This is Geology Bites with Oliver Strimpel.
The Amazon basin is the most biodiverse region on Earth.
It is the home of one in five of all bird species, one in five of
all fish species, and over 40,000 plant species.
How did this come to be? Can we answer this question just
by looking at the present day climate, soil and other aspects
of the environment? Or do we have to look at the
region's history? Karina Horne has shown that we
need to go back at least 23 million years to the early
Miocene to consider two key geologically caused drivers of
biodiversity, the rise of the Andes and marine incursions.
She is an associate professor in the Institute for Biodiversity
and Ecosystem Dynamics at the University of Amsterdam.
Karina Horne, welcome to Geology Bites.
Thank you very much for inviting me.
It's a great honour to be part of this series.
The Andes rose on the western shore of South America, while
the Amazon basin lies far to the east, extending all the way to
the Atlantic Coast. How can the rise of the Andes
affect biodiversity on the other side of the continent?
Yeah, that's an interesting point.
We know from tectonic models and also from geophysical models
that the central Arnors and the northern Arnors had a strong
uplift in the Neogene and this affected the climate.
It generated an orographic barrier and it also we have
fermented erosion processes. So we see this effect of uplift
in the Amazon basin. So because also there was
another effect which was subsidence on the eastern flunks
of the Andes. And so there was accommodation
space for sediments to arrive. And those processes play a very
important role in reshaping not only the landscape and the
topography, but also creating a lot of geological changes and
Palo environmental changes in the Amazon basin.
And for that reason we have to see the history of the Amazon
also in the context of the uplift history of the Anders.
So let's talk a bit more about some of the aspects you
mentioned. How does the increasing
topography of the Andes affect the climate in the Amazon basin?
If you think of the the central and northern Anders, now they're
they're very important or a graphic barrier.
So they're about 7000 meters in the highest peaks in Peru and
6000 in the northern Anders. So this orographic barrier
intercepts the intertropical convergence on these humid air
masses that come from the Atlantic.
And so they're intercepted and therefore the increased
precipitation rates on the intercepting flunk of the arms
and creating a rain shadow at the other side.
And with that, they also generate, of course, erosion
processes. And so this orographic barrier
also creates therefore an elevation gradient and a
climatic gradient. So we see that we have high
precipitation and high temperatures at the lower flunk.
And then as we go up the mountain, of course temperatures
decrease. And especially at mid elevation,
we have very high precipitation levels.
And that generates the cloud forest, which is super rich.
And we have the Alpine zone, which is much colder and more
arid. And so we have already high
diversity at the mountain flunks itself.
But also this effect of intercepting the humidity also
leads to increased precipitation in the western Amazon.
So we see a differentiation between the eastern and the
western Amazon. And there's also already a
geological difference between, of course, having these
mountains in the West and also the crat on the old crystalline
lowlands in the eastern Amazon. So there's really a big division
in terms of climate, but also in geology for the Amazon that is
generated by the Onlean uplift. Let's talk a bit about the
geology, because obviously the topography increases the rate of
erosion and provides sediments that are carried by rivers into
the Amazon basin. Are these sediments different
from those that were already present in the Amazon at the
time? Yeah, that's very interesting
aspect. When you walk around or when you
travel by boats along the rivers, there's a huge
difference in the waters of the Amazon region.
So you have the white water rivers which are derived from
the Anders and you have the black water rivers, for
instance, that are derived from the Craton or the Clearwater
rivers that are derived from the other Highlands that you have in
the in the Amazon. So the rivers on themselves
already reveal a difference in sediment composition.
And so the Eastern part of the Amazon dominated by the Kraton
is weathered surfaces. It's a very weathered profile.
So those are very stable in terms of composition and also
depleted of nutrients. So they have a very distinct
geochemical signature. So geochemists can
differentiate. The sediments that are older
than 1 1/2 billion are of Kraton and younger than 1 1/2 billion
are Ambien. They also have characteristic
heavy mineral composition if you were to look at that way, so
stable minerals from the carotone and unstable minerals
from the metamorphic rocks in the onus.
