cc >> Tom Zinnen: Welcome,
everyone, to Wednesday
I'm Tom Zinnen. I work Nite at the Lab.
Biotechnology Center. I also work for UW Extension
Cooperative Extension, and on behalf of those folks and our
other sponsors, Wisconsin Public
Association, and the Science Television, Wisconsin Alumni
Wednesday Nite at the Lab. Alliance, thanks for coming to
night, 50 times a year. Tonight, We do this every Wednesday
introduce to you Eric Carson. He's a fluvial geomorphologist
with the Wisconsin Geological and Natural History Survey, and
he's an assistant professor in
Environmental Sciences. His thcurrent research interestsof
include Quaternary landscape
near forming glaciers, uh-oh, dnear former glacier margins in
the upper Midwest and intermontane west.
I take that to mean he studies
the drew back. >> Exactly.iers
The impacts of post-glacial climate change and historic land
use on sediment mobility, flood behavior, and land from genesis.
And applications of Quaternary
record of North American geochronology to the glacial
here. He received mid-conhis BS from West right
Virginia University in 1996, his
in 1998 and 2003, respectively, and was a lecturing professor at
San Jacinto College in Houston, Texas, from 2003 to 2008.
Please join me in welcoming Eric
[APPLAUSE] >> Eric to Wednesday Nite at the Lab.
Thank you all for showing up. I appreciate the turn out and
the opportunity to talk about some of the research that I'm
doing here at the Wisconsin Geological Survey.
I was hired at the survey four
summer of 2008, and the Wisconsin Geological Survey has
had a long record of Earth
relating to the glaciers, relating to the glacial record
of Wisconsin, which certainly isn't surprising given the
extensive record here, but
with having people with an haven't had much of a record
the state. And so when interest in streams working in
was that I would be turned loose I was hired the idea
the state, the driftless area, in the southwestern corner of
glaciers and allowed to do my own thing and study the geologic
processes there. So as a
to think of Wisconsin looking something like this rather than
the way we see it today. [LAUGHTER]
I'll wait and see if we can get a pointer instead of just an
hour glass symbol there. Okay,
is if we go back in time, maybe 18,000-20,000 years ago, this is
the image of what Wisconsin would have looked like.
It was covered by the southern
Sheet. So the ice margisheet that coverede Ice
all of modern Canada and
United States came down, and extended down into northern
Midwest and into Wisconsin, it as it came down into the upper
and partitions. And diacross Wisconsin, you canbes
see they're labeled here, the Superior, Chippewa, Wisconsin
Valley lobes, and then down in
the Green Bay lobe and our neck of the state, we have
And the Green Bay lobe you can the Lake Michigan lobe.
into the area of the Baraboo see extended right down here
west of Madison. You can Hills and down to just south and
up Glacial Lake Wisconsin. But also see that it dammed
large area here in the then you can also see this
and this is the driftless area. soutNow, if we pull away thete,
glaciers and look at things as
itself still stands out pretty it is today, the driftless area
the landforms that clearly, pretty distinctly in
If we look at it, you can still see the effects of the last
glacial cycle on the landscape. So here's the margin and behind
it the landscape is entirely
processes that have gone on. derived from the glacial
area, it's primarily stream Whincision that's happened.ess
Now, in the previous slide we saw what the last glacial cycle
looked like with ice coming down
from the northeast, but during primarily from the north and
the last 2.5 million years or tso, there have been numerous
cycles of glaciations. And
driftless area stands out in the so during this time this
escaped glaciation entirely.
We will restart later.. . [INAUDIBLE]
Okay, so we see a landscape that's very distinct
in the upper Midwest. We have upland surfaces that are
covered by a thick mantel of
during the glacial cycles. wind-blown silt that's blown in
River Valley that's incised We several hundred feet.sin
This is taken from Ferry Bluff
about 250 feet, I believe, from where this photo was taken down
to the river. And then
Wisconsin River Valley, the valley itself was actually dug
out another 200-300 feet down and has filled up with sediment.
You can see the nude beach
If you want to look that in the distance there.
[LAUGHTER] And in wbetween these upland.
surfaces and the deeply incised Lower Wisconsin River
Valley, we have a landscape that
not seen anywhere has a else in the Midwest.that's
And so if we sort of take a step
a whole, we can see how this back and look at the Midwest as
to be when we look at the record area came to be and why it came
So on here we have the three of Quaternary glaciations.
that have occurred during majothe Quaternary period.ons
So in the gray area here in Iowa
what we refer to as the dopre-Illinoian glaciation.ve
This was a cycle of glaciations that occurred starting about
2.5 million years ago and extending to about 500,000 years
ago. Primarily, that
in western Canada and flowed ice was centered
northwest into the down from the north and the
Then from a period of about 300,000 years ago to 130,000
years ago we had what was referred to as the Illinoian
glaciation. So these
gold, and there's our pointer. deposits are shown in
and clearly derive their name from being well expressed in the
state of Illinois and bound to
here on the south the dand the southeast. down
And then most recently we have
glaciation. So this the Wisis the entire areasconsin
that's shaded in green. And this was an ice cap that was
centered more in central Canada over towards the Hudson Bay
more. So the ice was
down from the north and the northeast into the region.
