cavity through the tubing to the surface. In 1948 and 1949 there was considerable damage to the well from rockfalls and it was plugged in 1950.
The progression from single water force well to water injection or deep pump well to plugging is typical for wells 1 to 16. Wells 17, 18 and 21 were drilled for deep pump well pumps, well 19 as an injection point. Figures 29 and 30 show the locations and development of the wells of the main brine field from 1920 to 1954. It must be emphasized that the term "general cavity" does not imply an extensive uninterrupted cavern, but a zone of generally interconnected wells from which brine could be pumped.
This brine had originated from water injected in a number of other wells.
Well 4 produced 484 000 tons of salt as brine until 1946 and probably very little after this.
Unfortunately, this figure cannot be used as a basis for calculation of cavern size. Production in the first
7 years was divided between the B and D Salts, probably concentrated in the latter, but to an unknown
68 LEGEND
Active Plugged Water force, single well _|_
Air lift
Water injection —^
Deep well
;ure 29a. Plan view of Sandwich site showing development of brine field, 1920. Figure 29b. Plan view of Sandwich site showing development of brine field, 1925-1930.
70
72 DETROIT RIVER
Figure 30. Extent of interconnections in salt beds at various time intervals, 1925-1954.
73 extent. After its conversion to a deep pump well, the well extracted brine which had been produced elsewhere, presumably closer to the injection point, since fresh water is almost totally unsaturated.
Company records clearly show that a large excess of water was injected over the volume of retrieved brine. Factors of from 2 to 6 times the brine pumping rate are quoted for water injection. The excess water presumably leaked to other levels or formed brine of variable saturation, creating a larger cavern than would be interpreted from calculations using salt production figures. To extrapolate the figure of 484 000 tons into a morning glory-shaped cavern in the B Salt with a height of 61 m and of a certain radius, centered around well 4 would, therefore, be utterly misleading. Quantitative conclusions concerning cavern development and lengths of unsupported spans must therefore be kept at a very general level.
The well records enable the determination of the location of rockfalls in 3 dimensions. These data are only available in wells which were active or being drilled at the time of a rockfall. However, the following summary of the history of well repairs shows a broad trend which culminated in the rockfall of February 1954. A. Robinson (personal communication) believes that much of the work performed at the 427 m level was of dubious necessity. The repairs reported at higher levels are more reliable indicators of damage and are in fact more relevant to the problem than the deeper events.
1902-1925 Figure 31 is a sketch map of the Sandwich site showing the location of each well and depiction of repairs performed on each well. It is clear that solution was widespread at the D-Salt level since most rockfalls were at the 1200 to 1250-foot (366 to 381 m) levels. By 1920, wells 1 and 3 had connected necessitating the use of an air lift at well 3 and eventual abandonment of well 1 in 1922. Casing in well 3 extended to only 236 m, so the production from this well came probably from the F (upper) Salt.
1926-1930 This was a period of rapid expansion, 9 new wells being drilled. The wide extent of solution of the D Salt is shown by the cavities discovered during drilling of well 13. In theories of cavern
74 Figure 31. History of repairs, Sandwich brine field, 1902-1954. The first date gives the date of drilling, usually as a single well injection system. If drilled as any other type of well it is shown thus; AL-air lift;
DW-deep pump well; Wl-water injection. If caving or cavities were encountered, CAV is shown, with the depth in feet. The dates below the first one are those when repairs were needed at the depth in feet shown.
If the well was converted to a different type (AL, Wl, DW), plugged (P) or replugged (RP), the date for that work is also shown.
75 roof failure, it is usually postulated that the immediate roof collapses whereupon the succeeding higher
units find themselves unsupported and the void migrates upwards. Since practically all observed rockfalls
are concentrated at the levels of the 3 salt beds there was clearly no general upward migration of a cavern
roof from the B Salt Wells 2 and 5 were abandoned and plugged in 1928 because of rockfalls at the F-
Salt level. This is probably due to leaky casings causing dissolution at this level, since when well 12 was
drilled in 1929, about 10 m from well 5, a cavity at 335 m was encountered. Wells 5 and 12 directly
underlie the area which was to become the sinkhole. Clearly the fabric of the substratum was deteriorating
significantly at least 25 years before the surface manifestation. A further point of interest is the repeated
need to re-plug well 3. From 1920 to 1930 this well was poorly plugged and was probably acting as a
conduit for fluids between all 3 salts. By the end of 1930 the "main cavern" connected at least 5 wells.
(1, 2, 3, 6, and 11).
1931-1935 This was a period of rapid change in the character of the brine field. At the end of
1935, wells 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 13, and 14 were connected by the main gallery, of which only
7 (air lift), 9 (water injection) and 13 (deep pump well) were operational. Well 12 had suffered rockfalls at 1090 feet (332 m) and was plugged in 1931. At that date the rock beneath the future sinkhole was therefore in an unstable state about 335 m below the surface, 140.2 m below the base of the Sylvania
Formation.
1936-1940 Wells 4, 10 and 17 had been added to the "main gallery" by the end of 1940. Wells
4, 7 and 10 injected water into the gallery at that time, with wells 13 and 17 extracting brine. Well 9 was an injection well until 1939. Rockfalls affecting these wells, which are situated around the edge of the brine field, were restricted to the 1400 foot (427 m) level, suggesting a very slow deterioration of the roof of the (possibly quite restricted) cavity in the B Salt.
76 1941-1945 The most significant event in this period was the attempted drilling of well 20 in 1945,
61 m east of the future sinkhole site. This well was never completed due to extreme difficulties
encountered during drilling. Cavities were found near the 305 m level but more significant was the discovery of a large cavity in the Sylvania Formation sandstone at 156 m. This is the first suggestion of
deterioration above the F Salt, and suggests that the conditions needed for the generation of running sand
as stated by Stump (1980), that is failure in the unconfined state with subsidence of a plate-like mass of
sandstone, were being fulfilled.
In 1943 well 19 was drilled as an injection well. In 1945 rockfalls caused breaks in the casing at the "upper levels" (presumably the F Salt). The top of the casing dropped 0.45 m. According to Piper
(1954) the casing could not be completely repaired and it was merely "picked up" and injection continued.
This effectively created free access for water into the F Salt.
1946-1954 In 1947 well 15 connected with the main cavity and was converted to a deep well pump. This made the "main gallery" at least 760 m across in the west-east orientation. Also in 1947 well
21 was drilled but with great difficulty due to caving from 361 to 434 m; a crevice was observed in the
Sylvania Formation. In 1950 well 4 was finally plugged after rockfalls at 350 and 315 m.
From 1950 to 1954 very few repairs to wells were necessary to maintain production. This was a time of massive production, a large proportion of which came from deep pumps in wells 13, 15 and 21, but mainly from well 15. All the water creating the brine was injected through well 19, which was injecting an excess of 50 to 100% water over brine extracted. It is probable that this water was injected mainly into the D-Salt levels, which connected with virtually every other well on the site. A. Robinson has suggested (personal communication, 1981) that local aquifers (perhaps even the Sylvania Formation) were being robbed to generate the brine. In any case, it is clear that a large excess of water over brine
77 being pumped out was gaining access to the Salt beds.
The above review of the production and repairs records shows that the fabric of the rock underlying the brine field deteriorated steadily throughout the period prior to 1954.
There are 2 significant conclusions to be drawn relating this deterioration to sinkhole formation.
First, there was, by the early 1940s, a comprehensive system of lateral interconnections at the D-Salt level.
It may be that this level was the main producing unit but this can only be confirmed by drilling. In addition, a three dimensional network of channels available to injected water and resulting brine was probably developed by the efficient vertical conduits provided by poorly plugged wells and the surrounding rock, which was either highly fractured (non-salt beds) or dissolved (salt beds). This network effectively constituted the "main gallery" or "general cavity".
The second conclusion is that the zone around wells 5 and 12 was deteriorating as soon as well
5 was drilled. Salt was probably being dissolved from the F-Salt horizon for the duration of the production life of these wells. The F Salt was, in effect, part of the "general cavity" into which water was pumped for over 20 years after abandonment of wells 5 and 12. It is therefore likely that the deterioration continued after "plugging". The scale of this deterioration caused the rate and magnitude of the surface subsidence to be virtually imperceptible. However, when the zone of fractured rock reached the bedrock surface the rate of deformation presumably accelerated markedly, producing a large depression very rapidly on February 19, 1954.
All the conclusions and suggestions made above are tentative, since the data from which they are derived are few and selective in both temporal and spatial senses. However, they do provide a framework within which it is possible to interpret the processes of sinkhole formation.
78 A MODEL FOR SINKHOLE FORMATION AT SANDWICH BRINE FIELD
That the sinkhole at Sandwich brine field was caused by solution mining cannot be disputed. The problem involved in interpreting the process of sinkhole formation is to determine the mechanism of upward void migratioa The process is best defined in terms of void migration rather than rock migration since there may be phase changes involved.
Three mechanisms of void migration may be envisaged: (a) simple, dry stoping of fractured rock;
(b) grain by grain movement through cracks and other openings; and (c) dissolution. The single driving force for each process is gravity.
