STRATIGRAPHY AND PALEOECOLOGY OF PLEISTOCENE DEPOSITS
ASSOCIATED WITH THE GIANT GROUND SLOTHS RECOVERED FROM
WEST TARKIO CREEK BEDS, PAGE COUNTY, IOWA
by
Harold A. Ray
An Abstract
of a thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Arts
In the Department of Biology and Earth Science
University of Central Missouri
August 2013
ABSTRACT
by
Harold A. Ray
The recovery of an adult and two juvenile individuals of the giant ground sloth
Megalonyx jeffersonii in 2001 from the sloth site along West Tarkio Creek, Page
County, Iowa, is unique. Two sediment cores were taken in order to examine the
paleostratigraphy and paleoecology of the sediments associated with sloths.
Analysis of the cores began with detailed soil and sediment descriptions.
Carbon isotope, radiocarbon, particle grain size, and phytolith samples were
extracted from the cores. Radiocarbon results indicate the age associated with
the M. jeffersonii, in excess of 43,500 years before present, is significantly
greater than once assumed. Analysis of the sediment portrays a landscape
adjacent to a stream system that would periodically flood and inundate the area
depositing local sands that are interbedded with finer sediments and possible
paleosols. Phytoliths and carbon isotopes recovered near the sloth recovery
horizon suggest an ecological system dominated by forests and sedge.
STRATIGRAPHY AND PALEOECOLOGY OF PLEISTOCENE DEPOSITS
ASSOCIATED WITH THE GIANT GROUND SLOTH RECOVERED FROM
WEST TARKIO CREEK BEDS, PAGE COUNTY, IOWA
by
Harold A. Ray
A Thesis
presented in partial fulfillment
of the requirements for the degree of
Master of Arts
in the Department of Biology and Earth Science
University of Central Missouri
August 2013
© 2013
Harold A. Ray
ALL RIGHTS RESERVED
STRATIGRAPHY AND PALEOECOLOGY OF PLEISTOCENE DEPOSITS
ASSOCIATED WITH THE GIANT GROUND SLOTH RECOVERED IN WEST
TARKIO CREEK BEDS, PAGE COUNTY, IOWA
by
Harold A. Ray
August, 2013
APPROVED:
Thesis Chair: Dr. Stefan Cairns
________________________
Thesis Committee Member: Dr. James Loch
________________________
Thesis Committee Member: Dr. Gary Krizanich ________________________
ACCEPTED:
Chair, Department of Biology and Earth Science: Dr. Fanson Kidwaro
UNIVERSITY OF CENTRAL MISSOURI
WARRENSBURG, MISSOURI
ACKNOWLEDGEMENTS
I would like to thank Dr. Adel Haj for his direction and support in this
research and assistance in the collection of data. Thank you to the Athens and
Tiemanns, the property owners, without whose support none of this would have
been possible. I would sincerely like to thank Dr. Stefan Cairns, my Thesis
Chair, for his continued support of this research and for his energy in helping me
to complete this thesis. I would also like to thank Dr. James Loch and Dr. Gary
Krizanich, members of my Thesis Committee, for their support, assistance, and
knowledge. My thanks to the Quaternary Materials Laboratory at the University
of Iowa for particle size analysis and to the Keck Paleoenvironmental and
Environmental Stable Isotope Laboratory at the University of Kansas for the
carbon isotope analysis. Last, but not least, I would like to thank my wife, Penny
Ray, for all she did to help bring this research and thesis to fruition. Thank you to
all the staff and faculty within the Department of Biology and Earth Science and
to the University of Central Missouri.
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TABLE OF CONTENTS
Page
LIST OF FIGURES……………………………………………………………………xii
INTRODUCTION………………………………………………………………………2
METHODS……………………………………………………………………………..8
Core Collection…………………………………………………………………8
Core Description………………………………………………………………10
Particle Grain Size Sampling………………………………………………..12
Geochemical Sampling………………………………………………………15
Phytolith Analysis…………………………………………………………….17
RESULTS..…………………………………………………………………………...18
Core Description Results…………………………………………………....18
Particle Size Analysis Results…..………………………………………….22
Carbon Results……………………………………………………………….25
Phytolith Results……………………………………………………………..29
Radiocarbon Results………………………………………………………...32
DISCUSSION..………………………………………………………………....…….34
CONCLUSIONS……………………………………………………………………...46
REFERENCES CITED….……………..……………………………………………49
APPENDICES
A.
B.
C.
D.
E.
F.
Soils…………………………………..…………………………………...52
Carbon Analysis (Raw)………..………………………………………...57
Particle Size Analysis by Weight……………………………………….58
Particle Size Analyses (Raw)……..…………………………………….60
Phytolith Analyses (Raw)…………………………………..…………....62
Radiocarbon Data (Raw)………………………………………………...64
xi
LIST OF FIGURES
Figure
Page
1. Satellite photo of Athen farm…………………………………………………….3
2. Surface geology map of Iowa…………………………………………………....4
3. Core Logs of Sites SL-1 and SL-2B…………………………………………….11
4. Modern Soils Pyramid…………………………………………………………………14
5. Core SL-1 particle size analysis…………………………………………………23
6. Core SL-2B particle size analysis……………………………………………….24
7. Carbon analyses of core SL-1…………..………………………………………26
8. Carbon analyses of core SL-2B…………………………………………..…….27
9. Slide of phytoliths – sedge achenes……….……………………………………30
10. Slide of phytoliths and charcoal……….………………………………………..31
11. SL-1 and SL-2B PSA comparison……….……………………………………..39
12. Carbon comparison of SL-1 and SL-2B……….………………………………41
xii
STRATIGRAPHY AND PALEOECOLOGY OF PLEISTOCENE DEPOSITS
ASSOCIATED WITH THE GIANT GROUND SLOTH RECOVERED IN WEST TARKIO
CREEK BEDS, PAGE COUNTY, IOWA.
Photo courtesy of sciencemag.org
1
INTRODUCTION
Towards the end of the Last Glacial Maximum, the farthest reach of
glaciation into the Lower 48 United States, large mammals roamed across North
America. Among these large mammals or megafauna, was the giant ground
sloth, Megalonyx jeffersonii. Adults could reach 4 meters in height and weigh up
to 1000 kilograms and have a girth at the waist of 6.5 meters (Title Page Photo).
Their diets are considered to have been plant fibers, including tree leaves and
small saplings (McDonald, 1998).
In 2001, the first of three Pleistocene giant ground sloths was discovered
emerging from a stream bank in rural Page County, Iowa (Figures 1, 2). The first
specimen recovered was an obvious adult, the sex of which has yet to be
determined. Later digs, in 2006, were to discover not one, but two juveniles.
Significantly, these two juveniles were of different sizes and, therefore, ages.
This led researchers at the University of Iowa to ask whether adult giant ground
sloths kept multiple young with them or whether the adult Megalonyx adopted a
stray juvenile. No matter what social strategies giant ground sloths adopted
within the family unit, this is the first find of an adult and two juvenile M. jeffersonii
together. Analysis of the sedimentary context of these fossils was undertaken in
hopes of providing an insight into the paleoecology and paleoenvironment in
which these sloths lived.
2
Sloth Site
SL-2B
M32 Hwy
SL-1
322nd St.
Figure 1. Satellite photo of the Athen farm and sloth research site. Core sites
SL-1, SL-2B, and sloth site are shown with arrows and flank West Tarkio Creek.
Satellite photo courtesy of USGS.
3
Figure 2. Surface geologic map of Iowa showing approximate location of
research site (within circle at bottom left of figure) located in Page County, just
across from the Missouri – Iowa border. The Des Moines Lobe, in the upper
center of the map, represents the furthest reach of Pleistocene glaciation into the
state. Image courtesy of Iowa Geological Survey Bureau.
4
Stratigraphy insights can be gained through particle grain size analysis
(PSA) revealing stream system dynamics. Results from these grain size
analyses which show a percentage relationship of sand, silts, and clays within
the stratigraphic units may allow a determination of whether a soil or alluvial
sediments were aspects of these layers. Alluvial sediments are the result of an
active stream system and the type of sediments being transported and deposited
can reveal energy levels of the stream system over time. Any soils found within
cores indicate a time within the stratigraphic section that indicated little to no
stream dynamics due to the time involved in soil formation. The two soil cores
recovered, one from the north side (SL-2B) and one from the south side (SL-1) of
the stream system, when laid out end to end in the lab show the stratigraphic
section of the site. These cores showed evidence of what part the stream
system has played in the area.
Another objective of this research was to deduce the ecology of this area
of southern Iowa at the time the sloths were alive. This entailed examining
carbon isotopes from samples taken at various depths within the core. It
indicates whether grasses (C4) or forest (C3) vegetation were present on the land
surface during the time of the giant ground sloths. Total organic carbon (TOC)
analysis of the south core revealed the amount of vegetation that grew in the
area over time. This will give an indication of whether whatever vegetation was
growing was sparse or dense.
Phytolith analyses were taken from morphotype assemblages obtained
from core SL-1. Phytoliths are generated as groundwater flows through the
5
plants system and is left as silica. After the plants die, phytoliths remain on the
surface and are subsequently buried as new soils and sediments form. These
phytoliths provide further evidence as to the types of vegetation that thrived on
the surface.
Determination of a timeline, or chronology, will be assisted by the use of
radiocarbon analysis. This gives an absolute date on specific stratigraphic
sections. At random depths of the soil cores woody material was discovered and
retrieved for analysis by radiocarbon dating. Several plant and wood material
pieces will be outsourced to Beta Labs, Miami, Fl. in order to place the entire soil
stratigraphy in a chronological context to give the fossil finds both relative and
absolute dates. These dates will be correlated to the soil stratigraphic section
and analyses of PSA, carbon, and phytoliths.
The Continental United States has endured two major glacial incursions
during the Quaternary Period which began approximately 2.58 million years ago.
During this period, these glaciations, given the names Illinoian (~300,000 to
130,000 years ago) and Wisconsin (~110,000 to 11,000 years ago) glacial
episodes, advanced southward with the Wisconsin eventually reaching what is
today southern Iowa and northern Missouri. These glacial episodes were the
catalysts for the current geomorphology present in upper United States (Figure
2).
