7 Paleozoic B l a c k Shales
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Ontario-
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P o s s i b l e Oil S h a l e s J. F. BARKER and R. D. DICKHOUT—University of Waterloo, Department of Earth Sciences, Waterloo, Ontario, Canada D. J. RUSSELL and M. D. JOHNSON—Ontario Geological Survey, Engineering and Terrain Geology Section, Toronto, Ontario, Canada P. GUNTHER—Petro Canada, Geological Research and Services, Calgary, Alberta, Canada Three black, organic-rich, Paleozoic-age shales occur i n southern Ontario - the Ordovician Whitby ( B i l l i n g s ) Formation and the Devonian Kettle Point and Marcellus Formations. In the Whitby Formation, the most organic-rich zone i s the Lower or Collingwood member. It i s 1.5 to 7 m thick, carbonate-rich with organic carbon content up to 13%. Organic richness is quite variable but the richest areas along the Whitby subcrop occur from Manitoulin Island to C o l l i n g wood. Fischer Assay oil yields range up to about 60 litres/tonne (14 U.S. gal/ton). The Whitby Formation appears to have reached a marginally mature thermal maturation l e v e l and so bitumen i s a significant component of the organic matter. The bulk of the organic matter i s kerogen, dominantly type I and type II, and of marine o r i g i n . The Kettle Point Formation subcrops in southwestern Ontario. It i s up to 60 m thick, with organic carbon values usually i n the range 5%-16% and Fischer Assay oil yields up to 70 1/t (17 gal/ton). The organic matter i s dominantly kerogen of marine o r i g i n and has attained only an immature thermal maturation stage. A p a r t i c u l a r l y r i c h upper zone i s present over much of the subcrop area and its thickness seems to be cont r o l l e d by post-Kettle Point erosion. Although studies are still preliminary, especially for the Devonian shales, the Kettle Point Formation appears to have the most potential for shale oil production i n southern Ontario. H i s t o r i c a l l y , shale o i l was produced i n Ontario from a plant near Craigleigh, on Lake Huron. In 1859, rock of the Ordovician Whitby Formation was retorted to produce fuel and lubricants. In 0097-6156/ 83/0230-0119S06.00/0 © 1983 American Chemical Society Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
1863, t h i s o p e r a t i o n became uneconomic i n the face o f the conv e n t i o n a l crude o i l newly discovered near O i l S p r i n g s , O n t a r i o . In 1981, the Ontario G e o l o g i c a l Survey began a program t o assess the resource p o t e n t i a l of the Whitby Formation and the other b l a c k shales of O n t a r i o . P r i o r t o t h i s study, i n f o r m a t i o n on Ontario's b l a c k shales has been very sparse due to poor o r non-existent exposure and l i m i t e d subsurface i n f o r m a t i o n . E x i s t ing data suggested three u n i t s were s u f f i c i e n t l y o r g a n i c - r i c h to warrant f u r t h e r s t u d y — t h e O r d o v i c i a n Whitby and the Devonian K e t t l e P o i n t and M a r c e l l u s Formation ( 1 ) . The i n i t i a l phase of the p r o j e c t i n v o l v e d shallow sampling of the Whitby Formation by diamond d r i l l i n g a t 20 l o c a t i o n s . These s t r e t c h e d from M a n i t o u l i n I s l a n d t o Toronto (see F i g u r e 1) and t o Ottawa, where the s t r a t i g r a p h i e e q u i v a l e n t B i l l i n g s F o r mation i s present. I n 1982, 20 boreholes were l o c a t e d on the K e t t l e P o i n t subcrop and 4 boreholes were l o c a t e d on the Marc e l l u s subcrop. L i t h o l o g i c a l and geophysical l o g s f o r these boreholes are i n p r e p a r a t i o n . A p r e l i m i n a r y organic geochemical study o f the Whitby Formation ( 2 ) i s i n press. Studies of the paleontology, s t r a t i g r a p h y and sedimentology, mineralogy and i n o r g a n i c geochemistry o f the Whitby Formation a r e underway. This paper emphasizes the organic geochemistry of these b l a c k shales. Geology of the B l a c k Shales The Upper Devonian K e t t l e P o i n t Formation i s a c o n t i n u a t i o n of an e x t e n s i v e s e r i e s of b l a c k shales which a r e known across e a s t e r n North America; the u n i t i s approximately c o r r e l a t i v e w i t h the Antrim shale of Michigan, the Chattanooga shale of Alabama and Kentucky, the New Albany of Indiana, and the Ohio shales of Ohio. The K e t t l e P o i n t s t r a t a u n d e r l i e a broad band of southern Ontario between Lake E r i e and Lake Huron and a r e f l a t l y i n g o r g e n t l y d i p p i n