The first process, simple dry stoping, involves blocks, isolated by pre-existing or new fractures, falling from an unsupported roof onto the cavern floor or pile of fallen blocks below. The void ratio of the resulting rock pile would depend on the size and shape of blocks and their rate of accumulation.
The second mass transfer process is the grain by grain movement of fundamental particles through cracks and other openings. The void ratio of such a transported mass would be relatively small. Moreover, grains of sand would migrate along pathways too small for movement of joint-isolated blocks.
The third process of mass transfer is that of dissolution. Salt will inevitably be dissolved, if available, at the top of a cavern or system of openings full of density-stratified brine. As dissolution proceeds the solution density of the brine increases and the brine settles to the base of the cavity. This mechanism depends on the persistence of a stratified brine which was assured at Sandwich brine field by the injection of water and extraction of saturated brine at the top and bottom, respectively, of the general cavity until 1954.
79 The previously published mechanisms for formation of sinkholes in the Windsor-Detroit area assign most significance to the first 2 listed processes. Solution extraction is considered purely the mechanism by which a void was produced at the B-Salt level. The classic explanation of Terzaghi (1954) involves dry stoping alone. Based on assumptions of high bulking ratios, however, the build-up of fallen rock would have likely halted void migration before the bedrock/overburden interface was reached.
Alternatively, the tendency of layered rock to "corbell" (form an arch over the opening) may have stabilized it No systematic study of these features and processes has been made; observations of the limited number of roof falls in dry salt mines in the Salina Formation may provide useful information.
The process implied by Terzaghi (1970) is one of "slow stoping" (i.e., gradual lowering of relatively undisturbed layers of rock into a void; see Figure 8). This is perhaps a more likely process than the catastrophic roof collapse. According to Stump (1980), "slow stoping", together with less significant subsidence of overlying intact layers induces stresses, which, combined with regional stresses, would cause the Sylvania Formation sandstone to fail in unconfined compression. The sand thus generated would be subject to "granular stoping". Stump's model therefore combines the 2 entirely physical methods of mass transfer.
Any model for sinkhole formation must attempt to explain the presence, and absence, of craters in specific areas. Stump (1980) states that in areas where a sinkhole formation did not occur "it seems logical to assume the horizontal stress field never developed...to sufficient extent". Stump's model depends on the addition of regional high horizontal stresses to the beam or plate stresses set up by subsidence into a void. Since the regional stresses will probably not be diminished at depth at any location, the absence of sinkholes must be caused, according to this model, by lack of initial subsidence of the sandstone. It is not possible to make any conclusions regarding non-occurrence of sinkholes from the work reported here.
However, the information set out in Chapter 4 allows an explanation of why the sinkhole formed over an
80 area from which brine had not been directly extracted for over 20 years.
Volumes of salt extracted from any salt bed cannot be estimated because of the lack of control over the injection process. Dowhan (1976) found the supposed target bed intact when drilling a solution mining-related depression on nearby Grosse lie. It may be that a similar situation existed at Sandwich. In that case, the relevance to the sinkhole of any calculations involving the 60 m thickness of the B Salt
(Nieto-Pescetto and Hendron 1977) is doubtful.
A model for sinkhole generation which explains the occurrence and location of the Sandwich event is presented below. This model is based on: a literature review, an analysis of company records; the information on the engineering properties of the Sylvania Formation sandstone; and discussions with T.
Piper (BASF Wyandotte), A. Robinson and A. Letts (Canadian Salt Company).
Solution mining, as practiced at Sandwich until 1954, was an inexact process. The location of the dissolved rock salt and the route of the generated brine, after extensive well interconnection occurred, were both virtually unknown. Although these factors were not seriously considered in previous investigations the present author considers them of critical importance in determining the eventual location of the sinkhole. It is clear from production and repair records that the explanations based on the collapse of a chamber generated by dissolution between 426 and 488 m below ground level is a gross oversimplifica tion.
Before 1946 very little thought was put into the impact that individual operating decisions had on the integrity of the brine field as a whole. During brining operations, it was assumed for some time that water was being injected into the B Salt unit (426 to 488 m). Continuous rockfalls eventually forced the realization that the D Salt (366 m) had been subjected to extensive leaching providing pathways for lateral
81 movement of fluids at this level. Repairs made necessary by the rockfalls were made, at first, without
regard to the implications of the damage to the overall situation. Wells which could not be salvaged were plugged, some rather poorly. Casing from these wells was pulled for pressing short-term economic reasons.
This probably allowed relatively free vertical movement of fluids in the region of old wells. Thus, by the late 1940s a system of conduits existed. Allowing vertical and horizontal movement of fluids to occur without constraint (Figure 32).
The rock around wells 5 and 12 (underlying the eventual collapse area) was in poor condition at an early stage. This is evidenced by the rockfalls which occurred at the F-Salt level (around 335 m) in
1928 and 1931. The vertical connection in this area probably extended from the B to the F Salt from this time onward (Figure 33). The first symptom of this deterioration was a body of brine encountered at 1200 feet (360 m) during drilling of well 5. This may have been a naturally occurring "wild brine", or could have originated from wells 1 to 4. In any case, well 5 was the first to intersect "wild brine" and was the site of the eventual collapse.
In the late 1940s and early 1950s most water was injected into the "general cavity" through well
19. Brine was extracted from wells that would cause a general movement of fluids across the brine field
(see Figures 29c and 29d). During production well 19 was recognized to be discharging into the D-Salt level indicating that undersaturated fluids were moving east traversing the area of extensive vertical connection. In this area the fluids may have entered a complex density-stratified brine system centred on wells 5 and 12, perhaps sustaining the ability of the upper levels of the system to dissolve salt.
Alternatively, the poorly plugged wells 5 and 12 and the surrounding fractured rock extending into the
Devonian carbonates and sandstones may have allowed free transmittal of groundwater into the brine system.
82 J L J L •L, .1 ,.L
I , 1
T—
SYLVANIA
1 1 1 I I 9 ,' f T
l L
i r
hr1
l <- l J\ £- L " F-SALT
Figure 32. Model for sinkhole formation, early stages, pre-mid 1930s.
83 Figure 33. Model for sinkhole formation, 1930s and 1940s.
84 The bulk of production in this period may therefore have been predominantly from the F Salt.
Saberian (1977) showed that dissolution rates are greatest where salt overlies the undersaturated brine.
Upward movement of the "void" may therefore have been quite rapid at this stage (Figure 33). Figure 33 shows collapse to have occurred into a small cavity in the B Salt. No direct evidence for this exists and collapse at this point may not even be necessary for void propagation to continue.
As dissolution of the F Salt continued the overlying beds would have subsided, as an increasing area of rock above the F salt was undermined. It is at this stage that compressive failure of the Sylvania
Formation sandstone would have occurred and sand may have started to migrate slowly downwards, grain by grain, through joints. Eventually the unsupported roof overlying the brine began to stope. The style and rate of stoping may have been such that the bulking ratio was low. Whatever the case, this conventional dry stoping needed to migrate only 106.7 m (i.e., until it reached the base of the sandstone). Granular stoping would then be permitted at a greatly accelerated rate as the sand grains drained through a rubble column filling in voids created by dry stoping (Figure 34). This stage probably occurred in 1952-1953 as signalled by the increased rate of surface subsidence. When granular stoping was complete, the void was about 106.7 m from the rockhead. Conventional dry stoping would then account for void migration to the base of the glacial clays. Viscous deformation of these plastic materials may have been a significant factor in the slumping of these glacial deposits enabling a relatively minor increase in void ratio during this apparently rather rapid process (Figure 34).
SUMMARY
This analysis of the 1954 sinkhole over brine workings at Sandwich, near Windsor, has involved 3 aspects:
(a) a review of the mechanisms of sinkhole formation previously proposed for the Windsor
sinkhole and the nearby examples on Grosse He;
85 Figure 34. Model for sinkhole formation, 1950-1952.
86 Figure 35. Model for sinkhole formation, 1952-1954. (b) determination of the geotechnical properties of the sandstone units of the Sylvania
Formation;
(c) a review of the production and well repair records for the Sandwich brining operation
from 1902 to 1954.
It is concluded that the sinkhole occurred because of the presence of the Sylvania Formation sandstone at a depth intermediate between the surface and the salt-producing units of the Salina Formation.
The Sylvania Formation is a thin wedge of quartz sandstone forming the base of the predominantly carbonate Detroit River Group. It is composed of very well sorted, fine-grained quartz grains with heavily intergrown or overgrown quartz-quartz contacts. Variable amounts of dolomite act as cement in certain parts of the unit. In the purer sections, the heavily intergrown quartz-quartz contacts cause the sandstone to exhibit explosive failure on unconfined compression. This failure mode causes the intact sandstone to transform into running sand, which permits migration downwards through fractured rock.
The analysis of production records has shown that a zone of cavities and/or caved rock existed beneath the eventual sinkhole area over 20 years before the sinkhole formed. Gradual subsidence over the entire solution mining site was indicative of this localized decrepitation and of the dissolution of salt at levels higher than those which were assumed to be dissolving. A network of horizontal and vertical pathways for fluids, made up of poorly plugged wells and the "extracted" salt beds existed at the site throughout the period from the early 1930s to the time of the collapse.
