cambrian period

ediacaran biota

there were animals, but most of them: did not belong to modern phyla, no legs, fins, etc., no obvious sense organs, no obvious body openings, no mineralized skeletons, no burrow into the sediment (not deeply)

cambrian biota

almost all modern phyla with skeletons appeared; animals with legs, fins, body opening, sense organs, and skeletons were abundant. marine ecosystems are relatively modern: herbivory, predation, suspension feeding, etc., were present. burrowing and bioturbation increased

Laurentia

coastlines become passive margins all the way around. sedimentation accommodate by: sea level rise, thermal subsidence. almost entirely drowned by the end of the period.

sediment sources

silicates weathering from continent, carbonates precipitating from water, biogenic carbonates

marine sedimentation

dominated by terrigenous sands: mature silicates, evidence for wind-based weathering. carbonates on shelf edges, far from terrestrial sources. toward end of cambrian, continent is flooded

great unconformity

cambrian material is much younger than many of the underlying rocks. widespread erosion/non-deposition

sedimentoligical trends

dominated by silicates, shift to carbonate dominance toward end of period, sea level starts low and rises, underlying pre-cambrian rocks are often eroded and MUCH older than cambrian rocks

cambrian explosion

first mineralized skeletons in several lineages. massive increase in biodiversity visible in the fossil record, almost all phyla with mineralized skeletons originate at this time

phyla

major clades within the animal kingdom that are characterized by a particular body plan that describes their major morphological features 

mineralized skeletons

minerals for structure and protection: calcite/aragonite, apatite, silica

Cambrian life

huge increase in diversity of animals and preservation. Large increase in production and diversity of mineralized skeletons. Almost all animal phyla with mineralized skeletons first appear in Cambrian period

ediacaran trace fossils

simple horizontal burrows; microbial mats cover seafloor, animals can attach to mats

cambrian trace fossils

some are more complex, branching, and/or probing vertically into the sediment (increased burrowing); bioturbated “mixed layer” replaces mats, sediment surface less stable. increase in predation and predator effectiveness = deeper burrowing and more active motility