Soil management in pre-Hispanic raised field ... - Wiley Online Library

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Soil Management in Pre-Hispanic Raised Field Systems: Micromorphological Evidence from Hacienda Zuleta, Ecuador Clare Wilson,1 Ian A. Simpson,1 and Elizabeth J. Currie2 1

Department of Environmental Science, University of Stirling, Stirling FK9 4LA, Scotland, United Kingdom 2 Department of Archaeology, University of York, King’s Manor, York YO1 2EP, United Kingdom Soils-based evidence derived from thin section micromorphology is used to explore contrasts in pre-Hispanic and Hispanic arable land management practices associated with raised fields in an inter-Andean valley of Ecuador. Differences in textural pedofeature characteristics suggest that, where they are found in the same locality, camelloń systems were more intensively manured and cultivated than wachu systems. Both, however, were more intensively managed than traditional Hispanic arable fields. The importance of the camelloń in pre-Hispanic agriculture is emphasized by soils-based evidence that highlights the efforts made to clear these fields of volcanic ash after the Quilotoa eruption of ca. A.D. 1280. This research suggests that, in an andosol context, pre-Hispanic and Hispanic arable land management practices leave relict and fossil soil micromorphology features that can be used to interpret land use intensities. 䉷 2002 Wiley Periodicals, Inc.

INTRODUCTION Raised fields are a predominantly wetlands agricultural management regime with different forms found throughout the pre-Hispanic Americas. Examples include the well-known chinampas of Mexico (Coe, 1964; Armillas, 1971) and those found high on the altiplano along the shores of Lake Titicaca in Bolivia (Smith et al., 1968). In Ecuador, raised fields can be found both on the floodplains of coastal areas such as the Guayas Basin (Parsons 1969; Denevan et al., 1985), and high in the interAndean valleys between the Cordilleras Occidental and Oriental (Batchelor, 1980). Here they are usually referred to as camellones, with a raised area between ca. 2.5 and 3.5 m wide and several meters long created by excavation of ditches and the mounding of excavated materials. The ditches facilitated drainage in the swampy valley bottoms, while the water itself regulated the surface temperature of the growing area and kept it frost-free at higher altitudes, thereby facilitating the production of frost-sensitive crops like maize or potatoes. Organically rich debris periodically cleaned out of the ditch fills was redeposited on the growing surface and was an efficient fertilizer, in combination with other available manures, such as human and guinea-pig dung, and, where available, camelids (Knapp, 1984, 1988, 1991). Ridged fields, or wachukuna, are also found in the inter-Andean valleys, and their narrower wavelength of around 1 m from the center point of one ridge (loma) Geoarchaeology: An International Journal, Vol. 17, No. 3, 261– 283 (2002) 䉷 2002 Wiley Periodicals, Inc. ● DOI: 10.1002/gea.10015

