THE SEDIMENTOLOGY AND PETROLOGY
OF THE EARJ... Y PROTEROZOIC GOWGANDA FORMAT ION
AROUND GOWGANDA - ELK LAKE, ONrARIO, CANADA
A THESIS
SUBMITTED TO THE FACULTY OF TllE GRADUATE SCllOOL
OF THE UNIVERSITY OF MINNESOTA
BY
LAWRENCE COLLINGER ROSEN
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
OF SCIENCE
APRIL 1965 ABSTRACT
Evidence for glacial-marine sedimentation in the Gowganda
Formation (Huronian Supergroup) in the Gowganda - Elk Lake area of northeastern Ontario changes · the previously known regional distribution of continental glacial and glacial-marine sedimentary facies. Lindsey (1969) interpreted the Gowganda to be a marine deposit in the south (Espanola-Whitefish Falls area) and a continental deposit
in the north (Cobalt area) which includes the area of this study.
In the study area, the Gowganda rests unconformably upon the
Archean basement. The subhorizontal format ion is from 0 to >1600 ti1 thick (based on drill hole data) and no complete sections are present.
It is a heterogeneous assemblage of d iamict it e, art hocong lore er ate, graywacke, arkose, siltstone, argillite, dropstone laminite, and sedimentary breccia. Lateral and vertical f a cies changes can be rapid; however, the graywacke-argillite association is abundant, widespread, and constitutes the dominant fac ies. Diamict ite is a prominent lithology and varies from massive to weakly stratified with ci.asts up to 1.2 m in apparent diameter; units vary from a decimeter to as much as 20 m in thickness. Contacts with other units can be sharp) irregular, or gradational. Diamictite is restricted to the lower two- thirds of the formation. Orthoconglomerate and massive to thick bedded arkose, occasionally cross-bedded, are most common at the base of the section and again near the top.
Interbedded graywacke, siltstone, and argillite commonly constitute fining-upward sequences from 2 cm to 4 m thick in the lower
ii portion of the section and both fining-upward and coarsening-upward sequences in the upper part of the section. Internal stratification includes graded beds, ripple marks, laminations, and convolute bedding. In addition, features such as ripped-up clasts, flame structures, and other loading phenomena are present. Thinly laminated siltstone and argillite sequences with dropstones as large as 30 cm are present in the lower two-thirds of the section. They are more common in the central and western portions of the study area.
Dropstone sequences are as much as 40 m thick, while individual units vary from 1 to 5 m thick. Sedimentary breccias and units with soft- sediment deformation structures are fairly widespread but constitute a minor part of the section; units vary from 0.5 to approximately 4 m thick.
Paleocurrents in the Gowganda and overlying Lorrain Formation have vector means of 143° and 168°, respectively. The low variance
(2718) in the I..orrain suggests deposition in a fluvial environment.
Detritus composing the Gowganda Formation was from a granite- greenstone terrane which underlies the formation and crops out locally in the study area and to the north.
The chemical index of alteration (CIA) suggests that climatic conditions were initially moderate, deteriorated to frigid conditions, and eventually returned to a more moderate climate. Gowganda rocks are typically Na-rich and probably reflect the source The diamictites are depleted in Fe and Mn relative to crustal abundances and this suggests that the diamictites were deposited in a marine environment.
iii The deposit iona 1 model for glacial-marine sedimentation in the
Gowganda Format ion is based on Antarctic models and involves an ice shelf. Proximal deposits include massive and stratified diamictites.
Intermediate and distal deposits contain dropstone laminites.
Meltwater is minimal or absent. In this model, weakly stratified diamictite and thicker, massive diamictite are interpreted to be the products of rapid fallout of abundant debris beneath an ice shelf. The generally thinner, massive diamictite is attributed to submarine gravity flow mechanisms. The fining-upward and coarsening-upward sequences reflect the changing conditions within the basin as
increases and decreases in both energy and sediment supply occurred, possibly due to fluctuations in the position of the ice margin. The graywackes resulted from the interaction of various types of sediment gravity flows, dominantly turbidity currents with subordinate fluidized/liquidized flows and possibly grain flows. The more well- sorted sandstone, siltstone, and argillite may represent more normal marine sedimentation. Breccias and deformed units represent either resedimentation from unstable depositional sites or tectonic instability. The vertical distribution of diamictite and dropstone facies suggests two major ice advances occurred, separated by normal marine deposition. Amelioration of the climate in late Gowganda time is indicated by the lack of glacial features in the rocks.
Sedimentation appears to have been largely marginal marine to deltaic; a transition to fluvial dep1Jsition occurs at the top of the section and is evident in the overlying Lorrain Formation.
iv ACKNOWLEDGEMENTS
I would like to express my gratitude to the individuals involved
in the conception; evolution, and at last, the completion of this
thesis.
The project was first suggested by Dan Innes, who provided a valuable introduction to the Huronian Supergroup and encouraged my
field progress. I am indebted to Falconbridge, Ltd., whose Timmins
office staff helped in my professional development. Falconbridge also
provided generous financial assistance for my field work, the making
of thin sections and geochemical analysis of samples. I would also
like thank my field assistant, Clive Martin. His hard work,
companionship, and sense of humor was valued. He also instructed me in
the finer aspects of shooting tequila.
I wish to thank the faculty of the geology department at UMD for
their contributions in furthering my education. In particular, I am grateful to my advisor, Dr. R.W. Ojakangas, and the other members of my thesis committee, Dr's C.L. Matsch and J.A. Grant. Their helpful
insight and numerous suggestions for the manuscript aided greatly in
producing the final draft. Special thanks are given to Dr. Ojakangas and Dr. Matsch for their visit to my field area. They endured fcur- wheel drive treks, motorized canoe journeys, and single-engine float plane flights in order to view important exposures. Considering they are OAE's, I am certain their adventures with me were also exciting.
Finally, I would like to express my gratitude to my family and
friends. Their encouragement, under st anding, and sup port throughout this endeavor made my work easier. v TABLE OF CONTENTS
Page .ABSTRACT. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ii
ACKNOWLEDGB1ENT S. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • v
TABLE OF CONI ENTS ••••••••••••••••••••••••••••••••••••••••• I' • • • • • • • • V1
ILLUSTRATIONS...... • • . • • . . . . • . • • • • . • • . . . • • . • . . • . • • • ...... • . • • • • • . . ix
TABLES •••••••••••••••••••••••••••.•••••.••••••••••••••••..•••••.••• xii
CHAPTER 1 - INTRODUCTION...... l
Purpose .. ..•...... _...... l Location...... l Previous Work ....•.••...•...... •.....•...••...... 4 Present Study...... 9
CHAPTER 2 - REGIONAL GEOLOGY ••••••••••••••••••••••••••••••••••••••• 10
General Stat enent ...... 10 Arc he an • •••.•.••••••••••••.•••••••••••.•..••..••••••••••••.••• iO Prot ere zoic ...... 12 Phanerozoic ...... 25 Cenozoiic. 25
CHAPTER 3 - LITHOLOGY OF THE GOWGANDA FORMAT ION. • • • • • • • • • • • • • • • • • • • 21
General St at anent...... • ...... 27 Terminology ...•..•...... 1t••••••••••••••· 29 Strat·igraphic Column ...... 30 Sandstones •••••••••••••••••••••••••••••••••••••••••••••••••••• 32 Diamict it es ...... •..•...... •...••..... 36 Lonestone-bearing Sedimentary Rocks •••••••••• ., •••••••••••••••• 43 Orthoconglomerates ..•...... •...... •..... 44 Siltstones •••••••••••••••••••••••••••••••••••••••••••••••••••• 45 Arg il lit es ...... 49 Breccias ...... •...... •...... 50 Chaotic/Slumped Units ...... 53 Sedimentary Structures ••••••••••••••••••••••••••••• 53
CHAPTER 4 - ARCHEAN-PROTEROZOIC UNCONFORMITY ••••••••••••••••••••••• 59
CHAPI'ER 5 - STRUCTURE •••••••••••••••••••••••••••••••••••••••••••••• 70
Fo 1 ds . • • • • • • . . • • • . • • • • • . • • • . . . • • • • . • • . . • . • • • • . • • . . . • • . . . • • . • . . 7 0 Faults ...... •...... •...... 71
vi TABLE OF CONTENTS
CHAP'r ER 6 - PET ROG RAPHY. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 7 3
Procedure ...... 73 Mineralogy ...... •...... 73 Quartz ...... •...... 77 Feldspar ...... 78 Rock Fragments...... 7 9 Matrix • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • 7 9 Cement...... • ...... 80 Accessory Minerals •• •.••••••••••••••••••••••••••••••••••••• 80 Compositional and Textural Features ••••••••••••••••••••••••••• 81 Diamict it es ...... 81 Sand st ones...... 83 Lonestone-bearing SedimentaTy Rocks ••••.•••••••••••••••••••• 89
CHAPTER 7 - GEOCHEMISTRY •••••••••••••.•••••.••••••••••••••••••••••• 91
General Statement ...... 91 Chemical Alteration and Weathering ••••••••••••••••••••.••••••• 91 Other Characteristics •••••••••••...••••••••••..•..•..•..•••.•• 95
CHAPTER 8 - PALEOCURR&'IT ANALYSIS AND PROVENANCE ••••••••.••.•••...• 101
Paleocurrent Analysis ...... 101 Provenance ...... a •••••••••••••••••• 104
CHAPTER 9 - SEDIME.t-.'TAT ION •••••••••••••••••••••••••••••••••••••.•••• l 07
Interpretation of Depositional Processes •••••••••••••••••••••• 107 Introduction ...... 107 Basal Sequences ...... ••...... •....•.•....•...•... 107 Gra1·wacke Sandstones ..•...... •...... 109 Argil lite and. Siltstone...... 111 Laminated Lonestone-bearing Sedimentary Rocks ••••••••••••••• 113 Diamictit e ...... 115 General Discussion •••••••••••••••••••••••••••••••••••••••• 115 Origin of Gowganda ••••••••••••••••••••••••••••• 117 Massive Diam.ictite ...... •...... 117 Stratified Diamictite ••••••••••••••••••••••••••••••••••• 119 Arkose and Lithic Sandstone ••••••••••••••••••••••••••••••••• 120 Sedimentary Breccias ...... 122 Chaotic/Sluraped Unita ...... •....•...... • 123
vii TABLE OF CONI ENT S
CHAPTER 10 - DEPOSITIONAL MODELS ••••••••••••••••••••••••••••••••••• 124
Introduction •••••••••••••••••••••••••••••••••••••••••••••••••• 124 Discussion of Models in the Literature •••••••••••••••••••••••• 128 Arctic Models ..• ...... •...... 129 Antarctic Models .•. ....•.•.....•...... •.••...... •• . 133 Model of Gowganda Sedimentation •••••••••••••••••••••••••• -••••• 137 Depositional History ••.....•••.•....•...... •.....••..•....•. 145
CHAPTER 11 - TECTONIC SETTING •••••••••••••••••••••••••••••••••••••• 149
SUMMARY AND CONCLUSIONS •••••.•••••••••••••••••••••••••••••••••••••• 154
REFERENCES •••••••••••••••••••••••••••••••••••••••••••••.••••••••••• 158
APPENDIX A...... • • • • • • • • • • • . • • • . . • • • • . • • • • • • • • • • • • • • . . • • . . • • • • . . • • • Al
APPENDIX B. • • • • • • . • • • • • • . • • • • • • • • . • • • . . . • • • • • . . . . • • . • . • • • • . . • . . . • • • Bl
viii ILLUSTRATIONS
Figure Page
1.1 Location map of Ontario with study area outlined •••••••••••••• 2
1.2 Map of study area showing the distibution of the Gowganda Format ion ••...•.••....•••. . • . • • • . . • . . . • . . • . . . . • . • ...... 3
2.1 Regional geology of the area north of Lake Huron ••••••••••••• 11
2.2 Photograph of climbing ripples in a fine-grained sandstone of the McKim Formation south of Espanola ••••••••••.•••••••• 15
2.3 Photograph of staurolite-bearing interflow rocks of the Stobie Formation at the Stobie-Frood Mine Complex •••••••••• 16
2.4 Photograph of a elastic dike of Bruce Formation cutting rocks of the Espanola Formation ••••••••.••••••••••••••••••• 18
2.5 Photograph of large-scale cross-bedding in quartz sandstone of the Serpent Formation south of Espanola •••.•.••••••••••• 19
2.6 Photograph of trough-style cross-stratification in arkose sandstone of the Lorrain Formation •••••••••••••••••••••••.• 20
2.7 Photograph of planar-style cross-stratification in Lorrain Format ion sandstone...... 23
2.8 Photograph of intraclast conglomerate of quartz-rich siltstone fragments in the Gordon Lake Formation ••••••••••• 24
2.9 Photograph of quartz sandstone of the Bar River Formation on Welcome Lake .••.•.•....••.••••...... •..•....•..••.... 21+
3.1 Sandstone classification scheme ...... 28
3.2 Generalized stratigraphic column of the Gowganda Formation in the Gowganda - Elk Lake area ...... 33
3.3 Photograph of medium-grained graywacke with outsized clasts and load structures from Firth Lake •••••••••••••••••••••••• 34
3.4 Photograph of clast-rich diamictite from roadcut along Hwy. 560 east of Gowganda •.•..••••••.•.••...••.•.••.••..••••..•• 37
3.5 Photographof massive diamictite with chlorite-rich matrix from a roadcut along Hwy. 558 •••••••••••••••••••••••••••••• 38
3.6a Photograph of clast-rich weakly-stratified diamictite with possible inverse grading ...... 41
ix ILLUSTRATIONS
Figure Page
3.6b Photograph of diamictite interbedded with lonestone-bearing lam.inites ...... •...... •• 41
3.7a Photograph of large (0.3 m) granitic lonestone in laminite sequence exposed on shore of Firth Lake •••••••••••••••••••• 42
3. 7b Photograph .of smaller lonestone in laminit e sequence from Banker Bay, Gowganda Lake •.•...... ••..••..•...... •.••..... 42
3 .8 Photograph of moderately-sorted orthoconglomerat e from west shore of Bobtail Lake ••.•..•.••..•.•••.•••..••.••.••.•...•. 47
3.9 Photograph of well-sorted amd stratified quartz-pebble-rich orthoconglomerate along Hwy. 560 west of Lost Lake ••••••••• 48
3.10 Photograph of red and green argillite beds with irregular and lensing stratification ...... 51
3 .11 Photograph of slab bed specimen of argillit e showing soft- sediment deformation features •••••••••••••••••••••••••••••• 51
3.12a Photograph of sedimentary (intraclast) breccia from the northeast shore of Firth Lake ••.•••••••••.•••••••.••••••• 52
3.12b Photograph of blocky, angular clasts of thinly-bedded, laminated argillite in a muddy matrix •••••••••••.•••••••••• 52
3.13 Photograph of slumped unit showing deformed laminae around granitic clasts from south shore of Babs Lake •••••••••••••• 54
3.14 Photomicrograph of small-scale scour in hematite-rich silty fine-grained sandstone ..•..•.••.•••...•.•...•••••••••.•.•.• 54
3.15 Photograph of rippled, hematitic silty arkose from the top 30 m of the Upper Coleman Member ••••••••••••••••••••••••••• 57
3.16 Photograph of soft-sediment deformation (convolute bedding) in a laminated siltstone ••.•••••••••.••.••••••.•.•••.•••••• 57
4.1 Map of the study area with sites where the Archean- Proterozoic unconformity was examined •••••••••••••••••••••• 60
4.2a Photograph of regolith composed of granodiorite and its weathering products ••••••••••••••••••••.••••••••••••••••••• 62
x ILLUSTRATIONS
Figure Page
4.2b Photomicrograph of sample from regolith deposit. Mineral aggregate of sericite, biotite, chlorite, magnetite, and leucoxene after original hornblende •••••••••••••••••••••••• 62
4.3 Photograph of angular fragments of Archean basement from unconformity exposure. Fragmentation possibly caused by frost-wedging ...... •....•..•...... 65
4.4 Photograph of blocky, angular clasts of metasedimentary rock from unconformity, northwest shore Obushkong Lake ••••• 65
4.5 Photomicrograph of cross-section of the Archean-Proterozoic contact showing possible groove in basement rock .•••••••••• 67
4.6 Photograph shows the Archean-Proterozoic contact dipping steeply to the east ...... •...... 68
6.1 Plot of Q:F:L ratios for samples of diamictite and graywacke ...... •...... 82
6.2 Photomicrograph of massive diamictite •••••••••••••••••••••••• 84
6.3 Photomicrograph of stratified diamictite ••••••••••••••••••••• 84
6.4 Plot of Q:F:L ratios of sandstones with <15% matrix •••••••... 85
6.5 Photomicrograph of arkose sandstone ••••••••••••••••••.••••••• 88
6.6 Photomicrograph of quartz grain with its long axis in a vertical orientation. Beds beneath quartz grain are de- pressed under it ...... 88
6.7a Photomicrograph of lonestone which is an aggregate of grains and has a graywacke-like texture •••••••••.•••••••••• 90
6.7b Photomicrograph of a graywacke-aggregate lonestone which has a minimal effect on the substrate •••••••••••••••••••••• 90
7.1 Histogram of CIA values calculated for samples of argillite and diamict it e...... • ...... • ...... • • • . . . • . . 94
7.2 Diagram of the relative abundance of Cao, and K20 from samples of diamictite and compared to the Archean Shield average•••••••••••••••••••••••••••••••••••v• 98
1.3 Plot of weight % FeO versus MnO from samples of diamictite. Results compared to other studies and crustal abundance •••• 99
xi ILLUSTRATIONS
Figure Page
8 .1 Rose diagrams of uncorrected paleocurrent measurements for the Lorrain and Gowganda Formations •••••••••••••••••••••••• 102
8. 2 Rose diagrams of corrected pa leocurrent measurements for the Lorrain and Gowganda Formations •••••••••••••••.•••••••• 103
9.la Summary of the principal sedimentation mechanisms of sediment gravity flows ...... ••...... 110
9.lb Hypothetical evolution of a single flow either in time or in space ..•...... •...... 110
9.2 Summary of the main deposit types formed during deposition from sediment gravity flows •••••••••••••••••••••••••••••••• 112
10.l Lindsey's (1969) paleogeographic reconstruction of proposed marine - fresh water trans it ion in the Gowganda Format ion •• 138
10.2 Generalized section from Nicol Twp. with interpretation of glacial activity/position of ice margin •••••••••••••••••••• 141
10.3 Generalized section from Milner Twp. with interpretation of glacial activity/position of ice margin •••••••.••••••• : •••• 142
10.4 Gowganda Formation column with interpretation of relative glacial activity ...... 143
10.5 Model of glacial-marine deposition for the Gowganda Formation in the Gowganda - Elk Lake area •••••••••••••••••• 144
TABLES
Table Page
2.1 The groups, formations, and lithologies which comprise the Huronian Supergroup ••••..••••.•.••••.••••••••.••••••.••.•.• 14
6.1 Modal analyses of 38 point-counted thin sections ••••••••••••• 74
7.1 The chemical index of alteration (CIA) values and the oxides in molecular proportion used in the calculations •••• 93
xii INTRODUCTION
Purpose
The primary purpose of this investigation is a detailed study of the Gowganda Formation near its northern outcrop limit in the north- central portion of the Cobalt Embayment in northeastern Ontario. The origin of the Gowganda Formation has been a subject of controversy, and reinterpretation of the constituent lithofacies is needed in view of recent developments in our understanding of sedimentary structures and stratification sequences. Therefore the petrology and sedimentary structures were analyzed to determine (1) the provenance of the sediments, (2) environments of deposition,(3) sedimentary processes,
(4) depositional model, and (5) the tectonic setting of the formation.
Location
The Gowganda Formation crops out for approximately 400 km, from
Sault Sainte Marie, Ontario, in the west to Noranda, Quebec, in the east. This investigation concentrated on the occurrences of the
Gowganda Formation around the towns of Gowganda and Elk Lake, Ontario, in the northeastern part of the outcrop area. The thesis area includes portions of thirteen townships within the mining district of
Timiskaming and covers over 1000 square kilometers.
Access is by Provincial Highway 560, which traverses the area in an east-west direction and can be reached from Sudbury, Ontario, via
Provincial Highway 144 (Fig. 1.1). Various logging and mining roads and the Hydro-Electric Power Commission road in the area are amenable
1 Figure 1.1 Location map. Study area is in northeastern Ontario, Canada, and is shown in more detail in Figure 1.2.
2 STUDY AREA
Oowganda fm.
