- Email: [email protected]
3400 years of agricultural engineering in Mesoamerica: lama-bordos of the Mixteca Alta, Oaxaca, Mexico
Journal of Archaeological Science 40 (2013) 4107e4111
Contents lists available at SciVerse ScienceDirect
Journal of Archaeological Science journal homepage: http://www.elsevier.com/locate/jas
Focus article
3400 years of agricultural engineering in Mesoamerica: lama-bordos of the Mixteca Alta, Oaxaca, Mexico David S. Leigh a, *, Stephen A. Kowalewski b, Genevieve Holdridge a a b
Department of Geography, The University of Georgia, Athens, GA 30602, USA Department of Anthropology, The University of Georgia, Athens, GA 30602, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 February 2013 Received in revised form 26 April 2013 Accepted 9 May 2013
The origins of early Mesoamerican agricultural techniques are not well established. Our charcoal-derived radiocarbon chronology dates cross-valley check dams, or lama-bordos, buried by up to 11.5 m of sediment in arroyos near Coixtlahuaca, Oaxaca, Mexico. Now it is clear that people in highland Mexico built lama-bordos at least 3400e3500 years ago, several hundred years earlier than previously dated engineering systems in Mesoamerica. Lama-bordo systems evolved as intensively and extensively managed landscapes coeval with climate shifting to more arid conditions. They provide clear examples of human-produced stratigraphy and artificial landscapes (stair-stepped valleys). More importantly, these lama-bordo systems signal a major cultural tipping point toward sedentary agricultural life and solidify our understanding of the Neolithic transition in Mesoamerica. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Geoarchaeology Anthropocene Arroyo Gully Check-dam
1. Introduction Little is known about the technology and engineering of Mesoamerican agriculture prior to w3000 cal BP (calendar years before A.D. 1950 or “present”). Here we present the earliest reported ages, circa 3400e3500 cal BP, for agricultural terraces known as lamabordos in the Mixteca highlands near Coixtlahuaca, Oaxaca (Fig. 1). Lama-bordos differ from hillside contour terraces as they are cross-channel check dams (water and sediment traps) transverse to stream valleys (Johnson and Renwick, 1969; Spores, 1969). They represent major investment of human labor, time, and upkeep consistent with sedentary life. Their pristine form is an arrangement of continuous stair-stepped segments of the alluvial valley from the headwaters down to the trunk streams (Fig. 2), which eliminates the natural channel. Some pre-Columbian lama-bordos still are in use today, but rampant erosion following Spanish conquest destroyed most. The time of initial lama-bordo development has been difficult to establish, but a single date of 3200e2780 cal BP (Beta-189677) recently was reported for soil organic carbon immediately
* Corresponding author. The University of Georgia, Department of Geography, 204 GeographyeGeology Building, Athens, GA 30602, USA. Tel.: þ1 706 542 2346; fax: þ1 706 542 2388. E-mail address: [email protected] (D.S. Leigh). 0305-4403/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jas.2013.05.009
underlying a lama-bordo near Nochixtlán, Oaxaca, which is “one of the earliest agricultural features in Mexico recorded in stratigraphic context” (Mueller et al., 2012; pp. 125 & 133). Our radiocarbon dates push this agricultural technology centuries earlier and closer in time to the beginning of the Early Formative cultural period (4000e3200 cal BP). These lama-bordos provide the best archaeological evidence of a major cultural tipping point, the commitment to sedentary agricultural life. 2. Study area As part of a larger archaeological survey project in the Río La Culebra valley near Coixtlahuaca (Fig. 1) our geoarchaeological field work targeted deeply buried remnants of lama-bordos (up to 11.5 m deep) preserved in gullied alluvial valleys or arroyos (locally known as barrancas). The valley is filled with stratified silty alluvium that includes several cut-and-fill sequences and multiple buried A horizons. We focused on Barranca Sandage, a 4 km2 catchment flowing northwest from its headwaters at 2360 masl down to about 1800 masl into Río La Culebra (Fig. 1) at the large archaeological site of Inguiteria (Kowaleski et al., 2011). Bedrock primarily consists of calcareous siltstone of the Yanhuitlan Formation (Kirkby, 1972), a yellowish-brown to reddish-brown lacustrine deposit. The landscape is highly eroded and a 0.5e3.0 m thick duricrust weathering zone of calcrete (pedogenic calcium carbonate cement locally known as endeque) drapes most of the land surface, except the
4108
D.S. Leigh et al. / Journal of Archaeological Science 40 (2013) 4107e4111
Fig. 1. Location images of the study sites and environs. (A) The topographic map of Barranca Sandage is from the 1:50,000 map of San Juan Bautista Coixtlahuaca (INEGI/ Dirección General de Geographia, 2002) and it shows the location of remnant preColumbian lama-bordos (black line symbols crossing stream lines), including sites LBV (174101100 N, 97 180 2900 W) and LB175 (174101300 N, 97 180 3800 W). Contour interval is 20 m. (B) Landscape photograph of the middle portion of Barranca Sandage (looking southwest) illustrating the gullied and highly eroded nature of the landscape. The town of Coixtlahuaca is about 5 km north of Barranca Sandage and the city of Nochixtlan is about 26 km to the south.
