The ancient agricultural landscape of the satellite settlement of Ramonal near Tikal, Guatemala

Quaternary International 265 (2012) 101e115

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The ancient agricultural landscape of the satellite settlement of Ramonal near Tikal, Guatemala Richard L. Burnett a, Richard E. Terry a, *, Marco Alvarez a, Christopher Balzotti a, Timothy Murtha b, David Webster c, Jay Silverstein d a

Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84602, USA Department of Landscape Architecture, The Pennsylvania State University, University Park, PA 16802, USA Department of Anthropology, The Pennsylvania State University, University Park, PA 16802, USA d Intelligence and GIS Section, Joint POW/MIA Accounting Command, Hickam AFB, HI 96853-5530, USA b c

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 17 March 2011

Soil science methodologies often enrich archaeological reconstructions. In the Maya Lowlands of Mesoamerica, stable carbon (C) isotope ratio (d13C) analysis of soil organic matter (SOM) from profiles near ancient archaeological sites has been used to interpret the vegetative histories related to ancient maize agriculture. Due to distinct photosynthetic processes, the decomposed organic matter from the cultivation of maize can be distinguished from SOM derived from native forest detritus. The recalcitrant nature of humic substances allows for this distinction to be preserved through time. This study evaluates SOM d13C from 98 soil profiles near Tikal, Guatemala to identify areas of ancient Maya agriculture and the staple crops used. Ancillary physical and chemical properties of the soil profiles were examined to facilitate and to supplement the interpretation of the isotope data. Most of the soils analyzed in this study are shallow Haprendolls with limited C isotopic evidence of prehistoric vegetation changes. The deeper, well-developed Argiudolls and Hapludolls contained strong evidence of vegetation changes associated with ancient maize agriculture. Areas with strong d13C signatures of ancient C4 vegetation corresponded with foot- and toeslope locations, high clay content and low phosphorus (P) levels. The shallow backslope soils lacked significant evidence of ancient agriculture. The connections between profile location, settlement, isotope data, and P levels enable the identification of both agriculture production zones and enhanced understanding of stable C isotope dynamics in soils within the unique physiographic and archaeological surroundings of the Maya Lowlands. Ó 2011 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction Evidence of ancient agriculture in the Maya Lowlands, in the absence of the material evidence of intensification, is difficult to identify beneath the dense forest canopy and in the tropical climate where preservation of organic materials is poor (Murtha, 2009). In addition to contributions from archaeology, knowledge of Maya subsistence, agriculture, and paleoecology has been reconstructed from various sources including paleolimnology (Brenner et al., 2002; Anselmetti et al., 2007; Mueller et al., 2010), palynology (Leyden, 2002), pedology (Wells and Terry, 2007), ethnology (Cowgill, 1961; Nations and Nigh, 1980; Atran, 1993; Dunning and Beach, 2004; Jensen et al., 2007), historical accounts (Ponce and

* Corresponding author. Fax: þ1 801 422 0008. E-mail address: [email protected] (R.E. Terry). 1040-6182/$ e see front matter Ó 2011 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2011.03.002

Noyes, 1932; Landa and Tozzer, 1941), epigraphy (Taube, 1985), and combinatory approaches (Dunning et al., 1997; Beach, 1998b). The pedological approach derives its interpretations from the application of soil science methods to archaeological questions. In lieu of structural evidence of ancient agriculture such as terraces or ditches, soil physical and chemical characteristics can reveal information about past cultivation practices. Soils contain information about the past that can be gleaned through observation and laboratory tests. Gerald Olson, who conducted a soil survey of the central portion of Tikal, observed long ago that the soils of Tikal “have retained records of certain activities of the ancient Maya” (Olson, 1977). Geochemical analyses have become particularly useful in the identification of ancient human activities including ancient maize production. For example, phosphorus (P) and heavy metal concentrations in the soil can be indicators of past household activities such as preparation, consumption, and disposal of food

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materials, and the use of minerals in workshop activities (Terry et al., 2004). Likewise, the physical and chemical characterization and taxonomy of soils may provide evidence of suitability for agricultural production (Fedick, 1994, 1995; Murtha, 2002, 2009; Jensen et al., 2007; Johnson et al., 2007a; Sweetwood et al., 2009). Finally, Webb et al. (2004, 2007) and others have proposed that the analysis of stable carbon (C) isotopes in soil organic matter (SOM) can be used to identify remains of ancient C4 vegetation related to maize agriculture (Fernandez et al., 2005; Johnson et al., 2007a, 2007b; Wright et al., 2009). Wright et al. (2009) recently summarized the use of stable C isotopes within soil profiles as an indicator of past climate and vegetation changes related to forest clearance and agricultural production. Of particular relevance to this study is the research conducted in the greater Caribbean Basin including Mesoamerica where d13C values from lake and cave sediments and soils have been connected in some cases to C3/C4 vegetation shifts (Powers and Schlesinger, 2002; Lane et al., 2004, 2008; Driese et al., 2007; Polk et al., 2007; Beach et al., 2008; Sweetwood et al., 2009). Stable C isotope ratios illustrate past vegetation shifts associated with forest clearance for maize agriculture. The tree and vine species of the Petén utilize a specific C3 photosynthetic pathway while maize, a C4 plant, uses a different pathway for photosynthesis. C3 and C4 plants assimilate different amounts of stable C isotopes as they incorporate carbon dioxide into their plant tissues resulting in unique isotope ratios (Webb et al., 2004, 2007; Fernandez et al., 2005; Johnson et al., 2007a, 2007b; Wright et al., 2009). These characteristic isotope ratios are in turn transferred to the soil organic matter as plant tissues decompose and recalcitrant humic substances form. In an ecosystem normally dominated by C3 forest vegetation, a long period of agricultural clearing and C4 plant cultivation can be detected by examining the relative abundances of stable C isotopes within soil profiles. The determination of d13C levels greater than 27&, typical of C3 plants, is evidence of an ancient vegetation shift to C4 plants. A change in d13C within soil profiles of at least 4& has been used as a benchmark to attribute the change to a C3/C4 vegetation shift as opposed to microbial fractionation of C isotopes during diagenesis of the SOM (Balesdent and Mariotti, 1987; Boutton, 1996; Martinelli et al., 1996; Powers and Schlesinger, 2002). Maize was likely the only C4 plant cultivated by the Maya and also served as their staple crop (Healy et al., 1983; Turner and Miksicek, 1984; Tieszen and Fagre, 1993; Lentz, 1999; Webb et al., 2004). Thus, a shift of 4& or greater in d13C values can reasonably be attributed to ancient maize agriculture. This approach has been utilized at multiple archaeological sites and in a variety of landscape types across the Maya Lowlands. The strongest isotopic evidence of ancient maize agriculture has come from relatively level areas (Webb et al., 2007) including deep, welldeveloped valley bottoms (Fernandez et al., 2005) and gently sloped, well drained soils (Johnson et al., 2007a). Significant evidence has also been associated with toeslopes, rejolladas (karst depressions), seasonal bajos (wetlands), and terraced hillsides (Webb et al., 2004; Johnson et al., 2007b; Beach et al., 2008; Wright et al., 2009). Application of this method to the study of ancient Maya agriculture is relatively recent. Webb et al. (2004) suggested that the method be used in connection with soil surveys to better understand ancient agricultural dynamics. Other researchers have suggested that more detailed sampling within soil catenas be used in order to better estimate agricultural extent (Johnson et al., 2007a). The evidence from prior research suggests that seasonal bajos and deep, gently sloping areas as well as terraced soils were used in ancient maize agriculture while the evidence from steeper slopes and hillcrests is less conclusive. The agricultural interpretations applied by researchers to the isotopic data in these studies have been corroborated by other