Interspersed between episodic advances of glaciers are the interglacial
periods. One such period is known as the Sangamon Interglacial, which
6
occurred within the approximate timeline of 125,000 to 75, 000 years ago. This
timeline was produced through investigative techniques on soils and sediments
located in Sangamon County, Illinois, from loess deposits laid down during this
period (Markewich, et al., 2010).
As these glaciers advanced, they scoured out great sections of land,
numerous valleys, and moved billions of tons of material (Figure 2). When the
glaciers melted approximately 11,000 years ago, meltwater would fill in these
scoured areas yielding lakes and ponds, the valleys now housed stream
systems, and the material (known as till) pushed and carried by these glaciers
became some of the highest hills in the central states.
7
METHODS
The methodology used to collect samples and to extract data from those
samples included coring the stratified layers of soil and sediment in areas
encompassing the location where the giant ground sloths were found. Samples
obtained from the sediment cores will be used for particle size analysis, carbon
isotope, total organic content, and phytolith analysis.
Core Collection
Sediment cores were extracted from two sites on opposite sides of the
sloth site (Figures 1, 2) using a trailer-mounted Giddings hydraulic soil probe
equipped with 7.6cm and 12.7cm sample tubes. Cores were pushed through fine
and medium-grained alluvial sediments and were then terminated on contact with
country rock or coarse bar sediments. Cores were recovered in sections up to 1
meter in length, depending upon density of the sediment and the ability of the
probe to push. Core segments were extruded and covered with a plastic wrap to
aid in moisture retention and then covered with foil. Cores were then labeled for
direction, size, and core depth.
At core site SL-1, an auger was used to determine the thickness of the
underlying bar. A sample of these bar sediments was retrieved and catalogued
for later analysis in the Soils Lab at the University of Central Missouri (UCM).
8
The geographic location of the core sites and their elevation was
determined with a WAAS-enabled (Wide Area Augmentation System) Global
Positioning System (GPS) unit. Recorded elevation for core site SL-1, on the
south bank side of the stream, was 312.6 meters above sea level and a GPS
location of 15 300303E, 44 94277N. SL-1 terminated at 1065cmbs (centimeters
below surface).
Core SL-2 was a failed attempt. The core tube became fouled as it
reached an impenetrable till sediment at a depth of 3 meters. The Giddings Soil
Probe was repositioned laterally westward approximately 3 meters from the
original core site, and was designated SL-2B. Site SL-2B, located on the north
bank of the stream, at an elevation of 304.4 meters with a GPS location of 15
300415E and 44 95032N. SL-2B terminated 912cmbs when the Giddings Soil
Probe contacted the surface of a thick blue-grey clay horizon that could not be
penetrated. An auger sample of this blue-grey clay was found to be consistent
with the matrix in which the giant ground sloths were found.
9
Core Description
Cores were transported from the field to the Soils Laboratory at UCM for
description, analysis, and preparation for further laboratory testing. Detailed core
descriptions (Figure 3; Appendix 1) of soils and horizons were written following
standard procedures and terminology (Schoenberger, et al., 1998; Birkeland,
1999). Cores were split with a large blade along vertical axes allowing horizons
to be identified based upon obvious changes in strata, color, and sediment type.
Alluvial sediments are those sediments, including sands, silts, and clays,
which were transported and deposited by a stream system. The alluvial
sediments were subdivided into stratigraphic units based on bounding
unconformities. Paleosols, buried soils, and horizons were identified on the basis
of bedding, lack of non-pedogic facies, or primary structures (Horton, et al.,
2001). In soil taxonomy, buried soils are soils which have alluvial or eolian
sediments deposited after their formation. This concept was developed for use
on flood plains where a dike burst or a levee breach deposited sediment on a
preexisting soil (Smith, 1986). Paleosols and buried soils were classified to the
taxonomic subgroup level, following the procedures set by U.S. Department of
Agriculture, Soil Survey Staff (1999).
10
Figure 3. Core logs of SL-1 and SL-2B shown in relative vertical position.
Sample horizons and intervals indicated.
11
Particle Grain Size Sampling
Particle grain size samples were taken from the lower sections of each
core in order to focus upon the context of the giant ground sloths. The upper
sections of the alluvial sediment in such a dynamic stream system as that of
West Tarkio Creek were expected to be exceptionally young in age and to offer
little information applicable to this research. Samples for particle size analysis
were made at intervals of approximately 10cm through the lower portions of each
core with 400g - 600g of sediment recovered for each sample.
Particle grain-size sample preparation was conducted using a modified
version of the pipette method and compared to a known loess standard (Soil
Survey Staff, 1999). Samples were oven-dried at approximately 135 ° F and
ground using a Custom Laboratory Equipment DC-5 Soil Grinder. A 10g fraction
of finely ground sample was treated with a solution of 10ml hydrogen peroxide
and 10ml acetic acid solution for at least 12 hours in order to remove any organic
material. This process was repeated for those samples with an extremely high
organic content. Samples were then boiled to eliminate unreacted peroxide. A
sodium metaphosphate solution was added and samples were then shaken for a
period of at least 12 hours to disperse the clay fraction. Samples were
transferred to 1000ml tubes. Distilled water was added to the tube in order to
bring the total volume to 100ml. Tubes were stirred and aliquots of clay and silt
were drawn from the solution at appropriate time and depth (Soil Survey Staff,
1999). The sand fraction was removed and recovered by wet-sieving each
sample. Samples were subsequently dried and weighed with the mass
12
recovered for each grain-size converted to weight-percent clay, fine-silt, coarsesilt, and sand (Appendix A). Soil textures were interpreted from sediment grainsize percentages using a modern soils pyramid (Figure 4).
13
Figure 4. Modern Soils Pyramid. Modern soils pyramid showing percentages of sand,
silt, and clay. Pyramid calculates soil type produced by separate percentages of sand,
silt, and clay to formulate soil type. For example (shown on chart): 40% of clay
separate/30% of silt separate/30% of sand separate = a clay loam type of soil. Soil chart
courtesy of USDA (usda.gov).
14
Geochemical Sampling
Carbon was sampled at depth on both the SL-1 and SL-2B core sites
(Figure 3). Samples were collected at 5cm increments from depths of 610cmbs
to 1035cmbs. Surface and surface soil (10-20cm depths) carbon was not tested
due to direction of this research and such carbon that may have been present at
the surface would have in all probability shown a decrease in carbon present.
This type of ¹³C depletion has been observed and understood in modern surface
layer soils and is related to fossil-fuel introduction into the atmosphere (Boutton,
1996).
Carbon analysis was performed on the bottom half of the cores assuming
that this portion of the cores would prove informative for the giant ground sloth.
In a dynamic stream system, as seen in the present West Tarkio Creek, alluvial
sediments and soils in the upper half of the cores will be more recent in
chronology. Surface soils and carbon associated with the surface was not tested
due to possible contamination with airborne carbon associated with the historic
burning of fossil fuels.
Initial preparation of the geochemical samples involved their
decalcification. Samples were dried in an oven at approximately 135° F and
homogenized with mortar and pestle. Approximately 1.25 ml of the homogenized
sample as placed into a 50ml glass tube, reacted with 10ml of 1N hydrochloric
acid solution, and centrifuged to concentrate the sample. The reacted liquid was
decanted and the sample was acidified a second time. After the second
15
application of HCl, a pH Hydrion Product test strip was used to check pH of the
liquid. If the test indicated a neutral solution, the acidification process was
repeated until all carbonate was dissolved. Samples were then rinsed at least
twice with approximately 40ml of distilled water to remove chlorine. Samples
were then stirred, centrifuged, and the waste water was discarded. The rinsed
samples were dried at approximately 135°F, removed from the tube, pulverized
with a ruby mortar and pestle, and transferred into a screw-top vial for storage
and shipment to Keck Paleoenvironmental and Environmental Stable Isotope
Laboratory at the University of Kansas for carbon isotope analysis.
Carbon samples were flash combusted at approximately 1800°C
producing carbon and nitrogen gas compounds. These compounds were carried
by a continuous flow of helium and passed through a series of catalysts to
convert remaining CO to CO2. Carbon dioxide was measured versus a CO2
reference tank allowing δ13C to be calculated. Analysis was completed using a
Costech 4010 elemental analyzer (EA) in conjunction with a Thermo Finnigan
MAT 253 Isotope Ratio Mass Spectrometer (IRMS).
Organic carbon content (Organic C%) was determined using DORM-2
(Dogfish Muscle) as the standard. The normalized area of mass 44 (CO2) is
plotted versus the mg carbon content of the DORM standard. A carbon content
calibration curve was generated upon which all sample mass voltages generated
by the MAT 253 IRMS are then applied to determine the sample carbon content.
16
Phytolith Analysis
Phytolith morphotype samples were taken from four soil samples of
sediment core SL-1 at depths of 874-882, 882-892, 900-910, and 1010-1035
cmbs close to the sloth core matrix. Soil samples were ground mechanically and
filtered through a #10 standard sieve. A 10g subsample was then mixed with 50
ml distilled water in order to enable measurement of pH from the soil solution.
Samples were then decalcified, deflocculated, and sieved through a nested stack
of standard sieves (#60 and #270) into a sieve pan. Each sand fraction was
rinsed with distilled water and transferred to vials for storage. The contents of
the sieve pan (silt and clay fractions) were transferred to 1000 ml beakers. The
silt and clay fractions were separated using standard settling times (Albert, et. al.,
2011). Phytoliths were isolated from the silt fraction by heavy liquid flotation and
mounted on microscope slides using balsam, at the Keck Paleoenvironmental
and Environmental Stable Isotope Laboratory at the University of Kansas.
17
RESULTS
The results associated with this research were based on core description,
particle grain size, radiocarbon, and phytolith analyses. All results were compiled
to offer a concept of stratigraphy, paleoecology, and chronology associated with
the giant ground sloths.