So you can see that by measuring the chemistry of the sediments
in outcrops and you see it in the rivers.
And so when you travel around in the field, you see for instance
also clays that are typically blue, very bright and have a
very different composition of for for instance, these silici
classic sediments, pure quartz and grey clays that are derived
from the cratum. So the unders is like a big
fertilizer of Amazon and western Atlantic.
Where new ecosystems created specifically as a result of the
Andes driven changes in climate and the riverborne sediments
that you just talked about. Yeah.
So there were big changes happening in the Amazon in
relation to this onion uplift. So a lot of the changes are
driven on one side by this particular geological
configuration, by this changes in mantle convection.
And due to this slop subduction that we learned from the
geophysicists have played an important role.
And so that has generated on one side the uplift, but on the
other side the subsidence. And through that, we've had a
very unique system there, which is this Fluviolac stream, but
we'll call it the Pay Bass Mega Wetland that really transformed
the environment and it extended over more than 1,000,000 square
kilometres and it had a long existence, we think from the
geological record that existed for almost 10 million years.
Pay Bass, you said. Yes, it's called Paybas system
based on the typical outcrop at Paybas, which is in Peru.
It's an amazing setting because it seems it was like a cradle of
spectation. So it opened up the opportunity
for taxa that were not in the region that that settled there
because of dispersal from elsewhere.
And they found a suitable environment.
And that applies to molluscs and ostracots.
Ostracots, these tiny crustaceans and molluscs as
well. They diversify very much in that
system. And they created a complete new
ecosystem that wasn't there. And of course it was all sort of
other organisms related in this traffic chain.
So it had a very big variety of reptiles, for instance, that
were also able to feed on these mollusc.
And there was a very diverse aquatic fauna.
And in terms of vegetation, we know there was a diverse
rainforest already in the periphery of the system, but
also marshland swamps by palms that now are extinct.
So that system existed because of these special geological
circumstances were created, but after some time, it also
disappeared. So at some point, because of
this subduction process, there was a eastward tilt.
The sedimentary basins in the western Amazon got overfilled
and this system, this paper system that existed for so long,
then transitioned into a flu field system into the
transcontinental Amazon. And we know that from both the
sedimentary record in the western Amazonian basins, but
also from the marine basin in the Atlantic site where the
Amazon River sediments arrive. And so from the western
Amazonian basins, we know that this effect of the uplift of the
unders started to be recorded in the Miocene.
So we know about 60 million years.
We see already that there is a high elevation unders because of
the type of deposits we get. We get pollen and spores, which
is the reproductive material of plants.
We get them deposited in the sediment basin and they show us
that there was a high montane vegetation in the unders at the
time. And then we see in the marine
record that we get sediments of Ambien origin.
We get them around 10 million years.
So we see how this system based on the sedimentary record on
land, we see how this wetland disappears and we see the
emergence of the Amazon River and we see the arrival of this
river in the sediments of the marine record.
So that's how we follow the story.
We don't see a similar burgeoning of biodiversity next
to newly formed mountain chains in all other locations, so there
must have been other factors at play here as well.
In my introduction, I also mentioned that marine incursions
were an important driver of biodiversity.
Is that part of what makes the Amazon different?
Yeah, definitely. But we have to go back again to
this complex geological history first, because it's in the 1st
place, this subsidence that's triggered by the special mantle
convection and the slop subduction that generates this
opportunity for marine incursions to reach the area.
But also, beside Andion uplift and flat slab subduction, the
sea level rise caused by global warming during the early and
middle Miocene help facilitate the marine incursions.
For sure, that's a very important driver.
And when at some point this process stopped and then marine
incursions are no longer possible also because of
blockages with the pathway which we think was from the Caribbean
and maybe even from the Pacific. So it is in the 1st place driven
by the geological processes. And then the marine incursions
have a very important role in, well, also fertilizing the
Western Amazon. But that is one thing.
That's the geochemical aspect of bringing in new nutrients.
But on the other side, it's also a very interesting aspect of the
evolutionary history because we have all these organisms that
have thrived there and some of them adopted there.