And so when we see this, we see that the driftless is this one
spot that stands out that was never surrounded by ice all at
one time but at the different time periods, it has been
surrounded and it is the one
by ice. Okay, if we area thalook back at the covered
topographic map, what I'm going to do here is highlight the two
areas where I've been primarily working since I've started at
the Wisconsin Geological Survey,
I'm going to be talking about. and these are the two areas that
some work here in Grant County. So the southwestern most county
in the state. This is the area where the
pre-Illinoian, or oldest, glaciations have budded against
the driftless area. So I'll talk about some of the
work that has been teasing out
distribution of those deposits. And then back here closer to
home in Madison, right along
margin, work that I've been doing pinning down the exact
timing of the glacial record. Okay, so let's start down in
Grant County. So up in
have a DM of the county. the left corner here we
here, the Mississippi River flowing along here, and the area
that's covering the majority of the slide is highlighted here in
gold. I guess it's
years ago now my PhD adviser, Jim Knox, was doing some work
down in this area, put in a core
of Glen Haven. That core hole right here above the town
high bluffs, so right at the location is up on the
Mississippi River. Much veryof the landscape here is the
buried by wind-blown silt. So there's 15, 20, 25, as much
as 30 feet of wind-blown
When Jim put in this core, he found, I think my recollection
is, right around 28 feet of this wind-blown silt on top the
bedrock. And then right down at the base
right before he hit bedrock, he hit about two feet worth very
dense, dark gray clay that had
found in the bedrock flecks of minerals that aren't
And what he interpreted this around here.
glacial advances. That is as one of the pre-Illinoian
from one of these pre-Illinoian advances that was coming in from
the west from Iowa and Minnesota
modern bluffs above the and actMississippi River.nto the
Not surprisingly, he wasn't able to find it in any other
locations. Partially
the fact that back in the '80s this has to do with
didn't give him the ability thto core many locations veryhad
effectively and partly because
deposit that may be a half if we're thinking of a glacial
there's probably not a very miextensive record of it left.,
Probably most of it has been eroded away.
So it might have been just good fortune on his part that he
found that deposit in that one location.
Now, when I showed up and began working, I had access to a
quicker, more portable coring mechanism, and so in the past
two years I've put in a whole series or cores here trying to
find more of this same deposit. And to give you an idea of how
patchy this material can be,
He calls this his Adrian site because the Adrian family owns
the land. The first core I put in was
within a hundred feet of where his core was.
And when I put the core in, it
wasn't any tilling in my coring location a hundred feet away.e
So sort of an idea of how patchy
So I put in maybe two dozen, this old material could be.
What you can see here is a very limited area right along the
bluff where I found several additional cores that had this
old till right at the base. So
that we do have the presence it's a really good indication
Like I said, the fact that there of ice up on this surface.
locations that there was no artill, the fact that we'reare
finding those intermixed, like I
because the age of this till. sOne of the other interesting
things that I found in the
two locations that are shown in cgold, and rather than findinge
till, what I found in those two locations was thick
accumulations of
And that's exactly the kind of sand and gravel.
right in front of a glacier. thing that you typically see out
landscape position, in this part Glaciers that are in this
the geologic history tend to of the world, in this time in
their margin flushing a lot of have a lot flowing around at
and carrying a lot of sediment, and a lot of that is sand andm
gravel, that this outwashes,
And it was in some ways unsurprising but in some ways
very gratifying to be able to find it in these two locations,
further evidence of this glacial advance.
So it gives us an idea that we
coming up. Now, the had iMississippi River atcape
this time probably was not
probably in somewhat a similar incised as deeply as it is now,
have the good evidence of ice coming across what is today thel
Mississippi and occupying just
outwash coming out. Now, barely into Wisconsin with
additional work in the driftless when we compare this to
only pre-Illinoian deposit that we can find in Grant County and
in western Wisconsin. So
going to be the margin of the glacial deposits that I
identified. There are also additional
deposits right here in the mouth
These are referred to as of the Mississippi River.
These were identified by Jim the Bridgeport Deposits.
and John Attig in my office. Knox in the geography department
advance. In the case It is also a pre-Illinoian ice
I've done, if I can get my of the coring that
done in this area, the fact that pointer, the coring that I've
are pretty much demonstrated by the fact that they're covered by
this thick accumulation of
of silt that dates well back wind-blown silt, 25 or 30 feet
So that's what demonstrates the age of these deposits.
In the case of the Bridgeport deposits here in the mouth of
the Mississippi, there is additional information that
gives us a little bit better chronologic control.
