Evolution of Shallow-Water
Mikhail B. Burzin, Françoise Debrenne, and Andrey Yu. Zhuravlev
Features of Cambrian level-bottom communities that inhabited carbonate and siliciclastic substrates are outlined. A high diversity of level-bottom communities with multiple trophic guilds was established in the Early Cambrian, replacing largely microbial-dominated Vendian ecosystems. Taxonomic richness of Early Cambrian communities contrasts with relative impoverishment of their Middle and Late Cambrian counterparts. Displacement of communities was common, and entire communities might migrate into areas with more favorable conditions if their original habitats suffered a crisis.
CAMBRIAN DEPOSITIONAL SYSTEMS can be divided into clastic and carbonate regimes, because substrate type strongly influences community composition. These aspects of sedimentation were in general controlled by climate and the size of the area available for denudation. With few exceptions, environments of carbonate sedimentation were restricted to low latitudes and siliciclastic-dominated settings occurred mostly in temperate conditions. The Siberian Platform throughout the Cambrian exemplified carbonate-dominated habitats. Baltica, Bohemia, and Avalonia represented regions where siliciclastic sedimentation prevailed. Laurentia and Australia were characterized by a mosaic of facies.
Although the entire set of trophic guilds existed from the beginning of the period, Cambrian guilds were different even from their Ordovician successors and probably had already changed significantly by the end of the Cambrian. Tables 10.1 and 10.2 display the ecospace utilization by Cambrian organisms that are preserved now as body fossils.
Benthic primary producers were represented chiefly by probable calcified cyanobacteria (e.g., Obruchevella) and by carbonaceous algae (e.g., Margaretia) and possible