Comments on: Geologic Misconceptions: “Layer-cake” stratigraphy

By: BrianR

BrianR — Wed, 14 May 2008 15:24:41 +0000

Barnaby … go to the “About” page and you’ll find my contact info.

By: Barnaby

Barnaby — Wed, 14 May 2008 14:48:30 +0000

Hi, I’m part of a team of translators (English-Spanish)working in a proyect related to terms included in the field of geology. We are very interested in the information we have seen in your blog and would like to know how to contact you and if we may forward some questions.
Thank you very much
Barnaby

By: goodSchist.com » Blog Archive » The GeoBlogosphere Review #1

goodSchist.com » Blog Archive » The GeoBlogosphere Review #1 — Wed, 13 Feb 2008 07:37:20 +0000

[...] Allochthonous states the obvious, referring to Brian’s post in the Accretionary Wedge #5; Brian might not like it, but I think this t-shirt is pretty [...]

By: on-the-rocks

on-the-rocks — Sat, 02 Feb 2008 14:09:48 +0000

Years ago I did some quadrangle mapping along the Flint River, just north of Lake Blackshear, on the Georgia Coastal Plain, for the Georgia Geologic Survey.

On a nearby tributary, Turkey Creek, in an asymmetrical valley, one could sit on a bluff composed of Middle Eocene Lisbon Fm., Late Eocene Clinchfield Fm., and a cap of Miocene Altamaha Fm. (fluvial deposits). Across the creek, Quaternary alluvium of the modern floodplain overlay the Miocene Altamaha Fm. at the same elevation of the Middle Eocene Lisbon at the base of the bluff. In other words, you couldn’t correlate from one side of Turkey Creek to the other.

Five miles to the southeast, a well log recorded 60 feet of Late Eocene limestone above the Clinchfield Fm., totally missing from the Turkey Creek bluffs.

A mile and one half to the west, along the Flint River (east bank), the Miocene Altamaha overlay the lower Middle Eocene Congaree/Tallahatta (the Lisbon and Clinchfield were missing).

My boss didn’t believe me and hired one of the elder statesmen of Georgia geology, Tom Crawford, to field check my work. After a couple of days in the field, Tom agreed with me that the geology was screwed up. He suggested a couple of minor map changes just to mollify the boss and to just leave the rest to someone else to straighten out, as the mapping project schedule didn’t permit a detailed study of the area. He was able to explain the situation to the boss.

Previous workers had suggested some sort of subsurface structures in the area, but had not attributed any surface oddities to the structures (maybe they just ignored them). There is a thesis/dissertation project awaiting someone there.

By: The Accretionary Wedge #5: Geological Misconceptions and Pie « The Accretionary Wedge

Fri, 01 Feb 2008 19:21:21 +0000

[...] analogies - but he hasn’t thought of any pielike concepts in geology, maybe you can help? Brian objects to the “layer cake” analogy, suggesting that perhaps we should use lentils instead. Lentils? I guess I’ve seen recipes for [...]

By: Accretionary Wedge #5: Geological Misconceptions and Pie

Accretionary Wedge #5: Geological Misconceptions and Pie — Thu, 24 Jan 2008 22:55:53 +0000

By: saxifraga

saxifraga — Wed, 23 Jan 2008 21:22:50 +0000

Great post. I work on sedimentary architecture on various scales, so this is right up my alley. Excellent idea for a misconception.

By: Billy

Billy — Wed, 23 Jan 2008 16:48:57 +0000

Brian R.: It’s worth doing. Back in the 70s, my dad did a lot of work with the geological maps to produce a color-coded version. If memory serves, the most interesting area (geologically speaking) is the east end where the Colorado is running North-South before taking the right turn through the Coconino and Kaibab plateaus. I think (and again, its been a while so I could be wrong) that the Grand Canyon Group shows up a lot on the North side of the canyon (geographic west). The outcroppings near Phantom Ranch are fairly small.

I haven’t been back there since 1988 (sister’s funeral) and haven’t been into the canyon since 1978. One of the absolute best ways to see the geology (if you’re not a hiker) is by raft or dory. The fluted schist (man, that sounds dirty, doesn’t it) in places in the inner gorge are incredible. And don’t worry. The side hikes up the canyons get hou to plenty of sedimentary outcrops.

By: BrianR

BrianR — Wed, 23 Jan 2008 16:25:13 +0000

Lab Lemming and Tuff Cookie … perhaps we should someday have a cake/pie creating contest … whoever makes the most creative geologically-inspired baked good wins!

Billy … thanks for the nice words. I hate to admit it, but I’ve never been down to the bottom of the Grand Canyon. I’ve only been there once and that was only at the rim for a family reunion. It’s still on my list.

By: Billy

Billy — Wed, 23 Jan 2008 15:57:03 +0000

Back in the 70s my dad was a district ranger (interpretation) on the south rim of the canyon. We lived there for five years. He also taught a course called “The Geology of the Grand Canyon” through Yavapai Community College. I (when I was 12) took the course (I brought it up to the minimum necessary students). One of the biggest shocks for the students was on one of the field trips down to Phantom Ranch at the bottom of the Grand Canyon. Dad showed them the Grand Canyon series atop the Great Uncomformity. Some of the students just could not get their mind around sedimentary rocks at an angle. Another on which confused some of the students was the Temple Butte Limestone (wedged in between the Redwall Limestone and the Tonto Formation) which is thin, spotty and found in lenticular cells not more than 40 metres wide in the East end of the canyon, but the further west one goes, the thicker it is.

Good post. I enjoy your site. Even though I am an historian, the geology of my youth keeps rearing up and sending my mind in new directions.

Incidentally, if you find yourself in Northeastern Pennsylvania, there is a roadcut near Wilkes-Barre, PA (Route 309, Cross-Valley Expressway) which shows shale lenticles about 10 to 15 metres across and up to 1 to 1.5 metres thick.