New to the GIS map: Aeromagnetic & Gravity Anomaly map layers highlighting the Midcontinent Rift (among other things).

Recently, two layers were added to the Wisco Geology GIS map:

•  Aeromagnetic: This map layer is a composite made from aeromagnetic surveys in Wisconsin.  Maps like this are used for mineral exploration.  Source: USGS and others.

• Bouguer Gravity Anomaly: This map layer shows where variations in gravity occur due to changes in rock type, density or thickness.  Source: USGS and others.

The most striking feature of both layers--but especially the gravity anomaly map layer--is the swath of red color in western Wisconsin extending into Minnesota and Iowa. This area was flooded by huge amounts of lava about a billion years ago as the continent started to split and pull apart. Today, this is called the "Midcontinent Rift". The lava cooled to form basalt within the rift zone.  The basalt here could be many miles thick and it is generally more dense than the surrounding rock types. For these reasons, the gravity anomaly map layer shows the rift as an intense "gravity high" zone.

Aeromagnetic and gravity surveys became more extensive in the 1940s as remote sensing technologies were developed. Before this time, the existence of the Midcontinent Rift was not known. Geologists were aware of igneous rock outcrops including basalt at places like Big Manitou Falls and at the Dalles of the St. Croix River / Interstate Park, but the full extent and cause of these igneous rock formations were not understood until the 1960s when plate tectonics became more well understood and geologic mapping became more complete across the globe.

The Midcontinent Rift system shut down before the continent was torn completely apart.  If rifting had continued here, the geology of this area might have resembled the Great Rift Valley of Africa and would have eventually filled with sea water to form something like the Red Sea. You can see that Lake Superior sits within the rift zone. Most people believe the Great Lakes were formed by glaciers, and is largely true, but the underlying rift influenced the formation of Lake Superior. You can read more about it in this article by geologist Dr. John C. Green of the University of Minnesota-Duluth.

Click here to check out the Wisconsin Geology GIS map.  Once in, turn on the Aeromagnetic and Gravity Anomaly layers (these are both near the bottom of the layer list to the right of the map).

Note:  I georeferenced existing maps to add these to the Wisco geology app. If you study geology, you have probably seen these maps before.  What's interesting about viewing these in the Wisconsin Geology GIS app is that as overlays, you can view these in context with the other map layers such as outcrops.

Meet up with a 2.8 billion year old from Wisconsin

Looking to meet up with a 2.8 billion year old?

We found your match.

Your can turn the GIS app into an online dating site (albeit for seniors) by doing the following:

1.  Click here to open the Wisconsin Geology GIS map
2. Click the  "Filter" button near the upper right of the map, then toggle on the "Age Dated" filter. 

 

 

The mapped outcrops will then show only those that have been dated.  Click on those outcrops for a profile of each.

The oldest rock outcrops in Wisconsin are found in the central part of the state.  Just east of Marshfield, a gneiss outcrop has been dated around 2800 - 3000 million years old by a geologist named W. Randall Van Schmus.  Randy gets around and has dated a LOT of rocks around the country.

You'll see several outcrops dated by Van Schmus along the Black River in Clark and Jackson Counties, specifically near the Arbutus Dam.   You'll find rock outcrops older than 2000 million (2 billion) years old along the Wisconsin River in Wood and Portage Counties as well.  These are of course mapped on the Wisconsin Geology GIS app.  Love begins here (opens the GIS map).

Extraterrestrial Impact Craters in Wisconsin

Incoming asteroid!   This nightmare scenario has inspired plenty of bad movies, but the reality of these events is supported by lots of good science. It has happened many times before:  Indeed, Earth is whacked by space rocks from time to time, and the big chunks have significantly impacted the planet while making an abrupt stop here.

The Earth Impact Database lists 190 confirmed impact structures on Earth.  Two of these are located in Wisconsin, and of course the Wisconsin Geology GIS app has them mapped! Read on to find out more about each, and where to look for the geological version of ET.

The "Rock Elm Disturbance"
An asteroid perhaps 600 feet in diameter smacked into what is now eastern Pierce County Wisconsin somewhere between 450 and 500 million years ago, piercing through hundreds of feet of bedrock and leaving a crater nearly 4 miles in diameter in its wake.  The crater has been nearly erased over time by geological deposition and erosion. It is still faintly discernible on the Wisconsin Geology GIS map:  Click here to zoom to the location of the crater,  then study the "hillshade" effect closely.  See it?  Look in the area that is today between County Road CC on the west, County Road HH on the south, County Road S on the east, and 570th Ave on the north. Within a roughly circular area, the drainage pattern is different within the crater than it is in the surrounding area. Drainage and erosion appear to have been influenced by the underlying crater. Some geologists believe this impact was just one of many that rocked the Earth during the Middle Ordovician Period. Several other possible impact craters of perhaps the same age are being studied in Oklahoma, Iowa, and in Lake Superior.