proxies indicating periods of forest clearance for ancient Maya agriculture. These proxies include soil and sediment deposition, lake sediment stratigraphy, pollen data, P and charcoal levels, and radiocarbon dating (Anselmetti et al., 2007; Curtis et al., 1998; Dunning et al., 1998; Brenner et al., 2002; Meuller et al., 2010; Rosenmeier et al., 2002a, 2002b; Rue et al., 2002; Beach et al., 2006, 2008, 2009; Dunning and Beach, 2011). These evidences demonstrate that much of the forest vegetation was cleared for agriculture and significant soil erosion occurred in the Middle and Late Preclassic Periods (700 BC to 250 AD) but lower amounts of erosional deposition occurred during the Late Classic population maximum (250 AD to 830 AD) (Anselmetti et al., 2007). The sediment proxies also exhibit the return of forest vegetation after the Terminal Classic abandonment (ca. 900 AD) (Meuller et al., 2010). Ancient terraces, constructed soil retention features, drained fields, and canal systems indicating zones of cultivation have been discovered in many parts of the Maya Lowlands, (Siemens and Puleston, 1972; Turner, 1974; Puleston, 1977, 1978; Turner, 1979; Turner and Harrison, 1981; Bloom et al., 1983; Healy et al., 1983; Siemens, 1983; Dunning and Beach, 1994, 2004; Fedick, 1994; Beach and Dunning, 1995; Jacob, 1995; Pohl et al., 1996; Beach et al., 2002; Murtha, 2002; Baker, 2007; Beach et al., 2009; Murtha, 2009). Despite years of settlement archaeology, no such structures or features have been conclusively identified at Tikal (Puleston, 1973, 1978; Pope and Dahlin, 1989; Webster et al., 2007). Fialko (2000b), however, has identified hydraulic management features near the Bajos Zocotzal and Ixtinto southwest of Tikal, and evidence of canals has been discovered near Yaxha further southeast of Tikal (Culbert et al., 1997; Kunen et al., 2000). Silverstein et al. (2009) hypothesized that portions of the great earthwork of Tikal served as a limestone filtration trench for the collection of runoff from the foot- and toeslopes and as a conveyance for water to local impoundments such as the Aguade el Duende northwest of Tikal. Features that may be canals or causeways of ancient origin have also been reported by aerial survey and in remotely sensed images of Bajo de Santa Fe northeast of Tikal (Dahlin et al., 1980; Sever and Irwin, 2003; Fialko, 2005; Weller, 2006; Saturno et al., 2007). In sum, the identification of ancient croplands at Tikal has not been as certain as at other sites. Knowledge of portions of the landscape used for ancient fields and the history of use, would allow archaeologists to determine the subsistence crops and strategies used by the people of this famous polity. According to the sustaining area hypothesis (Haviland, 1965; Puleston, 1983), the peripheral sites near Tikal functioned as important administrative outposts for agricultural and economic production and maintained direct cultural, political and dynastic ties with Tikal (Lou, 1997; Fialko, 2005). The adjacent settlements of Ramonal and Chalpate (hereafter referred to as Ramonal) are connected by a 500-m causeway and are located on the eastern earthwork of Tikal (Fig. 1) (Puleston and Callender, 1967). The settlement is on the well drained upland soils in close proximity to seasonal wetlands (bajos) with heavy clay soils. This study was initiated to evaluate the agricultural importance of the soils and other resources at Ramonal. The location of Ramonal in proximity to the earthwork and to both upland and bajo soil resources may have ranked Ramonal as an important strategic and economic satellite of Tikal. The seasonal bajos found on the northwest, southwest and southeast sides of Ramonal (Figs. 1 and 2) are dominated by corozo palm (Orbignya cohune). Multiple accounts of contemporary bajo cultivation are reported in the literature (Cowgill, 1961; Cowgill and Hutchinson, 1963; Fialko, 2000b; Johnson et al., 2007b; Wright et al., 2009), including a noted preference by milperos (local farmers) for palm bajo and corozo bajo in particular (Culbert et al., 1996, 1997; Sever, 1998; Kunen et al., 2000; Sever and Irwin, 2003).

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103

Fig. 1. Map of the Satellite center of Ramonal near Tikal superimposed on a topographic map.

Corozo bajos are better drained than other bajo types and retain adequate moisture for cultivation during the dry season (Culbert et al., 1997; Kunen et al., 2000; Gidwitz, 2002). Cowgill (1961) reported that corozo is one of the tree species that milperos let stand when clearing land for milpa (corn field); likely due in part to

its useful fruit and fronds (Martínez and Galindo-Leal, 2002). Whether corozo bajos were preferred by the ancient Maya is unknown, but Coe and Haviland (1982) speculated they may have been highly favored by farmers. Given the location of bajos in proximity to settlement at Ramonal, there may have been forest clearance, maize agriculture, and erosional deposition on those soils. This study examines the potential of the stable C isotope method on a large profile population (n ¼ 98), sampled at a high resolution (one per 1.89 ha), to gain a better understanding of the vegetative histories of soils affected by multiple environmental factors such as hillslope position, soil type, and agricultural potential. The large sample size enables the use of geostatistical methods such as kriging. The geospatial analysis of stable C isotopes and other soil properties provides a better understanding of the ancient agricultural landscape surrounding Tikal.

2. Methods and materials 2.1. Collection of soil Profiles

Fig. 2. The Ramonal study area is shown with profile numbers and locations. Elevation contours are in meters above mean sea level. The large filled circles represent profiles with >4& isotopic enrichment. The other unique symbols (squares, triangles, open circles) represent profiles discussed in the text.

Archaeologist Timothy Murtha designed the soil profile collection based on a centric systematic area-sample method (CSS) that had been stratified using a supervised classification. Systematic sampling was used over the preferred random sampling due to the length of the field season, the difficulty of obtaining reliable GPS points, and navigation under the dense canopy cover. The CSS method allowed for representation of the entire Ramonal study area in a gridded fashion. It is assumed that there is no periodic variation such as a sine-wave in the collected data allowing the data

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Table 1 Average properties of soil profiles and surface (A) horizons (n ¼ 98). Profile

Minimum Maximum Mean

Depth

Slope

Clay

cm

%

g/kg

15 124 51

0 11 4

280 960 550

pH

5.5 8.1 7.6

P

K

mg/kg

mg/kg

2.2 15.5 7.8

41 538 169

to be analyzed as random (Milne, 1959). The soil resource study of Ramonal was part of a larger project devoted to the restudy of the Tikal earthworks and their implications (Webster et al., 2007). Remote sensing imagery (including Landsat 7 satellite and Airborne Synthetic Aperture Radar (AIRSAR)) were used to classify each of 185 ha into one of thirteen classes. A total of 98 soil profiles were collected, representing a fifty percent sampling of each class. Profiles were taken from near the center of each hectare sampled. The ancient structures and locations of soil profiles at the site of Ramonal are shown in Fig. 2. Soil profiles were collected by bucket auger (AMS, American Falls, ID) at 10- to 20-cm depth intervals. Profiles were sampled to bedrock or to a depth of approximately 1 m. Profile segments were placed in Whirl-pak bags for transport to the Brigham Young University Soils Laboratory (Provo, UT) for analysis and classification. The geographic location (UTM) of each profile was recorded at the time of collection using a MobileMapper GPS/GIS device (Magellan, Santa Clara, CA). 2.2. Physical characterization The soil profile samples were air-dried and master horizon designations and depth intervals were assigned. Both dry and moist Munsell color along with soil structure and consistence were recorded. Redoximorphic features were noted if extant. Gravel and rock were removed and soil aggregates were crushed by mortar and pestle to pass a 2 mm sieve in preparation for physical and chemical analyses. The soil textural class was determined for each master horizon using the hydrometer method (Gee and Bauder, 1986). The coefficient of linear extensibility (COLE) was measured for each B horizon (Schafer and Singer, 1976). Slope values and hillslope position categories were derived from AIRSAR and Shuttle Radar Topography Mission digital elevation models. Diagnostic horizons were assigned and USDA taxonomic classification to the great group was determined for each profile (Soil Survey Staff, 2006). 2.3. Analysis of chemical properties The pH of each surface horizon was measured in a 1:2 soil to water mixture by glass electrode. The plant available P and potassium (K) levels for each surface horizon were determined by Olsen sodium bicarbonate extraction (Olsen and Sommers, 1982). The total C and total nitrogen (N) contents of each master horizon were determined by dry combustion using a Costech elemental analyzer (Valencia, CA). The calcium carbonate equivalents (CCE) of the master horizons were measured by reverse titration of samples treated with an excess of hydrochloric acid (HCl) (United States Salinity Laboratory Staff, 1954). The organic C content of each master horizon was derived by subtracting the carbonate C from the total C. Each profile segment was sub-sampled and further ground with mortar and pestle to pass a 250 mm sieve in preparation for isotope

Tot N

Tot C

22.0 308.4 138.5

Change in

d13C

d13C

Org C

CCE %

&

&

20.3 230.8 83.0

0.9 82.0 46.3

-28.95 -26.12 -27.55

0.00 5.73 1.41

g/kg 0.7 18.6 7.8

Surface

analysis. The samples (2 g) were acidified with 1 M HCl and heated in a water bath to 70  C for at least 2 h to remove calcium and magnesium carbonates. The humic and fulvic acid fractions of the SOM were removed by alkaline pyrophosphate extraction (Webb et al., 2004, 2007; Wright et al., 2009) and stable C isotope ratios (13C/12C) of the humin fraction were determined on a Thermo Finnigan isotope ratio mass spectrometer (Waltham, MA) coupled with a Costech elemental analyzer (EAIRMS). Geostatistical analysis of soil profile depth, clay content, Olsen extractable P, and the d13C enrichment of soil profiles was conducted with Surfer Software (Golden, CO) using variogram analysis and a kriging model.

