Geology Reference
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Fig. 7.14. Reef cements. Many Middle and Late Permian reefs are characterized by frameworks consisting of low-growing
encrusting organisms and up to 60% of coeval marine cement.
A : Sequence consisting of submarine radiaxial fibrous cement (1) growing on Archaeolithoporella and blocky calcite ce-
ment (2). The marine cement forms yellowish isopachous crusts (0.5 to 2.5 mm) surrounding small patches of sessile organ-
isms. The crust consists of ray crystals containing ghosts of thin straight-edged, fibrous crystals with a width of up to 25 m.
The crust shows a faint zonation. Note the distinct and sharp upper boundary of the cement crust. The fabric of this cement
indicates an aragonite precursor cement. In contrast, the overlying coarse blocky cement (2) consists of euhedral, non-
ferroan calcite crystals that have suffered aggrading neomorphism also partly cannibalizing its underlying marine cement.
The outer sometimes rounded and irregular boundary of these blocky cements may be explained by solution effects. The
remaining pore space was filled by fine-grained, silt-sized carbonate with abundant, sometimes euhedral dolomite crystals (3).
B : Radiaxial fibrous cement growing on biogenic encrustations mainly made by Archaeolithoporella (see Pl. 98/8). The
outer part of the laminated structure has been eroded and filled with peloids (arrow) prior to the formation of the marine
radiaxial fibrous cement exhibiting a distinct aragonite precursor fabric. The limestone was affected by fracturing and shear-
ing. Microcracks are closed by several calcite generations.
Interpretation : The sample comes from a reef formed on the upper platform slope (Flügel et al. 1984). The framework was
stabilized by pervasive marine cementation. The white, bladed calcite cement originated in a shallow burial environment
influenced by meteoric waters. The infilling of a dolomitized carbonate silt points to a change towards vadose conditions.
Middle Permian (Guadalupian): Straza near Bled, Slovenia. Scale is 2 mm.
Box 7.7. Selected case studies of reef diagenesis. An overview is given by Schroeder and Purser (1986). Marine cemen-
tation, concurrent internal sedimentation, and bioerosion are the most important factors controlling early marine lithifi-
cation within many reef environments.
Holocene: Buddemeier and Oberdorfer 1986; Dullo 1986; Friedman 1974; Ginsburg et al. 1971; Jindrich 1983; James
et al. 1976; Land and Goreau 1970; Lighty 1985; Macintyre et al. 1968, 1977; Marshall 1986; Marshall and Davies
1981; Schroeder 1972
Tertiary: Aissaoui et al. 1986; Armstrong et al. 1980; Asquith and Drake 1985; Pomar et al. 1994; Schroeder 1986; Sun
and Esteban 1994
Cretaceous: Alsharhan 1985; Enos 1986; MRabet et al. 1986; Reitner 1986
Jurassic: Benito et al. 2001; Joachimski and Scheller 1987; Koch and Liedmann 1996; Koch and Schorr 1986;
Matyskiewicz 1989; Schroeder et al. 1996; Sun and Wright 1998
Triassic: German 1968; Henrich and Zankl 1986; Lakew 1994; Mazzullo et al. 1990; Russo et al. 2000; Satterley et al.
1994; Sotak and Lintnerova 1994; Zankl 1971; Zeeh et al. 1995; Zorn 1971
Permian: Chaiuachi and MRabet 1989; Cross and Klosterman 1981; Dunham 1972; Given and Lohmann 1986; Liu
and Rigby 1992; Mazzullo and Cys 1977; 1979; Mazzullo et al. 1990; Scherer 1986; Schmidt 1977; Stemmerik and
Larsen 1993; Tucker and Hollingworth 1986; Wendt 1977
Pennsylvanian: Davies 1977; Davies and Nassichuk 1990; Soreghan and Giles 1999; Wahlman 2002
Mississippian: Ahr and Ross 1982; Bathurst 1959; Miller 1986
Devonian: Hurley and Lohmann 1989; Kaufmann et al. 1999; Kerans et al. 1986; Krebs 1969; Machel 1986; Mountjoy
and Walls 1977; Wong and Oldershaw 1981; Schneider 1977; Walls and Burrowes 1985; Webb 2002
Silurian: Cercone and Lohmann 1986; Frykman 1986; Petta 1980; Savard and Bourque 1989
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