The ND112 Complex

INTRODUCTION

A recently developed field area, designated “ND112″, exhibits a fascinating assemblage of geologic environments reflected in a myriad of deskcrops. We have identified 14 unique geologic horizons occurring over an area of 4.5 by 6 meters. In this report we briefly describe, map, and give preliminary interpretations on the history of the ND112 region. Relative ages of deskcrops are based on historical records and oral histories of the indigenous peoples of the area.

ND112 is a geographically isolated region, only accessible via a single restricted access route. No other environments are visible from the confines of ND112, which has resulted in a significant loss of inhabitants (50%) in recent months.The population reduction has allowed the remaining locals, or Grads as they call themselves, to flourish and has the added bonus of making deskcrop access easier. However, we learned in the course of our investigation that mass wasting during the exodus caused the loss of several deskcrops in the SW, including coal, olivine sand, vesicular basalt, slag, and cobbles of quartz sandstone and agate. The loss of these invaluable deskcrops severely limits our investigation of ND112’s southwest.

GEOLOGIC SETTING
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Geophoto: petrified wood

Segmented petrified log in the Blue Mesa Member, Petrified Forest National Park 2010

What rolls down stairs, alone or in pairs? That’s right kids, it’s Log! This half-meter diameter log was buried some 200 Myr ago and its organic content was replaced by silica (a process called permineralization). One thing I’ve always wondered: If we split wood parallel to the long axis, why is it so common for petrified wood to break along such nice planes perpendicular to the grain (as it is here)?

Enjoy the rest of the great photos that are sure to come on the last day of Geology Photo Week! Visit the Georneys post that started it all, or view my previous photos from this week (click thumbnails to view post + description):

Get your own Blammo! Log here:

Miss the reference? Watch the commercial

Geophoto: Antelope Island

Antelope Island from the air, Salt Lake City, Utah 2007

Today’s contribution to the geology photo week geomeme is Antelope Island. This shot was taken on approach into Salt Lake City. Antelope Island is one of the ranges that makes up the Basin and Range Province of the western United States. The island is particularly photogenic as it is surrounded by the Great Salt Lake, which makes for fantastic plays of contrasting colors. Turns out it’s a state park as well!

Take your own photo on approach:

Geophoto: pink salt

Pink salt exposed in wall of mine tunnel operated by American Rock Salt Co., Geneseo, NY 2006. Outcrop is ~1 meter high (apologies for lack of scale!).

Round three of this week’s geomeme of a picture-a-day (previous entries here and here) features halite, a.k.a. rock salt! Pink (or pinky orange) halite, to be more specific. The mine, run by American Rock Salt, is the largest operating salt mine in the United States (3+ million tons annual production). This pink halite is located in the mine wall ~1,400 feet underground, where it remains minus the football-sized chunk we removed for display in our department collection!

Get a tour and take your own photo!

Geophoto: Centralia coal fire

Smoke and cracks are signs of an uncontrollable subsurface coal fire, Centralia, PA, October 2006

Continuing the geology photo week started with yesterday’s dikes and pillows, today’s picture is from the borough of Centralia, PA, where an underground coal fire has been burning since 1962. The heat and volume change caused roads to crack and warp and left the ground unstable in some areas. As a result, the borough has been mostly deserted for almost twenty years and the 2010 census reported 10 residents. And that smoke isn’t just for show. The pavement was hot to the touch, and air escaping from cracks was too hot to hold your hand over for more than a second or two.

Go and take your own photo:

Geophoto: sheeted dikes and pillow basalts

Troodos Ophiolite sheeted dikes and pillow basalts on Cyprus, January 2007

Evelyn at Georneys initiated a geology photo week, which gives me the opportunity to share a photo for which I didn’t yet have a place. Ophiolites are oceanic crustal sequences that have been obducted and raised above sea level. To paint with a broad brush, the sequence (from bottom) is one of ultramafic rock, gabbro intrusions, sheeted dykes, pillow lavas, and sometimes topped by pelagic sediment. The Troodos Ophiolite on Cyprus is a fantastic example because it was sort of smeared over the island and at least a little bit of everything can be found at/near the surface. Here we see the sheeted dykes and pillow basalts at a grand scale!

Now go and take your own photo:

Six days in the crater: day one

Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6

This post is based on field notes and memories supplemented by background reading material from the Meteor Crater Field Camp that was held from October 17-23, 2010. The field camp was run under the NASA Lunar Science Institute and headed by Dr. David Kring of the Lunar and Planetary Institute.