3. Results The distribution of soil physical and chemical characteristics of the 98 profiles is summarized in Table 1. The average profile depth is 51 cm, although bedrock was not encountered within the upper meter of some profiles (Table 2). The minimum soil depth is 15 cm though nearly a third of the profiles have a depth of 60 cm or greater. Typical soils depths are illustrated in Fig. 3. foot- and toeslope profiles were greater than 60 cm in depth while backslopes profiles were as thin as 15 cm. The mean pH of the all surface horizons is 7.6. Seventy percent of the profiles are clay textured soils, nearly 20% are clay loams, and the remaining profiles are silty clay loams, silty clays, sandy clay loams, or sandy clays. All of the hillslope position categories are represented, with nearly half of the profiles located on footslopes and about a third of the profiles on backslopes. Typical hillslope positions along a transect from the west to east side of Ramonal are shown in Fig. 3. Most of the settlement and elite structures of Ramonal are located on the hill summits and shoulders (Fig. 2). The steep backslope soils are generally very thin (<40 cm). The footslopes are the gently sloped transitions between the backslopes and the nearly level toeslopes. All of the soils are Mollisols with nearly two thirds classified in the suborder Rendolls and the remainder in the suborder Udolls. The soil taxonomic great groups Argiudolls, Hapludolls, and Haprendolls are present among the 98 profiles. The geostatistical interpolation maps of various soil properties are shown in Figs. 4 through 7 including profile depth (Fig. 4), percent clay of the surface horizons (Fig. 5), Olsen extractable P of the surface horizons (Fig. 6), and the d13C enrichment for each profile (Fig. 7). The C isotope ratios of each profile segment were measured to discover evidence of ancient C3/C4 vegetation shifts. The average d13C value for the surface horizons of all profiles is 27.55& reflecting contemporary C3 forest trees and vines. The average 13C enrichment, or change in d13C with soil depth, is 1.41& (Table 1). The profiles were categorized into three groups of varying stable C isotope enrichment associated with ancient C4 vegetation. Seven percent of the profiles exceeded the 4& enrichment threshold providing strong evidence of ancient vegetation shifts from C3 forest to C4 crops and then back to contemporary C3 vegetation

Table 2 Properties of soil profiles with d13C enrichment greater than 4&. Soil Profile Great group

Depth

Horizon

Structure

Consistence

Soil Color

Texture

Grade, Size, Type

Dry

Dry

Clay

cm 21 Argiudolls

Class

g/kg 3, 0, 0, 0, 0, 0, 0, 0, 0, 0,

F, SBK VC, MA VC, MA VC, MA VC, MA VC, MA VC, MA VC, MA VC, MA VC, MA

VH VH VH VH VH VH VH VH VH VH

7.5YR 2.5/1 N 3/0 N 3/0 N 3/0 N 4/0 N 4/0 N 4/0 N 3/0 N 3/0 N 3/0

810

C

990

C

990

0e15 15e20 20e30 30e45 45e51 51e66 66e75 75e86

A Bt1 Bt1 Bt2 Bt2 Bt3 Bt3 Bt3

3, 0, 0, 0, 0, 0, 0, 0,

M, SBK VC, MA VC, MA VC, MA VC, MA VC, MA VC, MA VC, MA

HA VH VH VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR 10YR 10YR 10YR

0e15 15e22 22e40 40e52 52e60þ

A Bt Bt Btg Btg

3, 3, 2, 0, 0,

F, SBK M, SBK M, SBK VC, MA VC, MA

VH VH VH EH EH

0e15 15e25 25e35 35e45 45e55 55e65

A1 A2 A2 A3 A3 Cr

1, 1, 1, 1, 0, 0,

VF, SBK VF, SBK VF, SBK VF, GR F, SGR VF, SGR

0e20 20e34 34e50 50e70 70e88 88e99

A Bw Bt1 Bt1 Bt1 Btg

2, 2, 0, 0, 0, 0,

75 Hapludolls

0e20 20e40 40e60 60e80 80e90

A Bw1 Bw2 Bw3 Bw4

86 Hapludolls

0e20 20e30 30e40 40e50 50e60 60e70 70e85

A Bw1 Bw2 Bw3 Bg Bg Bg

62 Haprendolls

69 Argiudolls

pH

P

K

1

Total

Total

Organic

N

C

C

Change in CCE

1901894

28.08 26.99 27.19 24.32 25.80 23.94 23.09 22.82

5.26

229146

1902025

28.83 27.95 27.50 24.24 25.08

4.59

228043

1901909

28.91 27.10 26.11 24.91 24.56 25.54

4.35

229000

1902798

4.81

228872

1902827

257.4

27.65 26.08 24.93 22.84 24.41 23.02

20.8

0.18

3.4

41.4

40.3

9.3

C

0.19

1.2

12.2

11.1

9.0

980

C

0.18

1.4

17.2

15.6

13.5

2/1 3/1 3/1 4/1 4/1 4/1 4/1 4/1

850 950

C C

0.22

10.2 6.4

97.4 58.4

95.2 56.8

18.4 13.6

980

C

0.22

3.2

30.2

29.2

8.7

920

C

0.23

2.1

49.3

34.4

124.0

10YR 10YR 10YR 10YR 10YR

3/1 3/1 3/1 3/1 3/1

770

C

10.8

103.2

100.1

25.5

930

C

0.18

4.7

40.9

40.0

7.5

900

C

0.10

2.5

22.3

20.6

13.9

VH SH SH SH L L

10YR 10YR 10YR 10YR 10YR 10YR

2/1 3/1 3/1 4/1 4/1 5/1

460 450

C C

7.0 4.1

148.7 121.5

79.3 42.4

578.4 659.0

440 360

C CL

1.0 0.9

114.7 117.6

16.4 14.3

819.0 860.4

CO, SBK CO, SBK VC, MA VC, MA VC, MA VC, MA

VH VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR 10YR

2/1 2/1 4/1 4/1 4/1 4/1

760 790

C C

0.18

7.5 2.6

90.9 50.1

77.6 22.5

111.2 229.6

870

C

0.15

0.6

29.8

0.1

247.5

840

C

0.19

0.3

34.3

3.4

0, 0, 0, 0, 0,

VC, VC, VC, VC, VC,

MA MA MA MA MA

HA HA HA VH VH

10YR 10YR 10YR 10YR 10YR

2/1 2/1 2/1 2/1 3/1

920 970 860 910 870

C C C C C

0.33 0.11 0.11 0.11 0.11

2, 2, 0, 0, 0, 0, 0,

M, SBK M, SBK VC, MA VC, MA VC, MA VC, MA VC, MA

VH VH VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR 10YR 10YR

2/1 2/1 3/1 4/1 4/1 4/1 4/1

870 920 970 980

C C C C

970

C

3

7

5

FS

FS

FS

7.0

7.8

7.5

4.8

4.6

8.1

9.1

537.7

106.8

89.2

96.0

North m

229363

124.9

7.1

377.2

East m

4.78

127.4

FS

5.9

UTM Zone 16

27.79 27.26 26.84 26.68 27.31 26.87 26.01 26.44 25.47 23.01

10.5

1

6.2

d13C

&

g/kg TS

d13C

2

FS

7.8

4.1

111.1

4.5 2.3 1.4 1.1 1.0

36.8 22.4 40.2 28.5 45.1

27.4 12.7 14.5 6.8 11.1

78.5 80.5 214.3 180.8 283.4

26.41 26.00 22.29 20.68 21.28

5.73

228267

1901690

4

FS

6.3

3.9

75.6

4.7 2.6 1.5 1.0

53.7 26.4 13.2 7.5

50.3 22.9 9.6 4.3

28.5 29.4 29.9 26.8

228977

1902200

0.18

0.6

4.2

2.7

12.2

28.15 27.01 26.20 25.53 25.43 25.43 23.70

4.45

0.18 0.18 0.16

105

Texture, C ¼ Clay; CL ¼ Clay loam; Structure Grade; 0 ¼ Structureless; 1 ¼ Weak; 2 ¼ Moderate; 3 ¼ Strong. Structure Size, VF ¼ Very Fine; F ¼ Fine; M ¼ Medium; CO ¼ Coarse; VC ¼ Very Coarse; TK ¼ Thick. Structure Type, GR ¼ Granular; ABK ¼ Angular Blocky; SBK ¼ Subangular Blocky; PL ¼ Platy; SGR ¼ Single Grain; MA ¼ Massive. Consistence, L ¼ Loose; SH ¼ Slightly Hard; MH ¼ Moderately Hard; HA ¼ Hard; VH ¼ Very Hard; EH ¼ Extremely Hard. Slope Position, SU ¼ Summit; SH ¼ Shoulder; BS ¼ Backslope; FS ¼ Footslope; TS ¼ Toeslope.