LU B Faull llOAOllOUSE
: 9 El Road WALLIS tJ t7 -- --- (!j 8oddl•1 ollll•do
NHlh ¥ 1 --, I IJ 16 JO UMO • 1 1
1 I If 3f lf t Bl:ALE l:al3.440 FlguL·e 1.2 Map of tlae study area showing the occurrence of the Cowganda FormatJon. (Modified from 0.G.S. ·Map 2205.) to motor vehicles. Less accessible sites are reached by m:otorboat, floatplane, and helicopter. The topography is largely controlled by the bedrock geology but has been subdued in part by Pleistocene and Recent deposits. The area is one of moderate relief with a maximum relief of 120 m in southeastern Haultain Twp. near Flatstone Lake, where a north-trending ridge of Nipissing Diabase reaches an elevation of approximately 460 m above sea level. Similar elevations are attained in western Milner Twp., which is underlain by rocks of the Gowganda Formation. In contrast, lower elevations are commonly underlain by Archean metavolcanics. Drainage of the region is to the north via the Montreal River system and its five main tributaries; West Montreal River, Wapus Creek, Calcite Creek, Bear River, and the Makobe River. The economic base of the region is comprised of logging, tourism, and mining. Previous lim Early reconnaissance mapping along the north shore of Lake Huron by Murray (1847) and Logan (1849) delineated the major geological features of the area. The first workers to map in the Shiningtree, Gowganda, and Elk Lake areas were Burwash (1896), Collins (1913), and Knight (1907), respectively. Shiningtree is located approximately 50 km to the west of Gowganda. Recent mapping of the area, conducted by the Ontario Geological Survey, is on a scale of one inch equals one-quarter mile (1:15,840). 4 Reports on the geology with accompanying maps on a scale of one inch equals one-half mile (1:31,680) were published by Carter (1977) , Mcllwaine (1971, 1978), and MacKean (1968). Early theories on the origin of the Gowganda Formation proposed by Miller 0905) included volcanic fragmental and desert sedimentation. An alluvial fan-fluvial environment was suggested by Bain (1925) and McConnell (1927). The first person to propose a glacial environmerit was Coleman (1907) and this has remained the most popular model. He felt the abundance of ,' 'bowlder over such a large area, the presence of polished and striated stones, and close resemblance to the Dwyka Tillite of South Africa was evidence for glaciation. Coleman believed it represented continental glaciation (ice sheets) rather than local mountain glaciers. Schenk 0965) studied Gowganda rocks at the south end of Lake Timagami, situated about 90 km southeast of the study area. He described the unconformity with the Archean and noted that t h e basement rocks are polished and striatedJhe exposed rocks consist of three cycles of graywacke." and argillite-quartzite deposited on a mountainous (>900 m relief) pre-Gowganda topography. He concluded that glaciation was responsible for deposition of the conglomeratic graywacke and that the argillite-quartzite was indicative of interglacial or periglacial conditions. Paleocurrent data indicated a north to south transport direction. Ovenshine (1965) studied sedimentary structures in the Elliot 5 Lake-Bruce Mines area. These structures suggested that deposit ion of the "sparse boulder occurred by non-disperse flow which was ."linear, differential and not especially Non-disperse flow occurs in bulk transportation processes such as debris flows or glacial flow. Sequences of finer-grained, graded beds suggested turbidity current processes. He also believed that while ice-rafting of the megaclasts was responsible for producing some structures, there was a noticable lack of disrupted and folded beds expected due to impact. His conclusions favored aspects of a glacial environment for the origin of the sparse boulder graywacke. Lindsey (1969) attempted a more regional study of the Gowganda. In a paleogeographic reconstruction, he suggested that continental and marine facies can be distinguished on the basis of regular (i.e. varved) versus irregularly laminated argil lit es. His reconstruct ion places the area of the present investigation in the continenta l facies. Young 0970) correlated the Gowganda with deposits of similar lithology and age in the Upper Peninsula of Michigan, the Medicine Bow Mountains in Wyoming, and at Chibougamau in northern Quebec. Based on age, lithology, and chemistry, and supported by paleomagnetic and paleocurrent studies, he proposed the existence of a widespread Early Proterozoic glacial event. He suggested that homotaxial stratigraphic successions, specifically tillites overlain by aluminous quartzites, are time-stratigraphic markers for the North American Early Proterozoic that can possibly be extended on a global basis (Young, 1973). In more recent work, Young (1981) delineated fourteen 6 members within the Gowganda Formation in a section south of Whitefish Falls, Ontario. His paleoenvironmental interpretations place the lower nine members in a glacial-marine setting representing two major advances with an intervening non-glacial episode. The upper part of the formation shows no direct evidence of glacial influence; the presence of two major coarsening-upward sequences suggests prograding deltaic sedimentation. Miall (1983) has interpreted sedimentation of the Gowganda using drill core from its northern outcrop limit in Fallon Twp., Ontario, approximately 25 km north of the study area. He found evidence for a glacial-marine environment and proposed a depositional model incorporating an ice shelf. Card (1978) suggested that the materials comprising the Gowganda were derived and transported to the basin by glacial processes. He felt, however, that the mechanism for deposition of the massive, unsorted sedimentary rocks (diamictites) was largely by debris flows triggered by tectonic instability in the bas in. An early geochemical approach to the origin of the Gowganda was undertaken by Pettijohn and Bastron (1959) who analyzed argillites. They found that the samples were depleted in Cao, and the Na 20/K2o ratios were higher than in most pelitic rocks but similar to many graywackes. They invoked sodium-metasomatism to explain the anomalous geochemical imprint. Young (1969) examined the matrix materials of the diamictites in addition to the argillites. He concluded that regional variations in the chemical compositions of the matrix materials 7 reflected the difference in source terranes. The argillites were more homogeneous. Young also noted a relative enrichment of iron and magnesium in the diamictites and thought it could be explained by the breakdown of mafic minerals. Recent studies involving trace elements have been conducted by McLennan, Fryer, and Young (1979). They used matrix material from Gowganda diamictites to estimate rare earth element (REE) abundances for the post-Kenoran upper continental crust. Their analyses supported earlier conclusions regarding a more mafic source for the Gowganda area and a more felsic source for the Bruce-Mines-Blind River area. They also noted that the Gowganda samples caused a deviation in the chemical evolutionary trend of the Huronian rocks and suggested this was due to the supposed glacial origin of the Gowganda. Nesbitt and Young 0982) measured the degree of weathering from chemical analysis of lutites and diamictite ·matrices in the Huronian Supergroup by calculating a chemical index of alteration (CIA). The resultant values were used to infer plate motions and climate during deposition of this early Proterozoic sequence. Further discussion of the geochemistry of the Gowganda from previous work will be presented and compared with results from this study later. Efforts ·to determine the paleolatitude of the Gowganda at the time of deposition using paleomagnetism have yielded less than satisfactory results. Symons (1967) first reported a paleopole position for Gowganda sediments of 21.5° S, 82.5° E. In more recent work, the paleopole position was revised and located at 65° N, 123° W 8 (Symons, 1975). Morris (1977) reports a :'Remanence A." position for the pole at 66° N, 035° E. results produce estimated paleolatitudes of approximately 75° S, 60° N, and 30° N respectively for the region north of Lake Huron during Gowganda time. Present Stud_y Field work was conducted during the summer of 1981 with follow-up and re-examination of some sites the succeeding summer. Orientation in the field was achieved by use of aerial photographs in conjunction with geological maps published by the Ontario Geological Survey. Some traverses were designed to- visit areas where the Archean-Proterozoic unconformity is Others were designed to locate sections for the measurement and description of the exposed stratigraphy. Pebble counts for lithology and .clast size determination on diamictites and orthoconglomerates were recorded where appropriate. Strikes and dips of bedding and measurements of paleocurrent indicators were taken with a Brunton compass. Samples were collected for petrographic examination and geochemical analysis. 9 REGIONAL GEOLOGY General Statement The study area is near the northern edge of the Cobalt Embayment, part of the Southern Structural Province of the Canadian Shield. Deposits of Archean, Proterozoic, and Phanerozoic age are present (Fig. 2.1). Archean The Archean age rocks of the Superior Province comprise a major tectonic subdivision of the Canadian Shield (Stockwell, 1964). Archean rocks lie mainly to the north of the study area, though some do occur within the area and are always found to underlie the Gowganda. The Archean terrane is comprised of alternating volcanic-sedimentary zones (greenstone belts) and migmatitic granite-paragneiss zones, typical of shield regions around the world. While structural styles are varied and complex, structures are predominantly east-trending and commonly feature isoclinal folding and steep to vertical strike-slip faults. The general grade of metamorphism is low to medium greenschist; however, areas of amphibolite and granulite grade exist. The general stratigraphy consists of sequences of mafic to felsic metavolcanics with subordinate ultramaf ic and alkalic metavolcanics. Metasediments formerly classified as either Keewatin or Timiskaming are found within and overlying the metavolcanic sequences. The metasediments include conglomerate, sandstone, mudstone, marble, iron- formation and ferruginous cherts. The metavolcanics and metasediments 10 QJ PALEOZOIC 11 CAMlllAH · DIVONIAH HDIMINIS PROTEROZOIC =<::::;- 10 OUll QIOUP t MAflC IOHIOUI IOCKI J.+ v I Ul.llC IOHIOUI IOCIU Tlmml'l.( . 1 AHIM1•11 o•our • HUIOHIAN 1ut1101our ARCHEAN I OIAHITIC IOCkl 4 MhJMAllflC IOCll I MAPIC/UUIAMAflC IOHIOUI IOCICI I MllAllDIMIHJAIY IOCKI I MllAYOlCAHIC ROCKS I-' I-' • cP (j) c::::n '-.....L 'U .p-· \ • v;g ""2: . .·- '# . • &• """' '·'• 2' '• ,. / / . . ---....__ -- . . Espanola .,.,..,, . Z!/ . CJ Nor lh + ------·______r n11:1 1 c. !. l .· Scole 1 : 1,800,000 0 60 Kllomelora l-==-t t--·:==j___ _.. 0 Mii., Figure 2.1 Regional geology of the area north of Lake Huron (modified after OGS Map #2440); have been intruded by mafic and ultramafic rocks, which in turn have been intruded by felsic plutons supposedly emplaced at the time of the Kenoran Orogeny (Stockwell et al., 197 0). The final intrusive phase involved emplacement of mafic rocks. These are the north-trending diabase dikes 1n the study area, which are part of the Matachewan swarm, dated at 2,690:t93 m.y. using Rb-Sr whole rock analysis (Gates and Hurley, 1973). Proterozoic The Early Proterozoic (Aphebian) supracrustal rocks of the Southern Province are referred to as the Huronian Supergroup. The term .'_'Huronian Supergroup" is used in accordance with the recommendation of the Federal-Provincial Committee on Huronian Stratigraphic Nomenclature (Robertson et al., 1969). Originally used in a time- stratigraphic sense, it is to be used in a rock-stratigraphic sense to designate Early Proterozoic supracrustal rocks of the Southern Province which are younger than the Superior Province granitic basement rocks and older than the Nipissing Diabase. Based on radiometric dating of the Archean basement rocks and the Nipissing Diabase, rocks of the Huronian Supergroup were deposited between approximately 2,500 m.y. and 2,150 m.y. ago (Van Schmus, 1965; Fairbairn et al., 1969). Direct dating of the Huronian rocks suggests deposit ion between 2,300 and 2,640 m.y. ago. Data provided by Fairbairn and others (.l 96 9) gave a Rb-Sr who le-rock isochron age of 2288:t.88 m.y. for Gowganda Formation sedimentary rocks around the town of Gowganda. Knight (1967, in Card, 1978) reported a Rb-Sr isochron 12 date of 2496:!;.145 m.y. for Spragge Group metavolcanics located southwest of Sudbury in Spragge Twp., which are thought to be correlative with the basal Huronian metavolcanics in the Sudbury region. The Huronian Supergroup has an aggregate thickness in excess of 12,000 meters and consists of largely siliciclastic sedimentary rocks displaying eye lical rep et it ion of conglomerates (diamict it es and/ or orthoconglomerates), pelitic rocks, and sandstones (Roscoe, 1969). Variation in formational thickness is common and locally lower members of the stratigraphy are notably absent. In general, there is a southward thickening of the pile. This is due in large part to the presence of more of the constituent format ions in the south. Progressively younger formations overlap the Archean basement as one mqves north. Locally, the change in thickness i n particular units is abrupt and is now marked by faults belonging to the Murray Fault System (Card et al., 1977). The average thickness of the Huronian Supergroup in the study area is usually less than 2500 meters while in the Sudi:>ury- Manitoulin area the average thickness is on the order of 10,000 meters. The Huronian Supergroup has been deformed and metamorphosed to varying degrees. North of Lake Huron in the Penokean fold belt the strata were compressed, producing moderately open to tight folds. The axial surfaces of the major folds are typically upright to slightly overturned to the north and the axes are aligned generally east-west. There is local variation. The grade of metamorphism ranges from low 13 GROUP FORMATION COMPOSITE LITHOLOGICAL SEQUENCE BAR RIVER auartztre, red siltstone GOROON LAKE varicolored 1Utatone Quartzite LORRAIN Cobalt UkOle re<1<1t1h aroilllt• and siltstone uollllt• GOWGANOA siltstone. oraywacke dlamic1ite. orthoconolomerare gray and pink arkoae SERPENT arkoae•suograywack• Quirke Lake dotomlle, 111ta1one ailtatone, graywacX• Hmeatone BRUCE dlemlctlle !.llSSISSAGI coarse 1ubaft(oa• Hough Lake PECORS argllllt1, slltalone RA!.ISAY LAKE dtamicUt• !.loKIM auograywacke, arotlllt• !.IATINENOA orltty suDarxo.. Elliot Lake COPflER CLIFF acid volcanic& SALMAY IE THESSALON PATER LAKE STOBI baatc votcanica LIVINGSTONE suoarxaae CREEK Table 2.1 The groups, formations, and lithologies which comprise the Huronian Supergroup (modified after Roscoe, 1969). 14 Figure 2.2 Climbing ripples in fine-grained sandstone of the McKim Formation. Outcrop occurs along Hwy. 6, 0.5 mile south of Espanola. The pencil points to stratigraphic top and current flowed from left to right. 15 Figure 2.3 Outcrop of pelitic interflow sedimentary rocks of the Stobie Formation at the Stobie-Frood Mine Complex at Sudbury. The rocks have been metamorphosed locally to amphibolite grade. The large, light colored crystals are 1staurolite. Bedding is vertical and tops to the right. 16 · greenschist to low amphibolite facies imposed by low to middle rank regional metamorphism during the Middle Precambrian (Card, 1978). The rocks around Gowganda and Elk Lake are only gently warped with dips of 5° to 20°, though steepening of dips occurs at fault margins. Metamorphic grade is generally low greenschist, although higher grades are found locally around intrusions. The Huronian Supergroup has been subdivided into four litho- stratigraphic groups in recognition of the cyclical sedimentation. These are, from bottom to top, the Elliot Lake, Hough Lake, Quirke Lake, and Cobalt Groups which incorporate nineteen format ions (Table 2.1). In the study area, however, only the Cobalt Group is present. The Elliot Lake Group consists of intercalated orthoconglomerate and sandstone of the Matinenda and Livingston Creek Formation, pelitic rocks of the McKim Formation (Fig. 2.2), and local accumulations of dominantly intermediate to mafic volcanic rocks and interflow sedimentary rocks belonging to the Thessalon, Pater, Salmay Lake, Elsie Mountain, Stobie, and Copper Cliff Format ions (Fig. 2.3). Gabbroic and anorthositic plutons of uncertain age appear to be genetically and spatially related to the volcanic rocks (Card, 1978). The Hough Lake Group consists of diamictites, orthoconglomerates, and sandstones of the Ramsay Lake Formation, pelitic units of the Pecors Format ion, and sandstones and orthocong lomerat es of the Mississagi Formation. A similar pattern of sedimentation is present in the Quirke Lake Group which encompasses the Bruce, Espanola, and 17 Figure 2.4 Clastic dike of material from the underlying Bruce Formation cutting rocks of the Espanola Formation. Note the concentration of clasts in the center of the dike. Photo taken at outcrop along Hwy. 6 near Clear Lake, south of Espanola. 18 Figure 2.5 Large-scale crossbedding in quartz sandstone of the Serpent Formation. Outcrop along Hwy. 6 south of Espanola. l 9 Figure 2.6 Trough-style cross-stratification in arkose sandstone of the Lorrain Formation. Direction of current flow is toward the viewer. Outcrop is in central Roadhouse Twp. 20 Serpent Formations (Fig. 2.4 and 2.5). Notably, both the Bruce and Espanola Formation have calcareous and dolomitic units containi ng up to 50% carbonate minerals. The Cobalt Group includes the Gowganda, Lorrain, Gordon Lake, and Bar River Formations, but the latter two are absent in the region under investigation. The Gowganda Formation is the lowest member in this group and its contact with the underlying Quirke Lake Group is either abrupt without evidence of erosion, transitional, or erosional. In the study area, the Gowganda rests unconformably upon the Archean basement and no occurrences of older Huronian formations are known. The overlying Lorrain Formation has a conformable and trans it ional contact with the Gowganda. The trans it ion zone covers a narrow stratigraphic interval of 15 to 30 meters, characterized by a change from predominantly silty sedimentation in the Gaw g anda to planar and trough cross-bedded arkoses and quartz sandstones in the Lorrain (Fig. 2.6). While arkoses and quartz sandstones are the dominant lit ho log ies of the Lorrain, oligomict ic orthoconglomerates and pebble or cobble lag orthoconglomerates occur in subordinate amounts at various levels in the formation. The Lorrain has been subdivided into six litho-stratigraphic members in the Sudbury- Manitoulin area (Card, 1978). The succeeding Gordon Lake Formation has been shown to be conformable with the Lorrain and the contact has been reported as gradational over 9 m and marked by interbedded silty sandstones and siltstones with abundant ripples (Card et al., 1977). Elsewhere, the 21 transition is from hematitic quartz sandstones with trough and . planar cross-beds (including herringbone cross-beds) to siltstones with abundant ripples (Fig. 2.7). A conformable yet abrupt contact exists in McGiffin Twp. to the south of the study area. The Gordon Lake Formation consists of various colored siltstones and sandstones; anhydrite and gypsum are present in more northern exposures. The siltstones can be divided into two types; an argillaceous siltstone and a siltstone" which is actually composed of well-sorted silt-sized quartz grains. Intraf ormat ional conglomerates composed of this cherty variety are common (Fig. Sedimentary structures are abundant and include dessication or synaresis cracks, ripple marks, and soft-sediment deformation structures. The uppermost formation of the Cobalt Group is the Bar River Formation. Its contact with the Gordon Lake is conformable and gradational. The primary lithology is orthoquartzite that is cyclically interbedded with siltstone, locally very rich in hematite. Cross-beds and ripple marks are common (Fig. 2.9). Only a minimum thickness is known for the Bar River (around 1100 m), since the top portion has been eroded away. The Huronian sequence has been intruded by dikes and sills of the Nip is sing Diabase. This name app 1 ies to the numerous gabbroic intrusions, dated at 2,150 m.y. (Van Schmus, 1965) that are also known for their close spatial and genetic re lat ions hip to the rich silver mineralization in the Cobalt and Gowganda silver camps. The dikes trend northerly, coinciding with the older Timiskaming 22 Figure 2.7 Planar-style cross-stratification in Lorrain Formation sandstone. This sequence is transitional with rocks of the overlying Gordon Lake Formation. Note the herringbone pattern of cross-stratification in the upper part of the photo. Outcrop on island in Welcome Lake, Valin Twp. 23 Intraclast conglomerate of quartz-rich siltstone fragments from the Gordon Lake Formation. Note the tabular shape of the clasts and the sharp, erosive bottom contact. Outcrop occurs along north shore of Welcome Lake, Valin Twp. Figure 2.9 Outcrop of the Bar River Formation on Welcome Lake, Valin Twp. Note one set of ripple marks near the water parallels the shore; a second set of ripples in overlying beds are at an angle to the first set. 24 Fa ult Sy st em which also appears to have influenced Huronian sedimentation. Differentiation of these intrusions has produced variations in composition and mineralogy allowing recognition of rock types including gabbro and granophyre (Card, 1978). The gabbro is medium-grained and composed primarily of zoned plagioclase ( labradorit e-byt own it e), clinopyroxene (augite), and orthopyroxene (bronzite) with minor amounts of ilmenite, magnetite, and quartz. The granophyre is finer grained and tends to be restricted to upper portions of sills or as irregular masses or dikes; the mineralogy is largely plagioclase Calbite-an-d-esine) and quartz with lesser and variable amounts of amphibole, biot it e, chlorit e, a pat it e, ilmenite, magnetite, microcline, and carbonate. Another series of mafic rocks was emplaced during late Precambrian time (Mcilwaine, 1978). These rocks are quartz diabase dikes and while distinguishable from the Nipissing bodies, uncertainty exists about their age. Younger olivine diabase dikes similar to the Sudbury swarm to the south are present and believed to be of similar age. The Sudbury swarm has been dated using Rb-Sr whole rock analysis and has yielded an age of 1460zi30 m.y. (Gates and Hurley, 197 3 ). Phanerozois Cenozoic The region is extensively covered by glacial deposits of Pleistocene Age. The thickness of these sediments varies locally and ranges from 0 to 150 m. These include a thin, discontinuous mantle of 25 ground and end moraine deposits, outwash sand and gravel, peat, and lake clay. A number of well developed southerly-trending eskers are present. Glacial striae suggest ice movement was both to the southeast and southwest. Some reworking of these sediments has occurred. 26 LITHOLOGY OF THE GOWGAHDA FORMATION General Statement The Gowganda Formation is a heterogeneous assemblage of elastic sedimentary rocks. The formation has been divided into two members, the Coleman and the overlying Firstbrook (Thompson, 1957; Robertson et al., 1969). The Coleman Member is comprised of diamictite,- orthoconglomerate, graywacke, arkose, .lit hie sandstone, subarkose, siltstone, argillite, and breccia. In contrast, the Firstbrook is largely laminated argillite and siltstone with minor amounts of sandstone and breccia. The laminae are very regular and typically described as varve-like. The Firstbrook Member is restricted to the Cobalt-I imagami area to the east; it is not known ."sensu stricto.'' in the Gowganda-Elk Lake region. In the study area, the Gowganda always rests unconformably upon the Archean basement. The formation has a sub-horizontal attitude and strata usually dip at less than 20°, except along fault zones or near intrusions of diabase, where beds may be nearly vertical or overturned. Formation thickness is highly variable, ranging from 0 to > 1600 meters. Inliers of Archean basement, onlapping of the Lorrain on the Archean, and drill hole data suggest that the pre-Gowganda topography was rugged; relief may have been in excess of 300 m and perhaps as much as 1000 m (Schenk, 1965). This irregular pre- depositional surface and some subsequent erosion have resulted in a variation in preserved thickness. No complete sections were encountered, either in exposure or in drill core. However, it does 27 L-°"o t Subarkoaa N 00 ,,1- .... c-'" 15 c..• "•' ARKO SIC LITHIC ARENITE ARENITE 0 FELDSPAR 50 ROCK FRAGMENTS Figure 3.1 Sandstone classification scheme (from Pettijohn, Potter, and Siever, 197 2 ) appear that the formation is thickest where graben-like structures in the Archean basement existed and in part controlled the sedimentation. This irregular predepositional surface has resulted in complex and sedimentation such that lateral and vertical facies changes occur over short distances. It is likely that several disconformities occur within the Gowganda and that certain members of the column may be locally absent. Given the low outcrop density of the area and the lack of good markers for stratigraphic control, the description of the stratigraphic column, from bottom to top, is generalized, tentative and may not be complete. Terninolou Field description of the facies and classification of the lithologies are based upon the usage of the following definitions and classification schemes. In the section on petrology, rock names are assigned after microscopic examination allowed refinement of grain size estimates and composition of the rock. Mudstone is a general term for a rock composed of a mixture of silt- and clay-sized material. is a fissile mudstone and is a mud rock hardened by metamorphism but lacking a slaty cleavage. Siltstone is a rock composed of greater than two-thirds silt-sized material and lacking fissility. Sandstone is composed of predominantly sand-sized materials. In addition to sand-sized framework grains, a significant percentage of finer-grained material may be present as matrix. The sandstone classification used here is based upon the scheme depicted in Figure 3 .1. 