Shallow-Marine Carbonates - Trace Fossils as Indicators of Sedimentary Environments - page 702

shallowing-upward cycles, below and between the grainstone/packstone beds
(e.g., the Oolite and Schaumkalk Beds). The marly limestone can be dolomitic
and contain features of subaerial exposure (e.g., desiccation cracks), thus docu-
menting deposition on low-energy tidal flats. Where dolomitization and exposure
features are lacking, rocks of the same texture can be interpreted as shallow sub-
tidal deposits. Inter- and subtidal environments can be differentiated on the basis
of the ichnofauna. Bedding planes of the dolomitic marly limestone (intertidal) are
covered by large and winding R. commune together with the fecal pellets Coprulus
oblongus ( Cruziana Ichnofacies, Fig. 8 E), resulting from feeding activity, prob-
ably by polychaetes. Desiccated parts of the tidal flat were apparently visited by
crustaceans, preferably following the weakened cracks between the desiccation
polygons and producing T. suevicus ( Glossifungites Ichnofacies). In contrast,
the subtidal marly limestone contains more ichnotaxa and is dominated by short
and oblique R. commune ( Fig. 8 F) accompanied by Protovirgularia isp.
4.2.4 Marlstone with Flaser Bedding: Protovirgularia isp.-Pholeus
abomasofomis Assemblage
This lithofacies mainly occurs in the middle part of the cycles (outer ramp) and
within the lagoonal facies (inner ramp). Its texture results from undulating and
flaser-like micrite layers separated by thin seams of marl. Although belonging
to the Cruziana Ichnofacies, the local and patchy occurrence of a firm substrate
indicates overprinting by the Glossifungites Ichnofacies. Bioturbation is mod-
erate to high, dominated by elongated bivalve burrows Protovirgularia isp.
(with only weakly pronounced chevron ornament due to the stiff to firm
substrate, Fig. 8 G), the supposed polychaete feeding trace R. commune (small,
inclined), the crustacean dwelling burrow P. abomasofomis , and more rarely,
other ichnospecies of Pholeus ( Fig. 8 H; Knaust, 2002 ).
4.2.5 Marlstone with Nodular Bedding: Planolites montanus-
R. commune Assemblage
This lithofacies occurs in the lower part of shallowing-upward cycles and con-
sists of thinly bedded and alternating mudstone and marlstone. Various disrup-
tions of the bedding result from synsedimentary deformation, reworking, or
diagenetic overprint. Many units contain reworked sediment in the form of
debris- and mud-flow deposits, where bioturbated sediment became unstable
and subject to reworking. Consequently, many reworked clasts are actually
disrupted burrows (ichnoclasts). All in all, a distal, outer ramp facies on a
distally steepened carbonate ramp can be inferred. Many intervals are highly
bioturbated and mainly contain Planolites montanus , R. commune (small,
inclined), and Protovirgularia isp. ( Cruziana Ichnofacies). Intergradations
between P. montanus and Protovirgularia isp. suggest that they were produced
by bivalves burrowing in soft versus firm substrate.