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

A Btg1 Btg1 Btg1 Btg2 Btg2 Btg2 Btg3 Btg3 Btg3

25 Argiudolls

Hillslope %

0e18 18e28 28e40 40e54 54e67 67e79 79e89 89e100 100e113 113e124

24 Argiudolls

Slope COLE

106

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

(Table 2) (Balesdent and Mariotti, 1987; Boutton, 1996; Martinelli et al., 1996; Powers and Schlesinger, 2002). About 20% of the profiles have enrichment values ranging from 2 to 4& providing weak evidence of ancient C3/C4 vegetation shifts (Table 3). The remaining 73% of the profiles have enrichment values less than 2& (Table 4). 3.1. Profiles with greater than 4& enrichment The physical and chemical properties of the profiles with changes in d13C with depth greater than 4&, indicative of ancient forest clearance and C4 vegetation that may have included maize agriculture, are summarized in Table 2. All of these profiles are located at footslope or toeslope landscape positions and have depths greater than 60 cm. It is possible that most of these profiles received runoff deposition from eroded hillslopes during the early clearing of forest vegetation for ancient agriculture (Anselmetti et al., 2007) and portions of the stable C isotope signatures found in these profiles may be spatially displaced (Fig. 3). Excluding profile 62, all of these seven profiles have B master horizons, most of which are cambic or argillic diagnostic horizons. Many of the B horizons also exhibit gleying and some have mottling. All of the A and B horizons of these profiles are in the clay textural class. All surface horizons had pH values amenable to most agronomic crops ranging from 6.2 to 7.8. These seven profiles all had surface horizons rich in organic C with the minimum being 27.4 g/kg (profile 75). Olsen extractable P levels of the surface horizons ranged from 3.9 to 9.1 mg/kg placing them in the low to medium ranges of nutrient sufficiency levels (Havlin et al., 2005, table 9e13). The K levels in the soil were greater than 75 mg/kg and the total N levels ranged from 4.5 to 10.8 g/kg in the surface horizons of the seven profiles. Six of the seven profiles exhibiting isotopic evidence of ancient C4 vegetation were within the Udolls suborder, with four in the great group Argiudolls and one in the great group Haprendolls. The profile with the greatest 13C enrichment (change in d13C with depth of 5.73&) (profile 75) is classified Hapludolls. 3.2. Profiles with 2e4& enrichment The majority of the profiles with 2e4& 13C enrichment are deep, dark, clay soils, largely from footslope and toeslope locations (Table 3) and over half of them are well developed with argillic horizons. Of the twenty profiles in this category, the great group designations consist of 11 Argiudolls, 5 Haprendolls, and 4 Hapludolls. Profiles 1, 27, 35, and 47 show moderate development manifested by their cambic, or weak developed, B horizons, and profiles 16, 46, 68, 90, and 91 show either gleying or mottling in the lower horizons indicative of saturation and drainage cycles. The pH values of the surface horizons range from 6.8 to 8.0. The Haprendolls generally were characterized by having higher pH values, higher CCE, and higher P levels than the other great groups (Table 3). The Argiudolls and Hapludolls showed greater variation, but typically had low to medium P levels according to generalized fertility recommendations (Havlin et al., 2005, table 9e13). Total N in the surface horizons of these soils ranged from 3.2 to 14.2 g/kg.

Fig. 3. Typical elevation changes and changes in soil profile depths with hillslope positions are shown along a transect from the west to east sides of Ramonal. Soil profile numbers along the transect are shown. Note the varying scales for UTM easting, surface elevation above mean sea level, and soil profile depth.

summits, and shoulders of the hills occupied by the ruins of Ramonal. Profiles in these positions were generally truncated due to ancient erosion. Among these profiles were foot- and toeslopes on anciently constructed platforms, patios and causeways of the site. The average pH is 7.6 and the CCE values are typically high with an average of 641 g/kg (Table 4). The organic C levels of the surface horizons range from 20.3 to 231 g/kg. Nitrogen values in those same horizons vary from 7.0 to 18.6 g/kg. Phosphorus and K deficiencies are rare. Some of these profiles are the steeper backslope and footslope soils. Eighty-three percent of these profiles lack argillic or cambic horizons. Weathered calcium carbonate parent material (Cr) horizons are common. The majority of these soils were in the great group Haprendolls (80%) with some Hapludolls (10%) and Argiudolls (10%). 4. Discussion 4.1. Geostatistical interpolation The geostatistical distribution of soil profile depths are shown in Fig. 4. The deepest soils are confined to the foot- and toeslope locations as well as some locations near summits. Settled areas and steep backslope locations have some of the more shallow soils. Profiles 53 and 56 to the west of the Chalpate causeway are Haprendolls located on shoulder and backslope topographic positions. These soils have relatively lower clay levels and parent materials

3.3. Profiles with less than 2& enrichment The soils with d13C enrichment values below 2& are shallower, lighter in color, and less clayey than the soils from the other two groups previously described. This group of profiles had an average depth of 44 cm and tended to be shallow over bedrock. Nearly half of these profiles (34 of 69 profiles) are from the backslopes,

Fig. 4. The geospatial distribution of soil profile depths at Ramonal.

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

107

transported to settled areas for processing and consumption would be readily fixed and preserved in these highly calcareous upland soils. The lime and mortar associated with settlement construction would further increase the calcium carbonate levels of these soils augmenting their capacity for P fixation. The d13C enrichment isopleths indicating the strongest isotopic evidence of past maize agriculture are identified in Fig. 7. The spatial distribution of areas with significant ancient C4 vegetation correspond well with the profile depth (Fig. 4) and clay content (Fig. 5) suggesting that the more level, deeper, clayey soils are those where ancient C4 vegetation associated with maize agriculture grew. The margins of the corozo bajo near the center of Fig. 7 also exhibit strong evidence of maize agriculture. The backslope locations are largely devoid of the isotopic signature of ancient C4 vegetation. Thus, the strongest evidence of maize agriculture is found in footslope and toeslope locations further away from settlement. Fig. 5. The geospatial distribution of soil clay contents (g/kg) of surface A horizons in soils at Ramonal.

are the architectural materials used in the construction of platforms and other structures. When the soil depth data are compared with the percent clay data from Fig. 5, a more accurate picture of where the most cultivable, dark, and deep soils of the area are located is revealed. The clay data highlight many of the same areas as do the depth data, but with the notable exception of the area to the west of the causeway. The most clayey surface soils are found in the localized upland depressions on the lower landscape positions. These areas are typically further from settlement and away from backslopes. The corozo bajo location is identifiable just to the east of the center of Fig. 5 with the highest surface horizon clay levels. The phosphorus data (Fig. 6) reveal a nearly inverse relationship to both the depth and percent clay data. The higher P levels track the settlement quite accurately along the higher upland locations, and the lowest P levels are found in the lower, more clayey soils. The higher P levels associated with settlement could have resulted from human activities related to food processing and consumption as well as the waste products from such activities (Fernandez et al., 2002; Terry et al., 2004). Surplus P from perishable consumables

Fig. 6. The geospatial distribution of Olsen extractable P levels (mg/kg) of the surface soils (0e20 cm) at Ramonal.

4.2. Profiles with greater than 4& enrichment Profiles 21 and 86 show indications of aggradation that resulted from ancient erosion (Fig. 2, filled circles). Both of these soils are located in local depressions (footslope and toeslope) in areas of relatively high settlement density. These soils are deep, high in clay content, have lower pH (<6.4), and low CCE (30 g/kg). Profile 21 is an Argiudolls and profile 86 is a Hapludolls. Both soils have high shrink-swell clays as indicated by the high COLE values in the B horizons (Table 2). Profile 21 has a deep argillic horizon and profile 86 has none. The lack of argillic horizons indicates a less developed soil possibly with pedogenic processes interrupted by deposition events. Profile 21, however, does exhibit clay accumulation in subsurface horizons and also appears to have been exposed to similar clay deposition. This difference can be accounted for since profile 21 is at a lower toeslope location, and is more level (1 versus 4% slope). These qualities and the lower pH and CCE of profile 21 would suggest a greater amount of water moving down through the profile. The increased water flow at this location could also account for the illuviation of clays to the lower horizons. Perhaps the most telling evidence of the occurrence of deposition at these locations is the presence of the Maya clay and some evidence of buried soil horizons (Beach, 1998a; Beach et al., 2006).

Fig. 7. The geospatial distribution of the change in d13C (&) with depth of soil profiles at Ramonal showing areas with strong evidence of ancient maize agriculture. Elevation contours are in meters above mean sea level.

Soil Profile Great group

Structure Depth

Horizon

Grade, Size, Type

Consistence Dry

108

Table 3 Properties of soil profiles with d13C enrichment between 2 and 4&. Soil Color Dry