alluvial valleys. Climate is semi-arid with annual precipitation averaging 528 mm, mostly concentrated during May through September. Average monthly temperatures range from 13.2 C (December) to 18.6 C (May) and annual extremes range from 5e 31 C (Servicio Meteorológico Nacional, 2010). 3. Methods We searched gully walls (many >11 m high) for exposures of lama-bordos, which Rincón Mautner (1999) had recognized in the vicinity, and chose two for dating that were most deeply buried and well preserved on the main stem of Barranca Sandage (Figs. 1 and 3, sites LBV and LB175). We preferentially dated >0.5 cm wide pieces of charcoal that lacked evidence of abrasion or rounding to minimize selection of extensively reworked detrital charcoal. Although there is potential for dating detrital charcoal older than the sedimentation event, careful selection of charcoal has produced reasonable radiocarbon chronologies for many alluvial stratigraphic sequences in arroyos (e.g. DeLong and Arnold, 2007; Butzer et al., 2008; French et al., 2009; Harvey et al., 2011; Pierce et al., 2011). Radiocarbon dating was done by the University of Georgia (UGA) Center for Applied Isotope Studies using standard pretreatment techniques (i.e. 1N HCl leach to remove carbonates) and
Fig. 2. Rare examples of intact and functioning lama-bordos. (A) Aerial view of intact modern lama-bordos (dark lines transverse to valleys that impart a segmented appearance) about 6.5 km north of Nochixtlan, Oaxaca, Mexico from Google Earth imagery (dark lines separating valley segments are lama-bordo walls). The image center is at 17 3101400 N, 97 140 0500 W. (B) Stepped valley of lama-bordos near the village of Huamelulpan, Oaxaca (photo courtesy of Veronica Pérez Rodríguez). These are rare examples, because in most places they have long been destroyed by erosion.
carbon isotope measurement with an accelerator mass spectrometer (AMS) dedicated to carbon. All calibrations were calculated using Oxcal 4.1 (Bronk Ramsey, 2009) and the IntCal09 calibration curve (Reimer et al., 2009) based on del 13C corrected 14C ages, and calendar years before present (cal BP) designates A.D. 1950 as “present”. Buried soils and sediments were avoided for radiocarbon dating because of their tendency to “inherit” humus from erosion and redeposition of much older strata, a problem also recognized by Rincón Mautner (1999). We tested two samples of plane-bedded fluvial sands near basal stones of LB175 for optically stimulated luminescence (OSL) dating by the single aliquot regeneration protocol (Murray et al., 1997; Murray and Wintle, 2000) at the UGA Luminescence Dating Laboratory. However, we found them totally unsuitable for OSL dating due to paucity of quartz grains and high likelihood for incomplete “bleaching” or zeroing. 4. Results and discussion The two dated lama-bordos (LBV and LB175, Fig. 3) are 5e6 m high and exclusively built of locally available endeque (calcrete) gravel, cobbles, and small boulders. The basal stones of each lama-
D.S. Leigh et al. / Journal of Archaeological Science 40 (2013) 4107e4111
4109
Fig. 3. Stratigraphy and chronology of the lama-bordos. (A) Sketch of the LBV site and radiocarbon sample locations. (B) Photograph of the LB175 site and radiocarbon sample locations. The prevailing material in both sections is silty alluvium with multiple buried A horizons. Stream flow would be from left to right in both images.
bordo consist of cobbles and boulders emplaced in a small trench dug into the pre-existing alluvium, perhaps as a foundation to prevent undercutting by floods. The stacked endeque stones are shingled so that the cross-valley walls lean upstream, indicating shingling was accomplished as sediment progressively accumulated behind the wall, rather than in a single construction event. It is impossible to know the full lateral extent of the lama-bordos, because younger erosion and alluvial filling have altered both sides of the valley at LBV and most of the eastern side of the valley at LB175. Sedimentology behind the lama-bordos (upstream) includes laminae and thin beds of clay as well as thin beds of fine gravel, sand, and silt (Fig. 4). Some beds include 3e10 cm thick rhythmites of sand or silt graded up to clay, which diagnostically represent high concentrations of sediment flowing into standing water. Downstream of the lama-bordos the sedimentology is more indicative of fluvial deposition, having massive overbank, and plane- or cross-bedded bedload sand, and lacking the laminated and rhythmically bedded lacustrine facies. The basal stones of the deeply buried lama-bordos are very near or slightly beneath the present-day stream base level, which indicates they initially were constructed when the stream channel was deeply incised into the alluvial valleys. Three charcoal dates came from within and adjacent to the basal stones of each lama-bordo. The youngest (and deepest) sample yielded an age of 3476e3379 cal BP (Table 1, 95% confidence interval range reported here and subsequently) from an l.5 1.0 1.0 cm piece of angular charcoal that was sheltered between boulders and cobbles within the LBV wall at 10.8 m below ground surface (bgs). This sample had virtually no chance of having been emplaced by fluvial transport and it probably was burned in close proximity and time to wall construction. The oldest sample (4061e3849 cal BP) came from within rhythmically bedded strata that accumulated about 10 m upstream of LBV. The third basal date from LBV and all three basal dates downstream at LB175 were derived from alluvium in very close contact with the basal 1.5 m of the lama-bordos and consistently yielded ages around 3600 cal BP (Fig. 3a and b; Table 1). A date of 3629e 3475 cal BP, obtained from charcoal at 7.43 m depth at LBV (at about 4 m above the basal lama-bordo) affirms the youngest age of 3476e3379 cal BP within the stone wall and indicates extremely rapid sedimentation behind the lama-bordo.
The horizontal beds in the lower three to four meters of the fill behind both lama-bordos are well preserved and show no evidence of disruption or bioturbation (e.g. Fig. 4). This indicates that the sediment was not exposed long enough to develop even minimal soil horizons and that people were not digging or cultivating in the sediment that first accumulated immediately behind the walls.