g to the north-west i n t o the Michigan B a s i n (see F i g u r e 1 ) . Rocks of the K e t t l e P o i n t unconformably o v e r l i e the shales and carbonates o f the Hamilton group and a r e o v e r l a i n ( i n the extreme north-west of the subcrop b e l t only) by the Bedford shales o f the P o r t Lambton Formation. The upper contact i s sharp. L i t h o l o g i c a l l y , the K e t t l e P o i n t c o n s i s t s of a dark grey, brown-grey t o b l a c k s i l t y a r g i l l a c e o u s s h a l e . The southern and c e n t r a l areas of the Formation are a l s o c h a r a c t e r i z e d by an abundance of green shale i n t e r b e d s . Large s p h e r i c a l concentrat i o n s a r e a l s o known w i t h i n the Formation; they a r e l o c a l l y termed " k e t t l e s " from which the Formation i s named. The u n i t has a maximum t h i c k n e s s of 60 metres i n O n t a r i o , but average about 28 m across the subcrop area. The Middle Devonian M a r c e l l u s Formation c o n s i s t s of b l a c k bituminous shale and minor a r g i l l a c e o u s limestone l y i n g conformably on the Dundee Formation limestones. I t s d e p o s i t i o n a l s e t t i n g resembles t h a t of the Whitby Formation and the M a r c e l l u s
Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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Figure 1. Outcrop or subcrop locations of Paleozoic black shales in southern Ontario.
Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
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i s a l s o c a r b o n a t e - r i c h . Thicknesses of up to 50 m are reported under Lake E r i e , but the M a r c e l l u s t h i n s and i s l e s s than 20 m t h i c k where i t subcrops on the n o r t h shore of Lake E r i e . The presumably more widespread M a r c e l l u s shales were s t r i p p e d o f f d u r i n g subsequent u p l i f t and e r o s i o n . The M a r c e l l u s i s unconformably o v e r l a i n by Hamilton Group shales and limestones beneath Lake E r i e , and by unconsolidated Quaternary g l a c i a l dep o s i t s up to 60 m t h i c k where i t subcrops under l a n d . The Upper O r d o v i c i a n Whitby Formation o v e r l i e s the Lindsay Formation of the Middle O r d o v i c i a n Simcoe Group. The Lindsay Formation i s a limestone w i t h interbedded shaley u n i t s . The c h a r a c t e r of the contact w i t h the o v e r l y i n g Whitby Formation i s v a r i a b l e and may be an important c o n t r o l over the organic cont e n t of the lower part of the Whitby Formation. The Whitby Formation i s o v e r l a i n by interbedded limestone and shale of the Upper O r d o v i c i a n Georgian Bay Formation. The Whitby Formation has been subdivided i n t o Upper, M i d d l e , and Lower (Collingwood) members ( 3 ) . The Upper member i s genera l l y a greenish-grey f i s s i l shale between 36 and 52 m t h i c k i n the study area. The Middle member i s a brownish-grey f i s s i l e shale between 5 and 26 m t h i c k . The Lower member or Collingwood i s a dark brownish-grey marl w i t h b l a c k shale i n t e r b e d s and i s 1.5 to 7 m t h i c k . I t i s sometimes h i g h l y f o s s i l i f e r o u s . Considerable l i t h o l o g i c a l v a r i a t i o n i s observed along the subcrop, but i t i s evident that the most o r g a n i c - r i c h zone of the Whitby i s the Lower (Collingwood) member which occurs i n a t r a n s i t i o n from carbonates of the Lindsay Formation to shales of the Whitby Formation. In f a c t , l i t h o l o g i e c o n s i d e r a t i o n s alone would r e q u i r e that the Collingwood member be i n c l u d e d i n the Lindsay Formation r a t h e r than i n the Whitby Formation. The Upper and Middle members appear to be much more c l a y - r i c h , a l though c o n s i d e r a b l y d i f f e r e n t geophysical responses are noted f o r the M a n i t o u l i n - C o l l i n g w o o d and Toronto areas. M i n e r a l o g i c a l data i s very l i m i t e d (4_) , but where c l a y minerals are a major f r a c t i o n , i l l i t e dominates over c h l o r i t e w i t h o n l y minor amounts of smectite c l a y s r e p o r t e d . A n a l y t i c a l Methods A n a l y t i c a l methods are described i n ( 2 ) . Standard methods were employed f o r t o t a l organic carbon (TOC) and F i s c h e r Assay (FA) analyses. Kerogen was i s o l a t e d by s o l v e n t e x t r a c t i o n to remove bitumen and a c i d d i s s o l u t i o n to remove m i n e r a l matter. Elemental a n a l y s i s was performed only on kerogen w i t h low ash content (