Twenty-two of us are spread out between three Chevy Suburbans, and it’s strange having legroom on a geology expedition. Not that there’s far to go. We are camped out in an RV park a mere 5.5 miles from our field site: Barringer Meteorite Crater. This is the first day of the first ever Meteor Crater Field Camp, and we are making the first trip first thing in the morning to my first visit to any crater, ever. Everyone’s ready to get started, and we don’t have long to wait. Our first stop is approximately fifteen feet outside the gates of our campsite, and we step out of the vehicles after realizing the stop wasn’t because of a forgotten water bottle or notebook.

View to south from RV Park

Sunset from Meteor Crater RV Park, panning from south (left) to west (right). I’ve ‘underlined’ the approximate extent of Meteor Crater’s rim (view large!), which is flanked by silhouettes of volcanic mesas.

At 5.5 miles out there’s not much of the crater to see and so we huddle around Dr. Kring, our fearless leader. He asks us to imagine standing at this exact spot 49,000 years ago* as Meteor Crater formed. “What would you see?” he asks us. Slowly we find our voices: A streak of light and a flash. A fireball. Wind whipping across the plains. A massive volume of ejected material rushing toward you. Then nothing because you are dead.

We learn we wouldn’t even last that long. At this distance the shock wave would reach you in less than a second, turning you inside out before the wind and heat simultaneously flash-cooked your body as it tumbled away in pieces with the desert sage. Oh well. Someone luckier and further away would have seen quite the show.

49,000 years later, as we pile back into the vans, it’s mostly sunny and warming past 50°F on the high desert plains of Arizona.

[*On the basis of thermoluminescence, 26Al, 10Be, and 36Cl studies, it’s generally agreed that Meteor Crater formed 48- to 49-thousand years ago. More recently, updated 36Cl reference material argues for an older age of 60- to 65-thousand years.]

Hiking on rim Meteor Crater

Uneven terrain on the crater rim

On the docket for our first day at the crater is a 3.7 kilometer (2.3 mile) hike along the rim, ~1.8 km clockwise before lunch, then retracing our steps counterclockwise. There’s House Rock (a.k.a. Monument Rock), the largest (intact) boulder on the crater rim at ~10 meters tall. Pile on two more House Rocks and you’d have a reasonable estimate of the meteorite diameter. And maybe at one time there really was another House Rock or two on top. Surface exposure age dates from the top of House Rock are younger than the 49,000 year formation age.

It wouldn’t be surprising if House Rock had initially been covered by ejecta. Erosion and weathering is evident everywhere at the crater. A gully running downslope beneath the crater museum rapidly cut through three layers of authigenic breccia, both exposing and halfway eroding a projectile fragment over a two year period. The breccias are so friable that when we later head into the crater, we aren’t allowed to touch or even go near the left side of the gully where the projectile is exposed.

On our CCW hike back we generate a little erosion of our own by scrambling down the crater wall a bit from House Rock to see something (else) awesome. We start out on Kaibab on the crater rim and walk down through Moenkopi, and end up back at Kaibab. The top slice of bread in the Kaibab-Moenkopi-Kaibab sandwich is ejected, overturned Kaibab. The bottom slice is in-situ Kaibab. And the meaty Moenkopi center is where it gets interesting. Look at the photo below. Both members of the Moenkopi are visible here. The pale reddish brown Wupatki (at left) is a massive sandstone underlying the dark, reddish brown fissile siltstone called the Moqui. The surrounding pale/tan blocks are dominantly Kaibab (limestone/dolostone), though most shown here are loose boulders.

Fold hinge in Moenkopi Fm

MC ejecta morphology

Idealized Meteor Crater ejecta morphology. Erosion has exposed the Moenkopi fold hinge. Image by David A. Kring.

Originally horizontal beds were uplifted during impact and now dip away from the crater. In the center of the above image, the Moqui member – the surface unit at the time – takes a sharp turn and winds up parallel to the crater wall. This is an exposed portion of a fold hinge, where a flap of target material was overturned to create an inverted stratigraphic sequence (see diagram).

There’s so much more to see at the crater. Sand fields, tear faults, shocked quartz…and we’re still just getting started!

So an igneous petrologist walks into Indiana…

…and says, “Hey, wait just a minute…”
It’s not a funny joke, or even a joke, really. It’s a thought that crosses my mind every now and again: What am I doing in the Midwest? I’m a hard rock geologist. Give me volcanoes and basalts, faults and structures…heck, I’d even settle for a roadcut. On a field trip to Michigan’s Upper Peninsula we didn’t see an outcrop until hour six. There is, however, plenty of this:

digging into shore of glacial lake Warren (NY)

Make your own GD roadcut.