Core Description Results
Soil profiles are typically divided into a series of “lettered” intervals based
upon physical appearance. These intervals, known as horizons, are given the
designations of O, A, E, B, C, or R. The O horizon denotes the organic layer
seen on the surface and may likely include grass and tree roots. The organicrich A horizon is commonly referred to as “topsoil”. The E horizon is generally
white or grey in color due to the leaching of minerals that occur in this layer. The
B horizon is the layer where clays are dominant. C horizons represent the partial
weathering of parent material, or source bedrock that comes into contact with the
above soil. The R horizon is the unweathered parent material, which is usually
the bedrock but can be of other materials. The sloth cores produced A, B, and C
horizons.
Core SL-1 had a surface layer of very dark brown A horizon silty loam with
common roots, evidence of a top soil (Figure 3). The A horizons continued down
to 23cmbs where A and B horizons merged and an AB horizon was presented.
At 62cmbs, this AB horizon showed a very dark grayish brown loam which was
18
friable and contained few common roots and may present a possible buried soil.
Below 85cmbs, the B horizon was dominant as a clay loam was seen with an
increase in silans and a decrease in organs and offered a gradual boundary.
The B horizons continued to a depth of 233cmbs where they began to merge
with a C horizon.
The transition from B to C horizons (233-289cmbs) was marked by a shift
in coloring from a strong brown to a more dark yellowish brown, a change from
clay loam to sandy loam, and the addition of a few fine to very fine pebbles. At
289cmbs a true C horizon with the same coloring and hue but with a boundary
marked by thin, white bedded sands and white weathered pebbles increasing
towards the base (Figure 3). These C horizons, generally a brown loam,
continue in depth until 898cmbs. At 898cmbs, a black, organic-rich, buried soil is
encountered. Beginning at 948cmbs, inter-bedded fine to coarse sands are
located within the horizons downward to the core termination at 1065cmbs.
The A horizon of core SL-2B surface layer was a very dark grayish brown
silty loam which contained shell fragments and few small pebbles. This horizon
continued downward to 75cmbs where a clear boundary marked a change to a B
horizon. The B Horizon was composed of silty clay loam which included an
organic/clay ped coating and medium roots. The B horizons continued
downward to a very abrupt base at 124cmbs (Figure 3).
The C horizons were indicated by a change to a very dark gray silty clay
loam containing fine and medium sand that was very rich in organic material.
19
The C horizons continued downward with very little change in structure, color, or
texture and exhibited very abrupt internal boundaries to 177cmbs. Between
177cmbs and 197cmbs clay loam became the soil type and many fine silt
laminations were present. Sand laminations are present at 197cmbs and
internally the boundaries change from very abrupt to abrupt in nature. The very
dark gray clay loam continued downward with little change until 277cmbs where
weathered crinoids appear and weathered pebbles of black shale are seen at
323cmbs. At 271cmbs loamy coarse sand bedding appears containing rounded
clay clasts, weathered rock fragments, and fine to medium root traces. Bedded
sands are now beginning to appear in these horizons (Figure 3).
A change from a very dark gray clay loam to black clay is seen at
349cmbs with many root traces and oxidation seen around roots. Woody
material was also located (375cmbs) and retrieved for later analysis at these
depths.
C horizons continue with a change in color and hue recorded at 397cmbs.
A black silty clay loam appears with bedded organic-rich clay and silt with few
fine pebbles included. A clear boundary marks the contact with the adjoining C
horizon beneath. The C horizon beginning at 417cmbs includes some fine
gravels and root/wood located between 440-450cmbs (Figure 3). A very abrupt
boundary may indicate a possible erosion contact.
At 471cmbs, loamy coarse sand appears with massive thin to medium
bedding and a coarse sand lens apparent. A black clay loam with organic-rich
20
clay and medium silt inter-beds is evident at 477cmbs. Clear and gradual
boundaries start to mark the delineations of the horizons at this depth.
The C horizon at 688cmbs shows a marked color change towards a light
brownish gray with fine to medium pebble-sized gravel appearing. Abrupt and
very abrupt boundaries can be seen for multiple horizons down in depth. A
possible buried soil is present at 866cmbs (Figure 3) where an organic-rich
unbedded black clay loam with few rounded weathered pebbles is found. The
core terminates at 912cmbs with a C horizon of organic-rich, very dark gray
sandy loam of medium bedding with random pebble gravel at the base. The
horizon ends with an abrupt boundary.
21
Particle Size Analysis Results
PSA results for cores SL-1 and SL-2B showed variation in sediment type
and amounts. SL-1 remained relatively unchanged down through the sampled
core and is dominated by coarse silt (Figure 5). A clay-rich interval was
encountered between 500-600cmbs. Sand intervals are encountered in SL-1 at
approximate depths of 600cmbs, 900cmbs, and 1000cmbs. Sand values in
particle grain size reached 60% by weight. The sandy interval at 900cmbs
overlies a probable buried soil.
SL-2B is much more varied and shows a dynamic architecture dominated
by coarse silt. There are two thin impulses of sand encountered at approximately
620cmbs and 900cmbs. At the end of one sand impulse at approximately
620cmbs, a possible buried soil has formed (Figure 6). At approximately
650cmbs to 700cmbs, larger sediments appear in the form of pebble to gravel of
significant size. Pebbles and gravels are observed again beginning at
approximately 835cmbs. Another possible buried soil is present at around
870cmbs. Just beneath the buried soil, an impulse of sand reappears at the
same time the larger sediments are again observed in the core. Gravels were
found throughout SL-2B and appear more common in the lower depths. The
lowest horizon, referred to as the Sloth Matrix, was sampled by auger and is 40%
coarse silt.
22
Figure 5. Core site SL-1 particle size analysis with accumulated data showing
cumulative weight percentages of sand, silt and clay. Particle size reported as
cumulative weight percent. The sample interval is indicated by the black rectangle at the
left side of the figure.
23
Figure 6. Core SL-2B particle size analysis giving cumulative weight percent
representations of sand, silt, and clay at depth. Possible buried soils are observed at
approximate depths of 630 and 880cmbs.
24
Carbon Results
Carbon analyses for this research included several directions and uses for
carbon retrieved in the sediment cores. Radiocarbon, Total Organic Content
(TOC) and carbon isotope analysis results were the data types interpreted.
Total organic carbon for core SL-1 (Figure 7) was sampled from 600 –
1035cmbs (Appendix B). From 600cmbs to 885cmbs TOC varied little and
remained below 0.25%, revealing a constant in vegetation content during this
time. In fact, TOC remained less that 0.50% to approximately 900cmbs showing
only a slight increase to that depth. A spike in TOC is seen from 900cmbs to
approximately 920cmbs rising to around 0.70% and appears to be coincident
with a probable buried soil located at this depth. At 920cmbs the amount of total
carbon remains fairly steady, ranging from 0.25% to 0.50%, until approximately
1020cmbs where a sharp increase in TOC begins. A 1.44% TOC value was
found at the lowest depth of the core.
TOC for Site SL-2B (Figure 8) showed a much greater range in variation.
Higher TOC values are observed from 417cmbs to 510cmbs with ranges from
1.71% at the top and 0.65% at the bottom of this interval. Lower depths, 515 –
907cmbs, produced lower TOC values, generally below 0.50%. Slightly higher
values at 637 – 652cmbs and 866 – 897cmbs, coincide with possible buried soils
recognized in the core descriptions.
Carbon isotope data (Figure 7) from SL-1 was recovered from the bottom
of the core at 1035cmbs up to 610cmbs, the initial depth carbon analysis point.
25
Figure 7. Carbon analyses of Core Site SL-1 showing δ13C carbon isotope and
total organic carbon content values. Side by side analysis show trends at
associated depths revealing lower depths had a higher TOC.
26
Figure 8. Core site SL-2B carbon analyses showing δ13C carbon isotope and
Total Organic Carbon content. Greater variation can be seen here at SL-2B
compared to SL-1. Red (darkened) zone at bottom of chart indicates sloth
matrix.
27
The uppermost samples of SL-1 had δ13C values of approximately -20‰
gradually shifting to approximately -15‰ at the base of the core. A rapid shift of
1.5‰ is encountered at approximately 900cmbs, associated with a buried soil
and an increase of TOC (Figure 7).
At the northern core site, SL-2B (Figure 8), sampled depths ranged from
417cm to 907cm. SL-2B δ13C values are more varied than SL-1, ranging from
approximately -17‰ to -26‰. Depths between 400-500cmbs revealed the least
negative values, with an approximate range of -17‰ to -22‰. From 500650cmbs, the δ13C values were the most negative. Intermediate values were
associated with the approximate depths of 700-900cmbs, hovering around -20‰.
An auger was used to recover till samples which lay beneath 907cmbs.
The bottom section of the till, found below 1000cmbs, is referred to as the Sloth
Horizon (Figure 8). This section of the till revealed a TOC of approximately
0.25% and had a δ13C value of approximately -24‰. These values are
consistent with the lowermost of the core samples.
28
Phytolith Results
Phytoliths were recovered from all 4 samples collected from the southern
core, SL-1. Depths of these samples were 874-882, 882-892, 900-910, and
1010-1035cmbs. Results from the phytolith samples revealed that woody plants
dominated and were present in all 4 samples. Rare grass was present in two of
the samples retrieved.
Also present is a species of fire-resistant vegetation, Cyperaceae,
commonly known as sedge (Figure 9). Comparison of multicellular phytoliths
observed in these samples with images from the GEPEG (Grup d’Estudis
Paleoecologics I Geoarqueologics) phytolith reference database (Albert et al.,
2011) and images from Neumann et al. (2009) and Piperno (2006), Cyperaceae
is present in all 4 samples from this study location.
Charcoal (Figure 10), like phytoliths, is very resistant to decomposition
and was present in all four samples in nearly equal amounts when examined at
200x magnification among samples. Charring may be seen on phytoliths causing
the phytoliths to appear dark, opaque, and present a shine. Charring is limited to
the grass morphotype. No evidence of any charred multicellular epidermals from
sedge achenes was observed in any samples.
The pH examined in the soils of all samples was neutral and the lack of
pitting, a characteristic of dissolution, should indicate viable recovery of the
phytoliths which reflects original vegetative composition.
