The Kaptlrnrin Formation - Harvard University...ties, fossil fauna are generally neither abundant...
Transcript of The Kaptlrnrin Formation - Harvard University...ties, fossil fauna are generally neither abundant...
WAMEAKUMA
The Kaptlrnrin Formation The Kapthurin Formation is exposed west of
Lake Baringo, Kenya, and forms the Middle
Hill 2002 and refirences therein). Hominid remains have been rccovcftd from sediments bracketed by
Pleistoctne portionofthe~mHillssequence(see
the Pumice Tuffmcmbcr(K2) and the 'Grcy Tuff;' now dated by the 'OArPAr method to between 509 9 ka and 543 f 4 ka @em and McBrearty 2002; Wood 1999). Archaeological sites arc a U r i i l e the Acheulian, MSA and possibly Sangoan and Faunsrmth. * TheseoccurwithintheMiddleSihsand Gravels member (K3) and tbc overlying Bddcd Tuff member (K4), the latter a complex of tufibous de positsandintercalatcd scdiment(Tal1m 1976,1978, Cornelissen et al. 1990; McBrearty et d. 1996; McBrearty 1999; Tryon and McBrearty 2002~). Tcphmstxatigraphic correlatim and a sequence of '"ArPAr dates on Wand lava document the tempo- ral succession and age of these sites. This work has demonstrated the complexity of the Acheulien-MSA aansitioq with intmtmtified Achwlian and MSA sites,andshown~thistransitimwithiatheBaringo basin had by -285 Ica (TIYOU and McBrtarty 200% b i n 0 and McBreglty 2002).
RiwarcbaeologicalresearchmtheKapthurin Formation focused on exposum north of the Ndau River, witb only cursory exambation of more south- erly areas (McBrearty a al. 1996566-570). slpvey in 2001 focused on -40 kmf of additional geologi- cally mapped Kapthurin Formation sediments (Martyn 1 969; Tallon 1976) soutb of the Ndau River, an area informally designated the "suuthem" Kapthurin Formation.
Middle Pleistocene shes from the 'southern" Kapthurin Formation of Kenya
Christian A. Tryon University of Connecticut Department of Anthropology
Storrs, Connecticut, 06269, USA E-mail: [email protected]
BOX U-2176
Introduction Fossil and genetic evidence is consistent with
an Afiican origin for Homo sapiens during the Mid- dle Pleistocene (Stringer and An- 1988; Howell 1999; M c B W and Brooks 2000). One notable feature of the Afican Middle Pleistocene archaeo-
Industrial Complex and its replacement by diverse industries of the Middle Stone Age (MSA) (Isaac 1982; Clark 1994; McBrearty 2001). Evidence for a suite of novel behaviors that characterize - modern& recentforagcrsisassociatcdwithh4iddlePkistocene MSA sites, and the earliest Homo sapiens fossils arc found with MSA artifacts (see Clark 1988; Deacoo and Deacon 1999; McBrearty and Brooks 2000 for recent summaries).
These data suggest significant behavioral changes during the Middle Pleistocene by hominids employing MSA technology. Previously, only broad contrasts between Acheulian and MSA sites were possible due to a lack of Afican sites with a well- preserved, dated, continuous sedimentary and ar- chaeological record spanning the Acheulian-MSA transition (Clark 1982; Wendorf er d. 1994). By examining this transition in detail, we may begin to understand the causes underlying hominid behavioral
to test recent hypotheses comlating the advent of the MSA with hominid speciation and dispersal (Foley and Lahr 1997; Lahr and Foley 1998,200 I). Recent research in the Kapthurin Formation of Kenya, which preserves a welldated sequence ofAcheulian and MSA sites, is therefore relevant to this discussion.
