Shallow-Marine Carbonates - Trace Fossils as Indicators of Sedimentary Environments - page 701

shoals in a shallow subtidal to intertidal environment. Because of the contin-
ued redeposition of sediment, bioturbation is rare and encompasses vertically
oriented trace fossils such as Lingulichnus verticalis ( Fig. 8 A), Skolithos isp.,
and Altichnus isp. ( Fig. 8 B). Marginal regions of the shoal bodies merge into
firm- or hardgrounds and may contain Balanoglossites triadicus and Trypa-
nites weisei . Minor cycles typically preserve an event bed on the top.
4.2.2 Lime Mudstone (Micrite): B. triadicus-T. weisei Assemblage
Discontinuity surfaces with firm- and hardground features are common
throughout the Lower Muschelkalk but are best developed as ravinement sur-
faces just below the grainstone/packstone beds (e.g., Upper Oolite Bed, Lower
Terebratula Bed). Thus, they occur either in front of the shoals in a very
shallow-subtidal to intertidal environment or in the back-shoal lagoon (subti-
dal). In front of the shoals, intense lithification with the development of thick
and multiple hardground layers took place, whereas slightly deeper areas farther
offshore and back-barrier lagoonal environments typically contain numerous
thin firmground layers. The bioturbation and bioerosion of such lime mudstone
layers is moderate to high with a low ichnodiversity, typically with few main
components. The continuous spectrum of burrows and borings with sharp mar-
gins demarcates firmgrounds with B. triadicus and R. jenense ( Glossifungites
Ichnofacies, Fig. 8 C), which progressively grade into hardgrounds with T.
weisei ( Trypanites ichnofacies, Fig. 8 D; Knaust, 2008 ). They are passively
filled by marly dolomite and probably originated on a lower tidal flat.
4.2.3 Marly Limestone with Horizontal Bedding: R. commune-
Thalassinoides suevicus Assemblage
The lower and upper portion of the Lower Muschelkalk succession, where the
facies shift from supratidal to inter- and subtidal conditions and back, is char-
acterized by platy limestone. This facies also occurs in the upper part of major
to hardground suite, exhibiting passively dolomite-filled R. jenense in cross section (R), a fragment
of a Balanoglossites triadicus system (B), and superimposed needle-like Trypanites weisei borings
(T) from the top margin. Glossifungites - Trypanites Ichnofacies. Upper Oolite Bed, Jena-Steudnitz
quarry (type area and type bed of T. weisei and B. triadicus ). (E) Dolomitic and marly limestone
with extensive R. commune (large, horizontal) on the bedding surface. Cruziana Ichnofacies (inter-
tidal). Basal Muschelkalk, Tannroda-B¨ ttelborn quarry. (F) Marly limestone with a stunt and
slightly inclined R. commune (small, inclined). Cruziana Ichnofacies (subtidal). Upper Wellenkalk,
Haufeld quarry. (G) Protovirgularia isp. within marly limestone with parallel bedding. Cruziana
Ichnofacies. Between Lower and Upper Terebratula Bed, Plaue quarry. (H) Pholeus bifurcatus
(incomplete) within flaser-bedded marly limestone. Cruziana Ichnofacies. Middle Wellenkalk,
T¨nsch¨ tz quarry.