A model for the process of sinkhole formation is suggested which takes into account the peculiar physical properties of the Sylvania Formation sandstone and the production and post-production practices employed at the site. It is likely that dissolution of the relatively thick F Salt occurred from the base
88 upwards. The void formed in this way allowed the rather strong, but fractured and brittle, overlying Upper
Silurian and Middle Devonian dolostones to collapse thereby undermining the overlying Sylvania
Formation. Under beam or plate stresses caused by this undermining, combined with the regional high horizontal stresses, the Sylvania Formation sandstone failed in unconfined compression. The running sand formed by this failure was then able to flow down through the fractured rock rubble column thereby forming a new void at a shallower level. This void then migrated to the surface by conventional stoping processes.
The methods now commonly used in the brine extraction industry are vastly improved over those of the first half of this century. The experience of 1954 at the Sandwich brine field has been a lesson to many brining operations in the importance of continuous monitoring of ground subsidence. Without the combination of the Sylvania Formation sandstone and the processes used at the Sandwich site it is unlikely that a collapse would have occurred. With the improved knowledge of the geology and engineering geology and with the better brine production practices now employed, it is unlikely that similar sinkholes will occur.
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Siever, R. 1962. Silica solubility, 0°-200°C, and the diagenesis of siliceous sediments; Journal of Geology,
v.70, p. 127-150.
Sippel, R.F. 1968. Sandstone petrology, evidence from luminescence petrography; Journal of Sedimentary
Petrology, v.38, p.530-554.
Stump, D. 1980. A hypothesis for sink development above solution-mine brine cavities in the Detroit area;
MSc thesis, University of Illinois at Urbana-Champaign, 81p.
Summerson, C.H. and Swann, D.H. 1970. Patterns of Devonian sand on the North American craton and
their interpretation; Geological Society of America Bulletin, v.81, p.469-90.
Telford, P.G. and Russell, D.J. 1981. Paleozoic geology of the Windsor-Essex and Pelee Island area,
southern Ontario; Ontario Geological Survey, Preliminary Map P.2396.
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Terzaghi, R.D. 1970. Brinefield subsidence at Windsor, Ontario; Third Symposium on Salt, Vol. II,
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94 APPENDIX 1 DRILL HOLE LOGS DRILL HOLE LOG: Wl
FROM TO 0' 97'0" (0 m 29.57 m) Overburden; no samples takea
97*0" 99.0" (29.57 m 30.18 m) Limestone: dark and brown grey, very fine crystalline tolitho- graphic. Minor oil staining; rare fossils and fossil debris.
99'0" 100'2" (30.18 m 30.54 m) Limestone: brown and dark brown, medium to coarse crystal line. Oil stained, highly fossiliferous (brachiopods), grading, as oil staining decreases into unit below.
100'2" 101 '3" (30.54 m 30.88 m) Limestone: blue grey, medium to coarsely crystalline.
101'3" 1017" (30.88 m 30.97 m) Same as 99'0" to 100'2"
101 '7" 105 '7" (30.97 m 32.19 m) Limestone: blue grey and dark grey, fine to medium crystalline, with some grey fine-crystalline limestone, nodules and chert stringers.
105'7" 106'3" (32.19 m 32.40 m) Same as 99*0" to 100'2"
106'3" 108'3" (32.40 m 33.01 m) Limestone: blue grey, fine to medium crystalline.
108'3" 112'2" (33.01 m 34.20 m) Same as 99'0" to 100'2", with some short non oil-stained sections.
112'2" 129' 1" (34.20 m 39.35 m) Limestone: dark grey, fine- to medium-crystalline, with patches oil stained in high moldic porosity zones. Becomes undulating banded and finer towards 116' where it is very fine with some medium crystalline.
129' 1" 141 '6" (39.35 m 43.13 m) Similar to above, but with zones of grey and blue grey, fine to medium crystalline limestone with many bryozoa, brachiopods and corals, often oil stained.
141 '6" 144'9" (43.13 m 44.14 m) Limestone: dark grey and brown grey, very fine crystalline with some medium crystalline, fossiliferous.
144'9" 147'0" (44.14 m 44.81m) Limestone: dark grey, faintly laminated, very fine crystalline to lithographic. Solution stringers 145'3".
147'0" 150'1" (44.81 m 45.75 m) Limestone: dark and buff grey laminated, finely crystalline.
150' 1" 154'5" (45.75 m 47.09 m) Limestone: dolomitic, very variable; buff grey, very fine to lithographic, laminated as 147'0" to 150'1"; brecciated and bioturbated grey limestone in brown matrix, blue grey very fine-crystalline limestone; grey brown, very fine to lithographic limestone.
95 154'5" 158'3" (47.09 m 48.25 m) Limestone: grey brown, very fine crystalline to lithographic, with massive colonial corals and solitary corals.
158'3" 162'3" (48.25 m 49.99 m) Limestone: buff grey, fine to very fine crystalline, becoming
laminated, grey, fine crystalline at 160'6".
162'3" 164'0" (49.99 m 49.99 m) Limestone: dark grey brecciated in brown,very fine crystalline.
164'0" 166'10" (49.00 m 50.87 m) Limestone: blue grey and dark grey laminated and nodular bedded, very fine crystalline to lithographic. 166'10" 178'0" (50.87 m 54.25 m) Dolostone: brown and buff grey laminated, very fine crystal line, porous. Laminae contorted below 169'; occasional non-laminated brown limestone, fossiliferous zones and stylo- lites.
178'0" 179'4" (54.25 m 54.65 m) Dolostone: grey and blue grey, very fine crystalline to litho graphic, faintiy laminated. Highly porous at base.
179'4" 183'3" (54.65 m 55.87 m) Same as 166'10" to 178'0"
183'3" 186'9" (55.87 m 56.94 m) Dolostone: dark grey and buff banded, slightly brecciated at top, fine crystalline, grades down into dark grey, fine-crystal line, highly porous dolostone.
186'9" 191 '3" (56.94 m 58.31m) Dolostone: brown and grey brown, non-laminated, fine crystalline. High matrix porosity, and moldic porosity high at 188'6", 190'0".
191'3" 203'11" (58.31 m 62.15 m) Dolostone: dark grey and buff, coarse banded and laminated, very fine to fine crystalline, porous. Rare brecciation and bioturbation, celestite nodules at 199'4".
203'11" 205'4" (62.15 m 62.58 m) Dolostone: blue grey and grey, very fine to fine crystalline, brecciated in parts.
205'4" 214'9" (62.58 m 65.47 m) Dolostone: brown and buff grey banded, becoming mainly brown, fine crystalline, porous. Very high moldic porosity 210'4"-213'4".
214'9" 216'5" (65.47 m 65.96 m) Dolostone: brown and grey banded as above, grading into sublithographic grey brecciated dolostone.
216'5" 217'0" (65.96 m 66.14 m) Dolostone: blue grey, very fine crystalline, with bioturbated and brecciated, grey, very fine dolomitic limestone fragments.
217'0" 218'11" ( 66.14 m 66.72 m) Same as 205'4" to 214'9".
96 218'11" 219T (66.72 m 66.78 m) Massive celestite.
219T' 221'1" (66.78 m 67.39 m) Dolostone: highly bioturbated and brecciated grey and buff, very fine crystalline to lithographic, with some coarse-crysta lline veining. Becoming nodular bedded, in lower foot.
221'1" 224*0" (67.39 m 68.28 m) Dolostone: buff and dark grey laminated, very fine crystalline, porous.
224'0" 23l'O" (68.28 m 70.41m) Dolostone: buff, very fine crystalline, porous. Bioturbated and brecciated locally. Large vugs at 224' to 226'.
231 '0" 234'1" (70.41m 71.35 m) Dolostone: laminated, grey and brown grey, very fine crystal line to lithographic. Heavily bioturbated and brecciated and contorted at base.
234'1" 238'8" (71.35 m 72.76 m) Dolostone: laminated brown and buff grey, fine to very fine crystalline, brecciated and laminated occasionally, highly porous.
238'8" 239'9" (72.76 m 73.09 m) Dolostone: buff, very fine crystalline, highly porous.
239'9" 242'4" (73.09 m 73.88 m) Limestone: laminated, grey blue and dark grey, very fine crystalline to lithographic.
242'4" 243'5" (73.88 m 74.19 m) Limestone: grey brown with some buff mottling, fine to medium crystalline.
243'5" 256'7" (74.19 m 78.21m) Limestone: laminated, grey and dark grey, very fine crystalline, with needle-like anhydrite crystals. Laminae contorted.
2567" 257'5" (78.21m 78.46 m) Massive anhydrite. End of hole.
97 DRILL HOLE LOG: W2
From To 0 74'0" (0 m 22.56 m) Overburden; no samples taken.
74' 91'6" (22.56 m 27.89 m) Bedrock; no samples taken.
91'6" 94'4" (27.89 m 28.74 m) Dolostone: brown grey and brown, very fine crystalline, porous. Variable moldic porosity, occasionally oil-stained; a few shale partings.