29
Figure 9. Slide of phytolith and charcoal (opaque) abundance: 874-882 cmbs
(Core SL-1). Circled phytolith is example of many multicellular epidermal from
sedge achenes.
30
Figure 10. Slide of phytoliths and charcoal from depth 900-910 cmbs (Core SL1). A mixture of grass morphotypes and abundance of charcoal is observed with
a sample of charcoal encircled.
31
Radiocarbon Results
Radiocarbon dating was performed on two samples through the use of the
liquid scintillation method and AMS. Radiocarbon ages are presented in
calibrated radiocarbon years before present (years BP). These radiocarbon ages
have been corrected for variations in 13C content and reported in 14C yr B.P. Two
samples, each of organic material, were recovered from the same core SL-2B.
The first sample was collected near the middle section of the core at 455cm. The
second was collected near the bottom of the core at 870cm extremely close to
the level where remains of Megalonyx jeffersonii were recovered. This lower
sample had the probability of revealing much as to when the giant ground sloths
in question roamed the plains of southern Iowa (Figure 3).
The sample at 455cm of woody material provided a Measured
Radiocarbon Age of 150 +/-40 years BP and a Conventional Radiocarbon Age of
140 +/-40 years BP (Figure 3). Data retrieved also showed a 13C/12C Ratio of
-25.4%, indicating that at the time this woody material was deposited, C3
vegetation was dominant. With this stream system having been active in this
area at this date, this type of vegetation may be explained as a riparian corridor
lined with trees. This recent dating, at this depth, can be explained through the
stream system and its continuous erosional and depositional functions. It also
indicates that this stream has been in place for some time in this area.
32
The sample recovered from 870cm below the surface was of
indeterminate organic material and yielded no Measured Radiocarbon Age. A
Conventional Radiocarbon Age revealed a >43,500 yrs. BP date (Figure 3).
33
DISCUSSION
Alluvial chronology, or dating sediments stratigraphically, was based on
radiocarbon dating of charcoal and bulk dating of soil and sediment. The ages
associated with charcoal are interpreted to be representative of the time of
deposition of associated alluvial deposits. Bulk soil and sediment ages of
paleosol surface horizons are representative of the maximum time of burial of
that stratigraphic unit.
Any discussion of radiocarbon dating for this research must rely on the
fact that there was little material for which positive radiocarbon dating could be
successfully performed. The two viable dates that were returned at SL-2B did
offer insight and valuable data in which correlation was to be found. However,
any further attempt at this site must recover viable material to gain additional
data. The relatively young date obtained at 455cmbs showed dating possibly
within the last century. For a steam system as active as West Tarkio Creek, this
date could be easily accepted. The date given for the lower of the two dates,
from 870cmbs, revealed a date >43,500 yrs BP. This date is a Conventional
Radiocarbon measurement. Even though a Measured Radiocarbon date could
be attained from the material, this “greater than” date will need to suffice until
further research can be performed. A Measured Radiocarbon dating would do
more for the confidence of this research, but this research will maintain that the
Conventional Radiocarbon age date will suffice. A date obtained this way may
signal that the 14 C activity was very low and nearly identical to the background
34
signal. When this is the case, indeterminate errors associated with the
background add non-measurable uncertainty to any result. The most
conservative interpretation of any date is infinite. In such cases as a
Conventional Radiocarbon Date shows an infinite determination, or a “greater
than” date, any corrections may imply a greater level of confidence than is
appropriate (Beta Analytic, Personal Communication, 2011).
Thus, with a conservative date of >43,500 yrs BP, we cannot, with any
certainty, put a date to this organic material which lies extremely close to the
sloth matrix. Yet, this material was collected at a depth just a few centimeters
above where the sloth matrix was situated allowing a certain determination that
the sloth remains are at least of a contemporary or greater age.
The date retrieved of >43,500 yrs. BP does much to alter the earlier
estimated age for the deaths of the giant ground sloths. This date was obtained
near the location of the sloth remains and until now it was estimated that the
sloths died at around 11,000 years ago which would place the event right at the
end of the last glacial timeline. This research does give reason to question these
earlier estimates.
Particle Size Analysis is a technique used to determine stream system
behavior or dynamics over time, through the analysis of the percentage of sand,
silt and clay. Changes in stream behavior are deciphered through
sedimentological, pedological, and geochronological characteristics of alluvial
sediments. Changes in stream discharge, flood frequency and magnitude can be
35
inferred through sediment grain size distribution, unit thickness, elevation, and
bar height (Haj, 2007; Knox, 1983, 1985, 2000, 2001; Brakenridge, 1981, 1985;
Baker et al., 1993). Buried soils located within alluvial units can signify a period of
stability within a floodplain or at least a time of slow aggradation. Changes in a
stream system can be seen through changes in its sedimentological and
geomorphological behavior and are recorded in the characteristics of its alluvial
units.
Such hydraulic characteristics are recorded in the alluvial units of West
Tarkio Creek. These units offer insight into the stream behavior, depositional
environment and the shifting position found in a meandering stream system.
Positional changes of the stream system, whether moving towards or away from
a position in the floodplain, can be observed through a change in grain size
within the sediment deposition.
Sitting in such close proximity (each core site is within 25 meters of the
actual stream channel) much of the upper layers of soil are from periodic flooding
associated with the creek. Energy from the stream system allows for differing
sizes of sediment to be eroded from upstream, transported downstream, and
finally deposited when the energy dissipates at varying stages to allow different
size and weight particles to eventually settle. Depending upon type and amount
of sediment, soils will form based upon percentages of sands, silts and clays
involved. Particle size analysis of these soils will break down the three types of
sediments allowing determination of soil type.
36
Both core sites (SL-1 and SL-2B) were evident with seasonal flooding as
seen when the PSA was accomplished. With this, there is a continuous amount
of material being deposited along the floodplain as can be verified with the dating
of woody material found in SL-2B at 455cmbs. This woody material yielded a
Measured Radiocarbon Age of 150 yrs. (+/- 40 yrs.) BP and a Conventional
Radiocarbon Age of 140 yrs. (+/- 40 yrs.) BP. This indicates over 4.5 meters of
material being deposited in less than 150 years, not including that which was
eroded to be deposited elsewhere.
Little of remarkable note surfaced on either core site until the lower depths
of each were placed under further analysis. Core Sites SL-1 and SL-2B (Figure
11) each show a definite change in soil type and texture at lower depths. SL-1
begins a departure from normal floodplain sediments at approximately 900cmbs
where a very dark to black loam/clay loam, organic rich buried soil is observed.
This buried soil extends for over a meter in depth. SL-2B starts to change as
depths increase past 6 meters below the surface. At approximately 630cmbs,
texture and particle size begins to fluctuate indicating a massive, bedded, dark to
very dark loam/clay loam buried soil.
Buried soils both need and take time to form. Additionally, stability is also
an applicable function in soil formation. Given this, for a buried soil to have at its
disposal all of these elements, it is probable no stream system coursed through
the topography on the surface at this time. Woody material recovered at a depth
of 870cmbs gives a Conventional Radiocarbon Age of >43,500 yrs. BP. This
37
depth of less than 0.5 meters above the buried soil indicates that the buried soil
had, in fact, time to fully develop.
Particle size analysis information on the full extent of both cores, SL-1 and
SL-2B can be seen in Appendix A. It lists in detail each core as to depth, soils
type, texture, and sediment.
38
Figure 11. SL-1 and SL-2B particle size analysis comparison showing percent values of
sand, silts, and clay. Possible buried soils are evident in both cores.
39
Carbon isotope analyses were used to reconstruct the vegetation
assemblages that existed in the area over time. What came to light was the slow
lateral movement of the stream channel within its floodplain. As this is a
characteristic found in channel behavior, it is necessary for the vegetation
associated with this stream system (i.e., riparian corridor) to move likewise. This
can be observed in the variation of C3 and C4 dominance depending upon
timeframe (Figure 12). There are also multiple timespans where neither trees
nor grasses showed clear domination over the other. Over the millennia changes
can be seen as to the type of vegetation. At times trees are the dominant
vegetation while at other times, grasses overtake the region. Changes in
vegetation offer glimpses into the aspects of a changing and dynamic climate
which the Upper Midwest United States has endured in the last 21,000 years,
especially of note since the Last Glacial Maximum. Clearly, C3 vegetation
dominated at these depths and with the associated paleoecological timeline.
Questions arise as to the reasons why core site SL-2B varies much over SL-1
since these two core sites are separated by only a matter of 50 meters, both
straddling West Tarkio Creek. This may be answered expediently by realizing
that the north core site may well represent the continued presence of a riparian
corridor. If this truly could be considered a viable answer it would have to include
the continued presence of an immobile channel. Given the geology associated
with West Tarkio Creek and the fact that it rests on country rock, this assumption
has some merit.
40
Figure 12. δ13C and Total Organic Carbon comparison of cores SL-1 and SL-2B
showing each site and relative depths. Sloth horizon is represented by the shaded
portion at the bottom of SL-2B.
41
While we do see that throughout the depths of SL-2B a value associated
with C3 vegetation (Figure 12), the organic carbon values fluctuate from 0.13% to
1.71% showing some correlation to δ13C data. With the δ13C showing little
variation and certainly no significant jumps in values, the TOC numbers indicate
that as the C3 vegetation dominates, organic carbon values remained relatively
low. However, data shows that when a mixed C3 – C4 assemblage is present,
TOC values rise significantly. This change is observed twice within the depth
chart, once at 417cmbs – 440cmbs and again at 464cmbs – 490cmbs. These
fluctuations may be explained by the fact that as the local vegetation increases,
an increase of overall material would logically involve a higher content of carbon
left on the surface.
Many factors come into play and influence whether C3 or C4 is the
dominant vegetation on the surface in any region. These factors include
atmospheric CO2, temperature, precipitation, competition among species, and
fires (Dorale et al., 2010; Paruelo and Lauenroth, 1996). Climatic factors
influence the growing seasons associated with what each vegetation type. The
mixed C3 - C4 plants seen in SL-1 are common to such climates in the Midwest
United States where a cool, moist spring produces C3 plants, and C4 grasses
reclaim dominance in warmer summer conditions.
