Quaternary Volcanic Ash Transformation in the Mayan Lowland

Quaternary Volcanic Ash Transformation in the Mayan

Lowland

by

Jim Milawski

B.S. University of Cincinnati, 2006

In Partial Fulfillment of the Requirements

For the Degree of

Master of Science

Geology

University of Cincinnati

Cincinnati, Ohio

Submitted April 15th, 2013

Advisors:

Principle Advisor: Warren Huff, University of Cincinnati, Department of Geology

Advisor: Kenneth Tankersley, University of Cincinnati, Department of Anthropology

Advisor: Barry Maynard, University of Cincinnati, Department of Geology

Abstract

Tikal, Guatemala is one of the largest Archaeological Sites of the Pre-Columbian Era.

Soil samples from Tikal and the surrounding Mesoamerican region were collected for

study of the clay component and chemical properties. The importance of the

discoveries within this research will supply archaeologists’ concrete evidence of soil

transformation from volcanic ash to smectite during the Mayan inhabitance (2,000 BC to

1600 AD). Mayan ceramics have been found to be made with volcanic ash as a

component, the source of the ash and the accessibility is made clear from research

proposed here. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and X-

Ray Fluorescence (XRF) have revealed the presence of volcanogenic deposits prior to

and including the Preclassic through the Postclassic Mayan cultural periods.

Decomposed volcanic ash in the form of smectite has been identified from samples

taken from areas of Mexico, Belize and Guatemala. Euhedrel quartz (50 µm, SEM) has

correlated with smectite identified from XRD, confirming quartz as volcanically

derived. XRF data of the geographically common dust blown Sahara-Sahel is the only

abundant non-volcanic dust source, and does not correlate with the soils from Tikal.

The Ni/Cr and Zr/Y trace elements identified from XRF are a more suited match with

Guatemalan and Salvadoran volcanic events. The existence of smectite within the dated

strata provides clues of the fertility of the soils during Mayan inhabitance.

Acknowledgements

Samples:

Provided by Dr. Ken Tankersley from Dr. Nick Dunning and Dr. Vernon Scarborough

The La Milpa BH-09 and BH-10 pits were excavated as part of the Programme for Belize

Archaeological Project, under the general supervision of Fred Valdez Jr., and with the

gracious cooperation of the Department of Archaeology, Ministry of Tourism and the

Environment, and the Programme for Belize. These excavations were carried out with

the support of a National Science Foundation grant to Vernon Scarborough and

Nicholas Dunning. The Bajo La Justa excavations were carried out as part of the Bajo

Communities Project, directed by Pat Culbert. This research was conducted as part of

Subproyecto Intersitios, directed by Vilma Fialko, as part of the larger Proyecto

Triangulo of the Instituto de Antropología e Historia (Guatemala). The Xcoch Zacate

pit was excavated as part of the Xcoch Archaeological Project under the general

supervision of Michael P. Smyth and supported by an NSF grant to Ezra Zumbro and

Smyth.

Laboratory Testing Techniques:

LST heavy liquid separation for microscopy work: Sarah Trishler

XRD raw data conversion and methodology: Mike Menard

ESEM images: Necati Kaval (University of Cincinnati, Chemistry Department)

Funding:

Graduate School: Dr. Peter Vogt and Bill Matulewicz (Wincom, Inc.)

Table of Contents

Abstract…………………………………………………………………………………….………...…...ii

Blank page…………………………….……………………………………….…………...…...iii

Acknowledgements…………………………………...………...……….………….……....….…...…iv

Table of Contents……………………………………………………………...…….……...…...v

List of Figure, Tables and Images………………………………………....….....…..……...……....vi

Introduction

General Introduction of Project and Findings…………………………….………………...….1-4

Sample Description and Location…………………………………………………………….…..4-9

Volcanic Ash Description……………………………………….……………………......….…...10-13

Bentonite Description and Identification Techniques………………….……………....…..13-15

Research Methods………………………………………………………….…………...…..……..15-20

Results

XRD…………………………………………………………….……………………...………...……....20

Introduction and Methodology…………...……………………………….………...…........…20-24

Sample Group 1…………………………………………………………………………….…….….24-35

Sample Group 2 & 3……………………………………….……………………...………..…….…36-57

ESEM/SEM………………………………………………………………………................…...….58-61

Microscopy……………………………………………………………………...………..........…...61-63

XRF………………………………………………………………...……………………...……..…...63-68

Sample Group 1………………………………………………………………………….……..……65-68

Conclusions……………………………………………………………………………...….……...69-71

Future Research……………………………………………………………………....…….……..71-73

References………………………………………………………………………..……………...…74-78

Figures (Body):

Figure 1: Surface, pit and core samples of reservoirs, ponds, karst depressions and the forest floor. (Figure provided by Dunning, N., 2012)

Figure 2: Map of Reservoirs in Tikal, Guatemala. The red circles indicate reservoirs that were sampled. (Scarborough et al., 2010)

Figure 3: Location of samples from Tikal Op 2B. Figure created by Chris Carr showing the area east of central Tikal, chiefly a large, convoluted depression known as the Bajo de Santa Fe, in which Aguada Vaca del Monte and Aguada de Terminos are located.

Figure 4: Satellite map of ash following the eruption of El Chichon in 1982. (Schneider et al., 1982)

Figure 5: Image of smectite molecule. (Wang et al., 2004)

Figure 7: Technical Guide; Munsell Color Scheme. (Image from http://dba.med.sc.edu/price/irf/Adobe_tg/models/munsell.html Adobe, 2000)

Figure 8: Xcoch Zacate Pit – south profile. (Dunning et al., 2006)

Tables (Body):

Table 1: Sample groups were established by the time of receiving them for analysis. Each sample set is from a different location.

Table 2: Soils Profiles of Arbusto sample location. (Tankersley et al., 2012)

Table 3: Soils Profiles of Corozo sample location. (Tankersley et al., 2012)

Table 4: Soils Profiles of Xcoch sample location. (Tankersley et al., 2012)

Table 5: Group 1 Samples

Tables (Results Section):

Tables 1a – 8a: XRD relative percentage data

Table 1b: XRF trace element data

Figures (Results Section):

Figures 1a – 30a: XRD graphs

Figures 1b - 3b: XRF graphs

Images (Results Section):

Images 1a – 9a: Zircon ESEM/SEM

Images 1b – 7b: Quartz Microscopy

Introduction

The Maya were a Mesoamerican civilization that inhabited portions of Central

American from 2,000 BC to 1600 AD (Tankerlsey et al., 2012). This culture was one of

the largest populations that existed during this time, their food supply was critical in

order to support a large human progression. The Maya civilization attained a high

population density and complex social order during their zenith in the Late Classic

period (Lentz, 2011). Agriculture was very important to the Maya, nutrient rich soils

were essential to provide sufficient crops. The possible existence of chinampa-like

intensive agriculture in the Maya and Gulf Coast lowlands was considered by Palerm

and Wolf (1956) and Caso (1965) years before the first raised fields were identified

(Puleston, 1977). These raised fields or “chinampa’s” are defined as the most intensive

system of agricultural production in Middle America by marsh farming or the farming

of muddy-bottom wetlands (Lot et al., 1979). Examples of these farming conditions have

been well documented throughout Tikal, Guatemala. This region was the heartland of

the ancient Maya civilization. Within Tikal, Maya urban centers or “garden cities” were

largely dependent on their immediate environments for their agricultural production

(Tankersley et al., 2012). Studying the soils of this time period and location will provide

insight into the chemical characteristics of the soils that were available for agricultural

purposes. Suitable soils for agriculture require the ability to store plant nutrients, while

also holding a sufficient amount of water. Guatemala has recently been affected by

drought in 2012, as was this same location at times throughout the Maya inhabitance

(Tankersley et al., 2012). The ability of soils to retain water from precipitation, without

immediate permeation to a deep groundwater table is imperative for successful

agriculture.

During the Mayan inhabitance of southern Yucatan Peninsula from 2,000 BC to

1600 AD, the soils were assumed to be derived largely from the weathering of

limestone. A thorough investigation of the mineralogy and elemental composition of

the soils throughout the previously inhabited Maya Region has not been completed. A

collaborative research project within the University of Cincinnati began in 2010

following the excavation of soils borings from eight reservoirs and three natural

depressions at the Maya ruins of Tikal. The original intentions of the soil samples taken

from Tikal, Guatemala were of archaeological and paleoenvironmental significance.

Studies of archaeological plant remains, molecular genetic studies of forest species and

forest surveys of the vegetation surrounding the Tikal Site Center have provided an

understanding of several key features of the Maya culture. It was found that a large

variety of forest species contributed to the subsistence base of the ancient Maya at Tikal

as food, fuel, construction material and for medicinal applications (Dunning et al.,

2006). Following the general identification of the soils (Figure, 2), AMS radio carbon

dating, and flora and faunal identification were used to date and identify the past

history recorded by past depositional events. Throughout the Mayan Lowland,

volcanic ash has been deposited from explosive volcanic eruptions observed in this past

decade (Schneider et al., 1982). El Chichon and other nearby volcanos to the south and

southwest of Tikal have been active prior to and during the Maya inhabitance and have

contributed volcanic ash deposition to the regions soils. The Tikal soil samples

exhibited chemical properties that were not typical of erosion from the region’s

Cretaceous limestone. Kaolinite is typically the clay mineral formed from the

weathering of limestone (Stahr et al., 2010). The presence of other clay minerals

described in this work suggests an outside source. Photographs taken from these

sample sites show properties of swell and shrink from fluctuations of precipitation

throughout the soils horizons. Soils characterized as vertisols were found during

sample extraction which signified the presence of expandable clays (Tankersley et al.,

2012). Vertisols are characterized by high amounts of these shrink-swell activities,

which are caused by water content fluctuations (Tankersley et al., 2012). An

examination of the soils from this region required further attention to explain the

history and pedogenesis of the region’s soils.

The focus of this project was to determine the source(s) and minerals involved

with the creation of Mesoamerican Soils during the Mayan inhabitance. X-ray

diffraction (XRD), X-ray fluorescence (XRF), heavy liquid separation using lithium

heteropolytungstates (LST), environmental scanning electron microscopy (ESEM) and

optical microscopy were used to determine the composition and possible source of the

mineralogy that has influenced the creation of the Mesoamerican Soils. Soil samples

were taken chiefly from Tikal, Guatemala, the Mayan Highlands, Mexico, and the

greater Caribbean region. These soils contain a significant amount of bentonite.

