Rare earth elements (REE) and stable isotope compositions (delta C-13
and delta O-18) of shark teeth and phosphatic coprolites were analyzed
from the Lower Maastrichtian layers of the El Haria Formation and two
sequences of the Paleocene-Eocene (P/E) Chouabine Formation in the Gafsa
Basin (south western of Tunisia) in order to trace the sedimentological,
climatic and oceanographic conditions.
The REE chemistry and their distribution in the two archives are the
same for each of the studied layers indicating that the coprolites and
shark teeth experienced the same early diagenetic environments. However
major differences occur between the Maastrichtian and the P/E reflecting
changes in the depositional conditions. The Early Maastrichtian burial
environment tended to be more anoxic with REE derived from reduced FeO.
While in the P/E the REE patterns mimic the modern oxic-suboxic
seawater, the REE source from remineralisation of organic coating could
have more significance.
The oxygen isotope compositions of the structural phosphates (delta
O-18(PO4)) indicate a stable and warm climate during both studied time
intervals. A small offset (-0.4 parts per thousand) in the delta O-18
value between the coprolites and shark teeth show minor thermal gradient
between bottom and surface water. The pronounced negative shift of 34%.
in delta C-13 values recorded in the upper part of the Chouabine
Formation was ascribed to the Paleocene-Eocene boundary. At the same
time the lack of negative change in the delta O-18 is explained by the
semi-closed situation of the Gafsa Basin, which situation also played an
important role in the evolution of the organic matters in the sediment
resulting in the exceptional low delta C-13 values. (C) 2008 Elsevier
B.V. All rights reserved.