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to the next, are thought to be associated with less intensive forms of cultivation in wetland areas. Land management practices associated with camellones and wachukuna formation supported a year-round production of crops and are believed to have provided the principal subsistence basis for high pre-Hispanic population densities (Knapp, 1991; Athens, 1992) and sociopolitical complexity represented by the large mound (tola) occupations and ceremonial sites of the region (Athens, 1978, 1980, 1992; Gondard and Lo´pez 1983; Salomon, 1986; Knapp 1991; Almeida Reyes, 1995; Currie, 2000; 2001). Despite the long and prolific history of research into pre-Hispanic raised field agriculture (Parsons and Bowen, 1967; Denevan, 1970; Seimens and Puleston, 1972; Parson, 1978; Darch, 1983; Knapp, 1984, 1988, 1991; Farrington, 1985; Turner and Denevan, 1985; Knapp and Denevan, 1985), nothing is known about the diversity of soil management practices associated with these field systems and their contrast with Hispanic colonial arable soil management practices. Furthermore, how soil management regimes were modified with the impact of external environmental disturbances such as volcanic eruption and ash deposition is little understood. These remain significant omissions, because understanding the diversity of soil management practices and responses to external impacts will serve to indicate more fully the position and significance of arable activity within pre-Hispanic society. One way of obtaining evidence on early soil management practices is through the analyses of soil properties because soils are dynamic natural bodies whose properties reflect the environment in which they have been formed. Thus, in cultural landscapes, identification of relict and fossil soil properties has the potential to help us understand early soil management and the organization of early agricultural societies (Simpson, 1997; Simpson et al., 1998a, 1998b; Adderley et al., 2000). Using soils evidence, this paper explores contrasts in arable soil management regimes associated with raised fields. The first contrast is between fossil camellones and wachukuna; hypothetically, where they are found in the same locality, camellones were more intensively managed than wachukuna. The second contrast assesses the impact of the Quilotoa volcanic eruption of ca. A.D. 1280; comparing pre- and post-eruption soil management regimes in both camellones and wachukuna produces the hypothesis that volcanic eruption marked a decline in the intensity of arable soil management practices, with possible subsequent recovery. Finally, a third contrast is made between the pre-Hispanic camellones and wachukuna and a present-day arable soil, managed in the traditional Hispanic colonial manner with ox-pulled plough, leading to the hypothesis that soil management was more intense in the pre-Hispanic period and would, therefore, have supported higher population densities per km2 of cultivated land. To test these hypotheses, we used soil thin section micromorphology to identify a range of features indicative of arable land management practices in areas already defined from field observation as early field systems. Such features potentially include a range of textural pedofeatures, fabric mixing and homogenization, microstructural characteristics, and the introduction of exotic materials (Courty et al., 1989; Gebhardt, 1992, 1995). It

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SOIL MANAGEMENT IN PRE-HISPANIC FIELD SYSTEMS, ECUADOR

is clear, however, that the creation and survival of such features will vary in different soil types (Carter and Davidson, 1998), and this study represents the first identification of micromorphological features associated with early arable activity in South American andosols (soils derived from volcanic ash and other volcanic ejecta). METHODS Study Area and Sampling Sites Hacienda Zuleta in Imbabura Province of the northern Ecuadorean highlands (Figure 1) was selected as a study area. Evidence of occupations spans the late pre-historic through the early colonial period to the present day. Late pre-Hispanic occupation is demonstrated in the form of large groups of tolas (artificial mounds) (Figure 2), and, during this period, tephra deposition indicates that the area was influenced by volcanic activity, with the eruption of Quilotoa ca. A.D. 1280 confirmed by its distinctive texture and inclusions (Hall and Mothes, 1994; Mothes and Hall, 1998; Currie, 2000, 2001). Ethno-historical sources suggest that the region was subjugated to the Incas ca. A.D. 1490, only shortly before the Spanish arrival (Larrain Barros, 1980; Espinosa Soriano, 1988), with early colonial period occupation characterized by a 17th century Jesuit-founded hacienda (Almeida Reyes, 1995; Stevens, n.d.). Traditional Hispanic farming practice continues to the present day with small fields (chacras) of maize, potatoes, and beans. These fields are cultivated using a range of implements, including ox-pulled plough, picks, adzes, and hoes, to create cultivation ridges known locally as huachos, a Spanish term derived from the Quichua wachu or wachukuna (plural). Sampling sites were all in the valley bottom of the Zuleta region on soils classified as desaturated andosols, with parent materials derived from fluvio-lacustrine sediments and recent pyroclastic ejecta (Winckell et al., 1997; World Reference Base, 1998). Three sites within the Zuleta region were selected to sample undisturbed soil materials using Kubiena tins — Sites 4 and 5 taking advantage of a water pipeline trench, and site La Cocha IV (LC IV; Figure 2). Site 4 contains firm morphological evidence of a raised field system, camellones, with plugs of volcanic ash within the associated ditches (Figure 3). The sampled sequence includes (i) the pre-camelloń land surface (samples 1 – 2); (ii) a pre-eruption phase camelloń ridge (samples 6 and 7); (iii) a secondary phase of camelloń development above the first, contemporary with the eruptive event dated to ca. A.D. 1280 (based on radiocarbon ages of 785 ⫾ 50 yr B.P., considered to be the most reliable, 840 ⫾ 50 yr B.P. and 900 ⫾ 150 yr B.P.; Mothes and Hall, 1998:117) (samples 4 and 5); (iv) a post-eruption recovery phase of cultivation activity, marked by tephra clearance and recutting of ditches, merging into the overlying soils (samples 3 and 4). Site 5 contains what has been interpreted as the smaller, although variable, ridge and furrow cultivation systems — wachukuna (Figure 4). The sampled sequence includes (i) the pre-agricultural land surface (base of samples 6); (ii) a pre-eruption phase of ridge and furrow cultivation (base of sample 4 and sample 5); (iii) the eruptive event (upper part of slide 4), dated to ca. A.D. 1280; (iv) a post-eruption