On the GIS map, a red X marks the approximate center of the impact structure (the central uplift) and there is an orange outcrop identified on the south rim where today the Rock Elm and Plum Creeks exit the impacted area.

Cross section of the rock strata in the area of the Rock Elm Disturbance.
Brown, B.A. WGNHS Survey Map 88-7

Topographic relief map of the Rock Elm impact site. Click to enlarge.

The Rock Elm Disturbance was first recognized in the 1940s by geological mapping of the bedrock of western Wisconsin.  Right in the midst of generally horizontal sedimentary strata, something had clearly 'disturbed' the rock layers in this area (hence the name) although at the time it was unclear to stratigraphers and other geologists just what exactly caused this unique geology.

Over the years, the existence of impact structures became more widely recognized in science.  Stratigraphers were not the only geologists involved in identifying impacts like this one.  Minerologists also got into the game.  For example, a mineral called reidite was found in the Rock Elm crater.  Reidite forms under very high pressure and has been found in nature in only 4 other locations on Earth, all within other known impact structures.   Gold, which is also sometimes associated with impact events, has been found in the beds of the streams flowing south out of the Rock Elm crater.  Gold, you say?  If I just distracted you with shiny golden objects, check out a blog article about gold panning in this area---yes, there is public land in and near the impact site.  Here is a very good video by Dr. William Cordua, a geologist who has studied this impact structure in detail. Additional references are linked below, and you can bring up more by doing a Google search on the "Rock Elm Disturbance".  The story is shaping up to be better than any Hollywood movie.
Update:  See also this interactive GIS map:   https://geologyinsight.maps.arcgis.com/apps/webappviewer/index.html?id=09ed828f4c8340419f4c93eb2aa447bd

Glover Bluff
Another impact structure is located in northwestern Marquette County Wisconsin (click here to view the location on the Wisconsin Geology GIS map).  This crater is between 1 and 5 miles in diameter. It is more difficult to recognize on the surface because it is mostly buried under the thick moraines of Wisconsinan glaciation. Quarrying activity has uncovered enough evidence of an impact to make this a 'confirmed' crater.  Fractured bedrock (including shatter cones) and impact breccia surround a central uplift, all telltale signs of a significant extraterrestrial impact. If you visit the area, please keep in mind this area is mostly private land--don't trespass!  Bruce Willis didn't save this area from the asteroid, and he won't save you from the wrath of the locals, either.

Meteoric fall
Smaller chunks--meteors--punch through the atmosphere and land without forming a crater. Once firmly planted on Earth, the meteors become meteorites. Lots of folks run around looking for meteorites--they are valuable and can be sold for more than a few hundred quids.  When Earth-born rocks are mistaken for meteorites, geologists have a solemn duty to inform the stone bearer of the meteorwrong.  There have been some famous meteorite discoveries in Wisconsin, however.  Near West Bend in Washington County, several metallic meteorites have been found--the largest pieces weighed over 400 pounds!  These so-called "Trenton Meteorites" are rather famous among the meteorite hunters.  A meteorite found near Algoma in 1887 is today located in the University of Wisconsin Geology Museum.

Go to the Wisconsin Geology GIS app for more.  Remember you can search the map:  Search terms like "meteor" or "crater" to bring you to known locations of such objects in Wisconsin.

References:

• Earth Impact Database (website), Planetary and Space Science Centre
  University of New Brunswick
• The Rock Elm Disturbance (web page),  Wisconsin Geological & Natural History Survey
• Rare Mineral Found in a Wisconsin Crater, Astrobiology Magazine, 2015
• Trenton Meteorites, Mindat.org

Gold in them thar Wisconsin hills?

I'll strike up a conversation about geology with anyone who is interested.  Often, this conversation turns to gold.  Literally.  When people think "geology" they often want to talk about the most malleable metallic mineral.

Wisconsin is not known for it's gold mines.  Unlike the San Francisco 49ers, our football team's gold color is more reflective of cheese than of the metal.

Yet, one could  point to places in Wisconsin and say indeed, there is  gold in them thar hills!

How much gold, you ask?  Well, one mine in Rusk County Wisconsin produced 334,000 ounces of gold in 5 years (1993 - 1997), not to mention 3.3 million ounces of silver, plus copper to boot.  Reading this, you might be licking your pickaxe while singing "Silver and Gold" along with Yukon Cornelius while you book a trip to Wisco.

