Herein we report an analysis of an Oxfordian (Upper Jurassic) paleoreef
located in the Swiss Jura Mountains. The paleoreef is located in a
Middle Oxfordian transitional interval in which sedimentation switched
from marl-dominated to carbonate-dominated deposits. The paleoecosystem
is composed of four successive fossil communities characterized by
microsolenid corals and organisms that specialized in suspension
feeding. Carbon isotopes measured from echinoid spine carbonates exhibit
a positive trend from similar to 1.0 parts per thousand to 2.5 parts per
thousand in delta(13)C values from the base to the top of the paleoreef.
Comparison of delta(13)C curves with organic matter and belemnites shows
different patterns not compatible with a global variation of the carbon
cycle. Similar fossil assemblages and stratigraphic sequences identical
in age are found along the continental margin of the Tethys-Atlantic
Ocean. This biolithostratigraphic succession corresponds to increasing
delta(13)C values of marine and biogenic carbonates, to the transition
from marl-dominated to carbonate-dominated deposits, and to the
development of carbonate platforms, which together suggest a change in
the carbon cycling regime within the Tethys-Atlantic Ocean system.