Fig. 4. Horizontal bedding and rhythmites immediately upstream of site LB175 (yellow ruler is 2 m long). Stream flow would be from left to right. Thin bedding and laminations of this sort are typical in the earliest sedimentary fill upstream of lama bordos, whereas massive, non-bedded, and bioturbated fills are typical higher in the stratigraphic section as the latest fills. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
4110
D.S. Leigh et al. / Journal of Archaeological Science 40 (2013) 4107e4111
Table 1 Radiocarbon dates (arranged by depth below ground surface at each site). UGA MS #
Site
Material dated
Context
Depth (m)
14 C Age (14C yr BP)
1 stdv. (yrs)
95% Max. (cal yr BP)
Median (cal yr BP)
95% Min. (cal yr BP)
8643 9228 9227 12643 8646 12642 8646 12641 8644 8647 9224 9226
LBV LBV LBV LBV LBV LBV LBV LBV LBV LB175 LB175 LB175
Charcoal Charcoal Charcoal Charcoal Soil Charcoal Charcoal Charcoal Soil Charcoal Charcoal Charcoal
Within basal lama-bordo (LB) stones Silty alluvium w0.3 m behind basal LB Silty alluvium w10 m behind basal LB Silty alluvium behind upper LB Silty Ab horizon near top of LB stones Silty alluvium above LB Silty alluvium well above LB Silty alluvium near top of outcrop Top of latest pre-colonial Ab horizon Within clay bed behind LB Within clay bed in front of LB Silty alluvium beneath boulder
10.81 10.75 9.60 7.43 5.45 4.35 3.24 1.28 0.68 7.45 7.40 6.85
3215 3360 3620 3320 3663 2600 2545 620 541 3384 3370 3430
26 25 25 25 25 25 24 20 23 26 25 25
3476 3688 4061 3629 4084 2763 2747 656 630 3693 3691 3824
3426 3603 3929 3539 3989 2743 2699 599 544 3629 3613 3680
3379 3486 3849 3475 3905 2716 2503 553 516 3569 3559 3614
Note: Calibrations were calculated using Oxcal 4.1 (Bronk Ramsey, 2009) and the IntCal09 calibration curve (Reimer et al., 2009) based on del calendar years before present (cal BP) designates A.D. 1950 as "present".
However, sediment higher in the section is pedogenically altered, bioturbated, and probably cultivated. The top of stones at LBV stands at about 5.7 m bgs, and a date on soil organic carbon at 5.4e 5.5 m bgs yielded an age of 4084e3905 cal BP, erroneously older than the underlying dates. A charcoal radiocarbon sample at 4.33e 4.36 m bgs yielded an age of 2763e2716 cal BP. Additional charcoal and soil dates higher in the section become progressively younger (Fig. 3a Table 1). Even though the soil sample at the top of the stones is obviously too old (exemplifying detrital inheritance of old carbon) these results indicate that sedimentation rates slowed around the time when no further stones were added to the wall. The lama-bordos, including many others in the barranca (Fig. 1a), apparently were facilitating long-term aggradation and filling of the valley throughout the late Holocene. The valley reverted to deeply gullied channels by the middle 1600 s when the land was abandoned following Spanish contact in A.D. 1521 (Rincón Mautner, 1999). A thin (0.5e1.0 m thick) uppermost strata of post-conquest vertical accretion deposits (e.g. Fig. 3a) indicates the lama-bordos continued to function at least for a short time following Spanish contact. Lama-bordo construction must have been initiated by 3400e 3500 cal BP, and perhaps a little earlier given that the system of wall construction would logically begin in the headwaters. The slight difference between the youngest date of 3476e3379 cal BP and the dates w3600 cal BP can be explained by a lag time to account for the age of cambium burned plus some time for fluvial emplacement of the charcoal. Early dates on these two lamabordos are roughly coeval with the emergence of the Mesoamerican Early Formative period at about 4000 to 3200 cal BP. This transition is marked by common use of pottery, more intensive agriculture, and an apparent shift from mobile to more sedentary life (Flannery and Marcus, 1983). Moist arroyos and barranca bottomlands were favored Late Archaic niches for early farmers (Flannery, 1973; MacNeish et al., 1975), and we see development of the lama-bordos logically as an adaptive management strategy to harness water, sediment, and plant nutrients in the context of human and climate pressures. Immediately prior to construction of these earliest lama-bordos the soils of the wide valley bottoms probably were vertically disconnected from the stream water and sediment flows due to incised stream channel conditions. This is indicated by radiocarbon dated strata in other parts of Barranca Sandage that clearly signal middle Holocene aggradation of valley fills up until at least 3700 cal BP (Leigh et al., 2012) in contrast to the stream beds several meters lower at around 3400e3500 cal yr BP when these earliest lama-bordos were constructed. Such a disconnection of water and sediment resources from farmland was
13
C corrected
14
C ages, and
rectified by construction of a lama-bordo system, and thus an agro-fluvial system within the entire valley, which persisted for thousands of years. Climatic change may have caused stream incision and the incentive to construct lama-bordo systems by 3400e3500 cal BP. A recent study of paleoclimate in southern Mexico (Bernal et al., 2011) indicates persistently moist conditions at 4000e5000 cal BP followed by a shift to significantly more arid conditions at about 4000 cal BP (possibly linked to increased El Nino/ENSO frequency). This late Holocene aridity was interrupted by brief swings back to intervals of wetter conditions. Such wet pulses under a prevailing arid climate are exactly the conditions that favor incision of arroyos (Bull, 1991; Waters and Haynes, 2001). Thus, it is quite possible that late Holocene arroyo incision was stimulated by the first major swing to wetter conditions, which Bernal et al. (2011) date at about 3700 cal BP, and early farmers adapted to the subsequent drier conditions and disconnected stream channels by building lama-bordos. 5. Conclusions Our minimum age estimate of 3400e3500 cal BP for initial construction of Mesoamerican agricultural engineering structures known as lama-bordos (cross-valley check dams) is at least two hundred years earlier than the oldest previously known lamabordo (Mueller et al., 2012). Generally, first evidence of dams, canals, terraces and other agricultural engineering features in Mesoamerica dates to about 3200e1300 cal BP (Lucero and Fash, 2006; Aiuvalasit et al., 2010). Pushing back the time of intensive landscape transformation by Mesoamericans is an important finding, but perhaps not as significant as the emerging general pattern. Mesoamerican agricultural engineering technologies developed much earlier than previously thought in low population-density Neolithic, not state-level, contexts, signaling a cultural tipping point of commitment to sedentary agricultural life. Acknowledgments Research was funded by National Science Foundation grant BCS1026254 via the University of Georgia Research Foundation, Inc., and Fundación Alfredo Harp Helú, with permissions of Instituto Nacional de Antropología e Historia as well as municipal and bienes comunales authorities of San Juan Bautista Coixtlahuaca. Baldemar García Lara, Ricardo García Juárez, and Leonardo Bazán Velasco provided essential help in field work. John Turk provided cartographic assistance and Katie Price provided useful comments on earlier manuscripts.