Bentonite is a common name given to the phyllosilicate clay, smectite and signifies

volcanic ash deposition. Smectite is generally derived from the alteration of volcanic

ash, or of hydrothermal origin which is less common (Fisher et al., 1997). Throughout

this paper, bentonite and smectite will be used to describe virtually the same chemical

composition. The abundance of smectite found within the Mesoamerican samples

confirms that the regions soils were heavily influenced by continuous and widespread

volcanic ash deposition. Without the repetitive deposition of volcanic ash, the amount

of smectite discovered would not be explainable.

Project Samples and Locations

There were a significant amount of soil samples taken from southern Mexico to

southeastern Guatemala (Mesoamerica). There were multiple intentions regarding the

sampling of these soils. The Tikal Research Group directed by Professor Lentz of the

University of Cincinnati’s Biology Department, utilized the samples for anthropological

research chiefly for the study of the Mayan Culture that once inhabitant the sampled

regions. A chronostratigraphic study of Maya reservoirs at Tikal, Guatemala was

completed from AMS radiocarbon sample dating. Measured radiocarbon years before

present (B.P.), were calibrated at two sigma, to define the soils within the cultural

period (Tankersley et al., 2012). Radiocarbon analysis provided dates from carbonized

plant remains and soil organic matter recovered from soils borings. Samples were

collected from excavation pits including wet and dry hand-augured cores. This work

established that the stratigraphy (i.e., soil horizons) extended from the pre-habitation of

the Mayan in the Late Pleistocene, 15,480 + 6014C yr. B.P. to at least the Late Holocene,

Post Conquest, 195 + 35 14C yr. B.P. (Tankersley et al., 2012).

The intended uses of the samples for this project were to identify the soils by

their clay mineralogy and trace element composition. The samples that were used for

this project were received as shallow pit samples (hand dug), shallow split spoon hand

augured samples and reservoir surface and sub-surfaces samples. The following is a

complete list of samples analyzed for this project. These samples have provided a

considerable amount of data which has derived largely from X-ray diffraction.

Sample Group Sample Set Sample

Group 1

Xcoch Zacate Pit 2 Unit 1 – Unit 4

LM BH-10 Unit 3 – Unit 12

LMD-09 Unit 3 – Unit 7

Bajo Justa Corozo Pit Unit ½ - Unit 7

LM BH-9 Unit 2 – Unit 6

Bajo La Justa Arbusto Pit Unit ½ - Unit 7

Group 2

Tikal NIEO Depth 0.0 – 368.0 cm

Tikal 17 Depth 0.0 – 190.0 cm

Tikal 21,22,23 Depth 0.0 – 129.0 cm

Group 3

Perdido Depth 0.0 – 203.5 cm

Vaca del Monte Depth 9.0 – 34.5 cm

Inscription Depth 0.0 – 120.0 cm

Table 1: Sample groups were established by the time of receiving them for analysis.

Each sample set is from a different sampling location within Mesoamerica.

Figure 2 (left): Map

of Reservoirs in

Tikal, Guatemala.

The red circles

indicate reservoirs

that were sampled.

(Scarborough et al.,

2012)

Figure 1 (left): Map of Mexico (west) to Guatemala (east). Surface, pit and core samples of reservoirs, ponds, karst depressions and the forest floor. The red-dashed circles indicate reservoirs that were sampled (Provided by Dunning, N., 2012)

Soils Profiles of Arbusto, Corozo and Xcoch Sample Locations

The below tables provided by Professors Nick Dunning and Vern Scarborough

show the color, organic matter (OM%), phosphorous content (P) part per million (ppm)

and the description of the soils. These profiles originate from Sample Group 1 of this

project, and show the characteristics of swelling and fine grained clays (slickensides).

Table 2: Bajo de La Justa – Arbusto Bajo Soil Pit - North Profile

Stratum Soil

Horizon

Color (Munsell) OM

%

P

(ppm)

Field Notes

1 A1 Very dark gray

(10YR3/1)

3.5 8 Clay loam; large hard crumbs

2 A2 Dark gray

(10YR4/1)

2.2 4 Clay loam; large, hard sub angular blocks

3 A3 Dark gray

(10YR4/1)

2.0 3 Clay loam; small, hard sub angular blocks;

scattered red-orange mottles; slickensides

4 C Gray (10YR6/1) 1.4 3 Clay loam; massive; abundant red-orange

mottles; slickensides

5 2Ab Dark gray

(10YR4/1)

2.7 4 Clay loam with coarse sand; massive;

slickensides

6 2AC Light gray

(10YR7/2)

0.9 1 Clay; massive; slickensides

7 2C White (10YR8/2) 0 0 Clay; massive; slickensides

Table 3: Bajo de La Justa – Corozo Bajo Soil Pit - East Profile

Stratum Soil

Horizon

Color (Munsell) OM

%

P

(ppm)

Field Notes

1 A1 Black (10YR2/1) 6.1 11 Clay loam with coarse sand; large hard

crumbs

2 A2 Black (10YR2/1) 6.2 10 Clay loam with coarse sand; large, hard sub

angular blocks

3 AC Dark gray (2.5Y4/0) 4.2 6 Clay loam; small, hard sub angular blocks;

slickensides

4 C Light gray

(10YR7/1)

1.5 4 Clay loam with coarse sand; massive;

scattered small white and red mottles;

slickensides

5 2Ab Very dark gray

(10YR3/1)

2.8 7 Clay loam; massive; slickensides

6 2AC Light gray

(10YR7/2)

1.3 3 Clay loam; massive; small orange/red

mottles; slickensides

7 2C Sascab and residual limestone

Table 4: Xcoch - Zacate Soil Pit – South Profile

Stratum Soil

Horizon

Color (Munsell) OM

%

P

(ppm)

Notes

1 O Black (10R2.5/1) 8.8 17 Charcoal-enriched; granular; dried algal mat

on surface

2 A1 Very dusky red

(10R2.5/2)

4.8 8 Small hard crumbs; scattered sherds

3 A2 Dusky red

(10R3/2)

3.9 2 Large hard crumbs; +/- 15% limestone

gravel; scattered sherds; irregular boundary

4 AC Dusky red

(10R3/3)

2.6 2 Large sub-angular blocks; +/- 25% limestone

gravel; scattered sherds and fire-blackened

small rocks

5 C Dusky red

(10R3/4)

1.9 2 Massive; a few cobbles and small boulders

Figure 3: Location of samples from Tikal Op 2B. Figure created by Chris Carr

showing the area east of central Tikal, chiefly a large, convoluted depression

known as the Bajo de Santa Fe, in which Aguada Vaca del Monte and Aguada

de Terminos are located.

Volcanic Ash description

The location of the samples taken across Mesoamerica for this project were

obtained from surface, pit and core samples of reservoirs, ponds, karst depressions and

the forest floor. These areas have widely variable conditions in terms of their

depositional environments. Reservoirs, ponds and karst depressions are great

collection areas for all types of erosive and aeolian deposition. These areas are also

locations that are either saturated with water and/or are areas during rainfall and run-

off events that are sites for water collection. Volcanic ash along with the presence of

clay minerals hydrates, preferential sheet like silicates (smectites) are created from this

hydration process (Grim and Guven, 1978). It was very convenient for the purposes of

this project that samples were collected in these ideal locations. If samples were to be

collected to specifically study the pedogenesis of the soils resulting from explosive

volcanism, these would be key locations.

Figure 4 (left):

Satellite map of ash

following the

eruption of El

Chichon in 1982.

(Schneider et al.,

1982)

Forest floor, pit and core samples have also contributed useful information in

determining the extent of volcanism during the life of the soils.

The El Chichon (nearby, active volcano) eruption of 1982 (Figure, 4) created an

enormous ash plume which spread to a nearby town causing damage to a church roof

and other buildings (Fisher et al., 1997). Volcanoes containing magma with a high Si

content can have the tendency to create larger ash fall deposits because of their

explosive nature. The majority of large volcanic ash deposits occur from eruptions

derived from rhyolite, dacite and andesite magma types (Grim and Guven, 1978). The

higher the Si contents of the magma, the higher the viscosity (Grim and Guven, 1978).

Ash deposits are found world-wide, occurring in higher prevalence and thickness near

volcanos or downwind from them. In the case of a large volcanic eruptions, ash can

travel very far distances due to its size (< 2 µm), and the distance it’s discharged into the

air. Eruptions occurring in Yellowstone National Park over the past 2.2 million years

have discharged 3,800 km3 of volcanic ash all across the western United States (Fisher et

al., 1997). In more recent times, the eruption of Mt. Pinatubo in 1991 exploded with a

tall (25 km high) and extensive ash cloud, covering large areas of the Philippines and

the Pacific Ocean (Fisher et al., 1997). The amount of volcanic ash deposited during this

event and others in the past have produced many bentonite deposits that are currently

being mined for an uncountable amount of uses. These bentonite deposits are

characterized the abundance of the clay mineral smectite, and the presence of a variety

of trace elements dependent upon the source of the volcanic ash and mineralogy of the

depositional environment. A high potential remains that the source of the ash which

covered Mayan inhabited areas could have traveled far, due to the chemical nature of

the regions volcanos and examples of current volcanism (Figure, 4).

The occurrence of ash falls across earth is widespread, majorly along plate

boundaries, subduction zones and hot spots (Grim and Guven, 1978). The degassing of

volcanoes is the major contributor to the eruption of ash falls and gases. Beneath the

center of a typical volcano, gases (H2O, SO2, CO2, CO, HCl, H2, H2S, HF, etc.) are

dissolved deep in rising magma (Fisher et al., 1997). As magma draws closer to the

surface through convective currents, pressure decreases. The decrease in pressure

liberates trapped gases that are no longer soluble in the molten material. As the magma

arrives within the volcano, the volcanos begin to swell due to the re-arrangement of the

chemical structure of the gases (swelling). Magma consisting of continental crust

(rhyolitic) can hold more water than oceanic crust (basaltic), resulting in larger amounts

of liberated water possible within more viscous (higher Si content) magma (Grim and

Guven, 1978). The higher the silica contents of magmas, the higher the viscosity. The

majority of large volcanic ash deposits occur from eruptions derived from rhyolite,

dacite and andesite magma types (Fischer et al., 1997).