29 Diamictite is a non-genetic term applied to lithified sediments which are essentially non-sorted or poorly sorted deposits composed of the full range of particle sizes from clay to boulder. Orthoconglomerate is composed of framework grains greater than 2 mm in diameter which are clast-supported; i.e. they are not matrix supported. A is a one-pebble-thick bed. Modifiers, where applicable, are attached to the rock name for further clarification of the textural and compositional aspects of a particular sample; for instance, a silty lithic sandstone is one which contains a significant percentage of silt-sized particles, with sand- sized rock fragments comprising at least 25% of the rock and exceeding the feldspar content. C9lEmE Usage of and Upper Coleman" is modified from Lower and Upper Gowganda of the Ontario Geo log ica 1 Survey (Card et al., 1977) and here represents a division between the lower two-thirds of the formation which has diamictites and lonestone-bearing units and the upper one-third which lacks these deposits (Fig. 3.2). The Firstbrook Member, as recognized in the Cobalt area, is not present in the study area. The subdivisions are based upon lithofacies associations observed in this study. Following is a highly generalized composite section, described from the top downwards. Coleman Member 15-30 m Hematitic Silty/Sandy Association. Hematitic siltstone intercalated with thinly bedded arkose. Crossbedding and 30 ripple marks present. Brecciated and slumped bedding common. Laminated argillite locally. Sequence is transitional with rocks of the Lorrain Formation. 50-100 m Upper Sandy Association. Less graywacke, more silty arkose and hematitic siltstone and argillite. Locally orthocong lomerat e, subarkos e, and thinly laminat etl argillit es. 100-300 m Lower Sandy Association. Graywacke and siltstone with some orthoconglomerate, arkose, and pebble beds. Sequence coarsens upward. 100-200 m Upper Pelitic Association. Contains siltstone, argillite, massive sandstones , pebble beds, lonestones, and may include thin diamictic units. Appears to coarsen upwards. 100-200 m Upper Sandy and Diamictite Association. Interbedded graywacke and siltstone with massive and weakly stratified diamictite. 75-100 m Middle Pelitic Association. Dominantly interbedded argillite and siltstone with fine-grained graywacke. 50-100 m Lower Sandy Association. Generally massive beds of graywacke with rare lonestones and occasional pebble beds. Stratification difficult to recognize. Appears to fine upwards. 10-50 m Lower Diamictite Association. Dominated by massive and 31 weakly stratified diamictites with a chloritic, silty, graywacke matrix. 100-200 m Lower Pelitic Association. Contains interbedded argillite, siltstone, fine-grained graywacke, lonestones, and minor breccia. Slumped, contoTted or folded bedding common. 0-100 m Boulder, cobble, and pebble orthoconglomerate with some arkose or subarkose interbedded. A thin regolith (<5 m) may be developed beneath it. Sandstones The sandstone types present are dominated by graywackes in both their geographic distribution and total volume. Arkoses are the next most abundant sandstone variety, while lithic sandstones are minor and subarkoses are rare. No orthoquartzites were encountered. Graywackes occur throughout the sequence; · they are widespread geographically. They are generally medium- to fine-grained, though coarse-grained, very fine-grained, and silty graywackes are not uncommon. Their sorting varies from fair to good and their color is usually medium to dark gray-green, owing largely to the abundant chlorite in the matrix. Some, however, are light pink, gray or reddish-brown. Graywacke beds may be massive, graded, or laminated. Cross-bedded or rippled units are not particularly common. Basal contacts are usually sharp, while upper contacts may be sharp or gradational. Massive beds may pass upward into graded or laminated beds. Subtle 32 UPPER COLEMAN MEMBER HEMATITIC SILTY /SANDY- UNIT UPPER SANDY UNIT LOWER SANDY UNIT 1 LOWER COLEMAN MEMBER • UPPER PELITIC UNIT UPPER DIAMICTITE AND SANDY UNIT MIDDLE PELITIC UNIT LOWER SANDY UNIT LOWER DIAMICTITE UNIT LOWER PELITIC UNIT BASAL ORTHOCONGLOMERA TE Figure 3.2 Generalized composite stratigraphic column of the Gowganda Formation. Black dots to the right of column denote lonestone-bearing rocks. 33 Figure 3.3 Pink beds are medium-grained massive graywacke sandstone. Green beds are medium- to fine-grained matrix-rich graywacke. Note outsized clasts of pink sandstone and load structures. Outcrop along west shore of island in Frith Lake, northern Milner Twp. 34 changes in grain size typically mark the boundaries between beds. Poor exposure hampered field identification of these changes, and recognizing Bouma sequences (Bouma, 1962) was difficult. No complete sequences were identified; most were top-cut-out or bottom-cut-out sequences. Typically these were AE and DE or CDE, respectively. The relative abundances of each are unknown. Small pebbles and ripped-up mud and sand chips are present within the graywackes. Soft-sediment deformation features, usually a loading phenomenon, are common. Bed thickness ranges from 2 cm to 4 m. Given the degree of exposure available, some of the thicker beds may be composite units. Graywacke is found associated or interbedded with siltstone and argillite as well as with diamictite. Graywacke is well exposed along the shores of Firth Lake in Van Hise and Milner Twps. (Fig. 3 .3). Arkose occurs at several levels in the stratigraphic sequence but is most common near the base of the formation and near the top. Grain size varies from fine to very coarse or pebbly, although medium- to coarse-grained examples are typical. The color varies from pink to gray-white, or cream. Most beds are massive or graded, with a range in thickness from 1 cm to 2 m. Only at the top of the column in a medium- to thinly-bedded sequence was cross-stratification found. The arkoses are thin-, medium-, or thick-bedded, with the latter two more common. Rock fragments are predominantly intermediate to felsic plutonics. Arkoses underlie, overlie, or are interbedded with deposits of orthoconglomerate or lithic sandstone, though they are not restricted to this association. Representative outcrops of arkose are present 35 along the east shore of Milner Bay in Gowg anda Lake and 1 es s accessible sites are in northeastern Mickle Twp. and northwestern James Twp. (Fig. 3.4). Lithic sandstones are commonly associated with units containing orthoconglomerate. They are found to overlie . or underlie Gradational contacts are common, especially where 1 it hie sandstone overlies ort hoconglomerat e. These sands tones can display normal graded bedding; however bedding ranges from massive to weakly laminated • The color is typically medium gray-green or pink. Grain size varies from fine to pebbly; however, medium- to coarse- grained sand is typical. Bedding thickness ranges from 0.5 cm to l m. Medium- to small-scale cross-stratification, generally planar foresets, is present. The types of lithic fragments and their relative abundances will be discussed in the petrology section. Subarkoses or feldspathic sandstones constitute a minor portion of the sequence. In two places, massive subarkoses were interbedded in the upper one-third of the column. The color varies from light pink to gray-white. They are generally medium- to fine-grained. Diamictj.t e_§ The presence of diamictite plays a key role in the paleoenvironmental interpretation of the Gowganda Formation. Although restricted to the lower two-thirds of the stratigraphic column, diamictite is fairly widespread in its geographic distribution. Two basic types occur: massive and weakly stratified diamictite. The massive variety of diamictite is characterized by a lack of 36 Figure 3.4 Clast-rich diamictite with sharp lower contact with underlying massive graywacke sandstone in roadcut on Hwy. 560, east of the town of Gowganda, Nicol Twp. 37 Figure 3.5 Massive diamictite with pink granitic clasts ."floating:• in a chlorite-rich graywacke matrix. Photo from outcrop along Hwy. 558, Bucke Twp. 38 stratification and sorting; however, crude normal grading was noted at the top of two units. Thickness varies from a decimeter to 20 m. Contacts are generally sharp or irregular. Massive units may be rich or poor in clasts greater than 2 mm in diameter (Fig. 3.4). These clasts are typically subrounded to rounded, though all shapes occur. Gran it iod rock fragments constitute between 45% and 90% of these clasts; mafic to felsic metavolcanics and metamorphic rock fragments are subordinate (Table 3.1). The largest clast observed was a boulder of granitic composition 1.2 m in apparent diameter. Locally wisps and deformed pieces of sandy material are found in the diamictites, particularly in units that are clast-poor. The matrix is mainly composed of medium- to fine-grained quartz and feldspar grains, with varying amounts of silt and clay. The abundance of chlorite in the matrix produces the typically dark green to black color on fresh surfaces. This dark matrix in which the predominantly pink or light colored granitoid clasts seem to float gives this lithology a striking appearance (Fig. 3.5). Excellent exposures of diamictite can be seen along Highway 560 between Gowganda and Elk Lake. Additional sites with good access occur along the Cook Lake Road in James Twp. and along the northeast shore of the western arm of Longpoint Lake in Chown Twp., which is accessible by boat. Weakly stratified diamictite is differentiated from the massive diamictites by the presence of stratification. Inverse and/or normal grading is present in some units (Fig. 3.6). As with the massive type, the weakly stratified variety may be clast-rich or clast-poor. Clast 39 PEBBLE COUNTS - DIAMIGrITES SITE ROCK TYPE 1 2 3 4 5 6 7 GRANITE* 37 55 71 80 38 75 55 SYENITE/MONZONITE 21 22 19 16 11 12 9 GNEISS 2 2 1 0 0 0 3 BASALT/GREENSTONE 12 9 6 3 32 4 13 FELSIC-INTERMEDIATE VOLCANIC 18 7 3 1 11 6 7 GABBRO/MAFIC PLUTONIC 0 2 0 0 0 0 1 METASEDIMENTARY/SCHIST 0 l 0 0 2 3 9 QUARTZ/ CHERT 9 2 0 0 6 0 3 IRON-FORMAT ION l 0 0 0 0 0 0 __...... --..... 100 100 100 100 100 100 100 1) Nicol Twp.; North of Hwy. 560 below firetower east of Gowganda. 2) James Twp.; 2 km south of Elk Lake east off of Cooke Lake Road. 3) James Twp.; 3.5 km south of Elk Lake. 4) Milner Twp.; 2 km west of Margueratt Lake. 5) Milner Twp.; Southwest of Elkhorn Lake. 6) Chown Twp.; Northeast of west arm of Longpoint Lake. 7) Haultain Twp.; Northwest shore of Obushkong Lake. *Note: Includes rocks ,.ith 20-60% quartz, 0-100% plagioclase of total feldspar, 0-100% alkali feldspars of total feldspar; mafic minerals such as biotite, amphibole, and pyroxene may be present and color index is generally less than 50. Table 3.1 Pebble counts from seven exposures of diamictite. 40 Figure 3 .6a Clast -rich weakly-st ratified diam ict it e with possible inverse grading. Outcrop occurs along Hwy. 560, east of Gowganda, Nicol Twp. Figure 3 .6b Diamict it e int er bedded with lonest one-bearing laminit es in roadcut along Hwy. 560 in Gowganda, Nicol Twp. 41 Figure 3.7a Large (0.3 m) granitic lonestone strongly depressed and truncated some underlying layers suggesting forceful impact. Outcrop along western shore of Firth Lake, Van Hise Twp. Figure 3.7b Smaller lonestone depressed layers below it and has a draping of layers over it. East shore of Banker Bay, Gowganda Lake, Nicol Twp. 42 ' · lithologies occur in abundances comparabie to those in the massive variety. The clay and silt content of the matrix is variable, but on the average, there is more sand-sized material and less clay and silt than in the massive diamictites. Chlorite remains the dominant clay and imparts its characteristic color to the rock. Beds are approximately 0.1-3.0 m thick, with sequences of beds up to 10-20 m thick. Contacts between beds are gradational, irregular, or sharp. The weak st ratification is recognizable both macroscopically and microscopically, but given the conditions of most outcrops, this facies is difficult to identify. Some of the best exposed examples are along Highway 560 in a road cut just east of the firetower near Gowganda. Lone§tone-Bearinz Sandstones Argillites Lonestones are outsized clasts whose presence requires an altogether Lonestones are commonly associated with structures which suggest forceful impact upon the substrate (Fig. 3.7). Lonestones are found that penetrate and truncate layers of sediment as well as deform, to varying degrees, the underlying and adjacent beds. Some layers are folded or convolute at the margin of the clast or merely deflected around it. In sandier sedimentary rocks there may be no observable 43 disruption of the substrate. Continued sedimentation following lonestone deposition commonly results in a draping of layers of sediments over the top and sides of the stone. The laminated beds are composed of sand, silt, or mud. The sand units typically have sharp lower contacts and may have sharp or gradational upper contacts. Load structures are sometimes developed where the sand beds overlie a muddier substrate. The silt and mud beds may display sharp or gradational lower and upper contacts and may be graded throughout. Bedding thickness varies from 0.5 mm in the mud and silt units to 0.5 m in the sandier units. Lonestone sequences are as thick as 40 m. Lonestones up to 30 cm in apparent diameter were seen. Lonestones also occur dispersed along bedding surfaces and some occur in groups or nests. Examples of this facies are present on the northeast shore of Banker Bay in Gowganda Lake and on the west-central wave-washed shores on Firth Lake. Orthoc0Dzl9merate§ Orthoconglomerates are found at various stratigraphic levels, but they are most common at the base of the formation and again near the top. These conglomerates typically contain subrounded to rounded clasts that range from pebble to boulder size. Sorting is variable from poorly to well sorted, but most are moderately sorted (Fig. 3.8). Greater angularity and poorer sorting characterize conglomerates which overlie the Archean basement; these are generally 5 m or less in thickness. The distribution of clast types in the orthoconglomerates in part 44 reflects the underlying basement lithology; however, intermediate to felsic plutonics tend to dcminate most assemblages regardless of the basement rocks beneath (Table 3.2). In contrast, one outcrop contained up to 35% quartz pebbles with mafic to felsic metavolcanics as the remaining dominant framework lithologies (Fig. 3.9). The matrix is typically medium- to coarse-grained sand, but may be either feldspathic or lithic in character. Chlorite content is variable. The morphology of some of these deposits is not readily evident, though some can be recognized as channel fills, with the channels scoured and cut into the underlying sediments. In addition, some appear to be wedge-shaped units and are relatively thicker, larger bodies, and commonly occur with interbedded arkoses or lithic sandstones. Conglomerates associated with diamictites are typically thinner deposits, approximately 1 to 2 m thick with generally sharp contacts. Examples of orthoconglomerat es can be seen along the west shore of Bobtail Lake in Leonard Twp., along Highway 560 southwest of Lost Lake in Nicol Twp., and in northwestern James Twp. Silt stones Siltstones are widespread in occurrence and are found throughout the formation; however, they are in much greater abundance in the lower two-thirds of the column. They display a variety of colors including green, gray, red, beige, black, pink or reddish-brown. They are medium- to and may be graded, laminated, or massive and some show cross-stratification. The laminated variety is regular or irregularly layered and these 45 PEBBLE COUNT - ORTHOCONGLOMERATES SITE ROCK TYPE l 2 3 GRANITE* 221( 53%) 166(38%) 12 SYENITE/MONZONITE 30( 7%) 3 ( <1%) 10 GNEISS 0( 0%) 11 ( 2%) 4 BAS.ALT/GREENSTONE 65 (15%) 67(15%) 10 FELS IC-INTERMEDIATE VOLCANIC 106(25%) 176(40%) 22 GABBRO/MAFIC PLUIONIC 0( 0%) 19( 4%) 0 METASEDIMENTARY/SCHIST 0( 0%) 0( 0%) 4 QUARTZ/ CHERT 0( 0%) 2( <1%) 37 IRON-FORMAT ION 0( 0%) 0( 0%) l m 444 100 1) Milner Twp.; East shore of Milner Bay, Gowganda Lake. 2) Leonard Twp.; West shore of Bobtail Lake. 3) Nicol Twp.; Along Hwy. 560, 2 km west of Lost Lake. *Note: Includes rocks with 20-60% quartz, 0-100% plagioclase of total feldspar, 0-100% alkali feldspars of total feldspar; mafic minerals such as biotite, amphibole, and pyroxene may be present and color index is generally less than 50. Table 3.2 Pebble counts from three exposures of orthoconglomerate. 46 Figure 3.8 Moderately-sorted orthoconglomerate from the west shore of Bobtail Lake in Leonard Twp. 47 Figure 3.9 Well-sorted and stratified quartz-pebble-rich ortho- conglomerate exposed in roadcut along Hwy. 560 west of Lost Lake, Nicol Twp. 48 varieties seem to occur in about equal abundance. Irregularly layered sediments are those displaying wavy bedding or variation in bedding thickness within a single bed. Beds range from less than 0.5 mm to 2 cm in thickness in sequences up to 1 m thick. Lower and upper contacts are abrupt or gradational, with the latter type appearing to dominate. Slumping and small-scale folding and can be seen as w el 1 as mic ro-f au 1 ting. This f a.c ies is commonly interbedded with sandstone, particularly graywacke, and with diamictite and argillite. A hematite-rich variety which has a distinctive red color displays smal 1 scale cross-stratification and occurs in the top 30 m of the formation, placing it in the transitional zone. This hematite-rich facies can be seen in northwest and north central Mickle Twp. and along Highway 560 south and west of Lost Lake. Other occurrences of siltstone with good access are on Firth Lake. brg i 11 i,t e_§ Argillites are fairly widespread in the lower two-thirds of the Gowganda, but are only locally developed in the upper one-third in this region. Argillites, although massive in places, are typically laminated (Fig. 3.10). Some show parting or fissility. They are either irregularly (lensing or discontinuous layers) or regularly laminated, with the former style more common. The color varies but is usually black, green, pink or red. In some cases, two colors such as red and green alternate. Laminations can vary from 0.15 mm to 2 mm in thickness and argillite units may range from 1 cm to 20 m. Small-scale folds and 49 slumps indicative of downslope post-depositional movement are evident in some outcrops (Fig. 3.11). Sometimes loading phenomena are seen where sand beds overlie argillite beds. Argillite is commonly interbedded with siltstone and graywacke and contacts are sharp, irregular or transitional. In one outcrop, an alternating black and green laminated argillite displayed a distinctive, though weak magnetic character. Examples of argillite are present in a roadcut about 1.5 km northeast of Lost Lake along Highway 560 and in some shoreline outcrops on Firth Lake. Breccias The breccias present in the study area are intraf ormational breccias. They are found at different stratigraphic levels and are generally restricted to sediments with grain sizes smaller than medium-grained sand. Fragments are typically angular to subangular; however, subrounded or rounded clasts were not uncommon. The size and shape of fragments vary and appear to be dependent on lithology; argillite clasts are often rectangular or blocky, whereas siltstone and sandstone clasts display irregular shapes and varying degrees of angularity (Fig. 3.12). The clasts are enclosed by grains of the constituent lithology; i.e. argillite breccia clasts have a mud matrix between them. Neither calcite nor quartz veins were found with these breccias, nor were signs of cataclasis evident. They seem to be stratabound, although exposures are limited and the overall extent of the breccia beds cannot be determined. Outcrops of this facies may be seen on Elkhorn 50 Figure 3.10 Outcrop of alternating red and green beds of argillite with minor sand and silt. Note the irregular and lensing nature of the stratification. Cliff face just east of Gorman Lake, Milner Twp. Figure 3.11 Slabbed specimen of red and green argillite showing soft- sediment deformation features. Note the isoclinal recumbent fold in the middle right side of the sample. 51 ..._....___ , Figure 3.12a Sedimentary (intraclast) breccia from northeast shore of Firth Lake, Van Hise Twp. Note the large clast in the central part of the photo displays a disrupted texture. Figure 3.12b Blocky, angular clasts of thinly-bedded, laminated argillite in a muddy matrix. Exposure occurs approximately 700 m west of Diabase Lake, Van Hise Twp. 52 Lake in Milner Twp. and at the north end of Firth Lake. Chaos icf S Chaotic or slumped units are present and most of the occurrences are in the lower two-thirds of the stratigraphic column. They typically involved well-bedded sequences, though this may be a bias produced by the ability to recognize disorder in a bedded unit compared to a massive, featureless unit. Identification of the deformed but apparently massive units was occass ionally possible on the basis of inclusions of generally deformed clasts of graywacke, siltstone, or argillite. Some of these disrupted sequences contain gentle to tight, even isoclinal or recumbent folds outlined by bedding surfaces. Large-scale slumping and movement of sediments is evident in the medium bedded, lonestone-bearing siltstone and sandstone beds near Babs Lake in Haultain Twp. Others are only slightly deformed with irregularly undulating surfaces. For the most part, beds evidently behaved in a ductile manner throughout a unit, despite the contrast in competency between layers, but some beds are fractured or faulted (Fig. 3.13). Sedimentary Structures The sediments which comprise the Gowganda Formation display a wide range of sedimentary structures. Bedding thickness varies from 0.5 mm to 20 m. Internal stratification was found in various lithologic units, but identification in the field was difficult and could only be determined under the most ideal circumstances. Types of internal stratification include normal and rarely inversely graded beds, ripple marks, laminations, and some planar and trough style 53 Figure 3.13 Slumped unit showing contorted, deformed laminae around granitic clasts. Note the deformed pink sandstone fragments. Photo from south shore of Babs Lake, Haultain Twp. Figure 3.14 Photomicrograph of small scale scour in hematite-rich silty fine-grained sandstone from the top 30 m of the Gowganda Formation. Photo taken in plain light. Field of view is 4x7 mm. 54 cross-beds. Small-scale scour and fill and larger channel fill deposits are present (Fig. 3.14). Features related to penecontemporaneous deformation such as flames, ball and pillow, convolute bedding, and other load structures also occur. In addition, there are slump structures and elastic dikes. Polygonal cracks also occur, but they are attributed to recent weathering. Structures resulting from lonestone deposition are common. Graded beds in the Gowganda Formation are typically found in the graywacke sandstones. In those rocks, a fine fraction is present as matrix and coexists with framework grains that gradually decrease in size upward to produce normal graded beds. In some instances, grading is developed at the base of diamictit es and sometimes at the top and do not appear to be separate sedimentation units. Ripple marks occur in the hematitic silty sandstones of the transitional zone (Fig. 3.15). The ripples are typically symmetric to slightly assymmetric with straight to weakly undulatory and rounded crests. Maximum crest heights are 2.5 cm and average 2.0 cm and ripple wave lengths average 5 to 6 cm. The ripple index, which is ripple wave length/ripple height (RI=L/H), is approximately 3. Since wind generated ripples have a ripple index >10, these ripples were formed in a subaqueous environment (Reineck and Singh, 1980). Given the morphology of the ripples, they are probably the product of a combined transverse current or wave small ripple mechanism operating in shallow water. Ripple cross-stratification related to C beds of Bouma sequences are fairly rare. Isolated ripples in thinly bedded and 55 laminated siltstone and argillite were noted locally. Finely laminated rocks are present and typically these rocks are argillite or siltstone. Lonestone sequences also tend to display laminations. whereas graywackes and other sandstones only rarely show it. Some of the argillites and siltstones are thinly interlayered and are recognized by the alternation of color and to a lesser extent by textural or compositional changes. These rocks could be referred to as rhythmites, which have been reported to occur in a number of different environments, including tidal, estuarine, marine, and glacial. The rhythmic alternation may be the result of seasonal changes, fluctuations in a stagnant basin, variations in the amount or type of material supplied to the basin, or turbidity or contour currents. Cross-bedding, either planar or trough type, is uncommon in the Gowganda of -this area. Planar or tabular foresets are best seen in the rocks which are trans it iona 1 to Lorrain Formation sandstones. These foresets are small-scale features in beds between 1 and 4 cm thick and averaging 2 cm. The length of foreset beds is typically <7 cm. Similar small-scale cross-beds were also found elsewhere in the formation, usually in units whose grain size is less than 0.125 mm or that of fine-grained sand. Trough cross-beds as part of scour and fill structures are present in arkosic and lithic sandstones in Van Hise Twp. but are not common. An example of channel fill occurs on the east shore of Milner Bay where boulder and cobble orthoconglomerate was deposited in a channel incised into coarse-grained arkose. Features indicative of penecontemporaneous deformation are relatively common and several examples of loading phenomena are 56 Figure 3.15 Rippled hematitic silty arkose from the Upper Coleman Member. Sequence is transitional from the rocks of the Gowganda Formation to those of the overlying Lorrain Format ion. Photo taken along Hwy. 560 west of Lost Lake, Nicol Twp. Figure 3.16 Soft-sediment deformation (convolute bedding) in a laminated siltstone. Exposure occurs in cliff just east of Gorman Lake, Milner Twp. 57 exposed along the shores of Firth Lake. Clastic dikes are present in northeast Mickle Twp. and Leith Twp. In each case the dikes are less than 5 cm in width, but limited exposure prevented viewing in three dimensions. Therefore it is not known whether material was injected upward from a source stratigraphically lower, or infilled into a disrupted substrate by subsequent sedimentation. An interesting outcrop below the f iretower east of the town of Gowganda exposes the Archean-Gowganda contact. Over a narrow interval of approximately 2 m, the basement is jointed and fractured. Intensity of fragmentation increases toward the contact and convers ly, decreases with greater distance until solid, intact basement rock is encountered. This feature might be the result of freeze-thaw cycles prior to Gowganda sediment at ion. Locally slump, fold, and convolute structures are present. Small- scale folds in thinly-bedded and laminated argillite and siltstone are fairly common (Fig. 3.16). The folds are often tight to isoclinal and are typically slightly overturned. 