Anthropogenic Geomorphology of Bajo Edges in the Maya Lowlands
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Geomorphology 331 (2019) 127–145 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph Margin for error: Anthropogenic geomorphology of Bajo edges in the Maya Lowlands Nicholas P. Dunning a,⁎, Armando Anaya Hernández b, Timothy Beach c, Christopher Carr a,RobertGriffin d, John G. Jones e, David L. Lentz a, Sheryl Luzzadder-Beach c, Kathryn Reese-Taylor f,IvanŠprajc g a Unniversity of Cincinnati, United States of America b Universidad Autónoma de Campeche, Mexico c University of Texas at Austin, United States of America d University of Alabama in Huntsville, United States of America e Archaeological Consulting Services, Ltd., United States of America f University of Calgary, Canada g Research Center of the Slovenia Academy of Sciences and Arts, Slovenia article info abstract Article history: Many early Maya cities developed along the edges of large structural or karst depressions (bajos). This topo- Received 19 March 2018 graphic position aided growing populations to more effectively capture and store rainwater, a necessity for Received in revised form 1 September 2018 year-round occupation of interior portions of the Maya Lowlands of Mexico and Central America. Ancient Accepted 2 September 2018 Maya forest clearance on sloping terrain led to accelerated soil loss and the aggradation of the bajo margins. Available online 4 September 2018 These newly created margins of colluvial lands became a focus of subsequent intensive agriculture and helped underwrite further urban expansion. We document this long-term landscape transformation with data derived Keywords: fi Maya Lowlands principally from eld investigations at Tikal, Guatemala, and Yaxnohcah, Mexico, but with reference to other Geoarchaeology Maya centers in the Elevated Interior Region (EIR). Data are derived from field investigations, interpretation of Ancient land use lidar imagery, and laboratory analyses. We present a model of three variants of bajo margin landscape change Environmental change with differences attributable to topography, lithology, hydrology, and cultural processes. We present preliminary Lidar data on crops that were cultivated on bajo-margin soils. We further describe how agriculture was adapted to evolving bajo margins as evidenced by systems of field walls, terraces, and ditches. © 2018 Elsevier B.V. All rights reserved. 1. Introduction that was partly the product of natural forces, but also was a cultural in- heritance that included transformations made in the soilscape, hydrol- Karl W. Butzer suggested years ago that metastable equilibria pro- ogy, and vegetation, and sometimes enduring landesque capital vided a useful model to track the fluctuating arcs of ancient civilizations (Dunning et al., 2006; Beach et al., 2015, Figs. 7, 12). Cultural inheritance (Butzer, 1980). Over time, Butzer's modeling of the long-term accom- also included the traditions of agricultural strategies, and included social modation of cultures to environmental change, including anthropo- and political systems that structured economic forces such as land ten- genic change, became more nuanced (e.g. Butzer, 1996), presaging the ure and the control of labor and goods (Webster and Murtha, 2015). introduction of resilience models in cultural and political ecology We report on investigations in and around Tikal (Guatemala) and (e.g., Berkes and Folke, 1998; Holling and Gunderson, 2002; Chaffin Yaxnohcah (Mexico), two ancient Maya cities that developed on the and Scown, 2018). Ultimately, such modeling has led to a more refined margins of large bajos, and compare our findings to those from other understanding of the ways imbalances can lead to societal transitions sites in the Elevated Interior Region (EIR) of the Maya Lowlands (Butzer and Endfield, 2012). This way of thinking underlies the under- (Fig. 1). We use changes in the soilscape to document the course of standing we have developed of the complex way in which ancient Maya interaction with these landscapes, including degradation and ag- Maya communities interacted with bajos, depressions with a range of gradation processes, as well as human response to these processes. wetland types within the interior of the Yucatan Peninsula. Specifically, This is a remarkable story of human adaptation to what initially may scores of generations of human activity took place within a landscape have seemed an incremental catastrophe involving soil erosion and re- lated changes, but which evolved into a foundation for population growth and urbanization. ⁎ Corresponding author. Yaxnohcah arose as an important urban center early on in the course E-mail address: [email protected] (N.P. Dunning). of Maya Civilization, with evidence for the construction of monumental https://doi.org/10.1016/j.geomorph.2018.09.002 0169-555X/© 2018 Elsevier B.V. All rights reserved. 