Cross Lake Project (1983-86)

Geologist P.G. Lenton Year 84 STATION 5409
EASTING 576501 NORTHING 6060879 ZONE 14 DATUM NAD83
Date of mapping 06/13/1984

STRUCTURAL DATA

PETROLOGIC DATA

Rock Number: 1

Rock Type: conglomerate
Field Description:

-running descriptive sec from S to N at W end of Beryl Dike Island
-interbedded sequence of quartz rich lithic sandstone showing abundant crossbedding and trough crossbedding, alternating with scour channels of polymictic lithic arenite conglomerate forming lenticular troughs and scours 30 to 50 m wide with a present trough depth averaging 35 to 40 cm
-troughs are normally graded into lithic sands with pebble pavements tops consistently south facing
-2 photos of cross bedded sands and conglomerate troughs
-tape scale extended 1 metre
-12 m of conglomerate sandstone exposed under an by 5.7 m massive conglomerate with 1 to 10 cm erratic clean sand horizons
-the massive conglomerate shows no sorting or grading until upper 1/3 of bed is above the sand layer
-the clast size is drammatically larger with a higher tonalite component
-down section from massive conglomerate returns to cross bed and trough units
-previous section has been highy polymictic but relativlly clean with a low percentage of mafic clasts
-15 m down section is a coarse matrix supported conglomerate still topping to the south (layering 066/85)
-conglomerate is 6 M thick passing down section into more trough and cross bed whits
-this coarse layer also contains thin calcareous and buff hornblende arkose
-sample taken in the second coarse polymict conglomerate layer /15 metres down section is 10 m layer of polymict conglomerate dominated by an abundance of 5 to 40 cm grey white grannadiorite cobbles
-that strongly resembles the unconformity on unit 1
-2 photos -tape scale extended 1 metre
-14 metres (in small bay) of polymict matrix supported pelitic conglomerate
-section continues into quartz rich trough and cross bed units
-this section is identical to all stations from 5400-5407 including the reappearance of numerous small mylonites
-next unit down section
-see contact on air photo is a thick section of festoon bedded quartz rich grey lithic sandstone, with minor pebble lag deposits and thin pavement conglomerate layers
-the festoon beds appear to be migratory channel occasionally with climbing ripples suggesting shallow water environment
-some pebbles retain obvious weathering rinds
-because the beds are festoon topping, it's indeterminate, but pebble lags seem to indicate the section is still south facing
-3 photos of festoon beds with scale extended 50 cm
-1 photo of weathered pebble
-sample 2 of festoon lithic sandstone
-pebbly layers and lags decrease down section
-next unit down section is a well sorted pebble conglomerate with 15% highly deformed mafic clasts
-average clasts size is 1/2 by 2 cm
-sorted conglomerate contains less than 1% exotic clasts sizes in excess of 5 cm
-35 m down section conglomerate is still moderatly well sorted but mean clast size has increase 2x6 cm and several 5 to 45 cm quartz rich calcareous arenite beds have appeared
-pelitic component of sorted conglomerate increases down section as shown by dramatic increase in garnet content
-base of this section is a 1 metre laminated calcareous sandstone which rest on a major conglomerate
-1 photo of the sorted garnetiferous conglomerate with arenite interbeds
-1 photo of the base laminated arenite
-tape measure rests on the top contact of the underlying mafic conglomerate
-next unit down section is an unsorted, ungraded mafic conglomerate with a clast size range from granule to 1 metre boulder
-clasts are dominantly silty sediment and mafic volcanic with minor tonalite, ultramafic and assorted hypabyssal intrusives
-35 metres in width
-base of mafic conglomerate is a variable 5-35 cm amphibolitic garnetite that probably represents a paleo regolith on the unconformitiy
-this rests on a section of highly deformed and altered garnet, hornblend dioxide bearing basaltic amphibolite
-textural inhomogenity suggests pillow basalt
-basalt is in contact on the north side at waterline with a tonalite boulder conglomerate similar to unit 1 uncomformity
-sample near the base of the mafic clast conglomerate
-sample of the garnetite 1 metre into the amphibolite
-(2 photos of the basal regolith showing 5 cm of laminated garnetiferous sand on top of the garnetite)
-(1 photo of altered basalt)
-(1 photo of tonalite boulder conglomerate on north side of basalt

Manitoba Geological Survey, 2017