An elusive record exposed: radiocarbon chronology ...

Azania: Archaeological Research in Africa

ISSN: 0067-270X (Print) 1945-5534 (Online) Journal homepage: http://www.tandfonline.com/loi/raza20

An elusive record exposed: radiocarbon chronology of late Holocene human settlement in the northern Congo Basin, southern Central African Republic Karen D. Lupo, Christopher A. Kiahtipes, Dave N. Schmitt, Jean-Paul Ndanga, D. Craig Young & Bernard Simiti To cite this article: Karen D. Lupo, Christopher A. Kiahtipes, Dave N. Schmitt, Jean-Paul Ndanga, D. Craig Young & Bernard Simiti (2018): An elusive record exposed: radiocarbon chronology of late Holocene human settlement in the northern Congo Basin, southern Central African Republic, Azania: Archaeological Research in Africa, DOI: 10.1080/0067270X.2018.1471798 To link to this article: https://doi.org/10.1080/0067270X.2018.1471798

Published online: 18 May 2018.

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AZANIA: ARCHAEOLOGICAL RESEARCH IN AFRICA https://doi.org/10.1080/0067270X.2018.1471798

An elusive record exposed: radiocarbon chronology of late Holocene human settlement in the northern Congo Basin, southern Central African Republic Karen D. Lupoa, Christopher A. Kiahtipesb, Dave N. Schmitta, Jean-Paul Ndangac, D. Craig Youngd and Bernard Simitie a Department of Anthropology, PO Box 750336, Southern Methodist University, Dallas, Texas, United States of America, 75275; bInstitut für Ur- und Frühgeschichte, Universität zu Köln, Nordrhein-Westfalen, 50823 Köln, Germany; cCentre Universitaire de Recherche et de Documentation en Histoire et Archeologie Centraficaines, Avenue des Martyrs, Université de Bangui, Bangui, Central African Republic; dFar Western Anthropological Research Group, 3656 Research Way, Suite 32, Carson City, Nevada, United States of America, 89706; e Ministère l’Enseignement supérieur, de la Recherche, de la Science et de la Technologie, Avenue des Martyrs, Université de Bangui, Bangui, Central African Republic.

ABSTRACT

Archaeological surveys and excavations in the NGotto Forest Reserve, Central African Republic, discovered 98 artefact concentrations or cultural features that included ceramic scatters, iron-ore mines and iron smelting features. These investigations provide, for the first time, a series of radiocarbon dates that chronicle the timing and context of prehistoric occupation along the northern margin of the Congo Basin rain forest in the Central African Republic. Thirty-three age estimates from 19 sites are distributed throughout the late Holocene and together document 2500 years of occupations. A number of the dates are from iron extraction and processing features that reflect extensive precolonial use of the area between about AD 1750 and 1840, while a radiocarbon date of 2179 ± 37 BP in direct association with pottery signals settlement by ceramic-bearing peoples perhaps as early as 350 cal. BC. Three radiocarbon dates from two sites reflect occupations during the purported hiatus and reduction in regional forest populations c. 1400-800 BP and five dates from four additional sites in southern Central African Republic rain forests also fall during this interval. In concert with scrutiny of summed probability distributions and potential artefacts embedded within the radiocarbon calibration curve, the number of these dates question the reality of this occupational hiatus, at least in the north-central Congo Basin. RESUMÉ

Des prospections et fouilles archéologiques effectuées dans la réserve forestière de NGotto, en République centrafricaine, ont permis de découvrir 98 concentrations d’artefacts ou restes d’activité, y compris des dispersions de céramiques, des sites d’extraction de minerai de fer et des fourneaux pour la fonte de ce métal. Ces études fournissent, pour la première fois, une série de datations radiocarbone qui retracent la chronologie et le

CONTACT Karen D. Lupo

[email protected]

© 2018 Informa UK Limited, trading as Taylor & Francis Group

ARTICLE HISTORY

Received 3 September 2017 Accepted 13 November 2017 KEYWORDS

Central Africa; chronology; Iron Age; pre-colonial; radiocarbon; rain forest

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contexte de l’occupation préhistorique le long de la bordure nord de la forêt tropicale du bassin du Congo en République centrafricaine. Trente-trois estimations d’âge provenant de 19 sites s’échelonnent tout au cours de l’Holocène tardif, et dans leur ensemble documentent 2500 années d’occupation. Un certain nombre de datations proviennent de contextes d’extraction et de traitement du fer qui reflètent une utilisation pré-coloniale intensive de la région entre 1750 et 1840 environ ap. J.-C. Par ailleurs, une datation au radiocarbone de 2179 ± 37 BP, directement associée à des céramiques, indique une occupation par des communautés utilisant la poterie, peut-être dès 350 cal. av. J.-C. Trois dates provenant de deux sites indiquent une occupation pendant c. 1400-800 BP, période qui avait été proposée comme un hiatus avec une réduction dans les populations de la forêt. Enfin, cinq dates provenant de quatre sites supplémentaires dans les forêts tropicales du sud de la République centrafricaine tombent également dans cet intervalle. De concert avec l’examen des distributions de probabilité sommées et des artefacts potentiels incorporés dans la courbe de calibration des datations radiocarbone, le nombre de ces dates remet en question la réalité de ce hiatus dans l’occupation, du moins pour ce qui est du nordcentre du bassin du Congo.

Introduction ‘ … just as no archaeologist would ignore or even throw away finds from excavation or surface survey simply because they do not relate to his specific interests, radiocarbon dates must never be discarded in the sense of being left unpublished’ (Wotzka 2006: 272).