At first you might think that’s soil…and you’d be correct, but that’s not what we were digging for. Beneath that veneer of Quaternary flim-flam is the edge of a glacial lake. That was in New York, but northern Indiana is rife with unconsolidated glacial deposits. In some areas you’ll dig 500 feet and still be scraping glacial drift off of your shovel. But maybe you’re persistent. Surely, you think, it all pays off when you hit bedrock. Could be, if you’re a fan of gray rocks…

Maybe you like nice big gray chunks of steadily accumulated, neatly bedded shale? Or how about some nice gray fossil corals in gray dolostone? Under the gray permacloud, of course.

Whoop-dee-freaking-doo.

Or, at least, that was my initial self-important, half-serious reaction. I know of many important, interesting, varied and difficult facets of sedimentary geology. Those two gray photos are from a summer research project to constrain an extinction boundary (primarily in NY). To get that internship, I had to submit an application. Get letters of recommendation. Say to myself, “Yes, I want to spend my time looking at black microfossils in black shale collected from cold black streams and battered core tubes. Give me a summer of that.” And in the end, a summer was enough and a bag of chips. It ended up as a way to narrow potential fields of study. Igneous petrology was my primary interest before and after that project, but at least afterward I could say I had tried something different.

The problem with Indiana was that it was too similar to New York in all the wrong ways. The bedrock geology spans over 150 million years from the Mississippian back to Ordovician time, but look at the dominant lithology (youngest to oldest): limestone, shale, sandstone, siltstone, shale, shale, dolomite, limestone, limestone, dolomite, and finally shale and limestone. I had such a bias against Indiana that none of these pictures are actually from the Hoosier state. And maybe that’s the problem: I haven’t tried it. Until recently, I hadn’t even researched Indiana geology, and what I found shouldn’t have surprised me. Turns out Indiana actually has some interesting geology for work and play, and most of it’s not more than four hours away: sand dunes, geodes, caves, impact craters..wait, what?

Kentland structure. Click to visit interactive USGS Indiana geology map

Yeah, there’s this anomalous bulls-eye on a map of Indiana’s bedrock geology. A puncture wound in the Mississippian-age siltstone of west-central Indiana, the Kentland impact structure. It left an ~8 mile diameter wide dome-like structure, bringing Ordovician dolomite to the surface where it remains exposed today. That’s pretty cool.

So there are no ancient volcanoes here. No columnar basalts or peridotite. It’s not paradise, but you’re all right in my book, Indiana.

Additional Info:

Indiana Geological Survey; maps of bedrock and surficial geology, and more.

Roadside Geology of Indiana, Mountain Press Publishing; where I first read about the Kentland crater.

McRocks reports of geode/mineral/rock collecting expeditions

Indiana Dunes National Lakeshore, National Park Service

500km from Sudbury

Impact craters are ubiquitous features on solid bodies in the solar system, but on Earth they’re rather annoyingly quickly eroded. The impact crater at Sudbury, Ontario is 1.85 Byr old with an initial diameter of between 150 and 260 kilometers. Sudbury remains an oblong scar on the Canadian shield, but little remains (or has been discovered/identified) of the ejecta. A recent paper by Cannon, et al. (2010) identified several localities of ejecta deposition in Michigan.

I had the opportunity in the Spring and Fall of 2011 to participate in a field trip to the Marquette area of Michigan, where there was supposed to be 40m of impact breccia in what the authors designate the McClure locality.

Google Earth mapWell I would walk 500 kilometers…

Estimates of crater ejecta distribution rely on a limited dataset of “small” nuclear explosions, a couple well-preserved terrestrial craters (Ries, Barringer Meteorite, Lonar, etc), and observations of lunar craters. Ejecta thickness is seen to decay following a power law where thickness t = 0.14 * (R^0.74) * [(r/R)^-3], where R = distance from crater center to site, and r = primary or transient crater radius. Using appropriate values here (R = 500km; r = 100km) gives a calculated ejecta thickness of ~30m at the Marquette area, a surprisingly spot on result.

But don’t get too bogged down by wishes and estimates and dry writing. The Sudbury impact didn’t deposit 40 meters of ejecta at this sole locality. Everywhere, in all directions at over 500 kilometers away would have been inundated with enough material to bury a ten story building!

