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Biotempo 2008, Volumen 8,
A GREENHOUSE TIME BEFORE THE ONSET OF AN ICE AGE
(Open Air Lecture and Demonstration in the «La Mina» Section
Reserva Nacional de Paracas (Ica, Peru) on May 30, 2008)
H. W. Pfefferkorn
1
V. Alleman
2
RESUMEN
Se hace una reseña de los diferentes logros alcanzados, durante los últimos veinte años de investigaciones
desarrolladas, en la localidad tipo de la faja paleoflorística de Paraca. La edad del afloramiento en La Mina es
Viseana y produjo una biozona única. La evidencia de varios ambientes de deposición contienen al menos seis
comunidades vegetales, incluyendo bosques monoespecíficos de Lycopsida en posición erguida, Sphenopsida y
Pteridospermas y además de varios conjuntos de flora aloctónicos. La vegetación se extendió a lo largo de
planicies costeras, meandros fluviales, canales tidales e islas barreras.
Palabras clave:
Perú, Gondwana, faja paleoflorística Paraca, paleoclimatología, Viseana, paleobosques.
SUMMARY
We present a summary of the past twenty years of continous investigations in the type locality of the Paraca
paleofloral belt. The type section in «La Mina» has an Visean age and developed a unique biozone. The
evidence of several environmental deposits contains at least six plant communities, including monospecific
forests of lycopsids in up-right position, sphenopsids and pteridosperms and other aloctonics sets of flora. The
vegetation extended throughout coastal plains, fluvial meanders, tidal channels and barrier islands.
Key words:
Peru, Gondwana, Paracas Floral belt, paleoclimatology, Visean, paleoforests.
1
University of Pennsylvania. Email:
hpfeffer@sas.upenn.edu
2
Museo de Historia Natural, Universidad Ricardo Palma. Email:
vmealleman@yahoo.es
INTRODUCTION
Professors Hermann W. Pfefferkorn, University of
Pennsylvania, Philadelphia, USA, and Vera Alleman,
Universidad Ricardo Palma, Lima, Perú,
demonstrated and explained on May 30, 2008, to an
audience of 22 persons the results of their research
on one example of ancient global climate change,
paleoecology, paleoenvironments, and paleobotany.
They demonstrated these results in the locality where
the research had been and is being conducted.
Among the participants were members of the field
research group from the Universidad Ricardo Palma,
University of Pennsylvania, staff from the Reserva
Nacional de Paracas, the director of the Ica Office
of the «Instituto National de Cultura», academic
presence of the Universidad Nacional del Altiplano
de Puno, professors and students of the Universidad
Ricardo Palma of Lima and the Universidad Nacional
San Luis Gonzaga de Ica.
History of «La Mina»
The presentation began with a general introduction
into the history and general geology of the area. A
Peruvian geologist named Fuchs discovered coal
seams and the Carboniferous age of these beds in
1900. In the following years a company was formed
to mine this coal. The company brought in two steam
engines rusted remnants of which can still be seen
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on the beach at La Mina and above the far end of
the section. They drove four tunnels and sank one
shaft but did not find enough coal to even fire their
own steam engines and the venture was abandoned
with a loss of the investments. What remains is the
name «La Mina» and rocks that contain an
outstanding example of paleoclimatic history of the
Earth.
History of previous paleobotanical research
The fossil flora of the La Mina section was first listed
by Fuchs in 1900 and correctly identified as
Carboniferous. However, all the names he used for
the fossils were incorrect. About every two decades
a geologist would collect material in the section and
send it to a paleobotanist who would write a
publication on the unusual and enigmatic plant fossils
that were so different from those known from other
parts of the world. Some of these publications
contributed new valid names but all had shortcomings
because the descriptions were based on collections
of loose material found on the beach that had already
undergone some weathering and lost important detail.
For instance, there are two common tree-lycopsids
present at La Mina that were both found and
demonstrated during the lecture. These two species
were described over the years by eight generic names
but all eight are incorrect.
