Introduction
These are copies from my (Ray) field notes taken while investigating Sithylemenkat Lake. This covers my exploration of the area from the spring of 1998 through today. The purpose of my investigations there is an attempt to prove (or disprove) the lake as being caused by meteor impact. I came up with a number of theories on what could have formed the lake. During these field notes I have made an attempt to prove or disprove the various theories, with some success.
I should point out that to date there has not been enough geologic work in the area to definitively prove the source of the lake. My favorite theories are a fault blockage of the lake and an impact crater.
Geologist: Ray Collins. Field Assistant: Matthew Jones.
We flew in to Sethylemenkat Lake from Lake Minchumina and did a brief exploration of the lake. We obtained samples from the exposed pluton (Location A) on the SE corner of the lake and we lowered a device to collect a sample from the bottom of the lake (Location B), as well as collected sand from the shore (Location C).
See map for approximate location of samples.
Geologist: Ray R. Collins. Field Assistant: Matthew Jones
Preflight objectives (ie what we set out to accomplish)
Flying in the Cessna 140, we arrived at Sethylemenkat Lake in the early afternoon. (See Photos) Our primary objective was to collect rock samples and to map the jointing in "Fault Bluff".
The following were sites examined for various data during this field trip. See map for approximate location of samples.
Location #1: east shore, by stream
This location is the mouth of a minor creek in the NE corner of the lake.
66° 07.82' N; 151° 21.99' W (by GPS)
I took some angle measurements of the surrounding areas to help act as a verification of the GPS. Caution: compass measurements, NOT corrected to true north. Declination the area is 27° .
We collected a bag of sand and a couple handfuls of pebbles from the beach.
Location #2: north shore
From location #1 we taxied the plane toward the NW until the snow drifts got too deep to taxi through, and then we walked.
This location is on the north shore at 66° 8.11' N; 151° 23.35'W.
Again I took angle measurements. See caution for locations #1.
We collected a chip from the boulder located on the beach. I suspect the boulder is from "Fault Bluff", and moved up the beach to it's present location by ice.
Location #3: exposed outcrop
This is about 1/5 mile N of the N shore on a rock exposure of Fault Bluff at 66° 08.073'N 151° 24.029W; error (as reported by GPS) 59 feet (~20 meters).
Fragment collected. About 100 feet (30 meters) NW another fragment with banding collected.
Location #4: Exposed outcrop
66° 08.068' N 151° 24.052' W; error (as reported by GPS) 59 feet (~20 meters).
N60° E to E hilltop
S33° E to south hilltop.
33 m W of previous (Location #3). 20 meter high cliff.
Jointing set #1:
Jointing set #2:
Sample: front left pocket; big = top; small = bottom
Face is fractured and in some areas badly decomposed.
Location #5: exposed outcrop
~50 meters W of #4
66° 08.028'N 151° 24.070' W
Nifty rock with very soft white mineral. This is probably a badly decomposed feldspar. Put in shirt pocket.
Location #6A: Exposed outcrop
66° 08.029'N 151° 24.291W
Jointing
Location #6B: Exposed outcrop
66° 08.036N 151° 24.252W
Jointing
Location #6C: Well eroded rock exposure
66° 07.973N 151° 24.456W; 15 meters accuracy
The cluff exposure in this area is badly eroded and pretty well decomposed. Several samples collected; jointing was not good enough to measure.
~30 meters to the W, photo 653 of banding in the rock.
Just to the west (30 meters), photo #653 of banding in rock.
Just (farther) west (50 meters total) "intruded" rock? This outcrop is the lowest exposed outcrop. See photos #654 and 655.
Location #7: Sandy shore
S50E - peak to the south
S37W - peak to the west (the north end of it)
GPS: 66° 07.926N 151° 24.471W error +/- 55 feet
Sand and some rocks collected
Location #8 (same as map location B): Large Hot Springs Hole
GPS: 66° 07.427N 151° 22.303W altimeter 750 feet; error 68 feet
Lowered weighted string to measure depth. Tied a knot at the water level when it hit the bottom. See photo.
Location #9: Small Hot Springs Hole
GPS: 66° 07.276N 151° 22.040W
Lowered weighted string to measure depth. Tied a loop at the water level when it hit the bottom. See photo.
This location was measured (with the GPS) as being 0.27 statute miles from shore.
Cabin
Loose sample in back
Geologist: Ray R. Collins. Field Assistant: Frances Nichols
Preflight objectives
Activities
We arrived the evening of the 22nd of April. We set up camp in the (badly damaged--by bear) cabin. No field work was done in the evening.
On the afternoon of the second day we went to the north end of the lake and took magnetometer readings starting from out on the lake and on up the hill.