Plant phytoliths (Greek, meaning “plant stones”) are generated as soluble
silica (monosilicic acid), found in groundwater, is absorbed through the root
system and as the groundwater runs its course through the plant it fills
intracellular and extracellular cavities. As the silica morphs, it mineralizes into
42
nearly exact three dimensional copies of the plant’s cell bodies. Phytoliths are
deposited on the surface of the soil when a plant dies and migrates downward as
more soils are produced above the deposit. This downward movement can be
expedited somewhat through bioturbation. Due to their inherent strength and
resistance from decay through time, phytoliths preserve information of previous
plant life within the soil.
The yield of phytoliths retrieved from the soil samples was very low.
Several factors could explain the reasons behind this: (1) lack of vegetation
which produces phytoliths; (2) local climate and soil conditions; (3) depth of the
samples; (4) poor preservation of the phytoliths. While not all plants produce
phytoliths, the plants that accomplish phytolith production are dependent upon
such factors as temperature, precipitation, and the pH of the soil. Though
phytoliths are resistant to decomposition, they may dissolve under the right
conditions. This can be readily seen in the litter of deciduous forests where it will
decompose at a faster rate and has a lower pH, being more acidic.
Phytolith analysis did much to concur with the carbon isotope analysis.
Phytolith morphotype assemblages were only recovered from the southern core
site, SL-1. They were recovered at lower depths, from 874cmbs to 1035cmbs,
which, considering the close proximity to the northern core site, SL-2B, should
yield similar results for morphotype. Even though they were not found in
abundance, those that were recovered were valuable in helping to describe the
paleoenvironment of the study area. Those that were recovered offered
evidence that at the depths found, forests were dominant. The depths are
43
associated with a timeline consistent with the Last Glacial Maximum and from a
period somewhat earlier. As such, this does correspond with the particle size
analysis showing that the current stream system was nonexistent during this
period. The deepest samples: 910-935cmbs and 1010-1035cmbs were the only
depths with a measureable concentration of phytoliths from grass species, but
still a very small component compared to the overall abundance of phytoliths.
This may indicate that at this time, the canopy was now open when these
sediments were at the surface and grasses were replaced as trees matured. All
of the grass species which were identified were from species that utilize the C3
photosynthesis pathway.
Being a wooded and forested area at the time of the demise of the three
giant ground sloths may indicate that they were simply feeding off of these trees.
If this was the case, the answers as to how they met their end now seems to get
further away. Without a noted stream system running through this area at that
time, death from drowning is now no longer a plausible issue.
The particle size analysis that describes stream behavior revealed much
about the evolution of West Tarkio Creek. Through the PSA, we could infer the
lateral movement of the stream, flooding events and their magnitude, and periods
of low flow. The data retrieved showed the workings of a 1st order stream over
multiple centuries. Exactly how long West Tarkio Creek has thrived as a steam
system is unknown and the data was incomplete for this study. Here is where
more and complete radiocarbon analysis would have been helpful. Yet, PSA and
other retrieved data does allow us to know when the stream system was not
44
present on the land in Page County, and that was at the time when these three
giant ground sloths were roaming southern Iowa.
Many of the questions asked have been answered by this research. Yet,
many were unable to be answered either due to incomplete data or due to the
questions only now being asked. Much in the way of knowledge about this area
of southern Iowa and the ecology associated with Megalonyx jeffersonii has been
gained and that was the purpose of this research.
45
CONCLUSIONS
Cores SL-1 and SL-2B reveal a separate geomorphological response
between them. SL-1, on the south side of West Tarkio Creek, is situated above
the floodplain. As such, the core reveals a more stable area with little input from
alluvial sediments. SL-2B rests squarely on the floodplain and its core shows
depositional activity responding to a vibrant stream system. Larger sediments
found throughout its depths reveal periodic flooding throughout its lifespan.
Buried soils seen at lower depths indicate times of stability at the SL-2B core site
when for significant periods of time the stream system did not actively impede the
process of soil formation.
Sediment deposition along the channel system of West Tarkio Creek
indicate that the stream has played a significant role in southern Page County for
millennia. Particle size analyses and corresponding data allow determinations of
probable correlation between sites SL-1 and SL-2B, terminating in a buried soil
with association to each core site. The current stream system, West Tarkio
Creek, has run its course through Page County for centuries, yet is only a recent
addition geomorphologically. Floodplain analysis confirms this channel has
incised and moved to its current depth and will not entrench further as it has now
channeled to bedrock.
With its contemporary setting situated on Iowa farmland, West Tarkio
Creek runs between a riparian corridor flanking each side. Carbon isotope
46
analysis and total organic carbon indicates the type and amount of vegetation at
present and in the past. Vegetation changes can be seen from one core to the
other and are representative of land use and productivity. Core Site SL-1, on the
south bank of Tarkio Creek, produced an average δ13C of -18.11‰ giving a clear
indication that C4 grasses have dominated that side of the stream system. Total
Organic Carbon (TOC) data shows a maximum content of 1.44%, which is a
relatively high amount and can be indicative of the type of vegetation, as grasses
are abundant and will leave this signature. Core Site SL-2B, on the other hand,
produced a much differing set of data. Where SL-1 was predominately of C4
vegetation, SL-2B was clearly an area where C3 vegetation, such as trees, was
dominant. With an average of -22.38‰ δ13C, which is on the lower aspects of
the C3 vegetation range, it still represents the abundance of trees. The TOC data
also suggests that any vegetation that was to be found on the north side of West
Tarkio Creek was in less abundance than that found on the south side.
Radiocarbon ages do much to place the data together. The woody
material found in the upper depth of 455cmbs gives a date of approximately 150
yrs. BP allowing the data to provide information on the working of the stream
system associated with it. However, the Conventional Radiocarbon Age
associated with the woody material found at the lower depth of 870cmbs proved
to be of much greater importance to one of the research questions. The remains
of the three giant ground sloths found at this site launched this and other
research initiatives, but each asked some general questions; “How old are these
giant ground sloths?” and “What was the land like back when they lived?” This
47
research has helped to provide answers to these questions. With the sloth
matrix situated below the level where the lowest radiocarbon age was
determined at >43,500 yrs, BP, it is not going to provide an absolute age of these
giant ground sloths, but will give some possibilities to as when they lived. Before
this research, the time they had lived was thought to be of a contemporary age
as the end of the last great glaciers, approximately 11,000 yrs,. BP. As for what
the land itself may have looked like, it was much like it is today, with forest and
grasses vying for dominance, yet without the stream system known as the West
Tarkio Creek.
Phytoliths found within core SL-1 aids in pinpointing vegetation to the
species level. Grasses seen at lower depths reveal the type of climate apparent
at the time these phytoliths were deposited within the soils. Sedge phytoliths
recovered clearly state the need for high amounts of water in the area. This can
either be the result of standing water, such as found in marshy areas, or from a
high water table which brings the needed amounts of water close enough to
sustain such vegetation types.
48
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51
APPENDIX A – SOILS
Site Name: SL-1
Location: South of West Tarkio Creek, Page County, Iowa
GPS: 15 300303E, 44 94277N
Landscape position: South slope
Elevation: 994ft.
Parent material: Alluvium
Vegetation: plowed surface
Slope: 0-5%
Date described: 11/23/2010
Described by: AEH and HAR
Remarks: 2” (5.08cm) and 3” (~7.6cm) diameter PT; described in laboratory and sampled at 5cm
and 10cm intervals and by horizon. Boundary considered at base of horizon.
Depth
(cm)
Soil Horizon
(weathering
zone)
Description
0-10
A1
Very dark brown (10YR2/2) silty loam, weak grade, medium
angular blocky, friable, common roots, non-effervescent, clear
boundary
10-23
A2
Very dark grayish brown (10YR3/2) loam, moderate grade,
medium size, granular to sub-angular blocky, very friable,
common roots, non-effervescent, very abrupt boundary
23-28
A3
Very dark grayish brown (10YR3/2) loam, platy, friable, common
roots, non-effervescent gradual boundary
28-62
AB
Very dark brown (10YR2/2) silty loam, moderate grade, medium
size angular blocky, very friable, common roots, bottom ~7mc
broken in core, non-effervescent, gradual boundary
62-85
AB2
Very dark grayish brown (10YR3/2) loam, strong grade, fine to
very fine size, very friable, ped coatings (10YR3/1) of medium
thick and continuous, worm borrows, many very fine rootlets,
thick discontinuous silans, non-effervescent , gradual boundary;
possible buried soil
85-126
Bt
Dark yellowish brown 10YR4/4) clay loam, strong grade,
medium size angular blocky, slightly friable, increase in silans
and decrease in organs from AB2 above, non-effervescent,
gradual boundary
126-146
Bt1
Brown (10YR4/3) clay loam, moderate grade, medium size
prismatic, slightly firm, ped coatings (10YR3/3) of multiple thick
and continuous silans and organs, non-effervescent, gradual
boundary
146-184
Bt1
Brown (10YR4/3) clay loam, strong grade, medium to coarse,
prismatic, slightly firm, organs ped coating thick and
discontinuous with few thin discontinuous silans, increase in
sand, non-effervescent, gradual boundary
52
184-206
B
Brown (10YR4/3) clay loam, strong grade, medium size, firm
prismatic to columnar structure, thick continuous organs darken
alternating with thin discontinuous silans giving banded
appearance, non-effervescent, possible buried soil, gradual
boundary
206-233
Bt
Brown (10YR4/3) clay loam, strong grade medium to coarse
columnar structure, firm silans dominate thin and discontinuous,
thick continuous organs, non-effervescent, clear boundary base
233-289
B/C
Dark yellowish brown (10YR4/4) sandy loam, moderate grade
columnar to massive, firm cutans thin very continuous, few fine
to very fine pebbles, non-effervescent, very abrupt boundary
289-343
C
Dark yellowish brown (10YR4/4) clay loam, boundary marked by
thin white bedded fine sands, pebbles and white weathered rock
increase towards base, non-effervescent, abrupt boundary
343-350
C1
Dark yellowish brown (10YR4/4) clay loam, massive, marked
increase in sands, black manganese concretions possible former
organic material, non-effervescent, abrupt boundary
350-383
C2
Grayish brown to brown (10YR5/2-5/3) sandy clay loam, Redox
Features: few fine dist.; massive, abundant pebbles of common
manganese concretion, large pebble of chalcedony (~2cm
diameter), non-effervescent, gradual boundary
383-442
C3
Grayish brown to brown (10YR5/2-5/3) sandy clay loam, Redox
Features: common medium dist.; massive, weak relict bedding,
few fine pebbles, non-effervescent, gradual boundary
442-658
C4
Brown (10YR4/3) sandy clay loam, massive, moderate relict
bedding, non-effervescent, gradual boundary
658-898
C5
Dark grayish brown (10YR4/2) sandy loam, massive, slight interbedding, non-effervescent, very abrupt boundary
898-912
C/Ab
Black (10YR2/1) clay loam, massive, organic rich, bedded,
buried soil, non-effervescent, gradual boundary
912-948
C/ABb
Very dark gray to very dark grayish brown (10YR3/1-3/2) loam,
massive, organic rich, bedded, non-effervescent, clear boundary
948-1010
C6
Grayish brown (10YR5/2) fine sand, non-effervescent, clear
boundary
1010-1050
C/Ab2
Very dark gray (10YR3/1) sandy loam, finely-bedded organic-rich
sediment, very fine sand inter-bedded, sample collected at
~1030cm for radiocarbon dating, non-effervescent, clear
boundary
1050-1065
C7
Dark gray to dark grayish brown (10YR4/1-4/2) coarse sand,
bedded, Fe staining in sands at top, non-effervescent, clear
boundary
53
Site Name: SL2B
Location: North of West Tarkio Creek, Page County, Iowa.