So some Organism disappeared because the conditions vanished
and that wetland was no longer there, but some of these species
adopted. A nice example of that are the
pink river dolphin. That's a very iconic Organism
that we all love, and it arrived from the oceans.
It came with the marine incursions such as fish as
welded and they adopted there and they persist.
So there is a legacy of these marine incursions in the fauna
but also in the flora. There are some species that we
think are really brought in by the marine incursions and
settled. There's certain coastal elements
that are found and established in the Amazon.
Is it possible to say how far into the continent the salt
water actually penetrated during these incursions?
Oh yeah, thousands of kilometers.
Some people have suggested this was just by transport of birds,
but we think there is a lot of evidence all along the pathway
to the Caribbean. So we have made an inventory of
localities and we find marine Organism of different kinds.
So we find marine protozoans that settled there and that we
know have existed for many generations.
We find marine alti like dinoflagellate cyst and we also
find mangrove pollen in large quantities.
And mangroves are typical for the coastal environment, but
they managed to settle there as well, and they really formed an
important vegetation unit for certain periods of time.
And there's also some sedimentological features and
this large founder that tell us that the marine incursions
reached thousands of kilometers into western Brazil.
That's fascinating. So that's really good evidence
for the marine incursions. What about the erosional and
soil change processes that you talked about?
Can we see the changing sediment composition and also changing
climate that you mentioned caused by the rise of the Andes?
Can you see that in the geological record?
Yeah. It was particularly important to
use some of the available court sections for that from the
Brazilian Geological Survey. And so we see this transition of
stable kratomic minerals in the base of the core in the early
myosin and then transitioning in the course of the early myosin
to middle myosin into Ambien sediments.
And So what we had seen an outcrop these contrasting type
of sediments, we also could follow that in core sediments.
And at the same time, by using Pollen's force, we could set up
a bio stratigraphic scheme to to attach some ages to these
sediments. And so that led us to propose
this model of having a transition in the early to
middle Miocene. And when you look at the
geological models of the omelets, that fits with what's
happening there. Subsequently, from the Atlantic,
we also see similar change. We see a change from kratomic
sediment to ambient sediment. When the Amazon River arrives
there, again, the geochemical imprint is left in the sediment,
and we see that there are 10 million years.
With the help of the subsurface sections, together with outcrops
of course as well, we can little by little piece together the
story. As you mentioned, most of the
Amazon region is actually on the Amazon Kraton, which is
extremely old and yes, OK, so it would be somewhat starved of
nutrients, but on the other hand it would have had plenty of time
to develop a lot of biodiversity.
So where we starting from a fairly bio diverse base if you
like, when all these events we're talking about with the
rise of the Andes took place? For sure.
The Amazon has been actually very diverse since the
Cretaceous Tertiary events and the famous events of the impact
and the transition to a tropical rainforest.
OK, that's not exactly Amazon. It's a bit further north.
The transition to this forest that we now think of tropical
rainforest, really initiates in the Paleogene.
Also, it's important to realize that the Amazon previously was
linked really with what is now the Orinoco base.
And so it was like a mega Amazon region.
This division only appeared in the late Miocene.
So the area was much bigger prior to this late Miocene
division. And so we know that that region
was very rich and also the kratom has been already rich.
However, this is a relative concept.
So between Eastern and Western Amazon, the Western Amazon is
much richer. And at global scale, it is the
biggest rainforest in the most biodiverse region in the world.
You mentioned palinology a moment ago, and a lot of your
research has been in the field of palinology, which is a study
of pollen and spores. Does the geological record in
the Amazon basin contain a fossil record of pollinance
pores and was that really how you determine the increasing
biodiversity during the Miocene? Yeah, the pollinance pores are
very good indicators of change in vegetation and also can give
us hints to climate. The reason we can work with them
is because they are everywhere. They are in your hair, in your
nose and in the Amazon. They also are deposited in the
fluvial and in the fluvulaca stream deposits.
