Early Ordovician sponge-Calathium-microbial reefs on the Yangtze Platform margin of the South China Block

Abstract

Early Ordovician (late Tremadocian to early Floian) reefs on the Yangtze Platform margin of the Hunghuayuan Formation at Zhangzhai section in southeastern Guizhou, South China show three types of reefs in two broad categories: microbial-dominated (stromatolite and lithistid spongeCalathium-calcimicrobial) reefs and metazoan-dominated (lithistid sponge-Calathium) reefs. These reef types represent different communities controlled by varying environmental settings. Stromatolites tended to develop in the shallow subtidal zone, whereas unlaminated calcimicrobial mounds and metazoandominated reefs thrived at greater depths. This is the first report on metazoan-dominated reefs at the platform margin of the Hunghuayuan Formation.

Untangling intricate microbial–sponge frameworks: The contributions of sponges to Early Ordovician reefs

“…References to: 1, Hong et al (2012); 2, Shapiro and Rigby (2004); 3, Kruse and Zhuravlev (2008); 4, Lee et al (2014); 5, Pratt and James (1982); 6, Cañas and Carrera (1993);7, de Freitas and Mayr (1995); 8, Church (1974) Toomey and Nitecki (1979); 13, current study; 14, Klappa and James (1980); 15, Desrochers and James (1989); 16, Pratt (1989b); 17, Kobluk (1981). under columnar to irregular-shaped thrombolites, massive corals, calathiids or lithistid sponges (Pratt and James, 1982;Li et al, 2014), they are interpreted as cryptic dwellers (Fig. 7).…”

“…Archaeoscyphia preserved in growth position have been interpreted as constructors and bafflers of micritic sediments in Early Ordovician reefs (Church, 1974;Toomey and Nitecki, 1979;Cañas and Carrera, 1993;Adachi et al, 2012;Li et al, 2014). In addition, subsidiary tabular to hemispherical anthaspidellid sponges commonly encrusted other reef constituents (Church, 1974;Cañas and Carrera, 1993;Adachi et al, 2013) (Fig.…”

“…The baffler refers to those organisms with erect forms, which could trap sediments in currents (e.g., Cañas and Carerra, 1993;Fagerstrom and Weidlich, 1999). The binder includes organisms mostly growing laterally, thus merging frameworks and consolidating sediments (e.g., Fagerstrom and Weidlich, 1999); these can be subdivided into encrusters, when locally covering the surfaces of constructors (e.g., Cañas and Carerra, 1993), and sediment stabilizers, when binding loose sediments in the basal parts of the reefs (e.g., Church, 1974;Li et al, 2014). In addition, those constituents occurring inside of cavities are considered as cryptic dwellers (Kobluk, 1988;Adachi et al, 2012).…”

“…Although the development of Early Ordovician reefs has been largely attributed to microbial binding and building processes (Cañas and Carerra, 1993;Webby, 2002;Adachi et al, 2009Adachi et al, , 2013, some reports have demonstrated that Early Ordovician skeletal frameworks built by skeletal organisms also constituted parts of the reefs (Toomey and Nitecki, 1979;Pratt and James, 1982;Adachi et al, 2011;Cuffey et al, 2013;Li et al, 2014). In this study, we document sponge frameworks in typical Early Ordovician microbial-sponge reefs from Korea, and assess the sedimentological and paleoecological functions of the sponges based on detailed petrographic descriptions.…”

“…1;Kruse and Reitner, 2014). The diversity and abundance of reef-building benthic organisms progressively increased during the Early Ordovician, and included worldwide occurrences of lithistid sponges and calathiids and local emergences of bryozoans, corals and stromatoporoids (Toomey and Nitecki, 1979;Pratt and James, 1982;Adachi et al, 2011;Cuffey et al, 2013;Li et al, 2014), and metazoans became dominant constituents of Middle Ordovician to Devonian skeletal-dominated reefs (Wood, 1999;Webby, 2002). Early Ordovician reefs represent, therefore, the transition from microbial-to metazoandominated reefs, and such reefs potentially provide key clues regarding the early evolution of skeletal-dominated reefs (Adachi et al, 2011).…”