Geoscience Reference
In-Depth Information
Gamblian
pluvials, respectively, Mid-Late and Late Pleistocene. The
Makalian
and
Nakuran
wet phases were younger and were believed to be post-Pleistocene in age.
Between each pluvial, there was a dry phase, or
interpluvial
. If the temporal equation
pluvial
=
glaciation was indeed correct, then by definition high latitude glaciations
were synchronous with low-latitude pluvials.
Almost by sheer force of personality, Leakey ensured that the idea of using pluvials
as stratigraphic markers for Africa, at least in a relative sense, was espoused at the
First Pan-African Congress on Prehistory, which he organised in Nairobi in 1947.
However, Leakey's views did not go unchallenged, although a number of influential
scientists did accept the glacial-pluvial model without demur.
Following in the footsteps of Nilsson's earlier work in the highlands of Ethiopia,
Budel carried out a reconnaissance survey of glacial and periglacial limits in the
Semien Mountains of Ethiopia in 1953 and concluded that during the last glaciation,
the snow-line in this locality had been around 700 m lower than it is today (Budel,
1954
). He also argued that during glacial times, places at lower elevations experienced
a pluvial climate and that the tropical deserts in the lowlands were also less arid than
they are today during glacial-pluvial phases. The botanist Hugh Scott also visited the
Semien Mountains and concluded that ' ...itappearslikelythatpluvialperiodsinthe
tropics were broadly contemporary with glacial phases elsewhere' (Scott, 1957-
1958
,
p. 11). In this he was particularly influenced by the work of Nilsson (
1931
;
1940
),
who referred to the Kanjeran snow-line and the Gamblian snow-line in the Semien
Mountains.
However, there were growing numbers of dissenting voices questioning the glacial
pluvial concept. For example, Kuls and Semmel (
1965
) investigated slope mantles
in the Godjam Highlands of Ethiopia and concluded that many deposits previously
attributed to periglacial solifluction during the so-called 'pluvial period' (
pluvialzeit-
licher Solifluktionsvorgange
) were in fact formed by recent weathering and erosional
processes without any need to invoke frost action.
A decade earlier, at the Third Pan-African Congress on Prehistory held in Living-
stone (in present-day Zambia) in 1955 and hosted by the archaeologist J. Desmond
Clark, concern was expressed at extending a climatic interpretation to describe Qua-
ternary stratigraphic sequences throughout the entire continent of Africa (Clark,
1957
;
Cole,
1963
). The South African geologist Alex du Toit (
1947
) had earlier expressed
grave misgivings in regard to over-enthusiastic cross-continental correlations based on
uncritical acceptance of the pluvial chronology, and Wayland had always advocated
caution in using the term pluvial. Delegates at the Livingstone Congress accepted that
Leakey's pluvial sequence may well have been valid for East Africa but concluded
that correlations across Africa needed to be supported by at least two independent
lines of evidence: geological, archaeological or paleontological.
At this same conference, the South African geologist H.B.S. Cooke went further
and called into question the climatic interpretation of the East African sites. Both