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Figure 1. The northern Highlands of Ecuador, showing location of Imbabura province.

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Figure 2. Hacienda Zuleta and environs, Imbabura province, showing distribution of mounds and ramp mounds (tola) and soil profile sampling locations.


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Figure 3. Profile drawing of site 4. This shows a well-defined sequence of ditches and ridge construction to form the camelloń. Sampling locations for thin section micromorphology are given (site 4; 1– 7).

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Figure 4. Profile drawing of site 5. Ditches and ridges are less obvious and smaller than those evident as part of the camelloń. Sampling locations for thin section micromorphology are given (site 5; 1– 6).

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recovery phase of cultivation activity marked by attempts at tephra removal and recutting of ditches (sample 3 and base of sample 2); and (v) the modern soil (top of sample 2 and sample 1). Radiocarbon measurements on wood charcoal from Site 5 (Figure 4) gave a calibrated 2 sigma date range of A.D. 1205 – 1290 (Beta 124722: 780 ⫾ 40 yr B.P.) from immediately below the ca. A.D. 1280 tephra, and a calibrated 2 sigma date range of A.D. 1185 – 1285 (Beta 124721: 770 ⫾ 40 yr B.P.) from immediately above the ca. A.D. 1280 tephra (Currie, 2000a). The LC IV site is continuously managed for arable produce using the traditional manual or ox-pulled plough to turn the soil and make furrows, with a spade used to weed. Cow dung is used as manure; potatoes are given two handfuls each when small, and when maize and beans are planted, manure is scattered just before sowing. Five undisturbed samples were collected in sequence down a profile exposed in this field, with three from the topsoil and two from the underlying subsoil (Figure 5). Thin Section Manufacture and Description Thin section slides were manufactured following the standard procedures of Murphy (1986). In summary, water was removed from samples by acetone replacement and impregnated in a vacuum using a CRYSTIC 17449 resin thinned with acetone; a MAKP LA3 catalyst was used to speed the reaction. Samples were left to cure for 4 weeks and then finished in an oven at 40⬚C for a further week. The cured blocks were sliced, and the chosen face lapped flat and then bonded to a flat glass plate. Excess material was sliced from the plate and the plate was then precision lapped to a thickness of 30 ␮m using a Logitech LP40 lapping machine. After

Figure 5. Profile drawing of La Cocha IV. Slight ridges are evident in this traditional ox-pulled plough field. Sampling locations for thin section micromorphology are given (La Cocha IV; 1– 5).