So this is a cross-section
River. So looking lookfrom as far west asnsin
about Sauk City, Wisconsin, right near the Baraboo Hills all
the way down to the mouth of the
Chien. So we see a Wisconsin River at Prairie du
surfaces here. This the bedrock surface of the
Wisconsin Valley that's buried
and gravel. And we'll by seveonce again restartf sand
later. [LAUGHTER]
We have the modern river surface
and then a series of terraces, shown here in the solid line
So surfaces built up of this a series of outwash terraces.
out of glaciers. So this sand and gravel that gets washed
ice that was at the Baraboo Hills carrying sand and gravel
down the Wisconsin River Valley and producing these terraces
that are mirror images to the modern river topography, just
higher surfaces. But
also have these thBridgeport deposits.we
In the mouth of the river,
There's a topographic landform there is an actual moraine.
for glacial deposits which is exceedingly uncommon
There is a terrace associated with it, and there is outwash
deposits associated with it, and
these ones that are associated they actually, you notice that
downward to the west. So with the modern river grade
the direction that the they're grading downward in
This Bridgeport deposit grades water is flowing.
It grades downward to the east. So right here is the Bridgeport
terrace, grades down to the east, and what this tells us is
that when ice was at this Bridgeport moraine location it
was coming from the west, coming
was completely blocking the mouth of the Wisconsin River.d
And, in fact, it was completely reversing the flow of the river.
And during this time, the river was flowing back to the east
back here towards the Madison/Sauk City area and in
some unknown direction flowing
Mississippi or perhaps flowing off by another root into the
It's demonstrated by both the slope of the terrace and also
the structure of the sediments
they were deposited by within the terrace tell us that
As far as age control on this, water flowing to the east.
paleomagnetic measurements Jim Knox and John Attig took
So they measured the magnetism from the sediment.
that was preserved in the sediments, and they have what we
refer to as a reverse polarity. So these were deposited, these
sediments were deposited prior
Earth's magnetic field reversed. to the last time that the
ago. So these deposits of thes
Bridgeport moraine and
greater than 790,000 years ago. In order to have a soft sediment
landform like this Bridgeport moraine still expressed on the
Earth's surface is actually pretty intriguing to us.
What this tells us is we
pre-Illinoian ice up against the had multiple advances of
Wisconsin. We have western margin of modern day
evidence that those two deposits, the deposits from my
coring up on the bluffs and the deposits from the Bridgeport
moraine, almost certainly were not the same age.
They were probably two
pre-Illinoian ice advances. But what we're seeing is at
multiple times we had ice coming
margin of the driftless area. Now, if we move to the opposite
end of things, if we move to the
right here in the Madison/Sauk east edge of the driftless area
up against the most City/Brecent ice margin. we're
We're up against the late Wisconsin ice margin.
And this is an area that's
the landforms are much more ipresent on the landscape so it
should be a much easier proposition to tackle.
It's also intriguing to us
the Wisconsin deposits are the because despite the fact that
age control on the exact most recent, we have very poor
I told you at the beginning that timing of events.
general, something less than the Wisconsin deposits are, in
geologists have a ballpark 30,000 years old, and we as
the late Wisconsin glaciation, understanding of the timing of
understanding of it. And but we don't have a very refined
considering that the history of studying glacial deposits here
in Wisconsin goes well back into the 19th century with TC
Chamberlin and Charles Van
And there's some very Hisegood reasons for it.ity.
This quote up here is from a
glacial deposits of Wisconsin. recent survey publication of the
Colgan, and what they know is that the late Wisconsin maximum,
the timing of exactly when the
constrained in Wisconsin because ice was fluctuating isn't
during that time period. And there isn't organic material
is important because radiocarbon organic material, of course,
has been our bread and butter tool for producing chronologic
control, for developing chronologic control.
And so in Wisconsin there simply hasn't been found any
significant amount of organic material during this huge window
that spans the peak of the
Now, we can look at this in the larger picture if we look at the
radiocarbon data
So this is from a publication that Lee Clayton from our office
put together back in 2001.
he's gone through the published literature and he's pulled out
all the radiocarbon ages from large wood.
That's important because having large organic material gives us
some context to where it was deposited.
And he's plotted it up with age on the vertical axis.
So going from 12,000 to 15,000
years ago. And then on years ago back to over 35,000
he's plotted it in its the horizontal axis
So here's the Illinois/Wisconsin position from north to south.
off to the right, Wisconsin stextending up to the left.ing
And as we move forward in time
what we see is that the northern from, say, 35,000 years ago,
receding. It recedes limit of organic material keeps
south until a peak farther and farther
And then this front of organic somewhere in the mid '20s.
again. Now, the obvious material interpretationng north
of this is that this is a reflection of the climate
changing and the ice advancing
the landscape begins to get covered with ice, clearly you're
not going to have organic material, certainly in the areas
that are covered by ice but also there's going to be an
additional fringe of land that
much vegetation growth. We isn't going to be supporting
evidence that during the late Wisconsin maximum here in the
upper Midwest there were
So the ground was permanently pefrozen year-round.s.
So this is a kind of condition
organic material to be growing. So this makes good intuitive
sense to us but it's problematic
understand the exact timing of because it crimps our ability to
were occurring. Beyond when the glacier fluctuations
issues with using radiocarbon dating in glacial environments.