94'4" 99'3" (28.74 m 30.29 m) Dolostone: laminated grey and dark grey, fine to medium crystalline, with light brown and buff, fine crystalline, porous, laminae, generally horizontal, rarely undulating.
99'3" 100'2" (30.29 m 30.54 m) Dolostone: laminated grey and dark grey, very fine crystalline, and dark brown, fine- to medium-crystalline laminae, horizontal and convoluted.
100'2" 101'3" (30.54 m 30.88 m) Dolostone: brown, very fine crystalline, porous, with vertical calcite vein. Moldic porosity at base.
101'3" 105'0" (30.88 m 32.00 m) Dolostone: brown and grey brown, very fine crystalline, laminated, mostly horizontal.
105'0" 107'0" (32.00 m 32.61 m) Dolostone: grey and buff, very fine crystalline to lithographic. Calcite veining brecciation at 106'5" to 106'9".
107'0" 107'9" (32.16 m 32.86 m) Dolostone: buff, very fine crystalline to lithographic, with moldic porosity (<5%). Calcite veins, stylolitic.
107'9" 108'9" (32.86 m 33.16 m) Dolostone: brecciated and bioturbated, grey and buff laminated, fine crystalline, with calcite veining.
108'9" 110'6" (33.16 m 33.68 m) Dolostone: grey, lithographic to very fine crystalline with some recrystallized to medium. Porous, matrix and moldic.
110'6" 110'10" (33.68 m 33.80 m) Dolostone: shaly, dark grey with nodules and stringers of very fine-crystalline grey limestone.
110'10" 111 *9" (33.80 m 34.08 m) Dolostone: blue grey, fine crystalline, with some medium crystalline, very high moldic porosity.
111'9" 112'11" (34.08 m 34.41 m) Dolostone: buff, fine to medium crystalline, highly porous, mainly moldic after sulphates, some sulphates present.
112*11" 113*11* (34.41 m 34.72 m) Dolostone: banded grey and buff, very fine crystalline to lithographic.
98 113*11" 117'6" (34.72 m 35.81m) Dolostone: buff, fine crystalline with recrystallization to medium; very high moldic porosity decreasing downwards; increasing matrix porosity at base.
117*6" 118*5" (35.81 m 36.09 m) Dolostone: calcareous, dark grey, fine crystalline, banded with buff dolostone.
118'5" 121*0" (36.09 m 36.88 m) Dolostone: calcareous, laminated grey and buff, very fine and fine crystalline, porous. Brecciated 119*1" to 119' 11".
121 '0" 124'4" (36.88 m 37.89 m) Dolostone: laminated and mottled dark grey and buff, very fine crystalline. Laminae horizontal and inclined, some calcite veining.
124'4" 125'3" (37.89 m 38.19 m) Dolostone: laminated brown, grey and dark grey, fine crystal line, locally brecciated.
125*3" 126'3" (38.19 m 38.50 m) Dolostone: grey, very fine crystalline to lithographic, with
calcite veining. High matrix porosity.
126'3" 127'0" (38.50 m 38.71 m) Core lost.
127'0" 127*6" (38.71 m 38.86 m) As 125*3" to 126'3", with dark/light grey banding.
127'6" 135*10" (38.86 m 41.42 m) Dolostone: buff, very fine crystalline, high matrix porosity with variable (up to 20%) moldic porosity. 135*10" 138*10" (41.42 m 42.34 m) Dolostone: laminated grey and buff, very fine crystalline, becoming buff, porous then laminated with dark grey at base.
138*10" 139*8" (42.34 m 42.58 m) Dolostone: very fine crystalline, grey intraclasts in dark grey matrix.
139'8" 140'0" (42.58 m 42.67 m) Massive anhydrite.
140'0" 143'3" (42.67 m 43.68 m) Dolostone: grey and buff grey, very fine crystalline, with bitu minous partings.
143'3" 145'9" (43.68 m 44.44 m) Dolostone: grey, very fine crystalline to lithographic. Shaly and bituminous partings at centre, then very high moldic porosity and white calcite stringers at base.
145'9" 150'3" (44.44 m 45.81m) Dolostone: laminated grey and dark grey, very fine crystalline, occasionally brecciated; very high moldic porosity at base.
150'3" 150' 10" (45.81 m 45.99 m) Dolostone: distorted laminae, grey and dark grey, very fine crystalline.
150'10" 152'7" (45.99 m 46.51m) Dolostone: grey and buff, very fine crystalline to lithographic, with a few bituminous laminae and sulphate blebs.
99 152'7" 154*1" (46.51 m 46.97 m) Dolostone: laminated grey, dark grey and buff, very fine crystalline, some bituminous laminae, porous. Contorted laminae at base.
154*1" 157'0" (46.97 m 48.90 m) Core lost.
157'0" 160T (47.90 m 48.80 m) Dolostone: laminated grey and dark grey, porous, very fine crystalline, rare moldic pores.
160' 1" 163'11" (48.80 m 49.96 m) Limestone: laminated dark and brown grey, very fine crystal line.
163'11" 168'6" (49.96 m 51.36 m) Limestone: grey, very fine crystalline, with shaly and bitumi nous partings and variable moldic porosity.
168'6" 177'4" (51.36 m 54.04 m) Dolostone: grey and buff, very fine crystalline, with solution features, bituminous partings and rare moldic pores. Rare darker bands, convoluted laminae and sulphates.
177'4" 178'3" (54.04 m 54.35 m) Dolostone: grey brown, very fine crystalline.
178'3" 186*3" (54.35 m 56.78 m) Limestone: dolomitic, buff and grey laminated and nodular bedded, very fine crystalline; sulphate blebs, with rare moldic pores after sulphate.
186'3" 207'4" (56.78 m 63.19 m) Limestone: grey and dark grey, fine and very fine crystalline, very high moldic porosity to 189', then less. Rare bituminous laminae.
207'4" 212'6" (63.19 m 64.77 m) Dolostone: laminated, buff and dark grey, fine crystalline; laminae horizontal except at 208', where there are stylolites, breccias, undulations.
212'6" 214'5" (64.77 m 65.29 m) Limestone: dolomitic, laminated grey brown and grey, fine crystalline.
214'5" 217'2" (65.29 m 66.20 m) Limestone: dolomitic, laminated grey brown and dark grey, fine crystalline, bioturbated and brecciated.
217*2" 218*8" (66.20 m 66.66 m) Dolostone: brown and buff, nodular bedded, fine crystalline, with some shaly partings.
218*8" 224'2" (66.66 m 68.34 m) Dolostone: buff, very fine crystalline to lithographic, becoming faintly laminated at base.
224'2" 224'9" (68.34 m 68.52 m) Limestone: dolomitic, blue grey, fine crystalline above a thin brecciated grey limestone with celestite blebs.
100 224'9" 233'9" (68.52 m 71.26 m) Dolostone: laminated grey and buff, fine and very fine crystal line with bituminous partings. Locally convoluted and brecciated; massive celestite at base.
233'9" 239'4" (71.26 m 72.94 m) Dolostone: grey and dark grey laminated, fine and very fine crystalline, bioturbated in parts with a few fossils. Grading into brown porous limestone at base.
239'4" 245'5" (72.94 m 74.80 m) Dolostone: grey and buff laminated, very fine crystalline. Brecciated, bioturbated with moldic porosity 240'-243\
245'5" 255'5" (74.80 m 77.85 m) Dolostone: grey and dark grey laminated, fine crystalline, with bituminous and shaly partings. Bioturbated 248'-255'.
255'5" 256'1" (77.85 m 78.06 m) Dolostone: dark grey and blue grey, fine crystalline, with some coarsely crystalline, stylolitic.
256'1" 262' 10" (78.06 m 79.83 m) Limestone: grey brown, fine crystalline, oolitic in places; some moldic pores and one large grey limestone nodule at 261 '6".
262'10" 265'3" (79.83 m 80.86 m) Limestone: brown, very fine crystalline, with bituminous partings at top, brown-grey ooliths and fossil debris at base.
265'3" 267'3" (80.86 m 81.47 m) Limestone: grey, fine crystalline, pisolitic and nodular bedded
with thick (1/4") bituminous partings.
267'3" 269'9" (81.47 m 82.24 m) Limestone: buff, fine crystalline with large solitary corals.
269'9" 272'2" (82.24 m 82.97 m) Limestone: dolomitic, dark brown, fine crystalline with bituminous stringers and large grey dolomite nodules. 272'2" 277'8" (82.97 m 84.64 m) Limestone: laminated dark grey and buff, very fine crystalline with some bituminous partings.
277'8" 279'1" (84.64 m 85.07 m) Dolostone: dark brown, fine crystalline with few bituminous partings.
279'1" 281'8" (85.07 m 85.86 m) Dolostone: grey, fine to very fine crystalline with some shaly partings.
281 '8" 290' 1" (85.86 m 88.42 m) Dolostone: laminated and mottled dark grey and grey, very fine crystalline with rare chert stringers and moldic pores.
