Palaeoenvironment and palaeoclimate of the Middle Miocene lake in the Steinheim basin, SW Germany: A reconstruction from C, O, and Sr isotopes of fossil remains


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Palaeoenvironment and palaeoclimate of the Middle Miocene lake in the Steinheim basin, SW Germany: A reconstruction from C, O, and Sr isotopes of fossil remains
Palaeogeography, Palaeoclimatology, Palaeoecology
Tuetken T., Vennemann T.W., Janz H., Heimann E.P.J.
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A differentiated reconstruction of palaeolimnologic, -environmental, and
-climatic conditions is presented for the Middle Miocene long-term
freshwater lake (14.3 to 13.5 Ma) of the Steinheim basin, on the basis
of a combined C, 0, and Sr isotope study of sympatric skeletal fossils
of aquatic and terrestrial organisms from the lake sediments.
The oxygen isotope composition for lake water of the Steinheim basin
(delta O-18(H2O) = +2.0 +/- 0.4 parts per thousand VSMOW, n = 6) was
reconstructed from measurements of delta O-18(PO4) of aquatic turtle
bones. The drinking water calculated from the enamel of large mammals
(proboscideans, rhinocerotids, equids, cervids, suids) has delta
O-18(H2O) values (delta(OH2O)-O-18 = -5.9 +/- 1.7 parts per thousand
VSMOW, n = 31) typical for Middle Miocene meteoric water of the area.
This delta O-18(H2O) value corresponds to a mean annual air temperature
(MAT) of 18.8 +/- 3.8 degrees C, calculated using a modem-day
delta(OH2O)-O-18-MAT relation. Hence, large mammals did not use the lake
water as principal drinking water. In contrast, small mammals,
especially the then abundant pika Prolagus oeningensis drank from
O-18-enriched water sources (delta O-18(H2O) = +2.7 +/- 2.3 parts per
thousand VSMOW, n = 7), such as the lake water. Differences in Sr and 0
isotopic compositions between large and small mammal teeth indicate
different home ranges and drinking behaviour and support migration of
some large mammals between the Swabian Alb plateau and the nearby
Molasse basin, while small mammals ingested their food and water
Changes in the lake level, water chemistry, and temperature were
inferred using isotopic compositions of ostracod and gastropod shells
from a composite lake sediment profile. Calcitic ostracod valves
(Ilyocypris binocularis; delta O-18 = +1.7 +/- 1.2 parts per thousand
VPDB, delta C-18 = -0.5 +/- 0.9 parts per thousand, VPDB, n = 68) and
aragonitic, gastropod shells (Gyraulus spp.; delta O-18 = +2.0 +/- 13
parts per thousand VPDB, delta C-13 = -1.1 +/- 1.3 parts per thousand
VPDB, n = 89) have delta O-18 and delta C-13 values similar to or even
higher than those of marine, carbonates. delta C-13 values:of the
biogenic carbonates parallel lake level fluctuations while delta O-18
values scatter around +2 +/- 2 parts per thousand and reflect the short
term variability of meteoric water inflow vs. longer term evaporation.
Sr-87/Sr-86 ratios of aragonitic Gyraulus spp. gastropod shells parallel
the lake level fluctuations, reflecting variable inputs of groundwater
and surface waters. Using a water delta O-18(H2O) value of +2.0 parts
per thousand VSMOW, water temperatures calculated from skeletal tissue
delta O-18 values of ostracods are 16.7 +/- 5.0 degrees C, gastropods
20.6 +/- 5.6 degrees C, otoliths 21.8 +/- 1.4 degrees C, and fish teeth
17.0 +/- 2.7 degrees C.
The calculated MAT (similar to 19 degrees C), lake water temperatures
(similar to 17 to 22 degrees C) and the O-18-enriched water compositions
are indicative of warm-temperate climatic conditions, possibly with a
high humidity during this period. Vegetation in the area surrounding the
basin was largely of the C-3-type, as indicated by carbon isotopic
compositions of tooth enamel from large mammals (delta C-13 = -11.1 +/-
1.1 parts per thousand VPDB, n = 40). (c) 2006 Elsevier B.V. All rights
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29/09/2012 17:23
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