Page 5 - Martini_al_Facies_2007
P. 5
Facies (2007) 53:389–400 393
Fig. 4 Microfacies from the Punta Bassano carbonate succession and stratiWcation, and of dense micritic peloids. MF4 Planar Wne microbial
interpretation of their distribution along the Upper Triassic (Carnian to laminated wackestone with fenestrae, composed of alternating layers
Rhaetian) carbonate ramp (MSL mean sea level; FWWB fair-weather of mudstone and very Wne-grained peloidal packstone, in places
wave base; SWB storm-wave base) (modiWed from Flügel 2004). Pho- grainstone. MF6 bioclastic packstone/Xoatstone with bivalves and
tographs show the more characteristic microfacies: MF5 Ostracod/ gastropods. MF2 Fine-grained peloidal wackestone/packstone show-
peloidal packstone to grainstone, made up of alternating layers of ing (top-right corner) cloudy calcite pseudospar, which has replaced
almost exclusively double-valved ostracods, lying parallel to the evaporite nodules. Scale bar is 200 m
subordinate and include foraminifers, bivalve shells, echi- MF6 The microfacies is a bioclastic packstone/Xoatstone
noderms and microbial/algal aggregates. Thin bioturbation (MF6). It contains bivalves, brachiopods and gastropods
trails are observed as well as low-amplitude stylolites, (Fig. 4), locally showing micritic envelopes (sensu Bathurst
which interrupt the layers, frequently. 1966). Ostracods, foraminifers and echinoderm remnants
are sporadically present.
Organic matter content is dominated by large debris of
vitrinite, frequently amorphised by fungi, algal spores and Lithofacies type 4
subordinate amount of equidimensional inertinite. Sorting
and rounding of organic debris are low. Thin layers of grey-beige limestone, 2–3 cm thick, charac-
terised by yellow to orange patina due to late burial dolo-
Lithofacies type 3 mitisation, which makes it well recognisable in the Weld.
The levels presently appear as undulating weathering
Shelly limestone consists of thin (up to 15 cm) beds of grey crusts, strongly fractured, on top of the homogeneous lime-
coarse bioclastic limestone. The bioclasts are essentially stone beds (lithofacies type 1).
represented by large (more than 2 cm) bivalve and brachiopod
shells, showing a coarsening-up arrangement. This lithotype MF7 The homogeneous microfacies is Wne- to coarse-
normally occurs interbedded with yellow-ochre clayey marl grained packstone/grainstone, containing very small sub-
intervals.
123