Volcanic ash and its degradation products have been seen to add fertility to soils,

aiding the agricultural aspect of a civilization (Tankersley et al., 2011). The Cation

Exchange Capacity (CEC) is very high for smectite due to the cumulative surface area of

clay particles and organic matter. Soil particles are negatively charged and as such are

capable of storing and supplying plant nutrients, many of which are positively charged

cations (Triantafilis and Buchanan, 2007).

Figure 5: Smectite is a

2:1 clay that consists

of two tetrahedral

layers with one

octahedral layer

between the two

tetrahedral layers.

Exchangeable cations

and water molecules

are located in the

interlayer position of

this phyllosilicate

mineral. (Wang et al.,

2004)

Volcanic ash is commonly documented in outcrops consisting of sedimentary

rocks, and when preserved, ash compacts well beyond its original thickness. For

instance, volcanic ash and bentonite layers in the Black Hills region consist of

Cretaceous materials which can be lenticular or long continuous layers (Grim and

Guven, 1978). Given that ash deposits are documented in many location, they can be

identified by their color, grain size and bedding characteristics in the field (Grim and

Guven, 1978).

Bentonite Description

Upon deposition of the volcanic ash onto many types of terrestrial terrain and

shallow marine environments, certain locations are preferentially suited for fast and

ideal chemical formation of ash to bentonite. There are a variety of known methods of

the formation of bentonite; this research solely focuses on the alteration of in situ

material volcanic ash (most common). Examples of in situ alteration of volcanic ash to

bentonitic material are the vast deposits from the Cretaceous age in Wyoming and

Montana (Grim and Guven, 1978). Following the deposition of ash, bentonite and ash

deposits can be characterized by the type of non-clay minerals present, associated beds

of ash or tuff, the high concentration of clay minerals and the absence of detrital

minerals The ideal environment for the formation of bentonite from ash is undoubtedly

a shallow, aqueous environment (Tankersley et al., 2012). It has also been noted that

high silica content (rhylotic to dacitic) of the volcanic ash or the presence of Mg in

nearby bedding can speed up the intensity of the conversion of ash to bentonite (Grim

and Guven, 1978). The presence of mixed layered clays are found in many locations

indicates that there are several forms of bentonite which depend on the starting ash

composition, the surrounding mineralogy, the presence of water and the depositional

environment.

There are a variety of known chemical properties of smectites, dioctohedral and

trioctohedral smectite are the two forms that can form. Smectite is an expansive 2:1

(dioctahedral) or 3:1 (trioctahedral) phyllosilicate mineral with varying compositions

depending on the interlayer cations present and the composition of the tetrahedral

sheets (Kloprogge et al. 1999). The dioctohedral form (Figure, 5) of smectite includes

clay minerals such as montmorillonite, beidellite and nontronite, while the trioctohedral

form includes the hectorite – saponite series of clay minerals (Grim and Guven, 1978).

The dioctohedral smectite minerals are typically more Fe and Al rich, while the

presence of Li in the saponite series of the trioctohedral group yields its character (Grim

Figure 6: Plasticity chart

showing results of

Atterberg limits on

undisturbed and oven-

dried samples.

(Atkinson, 2000)

and Guven, 1978). There are an abundance of possible combinations of cations presence

within these layers, so there are a number of possible arrangements which lead to

several classifications of smectite and mixed layered clays.

Bentonite Identification Techniques

There are several methods for the identification of bentonites, X-Ray Diffraction

(XRD) is the most common method employed. There are chemical and physical tests

that can be performed on material that appears to be bentonite. Identification can also

take place in the field or brought into the laboratory for evaluation. Given that

bentonites are documented in many locations, they can be identified by their color,

grain size and bedding characteristics in the field, as well as the presence of

volcanogenic phenocrysts. The plasticity of soils can be a physical determinant in

indicating the expansiveness of soils (Figure, 6). An instrument called an Atterberg Device

measures the liquid and plastic limits of soils. A geotechnical methods known as ASTM

CL = low-plasticity clay

CH = high-plasticity clay

ML = low-plasticity silt

MH = high-plasticity silt

OH = high-plasticity organic soil.

D4318 utilizes this device by revealing the swelling properties of clays (Atkinson, 2000).

Physical properties of clays provide insufficient chemical data in order to identify types

of bentonites found on earth. The ability to perform XRD on clays reveals information

regarding the clays crystallographic structure and chemical composition. Samples for

XRD preparation can be prepared as, but not limited to, powders, pellets, smears and

by evaporation. There has been much work with characterizing the 2 theta diffraction

angles and corresponding intensities of bentonites. There is a terrific key of powder X-

ray diffraction patterns supplied by Chen, (1977). This data provides known diffraction

values for around 240 different minerals, which includes many types of clay.

Identifying the different chemical characteristics can be done fairly easy with Chen’s

table. A researcher will identify smectite from its critical d-spacing, 2-theta and

intensity values. Smectite can be treated with ethylene glycol to observe the expansion

from its first order peak at 14.0 – 15.0 to 17.0 angles of diffraction (d-spacing values).

Other than the expansion from glycol, smectite can also be further reiterated by heating,

which identifies the smectites known collapse with increase in temperature.

Finally, there are many other methods for analyzing bentonites that have not been

mentioned: atomic absorption spectroscopy (AAS), mass spectrometry (MS), swelling

index, swelling pressure, and thermal conductivity. AAS can be used to quantitatively

determine the trace elements in a solid or a liquid. MS would provide ideas of mass

weights which could be identified from the known molecular weights of the different

forms of smectite. Besides identifying elemental smectites, this data could provide clues

to the nature of absorbed interlayer cations. Mass additions from the original structure

of the smectite could be subtracted from a standard smectite with open activation sites.

The swelling index (ASTM D 5890), of a soil is typically used by civil engineers during

the construction or renovation of something regarding soil. This method could help

identify soils as expansive when questioning if soils could contain a smectite

component. Osmotic pressure can give rise to a macroscopic stress acting

uniformly on the surroundings if the swelling is restricted to a volume smaller

(osmotic pressure) than that of maximum swelling (Karnland, 1998). The presence of

euhedral quartz grains does not tell us about the types of smectites present within the

bentonite, although it gives the investigator a firm confirmation for a volcanic origin of

the quartz grains. This helps when smectite is found in other testing methods but in

low amounts, so verification of volcanic origin from material within the bentonite can

reiterate that bentonite is likely present. Clay mineral identification of soils can be

completed on a quantitative and qualitative basis. Visually, soils can be matched by the

Munsell Color (Figure, 7), the cohesive properties and by grain size (sieve analysis).

Figure 7 (left): Munsell Color Scheme (Adobe, 2000)

The colors were simply identified as R for red, YR

for red-yellow, Y for yellow, etc. Each primary and

intermediate color was allotted ten degrees around

the compass and then further identified by its place

in the segment.

XRD (X-ray Diffraction)

The clay component of soils (< 2 µm) is frequently determined by powder X-ray

diffraction (XRD). Clay minerals are composed of crystalline structures and when

bombarded by X-rays, these structures diffract back at known angles and intensities

(Chen, 1977). For the purpose of this research project, XRD has proved invaluable in

identifying the clay components of samples taken from many locations across

Mesoamerica. The main objective of XRD for the analysis of these samples is to

determine the presence and quantity of volcanic components. Smectite has been

discovered throughout the majority of the tested soils from Mesoamerica. Likewise,

degradation products of smectite, kaolinite and chlorite, are found throughout the

samples. A large component of quartz is found throughout the samples, which

coincides with the composition and formation of smectite from volcanic ash. Quartz

analysis by XRD does not describe the amount of physical weathering of grains,

although this method is good for determining amounts of quarts present in these

samples. However, the presence of euhedral (i.e. well-formed crystal faces) as revealed

in SEM images would argue strongly for a volcanic origin. Calcite or calcium carbonate

was also identified across the sampled region. The Mesoamerican region is underlain

by Cretaceous limestone; the degradation of the bedrock across the region will continue

to add this elemental composition to the regions soils.

XRF (X-ray Fluorescence)

Trace element data collected throughout the collaboration of this project can be

used to compare the composition of the smectite rich soils collected with the tephra and

lava compositions of nearby suspect volcanos. Twenty nine XRF pellets were prepared

from Sample Group 1. A Rigaku 3070 X-ray Fluorescence spectrometer was used to

determine the quantitative amount of the trace elements; Mo, Ba, Co, Cr, Cu, Nb, Pb,

Rb, Sr, Th, U, V, Y, and Zn. The goal of this portion of research was to collect the trace

element composition of the samples for comparison with tephra’s and lavas found in

the database developed by Carr et al. (1987). It is clear from this analysis that each

sample location has a characteristic chemical signature of their trace element

composition.

Environmental Scanning Electron Microscopy (ESEM) & Optical Microscopy

These qualitative techniques were used to obtain visual images of quartz grains

and zircons in order to establish the amount and type of weathering as well as locate

trace minerals associated with volcanism. The presence of physically unaltered quartz

would point to a non-fluvial deposition due to its lack of weathering. Other possible

sources of SiO2 found within the regions soils can be traced to well know Aeolian quartz

form Africa. Central American soils have been known to contain quartz from Aeolian

transportation from Africa Sahara-Sahel dust (Tankersley et al., 2012). Although quartz

could provide a component to create the phyllosilicate minerals discovered within this

region, it lacks the metal cations required to build such silicate minerals as smectite.

Volcanic ash deposits and transformed smectite have been known to contain a zircon

component. Zircons are resistant to chemical and physical weathering. Dense minerals

such as zircons form during igneous processes and should be present within soils

containing a significant amount of volcanic deposition (Parrish et al., 2012).

Results: XRD Sample Preparation, XRD Parameters and Procedure:

Core, Pit and surface samples were received from various locations (Figure 1).

XRD analysis was performed over the two theta range utilized of 2 to 32 degrees, at a

step size of 0.5 degrees. After completion of XRD analysis, the peak threshold

parameter was set to 1.6, which removed low intensity peak and instrument noise.