Archaeological investigations in Central Africa have been conducted in a variety of contexts and provide important information on the chronology of human settlement. One of the fundamental research questions for the prehistory of the region is the timing and nature of human dispersals into the rain forest zones (e.g. Eggert 1992; Mbida et al. 2000; Oslisly 2001; Mercader 2002; Lavachery et al. 2005; Eggert et al. 2006; Meister and Eggert 2008; Neumann et al. 2012; Morin-Rivat et al. 2014). Although archaeological evidence is widespread, one of the more conspicuous gaps in this record is along the northern edge of the Congo Basin in the southern Central African Republic where the results of only a few archaeological projects have been reported. This is especially the case for radiocarbon age estimates as the only published dates from rain forest contexts are from Batalimo and a handful of associated sites south of Bangui (Bayle des Hermens 1975; Eggert 1987; Koté 1992; see also de Maret 1985; Van Neer 2000) and at Bécaré II and Sabélé (I and II) in the southwestern reaches of the country near Nola (Lanfranchi et al. 1998). While this paucity of radiocarbon data can largely be attributed to external social, political and especially economic issues, it nonetheless represents a noticeable void in the Central African archaeological record (cf. Wotzka 2006: Figure 3; MorinRivat et al. 2017; Figure 1). As part of three field visits to the Central African Republic rain forest we conducted archaeological surveys and excavations in four separate project areas (Figure 1). Given the lack of radiocarbon dates, one of our primary goals was to collect and process charred organic remains from sites across the region to develop a much-needed record

AZANIA: ARCHAEOLOGICAL RESEARCH IN AFRICA

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Figure 1. Plan of the NGotto Forest Reserve region, southern Central African Republic, showing the location of the Boua, Poutem, Bagbaya and Limbumba project areas.

of the timing of human occupation. The results of these investigations and analyses are presented below. Wood charcoal samples (and in a few instances charred Elais guineensis [oil palm] endocarps) from 19 sites were subject to radiocarbon assay and, together with previously reported dates from the southern Central African Republic (Koté 1992; Lanfranchi et al. 1998), provide a suite of chronometric age estimates that reflect persistent human use of the north-central Congo Basin over the past 2500 years. These age estimates offer evidence for the occupation of at least six sites during the heart of the marked decline in dated contexts documented elsewhere in Central African forested zones (Oslisly 2001; Wotzka 2006; Oslisly et al. 2013a, 2013b; Morin-Rivat et al. 2014, 2016) and the current project provides evidence for intensive late Holocene iron mining and smelting along the Lobaye River, especially near the end of the eighteenth century AD.

Project area and methods The archaeological data reported here come from surveys and limited excavations conducted in and adjacent the NGotto Forest Reserve (NFR) in the southwestern Central African Republic (Figure 1). The NFR is a triangular-shaped area encompassing some 3250 km2 along the northern edge of the Congo Basin. The forest contains a large segment of the southern Mbaeré River and is bounded on the east by the Lobaye River. The country’s border with the Republic of Congo marks its southern boundary. The Bodingué River parallels the southern boundary of the NFR and flows into the lower Mbaeré River to the Lobaye River, which continues its easterly flow to ultimately drain into the

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Ubangui River. These river courses represent major components of the vast, interconnected Congo River system that served as a regional conduit for economic, demographic and ideological exchange during the pre-colonial and colonial periods (Bahuchet 1985). The area is characterised by high annual average temperatures (∼25°C), extreme humidity and annual rainfall totals that often exceed 1500 mm, most of which falls during a prominent rainy season between May and November. Regional soils are generally nutrient-poor and are made up of deep deposits of weathered sands or somewhat shallower sandy clay-loams (Réjou-Méchain et al. 2008). Substrates in the region are predominantly Cretaceous sedimentary rock with less frequent exposures of Precambrian igneous material in the eastern NFR. Some areas contain oxidised exposures of weathered laterite. Floristically, the forest is located at the border of White’s (1983) Guineo-Congolian rain forest (GCRF) centre of endemism and the GCRF/Sudanian woodland transition zone. The extensive seasonally inundated floodplains and peatland swamps are covered by a mosaic of open Raphia sp. (palm) swamps, Uapaca sp. (Phyllanthaceae)-dominated riparian forests and lowland forest taxa that tolerate inundation such as Guibourtia demeusei (African rosewood) and Berlinia grandiflora. Sandy soils on the massifs separating the river valleys support semi-deciduous forest dominated by Manilkara mabokeensis (Sapotaceae) and Ongokea gore (boleko nut), as well as mosaics of wooded savannas and gallery forests where Celtis mildbraedii (Natal white stinkwood), Terminalia superba (limba/korina) and Musanga cecropioides (African corkwood) are abundant. The latter species are especially common on weathered clay-loam soils, but these plant communities also have high concentrations of pioneer taxa that would have been favoured by past anthropogenic disturbance (Réjou-Méchain et al. 2008: 670; Yongo 2003). Survey and excavations were undertaken in 2007, 2009-2010 and 2011. Field investigations centred on areas near Boua (also known as ‘Zoundode’), Poutem and the village of Bagbaya associated with prominent iron-ore mines and evidence for extensive pre-colonial smelting (Lupo et al. 2015). Excavations were also undertaken in the southwestern part of the NFR at Limbumba along the northern bank of the Bodingué River (Figure 1). Sites were identified by pedestrian surface reconnaissance, through interviews with local villagers and by reference to a large, hand-drawn heritage map constructed by representatives living in and adjacent to the NFR. Due to the thick ground cover of forest debris, surface reconnaissance was restricted to graded roads, wooded savannas (or ‘wet’ savannas; Bahuchet and Guillame 1982), selected footpaths and agricultural fields, along with the inspection of exposed sediment profiles associated with stream beds, diamond mines and brick and trash pits. Palaeoenvironmental investigations (notably the extraction of sediment cores) were conducted in conjunction with most of the NFR archaeological work (see Kiahtipes et al. 2011; Lupo et al. 2015; Kiahtipes 2016). Previous stable carbon isotope studies are reported by Neumer et al. (2008). Site locations were mapped using hand-held GPS units and selected sites were tested largely using 1 × 1 m and/or 1 × 0.5 m units that were hand excavated with picks, shovels and trowels. Excavations at Limbumba also employed 30 × 30 cm shovel probes to identify site boundaries. Except for the more extensive test excavations at Limbumba (9 m2 in area, including a 1 × 4 m trench), sites were investigated using between one and three test units that focused on exposing the archaeological deposits in profile and collecting datable organics from artefact-bearing layers. In a few instances we encountered exposed profiles containing a buried cultural-bearing horizon(s) and investigations