D.S. Leigh et al. / Journal of Archaeological Science 40 (2013) 4107e4111
References Aiuvalasit, M.J., Neely, J.A., Bateman, M.D., 2010. New radiometric dating of water management features at the prehistoric Purron Dam Complex, Tehuacan Valley, Puebla, Mexico. Journal of Archaeological Science 37, 1207e1213. Bernal, J.P., Lachniet, M., McCulloch, M., Mortimer, G., Morales, P., Cienfuegos, E., 2011. A speleothem record of Holocene climate variability from southwestern Mexico. Quaternary Research 75, 104e113. Bronk Ramsey, C., 2009. Bayesian analysis of radiocarbon dates. Radiocarbon 51 (1), 337. Bull, W.B., 1991. Geomorphic Responses to Climate Change. Oxford University Press, Oxford. Butzer, K.W., Abbott, J.T., Frederick, C.D., Lehman, P.H., Cordova, C.E., Oswald, J.F., 2008. Soil-geomorphology and "wet" cycles in the Holocene record of NorthCentral Mexico. Geomorphology 101, 237e277. DeLong, S.B., Arnold, L.J., 2007. Dating alluvial deposits with optically stimulated luminescence, AMS C-14 and cosmogenic techniques, western transverse ranges, California, USA. Quaternary Geochronology 2, 129e136. Flannery, K.V., 1973. Origins of agriculture. Annual Review of Anthropology 2, 271e 310. Flannery, K.V., Marcus, J., 1983. The Cloud People: Divergent Evolution of the Zapotec and Mixtec Civilizations. Academic Press, New York. French, C., Periman, R., Cummings, L.S., Hall, S., Goodman-Elgar, M., Boreham, J., 2009. Holocene alluvial sequences, cumulic soils and fire signatures in the middle Rio Puerco Basin at Guadalupe Ruin, New Mexico. Geoarchaeology-an International Journal 24, 638e676. Harvey, J.E., Pederson, J.L., Rittenour, T.M., 2011. Exploring relations between arroyo cycles and canyon paleoflood records in Buckskin Wash, Utah: reconciling scientific paradigms. Geological Society of America Bulletin 123, 2266e 2276. INEGI/Dirección General de Geographía, 2002. San Juan Bautista Coixtlahuaca E14D26, Oaxaca, Carta Topográfica 1:50:000. Instituto Nacional Estadistica Geographía e Informática. Johnson, K., Renwick, H., 1969. Rain and Storm Water Harvesting for Additional Water Supply in Rural Areas: Component Review on North America, United Nations Environment Programme. United Nations Environment Programme, Nairobi. Kirkby, M., 1972. The Physical Environmental of the Nochixtlán Valley, Oaxaca. Anthropology, Vanderbilt University, Nashville, TN. Kowaleski, S.A., Barba Pingarrón, L., Blancas Vázquez, J., Cortés Vilchis, M., Garciá Ayala, G., López Zárate, L., Ortiz Butrón, A., Pluckhahn, T.J., Steere, B.A., Vilchis
4111
Flores, B., 2011. Dos ciudades prehispánicas en Coixtlahuaca, Oaxaca. Cuadernos del Sur 16, 93e111. Leigh, D.S., Holdridge, G.H., Kowalewski, S.A., 2012. Millennial-scale Human Influence on Erosion, Sediment Yield, and Stratigraphy in the Mixteca Alta, Oaxaca, Mexico. Paper Presented at the Association of American Geographers Annual Meeting in New York, NY, February 27, 2012. Lucero, L.J., Fash, B.W., 2006. Precolombian Water Management: Ideology, Ritual, and Power. University of Arizona Press, Tucson. MacNeish, R.S., Fowler, M.L., Garcia-Cook, A., Peterson, F.A., Nelken-Turner, A., Neely, J.A., 1975. The Prehistory of the Tehuacán Valley. In: Excavations and Reconnaissance, B2-The Prehistory of the Tehuacán Valley, vol. 5. University of Texas Press, Austin. Mueller, R.G., Joyce, A.A., Borejsza, A., 2012. Alluvial archives of the Nochixtlan valley, Oaxaca, Mexico: age and significance for reconstructions of environmental change. Palaeogeography Palaeoclimatology Palaeoecology 321, 121e136. Murray, A.S., Roberts, R.G., Wintle, A.G., 1997. Equivalent dose measurement using a single aliquot of quartz. Radiation Measurements 27, 171e184. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurement 32, 57e73. Pierce, J.L., Meyer, G.A., Rittenour, T., 2011. The relation of Holocene fluvial terraces to changes in climate and sediment supply, South Fork Payette River, Idaho. Quaternary Science Reviews 30, 628e645. Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Bronk Ramsey, C., Buck, C.E., Burr, G.S., Edwards, R.L., Friedrich, M., Grootes, P.M., Guilderson, T.P., Hajdas, I., Heaton, T.J., Hogg, A.G., Hughen, K.A., Kaiser, K.F., Kromer, B., McCormac, F.G., Manning, S.W., Reimer, R.W., Richards, D.A., Southon, J.R., Talamo, S., Turney, C.S.M., van der Plicht, J., Weyhenmeyer, C.E., 2009. IntCal09 and Marine09 radiocarbon age calibration curves, 0e50,000 years cal BP. Radiocarbon 51 (4), 1111e1150. Rincón Mautner, C., 1999. Man and the Environment in the Coixtlahuaca Basin of Northwestern Oaxaca, Mexico: Two Thousand Years of Historical Ecology. University of Texas, University Microfilms, Ann Arbor. Servicio Meteorológico Nacional, 2010. Normales Climatológicas 1971e2000, Estacion 00020019: S. J. Bautista Coixtlahuaca, website of Comision Nacional del Agua (CONAGUA). Servicio Meteorológico Nacional, Mexico. http://smn.cna.gob. mx/index.php?option¼com_content&view¼article&id¼42&Itemid¼28 (last accessed 04.01.13.). Spores, R., 1969. Settlement, farming technology, and environment in Nochixtlan Valley. Science 166, 557e569. Waters, M.R., Haynes, C.V., 2001. Late Quaternary arroyo formation and climate change in the American Southwest. Geology 29, 399e402.