These peaks were identified in relation to their known d-spacing, 2 theta values and

intensities. The minerals targeted in this method were the clay sized fraction and

possible volcanic non-clay minerals including zeolites, zircons and quartz. The majority

of the samples analyzed by XRD contained the clay minerals smectite and kaolinite with

a predominant presence of quartz. The measurement range of 2 to 32 degrees was

broadened to 60 degrees for a few samples in order to detect minerals unseen within the

2 to 32 degree range. A few representative samples were saturated with ethylene glycol

to provide indications of the expandability of the samples analyzed. The expansion

from non-treated to treated glycol samples proved smectite identification positive from

d-spacing values shifting from 14-15.5 to 16-17 Angstroms (Chen, 1977) within the first

order peak for smectite. Further analysis could possibly yield the type of smectite

mineral present comparing XRD data for di and tri octahedral minerals. This method

proved successful. High mineral intensities were acquired and smectite was yet again

detectable in the majority of samples analyzed. The remaining parameters noted above

were conducted with the following exceptions. First, the theta range was occasionally

modified from the above to analyze the presence of mixed layered clays (smectite +

kaolinite, possible chlorite). The samples received for XRD preparation were either un-

sieved pit, core and surface samples or sieved fractions of the samples containing the

clay component ( < 75µm). Samples were heated to 350° C to observe any collapse of

the smectite structure and to 550° C to achieve complete crystallographic structure

degradation of kaolinite (Moore and Reynolds, 1997).

Measurement of the Relative % of Minerals Identified:

The following relative percentages are of the fine silt to clay sized fraction of the

samples received. The relative percentages of minerals were calculated from:

The counts per second (cps) were totaled for each individual sample analysis.

The sum of all peaks (cps) for each mineral was divided by the total cps for that

sample.

The total cps per mineral divided by the total cps in the sample gave the relative

% of that mineral per the sample analyzed.

XRD Preparation & Procedures:

Method 1:

Samples were received as un-sieved core samples around 2” in diameter. Soil

samples were prepared in a deionized water slurry, in 100 ml beakers. Following the

natural gradation of the particles in the beaker, a 5 ml pipette was used to take sediment

from the top portion of the water slurry. The glass slides were coated with the < 2µm

clay fraction according to Stokes Law. The minerals targeted in this analysis were

smectite and quartz, while also identifying any minerals that had a significant presence.

The majority of the samples analyzed by XRD contained primarily calcite, smectite and

quartz. After the measurement range of 2 to 32 degrees two theta was broadened to 2 to

60 degrees, many additional peaks were observed, although they were all associated

with calcite and quartz. Glycol samples were prepared to help with the positive

identification of smectite.

Method 2:

Core samples taken from Tikal and surrounding regions were received as <

75µm sieved samples. These samples were prepared as deionized water slurries, in 100

ml beakers. Following the natural gradation of the particles in the beakers, 5 ml

pipettes were used to take clay sized sediment and water from the top portion of the

suspended sediment. The minerals targeted in this method were the clay sized fraction

and possible present volcanic non-clay minerals (zeolites, zircons and quartz). The

majority of the samples analyzed for XRD contained smectite, quartz and calcite. The

measurement range of 2 to 32 degrees two theta was broadened to 60 degrees for a few

samples for detecting minerals potentially unseen within the 2 to 32 theta range.

Further peaks for calcite and quartz were identified, with no other minerals reflections

documented. A few samples were soaked (> 30 minutes) in ethylene glycol to provide

indications of the expandability of the samples analyzed. The expansion from non-

treated to treated glycol samples proved positive for smectite with d-spacing values

shifting from 14-15.5 to 16-17 angstroms (Chen, 1977) within the first order peak for

smectite.

Method 3:

This procedure was employed for samples that contained a small fraction of clay

sized material. The previous method utilizing the natural gradation of sediment in

beakers did not yield enough samples to prepare slides for XRD. Therefore, a Sorvall

Centrifuge was used to obtain an adequate amount of fine powdered sediment to smear

onto a glass slide. This method proved successful and high mineral intensities were

acquired. Smectites were again detectable in the majority of samples analyzed. The

remaining parameters noted above were followed with the following exceptions.

The counts per second (cps) used in Method 2 were occasional modified from the above

due to the presence of mixed layered clays (smectite + kaolinite, possible chlorite). The

samples received for XRD preparation were unsaved pit, core and surface samples.

Samples were heated to 350° C (collapse of the smectite structure) and 550° C (complete

crystallographic structure degradation of any associated kaolinite). There has been

much work with characterizing the 2 theta refraction angles and corresponding

intensities of bentonites. Utilizing the key index of powdered X-ray diffraction patterns

supplied by Chen, (1977) provides a quick and easy method for pattern interpretation.

There are several more comprehensive standards used to identify clay minerals by XRD

(Fink Index) although Chen’s key tables reveal commonly found clay minerals (around

240 different minerals).

Group 1 Samples: Six sampled locations across Mesoamerica

There are six different sample locations (Figure, 1) and 35 total samples for the

following XRD data. Air dried analysis was completed for the 35 samples. In addition,

ethylene glycol and heat treated samples have also been employed when needed for

further identification. Data variance between sampled locations is low, so a

representative sample from each location was utilized for further ethylene glycol and

heat treatment mineral verification. The majority of sampled locations all contain the

same clay mineral fingerprint with smectite and quartz found at all six sampled

locations (Figure, 11a). A number of samples also contained the clay mineral kaolinite.

This became apparent after heated air-dried slide samples at 550°C showed the

disappearance of the first and second order peaks (1st order: 7.15 Å )(2nd order: 3.57 Å)

(Figure, 1a). Chlorite also seems apparent in a few of the sampled locations (Figure,

10a). Heating samples to 550°C has aided in the collapse of the 1st order peak for

smectite (14.0-15.5) which discloses the chlorite (14.36 Å) that would have been

otherwise masked (Figure, 10a).

Table 5: Guatemala, Belize and Mexico Samples (6 Sampled Locations):

Xcoch Zacate Pit 2:

Air Dried EG 350 550 > 32 Theta

Unit 1

X

Unit 2

X X X

Unit 3

X

Unit 4

X

LM BH-10:

Unit 3

X

Unit 4

X

Unit 5

X

Unit 6

X

X

Unit 7

X

X

Unit 8

X X

X X

Unit 9

X

Unit 10

X

Unit 12

X

LMD-09:

Unit 3

X

X

Unit 4

X

Unit 5

X X

Unit 6

X

Unit 7

X

Bajo Justa Corozo Pit:

Unit 1/2

X

Unit 3

X

Unit 4

X X X

Unit 5

X

Unit 6

X

Unit 7

X

LM BH - 9

Unit 2

X

Unit 3

X X

Unit 4

X

Unit 5

X

Unit 6

X

Bajo La Justa Arbusto Pit: Unit 1/2

X

Unit 3

X

Unit 4

X

Unit 5

X

Unit 6

X X X

Unit 7

X

X

0

500

1000

1500

2000

2500

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

LM-BH_10_Unit 6_Heated to 550 LM-BH_10_Unit 6

Figure 1a: LM-BH-10; Unit 6 XRD Analysis of Air Dried and heated treated sample 550° C

2 theta

Inte

nsi

ties

(cp

s)

KA

SM

Collapsed SM

SM = Smectite KA= Kaolinite Q = Quartz

KA

Sample location: LM-BH-10

Summary:

This sample set contained the most apparent kaolinite mark in regards to the 6 total sampled locations. The material was received un-sieved. Each XRD sample from this location was prepared as a smear with the aid of a centrifuge. Each samples physical appearance (color) varied greatly over the nine total samples tested. It was obvious to the trained eye that these samples contained a high percentage of clay sized particles (sheen). Sample Unit 7 contained an abundant amount of gypsum, which was identified visually and it characteristic XRD pattern (strong d-spacing at 7.57) Clay Sized Minerals Present: Smectite: 21 – 96% Peaks (d-spacing): 1st order: 14.10 – 14.65 Kaolinite: 0 – 42% Peaks (d-spacing): 1st order: 7.14 - 7.40 Peaks (d-spacing): 2nd order: 3.57 Quartz: 0 – 60% Peaks (d-spacing): 1st order: 3.31 – 3.34 Peaks (d-spacing): 2nd order: 4.20 – 4.24

0

100

200

300

400

500

600

700

800

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

LMD-09; Unit 6 Air Dried

Figure 3a: LMD-09 XRD Analysis of Unit 6, Air Dried

2 theta

Inte

nsi

ties

(cp

s)

KA

SM SM = Smectite KA= Kaolinite Q = Quartz CA= Calcite

KA

Q

Q SM CA

Sample location: LMD-09

Summary: The XRD data from this location are mostly homogenous throughout. A few of the un-sieved powdered samples ran from this group showed positive signs of calcite and dolomite, likely due to the presence of larger grain sizes. The majority of the samples contained significant amounts of smectite and quartz. Kaolinite is apparent at a low amount, further ethylene glycol and heat treatment will likely reveal if chlorite is also present. Clay Sized Minerals Present: Smectite: 44 – 61% Peaks (d-spacing): 1st order: 14.10 – 14.65 Kaolinite: 14-19% Peaks (d-spacing): 1st order: 7.14 - 7.40 Peaks (d-spacing): 2nd order: 3.57 Quartz: 25 - 28% Peaks (d-spacing): 1st order: 3.32 – 3.34 Peaks (d-spacing): 2nd order: 4.22 – 4.25

0

200

400

600

800

1000

1200

1400

1600

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

LMD-09; Unit 7

Figure 4a: LMD-09 XRD Analysis of Unit 7, Air Dried

2 theta

Inte

nsi

tie

s (c

ps)

KA

SM SM = Smectite KA= Kaolinite Q = Quartz

KA

Q

Q SM

LMD-09 Continued:

0

200

400

600

800

1000

1200

1400

1600

1800

2 3 4 5 6 7 8 9 1011121314151617181920212223242526272829303132

Airbusto; Unit 4 Airbusto; Unit 4 400 C

Figure 5a: Airbusto XRD Analysis of Unit 4, Air Dried & Heat Treatment to 400°C

2 theta

Inte

nsi

ties

(cp

s)

KA

SM


KA

Q

Q SM

Partial Collaspe of Smectite, Chlorite presenet?