58 ARCHEA.N-PROIEROZOIC UNCONFORMITY The contact between the Archean basement rocks and the overlying Gowganda sedimentary rocks was examined at ten localities in the study area (Fig. 4.1). The nature of the relationship is unconformable and varies in terms of the style of weathering of the Archean rocks below the unconformity, the degree of preservation of weathered horizons, and the type of sediment which was ultimately deposited upon the basement. At sites 1, 2, and 3, the Gowganda rests on a granodioritic basement, part of the Round Lake Batholith. Site 1 consists of two exposures which are about 0.5 km apart on a north-south trend • At the northern one, the contact is sharp and dips to the west. Here the Gowganda is a orthoconglomerate with at least 90% granitic clasts. The granitic basement appears fairly fresh and intact. At the southern outcrop, the basement surface is irregular and weathered and passes upward into the Gowganda which is nearly an oligomictic orthoconglomerate (nearly 100% granitic clasts) with interstitial arkosic sand. The stones are angular at the base and vary from subangular to rounded passing upward; the 3 m thick sequence is unstratified and is overlain by a diamictite in which approximately 90% of the clasts are granitiod. Sites 2 and 3 are similar to each other and to site 1 and only site 2 will be described. The granodioritic basement rock in places is weakly foliated and moderately fresh. However, over approximately a 5 m interval, the rock appears to be increasingly more weathered. In 59 STUDY AREA d 03 \ ''\ '1 L ]Gowganda Fm. °'0 B Faull ROAOllOUSE :Q BRoad WALllS tJ =0 Boddlng olllludo + Hotlh O • I 11 16 10 Mlloo 0 10 20 30 Kllomelen SCALE 1:253,440 Figure 4.1 Map of the study area with sites (marked by stars) where the Archean- Proterozoic unconformity was examined. Site numbers described in the text. one place, blocky pieces of the granodioritic basement displaying diffuse borders are sitting in a matrix of weathered granodioritic material; grains are angular and some retain an interlocking igneous texture. Interstitially, hematite is quite abundant and coats grains. Feldspar is always altered and commonly replaced by chlorite, sericite, and epidote. Most of the amphibole is pseudomorphed by chlorite or altered to chlorite, sericite, and biotite with minor magnetite, hematite, ilmenite, and leucoxene. A layered intergrowth of mainly sericite, chlorite, biot ite, and very fine-grained leucoxene displays an unusual kinked habit, has frayed ends, and some cross-cut each other (Fig. 4.2). It is believed that this intergrowth is after original amphibole. The overlying Gowganda is a 100 m thick sequence of mainly orthoconglomerate with some interbedded arkosic sandstone. Practically 100 percent of the cobbles in the lower 20 mare obviously derived from the granodioritic basement. The minerals in the cobbles are altered and weathered to a degree intermediate between the relatively fresh basement and the material that occurs in a zone approximately 5 m thick above the basement and below the orthoconglomerate. This 5 m thick accumulation found between obvious Gowganda rocks and the basement proper is considered to be part of an ancient weathering profile (i.e. a regolith). At sites 4 and 5, the basement is moderately fresh and intact, composed of mafic to intermediate metavolcanics. The contact between the Archean and Gowganda is fairly sharp but irregular; the attitude of the surface is difficult to resolve due to limited exposure. 61 Figure 4.2a Regolith composed 100% of granodiorite and its weathering products. Outcrop occurs in northwestern James Twp. Figure 4.2b Photomicrograph of sample from regolith deposit. Layered mineral aggregates are intergrowths of sericite, biotite, chlorit e, ·magnetite, and leucoxene which have rep laced original hornblende. Surrounding material is largely quartz and plagioclase. Photo taken in plain light. Field of view is 4x7 mm. 62 At site 4, the contact strikes about east-west and dips to the north. No regolith is present. The Gowganda appears to lack st ratification and both orthoconglomerate and diam ct ite are present. Mafic to intermediate volcanics, felsic to intermediate plutonics, vein quartz, and iron-formation are rock types found in the subangular to rounded cobble-size fraction in which most of the clasts occur. At site 5, however, the contact appears sharper, steeper and strikes roughly north to northeast. subangular to subrounded boulders of metavolcanics occur at the base of the Gowganda. A sequence of well-stratified, rounded and sorted boulder to pebble orthoconglomerate follows; vein quartz pebbles are prominent and their content reaches 35% of the framework clasts. In contrast to the other unconformity site 5 has deposits that are part of the top of the formational column and therefore were laid in late Gowganda time. At all other sites in the study area where the unconformity is found, the sedimentary sequence lies in the lower two- thirds of the formation. At locality 6, the basement rocks are felsic metavolcanics, dominantly porphyritic dacit es. Iron-format ion is also present. In this exposure of the unconformity, there is a transition over approximately 2 m from fairly fresh and intact porphyritic dacite at the base which becomes fragmented into angular blocks as one moves upward toward the contact. Fragmentation intensifies nearer the contact; pieces are progressively smaller and remain quite angular (Fig. 4.3). The contact itself is an irregular horizon and contains abundant very angular to subangular dacite fragments and chert in a. 63 basal rubble which represents the lowest of the Gowganda sedimentary rocks. The dacite fragments are highly sericitized. Overlying this is a massive diamict ite. Site 7 is along the west-central shoreline of Obushkong Lake. The basement rocks immediately beneath the Gowganda are mafic to intermediate metavolcanics with interbedded schistose metasediments which have been intruded by felsic dikes. Less than optimal exposure · inhibited analysis of the contact. It appears quite irregular with a northeast-southwest strike and a moderate dip to the southeast (approximately 50°). The felsic intrusive is fragmented in places with sand to boulder size material visible. The metasedimentary rock fragments are commonly rectangular in shape and comprise the dominant clast type in this basal Gowganda deposit. The blocky and angular shape of the clasts and the unsorted character gives this conglomeratic deposit aspects of talus or fault scarp accumulation (Fig. 4. 4). At site 8 along the east-central shore of Firth Lake, the contact between the Archean and Proterozoic is again irregular and the attitude is unclear. The basement rock mid-way up the eastern shore is metagabbro which is extensively fractured and is moderately altered to l m below the Gowganda. The Gowganda is a moderately to poorly sorted orthoconglomerate and massive to weakly stratified. Clasts are typically subrounded cobbles and pebbles and are slightly more angular toward the contact. Boulders are not uncommon and may be as large as 2 m in apparent diameter. The ratio of granitiod fragments to 64 Figure 4.3 Angular fragments of Archean basement from an unconformity exposure near the town of Gowganda, Nicol Twp. Fragmantation possibly caused by frost-wedging. Figure 4.4 Blocky, angular clasts of metasedimentary rock derived from the Archean basement. Outcrop occurs along the northwest shore of Obushkong Lake, Van Hise Twp. 65 ' . volcanics and mafic intrusives varies from 3:1 to 1:2 and reflects the mixed source area. The interstitial component is a medium- to coarse- grained sand with abundant lithic fragments and scattered sulphide grains. Locality 9 is 0.4 km west of the southwestern shore of Elkhorn Lake where an isolated exposure of Gowganda rests on an inlier of Archean mafic to intermediate metavolcanics. At the unconformity, the basement is a felty, amygdaloidal basalt which is moderately altered and only weakly fractured to 2 m below the irregular, subhorizontal contact. The fractures are filled with sand- to pebble-size particles. The Gowganda is a very poorly sorted, unstratified basal conglomerate which is largely clast-supported. Clasts are predominantly subangular to subrounded and there is a significant proportion of subrounded felsic intrusive clasts in the conglomerate. This requires transport of material to the site, ruling out the possibility of this locality representing a site of preserved regolith development. Site 10 is near the west bank of Wapus Creek in western Milner Twp. where an inlier of the Archean is exposed. The basement rocks are mafic metavolcanics and a narrow dike of felsic composition separates the metavolcanics from the Gowganda sediments along the length of the exposed unconformity. The contact surface is fairly smooth and very gently undulatory. In places where the Gowganda has been removed, fairly straight shallow grooves are present. Figure 4.5 shows a cross- s ect ion of the contact and a possible groove in the basement. The contact strikes northeast and dips 50°-70° southeast. The attitude is believed to be the result of faulting, as determined by the 66 ..... Figure 4.5 Photomicrograph of a cross-section of the contact of the Archean-Proterozoic. Note the groove (center) in the plutonic basement rocks filled by siltstone of the Gowganda Formation. Photo taken in plain light. Field of view is 4x7 mm. 67 Figure 4.6 Archean-Proterozoic contact dipping steeply to the east. Basement rock is felsic plutonic, the Gowganda consists of laminated siltstone and argillite with lonestones. Attitude of contact the result of faulting which post- dates Gowganda time. Site #10 of Figure 4.1. 68 relationship of the overlying Gowganda (Fig. 4.6). These sedimentary rocks are finely laminated and thin- to medium-bedded siltstone and sandstones and contain lonestones. The strike and dip of these beds is the same as the contact with the Archean. This would indicate that the basement and Gowganda together were faulted and tilted into their present attitude. 69 STRUCTURE The Gowganda Format ion, as well as other Huronian rocks in the study area, is only gently warped in contrast to the moderately open to tight folds found in the Penokean Fold Belt to the south. In general, the Gowganda in the study area tends to strike north-south with gentle dips of 0°-20° to eit.her the east or west. Variations in t his pat t e rn occur but are of 1 it t 1 e s i g n if i can c e. In on 1 y t w o instances could folds be recognized in the Gowganda, one at the far west end of the study area near Bobtail and Mullen Lakes and at the far eastern end in central James Twp. These are open synclines with low relief and are inferred on the basis of bedding attitudes. No culmination of folds or parasitic structures were evident. Other synclines and anticlines are inferred from bedding attitudes of Lorrain Formation rocks in the southeastern portion of the study area. These are open structures with gently curved, generally northwest- trending axes. The wave-length of these folds is on the order of kilometers. The folds identified in the Gowganda are in areas where the formation is thin and therefore depth to basement is minimal. Without aeromagnetic or drill hole data, the depth to basement where folds in the Lorrain exist cannot be determined. It is possible, especially in the Gowganda rocks, that the structures reflect pre-depositional basement topography. That is, basement highs would have resulted in ::anticlines" and lows would have produced :·synclines-" as subsequent 70 Gowganda sediments draped the basement rocks. It is not certain whether this would account for the folds present in the Lorrain. Assuming that depth to basement is greater and that Gowganda sediments subdued whatever relief existed at the close of the Archean, then another explanation is required. Lovell and Caine (1970) proposed ideas regarding a Timiskaming Rift Valley System, a northwest-trending fault system that was active to varying degrees during Archean and Proterozoic time with some rejuvenation that post-dates the Paleozoic deposits of the region. It is possible that faults in the study area that parallel this trend are en echelon faults that are part of the system. Thus the undulation in bedding may be an expression of deeply seated faults present in the basement that do not reach the surface. Minor drag folds occur near faults and along intrusions of the Nipissing Diabase. These are small-scale features which include drag folds and overturned beds. Faults Numerous faults have been mapped by previous workers in the area and faults trend in roughly four main directions dominated by north to north-northwest structures concentrated in the western part of the study area. Other directions include northwest, northeast, and east. Recognition of faults was based on offsets in geological contacts, repetition of stratigraphy, shearing, and brecciation. Topographic lineaments on maps required further substantiation in the field before they were classified as faults. Major north-trending faults in Van Hise and Milner Twps. are splays off the Firth Lake Fault (Mcllwaine, 1978). Shearing and 71 ' . brecciation are common features and faulting has produced steep cliffs. Stratigraphic relationships suggest that movement along these north-trending faults was west side down. Other major north-trending fault systems occur in the Gowganda Lake-Obuskong Lake and Wigwam Lake area. An example of a northeast-trending fault is the Babs Lake Fault. Displacements of over 400 m and 100 m for the Nipissing Diabase and Gowganda Formation, respectively, suggests the presence of this fault. As mentioned earlier, some of the northwest-trending faults may be related to the Timiskaming Rift Valley System. This parallel array of lineaments, fractures and faults is prominent in the southeastern part of the study area where rocks of the Lorrain Formation and Nipissing Diabase comprise most of the exposed bedrock geology. 72 PEIROGRAPHY Procedure One hundred and twenty-four thin sections were examined. These were chosen on the basis of rock type, position in the geologic column, and geographic distribution. While not all outcrops were sampled, it is believed that a representative suite from the area was obtained. Of the 124 thin sections, 24 are of the Archean basement, the Archean-Gowganda contact zone, or the Gowganda sedimentary rocks within 1-3 m of the contact. The mineralogy of each thin section was described and estimates of the relative percentages of the minerals were noted. Since the metamorphic grade of the rocks is generally lower greenschist to sub-greenschist facies, primary textures have been preserved. Therefore grain size, shape, sorting, and other textural features were also described for later sedimentological analysis. Heels were stained for alkali feldspar and plagioclase. Thirty-eight thin sections were chosen for point counting. In each case, a total of 600 points was counted in random traverses perpendicular to bedding. The modes from 24 of the point-counted thin sections are presented in Table 6.1. Miner_elogy The sedimentary rocks which comprise the Gowganda Formation are a diverse assemblage of lithologies. Distinction of these varieties is in large part accomplished on the bas is of textural differences with subd iv is ions based on composition al differ enc es. Al 1 the rocks are composed primarily of the following components: quartz, plagioclase, 73 MODAL ANALYSES Samples Litnic AcC!llite ( xose I Gcaywelcxe Sa.nest.one RH- RH- RH- RH- ?II- RH- l Rode Volanic::Felsic: 6.17 6.50 5.50 5.83 5.17 2.33 o.oo o.oo 0.00 0.00 o.oo 0.17 0.00 Felsic-Incerndiate 4.83 6.33 5.00 10.83 4.33 2.33 0.33 o.ao a.co o.oo 0.17 0.17 o.oo Intemocii.ac.-+latic: 1.30 l.67 l.17 a.SJ B.B3 3.17 o.oo a.oo o.oo 0.00 0.00 0.17 0.33 /lafic: 0.17 0.33 3.00 0.50 1.50 5.oo a.co o.oo o.oo a.co a.co o.oo 1.50 B.17 12.33 20.17 7.33 2.67 8.17 1.17 a.co o.67 o.oo 0.17 l.83 l.83 K-felClpar-Qlart: 21.00 24.00 38.67 17.50 4.17 18.83 3.33 o.oo o.oo 0.17 o.oo z. 5o l.17 Matic: o.oo o.oo 0.00 0.00 o.oo o.oo o.oo o.oo a.co o.oo o.oo o.oo a.au Meta :Argillice-SJ.ace 0.17 a.oo a.oo o.oo o.oo 2.00 o.ao o.oo o.oa a.oo o.oo a.oo o.oa Sc:hisc 0.66 a.so 5.83 0.17 a.33 o.so 0.00 o.oo o.oo o.oo a. aa o.ao a.au Qlar:ite 2.50 1.00 3.33 o.oo o.oo 4.50 o.oo o.oo o.oo a.oo o.ao o.oo a.oo Greaisccne 0.66 a.so o.oo o.oo o.oo 1.83 o.oo o.oo o.oo o.oo o.oo o.oo a.au o.oo a.oo 0.00 a.17 a.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo s.nastaw 2.67 3.33 o.oo l.50 0.33 ll.!7 a.oo a.co o.oo o.oo o.oo o.oo o.oo Otmr Rock Fra9111ftt o.oo 0.!7 a.co a.so 0.33 1.33 o.oo o.oo o.oo a.co o.oo o.oo o.oo nxaJ. lladc 48.50 56.66 82.67 45.16 27.66 61.16 4.83 o.oo 0.67 0.17 0.34 4.84 4.83 Miscellaneous Grains: l·lwlcovite 0.17 o.oo o.oo 0.17 0.00 o.oo o.oo 1.00 o.uo a.co 6.au u.oo l.33 Biotite o.oo o.oo o.oo o.oo o.oo o.oo 0.00 1.66 o.oo o.oo o.ao 0.33 o.oo Oll.orice 6.17 2.50 0.00 2.00 1.50 3.33 7.66 2.16 0.66 o.oo 3 .so 2.33 4.17 0.33 4.83 o.oo 2.33 1.50 a.so 0.67 0.17 o.oo 0.33 l.67 6.83 Zircxn o:oo o.oo o.oo o.uo 0.00 o.oo o.oo 0.17 0.17 a. Jl u.uu 0.33 o.uu Other o.uo 0.17 o.oo o.oo 6.00 o.oo 0.00 0.17 , 0.17 0.17 o.oo 0.33 o.oo nxaJ. K1-llarwaua 6.67 7.50 5.50 4.50 9.00 3.83 8.33 S.33 I l.00 a.so 10.33 4.99 12.33 I I I Cer.t!nt :Quartz 0.00 o.uo o.oo o.oo o.oo o.oo l.G7 o.oo o.uo o.ou o.oo a.so 0.00 <:amcnate l.50 4.00 0.66 o.oo o.oo 1.17 o.oo o.oo I a.au o.oo o.oo o. oo 0.00 Clay o.oo o.oo o.oo o.oo 0.00 o.oo o.oo o.oo o.oo o.uu o.ao o.uu o.ou Matrix: Clay o.uo 0.83 4.00 0.83 3.J3 o.oo o.oo o.oo 40.00 21.17 33.17 ll.SJ U.JJ Olartz-¥elel!lpilr 0.33 0.67 1.17 0.17 1.83 0.66 o.oo o.oo I 23.n 12.83 14 .uu .17 4.J4 nxaJ. 2.83 S.50 5.83 l.00 S.16 l.83 1.67 o.oo 163.17 34.00 47.17 16.50 12.67 '10rM. 99.99 99.9H >9.S& 99.99 lOO.uo 100.00 1100.00 100.00 1no.01 Table 6.1 Modal analyses. Six hundred points counted in each sample and expressed as percentages. 74 MODAL ANALYSES Samples Massive Strat1tieo Ui.:im1ct1te Arkor.e RH- RH- };II- RH- RH- HI!- l Total ()>Utz 30.67 40.67 28.67 33.00 28.80 30.ll 30.80 35.84 36.83 32.67 53.50 62.17 39.83 FelCSPar: Pla9iOc1ase 14.00 17 .33 16 . 66 lJ.00 lJ.00 14.34 14.20 9.33 11.33 8.00 9.34 21.83 9. 67 Orthoclase 6.33 0.00 4.67 3.50 7.50 13.16 7. 70 6.33 8.00 5.17 19.00 13.50 27.33 Hicrocline 0.00 2.17 o.oo 0.50 l.30 l.33 0.50 0.34 2.67 0.50 0.33 C.00 5.00 Perthite o.oo l.50 0.50 0.00 0.50 o.oo 0.10 o.oo l.17 o.oo 4.67 o.oo 1.00 Total Peldapar 20.33 29.00 21.83 17.00 22.30 28.83 22.50 16.00 24.17 ll.67 34.34 35.33 43.00 Root Volcanicif'elsic 0.17 o.oo o.oo o.oo 4.00 0.34 2.20 o.oo o.oo 0.83 o.oo o.ou o.ou f'elsic-I.itemediate 2.50 0.17 0.83 o.oo 4.50 0.83 0.60 0.67 1.50 0.17 o.oo o.uo o.oo Internediate-+lafic 0.17 2.17 o.5o 0.17 2.00 o.oo o.oo 0.50 0.83 o.oo o.oo 0.00 o.ou Hafic o.oo 0.33 o.oo o.oo 3.40 o.oo o.oo 0.00 1.00 o.oo o.oo o.oo o.oo 6.16 4.33 3.34 0.66 2. 70 1.50 0.50 0.67 3.50 l.17 l.50 o.oo 0.84 K-feldspar-Q.Jartz 2.33 3.50 0.83 l.00 2.00 l.00 l.00 2.50 4.17 0.67 3.00 o.oo s.:n i'lafic o.oo o.oo 0;00 o.oo o.oo o.oo o.ao o.oo o.oo a.au a.co o.oo o.oo Meta :Aroillite-Slate 0.00 0.00 o.oo o.oo o.oo o.oo o.oo 0.00 o.oo o.uo 0.00 0.00 o.oo Schist o.oo o.oo o.oo o.oo 0.90 o.oo o.oo o.oo o.oo a.co a.co o.oo o.oo ().Lart:ite o.co a.co o.oo o.oo o.:o o.oo o.oo o.oo o.oo o.oo 0.00 o. oo o. oo Greenseaie o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo a.co 0.00 o.ou o.ou Seditil!llt tstone o.oo o.oo o.oo o.oo o.oo o.oo o.oo 0.50 0.33 0.67 o.oo 0.00 o.oo San Ctller ?.ocl< rragrrent O.ilO o.oo o.oo o.oo o.oo a.co o.oo 0.83 a.co 2.17 o.oo o.oo o.oo Total ltx:k !'ra 1'Dtal. Miscel.la>eaU8 5.50 3.67 6.56 6.17 l.80 1.00 2.00 3.33 5.34 4.33 2.49 2.50 1.17 Cenent-i'latrix: Ce!relt :Quartz o.oo o.oo o.oo o.oo o.oo o. oo o.oo o.oo o.uo o.oo o.ou o.oo o. ou cart>onate o.oo o.oo o.oo o.oo 0.20 o.oo o.oo o.oo o.oo o.oo 5.17 o.oo 9.83 Clay o.oo 0.00 o.oo o.oo 0.00 o.oo o.oo o.uo o.oo o.oo o.ou o.uo o.ou Hatrix:Clay 18.17 10.83 26.16 31.00 26.30 26.50 26.30 21.33 16.G6 33.17 o.oo o.oo 0.00 ().Jartz...-ekspar 14.00 5.33 11.17 11.00 o.oo 9. 70 14.00 17 .SU 5.66 lU.50 a.au o.ou o.oo Total 32.17 16.16 37.33 42.00 26.50 36.20 40.30 38.83 22.32 43.67 5.17 o.oo 9.83 TOrAL 100.00 100.00 99.99 100.00 99.90 100.03 99.90 100.00 99.99 100.02 100.00 100.00 100.00 Table 6.1 (cont.) 75 MODAL ANALYSES Samples /\rkose RH- RI!- Rl!- Rl!- RH- Rl!- RH- RH- RH- RH- m- Al- a1- a1- Bl- a1- 81- 81- 81- 82- 82- 82- Rocit or Mineral Cc"l'Ofl'!!1t 165 171 217 218 220 222 223 224A 208 218 220 ..:....::ra: Ccrm<11. noounciulose 6.34 10.33 8.J3 8.84 9.83 14 .00 13.50 18.33 16.17 5.3J B.17 C.OnrtD'I, Ulc:iulose 31.83 38.00 18.17 18.J3 27.00 41.50 37 .so 37. 83 28.33 26.33 33 . 33 PolycryscaJ.line 1.50 O.J4 8.00 7.00 3.83 4.16 5.67 5.67 7 .00 7 . J) 5.33 Chert 0.50 o.oo 6.83 6.50 2.67 0 . 17 o.oo o.oo 0.17 0.67 1.33 40.17 48.67 41.33 40.67 43.33 59.83 56.67 61.83 51.67 39.66 48.16 felcispar: Plagioclase 5.J4 6 .16 19.00 8.-50 1.J4 8.83 12.33 11.83 21.17 11.50 7.6'/ Orchoclase 36.66 31.33 8.50 8.66 5.83 2.34 6.84 2.50 6 .32 13.34 15.00 llicrocline 4.16 1.01 0.33 a.so 0.83 0.17 o.oo o.oo 0.34 4 .17 5.83 Pertnite 1.17 0.83 2.00 4.17 5.33 14 .66 12.83 10.00 4.00 4.67 3. 33 Total l'eldllpllr 47.83 39.33 29.113 1.83 5.113 26.00 32.00 24.33 31.83 33.68 41.83 Rock FraCJ!l!nts: Volcanic;Felsic o.oo o.oo 3.00 2.83 o.oo o.oo 0.00 o.oo o.oo o.oo o.oo Felsic-Internediatl! 0.00 o.oo 4.3J 4.50 0.83 0.00 o.oo o.oo o.oo 1.00 1.17 Incermodiate-!lal: ic o.oo o.oo 3.34 2.00 o.oo o.oo o.oo o.oo o.oo 2.00 1.17 Miltie o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo 1.67 0.00 o.oo o.oo 5.00 3.67 5.67 2.83 2.83 4.16 2.83 4.17 1.17 K-f elclsp!U"-()Jartz 3 .33 0.83 3.a3 2.33 2.00 4.00 2.50 2.17 1.33 7 .50 4 .17 Mafic o.oo o.oo o.oo 0.00 0.00 o.oo o.oo o.oo o.oo 0.00 a.co Meta :Araillite-Slaee o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo 0.50 Sdiist o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo cuarc:ite o.oo o.oo o.oo 0.00 o.oo 0.00 o.oo o.oo o.oo o.oo 0.00 Gr...,...scoo.. o.oo o.oo o.oo o.oo o.oo 0 .00 o.oo o.oo o.oo o.oo Sedil!ent :Mudstor...-Sil tscone o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo o.oo 0.00 o.oo Sanasc 'lUrAL 100.00 99.99 99.99 100.00 100.00 100.00 100.00 99.99 100.00 100.0l 100.00 Table 6.1 (cont.) 76 K-feldspar, rock fragments, and various clays and clay-like minerals dominated by chlor it e with subordinate sericit e. These framework grains, matrix and/or cementing components, and accessory minerals are described below. Quartz Quartz types identified include monocrystalline, polycrystalline, and chert. These varieties of quartz constitute 51% of the framework grains and 41% of the overall content based on the average of 38 point-counted thin sections. Monocrystalline or common quartz can be differentiated on the basis of whether or not the grain displays undulatory extinction. The undulatory type is the most abundant and accounts for 62% of the quartz types found in the samples; the non-undulatory variety accounts for about· 25%. The degree of undulosity is highly variable from grain to grain and cannot be attributed to the metamorphism of the sedimentary rocks. In general, the grains are free of inclusions. Polycrystalline or composite quartz grains consist of two or more quartz crystals. Internal crystal boundaries are distinct and vary from moderately straight to strongly sutured. Typically they display irregular to weakly sutured boundaries and show slight to moderate undulose extinction. The exceptions to this are uncommon and these grains are characterized by strongly sutured crystal boundaries, moderate to strong undulose extinction, and in some cases a weak preferred orientation of the crystals. Chert is also polycrystalline quartz with the individual crystals being microscopic in size; it is often referred to as microcrystalline 77 quartz. The relative abundances of quartz types are as follows: monocrystalline undulose accounts for approximately 64%, monocrystalline non-undulose 25%, and polycrystalline quartz is about 10% of the total quartz content. Chert accounts for less than 2% of the quartz types present. F$ldspar Feldspars are the second most abundant framework grains found in the samples; they account for approximately 32% of the framework grains and 26% of the total volume. Plagioclase is slightly more abundant than orthoclase and the two represent 86% of the feldspar content. The remainder is perthite and microcline occurring in roughly a 2:1 ratio. Plagioclase grains include albite, oligoclase, and andesine: based upon optical identification. In most thin sections, the degree of alteration from grain to grain is variable and is therefore believed to be primarily indicative of the severity of chemical weathering prior to deposition and burial; overall, fresh grains are in the minority. Alteration products are usually sericite and chlorite, with minor epidote and rarely calcite. The variation in alteration noted for plagioclase also exists for orthoclase. While most grains are at least slightly altered, the ratio of fresh to altered grains is higher than in plagioclase. The alteration commonly renders the grains a dusty brown in plain light and consists of sericite and other clays. 