Contents lists available at SciVerse ScienceDirect
Journal of Archaeological Science journal homepage: http://www.elsevier.com/locate/jas
Focus article
3400 years of agricultural engineering in Mesoamerica: lama-bordos of the Mixteca Alta, Oaxaca, Mexico David S. Leigh a, *, Stephen A. Kowalewski b, Genevieve Holdridge a a b
Department of Geography, The University of Georgia, Athens, GA 30602, USA Department of Anthropology, The University of Georgia, Athens, GA 30602, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 February 2013 Received in revised form 26 April 2013 Accepted 9 May 2013
The origins of early Mesoamerican agricultural techniques are not well established. Our charcoal-derived radiocarbon chronology dates cross-valley check dams, or lama-bordos, buried by up to 11.5 m of sediment in arroyos near Coixtlahuaca, Oaxaca, Mexico. Now it is clear that people in highland Mexico built lama-bordos at least 3400e3500 years ago, several hundred years earlier than previously dated engineering systems in Mesoamerica. Lama-bordo systems evolved as intensively and extensively managed landscapes coeval with climate shifting to more arid conditions. They provide clear examples of human-produced stratigraphy and artificial landscapes (stair-stepped valleys). More importantly, these lama-bordo systems signal a major cultural tipping point toward sedentary agricultural life and solidify our understanding of the Neolithic transition in Mesoamerica. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Geoarchaeology Anthropocene Arroyo Gully Check-dam
1. Introduction Little is known about the technology and engineering of Mesoamerican agriculture prior to w3000 cal BP (calendar years before A.D. 1950 or “present”). Here we present the earliest reported ages, circa 3400e3500 cal BP, for agricultural terraces known as lamabordos in the Mixteca highlands near Coixtlahuaca, Oaxaca (Fig. 1). Lama-bordos differ from hillside contour terraces as they are cross-channel check dams (water and sediment traps) transverse to stream valleys (Johnson and Renwick, 1969; Spores, 1969). They represent major investment of human labor, time, and upkeep consistent with sedentary life. Their pristine form is an arrangement of continuous stair-stepped segments of the alluvial valley from the headwaters down to the trunk streams (Fig. 2), which eliminates the natural channel. Some pre-Columbian lama-bordos still are in use today, but rampant erosion following Spanish conquest destroyed most. The time of initial lama-bordo development has been difficult to establish, but a single date of 3200e2780 cal BP (Beta-189677) recently was reported for soil organic carbon immediately
* Corresponding author. The University of Georgia, Department of Geography, 204 GeographyeGeology Building, Athens, GA 30602, USA. Tel.: þ1 706 542 2346; fax: þ1 706 542 2388. E-mail address: [email protected] (D.S. Leigh). 0305-4403/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jas.2013.05.009
underlying a lama-bordo near Nochixtlán, Oaxaca, which is “one of the earliest agricultural features in Mexico recorded in stratigraphic context” (Mueller et al., 2012; pp. 125 & 133). Our radiocarbon dates push this agricultural technology centuries earlier and closer in time to the beginning of the Early Formative cultural period (4000e3200 cal BP). These lama-bordos provide the best archaeological evidence of a major cultural tipping point, the commitment to sedentary agricultural life. 2. Study area As part of a larger archaeological survey project in the Río La Culebra valley near Coixtlahuaca (Fig. 1) our geoarchaeological field work targeted deeply buried remnants of lama-bordos (up to 11.5 m deep) preserved in gullied alluvial valleys or arroyos (locally known as barrancas). The valley is filled with stratified silty alluvium that includes several cut-and-fill sequences and multiple buried A horizons. We focused on Barranca Sandage, a 4 km2 catchment flowing northwest from its headwaters at 2360 masl down to about 1800 masl into Río La Culebra (Fig. 1) at the large archaeological site of Inguiteria (Kowaleski et al., 2011). Bedrock primarily consists of calcareous siltstone of the Yanhuitlan Formation (Kirkby, 1972), a yellowish-brown to reddish-brown lacustrine deposit. The landscape is highly eroded and a 0.5e3.0 m thick duricrust weathering zone of calcrete (pedogenic calcium carbonate cement locally known as endeque) drapes most of the land surface, except the
4108
D.S. Leigh et al. / Journal of Archaeological Science 40 (2013) 4107e4111
Fig. 1. Location images of the study sites and environs. (A) The topographic map of Barranca Sandage is from the 1:50,000 map of San Juan Bautista Coixtlahuaca (INEGI/ Dirección General de Geographia, 2002) and it shows the location of remnant preColumbian lama-bordos (black line symbols crossing stream lines), including sites LBV (174101100 N, 97 180 2900 W) and LB175 (174101300 N, 97 180 3800 W). Contour interval is 20 m. (B) Landscape photograph of the middle portion of Barranca Sandage (looking southwest) illustrating the gullied and highly eroded nature of the landscape. The town of Coixtlahuaca is about 5 km north of Barranca Sandage and the city of Nochixtlan is about 26 km to the south.
alluvial valleys. Climate is semi-arid with annual precipitation averaging 528 mm, mostly concentrated during May through September. Average monthly temperatures range from 13.2 C (December) to 18.6 C (May) and annual extremes range from 5e 31 C (Servicio Meteorológico Nacional, 2010). 3. Methods We searched gully walls (many >11 m high) for exposures of lama-bordos, which Rincón Mautner (1999) had recognized in the vicinity, and chose two for dating that were most deeply buried and well preserved on the main stem of Barranca Sandage (Figs. 1 and 3, sites LBV and LB175). We preferentially dated >0.5 cm wide pieces of charcoal that lacked evidence of abrasion or rounding to minimize selection of extensively reworked detrital charcoal. Although there is potential for dating detrital charcoal older than the sedimentation event, careful selection of charcoal has produced reasonable radiocarbon chronologies for many alluvial stratigraphic sequences in arroyos (e.g. DeLong and Arnold, 2007; Butzer et al., 2008; French et al., 2009; Harvey et al., 2011; Pierce et al., 2011). Radiocarbon dating was done by the University of Georgia (UGA) Center for Applied Isotope Studies using standard pretreatment techniques (i.e. 1N HCl leach to remove carbonates) and
Fig. 2. Rare examples of intact and functioning lama-bordos. (A) Aerial view of intact modern lama-bordos (dark lines transverse to valleys that impart a segmented appearance) about 6.5 km north of Nochixtlan, Oaxaca, Mexico from Google Earth imagery (dark lines separating valley segments are lama-bordo walls). The image center is at 17 3101400 N, 97 140 0500 W. (B) Stepped valley of lama-bordos near the village of Huamelulpan, Oaxaca (photo courtesy of Veronica Pérez Rodríguez). These are rare examples, because in most places they have long been destroyed by erosion.
