the base of the overlying Ramsay Lake Formation. The conglomerates
die out to the southeast by an increase in the proportion of inter-bedded sandstone wedges and a general reduction in grainsize(Roscoe, 1969; Robertson, 1976).
Most conglomerates are massive, however, some show
horizontal stratification. Trough cross-stratification ispresent in the pebble conglomerates in areas where numerous
sand-stone lenses occur. Occasionally the cross-sets can be traced
from the conglomerate into sandstone lenses. Sandstones inter-layered w i t h the conglomerate and forming units separatingcon-glomerate packages are generally trough stratified w i t h
cross-set a m p l i t u d e averaging approximately 12 cm. One example of large-scale (1 meter a m p l i t u d e ) planar cross-stratification was observed.
L i k e w i s e the majority of Matinenda sandstones w h i c h are not associated w i t h conglomeratic blankets are trough cross-stratified w i t h
largescale planar crossstratification only d o m i n a t i n g i n d e l t a i c d i s -t r i b u -t a r y channels (Fralick, in prep.). The l i -t h i c succession
probably represents g r a v e l l y l o n g i t u d i n a l bars (massive and p a r a l l e l s t r a t i f i e d conglomerate) which were reworked d u r i n g intervals of reduced discharge creating sand f i l l e d chuts channels and sand shadows b e h i n d topographic h i g h s down-bar (sandstone lenses). In one location a l o n g i t u d i n a l bar was traced l a t e r a l l y over 80 m and found to be gradational w i t h a major sand f i l l e d s i d e channel.
General s i m i l a r i t i e s w i t h the mixed gravel/sand sediments of parts
of the modern Donjek R i v e r ( W i l l i a m s and Rust, 1969; M i a l l , 1977) are suggested. More d i s t a l , crossbedded sandstones of the m i d d l e part
of the Matinenda Formation can be compared to deposits forming in shallow braided rivers of Platte type (Smith, 1970; M i a l l , 1977).
The u r a n i n i t e concentrates in more massive portions of the l o n g i t u d i n a l bars and as lags along horizontal reactivation surfaces in stacked bars (Fralick, in prep.). The bars themselves represent rare, discrete h i g h energy events in a succession that is dominated by braid-channel deposits (trough cross-stratified sandstones). The gravel bars are localized in the lower portion of the formation, u s u a l l y being confined to paleoval leys (Roscoe, 1969).
During deposition of the lower portions of the formation flow was from north to south. As time passed the regional paleo-flow d i r e c t i o n g r a d u a l l y changed to NW-SE and eventually to WNW-ESE (Fralick, in prep.). The swing in paleocurrent direction is
thought to reflect crustal subsidence to the east of the area in
which the Matinenda Formation was studied.E V I D E N C E OF A GLACIAL ASSOCIATION
The contact r e l a t i o n s h i p s between f l u v i a l Matinenda Formation sandstones and g l a c i a l Ramsay Lake Formation m i x t i t e s was investigated in an attempt to g a i n i n s i g h t into the p o s s i b i l i t y
that the Matinenda Formation was deposited on a g l a c i a l outwash p l a i n . F i v e pieces of evidence were found i n d i c a t i n g a g l a c i a l o r i g i n for at least the upper Matinenda sandstones: 1) g l a c i a l erosion and resedimentation of unconsolidated Matinenda m a t e r i a l ; 2) g l a c i a l override features present in the upper Matinenda Formation;
3) i n t e r b e d d i n g of g l a c i a l m i x t i t e and f l u v i a l quartzite; A) i n t i m a t e association between small Matinenda deltas and subaqueous g l a c i a l out-wash; 5) Zr/Hf ratios i n d i c a t i n g Matinenda sediments from d i f f e r i n g
source areas were w e l l mixed p r i o r to deposition.
Resedimented Matinenda D e b r i s
In the northern portion of the outcrop area g l a c i a l l y derived m i x t i t e s of the Ramsay Lake formation o v e r l i e both Matinenda f l u v i a l sandstones and McKim marine/lacustrine s i ltstone-shale
successions. Of these only the contact between g l a c i a l m i x t i t e s and f l u v i a l sandstones was studied. The contact is generally g r a d a t i o n a l w i t h the sandstone becoming massive instead of cross-s t r a t i f i e d and then the cross-sorting of the rockcross-s deteriorating. The decrease in sorting is caused by an increase in the m a t r i x content, the a d d i t i o n of sand grains of various sizes other than the usual coarse sand, and occasional quartz pebbles floating in the rock.
The amount of both m a t r i x and quartz pebbles increases upward.
The contact w i t h the Ramsay Lake Formation is extremely gradational
and is s i m p l y defined as where the first g r a n i t i c clast appears
in the succession. The t r a n s i t i o n zone ranges from 5 to 23 meters in thickness.
The massive nature of most of the transition zone indicates that sorting processes did not play an important role in its sedimentation. Further evidence concerning the depositional environment is provided by siltstone layers containing dropstones which are sometimes present near the base of the transition. This u n i t attests to the previous development of f r i g i d conditions and flooding of the area. The above combined w i t h the gradational contact the transition zone rocks e x h i b i t w i t h overlying g l a c i a l rainout m i x t i t e s (Fralick, in prep.) strongly indicates that the transition zone itself was deposited as a g l a c i a l rainout unit.
Debris in the ice mass acquired a stacked zonation reflecting the lateral lithofacies d i s t r i b u t i o n the ice passed over. Thus debris at the base of the ice was composed of the most proximal l i t h o l o g i e u n i t the ice passed over before it became a floating sheet, namely Matinenda Formation sandstones and conglomerates. Thus sediments from this source were the first to be liberated from the g l a c i e r during m e l t i n g . As m e l t i n g continued Archean debris incorporated further up paleoslope was deposited creating the transition to Ramsay Lake mixtites. Boulton (1972) has observed a s i m i l a r l i t h i c succession in the glacial debris of Antarctica and inferred the same process.
Microscopic examination of the Matinenda resedimented material indicates that the formation was not l i t h i f i e d prior to g l a c i a l erosion. There is also no evidence of any i n t e r s t i t i a l growth of cement, or of any overgrowths having formed on sand g r a i n s prior to scouring by ice advance.
The pattern of g l a c i a l advance described here contrasts w i t h that of other Huronian units. The M ississagi-Bruce transition is
characterized by 150 m of interbedded crossbedded sandstone and m i x t i t e (Long, 1976, 1977). By contrast the Serpent-Gowganda transition is