Texture Clay

Class

Slope COLE

g/kg 1 Haprendolls

A A Bw1 Bw2 Bw2 Bw3 Cr

2, 2, 2, 2, 2, 2, 1,

M, SBK M, SBK CO, SBK CO, SBK CO, SBK CO, SBK F, SBK

HA HA VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR 10YR 10YR

2/1 2/1 3/1 3/1 3/1 4/1 5/1

7 Argiudolls

0e25 25e35 35e50 50e67 67e80

A Bt1 Bt2 Bt3 Cr

2, 2, 2, 2, 2,

F, SBK M, SBK M, SBK M, SBK M, SBK

VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR

16 Argiudolls

0e15 15e30 30e45 45e52 52e64

A Bt Btg Btg Btg

2, 0, 0, 0, 0,

M, SBK VC, MA VC, MA VC, MA VC, MA

18 Argiudolls

0e15 15e34 34e45 45e50

A Bt Cr1 Cr2

23 Argiudolls

0e20 20e30 30e45 45e54 54e63

C

630 580

C C

510 550

C C

2/1 2/1 3/1 4/1 6/1

720 860 870 900 830

C C C C C

VH VH VH VH VH

10YR 2/1 10YR 3/1 N 4/0 N 4/0 N 4/0

820 970

C C

980

C

1, VF, SBK 2, F, SBK 0, VF, SGR 0, VF, SGR

VH MH L L

10YR 3/2 10YR 4/1 10YR 5/1 10YR 7/1

340 440 390 350

CL C CL CL

A Bt1 Bt1 Bt/Cr C

3, 3, 3, 3, 3,

M, M, M, M, M,

SBK SBK SBK SBK SBK

HA HA HA HA HA

10YR 10YR 10YR 10YR 10YR

2/1 3/1 3/1 3/1 8/1

770 880

C C

850 530

C C

0e12 12e22 22e32 32e46 46e60 60e75 75e85

A Bt1 Bt1 Bt2 Bt2 Bt2 Bt2

2, 2, 2, 0, 0, 0, 0,

M, SBK M, SBK M, SBK VC, MA VC, MA VC, MA VC, MA

VH VH VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR 10YR 10YR

2/1 3/1 3/1 5/1 5/1 5/1 5/1

780

C

930

C

930

C

0e12 12e24 24e36 36e40

A A Bw Cr

2, 3, 3, 0,

F, SBK M, SBK M, SBK VF, SGR

VH HA VH HA

10YR 10YR 10YR 10YR

2/1 2/1 2/1 5/1

660

C

730 490

C C

29 Haprendolls

0e14 14e21 21e31

A1 A2 A2

1, VF, SBK 1, VF, SBK 1, VF, SBK

VH VH VH

10YR 2/1 10YR 2/1 10YR 3/1

46

C

40

CL

30 Argiudolls

0e12 12e22 22e32 32e45 45e55 55e65 65e77þ

A Bt1 Bt2 Bt2 Bt3 Bt3 Bt4

3, 3, 3, 3, 2, 2, 0,

HA SH MH MH VH VH VH

10YR 10YR 10YR 10YR 10YR 10YR 10YR

2/1 3/1 3/1 3/1 5/2 5/2 5/2

820 940 950 0.11 980 0.11 950

C C C

0.18 0.11 0.11

C

0.11

C

0.11

0e14

A1

0, VF, SGR

L

10YR 3/2

450

C

27 Hapludolls

33

M, SBK M, SBK M, SBK M, SBK CO, SBK CO, SBK VC, MA

pH

%

630

26 Argiudolls

Hillslope

FS

7.7

Total C

Change in d13C

Organic

P

K

N

C

CCE

mg/kg

mg/kg

g/kg

9.3

143.6

14.2

185.7

132.2

445.8

7.0 4.4

160.0 176.1

97.9 94.7

517.3 678.3

3.1 2.7

186.8 177.2

97.0 91.3

13

d C

UTM Zone 16 East

North

&

&

m

m

3.56

228882

1902231

748.4 715.7

28.03 26.39 26.46 25.10 24.47 25.09 24.56

0.18 0.18 0.03 0.03 0.03 0.03

3

0.11 0.18 0.18 0.18

5

BS

7.5

6.6

85.7

13.4 6.8 2.8 2.4 1.2

141.9 72.0 66.5 51.6 56.5

133.2 61.0 45.2 33.7 30.1

72.1 91.7 177.2 148.9 220.1

27.81 27.05 25.29 25.68 25.31

2.52

228356

1902410

4

FS

6.8

4.6

158.4

9.8 5.1

103.2 49.9

102.2 48.9

8.5 8.4

229462

1901683

0.15

1.1

23.2

16.2

58.3

27.68 26.57 25.52 25.38 23.94

3.74

0.15

2

TS

7.7

7.9

161.4

13.0 9.4 5.3 2.8

287.2 269.9 257.1 246.2

203.2 179.1 152.7 133.1

699.9 756.3 870.3 942.1

28.36 28.18 25.90 26.82

2.46

229438

1901798

2

FS

7.3

6.2

213.8

10.3 7.0

92.8 78.4

88.9 68.9

3.29 7.92

3.05

229357

1902027

3.3 2.4

89.2 186.9

55.8 105.3

27.81 67.96

26.34 24.99 24.07 23.43 23.29

12.2

132.2

129.8

20.3

2.44

228184

1902004

0.16

6.2

61.2

58.7

20.5

0.10

1.4

13.4

11.7

13.9

28.88 28.55 28.09 27.27 27.73 27.42 26.44

8.0

82.3

65.6

139.2

2.00

228261

1902086

4.2 1.8

69.5 108.3

31.4 21.9

317.1 720.0

28.02 26.83 26.02 26.49

9.0

171.3

99.8

596.2

1.24

228432

1902151

3.8

134.1

45.3

739.8

26.41 25.45 26.69

6.3 4.0 2.4

66.3 35.1 19.6

54.8 24.9 9.7

96.1 85.0 82.9

2.23

228275

1901917

1.2

8.8

0.6

68.6

3.96

228763

1902189

0.00

0.18 0.15 4

5

FS

BS

6.8

7.5

6.8

7.5

219.5

118.3

0.16 6

BS

7.7

10.1

193.7

3

FS

7.4

7.4

180.7

6

SH

7.7

8.0

154.3

0.9

6.1

0.2

49.5

28.49 27.74 26.40 26.92 26.68 27.14 26.26

6.4

142.8

58.3

704.5

27.13

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

0e15 15e30 30e45 45e60 60e75 75e90 90e105

Total

Haprendolls

113.2

17.8

794.6

1

FS

7.3

6.9

442.0

6.0 4.9 3.6 1.4

59.2 40.8 47.9 110.4

55.9 37.4 25.1 11.6

27.1 28.1 189.6 823.7

27.77 27.08 25.49 26.37

2.28

228653

1901610

5

BS

7.8

8.5

244.9

7.9

156.9

70.7

718.0

2.55

228768

1901810

2.0

129.1

21.9

893.1

28.31 26.87 25.76

3.9

41.4

39.4

16.4

2.48

