Soil development on Middle to Late Pleistocene marine terraces in the Gulf of Taranto, southern Italy

lovinggudgeonMechanics

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

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Soil development on Middle to Late Pleistocene marine terraces in
the Gulf
of Taranto,
southern Italy


Daniela

Sauer
1
, S
tephen

Wagner
2
, Helmut

Brückner
3
, F
abio

Scarciglia
4
, Giuseppe

Mastronuzzi
5
, K
arl

Stahr
1


1
Institute of Soil Science and Land Evaluation,

Hohenheim University, Emil
-
Wolf
-
Str. 27, D
-
70599 Stuttgart, Germany;
2
Institute of Crop Science and Resource Conservation, Soil Science Division, University of Bonn, Nussallee 13, D
-
53115
Bonn, Germany;
3
Faculty of Geography, University of Marburg, Deutsc
hhausstr. 10, D
-
35032 Marburg, Germany;
4
Earth
Sciences Department, University of Calabria, Via Pietro Bucci


Cubo 15B, I
-
87036 Arcavacata di Rende (CS), Italy;
5
Department of Geology and Geophysics, University of Bari, Via E. Orabona 4, I
-
70125 Bari, Ita
ly

Corresponding author: Dr. Daniela Sauer, e
-
mail: d
-
sauer@unihohenheim.de


The staircase of Pleistocene marine terraces, which stretches with a width of about 25 km
along the Gulf of Taranto, southern Italy

(see Fig. 1)
, has been subject to discussion,
c
oncerning number, sedimentology, genesis and age of the terraces for decades.



Figure 1:

Location of the study area (grey rectangle) in the central part of the Gulf of Taranto. a: Outcroping Apulia
Foreland; b: Apennine carbonate platform; c: Molise
-
Sa
nnio
-
Lagonegro pelagic basin; d: Laga Fm, gessoso
solfifera; e: Umbria Marche pelagic basin; f: Liguride units; g: Magmatic units; h: Pliocene Quaternary
deposits; 1: Front of Southern Appenine orogenic wedge 2: main thrust front; 3: main faults.


Unfort
unately, the development of a solid chronology of terrace formation in the area is
impeded, because dateable material is rare.
A few

time pegs are provided by the
Brunhes/Matuyama boundary
,

which occurs between the terraces T10 and T11 and a
t
ephra
layer i
n terrace T8 that
is

attributed
to an eruption of

the Phlegraean Fields

that took place
500
-
600 ka BP
.

I
dentification of Senegalese fauna in some places, e.g.
Ponte del Re,

provided
evidence for the sea level during MIS 5.5
.

This paper contributes to sedi
mentation and landscape history reconstruction from a
pedogenetic view in the area between Metaponto and Pisticci in the eastern central part of the
Gulf of Taranto.
The marine terraces in this area are usually covered by alluvial sediments; in
some places
, aeolian deposits have accumulated on the terraces. Pedogenetic

investigation,
including field observations (e.g. soil colour, intensity of weathering, precipitation of
secondary carbonates) and
Fe
d
/Fe
t

ratio, silt/clay ratio and carbonate content, reveal
ed that the
usual sedimentation history in many sites included a period of soil formation between the
deposition of the marine and that of the alluvial sediments.

Soil formation on the marine sediments began immediately after the land surface fell dry, i.
e.
during the marine regression following the relative sea level maximum of the interglacial,
during which the respective marine terrace formed. The alluvial sediments accumulated some
time later, whereby synsedimentary pedogenesis continued.

Another cent
ral objective besides the described sedimentation history is, if soil formation
indicates progressive ages of the terraces. Field observation suggests a general trend of
progressive age:

Soils on the lower terraces T0 and T1 are weakly to moderately develo
ped
and have greyish
-

or yellowish
-
brown colours. Soils on the terraces T2 and T3 are more
reddish, and some of the soils on the higher terraces, especially on T7, are deeply developed
and red.

Maximum Fe
d
/Fe
t

ratios of the soils developed in the differen
t sediments have been plotted
vs. assumed terrace age (based on the existing time pegs and interpolation). The relationship
between Fe
d
/Fe
t

ratios and hypothetical terrace age has been calculated using only maximum
Fe
d
/Fe
t

values. It can be best described
by power or logarithmic functions, both describing a
strong increase in pedogenic iron in the first 100 ka which slows down afterwards.

However, soils on several terraces have Fe
d
/Fe
t

ratios below the resulting curve. This may be
explained by burial of th
e soils in the marine gravel layer

at an early stage of soil formation,
by erosion of the most intensively developed parts of the soils, and by rejuvenation of the
soils through dust input. In general, Fe
d
/Fe
t

ratios suggest a trend of increasing terrace a
ges
from the lower to the upper terraces.

This trend has been checked by plotting a second soil development parameter vs. assumed
terrace age. The selected second parameter is the molar total element ratio of
(Ca+Mg+K+Na)/Al, which reflects progressive si
licate weathering, accompanied by Ca, Mg,
K, and Na release and subsequent leaching, while Al is not leached.

The trend of (Ca+Mg+K+Na)/Al of the soils developed in the marine sediments also supports
the hypothesis of increasing terrace ages. It can be be
st described by a logarithmic function.
In contrast, the fluvial sediments exhibit low (Ca+Mg+K+Na)/Al ratios on all terraces, which
is probably due to pre
-
weathering.