Sunday, January 15, 2012

2008 November S Kaibab hike - selected geology highlights

Geology highlights from S Kaibab Trail Hike

Since the trail is named the S Kaibab we start off hike with the top of the Grand Canyon stack Kaibab Limestone

07:44 minutes down the trail we are into the Toroweap

07:45 Looking up from Toroweap we see a nice example of a Toreva block (ok, nice very small Toreva block slide)

07:53 Salt Dome example in the Toroweap – generally Salt Domes form wherever a prolonged period of flooding/evaporation occurs in an arid climate – here salt deposits above the low tide zone of the Toroweap sea are lighter than the rock above and later rose thru the Toroweap.

08:02 after traverse in Toroweap we encounter the Coconino

 begin a rapid descent thru the Coconino Sandstone where we see classic cross-bedding

08:07 Ooh-Aah Point obligatory photo

08:22 More steep descent thru Coconino – slowly as I needed to wait for the sun which I am ahead of at this point

08:55 nearing Cedar Ridge we are in the Hermit Shale.  Notice the Grand Canyon Supergroup (red Hakatai Shale) in the Cremation graben (across the river and below the Tapeats – later we will hike into it below the Tipoff on this side of the river).  The GC Supergroup is eroded away in much of the Grand Canyon but visible/accessible thruout this hike (in fact, we came this way to walk on and thru the Supergroup plus see it in several grabens).  The graben down dropped the Supergroup layers in the distant past so later erosion did not remove it.

Detail showing Hakatai visible across river

O’Neil Butte is a nice exposure of Supai Group Esplanade Sandstone

09:02 Supai Group

09:09 below Cedar Ridge we descend thru the Supai Group

09:29 went slightly off trail to photograph a nice example of a Breccia pipe (formed by collapse of a solution cave where the rubble was filled in/cemented by later sediments) – this is especially nice as the pipe later partially eroded out

09:44 Back on S Kaibab at Skeleton Point we get a good look at the Cremation Graben Supergroup Exposures on the other side of the river – we will be hiking thru this on this side of the river soon

09:52 we hike thru the Redwall limestone – notice the solution caves beside and above the trail

10:14 at base of Redwall photographed a nice exposure of Temple Butte (not as large as on N Kaibab, but this is prettier and I was S not N) – you can also reach out and touch this as it is just meters off the trail at end of last switchback before Muav – the sun was perfect on a great day in the Grand Canyon.  Temple Butte Limestone in the eastern Grand Canyon was deposited in river/stream channels forming a smiley face (do you see that shape in the below?).  It is not generally found as a separate layer in the eastern Grand Canyon (this changes as you go further west).
This purple in this smiley face is not typical of many Temple Butte lens exposures as they tend to weather into a blah slightly purple gray.

10:17 rapid descent thru Muav Limestone

10:51 hiking on the Bright Angel Shale we approach the Tipoff

11:13 hiking in the Shinumo Quartzite we see the Hakatai ahead

11:14 at Tipoff we get a great view of Tapeats on top of Hakatai Shale on this side of river as well as a view of the Hakatai on other side of the river (also in the Cremation graben) to the right is Shinumo Quartzite just as it should be (we just looked ahead and down to skip it for a minute) – the Hakatai was lifted up hundreds of feet above the rest of the Supergroup below it by a normal fault

11:18 house sized block of Shinumo Quartzite with trail blasted thru

11:26 Tapeats Boulder with Shinumo Quartzite pieces in it – oh yes, Shinumo fell off cliff at edge of Tapeats Sea into the Tapeats sand at water edge – Blacktail Canyon has (or had) a boulder in it in 2008 that is similar - see 2008 trip

Discussion of five criteria needed to form the Grand Canyon from lectures by Wayne Ranney (author of Carving Grand Canyon and other Geology texts):

1.    Large expanse of stratified rock (the Grand Canyon layers are known to extend across a very large area – some strata from well east of the Grand Canyon to west of Las Vegas).

2.    Variably colored (pretty/brightly colored in our case) – the different colors help make the strata obvious to non-geologists.

3.    Gently uplifted

4.    Eroded/Exposed by Big River(s)

5.    Dry Arid Environment near sea level (lacking the dry environment natural weathering would dominate and strip many layers completely; if well above sea level any deposits would almost certainly be eroded along with the mountains they lie upon; much of the grand canyon sedimentary rock was laid down in shallow seas or formed as part of near shore Aeolian deposits)

Wayne Ranney and Ron Blakey in Ancient Landscapes discuss and show on maps / images what the southwest US looked like when the various layers of the grand canyon were deposited (at sea level).  These support and elaborate on the five criteria discussed above.  I highly recommend Wayne's books.