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cleaning and polishing, the slides were then cover- slipped. The slides were examined at magnifications of between ⫻10 and ⫻400 in plane polarized light (PPL), under cross-polars (XPL), and in oblique incident light (OIL) using an Olympus BX50 polarizing microscope. Slide description follows the scheme outlined in the International Handbook of Soil Micromorphology (Bullock et al., 1985) and is recorded in standard summary sheets. Full descriptions are available from the corresponding authors. RESULTS AND DISCUSSION Hacienda Zuleta, Site 4 Pre-camelloń land surface. The pre-camelloń land surface represented in thin sections 1 and 2 (Figure 3; Table I) is a channel and chamber, and moderately developed blocky microstructured soil with a patchy, mid-brown, grey brown, and grey appearance in thin section under plane-polarized light. The soil becomes sandier and increasingly mineral with depth. Void space is moderately high (30 – 40% slide area) and is dominated by channels and planar voids. The intimate mixing of clays, silts, and organics suggests that biological activity was once important, resulting in homogenization of the soil matrix. However, as excremental features are rare and, where present, are strongly aged, bioturbation of this horizon has now ceased. The presence of typic iron nodules, sometimes within aggregates, and the zones of iron and clay depletion around the edges of macro voids are also noted. Gleying of the soil and redoximorphic iron redistribution appear to be a response to contemporary hydrological conditions as the depletion zones are universally situated around surviving macro-void systems. Two types of textural pedofeatures are present in this horizon: limpid and silty clay void coatings. Both types are rare occurrences, accounting for less than 1% of total slide area. Some limpid coatings include up to five silty microlaminations, suggesting periodic clay translocation and deposition. The silty clay void coatings are often overlain by, or are incorporated in, compound coatings of the limpid type. The distribution of both limpid and silty clay coatings, discussed more fully below, throughout this soil and their survival intact in a previously bioturbated soil, suggests that their deposition occurred following burial. The samples from this pre-agricultural soil were taken from beneath a ditch feature lying alongside an associated camelloń ridge (Figure 3). At the very top of thin section 2 is a layer of well-sorted, silty organo-mineral material stained brown along its upper surface by organic pigments and thought to represent sedimentation from within the ditch fill. Later, channel and planar voids cut through this layer, and relatively thin limpid clay coatings formed along their walls. Also at this level are grey lenses of sand and silt-sized volcanic ash. These ash lenses are up to 1 cm long by 0.5 cm wide with random basic orientations and straight, sharp edges. They are absent below about 5 cm within the pre-camelloń soil. Because these fine silty deposits are interpreted as sedimentation within the ditch from the raised growing beds either side of it, it suggests that these deposits must have been formed after


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Table I. Summary thin section micromorphology descriptions; Hacienda Zuleta, site 4.

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construction of the overlying agricultural soils. The lenses of ash material are too distinct, sharp-edged, and dense to represent incorporation through faunal turbation. Anthropogenic activity, such as digging for ditch clearance, following the deposition of an ash fall prior to the Quilotoa eruption of ca. A.D. 1280, found higher in the profile, may account for these features. Similar ash lens features have been identified within the site 5 thin sections, and further analyses are required to characterise this earlier ash fall. The primary camelloń feature. The body of the primary camelloń (Figure 3; thin sections 6 and 7; Table I) is found to be a moderately well-sorted silt loam, with a well-developed medium and fine subangular blocky structure. Again the soil has a channel and chamber, and blocky microstructure, but is finer textured than the underlying pre-agricultural soil horizon with moderate porosity (30 – 35% slide area). The fine organo-mineral fabric consists of intimately mixed silts, clays, and organic residues. The organic material has been very heavily altered and no longer exists as a distinct form; instead the organic material is present in the form of amorphous black punctuations and brown pigmentation. Charcoal is noticeably absent from the soil, suggesting that no combusted materials were added to the soil. The coarse mineralogy of silts and fine sands is similar in composition to the underlying soil, but the tephra element is found intimately mixed within the soil matrix. Limpid clay and silty clay coatings upon the walls of channel voids are present. The limpid coatings are dark red/brown in PPL and a matt dark brown in OIL and are more abundant and better developed in this context than the underlying one, reaching 500 ␮m in thickness (Figure 6). Similar features have been identified in archaeological contexts and characterized as having concentrations of organic matter and phosphorus within the clay, leading to the suggestion that there is a relationship between these features and the occurrence of animal manures (Macphail and Cruise, 2001). It is possible, therefore, that these features found in camellone soils are the result of animal manure application and that their occurrence and frequency are indicators of manuring practice intensity. The silty clay coatings are less well developed and are occasionally found coating or in compound coatings with the limpid features (Figures 6 and 7). This suggests at least some overlap between phases of translocation of these two materials. Silty agricutans are often interpreted as the result of slaking processes in which fine material from a bare, structurally unstable soil surface is washed though the soil profile. Such conditions are common in disturbed arable soils and so, in archaeological contexts, silty textural pedofeatures can be interpreted as evidence of cultivation activity (Jongerius, 1983; Macphail, 1986). Depletions and amorphous iron concentrations are other features of this context. Typic, moderately impregnated nodules up to 1000 ␮m in diameter tend to occur within the center of micro-aggregates away from coarse meso- and macro-sized voids, while the edges of these larger voids are lined by zones of grey and grey/ brown silt, depleted in clay and iron. These zones are up to 2000 ␮m wide, and in some cases, the material may have been translocated, resulting in jumbled, coarse-