Not only in the upper Midwest with the southern Laurentide Ice
Sheet margin but in many of the former ice sheet margins, the
permafrost conditions limit the amount of material you're going
to have. So there very often isn't a
whole lot of radiocarbon
extends back to the matemaximum ice conditions. that
In the cases that we do find
margins in glacial settings, organic material close to ice
with interpreting the ages. thThe first of them is that ans
glacial environment, a glacial
the landscape, having sediments ladeposited by the ice and byon
water in front of the landscape,
of setting. There's a this lot of water, a lot of kind
very saturated sediments, a lot of mobility of sediments and
mobility of the landscapes in whole.
There are a couple cases where
document how long glacial landscapes tend to be mobile
after the glaciers recede, and
there is cases where it's been in the published literature
has been mobile for hundreds to das much as 2,000-3,000 years
after the ice retreated away. Now, this is important to us
because what we as geologists are interested in is the time of
landform deposition because that's when the glacial action
is occurring. What the
what the radiocarbon dates are organic material and
landform stabilization. And able so if we have a lag ofng of
hundreds to thousands of years
crimp our ability betweto use radiocarbon.ing to
The final one is because we have
landscapes, because we have a spatial lag, often, betweenf
where we find radiocarbon material and where the ice
margin was, it's very rare that we have cases that we find
organic material that we can
positions. So we correlate to exact ice margin
geomorphology, from the landscape and the landforms that
are posited, we can tell where
the ability to pin down an exact the ice was we just don't have
What this leads to is sort of some circuitous routes, I guess.
is what you'd say for coming
margins were fluctuating. One of the very typical ways ofe
dealing with these issues of
environments is try to radiocarbon dates in glacial
mass. So if radiocarbon accumulatedates can'tse them in
tell us exactly where an ice
tell us when a specific location margin was, at least they can
And a great example of that is was covered or uncovered by ice.
up in east central Wisconsin, thup just north of Sheboygan.t's
So this is within the geology community, within the
geomorphology and certainly radiocarbon community, this is a
very significant site. This is actually one of the very
first sites that was dated
Two Creek forest bed is a location up in Sheboygan.
It was well behind the ice
maximum, so the location was margin when ice was at its
glacial maximum, ice was melting buried by ice, and following the
far enough to expose the back and eventually melted back
from ice. And after Sheboyit was exposed, aver it
spruce forest grew
And once this spruce forest had grown to maturation and was a
fully grown forest, the ice re-advanced and physically ran
over the forest. Up in
places where there are mature tree stumps still in place with
the trunk snapped off. You
mixed into the till. And can find entire tree trunks
there give us very good control on when that location was
uncovered by ice as it melted back and when it was buried
again as the ice
What it doesn't tell us, though, advanced forward.
retreated to expose it or how far south the ice advanced
again. Now, if you take numerous
locations like that, numerous locations where you have
radiocarbon dating that tells you a specific location was
exposed and uncovered by ice, you can start to marshal them
and get an idea in space and
what areas were time whuncovered by ice.ered and
So we express this in the geomorphology world in a diagram
like this which is called a time distance diagram.
So this has age on the vertical axis, going from old up to
young, and then distance
So in this case, we're looking along the ice margin.
Madison. And then from, the curve is theown to
generalized location of where the ice margin was.
Advancing we know that it had to
Cactus Rock here. We back off to expose Waterloo and
farther to expose Valders and the Sherwood sites.
Then there was an advance,
the Two Creeks forest. So therwe can get the generalose
pattern of ice advances and retreats, it still doesn't give
us exact ice margin locations and times and that's actually
really crucial. It's
going to try to model the dynamics of the Laurentide Ice
Sheet, if we're going to
mechanisms lead to its melting. It's crucial if we're going to
model climate, if we want to
firm midpoints for climate have firm starting points and
margin positions change as indicated by exact ice
It's important for, say, biogeography.
If you're interested in the migration of plant species in
the landscape, it certainly helps if you can know when
advances and retreats were
sense. So refining occurring and in a very detailed
been an interest within the geomorphology community.
If radiocarbon isn't a
dating is simply compromised in the upper Midwest during the
last glacial maximum, what we need to be interested in is
other methods in dating. And
up at the Wisconsin Geological about the time that I showed
and now collaborators had began exploring the utility of what's
referred to as optically
or OSL dating. And OSL stimulated luminescence dating,
attractive in this kind of dating is certainly very
rather than dating organic environment because OSL dating,
organic material like maradiocarbon does, OSL datingf
dates the amount of time that a sand grain has been buried away
from the sun. And so
like this an any glacial certainly and environment
Wisconsin we have enplenty of sand around.n
And so if you can measure the time that these sand grains have
been buried, then that's going
having organic material. Now, to gthe fundamentals of OSLf not
dating are up here. I'll
quickly. The idea is run through it really
particularly quartz grains, tend that mineral grains,
crystal lattice that are to accumulate electrons in their
surrounding rradioactive elements.of
Now, in any sedimentary package,
there's going to be quartz you have a sand bar on a river,
grains of other mineralogies grains, there's going to be
radioactive elements. Thorium, that are going to have
are the most common, and so as a potassium, and uranium
sand bar, buried in a dune or sawherever, it's going to bea
surrounded by these radioactive elements and the longer it's
buried, the more it's going to
And so if we measure the amount of electrons that have been
accumulated in a sand grain during the time since it was
last buried, it's going to give us an indication of how long it
has been buried. The
accumulation of energy is actually the optically
stimulated part of it.