carbon isotope measurement with an accelerator mass spectrometer (AMS) dedicated to carbon. All calibrations were calculated using Oxcal 4.1 (Bronk Ramsey, 2009) and the IntCal09 calibration curve (Reimer et al., 2009) based on del 13C corrected 14C ages, and calendar years before present (cal BP) designates A.D. 1950 as “present”. Buried soils and sediments were avoided for radiocarbon dating because of their tendency to “inherit” humus from erosion and redeposition of much older strata, a problem also recognized by Rincón Mautner (1999). We tested two samples of plane-bedded fluvial sands near basal stones of LB175 for optically stimulated luminescence (OSL) dating by the single aliquot regeneration protocol (Murray et al., 1997; Murray and Wintle, 2000) at the UGA Luminescence Dating Laboratory. However, we found them totally unsuitable for OSL dating due to paucity of quartz grains and high likelihood for incomplete “bleaching” or zeroing. 4. Results and discussion The two dated lama-bordos (LBV and LB175, Fig. 3) are 5e6 m high and exclusively built of locally available endeque (calcrete) gravel, cobbles, and small boulders. The basal stones of each lama-
D.S. Leigh et al. / Journal of Archaeological Science 40 (2013) 4107e4111
4109
Fig. 3. Stratigraphy and chronology of the lama-bordos. (A) Sketch of the LBV site and radiocarbon sample locations. (B) Photograph of the LB175 site and radiocarbon sample locations. The prevailing material in both sections is silty alluvium with multiple buried A horizons. Stream flow would be from left to right in both images.
bordo consist of cobbles and boulders emplaced in a small trench dug into the pre-existing alluvium, perhaps as a foundation to prevent undercutting by floods. The stacked endeque stones are shingled so that the cross-valley walls lean upstream, indicating shingling was accomplished as sediment progressively accumulated behind the wall, rather than in a single construction event. It is impossible to know the full lateral extent of the lama-bordos, because younger erosion and alluvial filling have altered both sides of the valley at LBV and most of the eastern side of the valley at LB175. Sedimentology behind the lama-bordos (upstream) includes laminae and thin beds of clay as well as thin beds of fine gravel, sand, and silt (Fig. 4). Some beds include 3e10 cm thick rhythmites of sand or silt graded up to clay, which diagnostically represent high concentrations of sediment flowing into standing water. Downstream of the lama-bordos the sedimentology is more indicative of fluvial deposition, having massive overbank, and plane- or cross-bedded bedload sand, and lacking the laminated and rhythmically bedded lacustrine facies. The basal stones of the deeply buried lama-bordos are very near or slightly beneath the present-day stream base level, which indicates they initially were constructed when the stream channel was deeply incised into the alluvial valleys. Three charcoal dates came from within and adjacent to the basal stones of each lama-bordo. The youngest (and deepest) sample yielded an age of 3476e3379 cal BP (Table 1, 95% confidence interval range reported here and subsequently) from an l.5 1.0 1.0 cm piece of angular charcoal that was sheltered between boulders and cobbles within the LBV wall at 10.8 m below ground surface (bgs). This sample had virtually no chance of having been emplaced by fluvial transport and it probably was burned in close proximity and time to wall construction. The oldest sample (4061e3849 cal BP) came from within rhythmically bedded strata that accumulated about 10 m upstream of LBV. The third basal date from LBV and all three basal dates downstream at LB175 were derived from alluvium in very close contact with the basal 1.5 m of the lama-bordos and consistently yielded ages around 3600 cal BP (Fig. 3a and b; Table 1). A date of 3629e 3475 cal BP, obtained from charcoal at 7.43 m depth at LBV (at about 4 m above the basal lama-bordo) affirms the youngest age of 3476e3379 cal BP within the stone wall and indicates extremely rapid sedimentation behind the lama-bordo.
The horizontal beds in the lower three to four meters of the fill behind both lama-bordos are well preserved and show no evidence of disruption or bioturbation (e.g. Fig. 4). This indicates that the sediment was not exposed long enough to develop even minimal soil horizons and that people were not digging or cultivating in the sediment that first accumulated immediately behind the walls.
Fig. 4. Horizontal bedding and rhythmites immediately upstream of site LB175 (yellow ruler is 2 m long). Stream flow would be from left to right. Thin bedding and laminations of this sort are typical in the earliest sedimentary fill upstream of lama bordos, whereas massive, non-bedded, and bioturbated fills are typical higher in the stratigraphic section as the latest fills. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
4110
D.S. Leigh et al. / Journal of Archaeological Science 40 (2013) 4107e4111
Table 1 Radiocarbon dates (arranged by depth below ground surface at each site). UGA MS #
Site
Material dated
Context
Depth (m)
14 C Age (14C yr BP)
1 stdv. (yrs)
95% Max. (cal yr BP)
Median (cal yr BP)
95% Min. (cal yr BP)
8643 9228 9227 12643 8646 12642 8646 12641 8644 8647 9224 9226
LBV LBV LBV LBV LBV LBV LBV LBV LBV LB175 LB175 LB175
Charcoal Charcoal Charcoal Charcoal Soil Charcoal Charcoal Charcoal Soil Charcoal Charcoal Charcoal
Within basal lama-bordo (LB) stones Silty alluvium w0.3 m behind basal LB Silty alluvium w10 m behind basal LB Silty alluvium behind upper LB Silty Ab horizon near top of LB stones Silty alluvium above LB Silty alluvium well above LB Silty alluvium near top of outcrop Top of latest pre-colonial Ab horizon Within clay bed behind LB Within clay bed in front of LB Silty alluvium beneath boulder
10.81 10.75 9.60 7.43 5.45 4.35 3.24 1.28 0.68 7.45 7.40 6.85
3215 3360 3620 3320 3663 2600 2545 620 541 3384 3370 3430
26 25 25 25 25 25 24 20 23 26 25 25
3476 3688 4061 3629 4084 2763 2747 656 630 3693 3691 3824
3426 3603 3929 3539 3989 2743 2699 599 544 3629 3613 3680
3379 3486 3849 3475 3905 2716 2503 553 516 3569 3559 3614
Note: Calibrations were calculated using Oxcal 4.1 (Bronk Ramsey, 2009) and the IntCal09 calibration curve (Reimer et al., 2009) based on del calendar years before present (cal BP) designates A.D. 1950 as "present".