logical word is the end Of the IMg-livad A&&
adaptations that drove this change, as well as begin
Survey Objectives and Results FUM investigations conducted in the southern
Kapthurin Formation were directed at the recovery
ing localities, as well as detailed tephrostratigraphic obmt ioas of the Bedded Tamember. Walkover survey of known exposures lasted f h m 8 May- 1 June 2001, followed by test trenching at GnJh-75 and
full-scale block excavation, with some 52-m2 excavated in 2001. 'lbnty sites, primarily surface
sites re-investigated (Table 1 and Figure 1). Tht
Of a d d i t i d archae~logical sitn and fossil ~ ~ l l e c t -
Koimilot (GRm-74). Koimilot WBS later Chosen for
scattm,werediscovatd~gthes\pvey,withfour
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Figure 1: Archaeological and fossil sites hm the southern Kapthrvin Famatian. Included arc archaeological andpelaeOntologicalsites~the2001 survcy(seeTable 1). Localities26-28wereinitialiyreportedbyMcBrtarty ef 2. I ,sw, plant
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SASES c4mtealt Wgraphy
Galh-13 artifactsandfauna K 4
-12 a r t i f a c t s a n d h K3
GnJh-64 mtifacts K4
GnJh-65 artifactsandf;auna K3
AtQibUtiOn
Acheulian-MSA
Acheulw
?ssngoan-MsA
Actaculh
~~~ ~
artifactsandfauna
artifacts
artifacts
artifacts
artifacts
artifacts
-
K3
K3
K3 and K4
K3
K3
K4
artifactssndhuna
artifactsandfauna
artifactsandfauna
fauna
K3 ?MSA
K3 Acheulian
K4 Achedim
K3 NIA
15
16
17
18
19
Loc. 112
Loc. 113
Loc. 114
Loc. 115
Loc. 116
artifacts
artifacts
idfacts
artifbasandfauna
artifactsandhuna
artifiicts
K3 Acheulian
K4 Acheulian
K4 Acheulian
K4? MSA
K4 MSA
K4 MSA
21
22
23
24
Koimilot (Loc. 118)
Loc. 119
N y ogonyek
Logumkum artifacts and fauna Ilosowuani Fm. M S A - R m t
Table 1: Southern Kapthurin FcUmation s i t s fomd during 2001 s u r ~ y
Site Name
Loc. 39
Loc. 40
Loc. 100
Loc. 101
Loc. 102 artifactsandfauna I K3 I Acheulian ~
Lac. 103
Loc. 104
Acheulian
Indctuminate
?Acheulian
Indeterminate
Acheulian-MSA
Acheulian
Loc. 105 GnJh-69
GnJh-70
GnJh-71
1 9 Loc. 106
Loc. 107
I l 1
~~
Loc. 108 I
12 Loc. 109 Grim-72 fa\pna K3 NIA
Loc. 110 -73
I 14 ~LQc. 111
Galh-8
GoJh-9
GoJh-10
GnJh-76
Go&- 1 1
GnJh-75
GnJh-74
GnJh-77
artifactsandhum I K4Moloccnesed I MSA-LSA GoJh- 1
GoJi-7
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approximate spatial extent of each site was deter- mined in the field, as was sedimentary and stratigraphic context. A Magellan 3 IS GPS unit pro- vided precise locational data, and - usell for attribution of a site to period or industxy were col- lected. Artifacts and fossils are presently housed at the Archaeology Division of the National Museums of Kenya (NMK) in Nairobi.
Southern Kapthurin Formation Paleontology and Archaeology
The 2001 survey was successll in identifl- ing a suite of previously unknown paleontological and archaeological localities h m southem exposum of the Kapthurin Formation. Sites o c d within alluvial and lacustrine sediments, in multiple temp raYstratigraphic contexts. Although in situ fossils were observed and recovered h m multiple locali- ties, fossil fauna are generally neither abundant nor well preserved in the southern Kapthurin Formation. Plant fossils are occasionally found, at times in growth position, within layers of &-fall tuf€(Tallon 1976, personal observation). Two tephra layers rich in both grass and leaf impressions bracket the excavations at Koimilot.
Archaeological variability in the southern Kapthurin Formation is comparable to that found north of the Ndau River (e.g. Cornelissen 1992; McBrearty et ul. 1996; McBrearty 1999). Sites at- tributable to the Acheulian Industrial Complex are well represented by handaxes and cleavers, produced from a range of fine-to-coarse grained lavas. These implements were prodyced from side and end-struck flakes, from cobbles (GoJh-12) and the Kombewa method (Gnlh-76). A large Levallois flake, similar to those used for handaxe production at LHA (Leakqr er a1 1969) was also recovered in situ from within the Bedded Tuff at GnJh-62. Picks, found in the Acheulian but often considered characteristic of the Sangoan, were found in situ at GnJh-66, and have been reported fiom elsewhere in the Kapthurin For- mation (Cornelissen 1995). Cores include a variety of single and multiple platform, discoidal and rare Levallois types.
containing rarc points and Levallois cores at GoJh- 13 and Grim-71, and more extensive s\irface scatters at Logumkum (GoJi-7), Nyogonyek (GoJh-1), and Koimilot (GnJh-74). Artifacts from Logumkum (Logumkum TV of Farrand et ul. 1976) include Lcvalloisanddiscoidalcores,Le~loiSpointSasweU as scrapers and bifacial points made on Levallois flakes; rare artiEacts are of obsidian. These lie on an up-fiiultcd sedimentary sequence of lacustrine sedi- ment and W, assigned to the Ilosuowani Foxmation (Tiercelin and Vicens 1987; Le Turdu et aZ. 1995). Nyogonyek is a large eroded area containing multi- ple dense patches of artifacts, many of them typo- logically Later Stone Age, first reported by Fanand et ul. (1976). An artifact concentration discovered in 2001 consists ofnumerous Levallois cores, flakes and points, produced by lineal as well as convergent andunipolarrecurrentmethods(cfB& 1994). The artifacts are apparently within down-faulted sediments of a lacustrine h i e s of the Middle Silts and Gravels member (Tallon 1976; Fanand et ul. 1976; McBrearty 1999).