290'1" 300'7" (88.42 m 91.62 m) Dolostone: dark grey and buff, very fine to fine crystalline.
300'7" 306'3" (91.62 m 93.36 m) Dolostone: dark grey and buff, mottled and laminated, very fine crystalline, with grey blue lithographic dolostone and chert nodules; stylolitic.
101 306'3" 307'8" (93.36 m 93.78 m) Dolostone: buff, very fine crystalline to lithographic, with small moldic pores and celestite.
307'8" 308'4" (93.78 m 93.97 m) Dolostone: dark blue-grey, very fine crystalline, with massive gypsum (>50%).
308'4" 319T* (93.97 m 97.26 m) Dolostone: buff, very fine crystalline, bioturbated and brecciated, rarely oolitic, occasional blue grey dolostone/chert nodules.
319'1" 321'0" (97.26 m 97.84 m) Dolostone: light brown, fine to very fine crystalline, highly
porous.
321'0" 323'0" (97.84 m 98.45 m) As 308'4" to 319T.
323'0" 329'8" (98.45 m 100.49 m) Dolostone: buff, very fine crystalline, laminated and mottled in places, porous. A few gypsum nodules. 329'8" 348'5" (100.49 m 106.19 m) Dolostone: buff and dark grey, very fine to fine crystalline. Rarely laminated, shelly or oolitic; occasional blue grey, very fine-crystalline dolostone.
348'5" 352'9" (106.19 m 107.53 m) Quartz sandstone: dolomitic, white, fine to medium grained, rounded grains, weak and friable.
352'9" 379'5" (107.53 m 115.64 m) Quartz sandstone: dolomitic, fine to medium grained, rounded grains, light grey, with dark bands of higher dolomite content. These are 1/2"-1" thick, (1.2- 2.5 mm) occasionally contorted by burrowing and show a dip of up to 5° when undisturbed.
379'5" 384'6" (115.64 m 117.20 m) Quartz sandstone: highly dolomitic, very dark grey, fine and medium grained, rounded grains.
384'6" 386'0" (117.20 m 117.65 m) Quartz sandstone: white with dark grey mottling; lithologies as above. Last 1' (30 cm) (approx.) is white, loose fine and very fine sand.
102 DRILL HOLE LOG: W3
From To 0' 74' (0 m 22.56 m) Overburden; no samples takea
74' 78'0" (22.56 m 23.77 m) Dolostone: laminated brown (oil-stained) and dark grey, fine crystalline.
78'0" 84'3" (23.77 m 25.69 m) Dolostone: grey and buff, fine to very fine crystalline, porous, with some bituminous laminae. Upper 1' (30.5 cm) oil stained.
84'3" 85'6" (25.69 m 26.06 m) Dolostone: brown and dark grey, very fine crystalline, bioturb ated, with some shale stringers and fossil fragments.
85'6" 96'3" (26.06 m 29.35 m) Dolostone: laminated grey and buff, very fine crystalline, increasing vuggy porosity at base.
96'3" 100' 10" (29.35 m 30.75 m) Dolostone: grey and blue grey mottled, very fine crystalline, to lithographic, some brecciation by calcite veining.
100'10" 103'0" (30.75 m 31.39 m) Dolostone: light brown, fine crystalline, sucrosic, stylolitic at base.
103'0" 108*1" (31.39 m 32.95 m) Dolostone: grey, fine to very fine crystalline, with very high
moldic porosity, decreasing downwards.
108'1" 110*1" (32.95 m 33.56 m) As lOO'lO" to 103'0".
110*1" 110*10" (33.56 m 33.80 m) Dolostone: light grey, fine crystalline. 110*10" 115*3" (33.80 m 35.14 m) As 103'0" to 108*1": with fenestral porosity; becoming laminated with buff, fine-crystalline porous dolostone, with some brecciated laminae.
115'3" 118*5" (35.14 m 36.09 m) Dolostone: laminated grey and buff, very fine crystalline with some brecciation.
118*5" 126'9" (36.09 m 38.65 m) Dolostone: buff, very fine crystalline, few dark brown laminae, restricted zones of high moldic porosity.
126'9" 131 '0" (38.65 m 39.93 m) Dolostone: dark brown and grey, very fine crystalline, porous, becoming grey, brecciated in dark grey matrix.
131*0" 134'2" (39.93 m 40.90 m) Dolostone: grey and dark grey, fine crystalline, with frequent bituminous and shaly partings, becoming less frequent and stringer-like at base.
134'2" 136'3" (40.90 m 41.54 m) Dolostone: grey, very fine crystalline to lithographic.
103 136'3" 146'10" (41.54 m 44.78 m) Dolostone: grey, very fine crystalline, with shaly and bitumi nous partings. Laminae commonly contorted. Becomes lighter grey, more contorted at base.
146'10" 149'3" (44.78 m 45.51 m) Dolostone: brown and dark grey, fine crystalline, porous, with some dark brown low porosity bands. Massive anhydrite at 148*3" - 148'9".
149'3" 152'0" (45.51 m 46.33 m) Limestone: grey and dark grey banded, fine to medium crystalline.
152'0" 156'4" (46.33 m 47.64 m) Limestone: grey fine crystalline to lithographic, porous, with a few dark brown mottles.
156'4" 169'5" (47.64 m 51.63 m) Dolostone: dark grey and grey laminated, very fine crystalline; brecciation, bioturbation, celestite at base.
169'5" 171*1" (51.63 m 52.15 m) Dolostone: buff, very fine crystalline to lithographic, celestite and high moldic porosity after sulphate.
171*1" 177'2" (52.15 m 54.01 m) Limestone: buff grey, fine to very fine crystalline, with some shaly partings, high matrix porosity, rare celestite.
177'2" 183'0" (54.01 m 55.78 m) Limestone: grey and buff, very fine crystalline to lithographic with many molds after celestite, up to 50% of rock, some bitu minous partings at base.
183*0" 186'4" (55.78 m 56.78 m) As above, but celestite present, no voids.
186'4" 190'4" (56.78 m 58.00 m) As 177'2" to 183*0".
190'4" 195'4" (58.00 m 59.53 m) Limestone: buff, very fine crystalline to lithographic, with rare bituminous and shaly partings, celestite.
195'4" 199'5" (59.53 m 60.78 m) Limestone: buff, very fine crystalline to lithographic, with zones of high moldic porosity after celestite and fossil frag ments, fossil fragments and up to 30% celestite at base.
199'5" 200'8" (60.78 m 61.17 m) Dolostone: dark grey, very fine crystalline with many shale partings.
200'8" 204'7" (61.17 m 62.36 m) Limestone: laminated dark grey and buff, very fine crystalline, laminae occasionally undulating.
204'7" 206'3" (62.36 m 62.88 m) Limestone: blue grey, very fine crystalline to lithographic, with some shale stringers.
206'3" 208'6" (62.88 m 63.55 m) Limestone: dolomitic, blue grey, fine crystalline with celestite.
208'6" 210'8" (63.55 m 64.22 m) Limestone: dolomitic, dark and buff mottled, fine crystalline.
104 210'8" 215'10" (64.22 m 65.81 m) Limestone: dolomitic, laminated light grey and grey, very fine crystalline to lithographic, laminae locally undulating, brecciated at base.
215'10" 216'2" (65.81m 65.90 m) Massive barite (?)
216'2" 223'9" (65.90 m 68.21 m) Dolostone: laminated grey and dark grey, very fine crystalline to lithographic, laminae contorted locally.
223'9" 224'8" (68.12 m 68.49 m) Dolostone: grey blue, lithographic intraclast breccia, stylolite at base.
224'8" 231'9" (68.49 m 70.65 m) Dolostone: laminated, mottled, brecciated, blue grey and buff, very fine to fine crystalline with some medium, celestite (?) veins.
231'9" 234'9" (70.65 m 71.57 m) Dolostone: buff grey, very fine crystalline to lithographic, porous, with celestite blebs. 234'9" 247'0" (71.57 m 75.29 m) Dolostone: laminated dark grey and buff, very fine crystalline to lithographic, with some shaly partings, some brecciation stylolites and distorted laminae.
247'0" 247T' (75.29 m 75.47 m) Dolostone: grey blue, very fine crystalline with some coarse
crystalline, fossil fragments and moldic pores.
247'7" 250'5" (75.47 m 76.32 m) As 231'9" to 234'9"
250'5" 254'4" (76.32 m 77.51 m) Limestone: buff, very fine crystalline to lithographic, porous, with light grey ooliths and corals. 254'4" 258'11" (77.51 m 78.91 m) Limestone: light grey and grey, oolitic and pisolitic, very fine crystalline, with thick bituminous partings.
258'11" 264'5" (78.91m 80.59 m) As 250'5" to 254'4": but darker brown, with rugose and
branching corals.
264'5" 266*7" (80.59 m 81.26 m) As 254*4" to 258*11"
266'7" 268'7" (81.26 m 81.87 m) Limestone: buff grey, very fine crystalline, fossiliferous; becoming bitumen stained, some flattened pisoliths. 268'7" 269'1" (81.87 m 82.02 m) Limestone: pisolitic and fossiliferous (corals) in bituminous, very fine crystalline matrix.