Elevation: 985ft.
GPS: 15 300415E, 44 95032N
Landscape position: upper bank of stream system
Parent material: Alluvium
Vegetation: Plowed surface
Slope: 0-5%
Date described: 11/23/10
Described by: AEJ and HAR
Remarks: 2” (5.08cm) and 3” (~7.6cm) diameter PT; described in laboratory and sampled at 5cm
and 10cm intervals and by horizon. Grain-size (pipette method) and carbon isotope analyses ran
on samples. Organic rich clay loam from 866-892cm in depth dated at >43,500 +/- RCYBP.
Depth
(cm)
Soil Horizon
(weathering
zone)
Description
0-33
A1
Very dark grayish brown (10YR3/2) silty clay loam, moderate granular,
sub-angular blocky, shell fragments, few small pebbles, noneffervescent, very abrupt boundary
33-59
A2
Very dark grayish brown (10YR3/2) silty loam, strong firm structure,
angular blocky, non-effervescent, abrupt boundary
59-75
A3
Dark grayish brown (10YR4/2) silty loam, moderate firm structure, subangular blocky, non-effervescent, grassy surface, few fine CaCO3
pebbles, many medium roots, clear boundary
75-97
B1
Very dark grayish brown (10YR3/2) silty clay loam, medium to firm
sub-angular blocky, non-effervescent, organic/clay coatings, medium
roots, gradual boundary
97-124
B2
Very dark grayish brown (10YR3/2) silty clay loam, firm sub-angular
blocky, non-effervescent, few medium roots, many fine roots, very silty
at base, very abrupt boundary
124-157
C1
Very dark gray (10YR3/1) silty clay loam, fine and medium sand, very
friable, non-effervescent, rich in organic material, very abrupt
boundary
157-167
C2
Very dark gray (10YR3/1) silty clay loam, inter-bedded silt and clay,
friable, non-effervescent, very abrupt boundary
167-177
C3
Very dark gray (10YR3/1) silty clay loam, bedded fine/medium sands,
rich in organic material, non-effervescent, very abrupt boundary
177-197
C4
Very dark gray (10YR3/1) clay loam, many fine silt laminations, noneffervescent, very abrupt boundary
54
197-217
C5
Very dark gray (10YR3/1) clay loam, many fine sand laminations,
fining upward sequence, non-effervescent, abrupt boundary
217-225
C6
Very dark gray (10YR3/1) clay loam, medium sand lens, noneffervescent, abrupt boundary
225-249
C7
Very dark gray (10YR3/1) clay loam, many fine sand laminations,
fining upward sequence, non-effervescent, abrupt boundary
249-264
C8
Very dark gray (10YR3/1) clay loam, fine sand laminations, fining
upward sequence, weathered crinoids fossils @ ~277cm, weathered
pebble of black shale @ ~323cm, non-effervescent, abrupt boundary
264-271
C9
Very dark gray (10YR3/1) clay loam, bedded fine to medium sand
lens, non-effervescent, abrupt boundary
271-292
C10
Very dark gray (10YR3/1) clay loam, loamy coarse sand bedding with
rounded clay clasts and weathered rock fragments, fine and medium
root traces, non-effervescent, very abrupt boundary
292-315
C11
Very dark gray (10YR3/1) clay loam, bedded sands, non-effervescent,
very abrupt boundary
315-330
C12
Very dark gray (10YR3/1) clay loam, loamy coarse sand bedding, noneffervescent, very abrupt boundary
330-337
C13
Very dark gray (10YR3/1) clay loam, bedded sands, non-effervescent,
very abrupt boundary
337-349
C14
Very dark gray (10YR3/1) clay loam, loamy coarse sand bedding with
large clasts (~3cm), non-effervescent, very abrupt boundary
349-367
C15
Black (10YR2/1) clay, strong firm to very firm angular blocky structure,
oxidation around roots, many root traces, non-effervescent, very
abrupt boundary
367-397
C16
Very dark gray (10YR3/2) inter-bedded clay loam and silty clay loam,
strong medium to coarse angular blocky structure, firm consistency,
wood @ ~375cm (collected), oxidized iron concretions around organic
material @ ~390cm, non-effervescent, gradual boundary
397-417
C17
Black (10YR2/1) silty clay loam, very firm, massive medium to coarse
thinly bedded structure, bedded organic-rich clay and silt with few fine
pebbles, non-effervescent, clear boundary
417-464
C18
Black (10YR2/1) silty loam, very firm, massive very thinly bedded
structure, some fine gravels, root/wood @ ~440cm-450cm, crossbedding, non-effervescent, very abrupt (possible erosion contact)
boundary
464-471
C19
Very dark gray (10YR3/1) silty loam, very firm, massive medium
bedded structure, organic rich, silt into clay bedded interval on angle,
non-effervescent, very abrupt boundary
55
471-477
C20
Brown (10YR5/3) loamy coarse sand, very firm, massive thin to
medium bedded, coarse lens, non-effervescent, very abrupt boundary
477-500
C21
Black (10YR2/1) clay loam, very firm, massive, organic-rich clay with
few medium silt inter-beds, non-effervescent, very abrupt boundary
500-582
C22
Dark gray (10YR4/1) clay loam, very firm bedded, reduced clay, few
medium organic pebbles and some sand, non-effervescent, clear
boundary
582-637
C23
Very dark grayish brown (10YR3/2) sandy loam, massive, friable, noneffervescent, gradual boundary
637-657
C24
Dark gray (10YR4/1) silty clay loam, finely bedded, very few medium
quartz pebbles, possible buried soil, non-effervescent, gradual
boundary
657-672
C25
Dark gray (10YR4/1) silty clay loam, bedded to medium inter-bedding,
jointing in clays at 45 degrees, graded transition from horizons C24 to
C26, few fine quartz pebbles, non-effervescent, gradual boundary
672-688
C26
Grayish brown (10YR5/2) sandy clay loam, finely-bedded, noneffervescent, clear boundary
688-694
C27
Light brownish gray (10YR6/2) fine to medium pebble-sized gravel,
finely bedded, non-effervescent, very abrupt boundary
694-787
C28
Black (10YR2/1) clay, this is from augured sample, non-effervescent,
clear boundary at bottom of core
787-795
C29
Dark grayish brown (10YR4/2) clay loam, firm, massive bedded,
organic-rich laminates at top, non-effervescent, abrupt boundary
795-804
C30
Dark yellowish brown (10YR3/4) fine very coarse sand, firm, massive
structure, large sand at base (~6mm), non-effervescent, abrupt
boundary
804-819
C31
Very dark gray (10YR3/1) clay loam, firm ,massive structure, fine to
medium feldspar sand lens, non-effervescent, abrupt boundary
819-866
C32
Light yellowish brown (10YR6/4) coarse sand, loose consistency,
~3cm burrow present, abundant angular medium-sized pebbles, noneffervescent, very abrupt boundary
866-892
C33
Black (10YR2/1) clay loam, firm, massive structure, possible buried
soil, few fine rounded weathered pebbles, no bedding, organic-rich
clay, joint facies with staining, non-effervescent, clear boundary
892-912
C34
Very dark gray (10YR3/1) sandy loam, very friable, massive fine to
medium bedding, organic-rich, bedding with random pebble gravel at
base, non-effervescent, clear boundary
56
APPENDIX B – CARBON ANALYSES (RAW)
Line
Identifier 1
Identifier 2
Date Analyzed
Amount (mg)
Ampl 44 (mV)
Area 44 (Vs)
δ 13C VPDB
Org C%
66404
66405
66406
66407
66408
66409
66410
66411
66414
66415
66416
66417
66419
66420
66421
66422
66425
66426
66427
66428
66429
66430
66431
66432
66437
66436
66435
66438
66439
66455
66456
66457
66458
66459
66460
66461
66462
66465
66466
66467
66468
66470
66471
66472
66473
66476
66477
66478
66479
66480
66481
66482
66483
66486
66487
66488
66489
66490
66506
66507
66508
66509
66510
66511
66512
66513
66522
66523
66524
66525
66527
66528
66529
66530
