Geology Reference
In-Depth Information
Plate 113 Standard Microfacies Type: SMF 3
SMF 3: Pelagic lime mudstone and wackestone with planktonic microfossils
Criteria: Micrite matrix with common to abundant pelagic microfossils (e.g. foraminifera, radiolarians, calpio-
nellids) or macrofossils (e.g. 'filaments' - Triassic to Jurassic, pelagic crinoids, graptolites). As shown by SEM
photographs, the micritic matrix of many Mesozoic limestones consists of accumulations of disintegrated cal-
careous ultraplankton (e.g. coccolithophorids, Pl. 7/3; nannoconids, Pl. 77/23). The type of the dominant pelagic
fossils should be indicated by letters e.g. SMF 3-C ALP (calpionellids), SMF 3 -F OR (pelagic foraminifera),
SMF 3-R AD (radiolarians), SMF 3-T ENT (tentaculitids). Occurrence: Basin (FZ 1-B) and open deep shelf (FZ 3).
Additional pictures: Pl. 6/6, Pl. 66/5, Pl. 73/3 (SMF 3-F OR ), Pl. 76/1 (SMF 3-R AD ), Pl. 76/7 (SMF 3-C ALP ), Pl.
91/3 (SMF 3-T ENT ).
1
SMF 3F OR . Pelagic foraminifera wackestone with single-keeled globotruncanids. Tests are generally well-preserved due
to the primary Low-Mg calcite skeletal mineralogy. Pelagic deep-water basinal facies (FZ 1). Late Cretaceous (Scaglia
rossa): Central Apennines, Italy.
2
SMF 3F IL . Thin-shelled pelagic bivalve ('filaments') wackestone. The thin, curved calcitic shells were originally re-
garded as planktonic algae and therefore called 'filaments' (see Sect. 10.2.4.2). The fossils are pelagic bivalves represent-
ing in parts shells of planktonic larval stages. Note the parallel arrangement of the shells pointing to some current control.
Dense accumulations (arrows) are caused by burrowing. The biofabric is characterized by dense and loose packing; little
variations in the sizes of the bioclasts, and good sorting. The paleobathymetric position of limestones with filaments is
controversial. Many authors regard the facies as an indication of bathyal deep-water settings, but others go for a littoral
environment. Deep shelf facies (FZ 3). Early Jurassic: Korfu Island, Greece.
3
SMF 3C ALP . Calpionellid wackestone. Arrows point to the few sections which can be used in taxonomic differentiation.
The fine-grained matrix consists predominantly of nannofossils and micropeloids better to be seen in SEM. Black patches
are bituminous matter. Deep basinal facies (FZ 1). Late Jurassic (Tithonian): Seebühel, Switzerland.
Fig. 14.15. SMF 3T ENT . Densely packed tentaculitid wackestone . All skeletal grains are shells of pelagic mollusks.
Tentaculitids contributed largely to the formation of Ordovician to Late Devonian open-marine and basinal micritic carbonates
(see Sect. 10.2.4.5). Deep basin (FZ 3A). Early Devonian: Frankenwald, Germany.
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