But wait, there's more.  Significant gold deposits have  been reported in Ashland and Marathon Counties as well.  Some deposits have names:  There is the "Northern Belle Mine" and the "Chicago Mine" between Drummond and Mellen in northern Wisconsin;  The "Reef Deposit" east of Wausau;  and the "Lynn Deposit" in Oneida County.    Of course, the gold in these deposits is not easily recovered.  These are "massive sulfide" deposits that would require expensive recovery operations.  Not to mention, the permitting process would be a nightmare and you'd face opposition from groups concerned about potential water pollution from this type of mine.  Want an example?  All of this is currently playing out with the "Back Forty" gold/copper mine just across Wisconsin's border in the U.P. of Michigan.

OK, so maybe you don't want to mine for gold using new-fangled technology or deal with modern-day politics, you just want to find gold the old-fashioned way: Panning.  There is hope.  Yes, you can pan for gold in Wisconsin and you might even find a little (just don't give up your day job and be sure to follow the rules).  One of the best sites to pan for gold in Wisconsin is at  Nugget Lake Park along Plum Creek in Pierce County.  The gold here may be associated with an impact crater known as the "Rock Elm Disturbance" formed during the Middle Ordovician Period somewhere between 430 and 455 million years ago. More on this crater in future blog posts.  Let's get back to the gold! 

So where does "X mark the spot"?  Right here on this blog, you'll find a treasure map:  Find gold on the Wisconsin Geology GIS web map by clicking here and then typing "Gold" into the search box in the upper left of the map.  You'll see a list of results; Clicking each result will bring you to the location in Wisconsin where gold may be found, including the examples given above.  Further, you have technology the old-timers could have only dreamed of:  The mapped locations include a popup with a link and Google Map directions.  Using our very own app, your smart phone will lead you right to paydirt!  You will be richly rewarded, though probably not in gold or other monetary form--your reward will most likely come from experiencing Wisconsin's great outdoors.  All that glitters is gold....in the form of Wisconsin's 15,000 sun-splashed lakes or the many other brilliant rocks and minerals you can find here. That's gold, Jerry!  Gold!

References:

• Wisconsin Department of Natural Resources (WiDNR), "Reclaimed Flambeau Mine" (web page) 
• Oneida County web site, the Lynn Deposit (web page).
• Aquila Resources, "Back Forty" mine web site 
• Wisconsin Geological & Natural History Survey (WGNHS) web site, minerals > gold page.

Welcome! A first post on why this blog exists, what it's about, who it's for, and where it's going.

Hi there and welcome!  I feel the need to write a short introduction before digging deeper into Wisconsin's geology.

Why did I create this blog?

I've had a lifelong fascination with Earth history, but I don't want to simply read about it -- I love to go  outdoors to see, touch, smell, and taste the Earth around me to see the evidence myself.  Also,  I like to map and document what I have seen, or hope to see in the future, and to try piece the evidence of the Earth's story together on my own.

And I happen to be living in Wisconsin.

Hence, this blog. And this app.

What's your reason for reading this? 

Most people are intrinsically interested about the Earth. As children, we examined rocks and wondered why they look the way they do.  Some are pretty. Some have interesting shapes.  Perhaps we visited state or national parks -- these are most always located near natural or geologic wonder.

As kids, we were given introductory lessons in Earth Science in school. Possibly, if we had a good teacher who really understood the subject and made it interesting, we learned something fascinating about the Earth.   Or, perhaps those early lessons didn't sink in.  Maybe we were distracted by other things (by adolescence, everyone is!).  Maybe we remained enthusiastic about Earth science, but by high school it just "wasn't cool" enough or "profitable enough" to take your studies in it further. 

Or perhaps you followed your passion for Earth science and became a geologist or related professional. Great!  I hope you continue reading too.  This project may not be for the professional geologist, but I hope even you find it useful.

Where is this going? 

I'm going to use this blog (and it's companion GIS mapping app) to dig deeper into Wisconsin's deep past.  My goal is to learn a lot myself as we go.   I hold a degree in this subject matter and I read as much as I can about it; However, I don't hold a PhD and I am not necessarily an expert in all of the topics this blog will explore.

 I hope you use this blog and the GIS mapping app as a guide to explore on your own.  If you are in Wisconsin, be sure to go outdoors!  I'll wrap up this post with one of my favorite quotes on geology:

"The best geologist is the one who has seen the most rocks".  Herbert Harold Read.