78 Perthite accounts for just under 10% of the feldspars present. However, its distribution in the rock types is uneven; some samples contain nearly 15% perthite, while others are devoid of this component. Perthitic textures seen include rods, strings, interpenetrating, an4 replacement features. Alteration of the microperthite is quite common, and variation within a single grain is common because of the varying susceptibilities of the two phases. Fragment§ Rock fragments constitute nearly 17% of the framework grains and about 14% of the total rock constituents; the actual content varies from 0 to 90%. The most abundant rock fragments are plutonic quartz- kspar (37%), plutonic quart z-p lag iocl ase (24%), f els ic-int ermed iat e volcanic (11%), felsic volcanic (8%), intermediate-mafic volcanic (6%), sandstone (3.8%), and mafic volcanic (3.4%); the remaining types each constitute less than 3% of the rock fragment total. Chert grains greater than 2 mm in diameter were treated as rock fragments; these and pieces of iron-formation occur in trace amounts ( <0.5%). Matrix The matrix consists of silt- and clay-sized components which are interstitial to framework grains of a sandstone and to pebble- and larger-sized clasts in diamictites. Silt- and clay-sized grains of chlorite, sericite, quartz, and feldspar are the major components of the matrix; minor components include epidote and unidentified clay minerals. The matrix content varies from 0% in the clean sandstones to 63% in graywacke and diamictite. The content of the 38 point- counted thin sections is 14.5%. The relative abundance of quartz- 79 feldspar silt to other matrix minerals occurs in a 1:2.3 ratio. Cement Cement is minor feature of most of these samples; where cement is present, it is quartz and/or calcite. Quartz cement is in the form of overgrowths on quartz grains. Some quartz grains show concave/convex or irregularly sutured boundaries. Calcite cement is typically a sparry calcite and some crystals are twinned. Where calcite cement occurs, it generally constitutes 4-5% of the rock, although one sample has 10%. Hematite and clay are found between framework grains or coating them, but are not abundant as cement. Accessory Minerals Accessory minerals in the samples are chlorite, opaques, epidote, muscovite, biotite, and trace amounts of zircon, tourmaline, and a pa tit e. The chlorite occurs as flakes and irregularly shaped grains. Some chlorite is likely primary, while the rest may be diagenetic or metamorphic in origin after original clay. Epidote is typically found as blebs or in aggregates and is considered to be of metamorphic origin. The opaques include iron-oxides and iron sulfides, specifically magnetite/ilmenite, hematite, pyrite, and chalcopyrite. Magnetite/ilmenite is blocky or subangular to rounded and may have a rind of hematite. Although some grains appear fairly fresh, alteration of magnetite, hematite, or both exist. Pyrite occurs as subangular to subrounded grains, irregular blebs, inclusions in quartz, and as 80 subhedral and poikilitic crystals. Pyrite is fresh or altered in varying degrees to magnetite, hematite, or both. Chalcopyrite occurs as discrete grains or irregular blebs. The muscovite might have grown from sericite during metamorphism. The zircon, tourmaline, and apatite are usually subrounded. C9mpositional .,ruu! Textural Features Diamict it es Massive and stratified diamictites display little appreciable differences in composition. Average quartz, feldspar, and lithic ratios (Q:F:L) for the samples are 54:36:10 and 51:34:15 for the massive and stratified varieties, respectively (Fig. 6.1). Lithic fragments are dominated by intermediate to felsic plutonics. A greater percentage of volcanic detritus is found in thin section compared with pebble counts in the field; intermediate to felsic volcanics predominate over mafic volcanic rock fragments. The ratio of plagioclase to K-spar ranges from approximately 1 :1 to 4:1 and tends to be around 3:2. The fine-grained clay-silt matrix content ranges from 16% to 42% and 22% to 44% for the massive and stratified diamictites respectively. The matrix is largely chlorite with sericite and lesser amounts of quartz and feldspar. The ratio of chloritic matrix to quartzo-feldspathic matrix is usually greater than 2:1. Both types of diamictites contain a wide range of grain sizes and the matrices contain very coarse sand to clay-sized particles (i.e. 2 mm-<0.0039 mm). Average grain size in the massive variety is generally in the lower end of the fine-grained sand range (0.125- 81 QUAIJl a STRATIFIED DIAMICTITE • MASSIVE DIAMICTITE • GRAYWACKE 00 0 ••a• 00 N a fiLD5rAa lllUIC fUOUAI LllHIC flAGMENU fU(,MfNU Figure 6. 1 Plot of the Q:F:L ratio for samples of diamictite and graywacke. 0.25 mm); the stratified variety tends toward the upper end of the fine-grained sand range (Fig. 6.2). Both types have grains which vary from angular to rounded. Most grains are subangular to subrounded, however, and no distinction can be made regarding the relative proportion of rounded grains and their distribution between the. two varieties. Redeposited material, consisting usually of sandy siltstone or fine-grained graywacke, occurs in both types of diamictite and may have a sub-circular or irregular and wispy shape. From the above description, it is apparent that massive and stratified diamictites are quite similar compositionally and texturally, though the stratified variety is slightly coarser grained. The major distinction between these types is the presence of stratification in one and the lack of it in the other (Fig. 6.3). If one employs the sandstone classification scheme for characterizing the matrices of the diamictites, they would fall in the feldspathic graywacke field. Sandstones The sandstones consist primarily of quartz, feldspar, lithic fragments and matrix or cement. Using the classification of Pettijohn, Potter, and Siever (Fig. 3.1), the following sandstone types are recognized; feldspathic and arkosic graywacke, arkose, lithic arenite, and subarkose (Fig. 6.4). The average Q :F :L for the graywackes is 65 :33: 2. They tend to be feldspar-rich with total feldspar content varying between 11% and 27% of the total and 28% to 41% of the framework grains. The plagioclase to K-spar ratio varies, but tends toward 1:1. Matrix content varies 83 Figure 6.2 Graywacke matrix of massive diamictite. Sand-size grains of quartz dominate with some plagioclase and K-spar. Altered volcanic rock fragment at left. Photo taken in crossed nicols. Field of · 4x hotomicrograp o strati ied iam1ct1te. Strat1f1cat1on is emphasized by concentration of quartz grains. Rock fragment is granitic. Photo taken with crossed nicols. Field of view is 4x7 mm. 84 c: al Cll Cll CIJ ,....; ..:: .. :I.. a Cll CIJ c: 0 .:.J Cll "O c: al Cll ... z ...a: ... c: < "'0 ... a: :z: "< "'0 ... 0: ::I"' " u... "' < c -4 0 • .- .. u... a 0 .:.J c = ..... 85 from 16% to 63% and averages 40%; chloritic matrix and quartzo- feldspathic matrix typically occur in a 2:1 ratio, respectively. Redeposited material (i.e. reworked Gowganda sediments), similar to that observed in some of the diamictites, is present in some of the graywackes. This may include obvious ripped-up clasts and material that may be deformed or have a wispy, irregular form. The grain size of the graywackes ranges from very coarse sand to clay and tends to be in the fine to very fine sand range (0.25- 0.0625 mm). They are typically poorly sorted to unsorted. The degree of grain rounding is highly variable from angular to rounded; however grains are generally subangular to subrounded. While graywacke beds are thick and massive, thin section examination reveals fine- scale stratification in some of the samples with beds on the order of 0.4-1 cm; this was not evident in the field. The layers are often wavy and irregular, though some are even. Despite such stratification, sorting within individual beds is poor. Arkose is feldspar-rich sandstone. Arkoses of the Gowganda Formation have an average of 38% of the framework grains as feldspar (Fig. 6.5). Plagioclase and K-spar occur in nearly a 2:3 ratio and perthite accounts for about 22% of the K-spar. The lithic content ranges from 0% to 21% of the framework grains and averages about 9%; felsic to intermediate plutonics account for over 77% of the lithic fragments with the remainder nearly all volcanics. The average Q:F:L value is 53 :38: 9. Most of the arkoses are medium-grained; those with a relatively higher percentage of lithic fragments are often coarse-grained. In the 86 majority of thin sections, grain boundaries have been altered by compaction and pressure solution. Where original boundaries are preserved, most grains are subangular to subrounded. Sorting varies from poor to fairly well sorted; the arkoses are generally moderately sorted. The mud matrix content is usually less than 4% and typically less than 1%. Calcite cement is fairly common and usually accounts for 4-5% of the rock. Silica cement is indicated by the sutured grains produced by compaction and solution, but the amount present cannot be ascertained with any accuracy. Beds are thicker than thin section scale; however, faint graded bedding was observed in one slide. Lithic arenites usually have greater than 50% of the framework grains as rock fragments and have an average Q:F:L ratio of 28 :19:53. Felsic to intermediate plutonic rock fragments typically constitute between one-half and two-thirds of the lithic content. Volcanics are the next most abundant, followed by minor amounts of metamorphic and sedimentary lithic fragments. Grain size varies, but most samples have a majority of grains in the coarse sand range (0.5-1.0mm). While variation in degree of rounding from very angular to subrounded exists, grains are generally subangular to subrounded. Whereas sorting may be poor, the rocks are typically moderately sorted. Matrix and/or cement content is less than 6%. Subarkose contains at least 7 5% quartz and feldspar exceeds the lithic content. Only two samples fall into this field of the Q-F-L diagram (Fig. 6.4). Grain boundaries in most grains have been 87 Figure 6.5 Photomicrograph of arkose with plagioclase and potassium feldspars. Note alteration of feldspars to sericite locally. Photo taken with crossed nicols. Field of view is 4x7 mm. Figure 6 .6 Photomicrograph of quartz grain with long axis in a vert- ical orientation and beds downwarped beneath it. From the lower pelitic association of the Lower Coleman Member. Photo taken in plain light. Field of view is 4x7 mm. 88 destroyed by pressure solution, but preserved show subangular to subrounded perimeters. One sample is medium-grained (0.25-0.5 mm) and the other is very fine-grained (0.125-0.25 mm); both are moderately to well sorted sandstones. The extensive pressure solution suggests silica cementation. Mineralogically and texturally, with the exception of the subarkoses, the sandstones are immature. The subarkoses are mineralogically submature and texturally slightly mature. Lonestone-bearing The lonestone-bearing rocks are also comprised of quartz, feldspar, lithic fragments, and matrix or cement. Texturally there are important features related to the lonestones. On the microscopic scale, a variety of different particles occur as lonestones; large grains of quartz or feldspar, lithic 0.5mm, and fairly round aggregates of material that are graywacke-like in In Figure 6.6, a l mm diameter quartz grain rests with its long axis nearly vertical and the layers beneath show appreciable downwarping. Another sample shows a granitic clast 2.5 cm long which not only deflected beds below it, but truncated layers of sediment as well. In Figure 6.7, a graywacke-like aggregate rests between layers of sediment with nearly equal amounts of warping around the lonestone giving an ambiguous sense of top and bottom. Locally, nests of grains occur and may shoy.g virtually no influence on the surrounding sediments. As these figures depict, the structures associated with lonestones vary from disruption of the substrate to minimal or negligible downwarping. 89 Figure 6.7a Lonestone here is an aggregate of grains with a graywacke-like texture. Note the angularity of grains in the aggregate and warping of beds around the aggregate. Photo taken in plain light. Field of view is 4x7 mm. Figure 6.7b Graywacke aggregate surrounded by subangular to sub- rounded quartz grains. This lonestone produced a minimal effect on the substrate. Photo taken in plain light. Field of view is 4x7 mm. 90 '· GEOCHEMISTRY General Samples were collected for chemical analysis of the major oxides. Ten samples are of basement rocks and the deposits immediately above the Archean - Proterozoic unconformity, eight samples of argillite/siltstone (including three samples of the Firstbrook Member from Barr and Firstbrook Twps., located approximately 30 km southeast of the st1Jdy area), and seven samples of matrices of diamictites. The chemical analyses results are presented in Appendix B. Chemical Alteration l!!ll! W_,S!atherj.n,g The use of lutites to infer climates based on major element chemistry was proposed by Nesbitt and Young (1982) the Lower Proterozoic Huronian Supergroup. Paleoclimates may be inferred by looking at the degree of weathering which is determined by calculating the chemical index of alteration (CIA): Molecular proportions of the oxide analyses are used in the calculations. The Cao proportion used is only the amount incorporated in silicates; corrections are made for apatite and carbonate. Low CIA values suggest less chemical weathering and higher values suggest greater chemical weathering. It follows that paleoclimatic conditions can be inferred on this basis. As examples, Pleistocene tills produce values near 50, whereas the average shale "is 70-75, Amazon cone muds 91 are approximately 80-85, and residual clays approach 100 (Nesbitt and Young, 1982). Following their method, the resultant values were calculated (Table 7.1) and plotted with data from Nesbitt and Young in Figure 7.L The argillites and siltstones of this study have an average value of 61. If separated on the basis of stratigraphic position, distinct differences emerge. The samples that come from the Lower Coleman Member have CIA values that range from 48-59 and average 55. In contrast, samples from the Upper Coleman Member and Firstbrook Member have CIA values which range from 62-67 and average 65. This compares with an average value of 62 for seventy-eight argil lite s.amples of the Gowganda Formation obtained from the Huronian outcrop belt (Nesbitt and Young, 1982). The average CIA value of sixteen samples from only the Cobalt area is 63. Diamictite matrix materials have a range in indices of 42 to 60 in the seven samples analyzed; the average value is 53. Nesbitt and Young (1982) analyzed seventy-seven samples of diamictite matrices from the Gowganda Formation throughout the Huronian outcrop area. The average value for their samples is 56. Their sixteen samples from the Cobalt area alone average 57. The CIA values cal cu lated in this study on average were lower than the average values presented by Nesbitt and Young in their analysis of Gowganda lutit es and diamictit es. As Figure 7 .1 depicts, the lowest values for lutites and diamictites are from this study, whereas the highest values are from Nesbitt and Young. Although the number of analyses in this study is small, the results suggest an 92 SAMPLE # ROCK TYPE OXIDES IN MOLECULAR PROPORTIONS CIA Al2o3 CaO* Na 2o K20 RH-81-24 Regolith 0 .1167 0. 007 5 0.0157 0.0140 75.83 RH-81-70 Granitic basement 0.1648 0.0136 0.0839 . 0.0100 60.52 RH-81-71 Regolith 0 .1403 0.0103 0.1250 0.0045 50.09 RH-81-73 Granitic basement 0.1501 0.017i 0.1115 0.007 9 52.37 RH-81-74 Regolith 0 .1628 0.0153 0.0540 0.0119 66.72 RH-81-168 Arg. I siltstone 0.1501 0.0328 0.1060 0.0218 48.31 RH-81-177 Siltstone 0 .1216 o. 0687 0.0111 0.0028 59.55 RH-81-178 Granitic basement 0 .1510 0.0374 0.0786 0.0063 55.25 RH-81-17 9 Diamictite matrix 0.1353 0.0187 0.1646 0.0040 41. 94 RH-81-201 Basaltic basement 0.1383 0.0859 0.0816 0.0025 44.86 RH-81-227 Diamictite matrix 0.1422 0. 0121 0.0854 0.0184 55.09 RH-81-236 Granitic basement 0.1579 0.0806 0 .1026 0. 0143 44.43 RH-81-237 Regolith 0.1775 0. 0107 0.0678 0.0248 63. 21 RH-82-201 Arg. Is iltstone 0 .158 9 0.0036 0.0582 0.0223 65 .39 RH-82-202 Arg. Is iltstone 0.1756 0. 0098 0. 0 536 0. 0312 64.99 RH-82-203 Arg. Is iltstone 0.1746 0.0032 0. 0 57 8 0. 0 27 3 66 .41 RH-82-204 Gabbroic basement 0 .13 93 0 .127 5 0.0455 0.0049 43. 92 RH-82-206 Diamictite matrix 0 .1412 0.0029 0.1060 0.0027 54.58 RH-82-207 Diamictite matrix 0.1589 0.0086 0. 0634 0. 03 27 60. 28 RH-82-209 Arg./siltstone 0.1746 0.0198 0.0665 0.0407 57 .8 9 RH-82-217 Diamictite matrix 0.1285 0 .0027 0.0820 0.0207 54. 94 RH-82-219 Diamictite matrix 0 .1461 0. 008 7 0.0881 0.0249 54.56 RH-82-223 Diamictite matrix 0 .1334 0.0469 0.0839 0.0064 49.30 RH-82-225 Arg./siltstone 0.2099 0.0025 0.0250 0.07 52 67.15 RH-82-228 Arg. Is iltstone 0 .177 5 o. 0078 0.0550 0.0463 61. 93 * Cao corrected for apatite and carbonate. Note: Samples RH-82-201,202,203 are from Firstbrook Member. Regolith refers to deposits which rest upon Archean basement rocks and probably represent paleosols developed prior to deposit ion of Gowganda Formation rocks. Samples RH-81-168, 177, 179, 227, RH-82-206, 207, 217, 219, 223 are from the Lower Coleman Member. Samples RH-82-225, 228 are from the Upper Coleman Member. Table 7 .1 The chemical index of alteration (CIA) is shown along with the molecular proportion of the oxides used in making the calculations. 93 51 • ••• 51 .a. L I "'' I 31 • • I • - 21 l .. ..i.I 70 ao 90 100 ei..ic.al iDdaz of alt•ratioa 1) Gavgand& Pia. - diaaictitu (77 •a.pl.. , !W.Oitt md YoUDg, 1982). 2) Gawgmda Pia. - diaa:Lct.itu from Cobalt ar- Ollly (16 •a.pl.. , Kll•bitt and Young, 1982). 3) Gawganda Fiii. - di.-icdtu (7 •a.plea, thia •tudy). 4) Gawganda Fiii. - argillitu (78 ..mp1 .., Mo.Oitt md YOUllg, 1982). 5) Golfguada Pia.·- argillit.. froa Cobalt ana oa.ly (16 •a.pl.. , Nlt.Oitt and Yoang, 1982). 6) Govganda Pia. - &rgillit.. (8 H•pl-, thia mtudy). Figure 7.1 A histogram depicting the distribution of CIA values calculated from samples of diamictite matrix and from argillite. The results are compared to values calculated by Nesbitt and Young (1982) . 94 overall trend of generally less chemical weathering in the study area compared to other areas where Gowganda sediments occur. It also suggests a change from less chemical weathering to greater chemical weathering with time. This is in agreement with the results of Nesbitt and Young. Analyses of samples from basement rocks and associated deposits at unconformities provide varied results. In terms of CIA, the average of five fresh Archean basement rocks was 50, which is similar to the value of 49 for average Archean shield in northwest Ontario (Shaw et al., 1967). In two pairs of analyses, deposits representing paleosols had values slightly higher than the underlying basement rocks, suggesting a moderate degree of chemical weathering. One pair of samples (RH-81-70,71) displayed the reverse relationship and may ref le ct a diagenet ic or metamorphic alteration. The apparently anomalous value from RH-81-71 reduces the average CIA for these ancient weathering horizons from 69 to 64. Fryer (1977) examined some paleosols at the base of the Huronian Supergroup. These weathering profiles were characterized by extensive leaching of Na, Ca, Mg, Mn, and Si and concentrations of K, Al, and Ti. Since such deposits in this study were not systematically sampled, no definitive statements can be made. However, leaching of Si, Ca, and Na and enrichment of K, Al, and Ti was revealed by the analyses; Fe enrichment occurred in most samples. Characteristics Plots of Cao, Na 2o, and K2o on a triangular diagram for argillites and matrix material of diamictites can be seen in Figure 95 7.2. Generally, the samples are Na-rich with the diamictite matrix samples plotting well within the Na 2o region of the diagram; argillite analyses show greater variability. Diamictites are seen to be quite soda-rich and low in both CaO and K2o, whereas argil lit es are typically depleted in CaO relative to Na 2o and K2o, which are present in nearly equal amounts. Angina (1966) examined the geochemistry of Antarctic pelagic sediments and found that elemental chemistry was useful in making distinctions between glacial-marine and continental glacial environments. He observed that glacial-marine sediments around Antarctica were notably deficient in Fe, Ti, and Ni and enriched in V and Cu relative to crustal abundances. Frakes and Crowell (197 5) noted modern glacial-marine sediments are depleted in Fe relative to their continental counterparts, while Mn may be depleted or enriched. Ancient glacial-marine sediments showed depletion in both Fe and Mn. The prevalence of reducing conditions in the marine environment and continued reducing conditions during diagenesis, whereas oxidation is prevalent in subaerial environments, might explain the distribution of Fe and Mn. Thus, Fe would be expected to be oxidized and concentrated in terrestrial tills, and, therefore, glacial-marine sediments would show relative depletion. The behavior of Mn may be linked to decreased detrital input which favors concentration of Mn. Sumartojo and Gostin (1976) analyzed the Late Precambrian Sturt Tillite in Australia for major oxide and trace elements. They plotted 96 weight percent Fe versus Mn and found the samples deficient in Fe and Mn and suggested the samples represented glacial-marine sediments. Figure 7 .3 is a plot of weight percent FeO versus MnO for samples of diamictite.matrix from this study with other averages for comparison. Although the data are scattered, the average from the present study is below the crustal abundance of Fe and Mn and similar to results of Young (1969) for the Cobalt - Gowganda area. The data therefore suggest that the Gowganda diamictites were deposited in a marine setting. If the diamictites are glacially derived, one would expect to see this reflected in the CIA: the older part of the sedimentary pile ought to contain more weathered material than the younger part. This would reflect progressive erosion through a pre-glacial regolith to fresh rock beneath. This study does not show such a trend. Several explanations are possible. In the chapter on the Archean-Proterozoic unconformity, it was shown that Gowganda rocks rest on relatively fresh Archean basement as well as an ancient regolith. Given the varied degree of weathering, material entrained by advancing glaciers would therefore produce diamictite displaying a wide range of CIA values. Another possibility is the homogenizing process produced by glaciation. Comminution of larger, fresher clasts could mix with finer, more weathered material and res.ult in a moderate CIA value. Another explanation is there are an insufficient number of analyses available from this study to reveal such a trend. It was stated earlier in this chapter, however, that CIA values from the Lower Coleman Member on .average were lower than 97 Cao • Argillite, Gowganda-Elk Lake area . (8 samples, this study). + Argilllte average, Gowganda-Elk l.ake area (8 uample1:1, this study). • l>iamicti te matrix, Gowganda-Elk Lake area (7 samples, this study). -+· Dia1oict!te matrix average, Gowganda-Elk Luke area (7 samples, thii; study). I) • 9 Argillite average, Gowganda Formation (9 samples, Young, 1969) • <>- ¢- Diamictite matrix average, Col.ialt-Gowganda area (9 samples, Youn!\, 1969) . • 9 • Dinmictite matrix averug«:, Bruce tlines-lllind ltiver area (7 sampleu, ¥011111\, 19(19). \0 • I) Archean Shield average, northwest Ontario (Shaw et nl., 1967). CX> ".• Na 0 3 so Figure 7 . 2 shows relative of Na o, Cao, and K o in samples of 2 arg1ll1te and diamictite. Additional points are for comparison2 to analyses by Young (1969) from samples of Gowganda argillite and diamictlte; data from Shaw and others (1967) of the Archean Shield. 8.0 * * ... * 6.0 •"° ¢ 0• -¢-* * ae• * 4.0 * 2.0 0 0.02 0.04 0.06 QD8 0.10 0.12 0.14 0.16 0.18 0.20 'I. MnO * Diamicdta matrix (Thia study). * Average diamictite matrix (7 samples, thia study). ¢ Average diamic:ita matrix, Bruce Minas-Blind R:l.ver area (7 Young, 1969). -0 Average diamictite matrix, Cobalt-Gavganda area (9 samples, Young, 1969). diamictite matrix, T1llita, Auatralic (25 samples, Sumartojo and Gostin, 1976). + Continental crustal abundance (Ronov and Yarosbavaky, in Mason and Moore, 1982). - Figure 7.3 Plot of weight % FeO versus MnO from samples of diamictite. Note that the samples from this study tend to plot below the crustal abundance. 99 values from the Upper Coleman Member. The geochemical analyses suggest that chemical weathering of Archean rocks occurred during initially moderate climatic influences which later deteriorated to frigid conditions during early Gowganda time and eventually back to a moderate climate in late Gowganda time. Gowganda rocks typically are Na-rich and this probably reflects the source area. Gowganda diamictites are depleted in Fe and Mn relative to crustal abundances for those elements and suggests that the diamictites were deposited in a marine environment. 100 PALEOCURREN.r ANALYSIS AND PROVENANCE Paleocurrent Measurement of paleocurrent indicators in the Gowganda Formation yielded only thirteen reliable readings. Given the dearth of readings, the overlying Lorrain Formation was chosen for additional measurements. Because of the transitional and conformable boundary between the two formations, it is believed that the Lorrain Formation measurements are accurate indicators of the general paleoslope during deposition of both of these formations. Accordingly, ninety readings of cross-bedding and channel axes were measured in Lorrain outcrops in the study area. Since structural complexity is absent and the present bedding attitudes are commonly the result of tilting due to block faulting, a simple one-tilt solution was used to return the beds to horizontal (Ramsay, 1961; Potter and Pettijohn, 1977). Uncorrected and corrected rcse diagrams for both formations are presented in Figures 8.1 and 8.2, respectively. The vector mean and variance were calculated for the Lorrain Formation using the method described by Potter and Pettijohn (1977) and Curray (1956). The degree of variance about a vector mean can be used as an indication of environment (Long and Young, 1978). While the variance for environments can overlap, it has been shown that fluvial deposits display varianc-e of less than 4000, whereas marine deposits generally have a variance of 6000-8000. Long and Young (1978) show that the Lorrain Formation displays aspects of fluvial, marine, and deltaic environments. 