Excavation at Koimilot (GnJh-74) recovered two stratified MSA assemblages (Tryon and McBrearty 2002b) (Figures 3 and 4). Over 2000 ar- tifacts were movered from the 36-m2 excavation at Locus 1, the stratigraphically lower of the two as- semblages. Artifacts occur in a -IO-cm-thick hori- zon within fine-grained overbank sediments, with refitting sets h m within the excavated area as well as between the excavation and surface finds. Is+ lated teeth and tooth hgments comprise the recov- ered fauna The lithic assemblage consists of casu- ally flaked large cobbles, as well as a dense debitage concentration and associated centripetally flaked cores that apparently reflect a Levallois mode of flake production. Retouched pieces are rare. Locus 2 is adjacent to and stratigraphically higher than Locus 1 (Figures 3 , 4 and 6). The 12-m2 excavation recov- ered -150 artifacts from within a 10-an-thick zone fiom five of the excavated meters. Artifacts are as- sociated with fine-to-coarse sands, and include large (max. length 2 10 cm) Levallois points and elongated flakes, a centripetally flaked Levallois core, a blade core and ochre. Future research will systematically explore differences observed between Locus 1 and
'
Middle Stone Age sites from the southern Kapthurin Formation include sparse surface scatters
Locus 2 at Koimilot, as well as comparison of these assemblages with other sites, seeking to document
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and explain temporal or functional variability within the MSA.
Tephrostratigraphy Multiple t e p h samples were collected from
measured stratigraphic sections, and energy-disper- sive electron microprobe (Em) analysis is currently in progress, using equipment housed at the mine Geology Laboratories, Yale University. Preliminary field stratigraphic, petrographic and EMP analysis of glass geochemistry suggest that tuffs underlying the archaeological deposits at Koimilot are compa- rable to the ‘hpper basaltic” portions of the Bedded Tuff identified by Tryon and McBrearty (2002a). Im- portantly, this makes Locus 1 and Locus 2 at Koimilo?, both assigned to the MSA, the youngest excavated assemblages thus far from the Kapthurin Formation, as all other known sites underlie these ”upper basal- tic” Bedded Tuff deposits. Additional tephra at Koimilot include deposits not previously observed. These include the “Koimilot tuff” and basaltic tuf€ deposits that are not part of the established tephrosequence of the Bedded Tuff member. The “Koimilot tuff serves as a local marker bed, and is a fine-grained dacitic tuff which likely has a distant source outside the Baringo basin, offering the poten- tial for long distance correlation such as has been achieved with deposits in the Lake Turkana basin (e.g. Brown 1994; Feibel 1999).
Additional preliminary EMP analyses have been undertaken for tephra at Logumkum, Nyogonyek and (30%-12. Ash deposits at Logumkum are unlike any presently known from the Kapthurin Formation, while those at Nyogonyek and GoJh-12 are tentatively identified as Bedded Tuff, with con- firmation pending subsequent laboratory reanalysis as well as the collection of additional field samples.
Conclusions The end of the Acheulian is a major Middle
Pleistocene archaeological event. The highly re- solved stratigraphic record of the Kapthurin Forma- tion provides the opportunity to examine basic is- sues of the chronology of the Acheulian to Middle Stone Age transition (Deino and McBrearty 2002; Tryon and McBrearty 2002a). Construction and com- parison of local sequences of archaeological and paleoecological change, such as those from the
Kqthurin Formation audKalambo Falls (Clark 200 I) is a necessary step for the formulation of hypotheses regarding hominid behavioral adaptations during and subsequent to the Acheulian-MSA transition. The additional sites discovered during the survey of the southern Kapthurin Formation, as well as excavation at Koimilot, expand both the site sample, as well as the time span of observable archaeological change in the Baringo basin.
Acknowledgements Work in the southern Kapthurin Formation was
conducted under a research permit &om the Govern- ment of the Republic of Kenya (permit no. MOEST 13/00 1 /3OC 229) and an exploration and excavation license h m the Minister for Heritage and Sports. Funding was provided by the L. S. B. Leakey Foun- dation, the Wcnner-Gren Foundation for Anthropo- logical Research, Inc., the Bill Bishop Memorial Trust, and the National Science Foundation (BCS- 0 I 18345). The success of the present investigation is due in part to my entire field crew, but most espe- cially Boniface Kimeu, Mustah Kirika Waweru and Simon Katkya. Sally McBrearty and Andrew Hill provided guidance and both material and moral sup- port. Lastly, I thank my parents and Rhonda Kauffman for their kindness and patience.
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