5

involved cleaning, mapping and describing the exposure and extracting datable organics from the anthropogenically modified layer(s). Excavated sediments were hand sorted and examined for artefacts and selected sediment samples were screened through 0.64cm mesh. Artefacts and ecofacts were collected from each tested site for analysis and in some instances only examples of the observed ceramic types were collected. Selected in situ charcoal samples from sub-surface investigations were sent to the Accelerator Mass Spectrometry Laboratory, University of Arizona or Beta Analytic, Inc. for accelerator mass spectrometry (AMS) analysis. Overall, test investigations were undertaken at 35 sites and 33 charcoal samples from 19 of these were assayed for radiocarbon age estimates. All the resulting radiocarbon dates are on charred organics recovered in direct association with cultural materials and are expressed as 14C years BP. Calibrated ages (cal.) were calculated with OxCal version 4.3 (Bronk Ramsey 2009) using the IntCal13 northern hemisphere calibration curve (Reimer et al. 2013). Summed probability distributions were computed using OxCal version 4.3 and plotted using the R statistical computing environment version 3.3.0 (R Core Team 2016). Although some artefacts and samples remain housed at the Department of Anthropology at Southern Methodist University, most of the other collections deposited at the Centre Universitaire de Recherche et de Documentation en Histoire et Archéologie in Bangui were stolen or destroyed when the facility was sacked during the coup d’état of 2013. Unfortunately, these materials included unanalysed ceramic collections and the following discussions on the types of associated ceramic artefacts are based only on the remaining collections and field notes.

The sites Surveys in the NFR identified nearly one hundred archaeological sites or artefact concentrations as well as a number of isolated lithic and ceramic artefacts. These sites contain a range of artefact types and densities in a variety of contexts and include slag mounds in secondary forests and agricultural fields, plus scatters of potsherds across open savanna woodlands and in modern road cuts through gallery forests. While some of the recorded artefact scatters occur in close proximity and likely represent portions of single sites, their distributions and the chronology of the sampled deposits reflect numerous occupational episodes spanning the late Holocene. Survey, test excavations and AMS radiocarbon assays of associated organics provide a first look at the occupational history of the rain forest’s northern boundary in the Central African Republic between the fifth century BC and the late nineteenth century AD. The results presented below are grouped by the villages used as our base camps while in the field. Boua and Poutem Numerous archaeological sites were identified in the Boua and Poutem vicinities with most discovered in wooded savannas and on two-track roads, including the primary east-west thoroughfare that connects the two villages. Fifteen artefact scatters were identified in the Boua vicinity (Figure 2) and charcoal from excavations at three of these was processed to obtain radiocarbon age estimates. Site Z02 was identified as a 50 m northto-south-oriented scatter of weathered ceramic fragments eroding out of a low berm

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Figure 2. Location of archaeological sites (circles) in the Boua project area (see Figure 1). Note the forested areas (green) broken by wooded savannas (yellow). Labelled sites were subject to radiocarbon dating.

that runs parallel to a footpath and shallow drainage south of Boua. The site had clearly undergone extensive deflation and erosion with only a veneer of the lowest cultural deposits remaining intact. A narrow profile excavated into a stretch of the eroding berm revealed

Figure 3. Location of archaeological sites (circles) in the Poutem project area (see Figure 1). Note the forested areas (green) broken by wooded savannas (yellow). Labelled sites were subject to radiocarbon dating.


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Table 1. Radiocarbon dates and calibrated calendrical age estimates on charcoal from sites in the vicinity of Poutem (P) and Boua (Z). Site

Specimen number

Laboratory number

P01

3

Beta-287971

P02

7

P02

Depth below surface (cm)

Radiocarbon age BP

8

220 ± 40

AA-96498

105

143 ± 34

1

AA-96496

49

1652 ± 37

P02 P02 Z02

3 9 2

Beta-282420 AA-96497 AA-96500

72 154 10

1690 ± 40 Modern 2179 ± 37

Z05 Z13 Z13

2 6 10

Beta-287972 Beta-282421 AA-96499

70 80 70

1230 ± 40 1140 ± 40 1264 ± 36

Calibrated age(s)

Percentage probability

AD 1524-1558 AD 1631-1694 AD 1726-1814 AD 1838-1868 AD 1917-1950 AD 1668-1782 AD 1797-1891 AD 1908-1947 AD 260-280 AD 324-437 AD 444-473 AD 486-534 AD 250-422 366-156 BC 134-116 BC AD 683-886 AD 775-985 AD 666-778 AD 790-868

