A. Moro et V. Cosovic, The rudists of Southern Istria - An example of environmentally induced succession within Santonian limestones, RIV IT PAL, 106(1), 2000, pp. 59-71
Citations number
46
Categorie Soggetti
Earth Sciences
Journal title
Rivista italiana di paleontologia e stratigrafia (Testo stampato)
Rudist bivalves thrived commonly in the shallow carbonate platforms of the
Cretaceous Tethyan realm. The presence of two vertically separated Rudist a
ssemblages along two well-preserved Upper Cretaceous sections of cape Mrler
a (southern parr of the Istrian peninsula) is interpreted as environmentall
y induced faunal replacement.
The first succession begins with pelagic limestones, followed by a mixed ra
diolitid-hippuritid assemblage, and by monogeneric floatstones-biostromes o
f radiolitids. The lower pelagic unit represents relatively open marine con
ditions while the uppermost radiolitid unit originated under more restricte
d marine conditions.
Radiolitid floatstones with rare Gorjanovicia bouquets represent the beginn
ing of the second succession. A mixed radiolitid-hippuritid assemblage, cha
racterised by radiolitid floatstones where rare large Vaccinites individual
s occur, replaces the Radiolitid assemblages in vertical succession.
In both sections, sea level changes were the most important factor causing
the replacement of rudist assemblages. Slight differences between the two s
uccessions could be attributed to differences in submarine topography. Radi
olitids and hippuritids might have occupied different biotopes within subti
dal environments of the Adriatic carbonate platform. Hippuritids preferred
more stable and deeper subtidal environments. By contrast, radiolitids pref
erred the shallowest parts of subtidal areas.
Therefore, these two major rudist groups may be used for determination of d
ifferent paleoecological conditions.