Geologic Overview
The Carboniferous beds (327 millions of years old)
occur in an uplifted area and the fault that is its
boundary can be seen in the cliff. The neighboring
down-thrown area consists of Tertiary (Eocene, about
45 million years old) beds that are more easily eroded
than the more resistant Carboniferous rocks. In the
far distance the group could see the next uplifted
block consisting of mostly red volcanic rocks of
Jurassic age (about 18 0 millions of years old). The
next uplifted block in the other direction at the
Mirador de Lobos consists of Precambrian rocks that
are more than a billion years old. These uplifted
(horsts) and down-thrown blocks (grabens) have
been formed due to the subduction of the Pacific
Plate under the South American Plate that produced
and still produces a fracturing, thinning, and general
uplift of the South American margin. However, some
areas subsided relative to others within the general
uplift.
Current research
Our own research began more than 20 years ago
when Professor Alleman discovered material in the
section that was much better preserved than any
published specimens. She contacted Professor
Pfefferkorn and the two have been the leaders of
this investigation since then. Over the years, students
from the Universidad Ricardo Palma in Lima, Peru,
and graduate students and postdoctoral fellows from
the University of Pennsylvania have participated in
the investigations. In recent years a colleague from
Brazil, Professor Iannuzzi, has also been part of the
team. Our research included taxonomy and
nomenclature of the plant fossils, reconstruction of
the plants, biostratigraphy, i.e. the determination of
the age of the beds, plant taphonomy, paleoecology,
and paleoclimatology. Over the years we have
progressed from the more basic to the more complex
questions. At every step of the way we have
presented our results in Spanish in Peru and in English
in international journals. Currently, the group has a
number of manuscripts in preparation.
MATERIALS AND METHODS
Materials
Plant fossils (leaves, stems, pollen organs, seeds, or
sporangia, rooting structures) and forests in
carboniferous rocks over an 170 meters thick section.
Methods: Reconstructing the whole plant
Plants are complex and large organisms that normally
fall apart before they get preserved. Thus, we find
and collect pieces. Out of the different parts, we
have to reconstruct a whole plant. In addition, even
in live many plants and plant parts can show a large
amount of variability. We have to collect and curate
(i.e. number, photograph, describe, and preserve in a
permanent museum) a large number of specimens
before we can judge what belongs together.
Afterwards we have to work with artists to make
drawings that show our conclusions. With new finds
these reconstructions are then to be revised as
necessary.
RESULTS
The age for the rock layers at La Mina
One of the most important questions is the age of the
rocks at La Mina. Fuchs (1900) identified the age
as Carboniferous and nobody has doubted this age
assignment since. However, the Carboniferous was
approximately 74 million years long and a more
precise dating is needed to make best use of all the
information gained from the research. A direct dating
is not possible because this occurrence of
Carboniferous rocks is isolated. Underlying rocks
are not exposed and overlying beds have been eroded.
No rock types are present that would allow dating of
the rocks through isotopes. The plant fossils are
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Biotempo 2008, Volumen 8,
actually the only available material to determine the
age.
The plant fossils encountered at La Mina on the
Paracas Peninsula are quite different from those
known from either North America and Europe or
from most localities in South America or other
southern continents and do not allow a direct
comparison. A critical evaluation of those plants
known from elsewhere gave a tentative age but only
the comparison with specific floras found in Bolivia,
Brazil, Niger in Africa, the Indian Subcontinent, and
Australia finally gave a precise age of late Visean
(about 327 million years ago). We could achieve this
goal only by including in our team a colleague from
Brazil and visiting museums in Paris for the African
material and in Australia. Between the members of
the team we have seen the material from each of
the locations we use for comparison except that in
India which we know only from the literature. Thus,
the question of the precise age could only be solved
by comparison with other countries and continents.
Duration of deposition for the La Mina section
Another question of interest is how much time the
late Visean beds of La Mina represent. The answer
can be given based on the fossil plants, the
environments of deposition, principles of stratigraphy,
and sequence stratigraphy. The overall composition
of the fossil flora does not change from the base of
the section to the top of the section. In other words
only one biozone is represented. Plant biozones in
the Carboniferous have an average length of 3 million
years, i.e. the flora was quite stable for long periods
of time. However, there are also biozones that are
only 1 to 1.5 million years long. In any stratigraphic
section most of the time is represented by gaps of
deposition that appear in the section as bedding
planes. This certainly is the case here, too. However,
there are no large gaps or hiatuses present in this
section. Thus, we can estimate the time it took to
deposit the rocks and use that as the lower limit for
the time duration. The different environments
discussed below could have formed over a relatively
short period of time geologically speaking. The section
is 170 meters thick. If we assume an overall
sedimentation rate of 1 mm per year after compaction
we would come to 170 000 years. This would
represent the rate of subsidence of the area that would
be a reasonable assumption. The sediments
themselves could have been deposited in as little as
10 000 years. However, that would require a very
high rate of subsidence and there is no other indication
why it should have existed in this area at this time.