See map for a rough idea of the route followed (M1 & M2).
|
Location # |
North Latitude (add 66° ) |
West Longitude (add 151° ) |
Estimate of distance, See note C |
Magnetometer reading, in gamma |
Time |
# times the reading was taken, and the range in gamma |
Comments |
|
1 |
8.07 |
23.05 |
50 |
56022.3 |
12:46 |
3; ± 0.2 |
Lake. Begin M1 going north |
|
2 |
8.05 |
22.99 |
100 |
55948.2 |
12:51 |
4; ± 0.1 |
Lake |
|
3 |
8.1 |
23.08 |
150 |
55908.4 |
12:56 |
3; ± 0.2 |
Lake |
|
4 |
8.13 |
23.03 |
200 |
55852.8 |
12:59 |
4; ± 0.3 |
Lake |
|
5 |
8.17 |
23.04 |
250 |
55764.5 |
13:02 |
3; ± 0.1 |
Lake. Note: from this point on we were carrying a rifle. See note A. |
|
6 |
8.18 |
23.13 |
300 |
55601.2 |
13:18 |
4; ± 0.5 |
Lake shore |
|
7 |
8.2 |
23.19 |
350 |
55495.5 |
13:27 |
3; ± 0.1 |
In 10 m spruce trees |
|
8 |
8.22 |
23.11 |
400 |
55353.4 |
13:35 |
4; ± 0.4 |
In clearing; same as location #23 |
|
9 |
8.21 |
23.18 |
450 |
58528.2 |
13:53 |
3; ± 1.0 |
In 2 m spruce trees |
|
10 |
8.21 |
23.22 |
500 |
57994.4 |
14:00 |
3; ± 0.1 |
In 2 m spruce trees at base of rise |
|
11 |
8.24 |
23.25 |
550 |
58874.7 |
14:06 |
3; ± 0.1 |
In 1 m spruce trees on side of rise |
|
12 |
8.26 |
23.26 |
600 |
59344.8 |
14:15 |
3; ± 0.8 |
In 3 m aspen on side of rise |
|
13 |
8.26 |
23.31 |
650 |
58255.4 |
14:23 |
3; ± 0.4 |
In 2 m aspen and spruce trees on side of rise |
|
14 |
8.27 |
23.37 |
700 |
57406.8 |
14:30 |
3; ± 0.4 |
In 2 m aspen and spruce trees on side of rise. See note D. |
|
15 |
8.28 |
23.46 |
750 |
58060.5 |
14:43 |
3; ± 1.0 |
Last location of this leg. In 2 m spruce trees on side of rise. See note D. |
|
16 |
8.39 |
23.28 |
750 |
57643.8 |
15:03 |
3; ± 0.4 |
This begins the return leg (M2; see map). We moved about 0.3 km eastward. Spacing about 70 meters. Location was in a tundra meadow. |
|
17 |
8.37 |
23.04 |
680 |
57536.5 |
15:14 |
3; ± 0.1 |
Tundra |
|
18 |
8.33 |
23.22 |
610 |
61610 |
15:24 |
5; ± 10.0(!) |
In 3 m spruce trees on side of rise. See note B. This site is in the bottom of a small (0.3 meter) dip that runs parallel to the shore and the proposed fault. Location is where the fault is believed to be. |
|
19 |
8.34 |
23.25 |
635 |
60832 |
15:29 |
4; ± 5.0 |
In 1 m spruce trees on side of rise. See note B. |
|
20 |
8.26 |
23.2 |
585 |
56250.5 |
15:33 |
3; ± 0.1 |
In 1 m spruce trees on side of rise. See note B. |
|
21 |
8.26 |
23.08 |
540 |
59397 |
15:45 |
3; ± 0.5 |
In 3 m spruce trees on side of rise |
|
22 |
8.23 |
23.14 |
470 |
58868.6 |
15:55 |
3; ± 0.6 |
In 2 m spruce trees on side of rise |
|
23 |
8.2 |
23.14 |
400 |
58395 |
16:03 |
4; ± 15 |
This is the same location #8 |
Note A
Due to fresh grizzly tracks we carried a rifle from location 5 on. However we were very careful to put the rifle down 25 meters or more from the site we took each measurement.
Note B
This location had a sharp spike gamma, so we backed up about 15 meters and took another reading. Then we took a third reading about 15 meters farther forward. This was to help determine if we were actually at the fault.
Note C
These numbers were estimated after the field trip, due the poor quality of the GPS readings.
Note D
Toward the end of the trek north (locations 14 and 15) we observed exposed bedrock. This area is very close to the "pass" just north of the lake (see airphoto geologic map).
Samples of quartz pebbles were collected from in front of the cabin prior to departure. See map location C. (These were made into thin sections to see if they had been shocked. No evidence of shock was found.)
Field Conclusions
The presence of bedrock so near the pass excludes the possibility that the pass was created by either landslide or terminal moraine. (Otherwise the surface would have to be debris.)
Write-up on the magnetometer data from the field trip.
(Proposed) April 24-25, 1999
Geologist: Ray R. Collins. Field Assistant: Matthew Jones
Unfortunately this trip was canceled due to bad weather.
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This page last messed with on 4/29/99