269'1" 280'4" (82.02 m 85.44 m) Dolostone: dark grey and grey brown, very fine crystalline to lithographic, some medium crystalline, porous. Occasional banding, mottling, bituminous laminae, fossil fragments.
105 280*4" 285'8" (85.44 m 87.08 m) Dolostone: grey and light grey, fine to very fine crystalline, porous, some celestite, faint laminations, fine to medium crysta lline at base.
285'8" 304'4" (87.08 m 92.75 m) Dolostone: grey brown and brown, very fine crystalline, fossil debris, indistinct lamination and brecciation by gypsum veins locally. Characterized by nodules of grey blue very fine- crystalline to lithographic dolostone and white earthy chert.
304'4" 309'5" (92.75 m 94.31 m) As above, but distinctly laminated.
209'5" 336'6" (94.31 m 102.57 m) Dolostone: buff and blue grey, very fine crystalline. Gypsum
masses; no chert.
336*6" 336*8" (102.57 m 102.63 m) Calcite-lined vug.
336'8" 338'6" (102.63 m 103.17 m) Quartz sandstone: dolomitic, white, fine to medium grained with some coarse. Grains are rounded, well cemented. 338'6" 347'10" (103.17 m 106.04 m) Quartz sandstone: dolomitic, white, fine to medium grained, grains subrounded, very friable, carbonate content varies very rapidly.
N.B.: Core was ground at each discontinuity, so depths are approximate.
347'10" 370'7" (106.04 m 112.95 m) Quartz sandstone: as above with increasing frequency of dolomite-rich dark bands, 1/2"-1" thick, often contorted or burrowed. Some bituminous streaks. 366'7"-368' lost.
370*7" 375'5" (112.95 m 114.42 m) Quartz sandstone: dark grey and grey mottled, highly dolomitic, fine to medium grained. Rock is stronger, less friable.
375'5" 384'5" (114.42 m 117.17 m) Quartz sandstone: mainly pure white as 338'6"-347'10" but some thin darker bands.
384'5" 402'0" (117.17 m 122.53 m) As above with increase frequency of darker bands. 385'10"-388'0" lost.
402'0" 410'2" (122.53 m 125.03 m) Alternating quartz sandstone and dolomitic sandstone bands: causing recovery as l"-2" discs. Some zones of grey dolomitic sandstone, but unit is characterized by rapid alternations. 407'-408' lost.
410'2" 424'6" (125.03 m 129.39 m) Dolostone: grey, very fine crystalline, with some fine to very fine sand. Stylolites.
424'6" 428'5" (129.39 m 130.58 m) Dolostone: grey and grey blue, fine, crystalline, sandy, with some white earthy chert. Less sandy at base.
106 428'5" 445'10" (130.58 m 135.91 m) Dolostone: grey blue and grey mottled, fine crystalline with nodular hard chert, stylolites. Bituminous partings and breccia- tion common at base. Very fine crystalline at 445'.
445'10" 461'7" (135.91m 140.70 m) Quartz sandstone: dolomite towards base, grains fine to medium grained, subrounded. Friable at top, more dolomitic, compact bands at base.
461'7" 463'6" (140.70 m 141.27 m) Dolostone: as 428'5" to 445'10"; top is sandy.
463'6" 468'0" (141.27 m 142.65 m) Dolostone: dark grey and grey blue, fine to very fine crystal line, with abundant chert at base.
107 APPENDIX 2: Descriptions of Sylvania Sandstone Thin Sections
Sample Number W2 346-46 (105.5 m)
Abstract A well sorted dolomitic quartz sandstone. Terrigenous grains are 100% quartz of very fine- to medium-sand size, cemented by or suspended in dolomite. Quartz-quartz contacts are typically short concave-convex. Super-mature. Dolomite is very fine to medium- crystalline.
Mineralogy Quartz 63%, Dolomite 32%, Void space 5%.
Texture Grain size: Sand grains have mean diameter of 0.174 mm and a mode median (0.18 mm) also in the fine sand range. 90% of the sand lies in the 0.098-0.35 mm range (very fine to medium sand). It is well sorted (Sj = 0.71mm), fine skewed (SK! = +0.14) and leptokurtic (KG = 1.49), and has no silt.
Grain shape: Grains are subangular to well rounded, mainly subrounded. Mean rounding = 3.84 (subrounded). Mean W/L = 0.69 (intermediate elongation).
Maturity: Supermature.
Fabric: 90% of quartz-quartz contacts are intergrown, usually meniscus-like. No vacuoles are present, but there are many terminated quartz crystals. Some thin overgrowths may be inherited. Evidence about age and type of intergrowths is equivocal, could be pressure-solution type or overgrowths or both. Dolomite cement and microdolomite masses are common. Floating quartz grains are about 5% of all quartz grains, concentrated in dolomite-rich areas.
Grain Contact Parmeters (means): Proportion of perimeter intergrowth 19.0% Number of contacts intergrown 33.% Number of interacting grains 5.6%
108 Sample Number W3 338-39 (Sample #2, at 103-1033 m: Fig. 3.6)
Abstract A moderately well sorted quartz sandstone, with dolomite cement Terrigenous material is 100% quartz, which is very fine- to medium-grained. Quartz-quartz contacts typically short concave-convex. Submature.
Mineralogy Quartz 83%, Dolomite 13%, Void space 4%.
Texture Grain size: Grains have a mean diameter of 0.21 mm, a median of 0.18 mm and a mode in the fine sand range. 90% of the grains are in the very fine to medium sand range (0.10-0.35 mm). It is moderately well sorted (S! = 0.68 mm),
fine-skewed (SKX = +0.19) and platykurtic (KQ = 0.85) and has no silt.
Grain shape: Grains are subangular to rounded, mainly rounded. Mean rounding = 3.96 (subrounded). Mean W/L = 0.63 (elongated).
Maturity: Submature.
Fabric: Quartz-quartz contacts are typically meniscus-like; some faint vacuoles show there to be secondary overgrowths. Also, some very small terminated crystal faces are present. Dolomite is present only as void fill, ranging up to 0.025 mm across. No floating quartz grains.
Grain Contact Parameters (means): Proportion of perimeter intergrowth 17.0% Number of contacts intergrown 26.0% Number of interacting grains 5.9%
109 Sample Number W3 362-63 (Sample #3, at 1103-110.6 m: Fig. 3.6)
Abstract A moderately well sorted quartz sandstone. Over 90% quartz, of very fine- to medium-sand size, with sparse dolomite cement. Grain contacts meniscus-like and more intensely intergrown. Submature.
Mineralolgy Quartz 91%, Dolomite 6%, Void space 3%.
Texture Grain size: Grains have mean diameter and a median of 0.21 mm and mode in the fine sand range. 90% of the grains are in the very fine to medium sand range
(0.96-0.33 mm). It is moderately well sorted = 0.67 mm), fine-skewed(SK X = +0.17), platykurtic (KQ = 0.80) and has no silt.
Grain shape: Grains are subangular to rounded, mainly subrounded. Mean rounding = 3.53 (subrounded). Mean W/L = 0.71 (equant).
Maturity: Submature.
Fabric: Grain contacts are meniscus-like to intensely intergrown, with concave-convex and straight-like sutures. Vacuoles absent. Some evidence of brittle failure of quartz grains before pressure solution (see below). Dolomite cement as void fill. Some sorting in fine (3-4 grain thick) bands; alternating .50 mm/. 14 mm median grain sizes. No floating grains.
Grain Contact Parameters (means): Proportion of perimeter intergrown 49.0% Number of contacts intergrown 57.0% Number of interacting grains 6.7%
110 Sample Number W3 373-74 (Sample #4, at 113.7-114 m: Fig. 3.6)
Abstract A moderately well sorted dolomitic quartz sandstone. Terrigenous grains are 100% quartz of very fine- to medium-sand size. Dolomite is very fine- to medium-crystalline. Quartz-quartz contacts typically straight. Dolomite as void fill cement and homogenous masses. Submature.
Mineralogy Quartz 65%, Dolomite 33%, Void space 2%
Texture Grain size: Quartz grains have mean and median diameter of 0.165 mm, and a mode in the fine sand range. 90% of the grains are in the very fine to medium
sand range (0.084-0.3J5 mm). It is moderately well sorted (ST = 0.67 mm), near
symmetrical (SKj = +100) and mesokurtic (KG = 0.99), with 1% silt.
Grain shape: Grains are angular to well rounded, mainly rounded. Mean rounding = 3.61 (subrounded). Mean W/L = 0.63 (elongated).
Maturity: Submature.
Fabric: Quartz-quartz contacts are generally heavily intergrown, often straight lines or concave-convex. Some overgrowths over vacuoles, but not common. Small quartz crystal termina-tions are present, so likely is combination of pressure solution and overgrowths. Dolomite is very fine- or medium-crystalline, rarely fine-crystalline. Void fill cement dolomite is monocrystalline. Floating quartz grains make up about 15% of total quartz, concentrated mainly in or near dolomite masses.