128 N.P. Dunning et al. / Geomorphology 331 (2019) 127–145 Fig. 1. Map showing the location of the Elevated Interior Region (EIR) within the Maya Lowlands and sites mentioned in the text. architecture and a large central reservoir sometime between 800 and 2. Regional setting 700 BCE (the beginning of the Maya Middle Preclassic period). The city continued to grow through the Late Preclassic, probably peaking 2.1. Physiography in the second century CE (Reese-Taylor et al., 2015, 2016a; Anaya Hernández et al., 2017). While Yaxnohcah continued to be occupied Ancient Lowland Maya Civilization occupied the Yucatan Peninsula by a sizeable population during the ensuing Classic period, its fortunes of Mexico and contiguous areas of Belize, northern Guatemala, and east- had apparently declined and little investment in monumental construc- ern Honduras and El Salvador, a region collectively referred to as the tion took place; nearly complete abandonment occurred after 900 CE. Maya Lowlands. Within this broader area lies an irregular physiographic Tikal grew at a slower rate in the Preclassic but became a sizeable center province often called the Elevated Interior Region (EIR), a karst area in the Late Preclassic (Martin and Grube, 2008; Dunning et al., 2015a). characterized by an acute lack of perennial surface water and almost Unlike, Yaxnohcah, Tikal continued to grow through much of the Classic no access to the groundwater table (Dunning et al., 2012). The carbon- period, with some notable hiccups, becoming one of the most powerful ate bedrock that underlies the EIR is chiefly Cenozoic limestone, though centers in the Maya Lowlands, until it too declined abruptly in the ninth pockets of older beds (e.g., Cretaceous limestone, sandstone, and gyp- century CE (Martin and Grube, 2008; Lentz et al., 2014). These two large sum beds) crop out in some places by faulting. This ancient faulting urban centers with their varying cultural trajectories offer insights into has strongly controlled karst solution processes in some areas, including the interactions of the ancient Maya with the soilscape in the EIR. Exam- inducing the development of the largest bajos (Perry et al., 2009). ining bajo margins at other sites within the EIR sheds further light on Bajos are a common feature within the EIR. While many use the term ancient Maya adaptations to a changing landscape. bajo for all low-lying swampy terrain, here we specifically address those N.P. Dunning et al. / Geomorphology 331 (2019) 127–145 129 depressions lying in the elevated (80 m or more above msl) interior por- soils on slope crests and backslopes on karst uplands are typically shal- tions of the EIR. Bajos range in size from less than a square kilometer to low, often skeletal Entisols, with Rendolls in local solution pockets and several hundred square kilometers. This size difference in part reflects slope breaks. Over the course of the Quaternary, deep, smectite-rich different origins. Smaller bajos (aka pocket bajos) are strictly the prod- clay sediments accumulated within bajos providing the parent material uct of limestone and sometimes evaporate dissolution, whereas the for Vertisols, the dominant soil type in these depressions and other, largest bajos have a significant structural component. Many of these more stable surfaces (Beach et al., 2018a, 2018b). Some bajos also con- larger bajos are associated with normal faults with prominent scarps tain pockets of Histosols in areas with perennial moisture. The develop- protruding out on at least one side. Dissolution and erosion modifies ment of soils at the slope interface between uplands and bajos varies grabens within these fault systems into rugged, complex karst land- depending on the abruptness of the slope break, local drainage, and his- forms (Marshall, 2007). These depressions extend into the northern tory of Holocene land cover. Present day soils along bajo margins are portions of the EIR, but in the north a combination of better drainage, predominantly Cumulic Haplorendolls and Haplustolls (Fig. 2). The for- less faulting and jointing, and less rainfall inhibit wetland development. mer typically overlie bedrock, whereas the latter often developed over The sites addressed in our research lie within the central to southern buried Vertisols. Some bajo edges as at Tulix Mul, Belize, were less sus- portion of the EIR. ceptible to geomorphic change because their gradients were too low for Bajos cover between 40 and 60% of the landscape across the south- much slope erosion and deposition. Here Vertisols formed over 7 to 2° ern and central parts of the EIR (Siemens, 1978; Pope and Dahlin, backslopes rather than Rendolls (Beach et al., 2018b).