they do to the sand grain Opin the laboratory setting.t
We need to know a couple things.
so that's basically how much We need to know the dose rate,
are in the surrounding sediment. uranium, potassium, and thorium
measured with a salinometer. So that can be relatively easily
some confidence, and this is an important one for our research,
we have to have some confidence that this sand grain has been
what we called zeroed out, and
electrons that accumulated in it what that means is that all the
its most recent burial. werWhat we know is that shortto
exposure to direct sunlight,
20 seconds of exposure of a sand something on the order of 15 to
flush its crystal lattice clean. grain to direct sunlight, will
think of the life cycle of a So this is interesting if you
and exhumed and transported sanand buried and exhumed andied
transported multiple times over.
was transported it was exposed And as long as the last time it
all the previously accumulated to enough sunlight to flush out
give us a good date for how long electrons, then it's going to
Now, within the OSL dating it was buried that last time.
new methodology. It was comoriginally conceived andely
developed 35 or 40 years ago. It's been about the last two
decades that it's been in common
this has been traditionally to use, and the way to deal with
where you can intuitively demonstrate that the sand grains
were transported far enough to be flushed clean.
The way that's been done has
where the sand was transported primarily been working in areas
wind-blown. So, intuitively, in the air column, transported
a sand grain was carried up in you can see if
be exposed to enough sunlight. the air column it was going to
press the boundaries of this, Wstarting to work in differento
geologic environments and address whether or not OSL
dating can be used and address
the sediments that we're going whether we can verify whether
flushed clean and are going tto be viable dating methods.
As a general rule, OSL dating is
about 300 years as a minimum, athat's how long it needs to be
buried to begin accumulating a
up to about 100,000 years. So meathat's when the sand grains,
becomes saturated with electrons
So that's the dating range. aThat fits perfectly into the.
late Wisconsin time frame. So it's the ideal tool in the
respect for using. The
and the setting that we're methodology, the location
was deposited in lakes applying this, is in sand that
So this is a different setting right on the ice margin.
that have typically been used, from the wind-blown environments
for us with dealing with the but it's got some great benefits
The first application of it, Wisconsin geologic record.
right when I showed up, we had this is work that was started
journal Geomorphology, was using this published last year in the
basins right here in OSL dating in two small lake
And so these are both up the Baraboo Hills.
They're not down high on the Baraboo Hills.
They're actually up high in Devil's Lake.
Let's zoom in on that. So here we have the Baraboo
Hills. The red line on here is the ice
margin. So everything to the east of
that was covered with ice, and
sort of shaded in white then in the larger image.ce is
And you can see that very convoluted ice margin in the
Devil's Lake area. So ice coming in, blocking the
Devil's Lake gorge to the north,
looping around, and there was this area in here up on top the
Baraboo Hills and this area over
that were ice free. And herin these two locations,lls
Feltz Basin right here with this
Basin here with this smaller large lake shown and South Bluff
that were formed precisely lake shown, there were two lakes
These were small valleys up on because the ice was there.
would drain down into the lowlands down to the Wisconsin
River, but during last glacial
were blocked by the maximumpresence of ice.inages
And so lakes formed and those lakes only existed while ice was
at its exact maximum. As
thinning and retreating back to the east, those lakes drained
and no more sediment
So the idea for us is that this is a perfect environment where
if we can derive reliable OSL dates from these, these dates
can be unambiguously and
the glacial event that happened eto the ice margin position.to
And so with numerous dates from the Feltz Basin area, numerous
dates from the South Bluff area,
average age of 18,500 years ago. all of them converged to an
case published of OSL dating Certainly this was the first
Certainly it was one of the very in a glacial environment.
timing of ice fluctuations first numeric controls on the
So it was certainly significant work in both those regards.
What does KA stand for? >> KA is thousands of years ago.
So 18.6 KA is 18,600
When we work with dating years ago. Sorry.
realm, we're very often concerned with two issues:
accuracy and precision. So
date we have correlate accuracy is how well does the
And the precision is how to the geologic event?
How much error is tightlyinvolved in it?ain it?
And one of the failings that we have with OSL dating right now
is that the, certainly with this
accuracy portion of it. It work we weren't able to test the
dating techniques, which was a was unsupported by other
weren't able to address. The worry to us but something we
is relatively poor second is that the precision
If we had, with this date here for OSL dating.
