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__Landscape Analysis, Stratigraphical And Geochemical Investigations
Of Playa And Alluvial Fan Sediments In Tunisia And Raised Bog Deposits
In Sweden: A Possible Correlation Between Extreme Climate Events And
Cosmic Activity During The Late Holocene

Lars G. Franzén1 and Thomas B. Larsson2

1 Physical Geography, Department of Earth Sciences, University of
Göteborg,
SE-413 81 Göteborg, Sweden, E-mail: lars at gvc.gu.se
2 Department of Archeology, University of Umea, SE-901 87 Umea, Sweden

Geomorphological signatures, and plays and alluvial fan deposits, all
point at a severe flooding catastrophe in central Tunisia c. 1000 B.C.
Precipitation must have exceeded 10,000 mm in a very short period.
Human activity during this period concentrated around wells, with an
increased need of heating as indicated by the very frequent occurrence
of unusually large fireplaces with heating stones imbedded in charcoal
(Larsson and Franzen, in press). The sediments deposited indicate
severe ground frost in an initial phase, i.e. large balls of loose
dune sand, imbedded in the lower part of the stratigraphies, objects
which could only have been transported in a frozen form. In spite of
being found in a 5 m thick sediment sequence the fire places have the
same apparent age according to 14 C-datings, indicating an extreme
rate of sedimentation. The playa investigated, Chott Nejla, is
normally dried out However, after heavy floods, it is a fresh water
lake, with a maximum depth of 15 m, if filled up to the thresholds. At
the natural playa outlet during pluvial periods, from an
archaeological point of view, a very rich site was found with signs of
a perhaps continuous settlement from 9000 B.C. to Roman times,
uncommon for the Capisien culture (Balout, 1955; Larsson and Franzen,
in press). The sediment sequence at the playa centre shows that the
most abrupt transition from aridity to very humid conditions at 1000
B.C., was followed by a very long lake stage. The lower lake stage
sediments of this event contain glassy spherules (5-100 gm dia) with a
very varying composition, from pure Fe-types to types with the same
basic composition as those found in the K/T-transition (e.g. Koeberl
and Sigurdsson, 1992). Other outstanding wet periods found in the
Tunisian material are 900-1000 A.D. and 1600-1700 A.D. In southern
Sweden, several raised bog deposits have been investigated for their
peat ash composition. Raised bogs, which receive all nutrients from
the atmosphere, is an ideal archive of atmospheric fallout, the rate
of peat accumulation being rather constant and the peat being easily
dated with 14 C. The investigation indicate strongly increased
atmospheric circulation in rhythmically appearing periods with high
peaks centred around e.g. c.2200 B.C., 1000 B.C., 400 B.C., 200 A.D.,
1000 A.D. and 1600 A.D. Harmonic analysis points at a periodicity of
570 years or 1140 years. Like in the playa deposits glassy spherules
were found, having the same basic composition as the Tunisian
material. In conclusion, both playa and alluvial fan deposits in
Tunisia, and peat in Sweden points at a very turbulent Holocene with
several sudden and dramatic climate event;, with unknown origin and
extent The cultural traces indicate periods of extremely cold and
humid conditions. The spherules found could be of volcanic origin but
they are not associated with any known major volcanism, and their
heterogeneous composition points at other formation mechanisms e.g.
cometary impacts in ocean shelf sediments.

_References: _Balout, L. 1955. _La Prehistoire du l'Afrique du Nord.
_Paris. Koeberl, C. and Sigurdsson, H. 1992. Geochemistry of impact
glasses from the K/T boundary in Haiti: relation to smectites and a
new type of glass. _Geochim. Cosmochim Acta _56(5):2113-2129. Larsson,
T.B. and Franzén, L.G. (In press). The _Capsien Culture at Ez Zaf Zaf,
Chott Nejla, Central Tunisia. _Preliminary Report, Univ. of Umeĺ,
Univ. of Göteborg, Sweden. Larsson, T.B. and Franzén, L.G. (In press).
_The anomalous dwelling sites of Oed Sequia, Central Tunisia. A
comparison between fire cracked stones in Tunisia and Northem Europe.
_Preliminary Report, Univ. of Umeĺ, Univ. of Göteborg, Sweden.
___________________________________

LARS FRANZEN (Ph.D., Gothenburg University, 1985) is Associate
Professor of Physical Geography of the department of Earth Sciences at
Göteborg University, Sweden. His research interests include the
Holocene climate development as detected in stratigraphies of raised
bogs in Sweden and playa deposits of Northern Africa. His studies has
lead to the discovery of several abrupt climate shifts in Post-glacial
times, the most pregnant of these being centered around 1000 B.C.
Cultural and other evidence point at prolonged periods of severe cold
and vast floodings associated with some these events.
_________________________________________________________________

Presented at the SIS Conference: [1]Natural Catastrophes during Bronze
Age Civilisations.

References

1. file://localhost/www/sat/cambconf.htm