Sample location: Bajo La Justa; Arbusto Pit

Summary: This sample set contained a significant quantity of smectite according to the air dried analysis. As represented below, the 1st order peak for smectite has a slightly higher 2 theta range (lower d-spacing). The material was received un-sieved. Each XRD sample from this location was prepared as a smear with the aid of a centrifuge. The core samples provided appeared to have a large amount of clay sized particles. There appears to be trace quantities of kaolinite, along with the likely presence of chlorite according to the appearance of expandable minerals exposed following heat treatment to 400°C. Running the air-dried sample at a slower speed may give further definition for the chlorite signature. Clay Sized Minerals Present: Smectite: 68 % Peaks (d-spacing): 1st order: 12.52 – 15.46 Kaolinite: 10 % Peaks (d-spacing): 1st order: 7.14 - 7.15 Peaks (d-spacing): 2nd order: 3.53 – 3.56 Quartz: 22 % Peaks (d-spacing): 1st order: 3.31 – 3.34 Peaks (d-spacing): 2nd order: 4.20 – 4.24 Chlorite: Was not further analyzed due to total collapse of smectite, revealing little to no chlorite.

0

200

400

600

800

1000

1200

1400

1600

1800

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Airbusto; Unit 3

Figure 6a: Airbusto XRD Analysis of Unit 3, Air Dried

2 theta

Inte

nsi

tie

s (c

ps)

KA

SM


KA

Q

Q SM

Arbusto Continued:

0

200

400

600

800

1000

1200

1400

1600

1800

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Corozo; Pit 1/2

Figure 7a: Corozo XRD Analysis of Pit 1/2, Air Dried

2 theta

Inte

nsi

ties

(cp

s)

KA

SM


KA

Q

Q SM

Sample location: Bajo La Justa; Corozo Pit

Summary: This sample set contained a varying quantity of smectite according to the air dried analysis. The material was received un-sieved. Air dried samples from this set were prepared using the pipette method and powdered samples were ran. A smear sample is required for further analysis of “Pit 6” to verify the presence of feldspars. Running the air-dried sample at a slower speed may give further definition for the kaolinite minerals present. Clay Sized Minerals Present: Smectite: 15 - 54 % Peaks (d-spacing): 1st order: 14.69 - 15.02 Kaolinite: 0 - 19 % Peaks (d-spacing): 1st order: 7.14 Peaks (d-spacing): 2nd order: 3.56 Quartz: 10 - 27 % Peaks (d-spacing): 1st order: 3.33 – 3.34 Peaks (d-spacing): 2nd order: 4.24 Calcite: 0 – 45 % Peaks (d-spacing): 1st order: 3.03

0

100

200

300

400

500

600

700

800

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Corozo; Pit 6

Figure 8a: Corozo XRD Analysis of Pit 6, Air Dried Powder

2 theta

Inte

nsi

ties

(cp

s)

CA

SM

SM = Smectite KA= Kaolinite Q = Quartz CA= Calcite F= Feldspar

Q Q

SM F

0

200

400

600

800

1000

1200

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

LM-BH-9; Unit 5

Figure 9a: LM-BH-9 XRD Analysis of Unit 5, Air Dried Sample

2 theta

Inte

nsi

ties

(cp

s)

KA


Q

Q

SM KA

Sample location: LM – BH - 9

Summary: This sample set contained a significant amount of fine grained quartz and smectite according to the air dried analysis. The material was received un-sieved. Air dried samples from this set were prepared using the centrifuge smear method and powdered samples were ran. Running the air-dried sample at a slower speed may give further definition for the kaolinite minerals present. There could be chlorite present, the ethylene glycol treatment would provide the identification. There is an unidentified peak at 6.581 d-spacing, although it may be noise due to its low intensity (103 cps). Clay Sized Minerals Present: Smectite: 36 % Peaks (d-spacing): 1st order: 14.90 - 15.23 Kaolinite: 10 % Peaks (d-spacing): 1st order: 7.19 Peaks (d-spacing): 2nd order: 3.58 Quartz: 50 % Peaks (d-spacing): 1st order: 3.34 Peaks (d-spacing): 2nd order: 4.25 Chlorite: Ethylene glycol treated sample.

0

100

200

300

400

500

600

700

800

900

1000

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64

Zacate Unit1

Figure 10a: Zacate Pit 2 Bulk XRD Analysis of Unit 1, Pellet

2 theta

Inte

nsi

ties

(cp

s)

Ca Ka/CH

Ka/CH= Kaolinite & Chlorite Q = Quartz Ca= Calcite

Ca

Q

Ca & Q Ka/CH

Sample location: Xcoch Zacate Pit 2

Summary: This sample set contained red (likely oxidized, Fe rich) coarse grain sized samples. Air-dried samples were prepared with the pipette method, although very low intensities were observed (500 CPS Max. The difficulty arises when there is very little < 0.5 g of clay sized particles within each sample. The centrifuge – smear method was employed here, there was not enough sample to prepare slides. The samples were dried and pressed into pellets for future XRF, these pellets were utilized to look at the bulk XRD mineralogy. The results for this sample group are not directly comparable to the other completed data sets. Clay Sized Minerals Present: There are weak intensities present of a kaolinite/chlorite mixture. The chlorite present

appears to be Fe-rich Chlorite due to the absence of the 1st and 3rd order peaks. Though

the intensities were rather low, the repetitiveness throughout the units signifies the

minerals. The majority of this sample group contains calcite and quartz. The below

graph is a good representation of the bulk XRD analysis of the entire Zacate Pit 2 Group

of samples.

0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

LM-BH-9; Unit 5 Corozo 1/2 Airbusto; Unit 4 LMD-09; Unit 7 LM-BH-10; Unit 6

Figure 11a: XRD Compilation of All Units, Air Dried Samples

2 theta

Inte

nsi

ties

(cp

s)

KA


Q

Q

SM

KA

Summary:

- The majority of the sampled locations have a very similar clay component,

although some of the bulk samples had much more clay then others.

- Smectite is present in nearly all samples tested and ethylene glycol treatment

provided confirmation in a few samples.

- Kaolinite was further confirmed following observations of the major peak collapses

after air-dried samples were heated for 1 hr. at 550°C.

Questions:

Does the compilation data below suggest that these locations have very similar

depositional environments? Does the smectite present below suggest heavy

volcanic activity? When the volcanic ash was deposited, what cations were

available to create the octahedral sheets within the smectite? Ca (CaCO3) or Mg/Ca

from MgCa(CO3)2? Are there other free cations present from previous source

erosional deposits?

Overview of XRD Test Method and Sample Description for Inscription Samples:

Inscription Core Samples (Figure, 2) were received as < 75µm sieved samples.

These samples were prepared using METHOD 2 (Page, 23). The depth of Inscription

samples analyzed ranged depths from 0.0 to 120.0 cm. The minerals targeted in this

analysis were the clay sized fraction (< 2µm). The majority of the samples analyzed by

XRD contained smectite, quartz and calcite. It appears that if the measurement range of

2 to 32 degrees two theta was broadened, more minerals could potentially be identified.

The 0-10 cm pipette sample was exposed to ethylene glycol > 1 day, the analysis proved

the positive identification for smectite.

Preparation of the Relative % of Smectite, Quartz and Calcite:

The relative percentages of quartz, smectite and calcite were calculated from

three steps. The total counts per second (cps) were totaled for each individual 10 cm

XRD result. The sum of all peaks (cps) for smectite and quartz were divided by the

total cps for that 10 cm sample. Finally, The total cps per mineral divided by the total

cps in the sample gave the relative % of that mineral for that depth interval.

Inscription 1 Pipette XRD Data

Depth: (0-10.0 cm to 110.0-120.0 cm)

Depth (cm)

Smectite Relative %

Quartz Relative %

Calcite Relative %

0 - 10 76 24 0

10 - 20 84 16 0

20 - 30 26 13 61

30 - 40 29 11 60

40 - 50 27 9 64

60 - 70 23 7 70

70 - 80 25 9 66

100 - 110 12 8 80

110 - 120 23 18 59

0 20 40 60 80 100

0 - 10

10. - 20

20 - 30

30 - 40

40 - 50

60 - 70

70 - 80

100 - 110

110 - 120

Figure 12a: Relative Percentages of Smectite, Quartz and Calcite ( < 75µm Grain Size) (Inscription Core)(XRD)(2 to 32 Degrres 2

Theta)(Pipette Samples)

Dep

th (

cm)

(In

scri

pti

on

1)

SmectiteRelative %

QuartzRelative %

CalciteRelative %

Table 1a: Total Average (INS; 0-10cm to

110-120 cm):

Smectite (Relative %): 36

Quartz (Relative %): 13

Calcite (Relative %): 51

Tikal XRD Data

Inscription 1 (0 cm to 10 cm)

0

100

200

300

400

500

600

700

800

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Inte

nsi

ties

(cp

s)

2 theta

Figure 13a: Inscription XRD Analysis of Sample 0 - 10 cm Pippete Preparation

SM

Q SM

SM = Smectite Q = Quartz

Q

0

100

200

300

400

500

600

700

800

900

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

0 - 10 cm 0 - 10 cm GLYCOL

Figure 14a: Inscription XRD Analysis of Sample 0-10 cm Pipette Preparation vs. Pipette + Glycol Treatment

2 theta

Inte

nsi

tie

s (c

ps)

Q

SM

EG-SM EG-SM

EG-SM

EG-SM

SM = Smectite EG-SM = Ethylene Glycol Smectite Q = Quartz

Overview of XRD Test Method and Sample Description for Vaca Del Monte:

Vaca Del Monte (VDM) 1 Core Samples (Figure 1) were ran primarily as

powders, one sample (29-30 cm) was prepared as a slide according to METHOD 2 (Page

25). The depth of Vaca Del Monte samples analyzed regarded depths from 9.0 cm to

34.5cm. The minerals targeted in this analysis were the clay sized fraction. Samples

analyzed with XRD contained smectite and quartz. It appears that if the measurement

range of 2 to 32 degrees two theta was broadened, more minerals could potentially be

identified. The 29.0-30.0 cm pipette sample was exposed to ethylene glycol > 1 day, the

analysis proved the positive identification of smectite.

Preparation of the Relative % of Smectite and Quartz:






Tikal Powder XRD Data Powder

Vaca Del Monte 1 (9-10 cm to 34-34.5 cm)

Depth (cm)

Smectite Relative %

Quartz Relative %

9-10 54 46

16-17 50 50

20-21 46 54

27-28 59 41

34-34.5 52 48

0 20 40 60 80 100

9-10.