101 N N LORRAIN FM. GOWGANDA FM. n =90 n =14 165° • ...... Standard Deviation 54° Standard Deviation 68° 0 Variance 2958 Variance 4570 186° Figure 8.1 Rose diagrams depicting uncorrected paleocurrent measurements for the Lorrain and Gowganda Formations. LORRAIN FM. GOWGANDA FM. N N n:: 110 n:: 14 t-' 143° 0 w Standard Deviation 52° Variance 2718 Standard Deviation 62° Variance 3851 Figure 8.2 Rose diagrams of paleocurrent trends in the Lorrain and Gowganda Formations corrected for bedding tilt using a simple one-tilt solut i on. In this study, the vector mean and variance calculated from paleocurrent data from the Lorrain Formation are 168° and 2718, respectively. In most cases, measurements were from beds in the lower one-fourth of the formation. The data suggest that paleocurrents generally flowed from north to south with local variation. Furthermore, it appears that the Lorrain Formation in the Gowganda - Elk Lake area was deposited in a f luvial environment. This suggests that the regional paleoslope during Gowganda sedimentation was one of generally north to south transport of material. An insufficient number of measurements preclude application of variance as an environmental indicator for the Gowganda Formation. The few readings from Gowganda sediments in this study trend southerly. Young (1968), working in the southern outcrop belt, reported a vector mean of 160° for cross-bedding in arenaceous Huronian Formations and clast fabric analysis in the Gowganda also supported southerly transport of sediment. Further support for the predominance of north to south transport is provided by Casshyap (1968), Lindsey (1966), and Schenk (1965). Provenance Paleocurrent analysis provides evidence of predominantly north to south transport of elastic sediments down the prevailing paleos lope. It is probable that material also entered the Gowganda depositional basin from the eastern and western margins of the basin. Regardless of the initial entry point, detritus was derived from a largely granite- greenstone terrane. This terrane is exposed to the north of the preserved northern limit of Gowganda rocks, as inliers within the 104 Gowganda outcrop area and as basement to the Cobalt Group rocks. Intrabasinal sources be seen at certain outcrops where Gowganda sediments contain clasts indentical to the basement lithologies upon which they rest. This clearly establishes local derivation for some of the detritus. Redeposition of some material in the basin is indicated by clasts of Gowganda siltstone and sandstone, showing varying degrees of rounding, incorporated in other Gowganda sediments. Extrabasinal sources for the sediments are suggested by the presence of chert, iron-formation, gneiss, and metasedimentary rock fragments found in the diamictites and sandstones. Whereas most of these lithologies are found in a greenstone terrane, the presence of the other clasts (e.g. gneiss) suggests a different and possibly quite distant source. Pebble counts suggest that the source area was dominated by granitic or felsic to intermediate plutonic rocks. This material may have been derived relatively nearby. Petrography shows that those lithologic types are the most common rock fragments in the sand size range; however, a larger percentage of felsic and mafic volcanics are present in this size range than in the larger size fractions. This probably reflects the differential response of these lithologies to mechanical abrasion and suggests that the finer-grained fragments, represented by volcanics here, tend to survive and retain their identity, whereas the coarse-grained fragments break down into sand, silt, or smaller-sized monomineralic grains. In a related sense, Young 105 (1969) suggested that the higher Fe and Mg found in diamictite matrix relative to bulk samples of diamictite is due to preferential breakdown of mafic minerals. The chemical analyses of argil lit es and diam ict it e matrix materials suggest a source area that was fairly homogeneous, one relatively low in CaO and enriched in Na 2o and to a much lesser extent K20 (Fig. 7 .2). This suggests a source composed of rocks which are compositionally similar to granodiorite. The apparent homogeneity may be due in part to the environment or mode of transport and deposition • . McLennan et al. (1979) suggested that the source area for the Huronian sedimentary rocks bad evolved from a suite dominated by tonalite- greenstone to one approximating granodiorite. Although their study concentrated on rare earth element patterns rather than oxides, data from the present study are in general agreement with the results of their study. 106 SEDIMEN'IATION Interpreta_sion .9.i DepositionaJ Processes Introduction The Gowganda Formation in the Gowganda-Elk Lake area contains a diverse assemblage of lithofacies and associated sedimentary structures which indicate a complex depositional history. The environment of deposition as well as the mechanisms and mode of transport and deposition varied in both time and space. Seguenc;es It is clear from the types of deposits present at the unconformity with the Archean basement that they do not represent similar environments and may be widely separated in time. Paleosols preserved in some locations have CIA values in the middle to high 60's (Table 7 .1 ). This would suggest that chemical weathering occurred and was promoted by a moderate climate. Locally a more severe, frigid climate is suggested by the fractured, jointed basement underlying massive diamictite; however, this is not supported by the CIA value (sample RH-81-24). The extremely angular shape of fragments from silt to cobble size and the change downward from abundant smaller fragments into fewer, larger clasts and eventually intact basement is similar to deposits developed in a periglacial environment. The angularity of the sediments reflects the dominance of mechanical weathering (i.e. frost- wedging) with no apparent transportion. The 100 m thick accumulation of well-rounded boulder, and 107 pebble orthoconglomerate overlain by arkose sandstone and resting on Archean basement in northwest James Twp. and similar deposits in northeast Mickle Twp. are interpreted as fluvial deposits. Detritus was shed off the flanks of the exposed Round Lake Batholith in earliest Gowganda time. Other sites where coarse, clast-supported material lies at the base of the formation suggest significant relief near basin margins. For example, the very angular, blocky clasts exposed on the northwest shore of Obushkong Lake are perhaps a talus accumulation. Whereas those examples of extremely coarse elastic accumulations at the base of the formation are indicative of sedimentation during early Gowganda time, the well developed orthoconglomerates with abundant quartz pebbles (up to 37%) along Highway 560 west of Lost Lake appear to represent deposition during late Gowganda time. Although this sequence rests unconformably on Archean rocks, it passes upward into hematitic siltstone and sandstone which are transitional to the arkoses of the Lorrain Formation. Possibly 1500 m or more of the Gowganda sedimentary record is in the sequence west of Lost Lake, due to nondeposition. Elsewhere in Milner Twp., the basement rocks have been eroded to a smooth, gently undulating surface upon which laminated siltstones with lonestones rest. This style of sedimentation occurs in a lower energy environment and deposition of this sequence might be explained in terms of facies changes along or across depositional strike. However, given the absence of an orthoconglomerate and arkose sandstone sequen<.:e above o·c below this laminated unit at this 108 locality, this suggests both a different temporal and environmental setting at this locality. Graywacke Sandstones The graywacke sandstones are subaqueous deposits. On the basis of internal stratification and organization (or lack thereof), bedding surfaces, and stratification sequences, the recognition of different facies is possible. The rocks display characteristics of sediment gravity flows or mass-movement deposits. Descriptive and genetic classification of deep-sea mass-transported sediments have been proposed by several workers. The best known descriptive scheme for sandy and finer sediments is the Bouma model (Bouma, 1962). Walker (197 5) presented a model for resedimented conglomerates. Genetic classification by Dott 0963), Middleton and Hampton (1973), and Lowe (1979,1982) have been based on the rheology of flows (Fig. 9.1). A review of the literature by Nardin et al. (1979) provides an excellent overview of mass- movement processes in a submarine environment. Massive sandstones with abundant muddy matrix (i.e. graywackes) and containing outsized clasts of argillite and sandstone occur in an out crop on Firth Lake and were described in the chapter on lit ho logy. These are similar to the slurry sandstones of Hiscott and Middleton 0979) who interpreted them as debris flows and cited sharp contacts and massive beds as evidence for debris flow and against turbulence. Lowe (1982) classifieci these as cohesive flows in which flow is laminar; the depositional mechanism is cohesive freezing. These sandstones could fit Facies F classification of Walker and Mutti 109 llJRBJOITY CURRENTS LOW-OENSllY 1 t t I I I (troction)-(lroction Clll'Jl"l)-{SUS11111Sion)\ I t , '-HIGH-OENSITY I t UQUmED FlOWS (suspension std.) - )::! - t FtUIOIZED FlOWS j t GAA1N FlOWS (frictional frHzinq)_.,/ / COHESIVE FtOWS (cohesive fr-euing)/ Figure 9.la Summary of the principal sedimenta- tion mechanisms of sediment gravity flows. (from Lowe, 1982) Depoalt REMOLDING Debris Flow UCUEFACTION . . UPWARD / / Sediment FLOW OF ._.§ ra;,, f:f Flow II' PORE FLUID Olf ...... e TURBULENCE GRAIN INTERACTION PRESSUR 8 rbtcJity Current / TRACTION l; Co,, ""6 . Centration Current Time and I or Space Figure 9.lb Hypothetical evolution of a single flow, either in time or in space. (from Middleton and Hampton, 1976) 110 (1973). Sediments which comprise Facies F are commonly muddy deposits that are the result of down-slope mass-movement processes. Other massive graywacke beds with or without dispersed clasts and apparently lacking dish structures or other fluid escape structures are common elsewhere in the study area and are also considered to be the deposits of cohesive (debris) flows. Because grain flow and liquified or fluidized flow can be genetically associated with debris flow, it is reasonable to expect that the deposits of these types of sediment gravity flow could occur with each other (Fig. 9.2). Though the role of grain flow and fluidized and liquified flow in transport of some of these sediments is suspected, conclusive evidence is lacking and may be unrecognized because of inadequate exposure. Graywackes which exhibit internal stratification, such as normal grading, cross-bedding, laminations, and load structures are interpreted as sediment gravity flow deposits in which flow behavior was turbulent. These are the deposits of high- and low-density turbidity currents (Lowe, 1982). Application of Bouma terminology is possible for these sediments. Generally two sequences occur, an AE and a base-cut-out DE or CDE. No complete A-E sequences were recognized in the field. These two groups conform to Facies C and D, respectively, of Walker and Mutti (1973), which are characterized as .'.'classical," turbidites and represent proximal (AE) and distal (BDE, CDE) deposits. Siltstone The fine-grained rocks display the following features; laminations, cross-bedding, rhythmic layering, loading structures, 111 ...j .sa c3 ...j • t I.I Figure 9.2 Summary of the main deposit types formed during deposition from sediment gravity flows. Lines without arrows connect mem- bers between which there probably exists a continuous spectrum of flow and deposit types but which are not parts of an evolu- tionary trend of single flows. Arrows con- nect members which may be parts of an evolutionary continuum for individual flows. The transition from disorganized cohesive flows to thick, inversely graded density- modified grain flows and traction carpets and to turbulent gravelly high-density turbidity currents is speculative but may occur (from Lowe, 1982) 112 convolute or bedding, and grading. Rarely they are massive. These deposits may be the result of low-density turbidity currents or deposition from other types of dilute suspensions. Deposits of this type are similar to Facies G of Walker and Mutti (1973) and are characterized as hemipelagic and pelagic deposits. These deposits can occur in a number of different environments such as a large lake, mid to outer continental shelf, submarine fan, submarine slope, or basin plain. Rhythmic bedding may reflect episodic events related to diurnal or seasonal effects in a fresh water or marine environment. Some massive argillit2 in the Gowganda may represent hemipelagic or pelagic sedimentation. Laminated Lgnesfone-bearinz Sedimentary Laminated fine-grained rocks with lonestones occur in the lower two-thirds of the formation. Emery and Tschudy (1941) and Emery (1955, 1963) discuss the possible mechanisms that might explain erratics or lonestones and criteria for recognizing the transport agent. Of the eight agents proposed, only three - wind, ice, and turbidity currents- are considered here. The other five agents are biological; therefore the age of the Gowganda Formation would seem to preclude their consideration; however, Jackson (1971) reported material of presumed biogenic origin intimately associated with lonestones in laminated sediments of the Gowganda. Even so, he believed the erratics to be ice-rafted debris. The size of most of the lonestones eliminates wind as an effective agent. The turbulence of a turbidity current would enable the current to support and transport larger stones; however, a 113 turbidity ·current would produce distinctive sedimentary structures and such features are absent in these rocks. Hume (1964) documented sand and small pebbles supported by water surface tension near Barrow, Alaska, but this process is not believed to be a significant contributor to the sedimentary record. Therefore, it is concluded that the medium- to thin-bedded, laminated, lonestone-bearing sequences should be interpreted as dropstone sequences; i.e. ice-rafted debris (IRD). Spjeldnaes (1981) has questioned the presence of IRD as a criterion for the onset of glaciation as suggested by Hopkins and Herman (1981) from coring of Cenozoic sediments in the Arctic. Spjeldnaes (1981) stated that development of sea or coastal ice due to a deteriorating climate could have produced tha deposits prior to true glaciation. Hopkins and Herman (1981) rejected this assertion and cited evidence such as textures on quartz grains resolved by scanning electron microscope, lithologies from a distant source, and degree of rounding that, when applied to IRD, can distinguishfhe difference between glaciation and winter ice. The widespread occurrence of dropstone units in the Gowganda, clast shape, degree of rounding, and presumably distant source for some lithologies suggest that these sequences are indicative of glaciation. In addition, the small sub-spherical graywacke-like aggregates described in the petrology chapter are nearly identical in character to material reported by Ovenshine (1970) and Goldstein (1983). Ovenshine described these aggregates as till pellets and 114 attributed their formation to glacial processes, specifically to ablation. Diamictite General Discussion Diamictite (Flint et al., 1960b; Flint, 1971; Dreimanis, 1982b), mixt ite (Schermerhorn, 1966), and pebbly muds tone (Crowell, 1957) are among the terms in the literature to describe mixed coarse-fine lithified sediments in a qualitative, non-genetic manner. Diamictite may be deposited in several different environments, subaerial and subaqueous. Blackwelder (1928) and Hooke (196 7) have described deposits and processes in arid and semi-arid alluvial fan environments in which mudf lows and debris flows produce diamictic deposits. Crowell (1957) discussed the origin of pebbly mudstones as submarine mass-movement deposits associated with slumping in a turbidity current environment. Kurtz and Anderson 0979) and Wright and Anderson Cl982) have identified debris flow deposits on the Antarctic continental margin. They have distinguished them from glacial-marine sediments. Fisher Cl 971) addressed classification of rocks composed of volcanic fragments. Certain pyroclastic and epiclastic deposits in a volcanic terrain have a diamict texture. The common feature of these deposits, regardless of environment, is that debris is transported en masse. The triggering mechanism or flow behavior as well as transport process may be inferred from the deposits. These aspects have been recently discussed by various workers (Middleton and Hampton, 1973, 1976; Lowe, 1976a, 1976b, 1979, 115 1982; Carter, 1975; Hein, 1982; Walker, 1975; Walker and Mutti, 1973; Fisher, 1971, 1983; Rodine and Johnson, 1976) concerned with primarily subaqueous processes. Glacial regimes have been evaluated by Flint (1971), Andrews (1975), Boulton 0972, 1975) and most recently by Dreimanis (1982b). The glacial environment is well known for diamictic deposits which have loosely been referred to as drift, moraine, or till. The recognition of ancient and recent glacial deposits is discussed by Harland, Herod, and Kr ins ley (1966), Schermerhorn (197 4) and recent reviews of glacial-marine sedimentation is presented by. Andrews and Matsch (1983) and Anderson (1983). Clast fabric may provide evidence of both transport direction and mode. Holmes (1941) described till fabric and reported clast long-axis orientation occurred in two preferred directions, one parallel, the other transverse to ice flow direction. He believed the former was acquired by sliding, the latter by rotation, with behavior dependent on stone form. Lindsay (1968), using computer simulation, examined clast fabric development in mudflows. Fabric is dependent on flow velocity and viscosity and develops and degenerates during flow; fabric is thus dependent on the time at which the flow freezes within the cycle. Lindsay felt that c-axis orientation of clasts could be used to distinguish mudf lows from tills and applied this to the Gowganda Format ion and the Squantum :'T (Lindsay et al., 1970). The study supported a glacial origin for the former and a mudf low origin for the latter. 116 Grading may be present in some diamictites. Naylor 0980) has examined the origin of inverse grading in muddy debris flows. Walker (197 5) noted four types of conglomerate beds deposited by mass- transport .mechanisms: graded-stratified, inverse-to-normally graded, graded, and disorganized. Hein 0982) described six facies from the Cap Formation, a deep-sea elastic assemblage, using a-axis orientation and clast imbrication as part of the analysis. All but one facies were attributed to sediment gravity flow in which liquified or fluidized flow, as indicated by abundant fluid escape structures, is the dominant mechanism. This type of deposit . is considered intermediate between those expected from turbidity currents and debris flows. Origin of the Gowganda Diamictite Diamictites in this study were divided into massive and stratified types. Outcrops invariably were poorly exposed and bedding surfaces extremely rare. As a result, clast-fabric analysis of bedding surfaces was not possible; however, cross-section exposures did permit analysis of presence or absence of organization within beds. The lack of clast-fabric data constrains against making a quantitative determination of environment and mode of deposition as did Lindsay and others (1970). Based on internal features of beds, bounding contacts, and stratification sequence, a general interpretation can be put forth. Massive Diamictite The massive variety of diamictite in the study area is believed to be the result of sediment gravity flow phenomena, specifically 117 subaqueous debris flow. The lower contacts are "typically sharp, deformed clasts of siltstone or are present locally, and rare normal grading may be present at the tops of some beds. These deposits are commonly interstratified with graywacke and argillite beds which display evidence of transport by sediment gravity flow. Lack of turbulence (i.e. lack of imbrication, no scoured basal contacts, etc.) suggests that debris flow was the operating mode. The rare grading bedding at the tops of beds could be due to mixing of water at the head of the flow. Mixing could result from turbulence generated by friction at the sediment/fluid interface (Middleton and Hampton, 197 3). Experiments (Hampton, 197 2) suggest that a transit ion from debris flow to turbidity current occurs from water mixing. The association of various types of sediment gravity flow deposits in a stratigraphic sequence could be expected. Middleton and Hampton (1976) diagrammatically represent the continuum of sediment gravity flow deposits and mechanisms. The role of ice in deposition of some of the sediments was established by the recognition of associated dropstone sequences. The similarity of debris flow deposits to till and tillite can pose problems in interpretation. The possibility of some of the thicker, massive diamictites being basal-till deposits or the result of abundant and continuous rain-out of debris from melting ice does exist. This will be discussed further under models for sedimentation. 118 Stratified Diamictite Stratified diamictites in this study are interpreted as the probable deposits of two major processes, sediment gravity flow and release from melting ice. Evidence for sediment gravity flow is the presence of inverse as well as normal grading and sharp contacts. Some weak fine-scale stratification could be the result of shear during flow (Middleton and Hampton, 197 3). The apparent lack of fluid escape structures would support debris flow and possibly grain flow for very coarse debris as primary transport modes. Poor exposure may have obscured the presence of fluid escape structures which would indicate fluidized and liquidized flow as depositional mechanisms. Stratified diamictite may be produced by subglacial melting of ice sheet. Evenson et al. (1977) suggested that debris flow was the dominant process in forming the Pleistocene Catfish Creek Till in Ontario. This was refuted by Gibbard 0980), who cited evidence supporting basal melting of an overriding ice shelf and argued that features characteristic of flow are present but minor. Gowganda stratified diamictites are generally sandier than the massive variety, locally have gradational contacts, and some are interbedded with coarse, graded arkosic sandstone. This type of Gowganda diamictite is similar to Type 2 and Type 3 sediments defined by Anderson et al.,(1980) and paratills of Domack and others (1980) from Antarctic continental margin. These were described as heterogeneous deposits, both texturally and mineralogically, displayed normal compaction, and the degree of sorting reflected the action of marine currents. These sediments were interpreted as deposits from floating 119 ice. Stratified diamictite exposed in a road cut on Highway 560 east of the town of Gowganda bears similarities to the Catfish Creek Till (Evenson et al., 1977; Fig. 6 from Dreimanis, 1979). Dreimanis 0979) considered these deposits waterlain tills and addressed the complexity and problems associated with waterlain till. The ability to differentiate subaquatic flow till from basal melting is the center of the controversy between Evenson and others (1977) and Gibbard (1980). Although the general environment for these deposits is similar, the process of deposition is distinctly different. For clarification of terminology, waterlain till, subaquatic flow till, and subaquatic melt-out till are secondary tills (Boulton and Deynoux, 1981) or allo- t ills (Dreimanis, 1983) deposited from glacier ice rather than by glacier ice. From the foregoing discussion, the complexity of the deposits and problems with interpreting their genesis is apparent. It is suggested that Gowganda stratified diamictites are the products of two non- exclusive processes. The first is subglacial, subaquatic melt-out of debris from floating glacier ice or from icebergs. The second is resedimentation of material via sediment gravity flow, possibly by debris and grain flow. The deposits of the first process are subject to modification by the second process as well as by local currents. Arkose Lithic Sandstone Deposits of arkose and lithic sandstone typically occur with orthoconglomerate, though arkose is not restricted to this association 120 and is more prevalent in the upper-third of the formation. These sandstone types are mineralogically immature and show a certain degree of textural maturity by their lack of interstitial mud. Some sandstone units have. beds with weak stratification or grading suggesting the action of currents in transport and deposition of the sediments, whereas many beds are massive. Scour and cross-stratification in some silty, hematitic arkoses near the top of the formation are strong evidence for currents. Wright et al. (1983) found sorted sands on the shelf and out onto the continental slope and abyssal plain in the Weddell Sea. Sorting had occurred on the shelf and transport to slope and plain was by sediment gravity flow through canyons and across the shelf break in intercanyon areas and down the continental slope. The massive arkose could be due to sediment flow; however, Powell (1981) documents structureless sands as part of his Facies Association II for tidewater glaciers. He attributes them to subglacial streams with high sediment concentration resulting in underflows that transport sand away from the ice front. Arkose and lithic sandstones associated with orthoconglomerate are interpreted as fluvial deposits. Where the association is with diamictite or deposits resulting from sediment gravity flow, the sandstones represent either sediment gravity flow deposits or current derived deposits. Currents may be normal marine currents or from discharge of meltwater from glacier ice. Discharge as underflow, interflow, or overflow depends on the concentration of sediment in the meltwater (Gilbert, 1982; Powell, 1Y83). 121 Sedjmentary Breccias The sedimentary breccias constitute a small portion of the total but are fairly widespread in occurrence. The characteristics of these rocks suggest resedimentation of material subsequent to an event that disrupted the sedimentary units which were the source of the clasts. Mechanisms capable of disrupting the substrate include tectonic activity (Carlson, 1978; Heezen and Ewing, 1952), slope instability, impacting bodies, turbulence generated by storms or high-density turbidity currents. bodies:.• prompts images of an extraterrestrial event which is certainly not plausible nor intended. Rather the effect of a calving glacier in shallow water (<100 m) to form icebergs is the intended meaning. It is possible that a berg will penetrate the water column and strike the substrate if sufficient momentum is attained during free-fall throuih air (Powell, 1983). This could produce liquifaction and slumping of material. The characteristics of the sedimentary breccias perhaps eliminate melting of stagnant ice beneath stratified sediments as a mechanism. Ice-disintegration features. tend to produce collapse structures such as folds, faults, or downwarped strata (Flint, 1971; Boulton, 1972). Typically they would not be stratiform as these breccias are. No direct evidence of ice was found with these breccias. Since direct evidence of ice is lacking, any or all of the other previously proposed mechanisms may have operated. The breccias are similar to the intraclast parabreccias of Spalletta and Vai (1984), who interpreted them to be seismites. Interestingly, a few of the 122 breccias occur close to faults and suggests that tectonic activity may have persisted through time along essentially the same zone with periodic reactivation. Active tectonism was penecontemporaneous with deposition of Huronian rocks along the Murray Fault zone (Card, 1978) to the south. Further data are needed to assess this possibility in the Gowganda-Elk Lake area. _fhaot icL SJ.11mpeg These units are generally widespread but constitute a small part of the total volume of rock. Their origin could be the same as the sedimentary breccias and glacial ice may have played a role also. In stratified units, the layers are commonly folded or contorted and rarely faulted. The sedimentary units appear to have moved as coherent masses. An overriding ice sheet might deform a soft sedimentary substrate (Dreimanis, 1982). This characteristically produces a fold style in which isoclinal synclines with low-angle axial planes dip up-glacier (Boulton, 1979). If the sediments are frozen, the substrate may behave like bedrock. Where folding has been seen in these Gowganda rocks, the orient at ion is random. Although documentation is lacking for deformation by ice, it must be assumed that ice was present in the system, since these rocks commonly show evidence of glacial ice (dropstones present). Though exposures are typically limited, it is concluded that these chaotic/slumped units represent mass movement deposits in which slumping and debris flow were the dominant processes. Locally, ice may have deformed unlithified sequences during glacial ice advance. 