3.2 32.7 43.3 0.9 15.3 44.5 35.1 15.8 3.4 77.0 3.4 11.6 95.4 93.0 2.4 95.4 95.4 81.4 14.0

a relatively thin, shallow deposit (∼10 cm thick) of charcoal-flecked fine sand and small ceramic fragments. A charcoal sample from this lens in direct association with undecorated ceramic sherds returned a date of 2179 ± 37 BP (AA-96500; Table 1) and is some of the region’s oldest evidence for the use of pottery. A scatter of artefacts and truncated pit features exposed in a deflated road cut was recorded as Z05. This site appears as a long linear smear of debris including charcoal, occasional pieces of iron slag and fragments of pottery. A test excavation measuring 1.0 × 0.5 m to a depth of 1 m exposed part of an intact pit feature yielding dozens of chunks of slag, small ceramic fragments and pieces of charcoal. Radiocarbon assay of charcoal recovered at a depth of 70 cm returned a date of 1230 ± 40 BP (Beta-287972; Table 1), marking a use-episode between cal. AD 683 and 886. Site Z13 was discovered by a local Bofi forager while attempting to dig a giant pouched rat (Cricetomys emini) out from its burrow. His efforts exposed a few chunks of slag and charcoal in a horizon between 62 and 90 cm below the modern ground surface. Subsequent archaeological excavations encountered additional pieces of slag along with a few plain (undecorated) degraded potsherds and fragments of fired/burned clay. Radiocarbon assay of associated charcoal returned dates of 1140 ± 40 BP and 1264 ± 36 BP (Beta-282421 and AA-96499, respectively; Table 1), which provide overlapping calibrated ages during the seventh century cal. AD. These dates, along with the calibrated age estimate from site Z05, fall within an observed decline in the number of radiocarbon dates in parts of Central Africa between the sixth and tenth centuries cal. AD (e.g. Wotzka 2006; Oslisly et al. 2013b; Morin-Rivat et al. 2014, 2016). Archaeological survey in the Poutem area identified numerous artefact scatters (Figure 3). Site P01 was discovered in a road margin just south of a prominent bend in the Lobaye River. Surface reconnaissance and test excavations found a shallow layer of

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charcoal-stained silt and sand containing ceramics and a few quartz core reduction flakes. At the bottom of this layer charcoal in direct association with ceramic sherds displaying roulette en fibre designs (cf. Livingstone Smith 2007: Figure 1A) returned an AMS date of 220 ± 40 BP (Beta-287971; Table 1) marking an eighteenth-century AD occupation. Although the quartz débitage may represent a separate occupation and the deposits are mixed, test excavations revealed no such evidence and it appears as if the stone artefacts are contemporaneous with the pottery and provide another lithic-ceramic association in a late Holocene Congo Basin site (see Livingstone Smith et al. 2017). Just east of Poutem, modern disturbance at the intersection of two roads exposed a deep sediment profile containing large potsherds. Systematic excavation of the P02 exposure encountered charcoal, quartz débitage, a quartz scraping tool and additional ceramics 48-75 cm below the modern ground surface from what appeared to be a pit feature that was approximately 70 cm in diameter. This pit feature yielded concentric rings of roulette en fibre pottery fragments surrounding a nearly complete smaller vessel (14.0 × 12.5 cm) with a slightly convex base and exhibiting both combed and roulette designs. Such pits, often with interments of ceramics within other ceramics, are a distinctive late Holocene pattern in tropical Africa (Eggert 1992; Wotzka 1995; Livingstone Smith et al. 2017). Radiocarbon assay of two charcoal samples from the pit feature at depths of 49 and 72 cm returned overlapping ages of 1652 ± 37 BP (AA-96496) and 1690 ± 40 BP (Beta282420), indicating that the ceramics and infilling sediments were deposited in a single event between the second and fourth centuries cal. AD. Like at site P01, the pieces of flaked quartz were found in direct association with ceramics and likely represent utilitarian artefacts used in scraping and incising tasks. Two samples of charcoal collected approximately 50 cm northeast of the feature at depths of 105 and 154 cm below the surface yielded modern and near-modern dates (Table 1). These samples were likely buried at this depth through modern quarrying of the lateritic crust that underlies the site area and subsequent filling of the adjacent excavated area. This activity would account for both the exposure of the intact second to-fourth-century AD ceramic feature and the deposition of disturbed material within the same excavation unit. Bagbaya A rich late Holocene archaeological record was discovered near Bagbaya (see Lupo et al. 2015) that included iron ore mines, slag mounds and low mound features in forests and savanna woodlands that appear to have been both iron working and habitation areas. Age estimates from radiocarbon analysis of charcoal from 13 of these sites are presented in Table 2. The two mines represent modified exposures of iron-rich volcanic deposits east of the Lobaye River. Several low mafic basalt outcrops and boulders occur between the two mines and suggest that they are in the same north-to-south-trending volcanic flow. Both quarries represent fissure and collapse structures containing excavated adits, pits and bulbous caverns that in some areas exhibit clusters of linear tool marks produced during mining activities. Conservative volumetric estimates suggest that some 1000 m3 of ore has been removed from the two sites (Lupo et al. 2015). Nineteen mounds of slag were recorded in the Bagbaya vicinity and seven of these features were subject to test excavations. A number of the slag mounds identified to us by the inhabitants of Bagbaya (which translates to ‘iron market’) are named after the clans that


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Table 2. Radiocarbon dates and calibrated calendrical age estimates on charcoal from sites in the Bagbaya vicinity. Specimen number