Basin, if we had radiocarbon of 18,600 from the South Bluff
error on that would probably be, date of 18,600 year, the lab
probably be 18,600 plus todayor minus 60 years.would
That's how precise
With OSL dating, currently the radiocarbon dating is.
plus or minus 10%. So 18,600 errors associated with it are
1900 years. >> What plusis OSL dating? or
OSL is dating how long the sand grain has been buried, how
long ago it was deposited.
Optically Stimulated >> What is OSL stand for?
Thank you. >> You're welcome.
When we're looking at this in the big picture, we wanted to
address both of these. We wanted to try to address the
accuracy issue to determine whether OSL dating can be
verified to have reasonable accuracy and hopefully through
laboratory techniques deal
And since we found several lake basins right here in the lower
Wisconsin River Valley, this
in having lake basins associated area is actually quite fertile
So from previous mapping that had been done by my colleagues
at the Geological Survey, we're aware of a whole host of small
lake basins that exist
We have several of them up here that are part of Glacial Lake
Wisconsin. We have a
that are out in front of the whole series of them
along the Lower Wisconsin River. maximum ice margin position down
that are behind the There'smaximum position. basins
So we have lakes in a variety of settings with a variety of
different mechanisms forming
test the OSL dating mechanism. them that we can continue to
last year or two. And for That'the rest of this talkng the
I'm going to focus in on these two locations.
So this is Black Earth Creek
down into the Lower Wisconsin flRiver, and this northwesterna
site I'm going to refer to as Marsh Valley.
It is in Marsh Valley. And
I'll refer to as the Swamp then this southeastern site
Valley. It's in an Lovers site or Swamp Lovers
that much of the land is unnamed tributary
And they love swamps so they an LLC by the landowners.
that owns their land. So named it the Swamp Lovers LLC,
Lovers Valley is what SwI'll be referring to.amp
And what I'm going to do is you're going to be seeing that
map area there
You'll be seeing it with quite a few times.
it zoomed in with topographic gand digital elevation models.g
So kind of keep that in mind
picture with the Wisconsin River of where we are in the bigger
the late Wisconsin maximum here on the eastern boundaries of itd
with Black Earth Creek cutting
portion of that area. So across the sort of central
from the geologic perspective. let's take a look at this
our office works on is One of the primary tasks that
So this is the surficial geology creation of geologic maps.
County. So this shows map thall the surficialr Dane
deposits in the county, mapped
And this is the area by two of my colleagues.
And just to give you sort of a that we are looking at.
everything in the greens are the big picture idea, basically
in the washed out sort of glwhitish buff color with theng
oranges and pinks, those are
in the eastern most stream ddriftless area. deposits
So we're seeing right up against
train against the this mdriftless area.aciated
So let's zoom in on here and
and the Swamp Lovers site. talk about the Marsh Valley site
During their mapping they Hactually identified this as a.
location that would have had a lake in it.
There's not a lake currently, but these are lake deposits that
are shown in, oops, excuse
Here in the Swamp Lovers Valley, me, that are shown in blue.
similar deposits just probably they identified that there were
map. So they knew not extethat there werer them to
lakes there, and the idea of why
streams is because both of them drain into streams that carried
outwash, carried that sand and
the glaciers. So Marsh gravel being flushed out from
into the Wisconsin River, Swamp Lovers Valley drains down into
Black Earth Creek, and you need to imagine that during glacier
times this outwash was coming down Black Earth Creek, it was
coming down the Wisconsin River,
and choking those valleys. and it was actually filling up
aggrading. They were They were what we call
and as they were filling up, it was damming up Marsh Valley, it
was damming up Swamp Lovers Valley, it was damming up, this
was Dunlap Creek up here. It
We focused in on these two for a did the same thing to it.
because not only were they very specific reason, though,
outwash on the main stream, but they were also in a position
where the ice at its very maximum position, at its very
maximum extent during the late
their headwaters. So we Wisccan see the green off onnto
the eastern part
And here we have the headwaters of the Swamp Lover Valley.
Here we have the headwaters of
extended no more than a mile or ta mile and a half into those
valleys. So it was
right at its maximum extent did it get into the headwaters of
those valleys. Why
It's important if we think of the processes that were going on
in those two valleys. And so this next set of maps
that I'm going to show are
sediment was accumulating a in these two valleys.how
And these actually date back to the time when John Attig and Lee
Clayton mapped this area. This
sediment would have is hbeen accumulated. that
So here we have that same map area I've been showing.
Wisconsin River up here, Black
west, and this is a time slice Earth Creek flowing off to the
its maximum. So we can taken while ice was advancing to
the northeast corner of the map, see the ice up here in
both Black Earth Creek and down the Wisconsin River damming up
lakes in our two sites. So a
And then if we step forward in lake here and a lake here.
its maximum and it was in the theadwaters of Marsh Valley and
Swamp Lovers Valley. And
headwaters of those valleys, because ice was in the
outwash was coming water was coming down and
And the outwash was actually down those valleys.
lake sediments. And then being deposited on top of those
retreat, as soon as it backed off no more than a mile or so,
it got out of Marsh Valley, it
and the supply of outwash down got out of Swamp Lovers Valley,
But there was still outwash coming down Black Earth Creek,
there was still outwash coming
they continued to aggrade. down the Wisconsin River, so
outwash. And so They conce ice began toup with
retreat, lakes were reestablished in those two
valleys. Now, that's
they had from doing their mapping, from understanding the
geologic processes. They
to go out and test it by coring. never had means or reason
now when I'm working with the SSurvey and we're interested ino
this OSL dating, all the sudden there is a reason to do it.
