The document summarizes a micromorphological study of soil samples from a Mississippian house structure at the Lawrenz Gun Club archaeological site. Microscopic analysis of the soil thin sections revealed that the house basin was rapidly filled in by humans with surrounding topsoil after abandonment, rather than being naturally reworked by water or other geological processes. Differences in organic matter and minerals between the living surface and overlying fill indicate the development of a soil post-dated the infilling event. Future work is proposed to further analyze site formation processes and occupation chronology through additional microscopic and chemical studies of the soil profiles.

1. Soil Stratigraphy and ResultsAbstract Methods
Site Formation Processes at Lawrenz Gun Club:
A Micromorphologic Analysis of a Mississippian Structure
Jonathan D. King1, Dr. William G. Monaghan2, Dr. Lara Homsey-Messer1
Indiana University of Pennsylvania1, Indiana University – Bloomington2
Location
Conclusions
Profile B
The Lawrenz archeological site is a Mississippian (900-1600AD) mound complex in the
west-central Illinois River Valley. Several archeological and geological studies have been
conducted to better understand the function and evolution of the site. Initial
geophysical investigations of the site revealed several mound complexes, house-like
structures, and paleochannels of the nearby Sangamon River. During the summer of
2015, one of the house structures was excavated and in-situ soil samples were taken
from the southern soil profile for micromorphologic studies. This form of analysis
involves creating thin sections to observe microscopic aspects of soils and sediments
such as grain size, orientation, organic distribution, and mineralogy. The primary
function of micromorphology in this study is to understand the processes that occur
during site formation (i.e. from habitation to abandonment to excavation) (Courty,
1992). This study reveals that the house basin has undergone rapid anthropogenic
infilling demonstrated by the poor sorting of grains and lack of any primary sedimentary
structures that would indicate hydraulic reworking. Additionally, the living surface of
the house and the overlying fill sediment display differences in organic distribution and
mineralogy, thus indicating that any modern soil development post-dates infilling.
In order to obtain in-situ, oriented sediment samples, 2x4”plastic electric boxes were
hammered into the southern profile of the burnt structure in two locations (see fig. 4
and 5). The first set (15A 1-8; fig. 5) was placed in the western end of the profile related
to exterior wall trenches where stratigraphy of the fill and rebuilding events were
relatively clear. The second (15B 1-6; fig. 4) was located well inside the structure, about
3 m from the western edge of the house (east relative to profile A). Samples were
oriented with the long axis of the boxes perpendicular to the ground surface, and the
“up” direction was noted on the boxes. Most samples were taken on boundaries of
major stratigraphic units that display distinct (or subtle) macroscopic changes in color
and/or texture. The boxes were sent to Applied Petrographic Services Inc. to be
impregnated with a blue epoxy resin (to highlight voids present in the samples), cut,
and mounted on 2x4” glass slides. These were cut and polished to create thin sections
that were analyzed using a polarizing microscope (Jana, 2006).
Future Work
This study provides details about site formation processes related to the infilling of a
Mississippian structure. The house basin was initially excavated, structural elements
were built, and the house occupied, which is indicated by the packed void structure
and minimal pedogenic sediments within and below the cultural horizon. The mixing of
the cultural and A horizons may indicate a brief hiatus between occupation and infilling
but is also likely related to human activity during the infilling (i.e., trampling or mixing
of cultural and fill sediment). The moderate to poor sorting and lack of primary
structures within the sediment indicates that the house basin was filled mainly by
intentional and rapid human activity. The relatively quick rate of infilling did not allow
for natural reworking of sediments. Lack of these natural sedimentary structures (i.e.,
sheet wash deposits) suggests that the basin was filled very rapidly, perhaps in just a
few weeks. The basin was likely filled in by alluvially-derived topsoil (i.e., mollic A-
horizon deposits) surrounding the house basin. Sangamon river derived alluvium is
indicated by the abundant quartz grains and fine-grained particles; relatively high
organic matter contents and root structures support an A-horizon origin. The
subsequent development of the soils post-date infilling signified by the lack of
weathering in the cultural horizon, the low amount (if any) of authigenic clays, and the
absence of a definitive B-horizon.
The cause behind the distinct contrast (even macroscopically) between profile A and
profile B has not been extensively analyzed. It would be expected to see similar
stratigraphy and composition between the two profiles. Perhaps there were various
sources of infill sediment that people were utilizing (i.e topsoil vs. recent flood
deposits).
• Quantitative analysis of soils such as XRF (X-Ray Fluorescence) or grain size analysis.
• Spending more time analyzing profile A.