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Figure 6. Limpid clay coatings with silty clay; site 4, sample 7; plane-polarized light.

textured coatings of silt and fine clay around the largest voids, rarely overlying the thinner limpid clay coatings. This pattern of depletion and impregnation again suggests periodic saturation of these main water-conducting voids and gleying of the soil. A marked fining of the material within the camelloń has also been noted with an increase in the proportion of fine silts and clays. The fine silty layer identified as ditch sediment provides a likely source for this fine mineral material. The material within the camelloń is relatively homogeneous and indicates thorough mixing of materials, indicative of long-term intensive cultivation, although strongly aged excremental features suggest that at least part of this mixing was biological. No evidence of individual depositional events remains, and the camelloń ridge has a remarkably consistent composition throughout. The secondary camelloń feature. Overlying the body of the primary ridge, the secondary camelloń feature (Figure 3; thin sections 4 and 5; Table I) is a similar structure, again with a finer texture than the pre-agricultural soil. The mineralogy is again similar, but the silt- and sand-sized tephra element is found not only within the body of the soil matrix, but also loosely around channel voids. Both types of clay coating are present but less abundant, with the limpid coatings more poorly developed than in the body of the primary camelloń and found as rare laminations within the silty clay. Iron nodules and common zones of depletion around channel

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Figure 7. Silty clay coatings; site 5, sample 4; plane-polarized light.

voids up to 3000 ␮m wide indicate periodic waterlogging. The few bowlike infills present indicate faunal activity. The main differences between the two camellones are the distribution of tephra grains and the weaker development of the limpid clay coatings within this context. Tephra grains, as well as occurring randomly within the main body of the soil matrix, are also found as loose, discontinuous channel infillings at the base of this secondary feature and appear to be downwash through the channels from higher up (Figure 8). The presence of this tephra points to an additional, but not substantial, inclusion of volcanic ash from the A.D. 1280 Quilotoa eruption. The presence of both silt and limpid clay coatings again indicates translocation processes, possibly in response to disturbance and animal manure inputs. Their presence in this secondary camelloń ridge suggests that translocation processes have certainly operated since its construction. The poorer development suggests that, for the limpid clay at least, the disturbance processes and manure inputs that may have led to their formation were not as pronounced as in the primary feature. This suggests that cultivation and manuring of the second camelloń system may have been for a shorter period of time, interrupted by the eruption and ash falls. Post-eruption phase, merging with surface soils. The lower horizon of the surface soil and uppermost part of the secondary camelloń ridge represented in thin


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Figure 8. Grey volcanic ash lenses; site 4, sample 2; plane-polarized light.

sections 3 and 4 (Figure 3; Table I), are a grey brown silt loam with a weakly developed, fine subangular blocky structure. The fine fabric is organo-mineral, and, although the dominant organic fraction is brown pigments, amorphous black and brown residues are more common than within the buried arable agriculture soils. Parenchymatic and lignified root tissues are also present within very few channel voids. The coarse fraction includes silts and sands of feldspar, horneblende, tephra, and quartz together with rounded yellow inclusions of hardened silt and clay thought to be volcanic muds. Excremental features are frequent and include bowlike infills and mammilate and spheroidal features. Depletions of clay and iron from around void walls are absent from this soil, although a few iron nodules are present within the center of the aggregates. Very rare fragments of red/brown limpid clay coatings are present within the body of the soil matrix. These soils have developed on volcanic ash and the underlying agricultural soils. Accretion of the profile to its present level is due to aeolian and pyroclastic inputs in view of the fine grain sizes and the nature of the mineralogy. A wider range and less heavily altered fractions of organic matter are present, consistent with the ongoing addition of organic material at the surface and root decay within the soil. Although there is some evidence of hydromorphism in this material, the redistribution of iron has been less severe than deeper in the section. The limpid clay