123 DEPOSITIONAL HODKLS Introduction The previous section discussed sedimentary units of the Gowganda Formation in terms of processes or genetic implications of the sedimentary features. The dominant theme is subaqueous deposition which is likely marine in nature and deposition from and possibly by glacier ice. Therefore, models developed for glacial-marine sedimentation will be discussed and a model most compatible with the lithofacies present in the Gowganda will be proposed. Criteria for recognizing process es and environments of deposit ion were treated briefly in the last section. A review of criteria used to distinguish glacial-marine, continental glacial, and mass flow origin of diamictite is useful before evaluating models. Several workers have considered criteria which facilitate recognition of diamict it e of continental glacial and glacial-marine origin in the sedimentary record. Anderson (1983) provides a review of criteria for distinguishing diamictites of different origin. The following is a brief presentation of his review. Glacial-marine diamictite may show sorting and vertical variation in grain size. The ice-rafted component (IRD) is controlled by the position of the calving line; this component decreases sharply in volume seaward of this line with no change in size. The marine component shows greater sorting and a decrease in grain size with greater distance from the shore. Till tends to be unsorted with virtually no vertical variation in grain size and only a slight decrease in ciast size with distance 124 from the source. In mass flow deposits, sorting is a function of the source material, clast abundance is variable, and clast size may decrease away from the source. Grain · shape in glacial-marine diamictite is dependent on the level of transport in ice basal,englacial, or supraglacial). Facets on clasts are common and sand grains are also more angular than in till. Till contains more rounded clasts and grains and faceted clasts are common. Mass flow diamictite may contain faceted clasts, but this likely reflects the source material and not the transport process. Glacial-marine units are typically thick and generally quite extensive; sequence thickness may be measured in kilometers. T il 1 units are thinner though equally as extensive. Mass flow deposits are typically thinner and less extensive than either glacial-marine or continental glacial deposits. Stratigraphic and facies relationships in glacial-marine sedimentation should show a decreasing glacial and increasing marine component in an offshore direction. Interbedded sediment gravity flow deposits turbidites) and marine fossils are strong evidence for glacial-marine sedimentation. Facies transition is dependent on water depth and may be due to isostatic and eustatic sea level changes associated with glacial activity. Till deposits may be juxtaposed and interbedded with periglacial deposits and may show a transition with marine environment. Continental till is associated with glaciofluvial and glaciolacustrine deposits; geomorphic features indicative of subaerial conditions (e.g. patterned ground) may be present. Mass flow 125 deposits show transitions typically in an offshore direction (assuming subaqueous origin) and commonly occur interbedded with other sediment gravity flow deposits. - Glacial-marine diamictite is characterized by mineralogic immaturity and abundant lithic grains. The clay-size fraction shows an enrichment in quartz relative to clay minerals and a deficiency of Fe relative to Mn in comparison to continental till. Typically extra- basinal detritus is present and soft sedimentary clasts are rare or lacking. Till is also mineralogically immature and clast lithology shows a greater affinity to bedrock when compared to glacial-marine deposits. Soft sedimentary clasts are rare. Mineralogic maturity in mass flow deposits reflects the source of the material and soft sedimentary clasts are generally common. Bounding surfaces of glacial-marine sediments are typically characterized by gradational upper and lower contacts. Till has sharp lower boundaries and may overlie striated bedrock and upper surfaces may be sharp or gradational. Mass flow diamictite typically has sharp upper and lower contacts. Stratification in glacial-marine deposits may vary from massive to finely laminated. Glacial lacustrine varves are generally extensive and graded whereas glacial-marine laminites tend to be lenticular and nongraded. Tili is dominantly massive, though stratification occurs in allo-till and ablation till. Mass flow deposits are massive or have contorted bedding surfaces; weak st ratification may develop due to shearing under flow conditions or reflect a relict texture. 126 Ice-gouge features should be common for glacial-marine bedding surfaces if water depths are sufficiently shallow (<250 m). Marine tillite may show ice-gouge features on top surfaces. Mass flow deposits have no ice-gouge features. Striations and glacial surface textures on grains in glacial- marine sediment should be present and abundance depends on the level of transport in the ice. Two or more directions of striations on clasts are common. Till displays similar features. Mass flow deposits will show glacial features if they have a glacial source. Otherwise striations due to mass flow will occur on softer clasts and may be multidirectional. Striations of tectonic origin should be unidirectional. Clast fabric in glacial-marine deposits is more random than in the other two deposit types. Fabric will depend on the matrix composition and may be modified by currents. Basal till typically has a strong long-axis fabric parallel to ice flow and a secondary one transverse to flow. Mass flow deposits vary in clast fabric from random to one identical to till. A sure indicator of glacial-marine sedimentation as opposed to glacial-lacustrine is the presence of marine fossils. Unfortunately, this criterion is not applicable to the Gowganda Formation. From the foregoing summary and the data presented in this study, it is clear that evidence supporting glacial-marine and mass flow origin of diamictite is present. Evidence for till (i.e. basal or lodgement till) is at best ambiguous. Furthermore, the apparent absence of glaciofluvial deposits argues against terrestrial 127 deposition of diamictite and the paucity of traction current deposits suggests the role of meltwater in the subaqueous depositional environment was not substantial or that preservation of such features was minimal. Discussion 2£. Models .!!! Literature Models of glacial-marine sedimentation have become common in recent years as workers in the Arctic and Antarctic have developed models based on data collected from examination of unlithif ied sediments via coring, seismic profiling, side-scan sonar, underwater photography, and observation of currently active processes. Others working with lithified deposits have modelled glacial-marine systems by inferring processes responsible for the lithofacies and stratification sequences. A now classic paper by Carey and Ahmad (1961) regarding glacial- marine sedimentation focused on the deposits expected from wet-based and dry-based glaciers. Wet-based glaciers were thought to produce great thicknesses of unfossiliferous till and little sedimentation from ice rafting. Resedimentation of material should occur. Dry-based glaciers should produce little till but would contribute a significant amount of ice-rafted debris. Seaward these sediments might grade into limestones that may contain dropstones. This pioneering work has since been criticized as both incorrect and inadequate; however, it was thought-provoking, influencing and stimulating subsequent investigations in glacial-marine sequences. Reading and Walker (1966) suggested two models of glacial-marine 128 sedimentation in their study of Eocambrian diamict it es in Finnmark, Norway. They recognized two glacial advances as part of an eight-stage depositional sequence. Their model relied heavily on elements of Carey and model, namely wet- and dry-based glacial regimes. In add it ion, sedimentation and fac ies re lat ions hips were controlled by eustatic and isostatic sea level movements and basin subsidence. A recent generalized model for sedimentation in glacial environments has been put forth by Boulton and Deynoux (1981). Their glacial-marine environment is divided into proximal and distal zones. The former is by high sedimentation rates and local erosion due to strong bottom currents; the latter is a shelf environment_ in which meltwater influences the stratified water mass and restricts marine circulation. Their model addresses formation of three genetic components; IRD, fines settling out of suspension, and sediments deposited by traction currents. Because of the meltwater component, their model bears similarity to other models of Arctic glacial-marine sedimentation which are discussed below. Arctic Models Models for Arctic glaciers include aspects of ice sheets and fjords. Boulton (1972) proposed a two-fold model for ice sheets based on observations of Spitsbergen glaciers and their deposits. The thermal regime of the ice sheet is the criterion for division. The complexity of the deposits reported in other studies and attributed to repeated glacial advance may actually represent deposition from a retreating glacier with a thick englacial load. Shaw (1977) questioned the widespread applicability of Boulton's model because it was based 129 on a maritime (i.e. wet) environmental setting. Shaw described features of tills in an arid polar environment and stated greater preservation of primary structures is enhanced due to lack of meltwater and its role in modification and resedimentation of material. Fjord sedimentation has been examined by several investigators and recent work which characterizes glaciers in the Gulf of Alaska and around Baffin Island forms the basis for many of these models. Gilbert 0 982a, 1983) identified four major processes in fjord sedimentation; including flocculation of fines, sediment gravity flows, ice-rafting, and meltwater transport of detritus. Fjord circulation is dependent on wind and freshwater input and deposits reflect seasonal variation. Flocculation of fines is suggested as the mechanism responsible for · the lack or absence of varves in this glacial-marine environment. Molnia (1983) emphasized high sedimentation rates in the Gulf of Alaska. He proposed a three phase wet-based model that initially has a terrestrial glacier terminus and lacks an IRD component. Phase two has the glacier terminus grounded on the continental shelf and the third phase has the ice beyond the shelf break and has a floating ice shelf. The third phase would be similar to Antarctic models (to be discussed later) except for the meltwater component and dip direction of the shelCs slope. Osterman and Andrews (1983) have assigned proximal, distal, and ice-rafted facies to glacial-marine sediments from cores taken in Frobisher Bay. Interpretations were based on sedimentological analysis 130 and augmented by the contained fossil assemblage. Mode et al. (1983) described a Quaternary sequence with cyclic sedimentation from Baff in Island. Their seven facies represented transgressive and regressive cycles developed during extensive glaciation with isostatically induced sea level changes. Their model calls for actively calving ice fronts rather than an ice shelf. Domack (1983), looking at Pleistocene deposits on Whidbey Island, Puget Sound, Washington, emphasized the role of isostatic adjustment in producing pronounced unconformit ies in a sequence. His model also has a meltwater component. Armentrout (1983) identified four lithofacies in the Neogene Yakataga Formation in which megachannels, interpreted as tidewater fjord deposits, are well exposed and comprise a major component of his fjord facies association. Powell 1983) described five facies associations observed in Glacier Bay, Alaska. Four of them form the basis of a predictive model for sedimentation by tidewater glaciers. His facies association I includes the sequences related to rapidly retreating tidewater glaciers in deep water with an actively calving ice front. Facies close to the ice front consist of reworked subglacially derived material, supraglacial debris, and ice-push moraines. Further out, iceberg zone muds are deposited and intertongue with interbedded sands and muds. Rates of calving and meltwater discharge are seasonal and few organisms if any are present in the ice-proximal zone. Water depth is sufficient to prohibit wind-generated waves from reworking sediments on the fjord floor. facies association for slowly retreating tidewater 131 glaciers with an actively calving ice front in shallow water has as key elements ice-proximal, coarse-grained morainal banks with ice- contact lateral and central fan deltas. Subaqueous sediment gravity flows are common and bottom sediments may be affected by tidal currents or wind generated waves. Facies association III involves slowly advancing or retreating tidewater glaciers rarely calving into shallow water and the deposits are dominated by lateral streams close to the ice front which build large lateral deltas along the ice face. Sand and gravel predominate in the ice-proximal zone and intertongue with mud distally. Turbidity currents are generated on the delta foreslopes. IRD content is variable and depends on the amount of debris in the ice and degree of ice loss through surface melting rather than calving. The fourth facies association contains deposits of a turbid outwash fjord in which ice has retreated to a terrestrial position. Coarse-grained glaciofluvial deposits migrate over large outwash deposits which are built up and prograde out into the fjord. Mud dominates distally and IRD is minor; small bergs are introduced by discharge of meltwater streams out over the outwash delta. Important features of the tidewater glacier facies association are the meltwater component and tidal currents or wind-generated waves. Meltwater may occur as overflow, interflow, or underflow depending on sediment concentration. Where underflow occurs, traction current deposits are generated. Stratified and cross-bedded deposits of deltaic accumulations and sorted gravels, sands and muds of outwash 132 origin are important. Evidence of tidal currents or wind-generated waves signifies open marine conditions in relatively shallow water and argues against the presence of a floating ice shelf. Antarctic Models Generalized models of Antarctic glacial-marine sedimentation have been suggested by several workers. A fundamental difference between the Antarctic models and the Arctic models is the presence of ice shelves and the absence of meltwater plumes in Antarctica. Drewry and Cooper (1981) recognized two principal facies, laminated deposits and massive aqueous till. They discussed four controlling factors of the IRD component. Their conclusions were that ice shelves are significant and important for continental shelf sedimentation due to appreciable bottom melting prior to ice calving. In addition, outlet glaciers which have a high sediment content and calve rapidly are major contributors to the IRD content in the open ocean. Orheim and Elverhoi (1981) emphasized the significance of IRD, which is mainly deposited on the outer shelf and upper continental slope. They considered IRD variation to be inversely related to the degree of ice cover. They cautioned others from concluding that an increase in IRD seen in cores reflects glacial expansion. They emphasized that it may just signify slow sedimentation rates. The following model of Antarctic glacial-marine sedimentation is a synthesis of a great deal of research by Anderson and his coworkers. Domack et al. (1980) examined clast shapes in the sediments and concluded that material was largely transported in the basal debris zone of the ice. Kurtz and Anderson 0 97 9), Wright and Anderson 133 (1982), and Wright and others (1983) have described the presence and characteristics of subaqueous sediment gravity flows in a glacial- marine environment. This work has provided criteria for distinguishing this sediment type from other glacial-marine deposits and established the importance of sediment gravity flow in transport of material on the Antarctic continental margin. Glacial erosion has produced pronounced relief on the continental shelf. Valley glaciers along mountainous coasts have eroded deep U- shaped glacial valleys as ice moved out onto the shelf in response to sea level lowering (Anderson et al., 1983). Elsewhere grounded ice sheets erode the isostatically depressed shelf. This rugged glacial topography is conducive to mass flow processes (Wright et al., 1983). These glacial troughs have been eroded to depths of up to 3400 m. Other evidence of widespread glacial erosion in the form of truncated strata was obtained by seismic profiling (Anderson and others; 1983). The Antarctic continental shelf is characterized by rugged topography with a general slope commonly toward the continent. The shelf is very deep owing to isostatic depression. Anderson and others (1983) state that after the ice sheet melts and isostatic rebound is complete, much of the shelf would still be at depths greater than 500 m. This suggests the glacial-marine sequence will be succeeded by marine sediments. Whereas sediment gravity flows are common on the continental slope and submarine fans at the base of slopes (Anderson et al., 1979), relief on the shelf is also sufficient to generate mass-flow deposits. Caution in interpretation 134 is needed since such deposits may occur on the shelf and may not represent deep-water sedimentation. Antarctic glacial-marine sediments of the continental shelf have been separated into three groups (Anderson et al., 1980). The first group consists of transitional glacial-marine sediments which are nearly identical to lodgement till and are considered sub-ice shelf deposits. A second group represent glacial-marine sediments from shallow portions of the shelf and shelf break - upper slope. These sediments are composed primarily of unsorted to poorly sorted sand. and gravel with a winnowed silt and clay fraction. Because some silt and clay has been winnowed, these deposits have been called residual glacial-marine sediments. The third group of glacial-marine sediments are called compound glacial-marine sediments. This group is presently the most widespread and is better sorted than the two previous groups. These sediments consist of mud and a minor IRD component. The biogenic component of the mud attests t ·o restricted terrigenous input and emphasizes the lack of a meltwat er component in the system. These three sediment types and their distribution depend on the specific sedimentary (glacial-marine) environment; three environments were recognized by Anderson and others (1979). These are (1) areas where ice shelves (large and small) and ice tongues extend onto the continental shelf, · (2) mountainous coasts where valley glaciers flow into the ocean, and (3) coasts with ice walls. Ice shelf environments and their associated sediments are affected by the thermal regime of the ice (Drewry and Cooper, 1981). 135 Large shelves would be expected to lose most of their debris by basal melting before ice calving develops, whereas small ice .shelves, due to basal freezing (Anderson et al., 1983) and ice tongues with rapid ice flow, will calve icebergs that still have a basal debris-rich zone. This behavior is responsible for the difference in distribution of IRD for this setting. Valley glaciers descend along the mountainous coast and directly deposit their load into the sea. Unlike ice sheets, debris may be entrained from valley walls or dumped on the glacier surface; however, the thermal regime and position of the equilibrium line in the majority of these glaciers inhibits formation of medial moraines (Anderson et al., 1983). In addition, the lack of englacial and supraglacial debris layers is due to little surface ablation; calving is the most significant ablation process. Thus, the polar regime is responsible for the absence of associated meltwater deposits in contrast to the valley glaciers in the Gulf of Alaska. Ice walls develop where glacial flow is so slow that glaciers grounded in shallow water are subjected to wave erosion. Finer-grained sediments would tend to be carried out into the ocean and the coarse fraction would be deposited in a narrow zone just out from the ice wall. The marine environment and its influence on sedimentation is largely controlled by shelf depth and configuration (Anderson and others, 1983). The great depth of the Antarctic shelf minimizes the effect of tides and wind-generated waves. Currents are presently more 136 active at the shelf break - upper slope than (Anderson et al., 1979), winnowing glacial-mar_ine sediments and transporting material down the slope. These sediments are interbedded with turbidites and debris flow deposits of the lower slope and rise (Wright and Anderson, 1982). In summary, this polar glacial-marine model emphasizes the importance of the specific setting, shelf configuration, water depth, and climate in glacial-marine sedimentation and facies distribution. Whereas the thermal regime role emphasized in other models can explain sediment supply, it does not effectively explain facies relationships. 9.£. Sedimentation .it! fu G2wgand$=lli .bili Regi9,!.1 Lindsey_'s (196 9) pa leogeograp hie reconstruct ion of Gowganda sedimentation suggested that glacial-marine conditions prevailed in the southern part of the outcrop area, while terrestrial glacial conditions existed in the northern part of the outcrop area, the latter including the present study area (Fig 10.1). The results of the present study, however, suggest that the glaciogenic lithofacies present in the Gowganda - Elk Lake area are indicative of glacial- marine sedimentation rather than continental conditions. After consideration of the models discussed in the previous section, aspects of the Antarctic model seem to fit best the observations in the present study area. The Antarctic model is appropriate for several reasons. The minimal presence of tract ion current deposits with the g lac iogenic facies argues against a significant meltwater component, a feature which characterizes temperate and Arctic glaciers. Lack of meltwater 137 Pafuoocuuont T1end I Scalu in milns ,J .. ... ! Oat Rivt.•r Fo1111 .11ion. 4 0 4 8 l _a 1 1 I I I ..(: ...--\ .Go11/011 LaAe Form.Jlio11. _,..-- 1 Lmrai11 Formation . I .1:.- \- Gnwg;uu/;i Fo1mJtio11. \ \ .J.Cl' A·l1111u.1ui F0tmt11ion. / North.,n limil of pr•· Gowgancla / llu1ot1iiln. \ MJri11u ·hcJh watc1 IOJcic1 / Lah I fl) ltiJ11Jitio11 in the Gowg.Jmld / Formatio11 ...... " -f-:•dy I. ,,/' r •Jiii ' J ,,,_,,,('" "-...... _ \ ilr9i/t,;.. "'- '-. \ ...... "·:::: I w co /' \ / \\ L•u11d1i• ! I\ / / \ t ""' 0 ' Figure 10,1 Lindsey's (1969) paleogeograpl1ic reconstruction of supposed marine-fresh water transition in the Gowganda Formation. Tl1e current study area lies to the north of the region depicted here and according to Lindsey, should contain lithofacies indicative of terrestrial glacial conditions (from Card, 1978). in Antarctica has been stressed by Shaw (1977) and Anderson et al., (1983). This is probably the most convincing e•1idence for proposing t he Ant a r ·c t i c m o d e 1. T h e 1 a ck o f em erg en t f a c i es or ma j or unconformities as a result of isostatic rebound suggest a deep or actively subsiding basin existed during Gowganda sedimentation. The fairly rapid facies changes, both horizontally and laterally, represent not only varied intensity of sedimentation and changing environmental conditions, but probably also reflect a depositional basin that may have had significant bottom relief. Such topography would be conducive to resedimentation of debris, though gentle slopes would not necessarily eliminate these processes (Rodine and Johnson, 197 6). The presence of an ice shelf or possibly just deeper water is suggested by the weakly stratified diamictites and the lack of evidence for tidal currents or wind generated waves which would modify the bottom sediments. The ice shelf would create a protective environment and some sorting of material would occur during settling through the water column. Some winnowing of the deposits by currents may have occurred. Proximal deposits consist of massive and weakly stratified diamict ite. Distal deposits have int erbedded, massive and laminated siltstone and sandstone with dropstones. Strata exposed around the town of Gowganda record both ice-proximal and intermediate to distal deposits and therefore reflect changing positions of the ice margin with time (Fig. i0.2). Strata 10 km to the west around the shores of 13 9 Firth Lake indicate sedimentation much further from an ice margin and probably in deeper water (Fig. 10.3). The !RD component is minimal (< 1%) and Boulton and Deynoux (1981) think that such sediments should not be considered glacial-marine. Although !RD input was minimal, its presence indicates that icebergs or floating ice was present. Indicators which suggest relatively deep water are interbedded graywackes, argillites, siltstones, diamictites, and orthoconglomerates. Structures present support the role of subaqueous sedimentary gravity flow p'I'-Ocesses in the deposition of these sediments. Such an association is characteristic of continental slope deposits and submarine fans developed at the base of the slope or at the mouths of submarine canyon systems incised into the continental margin, but are not exclusive to such environments. Indicators cf relatively shallow water are also present. A change from deeper water to more shallow water and possibly emergence is suggested by sediments in the upper-third of the formation where glaciogenic features are absent. Sediments in the Upper Coleman Member are dominated by silty sandstone that appears to coarsen upward. Although such sequences are characteristic of prograding deltaic sedimentation, more data are needed to support such a conclusion here. Young, (1981), however, has suggested deltaic sedimentation for upper members of the Gowganda Formation in the Espanola - Whitefish Falls area to the south. In addition, orthoconglomerate and sandstone at the top of the formation are overlain by shallow water, hematitic siltstone and 140 GENERALiZED SECTION ICE MARGIN NICOL TWP. -..,Lonestones Intermediate M.g. ·e.g. sandstone (graywacke) Proximal Oiamictite (crudely stratified) lntermedia te M.g. • e.g. sandstone (graywacke) Olamictlte Cmauive and crudely stratified) Proximal M.g. - e.g. sandstone Intermediate Proximal Dlamictlte M.g. - e.g. sandstone (arkose) Meltwater ? Polymlctic orthoconglomera le Siitstone and f.g. sandstone Intermediate ;::.