Grain Contact Parameters (means): Proportion of perimeter intergrown 52.0% Number of contacts intergrown 36.0% Number of interacting grains 5.2%
111 Sample Number W3 384-85 (Sample #5, at 117-117.3 m: Fig. 3.6)
Abstract A moderately well sorted highly dolomitic quartz sandstone. In detail, dolomite-rich and quartz-rich bands alternate. Quartz grains are very fine- to medium-sand size, dolomite has similar size range. Quartz-quartz contacts in quartz-rich bands typically heavily intergrown. Submature.
Mineralogy Quartz 56%, Dolomite 40%, Void space 4%.
Texture Grain size: Quartz grains have mean and median of 0.18 mm and a mode in the fine sand range. 90% of the grains lie in the very fine to medium sand range (0.1-0.32 mm). It is moderately well sorted (Sj = 0.70 mm), near symmetrical (SK, = -0.01) and musokurtic (KG = 1.00) with 4% silt (the most found in all the samples studied).
Grain shape: Grains are angular to well rounded, mainly subrounded to rounded. Mean roundness - 3.44 (subrounded). Mean W/L = 0.69 (intermediate elonga tion).
Fabric: Approximately 1 cm thick bands of quartz rich/dolomite rich rock. Quartzose rock is characterised by heavily intergrown contacts, either straight line or concave-convex. Obvious overgrowths are not common, but small quartz crystal terminations show overgrowths to be quite widespread. There are many floating quartz grains in the dolomite-rich bands.
Grain Contact Parameters (means): Proportion of perimeter intergrown 40.0% (much higher in quartz bands) Number of contact intergrown 57.0% Number of interacting grains 5.2%
112 Sample Number W3 397-98 (Sample #6, at 121-121J m: Fig. 3.6)
Abstract A very well sorted porous quartz sandstone. Terrigenous grains are all fine- to medium-sand size quartz. Most quartz-quartz contacts are concave-convex intergrown. Supermature.
Mineralogy Quartz 86%, Dolomite 3%, Void space 11%
Texture Grain size: Quartz grains have a mean of 0.20 mm, a median of 0.21 mm and
range from fine to medium sand (0.14-0.27 mm). It is very well sorted (ST = 0.20 mm), fine skewed (SK» = +0.20), leptokurtic (K Grain shape: Grains are angular to rounded, mainly subrounded. Mean rounding = 3.40 (subrounded). Mean W/L = 0.65 (subelongated). Maturity: Supermature. Fabric: Quartz grains are commonly intergrown (straight lines and concave-convex) with no obvious overgrowths. As usual, it is probably a combination of pressure solution and over-growths since small crystal termina tions in the voids. Voids are common, especially in "triangular" spaces between spherical grains usually dolomite-cemented. Grain Contact Paramenters (means): Proportion of perimeter intergrown 56.0% Number of contacts intergrown 65.0% Number of interacting grains 6.2% 113 Sample Number W3 404-10 (Sample #7, at 123.1-123.4; Fig. 3.6) Abstract Alternating quartz-rich/quartz-poor bands; quartz-rich are well sorted, porous quartz sandstone of fine- to medium-sand size. Dolomite is relatively fine-crystal line, and may be primary. Quartz-quartz contacts are concave-convex, intergrown. Quartz-rich bands are marginal mature/supermature. Mineralogy Quartz 57%, Dolomite 32%, Void space 11%. Trace of organic matter. Texture Grain size: Quartz grains have mean 0.192 mm, median of 0.191 mm and a mode of fine sand. 90% of the grains are fine to medium sand (0.12-0.27 mm). It is well sorted (S! = 0.78 mm), near symetrical (SKr = -0.03), mesokurtic (Kq = 1.01), with no silt Dolomite very fine- and fine-crystalline. Grain shape: Grains are angular to rounded, mainly subangular and rounded. Mean roundness - 3.00 (subangular/subrounded). Mean W/L = 0.67 (intermediate elongation). Maturity: Supermature/mature marginal. Fabric: Alternating quartz- and dolomite-rich bands, with many intergrown quartz-quartz contact in siliceous bands and numerous floating quartz grains in dolomite bands. Vacuoles not common, but are present as are small quartz crystal terminations. Good evidence for dissolution and reprecipitation on a single grain (see below). Floating quartz grains made up about 20% of quartz. Grain Contact Parameters (means): Proportion of perimeter intergrown 29.5% Number of contacts intergrown 49.0% Number of interacting grains 5.5% 114 Sample Number W3 413-14 (Sample #8, at 125.8-126.1 m; Fig. 3.6) Abstract A quartzitic dolostone. Dolomite is mainly very fine-crystalline (<0.016 mm). Quartz, which is concentrated in bands is well sorted fine- to very-fine sand with intergrown contacts in these bands. Mature. Mineralogy Quartz 33%, Dolomite 65%, Void space 1%, Gay Minerals 1%. Some organic matter is also present. Texture Grain size: Sand grains have a mean and median of 0.15 mm and a mode in the fine sand range. 90% of the grains are fine to very fine sand (0.09-0.26 mm). They are well sorted (Sr = 0.74 mm), near symmetrical (SKT = +0.02), mesokurtic (Ko =1.10) with 1% silL Dolomite all less than 0.05 mm. Grain shape: Grains are angular to rounded, mainly subangular. Mean roundness = 2.58 (subangular). Mean W/L = 0.68 (intermediate elongation). Maturity: Mature. Fabric: Rough segregation between quartz-rich and quartz-poor bands. 75% of the quartz grains are floating, in dolomite matrix; in the quartz-rich areas 5-10% are floaters. Straight-line contacts are common for touching quartz grains. A few clear vacuoles are present, but not in the floating grains, so no evidence as to whether any overgrowths are inherited. Grain Contact Paremeters (means): Proportion of permeter intergrown 24.0% Number of contacts intergrown 37.0% Number of interacting grains 4.8% 115 Sample Number W3 446-47 (Sample #9, at 135.9-136.2 m; Fig. 3.6) Abstract A very well sorted porous quartz sandstone. Grains are 100% quartz, of fine- to medium-sand size. Overgrowths over rounded, quartz grains are very common. Supermatu re-mature. Mineralogy Quartz 86%, Dolomite 2%, Void space 12% Texture Grain size: Entire quartz particles (i.e., including overgrowths) have a mean and median of 0.215 mm and a mode of fine sand. 90% of the grains fall in the range 0.15 to 0.295 mm (fine to medium sand). It is very well sorted (Sx = 0.8 mm), near symmetrical (SKj = 0.01) and mesokurtic (KQ = 1.00) with no silt Original grains would have smaller diameters, but probably would not fall out of the fine- to medium-sand range. Grain shape: Grains are angular to rounded mainly subrounded. Estimation of roundness difficult because of exaggerated overgrowths and intergrowths. Mean roundness = 3.3 (subrounded). Mean W/L = 0.73 (equant). Maturity: Mature-supermature (uncertainly due to rounding; probably supermature at deposition). Fabric: Extensively well developed overgrowths over vacuoles and intergrowths, usually convex-concave. "Triangular" pores between grains often empty, thus low dolomite/high void space. No floating grains. Main feature is the intense intergrowths of the quartz grains. Grain Contact Parameters (means): Proportion of perimeter intergrown 63.0% Number of contacts intergrown 68.0% Number of interacting grains 6.3% 116 Sample Number W3 459-60 (Sample #10, at 139.9-1403 m; Fig. 3.6) Abstract A well sorted porous quartz sandstone with some dolomite cementation. Grains are 100% quartz of fine- to medium-sand size, affected by over-growths and pressure solution. Supermature. Mineralogy Quartz 81%, Dolomite 9%, Void space 10% Texture Grain size: The quartz particles have a mean 0.193 mm, a median of 0.191 mm and a mode in the fine medium sand range (0.115-0.30 mm). 