Our first trip out in Spring 2011 had temporary success. We searched the area for a good hour or so, and our colleagues from Northwestern University eventually drove a bit further down the road and found a small outcrop. Hooray! Unfortunately, it was in an open pit of someone’s ongoing basement construction. Despite some fast talking by professors, the group was swiftly kicked out. A bit disheartened and rather hungry, we gave up for the trip and decided to look at a map before heading out on our next trip. At GSA we talked to THE ejecta guy, the one who found the outcrop and has published several papers on samples collected therefrom. Turns out we turned left where we should have gone right…

In October we returned and had almost immediate success!

Lots of big cherty bits in there! Click to view larger in Picasa album from the trip.

This was the first convincing piece of ejecta I found, and afterward I was too excited hunting around to take more photos. We returned the next day and found a nice – but highly weathered – continuous cropping out of ~4 meters of ejecta (still no photos), but we couldn’t find the upper or lower contacts or clear-cut glassy lapilli (supposedly concentrated near the lower contact). Close to the crater, high volumes of ejected material essentially buries the surrounding terrain. Distal (far away) ejecta has less volume but higher energy, and so it interacts with the surface more during deposition and incorporates more local terrain. I believe starting at ~2.5 crater radii from the impact, local material starts to make up the majority of the “impact” layer. Although the exact transition distance is fuzzy, at ~5 crater radii at Marquette we would certainly expect extensive incorporation of locally derived material. The impact layer at the McClure locality is supposed to lie directly over a banded iron formation, though there’s also a chert layer down there. I almost forgot to sample the site and had to grab a quick couple of samples on the way out:

Ejecta boulder, ~25x15x8 cm.  Centimeter scale.

Cut face. Larger clasts appear to be predominantly locally-derived chert

To access to the locality we sampled, turn right off of County Road 510 and park on the side of the road leading to the old bridge (no longer in service). The field photo was taken in the woods to the east of the road, where there are several large boulders and some really nice, smaller outcrops. The main outcrop (and where my sample was taken) is located near the arrow in the map below. I am not sure if the land is privately owned, so be courteous if you visit. In looking closer at the Cannon paper, it appears we weren’t at the exact McClure area, which they place at 46°33′N, 87°33′W (GMap link). Maybe we’ll try to check that out next fall. This was our sampled area:

References:

W. F. Cannon, K. J. Schulz, J. Wright Horton Jr., and D. A. Kring (2010) The Sudbury impact layer in the Paleoproterozoic iron ranges of northern Michigan, USA. GSA Bulletin, v. 122, pp. 50-75; doi:10.1130/B26517.1

F. Hörz, R. Ostertag, and D. A. Rainey (1983) Bunte breccia of the Ries: Continuous deposits of large impact craters. Reviews of Geophysics and Space Physics, v. 21, pp. 1667-1725.

T. R. McGetchin, M. Settle, and J. W. Head (1973) Radial thickness variation in impact crater ejecta: Implications for lunar basin deposits. Earth and Planetary Science Letters, v. 20, pp. 226-236.

Warren Dunes, briefly

In July my friend visited Notre Dame to run in the Sunburst (Half-)Marathon, and while he was around we took a trip to Warren Dunes State Park. Dunes occur over a broad area in the eastern shore of Lake Michigan (Sleeping Bear, Silver Lake, Cowles Bog, etc.), with Warren Dunes being one of the largest and most popular southernmost parks.

Peak ridge of a sand dune

This was my second trip to a sand dune field (my first was nearby Cowles Bog), and I’m consistently surprised by the variety of environments in such a small area. Some near-shore areas are almost all sand:

People scrambling up, also note group of three on horizon at right

But a few hundred meters down the shore, heavily vegetated sand dunes appear to be securely anchored in place:

Of course, looks can be deceiving and a closer inspection revealed exposed roots in some areas – a result of dune migration, or just short-term erosion?

Other than a few birds, trace fossils, and a heck of a lot of mosquitoes in the boggy inland area, there wasn’t much visible life on the dunes. That is, until we saw this guy (he was hard to miss)

The mosquitoes were so bad that we took the first opportunity we came across to get out of the bog and back into dune territory. Unfortunately, it turned out to be a steep face of a sand dune. We had to take a few breaks on the way to the top…

Here I used photo-documentation as an excuse to pause.

It was so steep that in some areas, even though he was so far away his footsteps would cause sand near me to collapse. My best estimate from maps of the area are that it was ~70 ft to the top, with this photo being taken ~halfway up. We did a quick 4 mile hike around the park to see some highlights, but I’m looking forward to a return trip next summer to learn a bit more about the area and spend some time on the beach.