Laboratory number


BB01b

30

AA-94530

90

168 ± 35

BB01b

31

AA-94531

112

207 ± 35

BB01b

29

AA-94529

50

215 ± 34

BB03b

36

AA-94532

24

148 ± 34

BB05b

41

AA-94534

61

187 ± 34

BB05b

32

AA-94533

24

231 ± 34

LL01b

80

AA-94535

40

412 ± 34

ML01

83

AA-94536

90

1938 ± 36

ND01

3

AA-94537

55

160 ± 35

ND02b

76

AA-94538

74

242 ± 34

NG01b

74

AA-94539

60

217 ± 48

NZ03

17

AA-94541

27

494 ± 34

NZ03 NZ03

12 23

AA-94542 AA-94540

33 29

593 ± 34 706 ± 35

OB01b

67

AA-94543

33

152 ± 35

OB02b

49

AA-94544

25

210 ± 34

OB05

54

AA-94546

25

131 ± 34

OB05

53

AA-94545

22

188 ± 39

OB06

63

AA-94547

28

131 ± 34

Site

b

Slag mound feature.

Radiocarbon age BP

Calibrated age(s)


AD 1659-1706 AD 1719-1826 AD 1832-1884 AD 1918-1950 AD 1641-1690 AD 1726-1813 AD 1918-1950 AD 1640-1690 AD 1728-1810 AD 1925-1950 AD 1666-1783 AD 1796-1891 AD 1908-1950 AD 1648-1696 AD 1725-1814 AD 1836-1877 AD 1916-1950 AD 1528-1550 AD 1634-1684 AD 1735-1806 AD 1930-1950 AD 1428-1522 AD 1575-1624 37-28 BC 24-10 BC 3 BC-AD 132 AD 1664-1708 AD 1718-1826 AD 1832-1886 AD 1912-1950 AD 1522-1574 AD 1626-1684 AD 1736-1805 AD 1935-1950 AD 1521-1590 AD 1585-1590 AD 1626-1706 AD 1720-1819 AD 1832-1880 AD 1915-1950 AD 1330-1340 AD 1396-1453 AD 1297-1413 AD 1249-1315 AD 1356-1389 AD 1666-1784 AD 1795-1891 AD 1908-1950 AD 1670-1799 AD 1728-1810 AD 1925-1950 AD 1670-1779 AD 1798-1894 AD 1904-1943 AD 1645-1700 AD 1720-1818 AD 1832-1880 AD 1915-1950 AD 1670-1779 AD 1798-1894 AD 1904-1943

17.6 47.6 11.4 18.8 32.2 46.9 18.2 32.2 46.9 16.3 45.8 32.3 17.3 20.8 50.1 4.6 19.9 3.3 42.0 38.6 11.6 79.6 15.8 1.3 2.5 91.5 5.6 0.2 28.9 41.1 11.0 47.0 29.9 7.5 5.6 0.2 28.9 41.1 4.4 15.1 2.1 93.3 95.4 77.5 17.9 47.3 30.5 17.6 39.6 48.5 17.3 39.6 40.7 15.1 21.3 48.2 6.8 19.0 39.6 40.7 15.1

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K. D. LUPO ET AL.

still occupy the village and claim ownership by virtue of ancestral ties. Tuyère fragments were observed on the surface of most mounds and in excavated deposits associated with blocks of slag and oxidised slag gravels. The slag in each mound consisted of vesicular angular and sub-angular blocks that appear to represent primary smelting detritus. A number of the features also contained a few plain-ware (i.e., undecorated) potsherds, charred palm nuts and/or furnace-related remains, including pieces of baked clay and burned termite mound matrix (Lupo et al. 2015). Radiocarbon assay of charcoal and charred E. guineensis endocarps from excavated slag mounds returned calibrated dates ranging from the seventeenth to the twentieth centuries AD (Table 2). These dates point to a brief and extensive phase of iron extraction and smelting during the last three centuries and the calibrated probabilities tend to point towards intensive smelting near the end of the eighteenth century cal. AD. Although estimates of slag volumes should be regarded with some scepticism (Iles 2016), volume approximations for the Bagbaya mounds equate to thousands of cubic metres and the level of production at this time must have approached other concentrated iron-smelting areas in the forests of West and Central Africa, including Bassar Period 2 in northern Togo (de Barros 1986) and Dapaa in Ghana (Goucher 1981). Six additional radiocarbon samples were collected from two large site complexes in wooded savannas and gallery forests just outside the NFR and to the east of the Lobaye River (Lupo et al. 2015: Figure 1). The OB complex contained a diffuse scatter of slag and ceramic sherds associated with low sediment mound features concentrated within a roughly 1 km island of wooded savanna bordered by semi-deciduous rain forest cover. Mound features and artefacts also occur within the immediate forested area and signal recent colonisation of the open area by forest. Residents of Bagbaya identified this area as the location of their ancestral village. Investigations at two of these features encountered tuyères, slag and plain and rouletted ceramics in buried charcoal-stained deposits, with one feature (OB06) containing smooth pieces of baked, brick-like clay that may represent furnace fragments. Radiocarbon analysis of associated charcoal samples returned duplicate dates of 131 ± 34 BP (AA-94546 and AA-94547) and three other overlapping age estimates of 152 ± 35 BP (AA-94543), 210 ± 34 BP (AA-94544) and 188 ± 39 BP (AA-94545) (Table 2). Calibrated age ranges for these samples span the sixteenth to the twentieth centuries cal. AD and support local oral histories. The NZ complex was found in a separate, larger wooded savanna and is marked by slag and roulette en bois and roulette en fibre ceramic sherds associated with five low mound features. Excavations at one feature (NZ03) exposed a lens containing pieces of slag, pottery, tuyère and fire-altered clay, plus a quartz hammerstone and quartz spall. Three associated charcoal samples were subject to radiocarbon analysis and mark at least two occupations during the thirteenth to fifteenth centuries cal. AD (Table 2). Four additional sites were recorded south of Bagbaya during a brief survey of wooded savannas and small villages near the confluence of the Lobaye and Mbaeré Rivers (see Figure 1). One, site LL01, is a partially deflated slag mound in an abandoned agricultural field containing abundant tuyère fragments and a few lithic artefacts. A portion of the feature had been excavated by local fishermen to extract slag for use as net weights, leaving an approximately 80 cm deep profile exposure. Charcoal from a dense layer of oxidised slag and tuyère fragments in the exposure returned an AMS age estimate of 412 ± 34 BP (AA-94535; Table 2) and marks a smelting episode near the end of the fifteenth century