90% of the particles fall in the 1.78-3.13 range (very fine to medium). The sand is well sorted (Sj = 0.78 mm), near symetrical (SKr = -0.02), leptopkurtic (KQ = 1.20) and has no silt. Grain shape: Grains are angular to rounded, mainly subrounded. Mean roundness = 3.60 (subrounded). Mean W/L = 0.66 (sub-elongated). Maturity: Supermature. Fabric: Form of quartz particles is very similar to that in W3 446-47, but no vacuoles are present However, overall it is very similar. Appreciable porosity is present but some has been cemented by dolomite. There is a coarse dolomite rich/poor alternation. Grain Contact Parameters (means): Proportion of perimeter intergrown 46.0% Number of contacts intergrown 59.0% Number of interacting grains 5.9% 117 APPENDIX 3: POINT LOAD STRENGTH TEST RESULTS SAMPLE NUMBER TEST MODE POINT LOAD INDEX (MPa) W2 345-346 Axial (A) 1.60 345-346 A 3.40 345-346 Diametral (D) 4.40 345-346 D 4.60 W2 346-347 D 0.83 346-347 A 1.49 W2 348-349 A 0.49 348-349 D Too Small to Measure W2 351-352 D 1.15 351-352 A 1.45 351-352 A 1.55 W2 354-355 D 1.30 W2 358-359 D 1.25 358-359 A 2.5 W2 360-361 A Too Small to Measure on Graph W2 362-364 D 0.70 W2 365-366 D Too Small to Measure on Graph 365-366 A 1.25 W2 368-369 A 0.56 368-369 A 0.35 368-369 D 0.33 W2 369-370 D 0.25 369-370 D 0.27 W2 370-371 D 0.25 370-371 A 0.31 W2 371-372 A 0.60 371-372 D Too Small to Measure on Graph W2 377-378 A 0.38 W2 379-380 A 2.00 379-380 D 0.95 W2 383-384 D 2.60 383-384 A 2.70 W2 384-385 A 1.30 384-385 D 1.75 W3 335-336 D 1.2 W3 338-339 D 1.3 338-339 A 0.68 338-339 A 0.63 338-339 D 1.25 W3 340-341 D 1.71 340-341 D 0.57 340-341 D 0.71 W3 344-345 D 0.71 344-345 A 0.75 W3 346-347 A 1.2 118 346-347 D 0.71 W3 349-350 D 0.30 349-350 D 0.43 W3 351-352 D 0.50 351-352 A 0.33 W3 354-355 D Too Small to Measure on Graph 354-355 D Too Small to Measure on Graph 354-355 A Too Small to Measure on Graph W3 357-358 A 0.20 357-358 D 0.30 W3 359-360 A 0.57 W3 362-363 D 0.31 362-363 A 0.75 W3 364-365 D N.A. 364-365 A 1.40 W3 366-367 D 0.56 366-367 D 0.62 W3 369-370 D 0.76 369-370 D 0.79 369-370 A 1.40 369-370 A 1.49 W3 371-372 D 1.80 371-372 D 1.30 W3 371-372 A 1.85 371-372 D 1.30 W3 373-374 A 2.50 W3 375-376 A 1.20 375-376 A 1.10 375-376 D 0.63 W3 378-379 D 0.71 378-379 A 0.58 W3 381-382 D 0.33 381-382 A 0.61 W3 384-385 D 0.88 W3 388-389 D 0.76 W3 390-391 D 0.25 390-391 D 0.80 390-391 A 0.71 390-391 A 0.73 W3 392-393 D 1.25 392-393 A 1.85 392-393 A 1.45 W3 394-395 A 1.50 394-395 D 0.90 W3 397-398 D 1.35 397-398 A 1.90 397-398 A 2.15 W3 399-400 A 1.35 W3 401-402 D 0.49 401-402 D 0.80 W3 403-404 D 1.39 403-404 D 1.24 403-404 A 1.79 W3 404-410 A Too Small to Measure on Graph W3 413-414 D 0.26 W3 423-424 D 0.40 W3 435-436 D 0.30 W3 435-436 A 7.75 W3 445-446 D 3.90 445-446 A 5.10 W3 446-447 D 0.60 446-447 D 1.10 W3 448-449 D 1.10 W3 450-451 D 0.70 450^51 D 0.51 450-451 A 1.10 W3 453-454 D 0.90 453-454 A 1.3 453-454 A 1.3 W3 456-457 D 1.60 W3 459-460 A 1.70 459-460 A 459-460 D 1.50 W3 461-462 D 1.25 461-462 A 0.81 W3 463-464 D 0.82 W3 335-336 D 1.20 335-336 A 1.20 W3 413-414 A 0.68 413-414 A 1.0 W3 463-464 A 1.75 W3 404-410 D Too Small to Measure on Graph 404-410 D Too Small to Measure on Graph 404-410 A 0.40 W3 403-404 D Too Small to Measure on Graph 403^04 A 0.27 403-404 A 0.43 120 COMPRESSIVE STRENGTH TEST RESULTS SAMPLE NUMBER COMPRESSIVE YOUNG'S MODULUS POISSON'S RATIO STRAIN AT COMMENTS STRENGTH (Cp)(MPa) (GPa) (@ 50% Cp) FAILURE W2 348-349 33.0 10.68 0.29 5.258x103 W2 349-351 23.2 0.30 8.713x103 W2 351-352 27.9 7.87 0.30 5.262x103 W2 354-255 38.6 12.00 0.14 5.832x103 W2 360-361 5.04 13.50 6.080x103 Questionable results W2 368-369 29.81 14.67 0.44 6.944x103 W2 378-379 35.71 16.30 0.8.6 6.065x103 W2 381-382 47.62 23.70 0.04 7.959x103 W2 383-384 Test Results invalid W3 335-336 88.16 17.60 0.23 @ 33.3%Cp, 0.17 @ 15%Cp 7.411x103 W3 340-341 36.40 9.92 0.85 @ 33.3%Cp, 0.66@ 25%Cp 6.681x103 W3 344-345 38.94 12.45 0.86 6.537x103 W3 346-347 54.76 13.67 Erratic-strain gage-readings 6.677x103 W3 351-352 29.22 6.83 0.78 6.975x103 W3 357-358 22.46 3.67 0.48 1.114x103 W3 359-360 28.19 6.13 0.23 6.938x103 W3 362-363 51.16 13.60 0.27 6.399x103 W3 371-372 71.50 15.00 0.27 7.536x103 W3 373-374 52.86 8.15 0.77 6.601x103 W3 384-385 21.44 6.69 5.222x103 Reading of Strain Gage Analyses Impossible W3 390-391 7.27 4.665x103 Poor Quality Test W3 392-393 52.71 12.10 0.12 7.030x103 W3 397-398 56.38 12.75 0.85 @ 25%Cp 7.886x103 W3 399-400 51.71 12.60 0.64 7.122x103 Questionable Results W3 401-402 12.84 9.187x103 Poor Quality Test W3 413-414 90.30 18.15 0.28 7.089x103 W3 423-424 103.84 20.0 0.10 7.713x103 W3 435-436 1.99 10.55 0.25 1.955x103 W3 446-447 112.76 19.00 0.21 8.634x103 W3 448-449 65.82 14.40 0.26 8.121x103 W3 450-451 42.24 9.40 0.19 6.993x103 W3 453-454 38.30 8.90 0.83 7.120x103 W3 456-457 56.16 14.55 0.44 5.006x103 W3 459-460 48.95 12.60 0.22 6.595x103 W3 463-464 55.06 13.50 0.09 7.418x103 121 CONVERSION FACTORS FOR MEASUREMENTS IN ONTARIO GEOLOGICAL SURVEY PUBLICATIONS Conversion from SI to Imperial Conversion from Imperial to SI SI Unit Multiplied by Gives Imperial Unit Multiplied by Gives LENGTH 1 mm 0.039 37 inches 1 inch 25.4 mm 1 an 0393 70 inches 1 inch 2.54 cm lm 3.28084 feet 1 foot 0304 8 m lm 0.049 709 7 chains 1 chain 20.116 8 m 1km 0.621 371 miles (statute) 1 mile (statute) 1.609 344 km AREA 1 cm2 0.155 0 square inches 1 square inch 6.451 6 cm2 lm2 10.763 9 square feet 1 square foot 0.092 903 04 m2 lkm2 0.386 10 square miles 1 square mile 2.589 988 km2 lha 2.471054 acres 1 acre 0.404 685 6 ha VOLUME 1 cm3 0.06102 cubic inches 1 cubic inch 16387 064 cm3 lm3 35.314 7 cubic feet 1 cubic foot 0.028 316 85 m3 lm3 1.308 0 cubic yards 1 cubic yard 0.764 555 m3 CAPACITY 1L 1.759 755 pints 1 pint 0.568 261 L 1L 0.879 877 quarts 1 quart 1.136 522 L 1L 0.219 969 gallons 1 gallon 4346 090 L MASS lg 0.035 273 96 ounces (avdp) 1 ounce (avdp) 28349 523 g lg 0.032 150 75 ounces (troy) 1 ounce (troy) 31.103 476 8 g 1kg 2.204 62 pounds (avdp) 1 pound (avdp) 0.453 592 37 kg 1kg 0.001 102 3 tons (short) 1 ton (short) 907.184 74 kg It 1.102 311 tons (short) 1 ton (short) 0.907 184 74 t 1kg 0.000 984 21 tons (long) 1 ton (long) 1016.046 908 8 kg It 0.984 206 5 tons (long) 1 ton (long) 1.016 046 908 8 t CONCENTRATION lg/t 0.029 166 6 ounce (troy)/ 1 ounce (troy)/ 34.285 714 2 g/t ton (short) ton (short) lg/t 0.583 333 33 pennyweights/ 1 pennyweight/ 1.714 285 7 g/t ton (short) ton (short) OTHER USEFUL CONVERSION FACTORS Multiplied by 1 ounce (troy) per ton (short) 20.0 pennyweights per ton (short) 1 pennyweight per ton (short) 0.05 ounces (troy) per ton (short) Note: Conversion factors which are in bold type are exact. Tlie conversion factors have been taken from or have been derived from factors given in the Metric Practice Guide for the Canadian Mining and Metallurgical Industries, pub- lislied by tlie Mining Association of Canada in co-operation with the Coal Association of Canada. 122 3268 ISSN 0826-9580 ISBN 0-7778-1496-X