16-17

20-21

27-28

34-34.5

Figure 15a: Relative Percentages of Smectite and Quartz ( < 75µm Grain Size) (Vaca Del Monte 1 Core)(XRD)(2 to 32 Theta)(Powder

Samples)

Dep

th (

cm)

(Vaca

Del

Mo

nte

Co

re)

SmectiteRelative %

QuartzRelative %

Table 2a: Total Average Bulk Powder (VDM; 9-10cm to 34-

34.5 cm):



Tikal XRD Data

Vaca Del Monte 1 (29 cm to 30 cm)

The Following data is for Sample 29-30 CM in which a pipette sample was analyzed

and treated with ethylene glycol.

0

200

400

600

800

1000

1200

1400

1600

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Inte

nsi

ties

(cp

s)

2 theta

Figure 16a: Vaca Del Monte XRD Analysis of Sample 29-30 cm Pippete Preparation

SM

Q

SM

SM = Smectite Q = Quartz

0

200

400

600

800

1000

1200

1400

1600

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Vaca Del Monte 29-30CM Vaca Del Monte 29-30CM Ethylene Gycol

Figure 17a: Vaca Del Monte XRD Analysis of Sample 29-30 cm Pippete Preparation vs. Pippete + Glycol Treatment

2 theta

Inte

nsi

ties

(cp

s)

Q

SM

EG-SM EG-SM EG-SM

EG-SM

SM = Smectite EG-SM = Ethylene Gycol Smectite Q = Quartz

Overview of XRD Test Method and Sample Description of Tikal 21,22,23

Tikal-TR-21,22,23 Core Samples (Figure, 1) were received for slide preparation

for XRD. METHOD 1 (Page, 23) was utilized for the sample preparation of this group.

The slides were individual prepared per 10 cm interval and analyzed for mineral

identification. The majority of the samples analyzed by XRD contained primarily

calcite, smectite and quartz. One sample from each data set of this group (Table, 1) was

prepared with glycol. Analysis of these samples resulted in the positive identification

of smectite.

Preparation of the Relative % of clay minerals, quartz and carbonates:






Tikal XRD Data

Tikal-TR-21 Core (0-10cm to 30-40cm)

Depth (cm)

Smectite Relative %

Quartz Relative %

Chlorite Relative %

Kaolinite Relative %

0-10 77 23 0 0

10-20 64 19 9 8

20-30 63 17 10 10

30-40 61 18 10 11

0 20 40 60 80 100

0-10

10-20.

20-30

30-40

Figure 18a: Relative Percentages of Smectite, Quartz and Calcite ( < 75µm Grain Size) (Tikal-TR-21 Core)(XRD)(2 to 32 Theta)(Air-Dried)

Dep

th (

cm)

(Tik

al-

TR

-21 C

ore

)

Smectite Relative%

Quartz Relative%

Chlorite Relative%

Kaolinite Relative%

Table 3a: Total Average (Tikal-TR-21; 0-10cm to 30-

40cm):



Chlorite (Relative %): 8

Kaolinite (Relative %): 7

Tikal XRD Data


Depth (cm)

Smectite Relative %

Quartz Relative %

Calcite Relative %

0-10 13 4 83 10-20 14 5 81 20-30 11 0 89 30-40 9 3 88 40-50 8 7 85 50-60 9 2 89

0 20 40 60 80 100

0-10

10-20.

20-30

30-40

40-50

50-60

Figure 19a: Relative Percentages of Smectite, Quartz and Calcite ( < 75µm Grain Size) (Tikal-TR-22 Core)(XRD)(2 to 32 Theta)(Air-

Dried)

Dep

th (

cm)

(Tik

al-

TR

-22 C

ore

)

SmectiteRelative %

QuartzRelative %

Carbonate(Calcite)Relative %

Table 4a: Total Average (Tikal-TR-22; 0-10cm to 50-60cm):




Tikal XRD Data


Depth (cm) Smectite Relative%

Calcite Relative %

0-10 18 82 10-20 21 79 20-30 10 90 30-40 16 84 40-50 15 85 50-60 4 96 60-70 7 93 70-80 4 96 80-90 18 82 90-100 20 80 100-110 30 70 110-120 21 79 120-129 35 65

0 20 40 60 80 100

0-10

10-20.

20-30

30-40

40-50

50-60

60-70

70-80

80-90

90-100

100-110

110-120

120-129

Figure 20a: Relative Percentages of Smectite and Calcite ( < 75µm Grain Size) (Tikal-TR-23 Core)(XRD)(2 to 32 Theta)(Air-Dried)

Dep

th (

cm)

(Tik

al-

TR

-23 C

ore

)

SmectiteRelative %


Table 5a: Total Average (Tikal-TR-23; 0-10cm to

120-129cm):



0

200

400

600

800

1000

1200

1400

1600

2 3 4 5 6 7 7 8 9 10111213141516161718192021222324252526272829303132

Pe

ak

In

ten

siti

es

(CP

S)

Figure 21a: Tikal TR - 21 (30 - 40 cm) Smectite 2 Theta Shift with Glycol Preparation

TR-21, 30-40cm

TR-21, 30-40(Glycol)

2 Theta

SM

0

200

400

600

800

1000

1200

1400

1600

1800

2 3 4 5 6 7 7 8 9 10111213141516161718192021222324252526272829303132

Pe

ak

In

ten

siti

es

(CP

S)


TR-22, 10-20cm

TR-22, 10-20 (Glycol)

2 Theta

SM

Q

Ca

Ca

SM SM

0

200

400

600

800

1000

1200

1400

1600

2 3 4 5 6 7 7 8 9 10111213141516161718192021222324252526272829303132

Pe

ak

In

ten

siti

es

(CP

S)


TR-23, 40-50cm

TR-23, 40-50 (Glycol)

2 Theta

SM

Ca

Ca

SM

Overview of XRD Test Method and Sample Description of Tikal 17:

Tikal-17 Core Samples (Figure, 1) were prepared according to METHOD 2&3

(Page, 23-25). The slides were individual prepared per 10 cm interval (0-10 to 180-190)

cm and analyzed for mineral identification. The majority of the samples analyzed for

XRD contained primarily calcite, smectite and quartz. It appears that if the

measurement range of 2 to 32 degrees two theta was broadened, more minerals could

potentially be identified.

Preparation of the Relative % of smectite, quartz and calcite:






Tikal XRD Data


0 20 40 60 80 100

0-10

10-20.

20-30

30-40

40-50

50-60

60-70

70-80

80-90

90-100

100-110

110-120

120-130

130-140

140-150

150-160

160-170

170-180

180-190

Figure 24a: Relative Percentages of Smectite, Quartz and Calcite ( < 75µm Grain Size) (Tikal-17 Core)(2 to 32 Theta)(Air-Dried)

Dep

th (

cm)

(Tik

al-

17 C

ore

)

SmectiteRelative %

QuartzRelative %


0

5

10

15

20

25

30

0-1

0

10

-20

.

20

-30

30

-40

40

-50

50

-60

60

-70

70

-80

80

-90

90

-10

0

100-…

110-…

120-…

130-…

140-…

150-…

160-…

170-…

180-…

SmectiteRelative %

QuartzRelative %

Correlation of Smectite & Quartz (Tikal-17 Core)

Tikal XRD Data

Tikal-17 Core (0-10cm to 180-190cm)

Depth (cm)

Smectite Relative %

Quartz Relative %

Calcite Relative %

0-10 15 6 76

10-20 17 6 66

20-30 10 4 68

30-40 1 6 83

40-50 15 4 63

50-60 17 5 62

60-70 20 6 66

70-80 24 7 68

80-90 19 6 71

90-100 18 5 74

100-110 19 6 66

110-120 18 7 69

120-130 21 8 65

130-140 20 6 71

140-150 17 7 73

150-160 14 5 77

160-170 14 5 79

170-180 4 2 91

180-190 1 1 98

Figure 25a (left): Excluding sample 30-40cm, an increase in smectite corresponds with an increase in quartz.

Table 6a: Total Average (Tikal-17; 0-10cm

to 180-190cm):




Overview of XRD Test Method and Sample Description of Perdido:

Perdido Core Samples (Figure, 2) were prepared according to METHOD 1 (Page,

23) as un-sieved core samples. The majority of the samples analyzed for XRD contained

primarily calcite, smectite and quartz. The measurement range of 2 to 32 degrees two

theta was expanded to 60 degrees two theta, many further peaks were found. All of the

peaks located past 32 degrees two theta were associated with Calcite. Glycol samples

were prepared and analyzed to in order to further identify the smectite.

Preparation of the Relative % of Smectite, Quartz and Calcite:





cps in the sample gave the relative % of that mineral for that depth interval. .

Tikal XRD Data Perdido Core (0-10cm to 200-203.5cm)

Depth (cm)

Smectite Relative %

Quartz Relative %

Calcite Relative %

0-10 17 6 65

10-20 9 3 88

20-30 7 1 92

30-40 10 5 85

40-50 1 5 95

50-60 9 3 88

60-65 9 3 88

65-75 7 3 90

75-85 23 5 72

85-95 13 4 83

95-105 13 4 83

105-115 32 4 64

115-125 41 4 53

125-135 85 5 10

135-140 84 7 9

140-150 5 4 91

150-160 31 16 53

160-170 39 20 41

170-180 62 14 24

180-190 81 13 6

190-200 6 6 88

200-203.5 17 3 80

Table 7a: Total Average (Perdido; 0-10cm to 200-203.5cm):


Quartz (Relative %) :6


0

10

20

30

40

50

60

70

80

900

-10

10

-20

.

20

-30

30

-40

40

-50

50

-60

60

-65

65

-75

75

-85

85

-95

95

-10

5

10

5-1

15

11

5-1

25

12

5-1

35

13

5-1

40

14

0-1

50

15

0-1

60

16

0-1

70

17

0-1

80

18

0-1

90

19

0-2

00

200-…

SmectiteRelative %

QuartzRelative %

Correlation of Smectite & Quartz (Perdido Core)

0

200

400

600

800

1000

1200

1400

1600

1800

2 3 4 5 6 7 8 9 101112121314151617181920212223242526272829303131

Peak

In

ten

siti

es

Figure 27a: Verification of the Smectite with Peak Expansion to 17Å (Perdido)(125-135cm)

Perdido 125-135CM (GLYCOL)

Perdido 125-135CM

2 Theta

Figure 26a (above): An increase in smectite occurs twice as depth increases. The first interval begins at 75 to 140cm, the second at 150 to 190cm, with maximum amounts at 125-140 cm and 170-190cm.