66533
66534
610-615
615-620
620-625
625-630
635-640
645-650
665-670
675-680
685-690
695-700
705-710
715-720
725-730
735-740
745-750
755-760
765-770
795-800
805-810
815-820
825-830
835-840
845-850
855-860
865-870
875-880
885-890
898-905
905-912
915-920
930-935
940-945
980-985
1010-1015
1020-1025
1030-1035
417-420
425-430
435-440
445-450
455-460
464-471
477-480
485-490
495-500
505-510
515-520
525-530
535-540
545-550
555-560
565-570
575-580
582-590
595-600
605-510
615-620
625-630
637-642
647-652
662-667
677-682
704-714
727-733
748-755
769-776
787-791
791-795
804-809
809-814
814-819
866-871
876-881
886-889
892-897
902-907
Core SL-1
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
Core SL-1
"
"
"
"
"
"
Core SL-2B
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
SL2B
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/6/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
8/9/2011
20.664
21.951
20.763
19.485
20.673
21.025
21.098
19.710
25.986
25.526
19.768
22.578
27.793
24.682
22.835
27.174
21.300
21.189
21.418
25.300
18.908
24.471
21.433
18.700
25.120
24.443
19.245
7.257
6.004
15.091
14.225
14.516
14.623
11.272
9.055
5.652
3.373
4.015
3.686
10.277
9.556
10.898
9.971
10.215
16.119
16.472
15.878
14.543
15.774
16.835
14.834
16.638
15.659
14.909
15.179
11.462
11.556
11.237
11.483
9.512
10.967
9.319
10.154
11.873
12.059
9.369
10.466
11.705
7.424
8.085
7.855
7.586
8.555
8.810
8.759
8.929
4058
4063
4645
4482
4274
4245
3394
3373
4555
5074
4261
5037
5777
5176
6344
7375
4320
6575
5429
7399
6121
6542
7190
6552
9771
9072
6545
8257
7478
8094
7627
6995
12575
10350
12840
13595
10529
10417
10239
16437
10291
20044
26689
25271
17067
19662
6096
5396
4776
4535
3708
6614
6673
9203
5670
7045
6517
5061
13682
11743
4517
2494
7401
8089
7624
7875
6304
2969
4035
6003
7369
9525
8677
8904
12024
7324
98.76
99.07
112.47
109.96
102.83
102.82
82.31
81.51
111.71
122.40
103.38
122.50
138.74
124.56
152.54
177.68
104.53
158.66
130.59
176.58
149.81
157.50
176.89
158.30
236.30
218.52
157.33
203.14
183.64
196.80
184.65
168.41
305.66
252.97
315.38
333.51
263.91
263.75
255.44
412.57
253.86
499.91
672.25
636.26
424.77
487.88
146.16
130.74
115.02
109.47
89.67
160.55
161.76
226.68
137.51
174.76
160.56
124.26
341.07
291.21
108.85
62.07
182.57
199.13
183.58
192.01
155.31
73.21
100.82
151.46
181.08
237.85
213.40
219.03
301.60
180.74
-19.75
-20.48
-19.39
-19.31
-19.73
-19.04
-19.23
-18.64
-18.73
-18.76
-18.83
-18.30
-18.82
-18.63
-17.99
-19.14
-19.95
-18.43
-17.97
-17.66
-17.69
-18.05
-17.98
-17.20
-18.09
-18.02
-17.98
-16.28
-15.77
-17.42
-17.36
-17.45
-16.34
-16.42
-15.83
-15.36
-17.69
-17.78
-17.08
-21.03
-20.29
-21.14
-18.23
-17.55
-20.63
-25.74
-24.47
-24.61
-24.01
-23.66
-24.01
-24.35
-25.67
-21.15
-21.00
-21.73
-21.62
-23.41
-25.55
-25.82
-22.54
-21.56
-19.52
-19.79
-19.92
-20.04
-24.12
-21.69
-19.87
-19.66
-19.57
-20.28
-20.15
-19.97
-21.21
-21.32
0.10
0.10
0.12
0.12
0.11
0.11
0.08
0.09
0.09
0.10
0.11
0.12
0.11
0.11
0.15
0.14
0.11
0.16
0.13
0.15
0.17
0.14
0.18
0.19
0.21
0.20
0.18
0.62
0.67
0.28
0.28
0.25
0.46
0.49
0.76
1.44
1.71
1.44
1.51
0.88
0.58
1.00
1.48
1.36
0.58
0.65
0.20
0.20
0.16
0.14
0.13
0.21
0.22
0.33
0.20
0.33
0.30
0.24
0.65
0.67
0.21
0.14
0.39
0.37
0.33
0.45
0.32
0.13
0.29
0.41
0.50
0.68
0.54
0.54
0.75
0.44
57
APPENDIX C – PSA by WEIGHT
Particle Size Analysis - Core SL-1 Per cent by Weight
Depth (cm) Sand%
Coarse Silt% Fine Silt%
Clay%
630-640
19.12
36.95
17.32
26.61
640-650
20.26
36.05
17.75
25.93
740-750
29.89
32.16
12.17
25.77
860-870
28.49
33.88
13.53
24.1
880-890
40.27
26.73
8.82
24.18
890-900
40.64
25.89
11.69
21.78
900-912
17.19
35.37
29.13
18.31
912-920
14.95
43.96
13.68
27.41
930-940
27.56
33.38
14.84
24.22
940-948
15.91
45.31
14.8
23.98
970-980
50.16
20.52
5.19
24.14
985-995
71.19
11.09
-1.2
18.91
995-1010
61.29
16.56
3.83
18.31
Particle Size Analysis - Core SL2-B (Upper) Per cent by Weight
Depth (cm) Sand%
Coarse Silt% Fine Silt%
Clay%
417-430
2.95
29.91
31.24
35.91
430-440
3
33.96
#####
#####
440-450
18.99
24.04
23.5
33.48
450-460
20.38
19.38
24.42
35.83
464-471
15.07
30.78
22.82
31.32
477-487
3.22
39.17
29.4
28.21
487-500
12.7
27.73
25.73
33.83
500-510
4.39
31.21
27.81
36.59
510-520
5.9
28.55
26.17
39.38
520-530
8.47
28.57
24.34
38.62
530-540
10.55
28.92
21.03
39.5
540-550
5.45
31.59
23.66
39.3
550-560
8.07
31.05
22.54
38.34
560-570
9.08
30.75
24.1
36.07
570-582
13.46
30.29
21.58
34.67
582-600
55.69
13.39
10.77
20.15
600-610
62.01
6.87
13.05
18.07
610-620
59.54
8.3
13.52
18.63
##### = No Data
58
Particle Size Analysis - Core SL2-B (Lower) Per cent by Weight
Depth (cm) Sand%
Coarse Silt% Fine Silt%
Clay%
18.79
13.01
620-630
60.25
7.95
637-647
6.69
37.97
25.34
30
647-657
7.16
35.11
25.17
32.56
657-672
6.02
32.37
27.85
33.75
672-688
11.33
33.25
23.62
31.8
694-710
13.24
30.82
27.21
28.73
710-722
15.58
32.28
25.18
26.97
722-740
23.89
28.27
22.62
25.22
740-756
26.78
28.86
19.99
24.38
756-770
24.6
26.36
22.86
26.17
770-787
15.87
30.18
25.73
28.21
28.34
25.22
31.72
787-795
14.72
31.03
16.68
31.12
801-819
21.17
866-874
18.05
28.45
26.13
27.37
50.98
21.81
10.13
17.08
892-902
902-912
43.7
19.83
16.2
20.27
40.41
14.32
20.75
1030-1038
24.52
59
APPENDIX D – PARTICLE SIZE ANALYSES (RAW)
Core Site SL-1 (Lower Depths)
Sample Description
Site ID
Sample ID
SC1
SC1
SC1
SC1
SC1
SC1
Loess Standard
SC1
SC1
SC1
Site ID
SC1
SC1
SC1
Loess Standard
SC1
630.0000
640.0000
740.0000
860.0000
880.0000
890.0000
900.0000
912.0000
930.0000
Sample ID
Weights (gms.)
Top depth
Bottom
(cm.)
depth (cm.)
Top depth
Empty flask Total flask Total sand
1
2
3
4
5
6
7
912.0000 8
920.0000 9
940.0000 10
640.0000
650.0000
750.0000
870.0000
890.0000
900.0000
Bottom depth
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
Empty flask
940.0000
970.0000
985.0000
948.0000 11
980.0000 12
995.0000 13
995.0000
1010.0000 15
14
10.0008
10.0004
10.0005
10.0008
10.0007
10.0008
10.0000
10.0000
10.0006
10.0000
Total flask
0.0000
0.0000
0.0000
0.0000
0.0000
10.0004
10.0009
10.0006
10.0000
10.0016
60
30.5376
29.8403
32.8716
32.8754
33.4135
33.2983
31.6969
31.6037
31.6335
33.2930
Total sand
31.2566
35.0433
36.5976
31.3470
36.1017
Total silt Total clay Sand tare
Silt tare
62.8370
63.5270
62.9416
63.1932
62.5400
62.0120
63.1073
63.3649
63.5125
63.1677
63.6747
63.1930
63.5895
63.0736
63.6203
63.3501
63.1002
63.3777
62.9426
63.2933
62.7269
63.4175
62.8465
63.0989
62.4573
61.9281
62.9755
63.2460
63.4095
63.0698
Total silt
Total clay
63.1042
63.2664
63.5563
63.4076
62.8083
62.6821
60.9635
62.5643
63.5503
62.3132
28.6250
27.8145
29.8821
30.0257
29.3859
29.2343
31.0856
29.8844
30.1389
30.5371
Sand tare
29.6657
30.0269
29.4778
31.0575
29.9713
Silt tare
63.0070
63.1929
63.5119
63.2739
62.7528
Clay tare
63.6080
63.1280
63.5249
63.0132
63.5597
63.2955
63.0509
63.3318
62.8739
63.2326
1
2
3
4
5
6
7
8
9
10
Clay tare
62.6220
60.9030
62.5169
63.5096
62.2673
11
12
13
14
15
Core Site SL-2B
Sample Description
Site ID
SL2B
SL2B
SL2B
SL2B
SL2B
SL2B
Loess Standard
SL2B
SL2B
SL2B
Site ID
SL2B
SL2B
SL2B
Loess Standard
SL2B
SL2B
SL2B
SL2B
SL2B
SL2B
Sample ID
PSA
PSA
PSA
PSA
PSA
PSA
417.0000
430.0000
440.0000
450.0000
464.0000
477.0000
PSA
PSA
PSA
487.0000
500.0000
510.0000
Sample ID
Weights (gms.)