228946

1902029

0.16

1.2

13.4

12.0

11.9

C

0.18

0.8

9.9

8.3

13.1

980

C

0.18

770 750 570

C C C

2/1 3/1 3/1 4/1

700 880 920 900

C C C C

0.19 0.20 0.15

10YR 10YR 10YR 10YR 10YR 10YR

3/1 3/1 5/1 5/1 5/1 5/1

850 950

C C

910

VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR

3/1 3/1 3/1 4/1 4/1

2, F, SBK 2, F, SBK 2, F, SBK

VH HA SH

A1 A2 Btg

1, VF, SBK 1, VF, SBK 0, VC, MA

A Bw1 Bw2 Bg1 Bg2

3, 2, 0, 0, 0,

A1 A2 A2 A2 A3

0, 0, 0, 0, 0,

VF, VF, VF, VF, VF,

L L L L L

10YR 10YR 10YR 10YR 10YR

3/2 4/2 4/2 4/2 4/1

400

35 Hapludolls

0e12 12e26 26e35 35e40

A Bw1 Bw2 Cr

3, 3, 3, 1,

M, SBK M, SBK M, SBK VF, SBK

400

CL

MH SH VH VH

10YR 10YR 10YR 10YR

2/1 2/1 2/1 5/1

880 910 820 460

C C C C

41 Haprendolls

0e12 12e30 30e44

A1 A1 A2

0, VF, SGR 0, VF, SGR 0, VF, SGR

L L L

10YR 3/2 10YR 3/2 10YR 5/2

410

C

370

SC

0e10 10e20 20e30 30e40 40e50 50e60 60e70 70e80

A Bt1 Bt1 Bt1 Bt2 Bt2 Bt2 Btg

3, 0, 0, 0, 0, 0, 0, 0,

M, SBK VC, MA VC, MA VC, MA VC, MA VC, MA VC, MA VC, MA

VH VH VH VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR 10YR 10YR 10YR

880

C

980

C

960

47 Hapludolls

0e17 17e31 31e50

A Bw Cr

3, M, SBK 3, M, SBK 2, M, SBK

SH HA MH

10YR 2/1 10YR 2/1 10YR 4/1

64 Argiudolls

0e15 15e30 30e45 45e55

A Bt1 Bt2 Bt3

3, 3, 0, 0,

M, SBK M, SBK VC, MA VC, MA

VH VH VH VH

10YR 10YR 10YR 10YR

67 Argiudolls

0e22 22e34 34e50 50e62 62e74 74e82

A Bt1 Bt2 Bt2 Bt2 Bt2

2, 0, 0, 0, 0, 0,

M, SBK VC, MA VC, MA VC, MA VC, MA VC, MA

VH VH VH VH VH VH

0e17 17e30 30e40 40e50 50e60

A Bt1 Bt1 Bt2 Btg

2, 0, 0, 0, 0,

CO, SBK VC, MA VC, MA VC, MA VC, MA

83 Haprendolls

0e15 15e30 30e40

A1 A2 A3

90 Argiudolls

0e15 15e27 57e70

91 Hapludolls

0e15 15e30 30e45 45e60 60e80

46 Argiudolls

68 Argiudolls

SGR SGR SGR SGR SGR

M, SBK M, SBK VC, MA VC, MA VC, MA

CL

0.22 0.16

1.6

115.2

16.7

820.7

0.4

4.2

2.8

11.3

28.20 27.55 27.47 26.29 25.72 26.92 26.00 27.36

5

BS

7.6

8.9

146.7

5.8 3.9 1.8

67.5 52.3 74.9

43.8 20.0 3.6

197.8 268.8 594.5

27.36 26.38 25.22

2.14

228887

1901951

3

TS

7.4

5.8

187.3

4.4 2.7 1.6 0.7

48.5 28.0 17.6 19.9

43.8 25.0 15.2 7.2

38.9 25.3 19.9 106.0

27.49 28.25 28.11 25.80

2.45

228665

1902712

4

TS

7.1

4.8

76.5

3.2 2.0

34.7 20.7

31.8 19.1

24.3 13.2

228772

1902814

C

0.22

0.0

19.8

2.3

145.8

28.22 27.88 26.66 25.84 25.86 26.15

2.38

0.22

870 960

C C

4.0 1.9

45.3 19.3

42.6 17.3

22.5 16.6

228876

1902910

960 970

C C

0.08 0.14

0.8 0.5

14.1 15.4

8.6 4.2

45.6 93.2

28.52 27.43 27.42 26.88 25.66

2.86

0.18

10YR 3/1 10YR 4/2 10YR 5/1

500 380 390

C SiCL SiCL

2

FS

7.8

15.5

192.9

3.9 2.6 1.8

112.7 104.0 101.4

31.5 18.7 11.6

676.3 710.6 747.9

27.78 26.40 25.14

2.64

229356

1902308

MH MH VH

10YR 3/1 10YR 4/1 10YR 5/2

450 440 980

C C C

2

FS

8.0

10.5

172.5

125.1 115.4 5.3

41.6 33.1 4.1

695.6 685.7 9.8

28.10 27.54 25.72

2.38

229254

1902188

0.18

4.5 3.0 0.8

VH VH VH VH VH

10YR 10YR 10YR 10YR 10YR

890 930 870 920 830

C C C C C

1

TS

7.4

7.0

197.5

4.5 2.7 1.5 1.0 0.7

43.4 23.5 13.1 7.6 16.1

40.6 19.2 11.5 4.5 0.9

23.6 36.0 13.7 25.7 126.5

27.95 26.53 26.12 26.33 25.32

2.63

229154

1902177

0.27 0.20 0.20 0.23

2/1 3/1 3/1 3/1 4/1 4/1 4/1 5/1

2/1 2/1 3/1 4/1 4/1

2

FS

7.2

6.9

121.2

0.19

4

TS

7.2

5.0

109

Texture, SiCL ¼ Silty clay loam; SC ¼ Sandy clay; CL ¼ Clay loam; C ¼ Clay. Structure Grade, 0 ¼ Structureless; 1 ¼ Weak; 2 ¼ Moderate; 3 ¼ Strong. Structure Size, VF ¼ Very Fine; F ¼ Fine; M ¼ Medium; CO ¼ Coarse; VC ¼ Very Coarse; TK ¼ Thick. Structure Type, GR ¼ Granular; ABK ¼ Angular Blocky; SBK ¼ Subangular Blocky; PL ¼ Platy; SGR ¼ Single Grain; MA ¼ Massive. Consistence, L ¼ Loose; SH ¼ Slightly Hard; MH ¼ Moderately Hard; HA ¼ Hard; VH ¼ Very Hard; EH ¼ Extremely Hard. Slope Position, SU ¼ Summit; SH ¼ Shoulder; BS ¼ Backslope; FS ¼ Footslope; TS ¼ Toeslope.

112.3

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

1.1

27.16 25.55 25.09 24.23 23.20

14e27 27e36 36e45 45e60 60e75

Soil Profile Great group

Structure Depth

Horizon

Grade, Size, Type

Consistence Dry

Soil Color Dry

Texture Clay

cm 2 Hapludolls

110

Table 4 Properties of representative soil profiles with d13C enrichment less than 2&.

