O. Weidlich, BIOEROSION IN LATE PERMIAN RUGOSA FROM REEFAL BLOCKS (HAWASINA COMPLEX, OMAN MOUNTAINS) - IMPLICATIONS FOR REEF DEGRADATION, Facies, 35, 1996, pp. 133-142
Rugose corals are known from allochthonous Late Permian reefal blocks
of the Al Jil and Ba'id Formation (Hawasina Complex), Oman Mountains.
In contrast to many Late Permian Rugosa found elsewhere in the Tethys,
they occurred in sponge reefs and contributed to reef construction. T
he waagenophyllid warm water coral fauna is moderately diverse compris
ing cerioid, thamnasterioid, and fasciculate taxa. In contrast to spon
ges, chaetetids, and low-growing reefbuilders, the corals secreted dia
genetically stable, most probably Mg-calcitic skeletons. Borings in co
ral skeletons are consequently well preserved providing important data
for the interpretation of reef destructive processes. Thin-section an
alysis revealed three taxa of infaunal borers including Entobia BRONN
1837, uncertain thallophyte borings, and borings of unknown bioeroders
. Macroborers were more important than microborers, because of the dom
inance of clionid sponges. Good evidence exists also for the occurrenc
e of two types of undetermined grazers which destroyed the coral surfa
ces. The amount and distribution of bioerosion is variable among diffe
rent coral taxa. The fasciculate coral Praewentzelella regulare FLUGEL
1995 was the favorate substrate. Up to 33% of the calices were bored.
Dendroid and compound corals were bored subordinately. Bioerosion of
these colonies does not exceed 2%. There is good evidence for substrat
e preference amongst the borers. Major controlling factors affecting b
orer distribution are believed to be variations of skeletal density an
d gross morphology. The borer assemblage could not limit reef accretio
n significantly. Factors controlling boring activity might have been q
uality of substrate, sedimentation rate, rapid incrustation of substra
tes, and competition for food with reef constructors including sponges
, chaetetids, and rugose corals.