The main thing pollen spores don't resist is repetitive
weathering, oxidation. So they need an anoxic
environment for preservation. So that is what we always
looking for is for organic material to extract pollen
spores from there. And then you need a good lab to
process the samples. But when you have everything
lined up, then you can extract this huge biodiversity of the
past from just a cubic centimeter of material.
And we find thousands and thousands of species and we only
little by little are understanding now this diversity
of the past. And it gives us an interesting
clue that, well, from one side, we know from studies on the
packaging that it was a diverse forest, but we also can tell
something about this huge diversity of the last 23 million
years in the Amazon. And, and we see big changes
depending on the environmental conditions on the chemistry of
the system, but we see a high diversity throughout.
We're now looking into later part in the the history with a
new core that has been drilled and it will be very interesting
to see if there's actually a decline in the late Miocene when
there's global cooling happening.
Are these spores the actual original organic material of the
spores or are they fossilized spores where the materials being
replaced by minerals? The pollen spores, they are made
of very durable component which is the sporopolynine, that is a
pollen wall that encapsulates the DNA, the plant DNA.
But that part is gone. But the sporopolynine is a
relict of the original plant. And retains the structure.
Yeah, exactly. So it retains its composition
and structure. And in fact we work with that
structure because Poland have a very distinct morphology.
And based on those morphological elements, we can classify them
and also relate them to modern species.
So we can assign a botanical affinity to them.
And in that way we can understand more about
composition of the forest and how the forest changed or how
the swamp palms changed. What else did you use to measure
the history of biodiversity, especially a fauna, in addition
to the flora? Yeah, the sediments of the paper
system that very rich in molluscs and in ostracods, but
also all kind of vertebrates. So these components tell us
about how rich this environment was and how diverse and also how
different it was in that we had a very rich system there that
was different from the present. It has been a very dynamic
environment. The Amazon is seen now as the
most rich forest and and that we should protect that.
But we learn from the fossil record that it has also been a
different system and that it has evolved a lot through time,
responding to climate change, from global warming to global
cooling and transitioning into the present.
So obviously you were able to access the geological record to
be able to find these spores and the fossils of the animals and
so on. But the present day Amazon is
extremely densely vegetated. How were you able to find any
outcrops there to make your measurements?
So first of all, we had a location in western Amazon in
Colombia that was our base camp that was an old prison just like
Papillon in the French Guiana almost.
And from there we could access the river and we travel along
the river to find out crops and at the same time also work
together with local assistant indigenous people who knew the
region well. So a lot of it was based on
interviewing them and asking them for advice.
And at some point, of course, they knew what I was looking
for. So that made it.
Easier and so we would travel to find out crops, but they are far
apart and it's not always easy. But of course a very important
element as well is working with court sections.
And obtaining that material was transformational for
understanding the Amazon because you have to tie out crops and
records together to get the bigger picture, to understand
really the stratigraphy and use biosatigraphy to put ages to
that. And so the combination between
outcrops and court sections is very crucial.
There are some oil wells in the region, I believed.
Did the oil companies cooperate with you and give you access to
some of their drill cores? Yeah, it's pretty rare for
companies to do that because it's all confidential
information. And I've tried many times, but I
was very fortunate and I'm also grateful to the possibilities
that were given by the Brazilian oil company Petrobras.
So there were several windows of opportunities that allowed us to
work with court sections in the Western Amazon, but also at the
mouth of the Amazon. And those opportunities have
really allowed us to advance our knowledge on the Amazon.
What are you working on at the moment?
At the moment, I'm trying to better understand the
composition of the mangrove coastal system.
So we talked about these marine incursions and the mangroves
that existed there. And nowadays, the mangroves of
the neotropics of northern South America, they're quite
impoverished compared to, for instance, the Asian mangroves.
But when we look at the past, for instance, the Miocene, we
already start noticing that there was more diversity in
mangroves than there is at present.
So we're intrigued about that and trying to better understand
that. Also trying to understand the
relation between geodiversity and modern distribution of
organisms. So trying different things to
still advance knowledge in the region.
Karina Horne, thank you very much.
Thank you so much. It was very nice to talk to you.
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