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cal. AD. A nearby site — ML01 —consisted of a 45 cm thick lens of dark, charcoal-flecked sediment, weathered ceramic sherds and snail shell exposed in the wall of a recent trash pit in the village of Moloukou. Assay of charcoal from near the bottom of the lens returned a date of 1938 ± 36 BP (AA-94536; Table 2: 3 cal. BC – cal. AD 132) and provides the earliest radiocarbon date for human occupation in the Bagbaya vicinity. Limbumba Limbumba is an eighteenth- to early nineteenth-century AD habitation site along the north bank of the Bodingué River in the southern part of the NFR (Figure 1; Table 3). The site was reported to us by the nearby inhabitants of Ndele as an ancestral village occupied by their grandparents and ‘those before them’. Investigations employed nine 1 × 1 m excavation units and a series of shovel probes that identified an approximately 100 × 80 m area of dark, charcoal-stained loamy sand containing abundant ceramic sherds. Excavations in the northeastern portion of the site encountered a sub-surface pit feature that was similarly rich in charcoal and pottery (Figure 4). Overall, hundreds of potsherds were recovered from limited excavations and included a variety of incised and combdragged designs, plus abundant roulette en bois and cordelette or flexible roulette patterns (Mercader et al. 2000: Figure 6; Livingstone Smith 2007). Additional materials include chunks of slag and iron ore, a small piece of shaped iron, charred palm nuts, a few quartz flakes, a modified/scratched quartz cobble and a small collection of mammal bones that represent the only archaeological faunas from our NFR investigations. The mammal remains include forest hog (Potamochoerus porcus) and blue duiker (Cephalophus monticola) teeth and a few small artiodactyl limb bone fragments. Both forest hog and blue duiker are extant in the NFR and are taken for food today by regional foragers and farmers, especially the latter (Lupo and Schmitt 2005, 2017; Schmitt and Lupo 2008). Four dates were extracted from buried charcoal associated with pottery in the darkly stained sediments and provide overlapping age estimates that place the occupation(s) of this site within the last three centuries AD (Table 3). An additional date of 2380 ± 40 Table 3. Radiocarbon dates and calibrated calendrical age estimates on charcoal from excavations at Limbumba. Site

Specimen number

Laboratory number


Radiocarbon age BP

LM

02F6

Beta-234983

30

120 ± 40

LM

03F7

Beta-233555

18

200 ± 40

LM

01F7

Beta-233556

48

2380 ± 40

LM

04F12

Beta-233557

51

210 ± 40

LM

05F12

Beta-234984

57

160 ± 40

Calibrated age(s)


AD 1675-1778 AD 1799-1942 AD 1642-1698 AD 1724-1815 AD 1834-1878 AD 1916-1950 741-687 BC 664-646 BC 550-384 BC AD 1530-1540 AD 1634-1696 AD 1725-1814 AD 1836-1877 AD 1916-1950 AD 1663-1710 AD 1717-1890 AD 1910-1950

36.1 59.3 24.8 47.7 4.6 18.3 8.5 2.3 84.8 0.6 28.5 46.2 2.9 17.1 16.8 60.8 17.8

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K. D. LUPO ET AL.

Figure 4. Excavation unit in progress at Limbumba showing the characteristically dark, charcoalstained sediment. Charcoal from the pit feature at left provided overlapping dates of 160 ± 40 and 210 ± 40 BP (see Table 3).

BP (Beta-233556) was extracted from woody charcoal and provides the oldest age estimate recovered from the NFR. The sample that returned this early date was collected from the bottom of a contiguous cultural-bearing lens exposed in trench excavations that showed no evidence of mixing. A few pieces of flaked quartz recovered from this lens may have been deposited with eighteenth- to twentieth-century food bones and ceramics, but it would not be surprising if the lithic detritus were associated with the early date and this alluring, river-margin setting supported multiple occupations that included an earlier Iron Age/Neolithic component c. 550-384 cal. BC.

Summary and discussion The distribution of calibrated radiocarbon dates from NFR archaeological sites contributes an important piece to the larger and rather fragmentary portrait of late Holocene human settlement of the Central Africa rain forest (e.g. Wotzka 2006; Eggert 2016). The record points to people inhabiting the NFR throughout the past 2500 years, including a cluster of dates c. cal. AD 1300-1600 during the Late Iron Age increase in dated sites/components documented in other portions of Central Africa (e.g. Wotzka 2006; Oslisly et al. 2013a; Morin-Rivat et al. 2014). Moreover, the results of radiocarbon assay identified a sizeable late Holocene iron production centre along the Lobaye River with multiple calibrated age estimates ranging from the seventeenth century to the early twentieth century cal. AD. Chronometric data from neighbouring forest contexts reveal an upsurge in cultural deposits during this time (Wotzka 2006; Morin-Rivat et al. 2014), but not at the scale discovered