Class

Slope COLE

g/kg 2, 2, 0, 1,

F, SBK M, SBK VF, SGR VF, SBK

MH SH L VH

10YR 10YR 10YR 10YR

2/1 2/1 7/1 2/1

750 680 440 510

C C C C

Haprendolls

15e44 44e58

Bw Cr

1, VF, SBK 0, VF, SGR

MH L

10YR 3/1 10YR 8/1

500 290

C CL

4 Haprendolls

0e20 20e30 30e40 40e52

A1 A2 A3 Cr

0, 0, 0, 0,

VF, VF, VF, VF,

L L L L

10YR 10YR 10YR 10YR

3/1 4/1 4/1 6/1

300 340 330 430

CL CL CL C

5 Argiudolls

0e12 12e20 20e30 30e40 40e50

A Bt1 Bt2 Bt2 Bt2

2, 2, 0, 0, 0,

M, SBK M, SBK VC, MA VC, MA VC, MA

VH HA VH VH VH

10YR 10YR 10YR 10YR 10YR

2/1 3/2 3/2 3/2 3/2

830 910

C C

0.23

920

C

0.22

6 Haprendolls

0e22 22e30 30e40 40e44

A1 A2 Cr Cr

1, 1, 0, 0,

F, GR M, GR VF, SGR VF, SGR

MH MH L L

10YR 10YR 10YR 10YR

3/1 4/1 6/1 6/1

500 430

C C

530

C

12 Haprendolls

0e20 20e38 38e50 50e68 68e74

A1 A2 A3 Bw Cr

1, 1, 1, 2, 0,

VF, SBK VF, SBK VF, SBK M, SBK VF, SGR

VH VH VH SH L

10YR 10YR 10YR 10YR 10YR

3/1 4/1 5/1 6/2 7/1

410 360 370 360 470

C SC CL CL C

15 Haprendolls

0e18 18e27 27e42 42e52 52e60

A1 A2 Cr1 Cr2 Cr3

2, 0, 0, 0, 0,

M, SBK VF, SGR VF, SGR VF, SGR VF, SGR

MH L L L L

10YR 10YR 10YR 10YR 10YR

4/2 4/1 6/1 7/1 8/1

380 470 420 470 460

20 Haprendolls

0e15 15e30 30e45 45e54

A1 A2 A2 Cr

1, 1, 1, 0,

VF, VF, VF, VF,

SBK SBK SBK SGR

VH VH VH L

10YR 10YR 10YR 10YR

4/2 5/2 5/2 7/1

0e20 20e30 30e40 40e50

A1 A2 Bt Cr

2, 2, 2, 0,

F, GR F, GR M, SBK VF, SGR

SH SH VH L

10YR 10YR 10YR 10YR

0e14 14e30 30e42

A1 A1 A2

1, VF, SBK 1, VF, SBK 0, VF, SGR

0e20 20e35 35e45

A Bw Bw

2, M, SBK 0, VC, MA 0, VC, MA

22 Argiudolls

39 Haprendolls 97 Hapludolls

pH

Total

P

K

N

mg/kg

mg/kg

g/kg 14.8 9.7 3.5 14.5

148.1 147.1 239.2 234.7

136.2 111.9 138.1 189.1

9.5 1.8

208.9 234.5

2

FS

7.5

5.7

94.5

4

FS

7.8

10.0

182.6

0.11

0.08

C

Change in d13C

Organic C

CCE

13

d C

UTM Zone 16 East

North

&

&

m

m

99.5 293.7 842.5 379.8

28.36 26.99 27.68 28.41

1.37

228067

1902405

0.32

228102

1902311

150.8 128.3

484.4 884.8

28.37 28.09

4

FS

7.8

9.9

122.8

16.1 8.0 4.5 3.4

288.3 237.4 239.3 247.9

221.6 155.1 144.9 141.5

555.7 686.2 786.6 886.3

28.82 28.67 28.32 28.54

0.50

228176

1902337

3

FS

7.5

5.8

95.3

11.2 6.9

106.0 57.4

103.8 56.4

18.4 8.5

1.31

228183

1902427

4.3 0.0

39.5 0.0

38.9 0.0

5.3 0.0

28.95 28.40 27.77 27.64 28.08

15.6 6.1

272.7 252.9

199.7 152.7

608.0 834.7

0.80

228363

1902307

4

BS

7.8

7.3

93.2

5.4

253.6

151.5

850.6

28.09 27.72 27.29 27.74

8

BS

8.1

8.7

174.4

13.5 6.0 7.2 3.6 3.3

298.8 259.3 257.4 252.4 259.1

200.8 149.6 150.5 139.3 143.2

816.6 914.1 890.6 942.6 965.8

27.58 27.91 27.94 27.21 27.06

0.88

228713

1902280

CL C C C C

2

FS

7.8

5.4

152.8

11.4 8.2 5.8 2.9 2.3

278.6 269.3 259.7 243.8 249.8

186.8 172.7 156.5 135.5 141.2

764.8 804.6 859.6 902.4 904.9

27.63 27.70 27.50 26.72 27.07

0.98

229377

1901598

470

C

2

TS

7.7

9.9

202.9

15.0

290.1

204.8

711.1

0.56

229437

1901944

450 410

C C

7.0 4.9

262.8 249.0

161.4 143.7

845.3 877.3

26.98 26.42 26.56 26.44

4/1 4/1 6/2 8/1

280 320 380 260

CL CL CL L

SH SH L

10YR 3/1 10YR 3/1 10YR 5/1

480

C

370

CL

VH VH VH

10YR 2/1 10YR 3/1 10YR 3/1

770

C

730

C

0.00 0.00 0.00 0.00

1

FS

7.6

6.9

122.5

10.5 6.6 4.8 1.6

256.6 262.6 253.7 251.7

167.6 163.1 148.4 137.5

741.8 829.4 877.5 951.8

27.30 26.86 26.49 26.80

0.81

229264

1901991

2

FS

7.7

7.1

240.5

6.5

126.0

61.0

542.0

0.27

228762

1901712

1.9

121.2

16.2

874.8

28.13 28.40 28.17

7.6

74.0

69.0

41.6

0.94

229173

1901909

4.2

43.6

33.1

87.6

26.76 26.25 25.82

0.00

0

FS

7.6

8.4

0.19

Texture, SC ¼ Sandy clay; CL ¼ Clay loam; C ¼ Clay; L ¼ Loam. Structure Grade, 0 ¼ Structureless; 1 ¼ Weak; 2 ¼ Moderate; 3 ¼ Strong. Structure Size, VF ¼ Very Fine; F ¼ Fine; M ¼ Medium; CO ¼ Coarse; VC ¼ Very Coarse; TK ¼ Thick. Structure Type, GR ¼ Granular; ABK ¼ Angular Blocky; SBK ¼ Subangular Blocky; PL ¼ Platy; SGR ¼ Single Grain; MA ¼ Massive. Consistence, L ¼ Loose; SH ¼ Slightly Hard; MH ¼ Moderately Hard; HA ¼ Hard; VH ¼ Very Hard; EH ¼ Extremely Hard. Slope Position, SU ¼ Summit; SH ¼ Shoulder; BS ¼ Backslope; FS ¼ Footslope; TS ¼ Toeslope.

231.1

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

A Bw Cr A

SGR SGR SGR SGR

Hillslope %

0e15 15e30 30e38 0e15

3

Total

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

At depths below 50 cm, both of these profiles have dark gray clays (N 4/0, N 3/0, 10 YR 4/1) mixed with light gray (10 YR 7/1) or greenish gray (10Y 6/1) clays (only the dominant matrix colors are reported in Table 2). These lighter colored clays are likely deposits of eroded soils from higher elevations. The mixed appearance of these dark and lighter clays (as opposed to depositional layers) in these lower horizons has resulted from argilloturbation. In the case of profile 21, the lower depths of the Btg3 horizon show less visual evidence of the greenish gray clay. Also, the darker gray matrix soil color of these intermingled horizons shifts from dark gray (N 4/0) in the Btg2 horizon to very dark gray (N 3/0) in the Btg3 horizon. This color value decrease with depth in a profile can be indicative of a buried horizon (Beach et al., 2006). The organic C levels in this Btg3 horizon are also 1.4 times greater than those of the superior Btg2 horizon providing further evidence of a buried layer. The change in d13C values with depth of profiles 21 and 86 reveals a gradual increase in 13C until the very deepest soil horizon where the greatest shift from one soil level to another of d13C values occurs (Fig. 8). Without this 13C enrichment at the deepest level of these profiles, neither of them would satisfy the 4& enrichment benchmark. As the deepest levels of these profiles show the greatest d13C enrichment, it is suggested that these horizons supported maize agriculture for some time prior to their burial by depositional events. The burial of these deep toeslope horizons by eroded soils that were less 13C enriched indicates that the eroded backslopes had been cultivated less extensively than the buried horizons of the foot- and toeslopes. The well-developed profiles 24, 25, 69, and 75 are dark, clay soils located away from settlement (Fig. 2, filled circles). All of them except profile 75 have argillic horizons indicative of their development and lack of disturbance. These profiles are among the most P depleted of those with greater than 4& isotopic enrichment. This indicates less household activity and increased crop harvesting which depleted the plant available P (Dunning, 1996; Dunning et al., 1997).

-28

-22

Profile 69 was the only profile of this group that showed any evidence of Maya clay deposition. At depth (88e99 cm), profile 69 has a dark gray (10YR 4/1) clay somewhat mixed with a light brownish gray (10YR 6/2) clay (Table 2). The COLE values of this profile were also similar to those of profiles 21 and 86 which were also impacted by deposition. The change in d13C values with depth of profiles 24, 69, and 75 (Fig. 9) is similar to the isotopic pattern of ancient maize agriculture described by Wright et al. (2009). These profiles have 13C enrichments at locations above the deepest profile layers, or have less 13C enriched soils below and above more enriched soils. These types of patterns provide compelling evidence of plant community shifts such as the generalized C3eC4eC3: forest-maize-forest paradigm suggests (Dunning et al., 1997, 1998; Beach, 1998a; Beach et al., 2006, 2008). At the 75e86 cm depth of profile 24 there is an isotopic signature of ancient C4 vegetation (Fig. 9). Above that at the 45e51 cm depth is the isotopic signature of a period of reforestation but there is another layer of C4 vegetation enrichment at the 30e45 cm depth and finally a trend back to C3 vegetative isotopic values in the surface layer (0e30 cm) indicative of plant succession resulting in the climax forest community present today. This pattern coincides with initial settlement and maize cultivation, an extended period of fallow or hiatus and reforestation, followed by another period of agriculture (Classic to Late Classic), and the eventual reforestation subsequent to abandonment. Profile 69 also has a peak in 13C enrichment at 50e70 cm depth with an underlying recession similar to those described, but the shifts occur at greater depths. This could likely be related to the evidences of deposition previously described. Profile 75 has the greatest d13C value and the greatest change in d13C with depth of all the profiles (in spite of having the highest d13C surface value of the seven enriched profiles). The most enriched value of 20.68& is at 70 cm, followed by a smooth gradation upwards to the surface and d13C values more characteristic of contemporary forest vegetation. The fact that values indicative of C4 plant enrichment occur from 50 cm down, suggest that this location may have been subject to ancient maize agriculture.

-20

-30 0

20

20

40

40 Soil depth, cm

Soil depth, cm

-30 0

δ13C, ‰ -26 -24

60

-28

δ13C, ‰ -26 -24

-22

-20

60

80

80

100

100

120

111

120 13

Fig. 8. The change in d C of the humin fraction with depth of selected profiles with greater than 4& enrichment.

Fig. 9. The change in d13C of the humin fraction with depth of selected profiles with greater than 4& enrichment.

112

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

4.3. Profiles with 2e4& enrichment Of the profiles with d13C enrichment of 2e4&, profiles 1 and 33 are noteworthy because they have enrichment values that are within 0.5& of the 4& benchmark. These profiles are affiliated with ancient settlement and appear to have been impacted by ancient construction and household activities (Fig. 2, squares; Fig. 10). Compared with many of the twenty profiles that have 2e4& enrichment, profiles 1 and 33 have lower clay content (<650 g/kg), higher P levels (8.0 mg/kg), higher pH (>7.7), and higher CCE (up to 75% or greater in subsurface horizons) (Table 3). These attributes are related to the structures and limestone-derived building materials upon which these profiles formed. Profile 33 has lighter color values than the other profiles suggestive of its limited development and disturbance (Olson, 1977). Profiles 1 and 33 are Haprendolls (Table 3). The higher P levels of profiles 1 and 33 lend further evidence to their connection with ancient household and waste disposal activities (Parnell et al., 2001; Terry et al., 2004). The relatively high d13C enrichment values could possibly be attributed to household food processing, consumption, and waste disposal. It is possible these areas adjacent to the settlement were amended with nutrient inputs such as night soil, nixtamal water (alkaline lime water used to soak maize) (Barba and Ortiz, 1992; Holliday and Gartner, 2007), and other organic amendments used to increase and maintain soil fertility (Dunning et al., 1997). Another interpretation is suggested by the trend of enriched d13C values (24.5 to 23.2&) in the ancient rooting zone (60e75 cm) of these profiles. Such values suggest cultivation of maize for some time before Ramonal was settled and built up by the construction of structures during the Early Classic (Lou, 1997) or Middle Preclassic (Fialko, 2000a). Perhaps as the population increased, areas once used for cultivation were subsequently put to use for settlement purposes. The penchant of the ancient Maya to settle on or adjacent to the best agricultural lands within the Maya Lowlands has been noted by multiple researchers (Bullard, 1960; Stevens, 1964; Voorhies, 1972;