0

500

1000

1500

2000

2500

2 3 4 5 6 7 7 8 9 10111213141516161718192021222324252526272829303132

Peak

In

ten

siti

es

Figure 28a: Verification of the Smectite with Peak Expansion to 17Å (Perdido)(135-140cm)

Perdido135-140CM(GLYCOL)

Perdido135-140CM

0

500

1000

1500

2000

2500

3000

3500

2 4 6 8 1012141618202223252729313335373941434547495153555759

Peak

In

ten

siti

es

Figure 29a: 2 to 60 Degrees Two Theta XRD Measurements (Perdido)(20-30cm & 60-65cm)

Perdido60-65CM

Perdido20-30CM

2 Theta

SM Ca Ca Ca Ca

Ca

Ca

Ca

Ca

2 Theta

Overview of XRD Test Method and Sample Description Tikal NIEO:

NIEO (Tikal) samples (Figure, 2) were received as sieved core samples and

prepared according to METHOD 2 (Page, 23). The slides were individual prepared per

10 cm interval (0-10 to 360-368) cm and analyzed for mineral identification. Throughout

the NIEO Core, a significant amount of calcite and carbonate minerals were identified.

Preparation of the Relative % of Smectite and Quartz:






Tikal XRD Data NIEO - 0cm to 368cm Core

Depth Smectite Relative %

Quartz Relative %

0-10 4 3

10-20 1 3

20-30 39 4

30-40 1 5

40-50 16 4

50-60 3 4

60-70 1 4

70-80 5 3

80-90 1 2

90-100 21 5

100-110 1 2

110-120 25 6

120-130 38 14

130-140 1 1

140-150 54 20

150-160 60 11

160-170 58 10

170-180 54 8

180-190 21 19

190-200 23 10

200-210 39 10

210-220 23 6

220-230 30 10

230-240 52 6

240-250 46 11

250-260 54 12

260-270 84 9

270-280 59 16

280-290 78 11

290-300 48 15

300-310 25 14

310-320 41 23

320-330 52 10

330-340 34 31

340-350 65 9

350-360 62 5

360-368 67 12

Table 8a: Total Average (NIEO 0-10cm to 360-368cm):



0 20 40 60 80 100

0-10

10-220

20-30

30-40

40-50

50-60

60-70

70-80

80-90

90-100

100-110

110-120

120-130

130-140

140-150

150-160

160-170

170-180

180-190

190-200

200-210

210-220

220-230

230-240

240-250

250-260

260-270

270-280

280-290

290-300

300-310

310-320

320-330

330-340

340-350

350-360

360-368

Figure 30a: Relative Percentages of Smectite and Quartz ( < 75µm Grain Size) (NIEO)(Tikal)

Dep

th (

cm)

(NIE

O C

ore

)

SmectiteRelative%

QuartzRelative%

ESEM

Quartz and zircon grains were isolated from Tikal and the southern Maya

Lowland soil horizons and identified under high magnification (>600x) with a Leica

MZ12 stereomicroscope and an Environmental Scanning Electron Microscope (ESEM).

Mesoamerican pit samples were gently ground (mortar & pestle) into powders for

density separation with the use of lithium polytungstate (LST). Samples were carefully

prepared in order to avoid abrasion that would crush or damage any of the crystals.

Samples were successfully separated according to the total sample density (light and

heavy fractions) by Sarah Trishler, a faculty member of the University of Cincinnati,

Geology Department. The specific gravity of the LST liquid used for this separation

was 2.75 g/cm3. Preliminary microscopy identified several zircons and quartz grains

which were then mounted on either of two stubs and viewed w/ ESEM. The quartz

grains viewed under ESEM were euhedral to bihedral “first quartz”, which provide

evidence for unweathered grains likely deposited from ash falls (Tankersley et al.,

2012). The zircons co-occur with the euhedral bypyramidal quartz and appear as

elongated dipyramidal tetragonal crystals about 250 µm in length with fluid inclusions

(Image 1a). Similar to quartz, zircons can withstand extreme changes in heat and

pressure without compromising their original composition and are direct evidence of

explosive volcanic events (Bindeman et al., 2006). Zircons are common in felsic,

granitic, and ultrapotassic igneous rocks, while also found to be a good identifier for

volcanic deposition (Fisher et al., 1997).

ESEM Summary

Stub 1: LM-BH-10, Unit 8 Filter 1 (heavy)

Image 1a- Zircon attached to low molecular weight mineral

Image 2a- Quartz Grain, 100 µm by 75µm grain dimensions

Stub 2: Corozo Unit 5, Filter 1 (heavy)

Image 3a-Zircon, 112 µm by 50 µm grain dimensions


Image 5a- Zircon, 200 µm by 50 µm grain dimensions

Image 6a- Zircon, 200µm by 50 µm grain dimensions

Image 7a- Zircon, 225 µm by 114 µm grain dimensions


Image 9a- Quartz, 75 µm

BSE: Back Scatter Electron Detector

GSE: Gaseous Secondary Electron Detector

ESEM Photographs from Sample Group 1

Image: 1a Image: 2a

Image: 3a Image: 4a

Image: 5a Image: 6a

Image: 8a Image: 7a

Microscopy

The first few sample sets received from the Tikal region (Tikal 0-190cm) were

analyzed through a microscope. The samples were received as hand core samples, the

soil was dry sieved in order to view dispersed grains under a microscope, while

keeping the fines intact for further XRD and XRF analysis. The microscope analysis

proved to serve two main purposes. Viewing the larger grains of sediment revealed the

abundance of angular quartz, which further supports the hypothesis of a volcanic ash

source as opposed to an African source of wind-blown quartz (Tankersley et al., 2012).

Due to the respective amount of volcanic ash currently deposited within the southern

Yucatan, the ash seems more likely to be a significant contributor to the amount of

quartz present within the sample interval. Regardless of this thinking, Saharan Dust is

rounded to sub-rounded at best which contrasts strongly with the observed quartz

within the Tikal samples (Tankerlsey et al., 2012).

Image 9a (left): Quartz SEM image to the

left. A low density mineral is attached to the

top of the grain.

Image: 9a

Image 1b: Tikal: 190-200cm Image 2b: Tikal: 190-200cm

Image 4b: Tikal: 170-180cm



X-ray Fluorescence (XRF)

Sample powders were prepared with a tungsten carbide ball mill and pressed

into briquettes at 2000 psi. A separate aliquot of each sample was heated to 1000° C for

one hour to measure the loss on ignition (LOI) for later use in preparing the total

elemental XRF data of each sample. Intensity data were converted to parts per million

(ppm) using bivariate and multivariate regressions applied to United States Geological

Survey, National Institute of Standards, and Japan Geological Survey rock standards.

Previous work (Figure 3) completed for the Tikal Research project took into account the

necessity of canceling out Sahara-Sahel Dust as a source of the quartz (Tankerlsey et al.,

2012). The presence of chlorite, euhedral bipyramidal quartz crystals, kaolinite,

smectite, and zircons, strongly suggests a volcanic ash source. Tikal is located in the

Sahara-Sahel Dust Corridor (Moreno et al., 2006) and African dust has been identified

as a major component of soils overlying other carbonate land masses in the Caribbean

Basin including Florida, the Bahamas, and Barbados (Muhs et al., 2007). To determine if



the volcanogenic minerals from the reservoirs of Tikal originated as airborne Sahara-

Sahel dust or volcanic ash, the trace element composition of the reservoir sediments

from Tikal was determined using whole rock X-ray Fluorescence Spectrometry

(Tankersley et al., 2012). Significant differences in the trace element content of sediment

from the reservoirs of Tikal and Sahara-Sahel dust were found in the ratios of Ni, Cr, Zr,

and Y (Tankersley et al., 2011). Element ratios are used rather than absolute amounts to

eliminate the effect of the large amounts of locally derived calcite. The trace element

content of Sahara-Sahel dust has a significantly lower range of Cr/Ni ratio and a higher

Zr/Y ratio than do the samples from Tikal (Figure 2) (Tankersley et al,. 2011).

The Ilopango TBJ eruption is the largest and best-documented Holocene volcanic

event in Central America (Hart and Steen-McIntyre, 1983). It occurred during the Early

Classic Period, sometime between A.D. 408 and 536 and its ecological and cultural

impact would have been felt throughout the Maya region (Dull et al., 2001). Professor

Payson Sheets of the University of Colorado kindly provided our team with samples of

the TBJ Tephra for comparison. Data for other volcanic components are available in the

database developed by Carr (Carr et al., 2007). Previous XRD analysis demonstrated

that the TBJ Tephra is composed of plagioclase feldspar with lesser amounts of quartz

(Tankersley et al., 2012). In other words, there are no clays in the TBJ Tephra, because

the volcanic ash is still unaltered, unlike the Tikal sediments where all the ash has

converted to smectite (Tankersley et al., 2012). It is possible that the abundance of calcite

in the Tikal reservoirs compared to the slopes of the Ilopango volcano accounts for this

difference (Cowgill and Hutchinson, 1963).

Weathering should not affect the trace element ratios for high-field strength

elements like Cr, Nb, Ti, Y, and Zr (Winchester and Floyd, 1977). Nickel is more mobile

than Cr in acidic soils under tropical conditions (Maynard, 1983), and accumulates

lower in the profile, which is the mechanism of genesis for lateritic nickel deposits

(Tankersley et al., 2012). However, it should remain fixed in the high carbonate

environment of these deposits. The Ni/Cr ratios in the individual cores at Tikal are

constant with depth, indicating that vertical migration of Ni has been minimal

(Tankersley et al., 2012). XRF analysis of the TBJ Tephra sample found a higher ratio of

Zr/Y than the sediments from the reservoirs of Tikal (Figure 3). Similar results were

obtained using the analyses in the Carr database. The XRF results for this thesis work

includes Table 3, Figure’s 1 and 2. Table 3 shows the Ti, Nb, Y, and Zr data collected for

30 samples with 5 different locations near or within Tikal, Guatemala (Figure 1). These

data generated an elemental composition signature for each sample location which is

shown in Figure 1. Elemental variations between the log values of Zr/TiO2 and Nb/Y

of sample locations is small, although when compared to the same elements as suspect

source volcanos, there is a separation. Figure 2 shows the Mexican and Guatemalan

volcanoes have a closer match in the Zr/TiO2 and Nb/Y ratios than the Salvadorian

data.