• Understanding why these profiles contrast in organic content.
• Establishing duration of soil development.
• Taking micromorphology samples from the cultural horizon in order to discern a
more detailed occupation chronology.
• A special thanks to Dr. Jeremy Wilson and the other staff for granting me the opportunity to
participate in the REU.
• The Hardwick family for granting our team access to the site and permission to excavate.
• Petrographic Services Inc. for preparing slides
• IUPUI and IU-Bloomington for allowing me to use their scientific facilities.
• Dr. Nick Deardorff for allowing me to use his photography apparatus and petrographic microscope.
Plow Zone (Pz)
Base of Mollic A-
Horizon(?)
House “floor”
15B-6
15B-1
15A-2
Profile A
Fig. 12: A horizon and cultural horizon boundary
highlighted by low organic content and compact voids
within cultural horizon.
Fig. 10: Channel void where a root once permeated the soil.
15A-1
15A-3
Fig. 19: Example of overall void structure and poor sorting
that is present throughout the entire profile.
Fig. 6: A small bedding plane differentiates the Pz and A horizon
boundary.
Fig. 17: Pottery sherd with quartz sand and shell temper.
Shell has been dissolved leaving only voids.
Fig. 15: Example of overall void structure and poor
sorting.
XPL
Fig. 13: Vughs (large non-connected voids) and poor sorting of
quartz sand, silts, and clays highlight general trends seen in all
samples.
15A-4
PPLXPLPPL
Fig. 8: Pottery sherd with quartz sand temper.
15B-4
Fig. 14: Slide 15A-1
Fig. 20: Slide 15A-4
Fig. 9: Slide 15B-4
Fig. 18: Slide 15A-3
Fig. 7: Slide 15B-1
Fig. 11: Slide 15B-6
Fig. 16: Slide 15A-2
House basin fill
sediments
8
5
4
3
2
1
1
6
2
3
4
5
6
7
Acknowledgements
Fig 3: Southern Wall ProfileEast West
References
Fig. 2: Magnetometry Map of the Lawrenz Gun Club Site
The Lawrenz Gun Club Site is a Mississippian (~900-1600AD) mound complex that lies
along the lower Sangamon River in the west-central Illinois River Valley. Mississippian
culture as a whole is characterized by large earthwork mounds, maize agriculture, and
chiefdom governments (King, 2015). This site in particular contains between 5 and 10
mounds, peripheral defensive palisades, and dozens of small rectangular structures.
This site initially started as a ceremonial complex and eventually evolved into a
palisaded village as a result of conflict with the Oneota tribe to the north. Based on
radiocarbon dates, the Sangamon river provided an extra layer of defense on the
northern side of the village.
The in-situ soil samples used in this study were taken from the southern soil profile of
an extensively excavated rectangular structure (“house”) (fig. 2). The macroscopic
stratigraphy (fig. 4 and 5) has 3 main layers. At the base is the cultural horizon (living
surface) that has been anthropogenically modified due to excavation and occupation
of the house. Above the living surface is the distinctive dark, organic-rich A-Horizon of
the local mollisol (prairie soil) (USDA). The uppermost light layer is the plow zone (Pz)
that is the result of Euro-American plowing of the topsoil.
The primary focus of this study was to determine whether or not the infilling of the
house basin was caused by natural or anthropogenic processes. Additionally, this study
was concerned with site formation processes (i.e. what happens between
abandonment and excavation) and establishing a relative chronology of site formation.
In order to achieve this, the micromorphology slides were used to examine
microscopic characteristics of the infill sediment such as grain size, orientation, and
sedimentary structures. The slides were also used to examine pedogenic (soil
formation) features such as clay distribution, organic distribution, and void structure in
order to determine the relative chronology of soil formation.
N
Fig 1: The Lawrenz Gun Club Site is located in Cass County along the Sangamon River
Background
Fig. 21: Applied
Petrographic Services
Inc. Laboratory
King, A. (2015, August 6). Mississippian Period: Overview. Retrieved April 1, 2016, from New Georgia
Encyclopedia website:
http://www.georgiaencyclopedia.org/articles/history-archaeology/
mississippian-period-overview
Courty, M. A. (1992). Soil Micromorphology in Archeology. Proceedings of the British Academy, 77,
35-39.
Jana, D. (2006). Sample preparation techniques in petrographic examination of construction
materials: A state-of-the-art review. In Proceedings of the Twenty-Eighth Conference on Cement
Microscopy (pp. 23-70).
Mollisols Map. (n.d.). Retrieved April 1, 2016, from United States Department of Agriculture
website: http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/maps/