And so out we went
This is us with what's called a geoprobe coring equipment.
The track vehicle on the left.
with hydraulic pressure it It's a direct push system from
the Earth and retrieves about an pushes a core barrel down into
barrel. Really nice, inch and a half diameter core
unit that we have access to. You really quick coring
in the dead of winter, and this was previous winter when wey
actually had a winter and had snow and that kind of thing.
[LAUGHTER] This is the
We had to do it in the winter. Swamp Lovers site.
tail end of the summer to do We have a short window at the
because the ground is either this kind of coring in the sites
it's dry. Otherwise, frozen or that tiny window when
that we couldn't get this coring rig out on to.
So we took advantage of the cold
2010, put in some cores to weather back in February of
like, to see if it was like what verify what the stratigraphy was
it was going to be a good setting for radiocarbon dating.
Collected cores, I want to tell you a little bit about what we
found in them before I actually show you the stratigraphy, show
you the layers of sediment in them.
We were pleasantly surprised at the volume of material, what we
refer to as paleoenvironmental
the conditions were like. We proxies, so indicators of what
assemblages of pollen, of phytolith, which are plant
remains, and also of diatoms, which are algae that lived in
the water column. That's
side of the image. Those what's shown on the far
All of those are very nice are freshwater diatoms.
indications about what the for us because they give us
the water temperature, climate, the water conditions,
So they started filling in and the salinity.
the conditions were like while flushing out the story of what
What we also found that really this lake was in existence.
our face for weeks after finding shocked us and put big smiles on
of organic material it was anin this lake.ich record
What is truly and honest to god,
to inflate the value I know we as scientists love
[LAUGHTER] Truly of our work...
an unparalleled record of organic material for radiocarbon
dating in the upper Midwest.
in these cores we found plant Fromacrofossils, identifiableke
pieces of aquatic vegetation. We found both terrestrial and
marine gastropods, snail shells that were living either in the
freshwater column or living on
And we found them from the top land and then getting washed in.
within a few centimeters of our core all the way down to
So stunning find in and of of the base of the core.
So let's look at itself to have all that.
So this is a column showing what the stratigraphy.
looked like. Like I said, the it is a marsh todayiment
in the Swamp Lovers site. So
marsh sediment, organic, rich mats of vegetation and fine
grained sediment mixed together.
around four meters of laminated, Beneath that we found right
Exactly what we'd expect from a lake..
So lake sediment. And on top of that we found
outwash, sand and gravel, beneath that we found yet more
lake sediment. So we
expect to find based on the understanding of the setting
from the mapping. This
we actually verify throws us for a loop when
[LAUGHTER] But we're the things we think.
In the very small red dots going to go with it.
sediment, these are four of the organic samples that I've had
radiocarbon dated. So you can see that they go
entirely through that lake
where it transitioned into a section from right at the top
bottom. So this is marsh all the way down to the
where we transition from sand and pebbles back into a lake
when ice was retreating. So all the sudden, literally for
the first time in the upper Midwest, we have a location
where we can easily identify
glacial processes and all the wsudden we have radiocarbon
material to give us a control.
everything we were originally looking for which was whether
we'd have good sediment for OSL dating, which, sure enough, we
have. So we have a
Dating, two samples from here at sample here for OSL
OSL dating. This is the ideal for us if we're for
interested in accuracy
All the sudden we get the precision of the radiocarbon
date, we also have the
radiocarbon and the OSL dating cross-verification of the
accuracy is there. So this to tell us whether or not the
for us. If we look is perfectly thrilling
bigger setting here, this is in a little bit
length of the valley from a northeast to southwest.the
This is what we found from
So here's a location up at the multiple coring locations.
through a similar stratigraphy. Here's our core shown on the
right that went down through the
And we actually weren't able outwash and into lake sediment.
penetrated all the way down to to retrieve samples, but we
valley. And then down the bedrat the southwestm of the
end, there's outwash that was piling up in the Black Earth
Creek. And that visually has a
different characteristic to it. Much larger material, different
mineralogy in it. So
being different outwash than visually recognizable as
valley. And then this that was coming down the
this diagram, we've got the flat although it's subtle on
former lake basin, and right surface of this marsh, this
empties into Black Earth Creek down at the mouth where it
the outwash at Black Earth there's a little rise here where
actually there. You can Credrive out on highway 14at's
and just on the east side of
see that. There's a Crosshouse on it, and youually
can actually see that it drops
Swamp Lovers Valley. So exactly identical to what we
had expected. If we look
a series of dates. So I'll at our dates, we have
top to bottom. With radiocarbon dates we have
an age of about 7700 calendar years BP when this lake
converted over to a swamp. We have at the other end of the
lake section we have dates that are right around 17,100 calendar
years for when the
So this lake was lake was established.
