INDICATIONS OF MAN-INDUCED CHANGES IN A SEQUENCE AND COMPOSITION OF FLOODPLAIN DEPOSITS IN BELARUS

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Feb 22, 2014 (3 years and 5 months ago)

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INDICATIONS OF MAN
-
INDUCED CHANGES IN A

SEQUENCE AND
COMPOSITION OF FLOOD
PLAIN DEPOSITS IN BE
LARUS


S. SAVCHIK
1
, N.MAKHNACH
2

1
The Institute of Geological Sciences, 220141 Minsk, st Kuprevich 7, Belarus

e
-
mail:

1

n
mahnach@ns.igs.ac.by
,
2

nmahnach@ns.igs.ac.by


INTRODUCTION

Changes in a sequence and composition

of floodplain deposits may be caused by both
natural and man
-
induced processes which occur
in river valleys or w
ithin the entire river drainage
areas. The immediate agents influencing

the character of deposition are divided into three
main groups: (1)fluctuations of the river channel
position (meandering, bifurcation); (2)changes in
river discharge caused by climat
ic and other
factors; and (3)landscape pattern change within
the river drainage area. The factors
corresponding to all the three groups may have as
natural as anthropogenic origin. But considering
recent time (the last several thousand years),

the landsca
pe pattern change is caused
predominantly by human activities in the river
drainage basin. These activities include
deforestation, agricultural development
(ploughing and pasturing), and watershed relief
change due to other actions such as urbanisation,
me
lioration, mining and so far. Recent changes in
the landscape pattern lead to an accumulation in
river valleys of specific floodplain deposits called
“muds” or “madas” (Starkel ed. 1996). The muds
related to a human development of watersheds
are referred t
o as poorly sorted clayey, silty
or/and sandy floodplain deposits, covering the
upper part of a section of river valley sediments
(Kalicki 1996). The process of an accumulation
of anthropogenic muds starts from

the deforestation and agricultural developme
nt

of river watershed. This facilitates sheet and
linear erosion and provides an abundance

of sediment supply. During the spring flooding
rivers become overloaded with sediments which
results in a deposition of unsorted muds that
differ significantly fro
m the natural floodplain
deposits.

FEATURES OF ANTHROPO
GENIC
-
RELATED MUDS

Previously the muds accomplishing

the sequence of fluvial deposits in river valleys
were referred as deposits associated mainly with
human impact on landscapes within the river
drai
nage areas (Mensching 1951). The later
studies revealed that poorly sorted muds have
been deposited in different environments of the
Late Glacial and Holocene (Starkel 1960,
Rutkowski 1987). But there are several character
features of man
-
induced muds whic
h differ them
from the natural ones. The deposits composing
anthropogenic muds are poorly sorted with

an obvious coarsening upward the profile. In
other cases this feature hasn’t been observed and
series of disorderly placed cycles of coarsening
-
fining up
wards deposits have been recorded.
Some researches completely exclude a possibility
of presence of gradually coarsening upwards
cycles in natural fluvial deposits (Allen 1970) so
far as the meandering rivers form cycles of fining
upwards sequences interrup
ted by thin layers

of abruptly coarsening sediments. The floodplain
muds of the both natural and man
-
induced origin
have been studied thoroughly in Poland.

The character features of these deposits, their
classification and palaeogeographical
reconstructi
on of sedimentation process are
reported in several comprehensive papers by T.
Kalicki (1987,1996), E. Niedzialkowska (1991).
Nevertheless there is much controversy seen in
an interpretation of the muds origin and in

a reconstruction of environmental cond
itions
under which they have accumulated.