Table 1b: Four trace elements analyzed from Sample Group 1. Trace element content of sediments from Tikal reservoirs and the greater Maya Lowland (Tankersley et al., 2012).

Location Provenience Depth Ti Nb Y Zr

Bajo La Justa Arbusto Pit Unit 1/2 1.0313 0.8657 1.5692 21.1230

Bajo La Justa Arbusto Pit Unit 3 1.0575 0.9124 1.3118 20.5060




Bajo Justa Corozo Pit 1/2 0.8980 0.6630 1.1167 17.2420

Bajo Justa Corozo Pit 3 0.9353 0.7193 1.2690 16.7390





La Milpa BH-9 Unit 2 1.1326 0.9950 1.0434 28.1130

La Milpa BH-9 Unit 3 1.2151 1.0335 1.0163 25.7170

La Milpa BH-9 Unit 5 1.1746 0.9908 1.3376 24.2930

La Milpa BH-9 Unit 6 1.1596 0.9557 0.7766 25.4870

La Milpa BH-9 Unit 4 1.1809 0.9853 1.0733 24.3180

La Milpa BH-9 Unit 3 1.0632 1.0107 2.0614 22.5270

La Milpa BH-10 Unit 4 0.6397 0.5181 0.9467 15.2690

La Milpa BH-10 Unit 5 0.8772 0.7567 1.2137 15.8820

La Milpa BH-10 Unit 6 0.4231 0.3791 0.3664 6.8562

La Milpa BH-10 Unit 8 0.3409 0.4662 4.0124 3.8260

La Milpa BH-10 Unit 12 0.2063 0.2019 0.1588 6.4735

La Milpa D-9 Unit 3 1.0075 0.9432 2.0401 13.7990

La Milpa D-9 Unit 4 0.8740 0.7701 1.6003 11.7540

La Milpa D-9 Unit 5 0.9078 0.8507 1.2947 12.6170

La Milpa D-9 Unit 7 1.0889 0.9251 1.5092 14.9380

Xcoch Zacate Pit 2 Unit 1 0.9447 0.8185 1.5012 10.5960




-2.00

-1.80

-1.60

-1.40

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

-2.00 -1.50 -1.00 -0.50 0.00

Log

Zr/T

iO2

log Nb/Y

Airbusto

Corozo

LM-BH

Zacatep

LM-DO

Figure 1b: (above). The trace element content of Maya Lowland samples from

Sample Group 1

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

-2.0 -1.0 0.0 1.0 2.0lo

g Z

r/T

iO2

log Nb/Y

MexicanVolcanoes

Tikal

GuatemalanVolcanoes

SalvadoranVolcanoes

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0.0 0.5 1.0 1.5 2.0 2.5

Zr/

Y

Ni/Cr

Tikal

1 Mexican

Volcanoes

2 Guatemalan

Volcanoes

3 Salvadoran

Volcanoes

4 Honduran

volcanoes

Saharan Dust

Antilles volcanoes

Ilopango

2

1

3

4

Figure 3b: (above). The trace element content of Tikal sediment samples compared to

Middle American volcanoes and Saharan Dust. Note the difference in the elemental

comparison between the dust and the rest of the locations analyzed.

Figure 2b: (above). The trace element content of Tikal sediment samples compared

to volcanoes in Guatemala, Mexico, and Salvador.

Conclusions

It has been shown that volcanic ash deposition with the influence of calcite from

underlying Cretaceous limestone forms the parent materials for the region’s soils. The

importance of this discovery informs researchers that explosive volcanism helped

renew and create the region’s soils (Tankersley et al., 2012). Without these volcanic

contributions, soils above the limestone bedrock would have likely remained skeletal

and posed significant problems for the long-term subsistence by ancient Maya

populations (Tankersley et al., 2012). Results from natural depressions and reservoir

sediments provide the first evidence for long-term explosive volcanism in the southern

Maya Lowlands. At Tikal and surrounding Guatemalan locations, volcanogenic

smectite, kaolinite, zircons, and unweathered crystalline quartz were found in strata

that radiocarbon dated from 800 BC to 1500 AD (Tankersley et al., 2012). These data

prove that ash fall from andesitic and/or rhyolitic volcanism blanketed the region

throughout the Mayan time period contributing to the pedogenesis of the soils. This is

apparent due to the amount of smectite present in the soils dated through the Mayan

Period, there would be no other explanation for the source of this clay mineral.

The data further provide insight into the following: (1) Smectite rich clays are

present all across the Mexico, Belize and Guatemala area dating (AMS Radiocarbon

dates) from the Preclassic to Postclassic Maya cultural periods; (2) The existence of

smectite within the dated strata provides clues for soil fertility at the time. Mayan

agriculture would likely benefit from these ash falls, contradicting certain viewpoints;

(3) A further understanding of the transformation of volcanogenic ash deposits to

smectite will be gained from the data collected and analyzed versus the chemical

compositions of source volcanism in the area. The educational impact and further

clues to the Mayan civilization have already added a wealth of information for

researchers to ponder in regards to this project. Following the conclusion of this project,

a comprehensive study of the soils across Guatemala, Mexico and Belize has provided

evidence of the volcanism during the Preclassic to the Postclassic Maya Periods. This

information is not only invaluable for researchers studying the Mayan civilization, it’s

the first well-documented pedogenetic study focusing on smectite for this geographical

location.

Decomposed volcanic ash-containing smectite has been identified within core,

pit and reservoir samples by X-ray diffraction. Due to the ample amount of smectite

primarily found as the clay component in these soils, the repeated ash falls have

drastically altered the chemical make-up of the regional soils. Euhedral and subhedral

quartz have been identified using microscopy and ESEM within the soils throughout

the Mesoamerican region. The presence of physically unaltered quartz points to non-

fluvial deposition due to its lack of weathering and abrasion. Other possible sources of

SiO2 found within the regions soils can be traced to well know aeolian quartz form

Africa. Although, quartz lacks the metal cations required to build such silicate minerals

as smectite. The XRF data obtained from the samples across Mesoamerica have

provided clues to the possible source(s) of volcanic ash, while also confirming the origin

of the smectite as volcanic. Comparing XRF data of the geographically common dust

blown Sahara-Sahel and Antilles sources and tephra from Guatemalan or Salvadoran

volcanoes reveals the soil smectite as volcanic (Tankersley et al., 2011). The Ni/Cr trace

elements identified from XRF correlate with Guatemalan and Salvadoran volcanic

events. Further investigation into the trace element composition of the regions soils and

possible volcanic sources would confirm deposition dates and source. Previous work

completed by Cabadas et al., of the National Autonomous University of Mexico

describes red soils on Eocene-Pliocene limestone of the Yucatán peninsula have been

documented to contain kaolinite formed within karst terrains (Cabadas et al., 2010).

Their proposed source(s) of the clay and trace element components has derived from

hurricanes, Sahara-Sahel dust and Central American volcanoes. Trace element data of

the soils within the Yucatán show a slight influence from Sahara-Sahel dust, with a

more significant agreement with Central American volcanism (Cabadas et al., 2010).

Future Research

There are three critical research areas that require attention for further

investigation in order to complete the full history of the region’s soils: (1) Uranium lead

dating of the discovered zircons (Image 1a -8a) could help establish the timing of these

ash events; (2) Further sample extraction of the magmas and ash of the Tikal and

southern Yucatan Region will provide more information on the source of volcanic ash.

Poor drainage and the Mg-rich limestone match the environmental prerequisite for the

hydration and transformation of volcanic ash to bentonite (Grim and Guven, 1978); (3)

The timing of the pedogenic processes involved with the degradation of the volcanic

ash necessitates further examination. This project has identified in detail the current

mineralogy and trace elementology of the studied locality. We have not taken into

account the rates of volcanic ash transformation to the current identified properties of

the soils. The ability to provide more information on the transformation timing would

provide further insight to the agricultural aspects of the Mayan culture. Was the

volcanic ash transformation expedient enough to add fertility to soils between the

Mayan farming cycles?

Zircons contain the element Uranium, which over time converts to lead at a

known rate and can be measured (Liu et al., 2011). Zircon dating has been used

through the 20th Century. Some of the oldest deposits on earth contain zircon crystals

that have been dated back to 4.3 billion yeas in Australia (Wilde et al., 2001). The half-

life of Uranium 238 is 4.5 billion years, which makes it an excellent tool for dating

ancient deposits (Mathez, 2000). For the purposes of this project the deposits are very

young by comparison so the error involved in the ages determined from these methods

would need to be pre-evaluated. Uranium lead dating of the inclusions within

discovered zircons can be dated using Sensitive High Resolution Ion Microprobe

(SHRIMP). This methodology has also been used to determine the ages of zircons

within bentonite deposits to define the Permian-Triassic Boundary (Bowring and

Schmitz, 2011). Similar analysis can be employed on samples obtained from this

project, or on future samples taken from the region. If these zircons could be dated with

precision, it is likely that the volcanic eruption which emitting these zircons could be

matched. Obtaining dates on the inner band of the zircons found in the 2009-2010

Figure 8. Xcoch Zacate Pit – south profile. (Dunning et al., 2006)

samples to define the date of formation would help identify the source volcano. Soils

samples collected for this project were carbon dated, although this information does not

define the age of the volcanic ash.

Volcanic Ash: Small jagged pieces of rocks, minerals, and volcanic glass the size of sand

and silt (Blong, 1984). El Chichon Tephra Composition: SiO2, Al2O3, CaO, Na2O, K2O,

FeO.

SiO2, Al

2O

3, CaO, Na

2O, K

2O, FeO + H

2O+ Ca,(OH)

2 (Na,Ca)

0.33(Al,Mg)

2(Si

4O

10)(OH)

2·nH

2O.

Volcanic Ash Composition + Leached Mineralogy of Bedrock Smectite general formula

The dioctohedral (trivalent) form of smectite includes clay minerals such as montmorillonite, beidellite and nontronite.

• Common Interlayer octahedral cations include: Fe+3

, Al+3

, Ca+, Na

+

CaCO3, CaMg(CO3)2

Ca + 2H2O Ca(OH)2

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Quaternary Volcanic Ash Transformation in the Mayan Lowland

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