However, sediment higher in the section is pedogenically altered, bioturbated, and probably cultivated. The top of stones at LBV stands at about 5.7 m bgs, and a date on soil organic carbon at 5.4e 5.5 m bgs yielded an age of 4084e3905 cal BP, erroneously older than the underlying dates. A charcoal radiocarbon sample at 4.33e 4.36 m bgs yielded an age of 2763e2716 cal BP. Additional charcoal and soil dates higher in the section become progressively younger (Fig. 3a Table 1). Even though the soil sample at the top of the stones is obviously too old (exemplifying detrital inheritance of old carbon) these results indicate that sedimentation rates slowed around the time when no further stones were added to the wall. The lama-bordos, including many others in the barranca (Fig. 1a), apparently were facilitating long-term aggradation and filling of the valley throughout the late Holocene. The valley reverted to deeply gullied channels by the middle 1600 s when the land was abandoned following Spanish contact in A.D. 1521 (Rincón Mautner, 1999). A thin (0.5e1.0 m thick) uppermost strata of post-conquest vertical accretion deposits (e.g. Fig. 3a) indicates the lama-bordos continued to function at least for a short time following Spanish contact. Lama-bordo construction must have been initiated by 3400e 3500 cal BP, and perhaps a little earlier given that the system of wall construction would logically begin in the headwaters. The slight difference between the youngest date of 3476e3379 cal BP and the dates w3600 cal BP can be explained by a lag time to account for the age of cambium burned plus some time for fluvial emplacement of the charcoal. Early dates on these two lamabordos are roughly coeval with the emergence of the Mesoamerican Early Formative period at about 4000 to 3200 cal BP. This transition is marked by common use of pottery, more intensive agriculture, and an apparent shift from mobile to more sedentary life (Flannery and Marcus, 1983). Moist arroyos and barranca bottomlands were favored Late Archaic niches for early farmers (Flannery, 1973; MacNeish et al., 1975), and we see development of the lama-bordos logically as an adaptive management strategy to harness water, sediment, and plant nutrients in the context of human and climate pressures. Immediately prior to construction of these earliest lama-bordos the soils of the wide valley bottoms probably were vertically disconnected from the stream water and sediment flows due to incised stream channel conditions. This is indicated by radiocarbon dated strata in other parts of Barranca Sandage that clearly signal middle Holocene aggradation of valley fills up until at least 3700 cal BP (Leigh et al., 2012) in contrast to the stream beds several meters lower at around 3400e3500 cal yr BP when these earliest lama-bordos were constructed. Such a disconnection of water and sediment resources from farmland was
13
C corrected
14
C ages, and
rectified by construction of a lama-bordo system, and thus an agro-fluvial system within the entire valley, which persisted for thousands of years. Climatic change may have caused stream incision and the incentive to construct lama-bordo systems by 3400e3500 cal BP. A recent study of paleoclimate in southern Mexico (Bernal et al., 2011) indicates persistently moist conditions at 4000e5000 cal BP followed by a shift to significantly more arid conditions at about 4000 cal BP (possibly linked to increased El Nino/ENSO frequency). This late Holocene aridity was interrupted by brief swings back to intervals of wetter conditions. Such wet pulses under a prevailing arid climate are exactly the conditions that favor incision of arroyos (Bull, 1991; Waters and Haynes, 2001). Thus, it is quite possible that late Holocene arroyo incision was stimulated by the first major swing to wetter conditions, which Bernal et al. (2011) date at about 3700 cal BP, and early farmers adapted to the subsequent drier conditions and disconnected stream channels by building lama-bordos. 5. Conclusions Our minimum age estimate of 3400e3500 cal BP for initial construction of Mesoamerican agricultural engineering structures known as lama-bordos (cross-valley check dams) is at least two hundred years earlier than the oldest previously known lamabordo (Mueller et al., 2012). Generally, first evidence of dams, canals, terraces and other agricultural engineering features in Mesoamerica dates to about 3200e1300 cal BP (Lucero and Fash, 2006; Aiuvalasit et al., 2010). Pushing back the time of intensive landscape transformation by Mesoamericans is an important finding, but perhaps not as significant as the emerging general pattern. Mesoamerican agricultural engineering technologies developed much earlier than previously thought in low population-density Neolithic, not state-level, contexts, signaling a cultural tipping point of commitment to sedentary agricultural life. Acknowledgments Research was funded by National Science Foundation grant BCS1026254 via the University of Georgia Research Foundation, Inc., and Fundación Alfredo Harp Helú, with permissions of Instituto Nacional de Antropología e Historia as well as municipal and bienes comunales authorities of San Juan Bautista Coixtlahuaca. Baldemar García Lara, Ricardo García Juárez, and Leonardo Bazán Velasco provided essential help in field work. John Turk provided cartographic assistance and Katie Price provided useful comments on earlier manuscripts.