In terms of sequence stratigraphy, the beach barrier
complex near the top of the section could represent
a sea level high stand. If that is the case all the beds
here belong to one sequence. Assuming this to be a
third order cycle the length of time would be typically
less than three million years. In summary one can
say that the exact duration cannot be determined at
this time but we can say that it was in all likelihood
between 170 000 and 1.5 million years. Further
research in this area and in other areas of the same
age will help us to narrow this time range in the future.
Environments of deposition
The environments in which the beds of the La Mina
section were deposited can be determined from a
combination of data from the rocks, i.e. their
composition (sedimentary petrology), grain size, and
sedimentary structures (sedimentology), and data
from the fossil floras. A detailed sedimentological-
sedimentpetrographic study is still outstanding but
preliminary investigations of our group allow a general
interpretation. The rocks in the lower part of the
section were deposited on a fluvial plain with small
meandering rivers. In the middle part of the section
tidal influence becomes noticeable. In other words
tides extended deep into the freshwater realm but
brackish influence may be present. The beds of a
tidal channel are overlain by coastal plain sediments
followed by the sands of a beach barrier bar complex.
In this complex a tidal channel is present that was
filled by sandy tidalites that represent as a first
approximation about 9 month of sedimentation. This
complex is in turn capped by another sequence of
coastal plain sediments. The plants contribute to this
interpretation by the presence of rooted horizon that
represent incipient paleosols and are indicators for a
short hiatus in sedimentation. A layer with stems
that are all oriented in the same direction indicates
its origin in a flood where the stems were felled and
oriented in the direction of the flow.
Trees and forests in place
One exiting observation are tree stumps that occur
in place. A forest was growing during an interruption
of sedimentation. A new flood event than covered
the base of the trees with sediment so that they died.
The parts of the trees not covered by sediment
decayed but those in the wet sediment were
preserved. We can see them today in one fluvial
unit in the middle of the section in side view and in
some beds of the coastal plain in map view in the
upper part of the section so that we can reconstruct
the actual forest with the proper diameter and spacing
of the trees.
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Fossil plant communities
We mentioned above that the overall composition of
the fossil flora does not change throughout the section.
However, if we collect only from a specific bed we
find that different plant communities lived in different
subenvironments of the fluvial and coastal plains.
There were forests that consisted only of either one
of the two common species of lycopsids. The
sphenopsid
Archaeocalamites
formed monospecific
thickets, as did some pteridosperms. However, there
were also plant communities with higher diversity and
representatives of all three groups both in the
backswamps and on the levels. We can so far
distinguish six different plant communities that lived
in the sedimentary environments and have been
reconstructed by us. In addition, there were one or
several extrabasinal floras that we find only as very
small swept-in fragments in specific beds. We do
not have enough data from these fragments to
reconstruct plant communities but we can name some
species that occurred only in these erosional
environments and not in the lowland depositional
settings. In this way these fragments widen our
horizon and preserve indications of what was
removed by erosion.
DISCUSSION
Climate change and the Paracas section
The fossil flora of the La Mina section represents a
climatic belt that existed on Earth only during the
latest Visean time. Professors Pfefferkorn and
Alleman first recognized it after they began their
research (Alleman & Pfefferkorn, 1988; Pfefferkorn
& Alleman, 1989) and they named it after the Paracas
section the
Paraca Floral Realm
. This work was
later refined and published (Iannuzzi & Pfefferkorn,
2002) showing that this belt existed between 30Ú
and 60Ú South on the Gondwana continent. The
Paraca Floral Realm is characterized by (a) plants
that can live only in a frost-free climate, (b) plants
that migrated from the tropics, and (c) endemic
species. A frost-free belt reaching 60Ú south
indicates an interval of strong greenhouse conditions
on Earth. It is important to note that the next geologic
stage, the Serpukhovian or Namurian A, saw the
beginning of the Carboniferous icehouse world. Thus,
the flora of Paracas tells an important story about
climate change and it took the decade long study of
this flora in this section to recognize this situation.