13

in the NGotto Forest. Although the Early Iron Age emerges in Central Africa approximately 2800 years ago (de Maret 2004; Essomba 2004 and references therein), it remains to be identified here or elsewhere (Eggert 1987; Koté 1992; Lanfranchi et al. 1998) in the forested regions of the southern Central African Republic. A handful of recent studies have used pooled probability distributions of Central African forest radiocarbon age estimates to infer late Holocene demographic trends (Lézine et al. 2013; Oslisly et al. 2013a, 2013b; Morin-Rivat et al. 2014, 2016). These studies emphasise two important events: a demographic expansion among incoming farming populations centred at the first centuries cal. BC/AD and a ‘hiatus’ or population crash around cal. AD 500. However, these interpretations of the radiocarbon record of Central Africa require a more careful consideration of the assumptions of summed probability distributions, biases introduced through sampling strategies and potential artefacts embedded within the radiocarbon calibration curve. To date, Wotzka’s (2006) review of the chronometric record remains the most carefully considered and is supported by the largest sample size (N = >600). Thus, this discussion attempts to triangulate the NFR radiocarbon data and neighbouring records from forested Central African Republic contexts (Table 4) within the larger archaeological sequence of Central Africa reported by Wotzka (2006), while drawing comparisons with geographically adjacent studies by Morin-Rivat et al. (2014, 2016) and the more ambitious claims of Oslisly et al. (2013a, 2013b). Together, these records offer relevant insights into the fundamental empirical issues surrounding our understanding of the settlement and occupation of the GuineoCongolian forest zone. Understanding the problems with such estimates and how best to interpret them requires a brief consideration of the assumptions used and methods employed. Oslisly et al. (2013a, 2013b) present the most problematic dataset as they directly equate the number of radiocarbon dates per century as a direct measure of population density and provide no supplementary data with which to replicate their analysis. The authors posit that the absence of dates between 700-1100 cal. AD marks a ‘hiatus’ or population crash in Gabon based on a subset of 76 dates (Oslisly et al. 2013b: Figure 3). MorinRivat et al. (2014, 2016) present a more sophisticated approach to the problem using summed probability distributions of 41 and 49 dates, respectively, through the OxCal calibration software (Bronk Ramsey 2009). Although the method is quantitatively more sophisticated, they also suggest an occupational hiatus during the same time frame. What these studies fail to consider, however, is that summed distributions of calibrated radiocarbon dates, either as histograms or as probability-densities, reflect the probability that one of the sampled dates will have a given range of dates and not the population of humans or archaeological sites. Furthermore, it is necessary to consider whether the peaks in histograms or probability-density distributions reflect, to any extent, over-estimations driven by plateaux in the radiocarbon calibration curve. Previously reported dates in the southern Central African Republic forest from Batalimo, Eyo, Bobélé II and probably also Sikilongo fall during this purported hiatus (Table 4). In the NFR, radiocarbon assays of charcoal from Z05 and Z13 (and possibly P02) also yielded dates within the hypothesised hiatus and, as noted above, show an overall greater representation of dates within the last couple of centuries (Figure 5). Summed probability distributions of the NFR records show some broad similarities to Morin-Rivat et al.’s (2014, 2016) results, but the bimodal distribution of dates is less

14

K. D. LUPO ET AL.

Table 4. Radiocarbon dates and calibrated calendrical age estimates on charcoal from excavations in Central African Republic forested contexts at Batalimo and neighbouring sites (Koté 1992: Table 10) and Sabélé I and II and Bécaré II (Lanfranchi et al. 1998). Component/ context

Laboratory number

Batalimo

ZVI

Bdy-462

240 ± 75

Batalimo Batalimo

ZVI ZII

Bdy-465 Gif-5898

1270 ± 125 1590 ± 90

Batalimo

ZIV

Bdy-304

1730 ± 120

Batalimo

ZVI

Bdy-581

1798 ± 101

Batalimo Batalimo

ZIII ZIII

Bdy-301 Bdy-306

1890 ± 130 1990 ± 210

Bobélé II Lingbangbo

CLb

Bdy-583 Bdy-464

1200 ± 100 110 ± 80

Lingbangbo

CLb

Bdy-255

430 ± 180

Lingbangbo Sikilongo

CLb -

Bdy-582 Bdy-303

559 ± 77 870 ± 210

Eyo

CLb

Bdy-579

1020 ± 115

Eyo

CLb

Bdy-461

1200 ± 120

Sabélé I Sabélé II

FPc CLb

LY-5921 LY-5922

630 ± 45 715 ± 35

Bécaré II

OSd

Beta-88067

1870 ± 70

Sitea

Radiocarbon age BP

Calibrated age(s)


AD 1470-1707 AD 1719-1826 AD 1832-1885 AD 1913-0 AD 552-1017 AD 255-301 AD 316-640 AD 29-39 AD 50-570 37-11 BC 2 BC-AD 428 AD 498-502 201 BC-AD 417 536-527 BC 522 BC- AD 436 AD 446-472 486-535 AD AD 658-1014 AD 1665-1786 AD 1792-1950 AD 1261-1710 AD 1717-1981 AD 1910-1950 AD 1277-1457 AD 694-746 AD 763-1432 AD 730-736 AD 769-1248 AD 606-1040 AD 1110-1115 AD 1283-1404 AD 1225-1233 AD 1243-1308 AD 1362-1386 21-11 BC 2 BC-AD 264 AD 273-331