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coatings are present only as small fragments integrated within the main body of the soil matrix as a result of bioturbation, with the silty clay coatings absent altogether. This suggests an absence of agricultural activity and reinforces the view that that formation of clay void coatings is related to arable land management, as seen in the underlying soils. Documentary sources indicate that the area was abandoned in the early 16th century following the Inca wars and given over to pasture (Larrian Baros, 1980; Espinosa Soriano, 1988). Although subsequent intermittent cultivation may have taken place, it remains in pasture today. Hacienda Zuleta, Site 5 Pre-cultivation land surface. The pre-cultivation land consists of a yellow/olive brown silt loam with a weakly developed fine subangular blocky structure. In thin section (Figure 4; base of thin section 6; Table II), the fine fabric is an organomineral mix of brown organic pigment, silt, and clay. Rare red/brown limpid clay coatings up to 75 ␮m thick are present in channel voids. Very little of this horizon was evident in thin section, but the description suggests the development of a soil very similar to the earliest land surface in site 4. Pre-eruption phase cultivation ridge. The slides from the cultivation ridge (Figure 4; thin sections 5 and the very top of 6; Table II) consist of an apedal, silt loam, brown and grey/brown in color. The fine fabric is organo-mineral with brown organic pigments and small amounts of amorphous organic residues mixed with silts and clays. There has been no significant fining of the material within the cultivation bed as was identified in the agricultural soil of the camellones in site 4. Tephra grains are both incorporated within the soil matrix and loosely clustered around the walls of channel voids that dominate the soil’s microstructure. Rare red/brown limpid clay coatings up to 100 ␮m thick are present lining channels, as are trace quantities of silty clay, black, coatings. Unlike the agricultural soil of site 4, these two types of pedofeatures have mutually exclusive distributions and no compound coatings are found. A very few amorphous iron nodules up to 1000 ␮m in diameter are present, and the only excremental features are bowlike infills and strongly aged mammilate features in a very few of the larger channels. The fabric of the soil is similar to the camelloń features investigated in site 4 and has been organically enriched as indicated by the level of organic pigmentation and darkening. However, this is not so pronounced as in site 4. The slight fining relative to the underlying soil is also not nearly so marked as in the camellones of site 4. The indications are, therefore, that these soils in this site may have been less intensively cultivated and manured than the camelloń soils. The distribution of tephra grains as loose discontinuous infillings in channel voids is a further difference between this and the previous site, suggesting an absence of biological or agricultural incorporation, with the ash having been allowed to lie upon the surface for some time. Pre-ash fall surface and ash deposits. The ash deposit and pre-ash fall surface (Figure 4; thin section 4) consist of an apedal, poorly sorted mid-brown and grey, silt loam, mineral and organo-mineral, with a patchy appearance. Lenses of grey


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Table II. Summary thin section micromorphology descriptions; Hacienda Zuleta, site 5.