Green, 1973; Puleston, 1973, 1983; Olson, 1977; Sanders, 1977; Turner, 1979; Ford, 1986; Pope and Dahlin, 1989; Fedick and Ford, 1990; Fedick, 1994, 1995; Dunning et al., 1997; Webb et al., 2007). A combination of some or all of these possibilities is also reasonable given the construct of an area settled due to its agronomic potential and in turn affected by human activity including construction, waste disposal, food processing, and gardening. While many of the same pedogenic and anthropogenic factors influenced the soils with 2e4& enrichment, isotopic evidence of ancient maize agriculture is weak. Discernible d13C enrichments are encountered in rooting zones (>30 cm) in many of these profiles including profiles 18, 35, 46, and 67 (Fig. 2, triangles; Fig. 11). Profile 67 shows a very gradual trend of increasing isotopic enrichment in the rooting zone while profile 46 has two enrichment shifts. Profiles 18 and 35 are similar with fairly pronounced shifts near the base of these relatively shallow profiles. Profiles 29, 27, 26, (Fig. 2, open circles) and 25 (discussed above) are spatially related starting with the backslope (profiles 29 and 27) and transitioning to the footslope (profiles 26 and 25). Descending down the slope, the isotopic enrichment within profiles increases from 1.2 to 4.6& while the zone of enrichment increases with depth starting at 17 cm in profile 29 and at 46 cm in profile 25 (Fig. 12). This trend exhibited on a multi-profile scale may indicate that this toposequence was agriculturally important and that mild erosion has occurred over extended periods. Agricultural soils likely eroded downward both weakening the isotope signal and causing it to be manifested at shallower depths on the backslope. The same erosion would, in turn, strengthen the signal while burying it deeper at profiles located on the lower foot- and toeslopes. 4.4. Profiles with less than 2& enrichment The 69 profiles with less than 2& C isotope enrichment make up the majority of the sample population of thin backslope soils, that if cleared of forest vegetation, would be subject to severe erosion. The backslope profiles are generally truncated as a result of ancient

δ13C, ‰

δ13C, ‰ -28

-26

-24

-22

-30 0

-20

20

20

40

40 Soil depth, cm

Soil depth, cm

-30 0

60

-28

-26

-24

-22

-20

60

80

80

100

100

120

120 13

Fig. 10. The change in d C of the humin fraction with depth of selected profiles with between 2 and 4& enrichment.

Fig. 11. The change in d13C of the humin fraction with depth of selected profiles with between 2 and 4& enrichment.

R.L. Burnett et al. / Quaternary International 265 (2012) 101e115

-30 0

-28

δ13C, ‰ -26 -24

-22

-20

20

Soil depth, cm

40

60

80

100

120 Fig. 12. The change in d13C of the humin fraction with depth of profiles along a toposequence.

runoff erosion. These soils are less suitable for sustained agriculture without adequate soil conservation practices. Many of this group of soil profiles was located at foot- and toeslope positions that reflect the platforms, patios, and causeways of the ancient site. Thus, ancient Maya construction and land use activities have significantly altered this group of soil profiles. There have been several estimates of soil formation rates in the Petén. Researchers have measured the accumulation of soils atop terminal classic structures and patio and plaza floors that have been protected from runoff erosion and deposition (Beach, 1998a; Fernandez et al., 2005; Johnson et al., 2007b). Fernandez et al. (2005) reported soil accumulation of 10e11 cm on top of leveled patio floors in 1200 years of abandonment of Piedras Negras, Guatemala. Johnson et al. (2007b) measured between 12 and 15 cm of accumulated soil atop patio floors since the rapid abandonment of Aguateca in about 800 AD. From these data, soil formation rates of between 0.09 and 0.15 mm/year have been estimated beneath forest vegetation in the southern Maya lowlands. The average soil depth of 28 backslope soils in the dataset from Ramonal was 41 cm and the median depth was 35 cm. With the assumption that 10e18 cm of soil formed since reforestation following the terminal classic, most of the steep backslope soils were between 0 and 17 cm deep at the time of abandonment. The backslopes profiles were very thin and probably of little agricultural value at the end of the Classic period. The steep backslopes were likely severely eroded, leaving little evidence of agricultural use (Fernandez et al., 2005; Johnson et al., 2007b). 5. Conclusions The stable C isotope evidence of the SOM from the collected profiles suggests a diverse vegetation history at some locations with strong evidence for past vegetation changes from C3 forest to C4 vegetation associated with ancient maize agriculture and back again to contemporary C3 forest. This stable C isotope evidence is preserved in the recalcitrant humin fraction of the soil organic

113

matter, allowing a glimpse at the past ecology of the area interpreted within the framework of the unique biological and cultural history of Ramonal. The strongest isotopic evidence of ancient maize agriculture is associated with deep, clay soils from foot- and toeslope locations. Many of these soils are in localized upland depressions or seasonal bajos surrounding the ancient settlement of Ramonal. Locations further from settlement are more developed with argillic horizons, but also have relatively lower plant available P levels. Significant evidence of ancient maize agriculture was also found at locations nearer settlement on less developed soils with relatively higher levels of P. Such soils indicate the possible effects of household activities such as intensive gardening, food processing, and food waste disposal. Most of the soil profiles collected did not provide strong evidence of ancient maize agriculture. This is not surprising because the sampling strategy was not opportunistic and included areas of high settlement density. The dual interest in areas of suspected agricultural importance as well as those areas where cultivation was less likely enabled the production of a dataset that highlighted the contrast of the landscape and emphasized the areas where cultivation was most likely. The supervised classification sampling strategy also enabled visualization of the dynamics and interactions of soil properties with carbon isotope ratios associated with ancient vegetation shifts. Acknowledgements This portion of the Re-evaluation of the Earthworks at Tikal, Guatemala project was funded by the National Science Foundation (Grant BCS-0443280) and by Brigham Young University. The Instituto de Antropología e Historia, the Consejo Nacional de Areas Protegidas, and the Parque Nacional Tikal of Guatemala granted permission for this research to take place. The Re-evaluation of the Earthworks at Tikal, Guatemala project thanks all those who assisted with the collection, preparation, and analysis of the soil samples. Special thanks goto Horacio Martinez and Kirk Straight for their contributions to this study. References Anselmetti, F.S., Hodell, D.A., Ariztegui, D., Brenner, M., Rosenmeier, M.F., 2007. Quantification of soil erosion rates related to ancient Maya deforestation. Geology 35, 915e918. Atran, S., 1993. Itzá Maya tropical agro-forestry. Current Anthropology 34, 633e700. Baker, J.L., 2007. The Wet or the Dry?: Agricultural Intensification in the Maya Lowlands. In: Thurston, T.L., Fisher, C.T. (Eds.), Seeking a Richer Harvest: The Archaeology of Subsistence Intensification, Innovation, and Change. Springer, New York, pp. 63e90. Balesdent, J., Mariotti, A., 1987. Natural 13C abundance as a tracer for studies of soil organic matter dynamics. Soil Biology and Biochemistry 19, 25e30. Barba, L., Ortiz, A., 1992. Análisis químico de pisos de ocupación: Un caso etnográfico en Tlaxcala, Mexico. Latin American Antiquity 3, 63e82. Beach, T., 1998a. Soil catenas, tropical deforestation, and ancient and contemporary soil erosion in the Petén, Guatemala. Physical Geography 19, 378e405. Beach, T., 1998b. Soil constraints on northwest Yucatan, Mexico: Pedoarchaeology and Maya subsistence at Chunchucmil. Geoarchaeology: An International Journal 13, 759e791. Beach, T., Dunning, N.P., 1995. Ancient Maya terracing and modern conservation in the Petén rainforest in Guatemala. Journal of Soil and Water Conservation 50, 138e145. Beach, T., Luzzadder-Beach, S., Dunning, N.P., Hageman, J., Lohse, J., 2002. Upland agriculture in the Maya lowlands: ancient Maya soil conservation in northwestern Belize. The Geographical Review 92, 372e397. Beach, T., Dunning, N.P., Luzzadder-Beach, S., Cook, D.E., Lohse, J., 2006. Impacts of the ancient Maya on soils and soil erosion in the central Maya Lowlands. Catena 65, 166e178. Beach, T., Luzzadder-Beach, S., Dunning, N.P., Cook, D., 2008. Human and Natural impacts on fluvial and karst depressions of the Maya Lowlands. Geomorphology 101, 308e331. Beach, T., Luzzadder-Beach, S., Dunning, N.P., Jones, J., Lohse, J., Guderjan, T., Bozarth, S., Millspaugh, S., Bhattacharya, T., 2009. A review of human and

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Cowgill, U.M., 1961. Soil fertility and the ancient Maya. Transactions of the Connecticut Academy of Arts and Sciences 42, 1e56. Cowgill, U.M., Hutchinson, G.E., 1963. Ecological and geochemical archaeology in the southern Maya lowlands. Southwestern Journal of Anthropology 19 (3), 267e286. Culbert, T.P., Levi, L., McKee, B., Kunen, J.L., 1996. Investigaciones arqueológicas en el Bajo La Justa, entre Yaxha y Nakum. In: Laporte, J.P., Escobedo, H.L. (Eds.), IX Simposio de Investigaciones Arqueológicas en Guatemala, 1995. Museo Nacional de Arqueología y Etnología, Guatemala, pp. 51e57. Culbert, T.P., Fialko, V., McKee, B., Grazioso, L., Kunen, J.L., Paiz, L., 1997. Investigaciones arqueológicas en el Bajo La Justa, Petén. In: Laporte, J.P., Escobedo, H.L. (Eds.), X Simposio de Investigaciones Arqueológicas en Guatemala, 1996. Museo Nacional de Arqueología y Etnología, Guatemala, pp. 377e383. Curtis, J.H., Brenner, M., Hodell, D.A., Balser, R.A., Islebe, G.A., Hooghiemstra, H., 1998. 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