D.S. Leigh et al. / Journal of Archaeological Science 40 (2013) 4107e4111
References Aiuvalasit, M.J., Neely, J.A., Bateman, M.D., 2010. New radiometric dating of water management features at the prehistoric Purron Dam Complex, Tehuacan Valley, Puebla, Mexico. Journal of Archaeological Science 37, 1207e1213. Bernal, J.P., Lachniet, M., McCulloch, M., Mortimer, G., Morales, P., Cienfuegos, E., 2011. A speleothem record of Holocene climate variability from southwestern Mexico. Quaternary Research 75, 104e113. Bronk Ramsey, C., 2009. Bayesian analysis of radiocarbon dates. Radiocarbon 51 (1), 337. Bull, W.B., 1991. Geomorphic Responses to Climate Change. Oxford University Press, Oxford. Butzer, K.W., Abbott, J.T., Frederick, C.D., Lehman, P.H., Cordova, C.E., Oswald, J.F., 2008. Soil-geomorphology and "wet" cycles in the Holocene record of NorthCentral Mexico. Geomorphology 101, 237e277. DeLong, S.B., Arnold, L.J., 2007. Dating alluvial deposits with optically stimulated luminescence, AMS C-14 and cosmogenic techniques, western transverse ranges, California, USA. Quaternary Geochronology 2, 129e136. Flannery, K.V., 1973. Origins of agriculture. Annual Review of Anthropology 2, 271e 310. Flannery, K.V., Marcus, J., 1983. The Cloud People: Divergent Evolution of the Zapotec and Mixtec Civilizations. Academic Press, New York. French, C., Periman, R., Cummings, L.S., Hall, S., Goodman-Elgar, M., Boreham, J., 2009. Holocene alluvial sequences, cumulic soils and fire signatures in the middle Rio Puerco Basin at Guadalupe Ruin, New Mexico. Geoarchaeology-an International Journal 24, 638e676. Harvey, J.E., Pederson, J.L., Rittenour, T.M., 2011. Exploring relations between arroyo cycles and canyon paleoflood records in Buckskin Wash, Utah: reconciling scientific paradigms. Geological Society of America Bulletin 123, 2266e 2276. INEGI/Dirección General de Geographía, 2002. San Juan Bautista Coixtlahuaca E14D26, Oaxaca, Carta Topográfica 1:50:000. Instituto Nacional Estadistica Geographía e Informática. Johnson, K., Renwick, H., 1969. Rain and Storm Water Harvesting for Additional Water Supply in Rural Areas: Component Review on North America, United Nations Environment Programme. United Nations Environment Programme, Nairobi. Kirkby, M., 1972. The Physical Environmental of the Nochixtlán Valley, Oaxaca. Anthropology, Vanderbilt University, Nashville, TN. Kowaleski, S.A., Barba Pingarrón, L., Blancas Vázquez, J., Cortés Vilchis, M., Garciá Ayala, G., López Zárate, L., Ortiz Butrón, A., Pluckhahn, T.J., Steere, B.A., Vilchis
4111
Flores, B., 2011. Dos ciudades prehispánicas en Coixtlahuaca, Oaxaca. Cuadernos del Sur 16, 93e111. Leigh, D.S., Holdridge, G.H., Kowalewski, S.A., 2012. Millennial-scale Human Influence on Erosion, Sediment Yield, and Stratigraphy in the Mixteca Alta, Oaxaca, Mexico. Paper Presented at the Association of American Geographers Annual Meeting in New York, NY, February 27, 2012. Lucero, L.J., Fash, B.W., 2006. Precolombian Water Management: Ideology, Ritual, and Power. University of Arizona Press, Tucson. MacNeish, R.S., Fowler, M.L., Garcia-Cook, A., Peterson, F.A., Nelken-Turner, A., Neely, J.A., 1975. The Prehistory of the Tehuacán Valley. In: Excavations and Reconnaissance, B2-The Prehistory of the Tehuacán Valley, vol. 5. University of Texas Press, Austin. Mueller, R.G., Joyce, A.A., Borejsza, A., 2012. Alluvial archives of the Nochixtlan valley, Oaxaca, Mexico: age and significance for reconstructions of environmental change. Palaeogeography Palaeoclimatology Palaeoecology 321, 121e136. Murray, A.S., Roberts, R.G., Wintle, A.G., 1997. Equivalent dose measurement using a single aliquot of quartz. Radiation Measurements 27, 171e184. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurement 32, 57e73. Pierce, J.L., Meyer, G.A., Rittenour, T., 2011. The relation of Holocene fluvial terraces to changes in climate and sediment supply, South Fork Payette River, Idaho. Quaternary Science Reviews 30, 628e645. Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Bronk Ramsey, C., Buck, C.E., Burr, G.S., Edwards, R.L., Friedrich, M., Grootes, P.M., Guilderson, T.P., Hajdas, I., Heaton, T.J., Hogg, A.G., Hughen, K.A., Kaiser, K.F., Kromer, B., McCormac, F.G., Manning, S.W., Reimer, R.W., Richards, D.A., Southon, J.R., Talamo, S., Turney, C.S.M., van der Plicht, J., Weyhenmeyer, C.E., 2009. IntCal09 and Marine09 radiocarbon age calibration curves, 0e50,000 years cal BP. Radiocarbon 51 (4), 1111e1150. Rincón Mautner, C., 1999. Man and the Environment in the Coixtlahuaca Basin of Northwestern Oaxaca, Mexico: Two Thousand Years of Historical Ecology. University of Texas, University Microfilms, Ann Arbor. Servicio Meteorológico Nacional, 2010. Normales Climatológicas 1971e2000, Estacion 00020019: S. J. Bautista Coixtlahuaca, website of Comision Nacional del Agua (CONAGUA). Servicio Meteorológico Nacional, Mexico. http://smn.cna.gob. mx/index.php?option¼com_content&view¼article&id¼42&Itemid¼28 (last accessed 04.01.13.). Spores, R., 1969. Settlement, farming technology, and environment in Nochixtlan Valley. Science 166, 557e569. Waters, M.R., Haynes, C.V., 2001. Late Quaternary arroyo formation and climate change in the American Southwest. Geology 29, 399e402.