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volcanic ash and gravel-sized rounded inclusions of fine-grained yellow inclusions are common throughout this slide. The grey ash lenses consist of tightly packed pure sands and silts of tephra, feldspar, horneblende, and quartz and are up to 1 cm long and 0.5 cm wide with sharp edges. Tephra grains are also a frequent component of the main soil fabric. The large quantities of tephra in this context have been identified from comparable contexts as deriving from the ash fall of the Quilotoa eruption of ca. A.D. 1280 (P. Mothes and M. Hall, personal communication, 1998). The lenses of volcanic ash, common in this context, are again interpreted as evidence of anthropogenic disturbance and a “digging” over of the material in an effort to clear the cultivation surfaces. This is consistent with the macromorphological evidence of inverted ash lenses. Rare limpid clay coatings, up to 150 ␮m thick, are present lining channels. No coatings were observed within the lenses of volcanic ash, but those within channels running through the tephra-rich fabric were all intact. The suggestion is that at least one phase of clay translocation occurred following the ash fall. Excremental features are absent from this context. Surface soil. The surface soil, represented in thin sections 1, 2, and 3 consists of a weakly developed medium subangular blocky, silt loam soil, rich in organic matter, fading into an apedal, yellow/brown and grey, sandy silt loam with a patchy appearance. In the lower horizon, lenses of volcanic ash are frequent and, as in the underlying soil, these lenses have sharp edges and are up to 1.5 cm across. This soil also contains a few of the yellow, rounded inclusions; here they have textural characteristics similar to the surrounding soil fabric. The modern topsoil consists of a fine fabric dominated by amorphous organic residues together with phytoliths and trace quantities of pollen. The proportion of tephra grains within this horizon is lower than the underlying contexts, and the tephra is randomly distributed throughout the soil matrix or is found weakly clustered within bow-like channel infills. Other excremental pedofeatures include large ellipsoids (up to 1 cm) and mammilated channel infillings. Iron nodules up to 1000 ␮m in diameter occur in clusters across the slide. Very rare silty and limpid clay coatings are found within the basal portion of this soil, suggesting a limited phase of post-eruption cultivation here. Within the topsoil, only small fragments of the limpid coatings are found, mixed within the soil fine fabric. The formation of this soil appears to have included an early phase in which the underlying tephra-rich deposits have been dug in, resulting in the formation of ash lenses in the basal portion of this soil. The soil has then aggraded naturally through organic and aeolian mineral deposition. Biological activity is high in the topsoil of this andosol, and the clusters of iron nodules indicate periodic gleying. There are rare silty and limpid clay coatings present within the dug-over portion of this soil, but their limited occurrence from the topsoil supports the finding from site 4, that these textural pedofeatures are related to anthropogenic disturbance of the agricultural soils. The silty microlaminations within the limpid cutans suggest periodic deposition, while the spatial hierarchy of the two cutan forms as variously coating one another or forming compound coatings, suggests that the phases of translocation and deposition of the two textural types overlaps.


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Hacienda Zuleta, La Cocha IV The soil of this modern present-day profile, cultivated in the traditional Hispanic manner using manual or ox-pulled plough and cattle manures, is represented in thin sections 1, 2, and 3 (Figure 5; Table III) and is characterized by channel and chamber microstructures, with moderately high void space (25 – 40%). Coarse mineral materials include little quartz, feldspar, and hornblende, and very few tephras throughout the profile. Fine soil materials are organo-mineral and stipple speckled. Dark brown colors together with the more frequent occurrence of parenchymatic tissue and excremental pedofeatures distinguishes the surface soil horizon from the underlying brown and grey subsoil. These observations are consistent with continuous organic input to the soil surface, including the deposition and decomposition of organic manures. The occurrence of amorphous and cryptocrystalline ion accumulation features in the lower part of the soil profile confirms that the soil has been subject to periodic wetting and drying similar to the camelloń and wachu. Very few silty clay textural pedofeatures, generally less than 50 ␮m in thickness are evident throughout the soil profile, and very few limpid clay coatings are evident in only the lower part of thin section 3 at the interface of top soil and subsoil. Such observations support the suggestion that textural pedofeatures are associated with cultivation activity and manuring practices, although here their frequency and size is clearly different from those found in thin sections from the camelloń and wachu. This suggests that traditional Hispanic, arable land management may have been significantly less intense than that evident in pre-Hispanic field systems. CONCLUSIONS Micromorphological evidence from pre-Hispanic raised field systems at Hacienda Zuleta, Imbabura Province, has indicated that within a wet, gleyed, soil environment with persistent aeolian deposition, there are marked differences in limpid clay and silty clay textural pedofeature formation. Within the modern, uncultivated soil profile overlying the camelloń and wachukuna features, and in the underlying pre-agricultural soils, these textural pedofeatures are only very rarely present, as isolated fragments within the fine fabric of the soil. They are, however, found throughout the camellones and wachukuna, where they are most abundant and strongly developed within the body of the primary camelloń. The processes of their formation, therefore, may be related to the agricultural activity associated with these soils, with some of the translocated material penetrating into the pre-agricultural soil below the dug-over ditches, and with fragments of clay brought into the later soils through biological turbation processes. These observations suggest that the orange/brown or red/brown limpid clay could be related to animal manuring activity (Macphail and Cruise, 2001), while the silty clay can be attributed to soil disturbance associated with tillage activity (Jongerius, 1983; Macphail, 1986; Courty et al., 1989). There is now a clear need to further characterize these features by assessing their chemical composition and by considering the extent to which they are found in unmodified, uncultivated andosols.