53.6 26.2 5.9 9.7 95.4 4.9 90.5 0.5 94.5 0.6 94.5 0.2 95.4 0.2 93.7 0.5 1.1 95.4 38.9 56.5 80.1 11.9 3.3 95.4 2.1 93.3 0.3 95.1 95.2 0.2 95.4 1.5 82.8 11.1 0.7 88.1 6.6

a

An aberrant date of 140 ± 240 from Mondongué (Koté 1992) is not included. Stratigraphic layer containing cultural materials. c From a furnace pipe (tuyère) interior. d From oxidised sediment with slag (possible furnace interior). b

apparent. Null models based on an even distribution of radiocarbon dates at 50-year intervals, or five sets of randomly distributed dates of roughly equal sample sizes (N = 50), illustrate that both peaks and valleys in these distributions (Figure 5) are at least partially artefacts of the radiocarbon calibration curve. While there may have been an occupational hiatus in some portions of forested Central Africa c. 1300-800 years ago, the extant data in the northern Congo Basin, and careful consideration of the nature of those data, do not support this hypothesis. The conclusion to be drawn from these datasets is that the appearance of ceramic vessels and iron metallurgy in the Central African record is certainly associated with an increased footprint of human activities on the landscape and, as suggested by Morin-Rivat et al. (2014, 2016), with the potentially important impacts of recent human activities on forest cover in tropical Central Africa (see also Lupo et al. 2015).


15

Figure 5. The timing and scale of late Holocene human occupation in the north-central Congo Basin based on reported radiocarbon (calibrated) dates. Top to bottom: summed probability distribution of the 32 NFR dates (Tables 1–3); summed probability distribution of 41 dates from southeastern Cameroon and northern Republic of Congo (Morin-Rivat et al. 2014: Figure 2), 17 dates from forested contexts in the southern Central African Republic (Table 4), and all 90 dates presented above; summed probability distribution of dates at 50-year intervals and five random sampling runs.

Within the larger scheme of Central African prehistory and paleoenvironmental change, the NFR results support some of the broad conclusions outlined elsewhere. First, the appearance of ceramic vessels in the NFR archaeological record appears to have been contemporaneous with their appearance in other parts of Central Africa and fits within a broader increase in the visibility of human activities around the first centuries

16

K. D. LUPO ET AL.

BC/AD (Wotzka 2006). Second, although limited, NFR data on the temporal distributions of roulette-decorated ceramics match the spatio-temporal distributions reported by Livingstone Smith (2007), with the only modification (indeed, addition) to this record being the presence of roulette en fibre pottery in the Lobaye area just prior to 1500 BP (see Livingstone Smith 2007: 199–202). Furthermore, the increased visibility of past human activities and the density of dateable features appear to follow quickly after a general increase in the representation of light-demanding or pioneer taxa in palaeoecological records (see Lezine et al. 2013). Yet the NFR also shows a unique signature of extensive iron production associated with spatially discrete changes in fire activity and vegetation cover, followed by widespread forest rebound in response to colonial-era depopulation (Kiahtipes et al. 2011; Lupo et al. 2015; Kiahtipes 2016). Both the results of the overall distribution of dates from the NFR and the simple null models presented here demonstrate that the pursuit of additional well-resolved surveys and the recovery of radiocarbon age estimates remain a priority for unpacking the settlement history of Central Africa’s forests.

Acknowledgements Thanks go to Guy Amaye, Mark Caudell, Alain Kolet Guy, Eduard Mboula, Kristin Safi and Timothee Tikouzou for logistical support and/or technical assistance. Comments from two anonymous reviewers helped us to clarify and expand portions of our discussions that were admittedly in need; any shortcomings, however, are our own. Special thanks to the foragers and farmers in Boua, Baboundji, Poutem, Bagbaya and Ndele who welcomed us into their villages with open arms and provided friendship and support.

Funding Research in the NGotto Forest was supported by funding from Washington State University and a grant from the National Science Foundation (No. 0924242). Excavations at the site of Limbumba were supported by the National Geographic Society (grant: 38136-06). This research was permitted by the Central African Republic Ofﬁce of Scientiﬁc and Technological Research.

Notes on contributors Karen D. Lupo is a professor and current Chair at the Department of Anthropology at Southern Methodist University in Dallas, Texas. Utilising evolutionary theory, ethnographic records and ethnoarchaeological observations, her research examines human-animal interactions, vertebrate taphonomy and human ecology in both modern and prehistoric contexts. Christopher A. Kiahtipes is a post-doctoral researcher with the Universität zu Köln’s Institut für Ur- und Frühgeschichte - Forschungsstelle Afrika. He specialises in palynological analysis and Holocene human-environment dynamics in the Congo Basin and the Great Basin of western North America. Dave N. Schmitt is an archaeological consultant and Research Associate with the Department of Anthropology at Southern Methodist University. His research includes late Quaternary archaeology and mammalian biogeography in the Great Basin of western North America and ethnoarchaeological studies among Central African farmers and foragers. Jean-Paul Ndanga is an instructor and research archaeologist with the Centre Universitaire de Recherche et de Documentation en Histoire et Archeologie Centraficaines, Université de Bangui, Central African Republic. His research interests include lithic technology, prehistoric hunter-gatherers and Central African metallurgy.


17

D. Craig Young is a geoarchaeologist and Principal with the Far Western Anthropological Group in Carson City, Nevada. His research focuses on environmental influences and geomorphological processes affecting archaeological site formation and human interactions with changing late Quaternary landscapes. Bernard Simiti is an African historian and has served as a professor and Director at the Centre Universitaire de Recherche et de Documentation en Histoire et Archeologie Centraficaines, Université de Bangui. He is currently a Director at the Ministère l’Enseignement Supérieur, de la Recherche, de la Science et de la Technologie in Bangui, Central African Republic.

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