ANTHROPOGENIC
-
RELATED MUDS IN
BELARUS

There are very few sections containing
floodplain anthropogenic
-
related muds have been
studied and reported in Belarus. In the Dnieper
river valley an occurrence of man
-
induced

muds
marks starting point of wide
-
spread deforestation
and ploughing at 940 years BP. The large
-
scale
changes in landscape pattern of the Berezina
river basin near Borisov have started to be
recorded in floodplain sediments much later


340 years BP (Kali
cki, Sanko 1992; Kalicki
1999). Unfortunately, these two studied sites and
several more don’t provide enough evidences for
further reconstruction of human impacts on
sedimentation process in Belarussian river
valleys, which doesn’t make it possible to trac
e
the history of landscape alteration by man in this
area of Europe. Two more sections with muds
were studied by authors in the Adrov river and
Pochalitsa river valleys (tributaries of Dnieper
and Adrov respectively). In both sites muds form
from 1,5 to 1,
0 meter thick covers, overlaying
peat and floodplain deposits. The radiocarbon
date obtained from the Pochalitsa site allows to
assume that an accumulation of muds started
there 520
+
80 BP (IGSB
-
627), that very likely to
be conditioned by human activity in
the drainage
basin. The granulometric composition of muds
from both sites show irregular coarsening and

32

fining of deposits upwards which is very
different from underlying floodplain sediments.
Mud deposits are sorted much less then
underlying “natural” mud
s and especially then
channel alluvium. X
-
ray spectroscopy analysis
showed a significant decrease in Al
2
O
3

content in
muds, which may indicate a lack of clay fraction
that was removed by flood flow. All these
features of muds from the Pochalitsa and Adrov
sites allow to refer them as man
-
induced
sediments, which mark the beginning of large
-
scale development of neighbouring areas.

CONCLUSIONS

Man
-
induced changes in a sequence and
composition of floodplain deposits are used to
determine the starting point, du
ration and
intensity of large
-
scale human impact on

the landscapes of the river drainage basin. This
indicator together with archaeological,
geochemical and geomorphological data allows
to trace a development of human impact since it
appearance till the
recent time. Nevertheless
there are serious difficulties seen while
interpreting data obtained from studies of “man
-
related” muds. It leads to controversial
conclusions, which oftenly found in the papers on
this subject (sometimes even written by the same
author). Therefore the reconstruction

of anthropogenic alteration of landscape, based
on study of floodplain deposits should be
supplemented by studies of sequence and
composition of lake and peat deposits. It also
may be useful to pay attention on

the g
eoindicator of dune formation and
movement, which may mark the starting point
and an intensity of mass deforestation.



REFERENCES


Starkel L., ed., 1996, Evolution of the Vistula
river valley during the last 15 000 years, VI,
Geogr. Stud. Spec. Issue 9
.

Kalicki T., 1996, Overbank deposits as indicators
of the changes in discharges and supply

of sediments in the upper Vistula valley
-

the
role of climate and human impact. In:
Evolution

of the Vistula river valley during the last
15000 years, VI,
Geogr.

Stud. Spec. Issue 9.
43
-
60

Mensching H., 1951, Akkumulation und Erosion
Niedersächsischer Flüsse seit der Risseiszeit,
Erdkunde 5, 60
-
70.

Starkel L., 1960, The development of the Flysh
Carpatians relief during Holocene, Prace
Geogr.IG PAN 22 (in Polish).

Rutkovski J., 1987, Vistula river valley in

the Krakow Gate during the Holocene. In:
Evolution of the Vistula river valley during
the last 15000 years, II,
Geogr. Stud. Spec.
Issue 4, 31
-
50.

Allen J.R.L., 1970, Studies in fluviatile
sedimentation: a compa
rison of fining
-
upwards cyclothems, with special reference to
coarse member composition and
interpretation. In: Jour. Sed. Petrology, vol.
40, 298
-
323.

Kalicki T., 1991, The evolution of the Vistula
river valley between Krakow and
Niepolomice in late Vistu
lian and Holocene
times. In: Evolution of the Vistula river valley
during the last 15 000 years, IV, Geogr. Stud.
Spec. Issue 6, 11
-
37.

Niedzialkowska E., 1991, The textural diversity
of Upper Quaternary fluvial deposits in

the Carpatian foreland. In: : E
volution of the
Vistula river valley during the last 15 000
years, IV, Geogr. Stud. Spec. Issue 6, 119
-
146.

Kalicki T., Sanko A., 1992, Genesis and age

of the terraces of the Dnieper River between
Orsha and Shklow, Byelorussia . In: Geogr.
Pol., N60, 151
-

174.

Kalicki T., 1999, Evolution of some river valleys
of Belarus in the Late Glatial Age and
Holocene. In: Lithosfere,


10
-
11, 49
-
56.