-w: .... M.g. • f.g. sandstone (graywacke) Dlamictlte (massive to crudely stratified) Proximal Laminated argilllte and slltstone with sandy interbeds Distal Olamictlte (massive to crudely stratified) Proximal Slumped and chaotic unit Figure 10.2 Generalized section from Nicol Twp. with an interpreta- tion of possible position of the ice margin during sedimentation. 141 GENERALIZED SECTION ICE MARGIN MILNER TWP. Proximal M.g. - f.g. sandarone (graywacke) with lonHtonH Intermediate - M.g. - l.g. sandarone :;:•.-.:. ·:;. ;.:.: ·_;,.\ ; : "" Siltstone and f.g. sandstone (graywacke) Laminated argilllte and siltstone with sandy interbeds Distal Laminated argllllte Laminated argilllte and siltstone with sandy interbeds Figure 10.3 Generalized section from Milner Twp. with an interpreta- tion of possible position of the ice margin during sedimentation. 142 z c:< c: 0 ...J UPPER COLEMAN MEMBER HEMATITIC SILTY/SANDY UNIT UPPER SANDY UNIT NO GLACIAL ICE LOWER SANDY UNIT LOWER COLEMAN MEMBER UPPER PELITIC UNIT GLACIAL ICE UPPER DI AMI CT ITE ANO SANO Y UNIT MIDDLE PELITIC UNI'?' NO GLACIAL ICE LOWER SANDY UNIT LOWER DIAMICTITE UNIT • GLACIAL ICE • LOWER PELITIC UNIT BASAL ORTHOCOHGLOMERATE Figure 10.4 Generalized composite stratigraphic ·coiumn ·of the· Go'?ganda Formation. Dots to the right denote dropstones. 143 1-·e"'- ' \ '--..__ (t t-..__ ) .- '-· .. 1 • ...... 1 ..-·- ... .,__ .,;V< .,..,\ Str._;,(;u\ !':xv"\ n.-0 C, ,\\ , , / \ \ /11• ------, ± / \ / ;!._ ..1,e"\ \\oUJS , / \ (i , ,' ,(;"' ,/ / ' ( ( / ( / I-' ')' r Sholf bo Deposition§J Mistory Because the Gowganda Formation in this area is poorly exposed, a great deal of detailed field work and access to drill core will be needed to reconstruct the basin, patterns of sedimentation, and changes in environment through time. Therefore, details of glacial ice advance, retreat or minor ice-margin fluctuations cannot be resolved at this time. The following account of the depositional history is therefore general and subject to refinement. Initial sedimentation involved fluvial processes which deposited moderately well-sorted orthoconglomerate and arkose. Sedimentation was structurally controlled and occurred in paleovalleys which were probably largely tectonic in origin with perhaps as much as 1000 m of relief. The presence of a regolith with intermediate CIA values beneath these deposits suggests a moderate climate preceeded deterioration of the climate which lead to glacial conditions. Clear evidence of periglacial environments of any areal extent is lacking. Inundation by marine waters may predate the arrival of glacial ice. Basal sequences in the western part of the study area contain 145 either marine or glacial-marine deposits. Interbedded graywacke sandstone, siltstone, and argillite were deposited under widespread marine conditions. Intermittent tectonism in conjunction with active basin subsidence was responsible for the accumulation of a great thickness of sediments and their ultimate preservation. Ice advance into the area, due to growth of the ice sheet and/ or eustatic sea level lowering, probably isostatically depressed the basin further. Glaciogenic sediments were deposited from floating icebergs as dropstone sequences in more distal environments and as massive and stratified diamictite in more proximal zones. The latter are probablly sub-ice deposits and may have been deposited beneath a floating ice shelf. Topographic highs in the basin would help stabilize an ice shelf which in turn might buttress the ice sheet (Thomas, 1979). Migration of the grounding line in response to changes (i.e. sea level, ice thickness, changes in the ice shelf) is dependent on the slope of the sea bed. Extremes in grounding line position are likely where the sea bed slopes shoreward. Res edimentat ion of debris occurred, probably due to slope instability instigated by tectonic disturbance, rugged bottom topography, or high sedimentation rates. Evidence for diamictite directly deposited by glacial ice (i.e. ortho- till) is equivocal. Recognition of such a til 1 facies would help to reconstruct positions where the ice was grounded. Major ice advance into the basin occurred twice. This conclusion is supported by the presence of glaciogenic deposits at two levels in the column separated by marine sediments. Insufficient data 146 are available to provide greater detail of the duration of the glacial or interglacial stages. Fining-upward and coarsening-upward sequences reflect changing conditions within the basin as increases and decreases in both energy and sediment supply occurred. The distribution of rock types, in part, is the result of advances and retreat of glacial ice from the north. Amelioration of the climate is indicated by the lack of glaciogenic features in the upper part of the formation, referred to in this study as the Upper Coleman Member. Retreat of the ice and collapse of the ice sheet may have been rapid. Whether the retreat of ice was gradual or rapid, the causes of this behavior may have been induced by a milder climate or a function of several interrelated changes (Denton and Hughes, 1981 ). Collapse of the ice sheet would be expected to cause a eustatic rise in sea level; isostatic rebound of glacially depressed areas may offset or exceed the rise in sea level due to melting ice and result in emergence of land. This can be complicated further by isostatic loading produced by transgressing marine waters. The Gowganda sequence shows evidence of continued submergence until possibly late Gowganda time; the deposits do show a transition from deeper water to shallower water sedimentation. It is not clear whether water depth in the basin was controlled more by isostatic and eustatic sea level adjustments related to glaciation or changes in sedimentation rates and basin subsidence. The sediments of this shoaling upward sequence are predominantly silt and s·and and in a gross sense the sequence coarsens 147 upward. Graywacke sandstone diminishes in abundance whereas arkose increases. A milder climate would generate meltwater, producing significant discharge which could transport and eventually deposit large of detritus. The ice at this point in time would no longer be a marine ice sheet but an ice sheet located far enough from the basin such that no direct glaciogenic features are present in the marine sequence. Gowganda rocks at the top of the formation represent shallow water; they might include some subaereal deposits. Rock types consist of well-sorted orthoconglomerate, arkose, interbedded hematitic silt and sand, and thin-bedded laminated silty argillites. It is conceivable that some of these are glaciofluvial and glaciolacustrine deposits; however, no evidence of ice exists with these deposits to further substantiate this possibility. The Gowganda Formation is conformable with the Lorrain over a stratigraphic interval of 15-30 m. As previously mentioned, a fluvial-deltaic origin is suggested for the arkose and thin orthoconglomerate in the basal portion of the Lorrain Formation in the study area. 148 TECTONIC SETTING The Gowganda Formation is the lowest formation of the Cobalt Group which is the youngest group of the Huronian Supergroup. Interpretations of the Huronian.'s tectonic setting was originally set forth in geosynclinal terminology and more recently using plate tectonic concepts. Young (1971) considered a marginal paraliageosyncline in which subsidence was tectonically controlled whereas Dietz and Holden (1966) suggested the Huronian was the "miogeocline" portion of a geosynclinal pair. Card (1978) noted that the Huronian is bounded by Archean rocks to the north and south and suggested the depositional basin was a graben-like trough. Sims and others (1981) discussed the evolution of the Huronian basin and also believed the occurrence of Archean basement surrounding the basin was evidence for an intracratonic setting for these supracrustal rocks. Plate tectonic concepts have been applied to the Proterozoic rocks of the Great Lakes region with efforts concentrating more on the Lake Superior region. This tendency reflects the problems of correlating the Huronian Supergroup with other early Proterozoic successions in the Lake Superior region. The various interpretations have been summarized by Young (1983) and these models include northward-dipping and southward-dipping subducting plates. Young (1983) suggested the Huronian sequence was deposited in two stages; lower Huronian format ions were deposited during a graben st age and upper Huronian formations during a regional downwarping stage. He 149 interpreted this in terms of an aulacogen which opened into ari ocean to the east. Difficulties arise in -interpreting the Huronian in strict plate tectonic terms. The Wilson Cycle (Dewey and Burke, 1974) of rifting and formation of oceanic crust with subsequent closure and orogeny does not seem to have a clear counterpart in the Huronian s.equence. However, dogmatic adherence to such models encourages their failure to explain the rock record. For instance, one would hope to find an ophiolite suite, possibly in the northwest part of the Grenville province or near the Grenville Front. Does its absence negate the development of oceanic crust from rifting during the early Proterozoic or is it missing because it was not preserved following the Grenville event and subsequent uplift and erosion? As more detailed mapping is coupled with geochemical and geophysical studies, an appropriate model with greater appeal may evolve. A simplified approach to the question of tectonic setting is offered here. The Huronian Supergroup perhaps represents sedimentation, and to a lesser extent igneous activity, in the context of a passive continental margin and may be likened to the Atlantic type. Initial rifting of the basin resulted in extrusion of fissure-type volcanics which occur at the base of the Huronian sequence along the north shore of Lake Huron. To the north in the study area, attenuation of the crust resulted in a segmented Archean basement creating basins and platforms. Faulting apparently did not extend deep enough here to tap a magma source. Subsidence of the basin was tectonically controlled 150 and the cyclic sedimentation of the three largely regressive sequences may have been due to fluctuations in volcanic activity further to the southeast (in the Grenville province?) which may have caused sea-level fluctuations. Sea-level changes were also the result of isostatic and eustatic responses related to glaciation. Clastic sequences dominate the Huronian stratigraphy, which on the whole are relatively coarse-grained arenaceous sequences. It has been suggested that some of the metasedimentary rocks in the northwest part of the Grenville province are the distal equivalents of the Huronian rocks; some paleocurrents though suggest northerly transport (Sims and others, 1981). This suggests that 1) some of the rocks are not distal equivalents; and 2) they either represent the detrital input from the other side of an intracratonic basin (Sims et al., 1981) or from a continental land mass on the opposing side of a spreading ridge. The Huronian basin was mildly tectonically active throughout its life (Card, 1978) and the sedimentary pile is a thick wedge with facies indicative of shelf, slope, and possibly base-of- slope environments at the beginning of a regressive cycle. The shoaling upward sequences contain shelf and deltaic sedimentation and the cycles typically culminate in fluvial sedimentation; however, record of a transgression during sedimentation of the two youngest Huronian formations is an exception to this. The Huronian thickens toward the south, though this is due in part to the presence of a more complete section. Huronian sedimentation culminated in deposition of the Bar R.iver Formation, the youngest preserved formation in the sequence. The 151 Huronian was slightly deformed prior to the intrusion of the Nipissing Diabase (Card, 1978). It is possible that the extensive intrusion of mafic dikes and sills represents a renewed cycle of crustal attenuation as a prelude to attempted rifting of the craton. Lovell . and Caine 0970) suggested that the major northwest-trending faults around the Timiskaming-Cobalt-Kirkland Lake area define an ancient rift valley system which has possibly been reactivated through time. They further suggest that these faults penetrated deep enough to serve as feeders for some of the Nipissing intrusions. The presence of kimberlit e and alkaline intrusions were cited as support for their rift environment proposal. The tectonic setting for the Gowganda Formation, placed in the context of Huronian sedimentation, may be summarized as follows. Tectonism in early Huronian time produced a segmented craton in the study area whereas to the south, rifting with volcanism was initiated and possibly further southeast toward where the Grenville province is today, rifting may have succeeded in producing oceanic crust. Fluvial elastics are interbedded with the volcanics and were succeeded by marine elastics and minor carbonate. At this stage, sedimentation followed a cyclic pattern controlled by tectonism, beginning with normal faulting followed by downwarping with initial deposition of flysch-like deposits. As the basin filled, deposition was largely in a shelf environment and towards the end of a cycle deposition was in shallower water and finally in a fluvial environment. Igneous activity which emplaced the Nipissing Diabase may have been part of a renewed 152 ,. rifting event. The gross character of the Huronian Supergroup, in which the Gowganda Formation occurs, is similar to the sedimentary-volcanic accumulations which typify the Atlantic-type passive continental margin. As further data are obtained, a more precise model of the tectonic setting may be proposed. 153 SUKKARY AND CONCLUSIONS 1) The Gowganda Formation in the Gowganda-Elk Lake area consists of subhorizont·a1 sedimentary rocks at least 1600 m thick. It contains a diverse assemblage of rock types, including graywacke, diamictite, siltstone, argillite, orthoconglomerate, laminated fine-grained rocks with dropstones, arkose, lithic sandstone, and sedimentary breccia. The age of the Gowganda Formation is approximately 2.3 b.y. 2) Strata generally dip to the east or west at less than 20° with local variation; steepening of dip and minor folding occurs at fault margins. Broad synclines and anticlines may be due to draping of sediments over the basement or due to faulting at depth. This region was little affected by the tectono-thermal Penokean event. The regional metamorphic grade is subgreenschist to greenschist. 3) Detrital quartz, plagioclase, and potassium feldspar are the dominant framework minerals and are abundant in the matrix but subordinate to chlorite. Rock fragments are predominantly felsic to intermediate plutonic followed by felsic to mafic volcanic, metasedimentary, and sedimentary clasts. 4) Pebble counts of both diamictite and orthoconglomerate show a similar distribution of rock types noted during microscopic examination of thin sections. 5) Provenance of the detritus was largely from a granite-greenstone terrane located within and to the north of the depositional basin and some material may have been derived from a gneissic terrane farther to the no rt 1:1. 154 '· 6) Paleocurrents suggest a generally south-dipping paleoslope and supports derivation of debris from the north transported by southerly- flowing currents. 7) Calculation of the chemical index of alteration (CIA) suggests that a moderate climate promoted some chemical weathering of the Archean basement prior to Gowganda sedimentation. CIA values from the matrices of diamictites and argillites from the Lower Coleman Member average 54; argillite from the Upper Coleman average 65. This suggests climatic conditions at first inhibited chemical weathering and later were more conducive. This is interpreted as a change from a cold climate to a moderate or temperate climate. Gowganda rocks are Na-rich and this probably reflects the source area. Diamictites are depleted in Fe Mn relative to crustal abundances suggesting deposition in a marine environment. 8) The Archean-Proterozoic unconformity varies from one locale to another. Locally, a regolith may be preserved and elsewhere the basement rocks have been eroded to a smooth undulating surf ace. In some locations, the overlying Gowganda sedimentary rocks record deposition early in Gowganda time whereas another location has deposits of late Gowganda age; at least two-thirds of the sedimentary record is missing there. This suggests that the basin had a rugged topography with possibly 1000 m or more of relief and that the Archean-Proterozoic unconformity does not represent either the same time everywhere or similar environments. 9) Processes for transport and deposition of material included 155 sediment gravity flow for some of the diamictites and graywacke, glacier ice for dropstone sequences and some diamictites, fluvial transport for some arkose and orthoconglomerate, and some deposit ion of detritus by marine currents. 10) The Gowganda Formation in the Gowganda - Elk Lake area is divided into the Lower Coleman Member and the Upper Coleman Member on the bas is of glaciogenic features present in the former and absent in the latter. The Lower Coleman records widespread glacial-marine conditions; this includes two major glacial episodes separated by normal marine conditions. Evidence supporting glacial-marine conditions are a) presence of dropstones; b) finely-graded and laminated stratification; c) great thickness and areal extent; d) the association of diamictites with resedimented deposits. The Upper Coleman is a regressive marine sequence overlain conformab ly by the Lorrain Formation. 11) The best model of glacial-marine sedimentation for the Lower Coleman Member would include an ice shelf and would be similar to the polar regime present today in Antarctica. The environment involves a continental shelf characterized by deep water, rugged bottom topography, icebergs, and an ice shelf. In contrast to most Arctic models, meltwater is minimal. Proximal deposits consist of massive and weakly stratified diamictite. Intermediate to distal deposits have interbedded, massive, graded, and laminated siltstone and sandstone wit-h dropstones. Thin, massive diamictit es in this zone are likely the result of sediment gravity flow. Resedimented deposits, the products of mass flow processes, are common. 156 12) The tectonic setting of the Gowganda Formation, in the context of the Huronian Supergroup, may be similar to an Atlantic-type passive continental margin. 157 REFERENCES Anderson, J.B., 1983, Ancient glacial-marine deposits: Their spatial and temporal distribution: .iD Molnia, B.F.(Ed.), Glacial-marine sedimentation, New York, Plenum Press, p. 3-92. Anderson, J.B., Kurtz,D.D., and Weaver, F.M., 1979, Sedimentation on the Antarctic continental slope: in Doyle, L.J., and Pilkey, O.H. (Eds.), Geology of continental s"l"opes, Soc. Econ. Paleont. and Mineral. Spec. Publ. 27, p. 265-283. Anderson, J.B., Kurtz, D.D., Domack, E.W., Balshaw, K.M., 1980, Glacial and glacial marine sediments of the Antarctic continental shelf: J. Geol., v. 88, p. 399-414. 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Lake Superior Geol., p. 42-43. 170 APPENDIX A MODAL ANALYSES RH- RH- illi- RH- PH- ?H- ·rtH- RH- RH- RH- RH- Elli- 82- 81- 81- 81- 81- 81- 81- 81- 81- 81- 82- 82- 81- Mineral or Rock Component: 210 226 204 63A 54 25 221 160 93 194 214 216 225 Qua.ta: Cormx:n, nonunciulose 22 30 4 24 70 14 131 95 44 57 46 86 ill Comron, unciulose 91 52 11 llO 152 64 266 350 101 173 131 194 125 Polycrystalline 35 ll l3 36 l4 31 24 5 o 0 a 11 0 Chen: 3 o 0 l 2 2 o 0 l 0 2 0 0 Total QlarC 151 93 28 171 238 ill 421 450 146 230 179 291 236 Feldspar: !?laaioclase 44 58 3 47 55 31 29 74 48 67 63 61 ll9 Orthoclase 43 21 5 65 39 33 23 42 17 95 10 66 60 Hic::ocline 9 0 0 4 6 9 0 2 0 0 0 9 4 Perwite 5 10 0 9 11 15 38 0 0 0 l 15 2 Total Feldspar 101 89 a 125 ill 88 90 us 65 162 74 151 185 Fragments: Volcanic:Felsic 37 39 33 35 31 14 0 0 0 0 0 l 0 Felsic-InterITediace 29 38 30 65 26 14 2 0 0 0 l 1 0 Intemeciiate-Matic 9 10 7 5 53 19 0 0 0 0 0 l 2 Matic l 2 18 3 9 30 0 0 0 0 0 0 9 !?luconic:Plagioclase- Met:a :Argillite-Slace 1 0 0 0 0 12 0 0 0 0 0 0 Q Sch isl: 4 3 35 l 2 3 0 0 0 0 0 0 0 CUartzite 15 6 20 0 0 27 0 0 0 0 0 0 0 Greenstc:ne 4 3 0 0 0 11 0 0 0 0 0 0 0 Sedimenc :Hudscone-Sil !:st.one 0 0 0 l 0 0 0 0 0 0 0 0 0 Sandstone 16 20 0 9 2 67 0 0 0 0 0 0 0 Other Rock Fragmenc 0 l 0 3 2 8 0 0 0 0 0 0 0 Total Rode Fragments 291 340 496 271 166 367 29 0 4 l 2 29 29 t·liscellanecus Grains: _ Huscovice l 0 0 l 0 0 0 6 0 0 36 0 8 Biotice 0 0 0 0 0 0 0 10 0 0 0 2 0 Chlorice 37 15 26 12 9 20 46 13 4 0 21 14 25 2 29 5 14 9 3 4 l 0 2 5 10 41 Zircon 0 0 0 0 0 0 0 l l 0 0 2 0 Other 0 l 2 0 36 0 0 l l l 0 2 0 Total M:i.scellaneous 40 45 33 27 54 23 50 32 6 3 62 30 74 Cerr.enc-i-lacr u: Cerrenc:Quan:z 0 0 0 0 0 0 10 0 0 0 0 3 0 Carbonace 15 24 4 0 0 71 0 0 0 0 0 0 0 Clay 0 0 0 0 0 0 0 0 0 0 0 0 a :·la tr ix: Clav 0 5 24 5 20 0 l) 0 240 127 199 71 50 (;:.lari:z-?elespar 2 4 7 l 11 4 0 0 139 /7 84 25 26 Total 17 33 35 6 31 ll 10 0 379 204 283 99 76 'rorAL 600 600 600 600 600 600 i600 600 600 600 600 600 600 Raw data from point counted samples Al MODAL ANALYSES PJi- i'..G- RH- RH- Rh- ?.H- p.fj- 0uz..:-c;; : Cor:r.on, nonunuulcse 68 76 38 43 72 47 99 71 G<'i l!'.c 88 92 76 Cor;rron, unaulose 109 153 127 155 74 114 86 144 145 144 195 280 152 Polycrystalline 0 14 7 0 21 4 0 0 . 12 6 32 1 8 Cnert 7 1 0 0 6 1-_, 0 0 0 0 6 0 3 Total CUartz 184 244 172 198 173 182 185 215 221 196 321 373 239 Felc:lspu.r: Plagioclase 84 104 100 78 78 86 85 56 68 48 62 131 58 Or:.hoclase 38 48 28 21 45 79 46 38 48 31 114 81 164 i·licrocline 0 13 0 3 8 8 3 2 16 3 22 0 30 Pertni;:e 0 9 3 0 3 0 1 0 13 0 28 0 6 Total Feldspar 122 174 131 102 134 173 135 96 145 82 206 202 258 Rock Fragrrents : Volcanic:Fel.sic l 0 0 0 23 2 13 0 0 5 0 0 0 Felsic-Inter;;ediate 15 l 5 0 26 5 4 4 9 l 0 0 0 Interrreciiate-i•lafic l 13 33 l 12 0 0 3 5 0 0 0 0 lia±ic 0 2 0 0 20 0 0 0 6 0 0 0 0 Plutonic:Plagioclase-Quartz 37 26 20 4 16 9 3 4 21 7 9 0 5 K-reldspar-Quartz 14 21 5 6 12 6 6 15 25 4 18 0 32 Haric 0 0 0 0 0 0 0 0 0 0 0 0 0 :.l\.rgillite-Slate 0 0 0 0 0 0 0 0 0 0 0 0 0 Schist 0 0 0 0 5 0 0 0 0 0 0 0 0 Q'..iartzite 0 0 0 0 3 0 0 0 0 0 0 0 0 Greenst:one 0 0 0 0 0 0 0 0 0 0 0 0 0 Sec:lirrent:Hudstone-Siltst:one 0 0 0 0 0 0 0 3 2 4 0 0 0 Sandstone 0 0 0 0 3 0 0 2 0 0 0 0 0 Other Rock Fragrrent 0 c 0 0 0 0 0 5 0 13 0 0 0 '!'otal Rock Fragaents 68 63 33 11 123 22 26 36 68 34 27 0 37 Hiscellaneous Grains: Muscovite 0 0 0 4 0 0 l 3 0 l 0 0 4 oiotite 0 0 0 0 0 0 0 0 l 2 0 0 0 Chlorite 27 16 29 19 0 0 5 3 10 4 9 8 2 Opaques l 3 6 10 1 0 2 0 14 13 2 1 0 Zircon 0 0 0 l 0 0 0 l 0 0 0 l l Other 5 3 5 3 10 6 4 13 7 6 4 5 0 Total Miscel l aneous 33 22 40 37 11 6 12 20 32 26 15 15 7 Cerre.'1t:Quartz 0 ·o 0 0 0 0 0 0 0 0 0 0 0 Carbonate 0 0 0 0 1 0 0 0 0 0 31 0 59 Clay 0 0 0 0 0 0 0 0 0 0 0 0 0 Hatrix:Clay 109 65 157 186 158 159 158 123 100 199 0 0 0 Quartz-Feldspar 84 32 67 66 0 58 84 105 34 63 0 0 0 Total Cel!Ent-Ma.trix 193 97 224 252 159 217 242 233 134 262 31 0 59 'lUrAL 600 600 600 600 600 600 600 600 600 600 600 600 600 Raw data from point-counted samples A2 MODAL ANALYSES SAMPLE Rli- r:h- P.H- Pl!- RH- RH- F:!-i- Rb- NJ- Pli- RH- 81- 81- 81- 81- 81- 81- 81- 81- 82- 82- 82- Mineral or Rock Comr,;onem: 165 171 217 218 220 222 223 224A 208 218 220 Quarcz: Cor.rnon, nonunaulose 38 62 50 53 59 84 811 110 97 32 49 Conmen, unaulose 191 228 109 110 162 249 225 227 170 158 200 Polycrystalline 9 2 48 42 23 25 34 34 442 44 32 Chert. 3 0 41 39 16 1 0 0 1 4 8 Total CUartz 241 292 248 244 260 359 340 371 310 238 289 Feldspar: Placrioclase 32 47 114 111 188 53 74 71 127 69 46 Orthoclase 223 188 51 52 50 14 41 15 38 80 150 l·iicrccline 25 6 2 3 5 1 0 0 2 25 35 Pertnite 7 5 12 25 32 88 79 60 24 28 20 Total Feldspar 287 236 179 191 275 156 192 146 191 202 251 Rock Fragrrents: Volcanic:Felsic 0 0 18 17 0 0 0 0 0 0 0 Felsic-Interrrediate 0 0 26 27 5 0 0 0 0 6 7 Interirediate-Maiic 0 0 20 12 0 0 0 0 0 12 7 l·iafic 0 0 0 0 0 0 0 0 0 10 0 Plutonic:Plagioclase-Q.larcz 0 0 30 22 34 17 17 25 17 25 7 K-feldspar-Quartz 20 5 23 17 12 24 15 13 8 45 25 Hafic 0 0 0 0 0 0 0 0 0 0 0 Meta 0 0 0 0 0 0 0 0 0 0 0 Schist 0 0 0 0 0 0 0 0 0 0 3 Quaruite 0 0 0 0 0 0 0 0 0 0 0 Greenstone 0 0 0 0 0 0 0 0 0 0 0 Seair:ient:Mudscone-Siltscone 0 0 0 0 0 0 0 0 0 0 0 Sandstone 0 p 0 0 0 0 0 0 0 0 0 Other Rock Fragmmt 0 0 0 0 0 0 0 0 0 0 0 Total Rock Fragirents 20 5 ll7 95 51 41 32 38 25 98 49 Miscellaneous Grains: Viuscovite 6 0 0 0 0 0 0 0 1 2 0 Biotite 0 0 0 0 0 0 0 0 0 0 0 Chlorite 0 3 18 15 1 13 0 12 3 18 10 Ooaaues 3 14 6 11 0 0 3 4 0 2 0 zircon 0 0 2 0 1 0 0 0 0 0 0 Other 0 5 2 1 0 0 0 0 0 1 0 Total Miscel J aneous 9 22 28 27 2 13 3 16 4 23 10 Cerrent-Hatrix: Cerrent:Quartz 0 0 0 0 0 12 11 22 23 0 0 carbonate 31 0 28 43 12 19 0 11 40 0 1 Clay 12 45 0 0 0 0 22 6 7 19 0 f.latrix:Clay 0 0 0 0 0 0 0 0 0 20 0 (!Jartz-Felespar 0 0 0 0 0 0 0 0 0 0 0 Total Cellent-Matri.x 43 45 28 43 12 31 33 29 70 39 1 'lU.rAL 600 600 600 600 600 600 600 600 600 600 600 Raw data from point-counted samples. A3 APPENDIX B GmCllP.MICAL J\MLYSIS SAMPLE I SlOi Ti°'l Al20J FeOr CaO Na20 K20 l'1() P2CJs s lDI Rll-81-24 65.70 0.49 11.90 11.90 0.51 5.62 0.97 1.32 0.18 0.07 0.07 1.05 RH-81-70 65.80 0.40 16.80 5.31 2.89 5.20 0.94 0.10 0.12 ND 0.59 IUl-81-71 65.10 0.49 14.30 6.41 0.70 3.31 7.75 0.42 0.11 0.09 0.05 0.71 Rll-81-73 65.20 0.35 15.30 4.32 1.12 3.98 6.91 0.74 0.11 0.12 0.03 1.48 IUJ- 81-74 60.00 0.53 16.60 7.60 1.03 4.19 3.35 1.12 0.11 0.12 0.13 3.85 RH-81-168 65.50 0.26 15.30 3.25 2.01 2.77 6. 57 2.05 0.12 0.13 0.02 1.36 rm-01-177 65.40 0.53 12.40 7.85 3.99 4.44 0.69 0.26 0.19 0.11 0.01 3.88 Rll-01-178 65.00 0.49 15.40 5.31 2.32 4.03 4.87 0.59 0.13 0.17 ND 1.59 IUl-81-179 60. 70 0.67 13.80 7.80 1.14 6.12 10.20 0.38 0.14 0.07 0.05 0.17 Rll-01-201 55.50 0.85 14.10 9.81 5.02 6.17 5.06 0.24 0.16 0.15 0.13 3.09 IUJ- 81-227 65.50 0.42 14.50 5.02 0.76 4.03 5.29 1. 73 0.09 0.06 0.05 1.56 RIJ-81-236 60.20 0.60 16.10 6.70 4.77 4.43 6.36 1.35 0.15 0.19 ND 0.22 IUJ-81-237 55.70 0.83 18.10 5.91 0.85 5.15 4.20 2.34 0.09 0.19 ND 4. 77 RIJ-82-201 62.70 0.66 16.20 6. 91 0.31 3.06 3.61 2.10 0.07 0.00 ND 3.08 b:I Rll-82-202 59.20 0.66 17.90 7.39 0.76 2.84 3.32 2.94 0.08 0.16 ND 3.16 I-" Rll-82-203 59.20 0.73 8.16 0.38 3.28 3.58 2. 57 0.04 0.15 ND 3.00 RH-82-204 49.20 1.08 14.20 12.60 7.26 6.93 2.82 0.46 0.23 0.00 ND 3.47 Rll-82-206 66.40 0.50 14.40 5.14 0.33 2.89 6. 57 0.25 0.03 0.13 ND 2.16 IUl-02-207 61.80 0.65 16.20 6.39 0.72 2.93 3.93 3.08 0.06 0.18 ND 2.70 IUJ-82-209 57.70 0.70 17.80 6.85 1.35 3.58 4.12 3.83 0.09 0.18 ND 3.00 Rll-82-217 69.70 0.45 13.10 4.62 0.31 2.05 5.08 1.95 0.02 0.12 ND 1.54 IUl-82-219 66.30 0.46 14.90 4.52 0.69 2.55 5.46 2.35 0.06 0.15 ND 1. 77 Rll-82-223 61.10 0.69 13.60 6.12 2.80 4.54 5.20 0.60 0.14 0.13 ND 3.47 IUJ-82-2:.!5 56.00 0.84 21.40 6.10 0.30 2.38 1.55 7.08 ND 0.12 ND 3.39 Rll-82-228 58.60 0.71 18.10 7.09 0.70 2.54 3.41 4.36 0.01 0.20 ND 2.77 Chemical analysis of sarrples expressed in welght