CONCLUSIONS
The importance of long-term studies
All previous paleobotanical studies of the La Mina
section had been short-term affairs. Somebody, often
a geologist, had collected material for a few hours or
a few days and shipped it to a paleobotanist. Results
on single species could be achieved but it was
impossible to develop a coherent picture or solve the
most important questions. Only the systematic work
of our group that lasted in the beginning for a month
each year could begin to accumulate enough good
material to be able to address these questions. We
employed different methods of collecting and
observing, building in each successive stage on the
results of the earlier one. This is an example of the
value and necessity of long-term studies.
Why study paleobotany
Reconstructing 320 million year old plants, landscapes
and climates sounds exotic and interesting but the
question might arise what the relationship is to our
lives and why we should study it. The first answer is
that basic research is concerned with answering all
questions that arise. At the time basic research is
done there is normally just curiosity and applications
or importance of the answer might not be knowable
at all. However, this curiosity driven science has
turned out to be highly applicable and needed at a
later time. In other cases the results of curiosity
driven sciences have opened insights into other
currently critical areas. Actually, the countries that
had the highest support for basic science both
financially and in terms of esteem given to its pursuit
have shown the most dramatic advances in their
economy.
If we ask what the study of paleontology can
contribute to our current life, three short points will
demonstrate its importance. (1) «Civilization exists
by geological consent – subject to change without
notice» (attributed to the philosopher Will Durant).
All cultures can only exist within the framework set
by Earth systems and the current state of Earth
systems is the result of 4.5 billion years of Earth
history. Thus, we have to understand Earth systems
and their evolution in deep time to understand our
own current position. The next points are specific
examples. (2) When paleontologists analyzed the
consequences of the very large meteorite impact on
the Yucatan Peninsula 65 million years ago they
discovered an impact winter that lasted years with
deadly consequences for life everywhere on Earth.
Soon it became clear that similar worldwide
consequences would follow an attack with atomic
bombs. This lead the two largest nations to negotiate,
reduce their stockpile of atomic weapons and
principally give up on the idea of atomic war. Thus,
the result of a curiosity driven question lead to
consequences that are of benefit to all mankind. (3)
Global warming is of great concern to all of us. How
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Biotempo 2008, Volumen 8,
will the climate change? How will vegetation and
that means agriculture change? Only the study of
climate changes that have happened on Earth before
can teach us what to expect. Thus, the studies of
fossil plants have direct applicability to the predictions
for the future of mankind. (3) Our findings in the
Paracas section demonstrate that extreme conditions
can exist close to each other in geologic time. In this
case a greenhouse time just before the onset of an
icehouse time with glacial and interglacial times similar
to our current climate state. The obvious question
about the speed with which these changes occur can
only be answered by further research.
Thanks and outlook
We would like to thank the participants of the open-
air lecture for their interest and their excellent
questions. We will be happy to answer further
questions by e-mail or in person. Many of the
questions might be answered by our previous
publications that are available as PDFs on our web
pages or by those that we will put onto the Internet
shortly. Other questions might be answered by
publications we have in preparation. Some of these
will appear in the near future.
REFERENCES
ALLEMAN, V. & H. PFEFEERKORN 1988
Licópodos de Paracas: Significación geológica y
Paleo-climatológica.
Bol. Soc. geol. Perú 78
:
131 - 136, figs.
FUCHS 1900 Nota sobre el Terreno Carbonífero de
la Península de Paracas. Informes
Memas. Soc.
Ing. Perú, 2 (16)
: 1-4.
IANNUZZI, R. & H. PFEFFERKORN 2002 A pre-
glacial, warm-temporate floral belt in Gondwana
(Late Visean, Early Carboniferous).
Palaios, 17
:
571-590.
PFEFFERKORN, H.& V. ALLEMAN 1989 New
climatic Belt in Carboniferous of Southern
Hemisphere.
Abstracts 28 th International
Congress, Washington 2 -3
: 2-602.
Paracas Peninsula, south: general sight to the access at the Carboniferous outcrop (photo J.
Yovera).
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Field research group with section «La Mina» on the background.
Tree-lycopsid
Tomiodendron peruvianum
(Gothan, 1929) Pfefferkorn & Alleman
comb. nov
.
(in press),
in situ
, «Playa La Mina».
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Tree-lycopsid «
Cyclostigma» pacifica
Steinmann, 1929
on the beach, «Playa La Mina».
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