Top depth
Bottom
(cm.)
depth (cm.)
Top depth
Empty flask Total flask Total sand
1
2
3
4
5
6
7
500.0000 8
510.0000 9
520.0000 10
430.0000
440.0000
450.0000
460.0000
471.0000
487.0000
Bottom depth
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
Empty flask
PSA
PSA
PSA
520.0000
530.0000
540.0000
530.0000 11
540.0000 12
550.0000 13
PSA
PSA
PSA
PSA
PSA
PSA
550.0000
560.0000
570.0000
582.0000
600.0000
610.0000
560.0000
570.0000
582.0000
600.0000
610.0000
620.0000
14
15
16
17
18
19
20
10.0005
10.0002
10.0000
10.0009
10.0000
10.0008
10.0008
10.0009
10.0000
10.0007
Total flask
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
10.0000
10.0003
10.0009
10.0005
10.0008
10.0006
10.0012
10.0000
10.0006
10.0009
28.9169
28.1111
31.7781
32.0610
30.8914
29.5539
31.4392
31.1542
30.5773
31.1258
Total sand
30.5114
31.0809
30.0228
31.3968
30.7765
30.2244
30.8439
33.0337
36.1562
35.1994
Sample Description
Site ID
Sample ID
SL2B
SL2B
SL2B
SL2B
SL2B
SL2B
Loess Standard
SL2B
SL2B
SL2B
Site ID
SL2B
SL2B
SL2B
Loess Standard
SL2B
SL2B
SL2B
SL2B
SL2B
710.0000
722.0000
740.0000
Sample ID
Top depth
756.0000
770.0000
787.0000
801.0000
866.0000
892.0000
902.0000
########
Silt tare Clay tare
63.4008
63.0108
63.5228
63.7621
63.6436
63.3144
63.6954
63.5591
61.0674
63.6779
62.5449
36.1770
63.0579
63.2469
62.7079
62.8284
62.9497
63.1606
63.5036
62.6142
63.2325
62.8528
63.3800
63.6111
63.5079
63.1700
63.5635
63.4098
60.9060
63.5136
Total silt
Total clay
63.6887
63.4514
63.1740
62.4496
63.1700
63.2091
62.7805
62.7141
62.3480
63.4142
63.3713
62.0256
63.3165
63.1178
63.1734
62.9679
63.3365
62.7826
63.0906
63.2382
28.6223
27.8111
29.8795
30.0228
29.3843
29.2323
31.0841
29.8837
30.1380
30.5362
Sand tare
29.6644
30.0258
29.4773
31.0565
29.9699
29.3163
29.4979
27.4646
29.9550
29.2444
Silt tare
63.5309
63.2997
63.0162
62.3164
63.0174
63.0583
62.6395
62.6366
62.2700
63.3336
62.4549
63.0921
62.974
63.1571
62.6294
62.7577
62.9072
63.0758
63.4119
62.5155
1
2
3
4
5
6
7
8
9
10
Clay tare
63.2745
61.9266
63.2180
63.0760
63.0773
62.8775
63.2496
62.7321
63.0453
63.1915
11
12
13
14
15
16
17
18
19
20
Weights (gms.)
Top depth
Bottom
(cm.)
depth (cm.)
620.0000
637.0000
647.0000
657.0000
672.0000
694.0000
Total silt Total clay Sand tare
Empty flask Total flask Total sand
1
2
3
4
5
6
7
722.0000 8
740.0000 9
756.0000 10
630.0000
647.0000
657.0000
672.0000
688.0000
710.0000
Bottom depth
Empty flask
770.0000 11
787.0000 12
795.0000 13
819.0000
874.0000
902.0000
912.0000
1038.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
14
15
16
17
18
19
10.0007
10.0003
10.0008
10.0004
10.0003
10.0007
10.0000
10.0007
10.0003
10.0000
Total flask
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
10.0002
10.0002
10.0005
10.0000
10.0006
10.0006
10.0005
10.0001
10.0006
61
34.6529
28.4856
30.6014
30.6311
30.5233
30.5595
31.4527
31.4444
32.5310
33.2162
Total sand
32.1288
31.6172
30.9509
30.7244
32.0903
30.6944
34.6027
31.8388
32.4088
Total silt Total clay Sand tare
Silt tare
63.2077
62.8053
63.2350
63.0980
61.1551
62.4166
60.9369
62.4049
63.9939
63.4203
63.2379
62.2745
63.2895
62.7308
62.1057
63.1591
63.1557
62.7182
63.5940
63.2351
63.1280
62.6666
63.0903
62.9436
61.0162
62.2764
60.7963
62.2742
63.8740
63.3091
Total silt
Total clay
61.0332
60.9366
62.4643
63.0774
63.2023
63.1473
63.6757
63.2420
63.0003
63.6122
63.4096
63.0570
63.4889
63.1231
62.3990
62.5673
63.3648
63.1148
28.6276
27.8166
29.8851
30.0288
29.3904
29.2353
31.0867
29.8865
30.1417
30.5387
Sand tare
29.6683
30.0298
29.4787
30.5270
29.9730
28.8897
29.5042
27.4690
29.9563
Silt tare
60.9103
60.8014
62.3216
62.9432
63.0825
63.0132
63.6075
63.1506
62.9124
Clay tare
63.1908
62.1993
63.2079
62.6462
62.0260
63.0871
63.1068
62.6506
63.5308
63.1740
1
2
3
4
5
6
7
8
9
10
Clay tare
63.5466 11
63.3389
62.9775
63.4420
63.0451
62.3304
62.5245
63.3140
63.0628
12
13
14
15
16
17
18
19
APPENDIX E – PHYTOLITH ANALYSES (RAW)
Phytolith morphotype assemblages were analyzed for four soil samples: 874-882, 882-892, 900910, and 1010-1035 cmbs (centimeters below the surface). Soil samples were mechanically
ground and sieved through standard sieve #10. A 10 gram subsample was mixed with 50
milliliters reverse osmosis (RO) water to enable measurement of pH from the soil solution.
Samples were then decalcified and deflocculated to enable fractionation and sieved through
nested stack of standard sieves #60 and #270 into a sieve pan. Each sand fraction was rinsed with
RO water and transferred to vials for storage. The contents of the sieve pan (silt and clay
fractions) were transferred to 1000 ml beakers. The silt and clay fractions were separated using
standard settling times. Phytoliths were isolated from the silt fraction by heavy liquid flotation
and mounted on microscope slides using balsam. Detailed preparation and microscopic analysis
procedures can be found in Rocheford (2009). Phytolith nomenclature used in this paper follow
the International Code for Phytolith Nomenclature 1.0 (Madella et al., 2005).
In general the abundance of phytoliths extracted from these soil samples was very low.
This could be due to several factors: (1) low abundance of phytolith producing vegetation; (2)
local climate and soil conditions; (3) sample depth from paleo-surface; (4) poor preservation of
phytoliths. First, it is well known that not all plants produce phytoliths. In addition, in phytolith
producing plants, the production of phytoliths is dependent on a number of factors including
temperature, precipitation, and soil pH, e.g. acidic soils increase the free silica available to plants
(Piperno, 2006). Depending on the age of the sediment samples (a proxy of burial depth), there
may be no modern analog of the paleovegetation. This is because the distribution of vegetation
communities is largely driven by climate conditions and the climate conditions of the distant past
have not existed in modern times. Phytoliths are deposited on the soil surface when a plant dies
and downward migration of phytoliths from the paleo-surface is dependent on bio- and pedoturbation of surface with subsurface horizons. Finally, while phytoliths are more resistant to
62
decomposition, under the right conditions they will dissolve. For example, litter in a deciduous
forest decomposes at a faster rate and has a higher pH (more acidic). However, the pH of the soil
solution for all four samples was neutral and was therefore not a factor in preservation of
phytoliths. In addition, the phytoliths in these samples did not exhibit pitting which is
characteristic of dissolution.
Based on microscopic observation of phytolith morphotypes, forest was the dominant
vegetation at the sampling location. The deepest samples: 910-935 and 1010-1035 cmbs were the
only ones with a measurable concentration of phytoliths from grass species and even so a very
small component compared to the overall abundance of phytoliths (Figure 1). This may indicate
that the canopy was more open when these sediments were at the surface and grasses were
replaced as trees matured. All grass morphotypes identified were from grass species that utilize
C3 photosynthesis pathway (Figure 2).
Like phytoliths, charcoal is very resistant to decomposition and is also present in all of
these samples. Charcoal abundance was characterized by quick scan of two rows at 200X
magnification, where each charcoal particle was counted. There is however, no significant change
in the amount of charcoal from one sample to the next. In addition, the phytoliths in the first two
samples exhibit no evidence of charring. Charring causes phytoliths to appear dark, opaque, and
shiny compared to uncharred phytoliths (Figure 3). Charring of phytoliths appears to be limited to
the grass morphotypes suggesting that the dominant forest vegetation was more fire resistant. One
species of fire-resistant vegetation is Cyperaceae, common name sedge, a typical understory plant
in forested areas. Through comparison of multicellular phytoliths observed in these samples
(Figure 4) with images from the GEPEG phytolith reference database (Albert et al., 2011) and
images from Neuman et al. (2009) and Piperno (2009), Cyperaceae is present in all samples from
this study location. No evidence of charred multicellular epidermals from sedge achenes was
observed in any of these samples. A more comprehensive examination and classification of
arboreal phytoliths would provide more detail on specific plant species for this area.
63
APPENDIX F – RADIOCARBON DATA (RAW)
BETA
SUBMITTER SERVICE
MATERIAL PRETREATMENT
MEASURED AGE 13C/12C CONVENTIONAL AGE 2 SIGMA CALIBRATION
297999 SL2B870-1 AMS-Standard delivery (organic sediment): acid washes NA
-19.9 o/oo > 43500 BP
297998 SL2B455-1 AMS-Standard delivery (wood): acid/alkali/acid
150 +/- 40 BP
-25.4 o/oo 140 +/- 40 BP
Cal AD 1660 to 1960 (Cal BP 290 to 0)
64