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Table III. Summary thin section micromorphology descriptions, Hacienda Zuleta, La Cocha IV.



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Variation in occurrence, frequency, and location of these features in soil profiles does, however, suggest marked differences in land management practices. On this basis, it is possible to suggest that the camellones were substantially more developed and utilized for cultivation than the wachukuna, with highly intensive animal manuring and tillage strategies. This could be due either to the wachukuna being cultivated over a shorter period of time than the camellones, or to the less intensive form of cultivation regime in the wachukuna system, or perhaps to a combination of both. A further distinction between the two systems is the compound coatings found in the camellones, compared to the mutually exclusive distribution of the two textural pedofeature types in the wachukuna, suggesting that manuring and tillage practices may have been integrated in the camellones but discrete in the wachukuna. In both systems, however, the presence of micro-laminations indicates that these coatings were laid down in a number of episodes, suggesting ongoing sequences of manuring and tillage. While ethnographic evidence of the traditional Hispanic arable practices in the Zuleta region indicates continuous tillage and manuring activity, the soils-based evidence of textural pedofeatures suggests that the level of activity is lower than in the pre-Hispanic arable land management systems. Although textural pedofeature indicators of both manuring and tillage are present in the traditional Hispanic system, they are rarer and less thick. These observations serve to emphasize just how intensive pre-Hispanic arable agriculture may have been, and perhaps needed to be, with a heavy emphasis on manuring and tillage to support high population densities. Observation of the distribution of volcanic ash in thin section permits assessment to be made of pre-Hispanic, arable land management responses to volcanic activity. Ash from the Quilotoa eruption does not appear to have lain for long on the camelloń ridge (site 4), because no biological incorporation of the material occurred. In contrast, volcanic ash from the Quilotoa eruption is more frequent within the upper surface of the wachukuna cultivation bed (site 5). Channel in-fillings of tephra suggest that the ash must have lain upon the surface for some time to produce these features. Lenses of volcanic ash, similar to those beneath the ditch feature of site 4, are also present within the latest pre-ash level and the overlying post-ash levels. These are thought to be the result of digging after the ash fall event with the ash-laden material incorporated into upper horizons; the excavators found that ash was not as thoroughly cleaned from the surface of this cultivation series as from those in site 4. This could be consistent with an interpretation that following the volcanic eruption, efforts to recover the agricultural basis of the community focused first upon the more intensively utilized camelloń systems in the center of the valley than the less intensively utilized wachukuna. Using soils-based micromorphology evidence, this research has served to highlight possible variations in arable land management practices in pre-Hispanic raised field agriculture and indicated its intensity relative to Hispanic practices. Further integrated pedological and archaeological research is required to more fully characterize soil variations in these agricultural systems and to determine precisely

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what these variations reflect, with consideration given to the periodicity of cultivation and shifts in demand for arable products. Thin section micromorphology offers a means of assessing these issues in the soil record, contributing to a more refined view of raised field agriculture. This work was originally carried out as part of “The Impact of Europe on Ecuador in the 16th Century” project, Department of Archaeology, University of York, through an Institutional Grant from the Leverhulme Trust, whose research support is gratefully acknowledged. We are indebted to the owners of Hacienda Zuleta, Galo Plaza and his nephew Fernando Polanco, for their considerable help and logistical support of the project during its different field-work phases. Sr. Rodrigo Chachalo and Senõra Avelina Sandoval are the owners of the property at La Cocha IV, and we would also like to acknowledge with thanks their co-operation. Freddy Acunã undertook much of the original field-work and is thanked for his invaluable contributions. Monica Bolanõs of the Instituto Nacional de Patrimonio Cultural, Quito, Ecuador, is thanked for her consistent support of this work. George Macleod manufactured the thin sections at the University of Stirling. We are grateful to Ronald Lippi, Charly French, and Richard Macphail for constructive comments on an earlier draft of the manuscript.

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Received June 6, 2001 Accepted for publication October 1, 2001

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