That gives us good radiocarbon established then.
retreating. It also cotells us that this lakeas
was in place on the landscape for something on the order of
10,000 years before it rolled over to being a marsh.
The OSL dates we have, and these
to calendars. You can datesee how tight the errorrted
is. This has an error of, what is
that? 170 plus 450, so about 600 years
is the total error on this
calendar years. The OSL labdate, this is 21,400 to
years plus or minus 3300 years. So a much larger spread
consistent with typically what
particularly what we're finding wewith OSL dating in lakend
settings. Down here we have an age
centered on 23,000, 23,500
Because of the errors, these years BP and 26,500 years BP.
statistically indistinguishable thrfrom one another.ally
We can't separate them, but what
We can say with confidence that wethe ice was at its absolutes.
maximum position probably for a relatively short amount of time
centered around 26,000
And we can also say that all of the dates, both radiocarbon and
OSL, show complete
As you get lower, you keep internal consistency.
which is exactly getting older and older ages
This is wonderful for us for our what we want to see.
It's wonderful for our empirical confidence for using OSL dating.
to now have these knowleradiocarbon ages.ocesses
If we look at this setting, we
17,100 years ago, when a lake nhad been established here.,
We can go to the
So this is a view of it. Marsh Valley site.
gorgeous little lake This is just an absolutely
So nice, flat lake plain setting setting just east of Mazo.
If you're out there in this thlittle lake basin, you can.
actually look around it and all the way around it you can see a
nice little break-in slope that was the former beach surface.
So you can still see the
This lake was actually in existence for quite a bit
longer. It was
20,100 calendar years ago based on, again, abundant radiocarbon
dating from within it. And
about 1500 years ago. So this ilake was in place on thel
landscape for something on
Okay, if we take the combination the order of 18,500 years.
Baraboo OSL ages, if we take the of all these, if we take the
site, and the radiocarbon ages OSL ages from the Swamp Lovers
the Marsh Valley site, we can fplot them up on here and seed
what kind of progress we're making of getting into that
window of no age control during the late Wisconsin maximum.
And this is what we get. So here's our radiocarbon age
from Swamp Lovers. The, oops, excuse me,
radiocarbon dates from Marsh
dots. This is the Valleyaverage OSL dateer red
from Swamp Lovers, and this is the OSL age from Baraboo.
Put them all together, they actually have, as a group of
three different locations that
they have very nice arconsistency with the ages.,
They're going into this wilderness that we've had
existing for a century
So this is something that is now of no age control.
geologists working simply thrilling for us as
Now, if we pull back up a step in this state.
all these different locations, to wrap up here, and I showed
excited on a number of fronts. this has us really excited,
it's not all that surprising In retrospect, looking back,
radiocarbon datable material that we didn't find any
These were up extremely high on the landscape, would have been
incredible hostile environments during the Wisconsin maximum.
They were also up on the Baraboo
tough place for stuff to grow quabecause that bedrock is sos a
inert. So it's not
have found organic surprising to not
To have found such an abundance of organic material from here in
Swamp Lovers and here in
confidence as we start coring into all these other lake basins
that are shown here that they're
of also having going to have a high probability
So we're going to build what radiocarbon material.
because we're only talking North is truly, it's not world class
continental record or glacial events that has no parallel as
far as its chronologic control. The nice thing is when we look
at these, these are all tied
well. So not only into difcan we date thatvents as
last glacial maximum that I've
a series of events that been twe can date as well.ere's
I mentioned these three lake
Glacial Lake Wisconsin. So basins up here are part of
into Glacial Lake Wisconsin indicates to us that it probably
existed multiple times going
maximum. So OSL dating back prior to the last glacial
could give us information about ice advances prior to the last
glacial maximum. We have
lake basins here in the Sauk a number of different
Ammunition Plant. There Ciare related to Johnstowner
position, they're also related
because these were dammed up to recessional Elderon position
Johnstown ice, and then they by outwash deposited by the
the Elderon position. So drained when ice was receded to
Johnstown position, they drained they formed because of the
We have this lake here in the East Baraboo Basin that was only
dammed up when ice was at this
call the Elderon phase. reWe have lake over here. we
This is Glacial Lake Middleton. It only existed when ice was at
this recessional phase that we call the Middleton phase.
So we have a whole range of different timing questions and
chronology questions that we can address with this.
Really high level of confidence,
on it. By the time really high level of excitement
this, particularly if we get the we're done with
that we're expecting, we'll have amount of radiocarbon material
OSL dating in these fully conenvironments.ability of
And so moving forward from that,
and start looking across the we can actually expand back out
Laurentide Ice Sheet and begin entire margin of the southern
And with that, I'd like to thank dating large-scale events.
any questions. you, and I'd be happy to take
[APPLAUSE]