what are the 4 most common categories of non-skeletal allochems?
peloids, coated grains, intraclasts, lithoclasts
What are the 3 types of coated grains?
ooids, pisoids, oncoids
What is Grapestone?
accumulation of peloids
How do intraclasts form? Lithoclasts?
pieces of CaCO3 sediment that have been partially lithified, then broken up and reworked to become a clast
What is the definition of Peloid?
small (<2 mm) spherical or ovoid particles of fine-grained carbonate mud that lacks internal structure
How do Peloids form? What is a fecal pellet?
most originate as fecal pellets; poop of organism that eats mud
What are 2 other ways that Peloids form?
1) mechanically disaggregate calcareous algal fragments 2) micritization of skeletal grains
What organisms can bore allochems into micrite?
algae & cyanobacteria
What are the 2 parts of all coated grains?
nucleus & a cortex of carbonate laminations
What is an Ooid? Pisoid? Oncoid?
Ooid: spherical particles of CaCO3 (<2 mm); Pisoid: >2 mm; Oncoid: biologically formed coated grains
Waves, currents, and tides do what to modern Ooids?
help them roll in order to grow via accumulation of mud layers
Why does the agitation of seawater lead to the chemical precipitation of carbonate laminae onto Ooids?
agitation causes less CO2 which means precipitation of CaCO3
What are the 3 stages of Ooid growth?
agitation & suspension, aragonite precipitation, resting
Why do some modern Ooids show concentric structure whereas others show a radial structure?
concentric: aragonite, modern ooids, normal marine/high energy; radial: Mg-Calcite, ancient ooids, hypersaline/lower energy
Is the outermost lamina of an Ooid older or younger than the laminae preserved in the interior of the Ooid?
outermost = younger
What is an Oolite?
the sedimentary rock composed mainly of ooids
What are 3 ways Pisoids are diff then Ooids?
pisoids are bigger; pisoids are irregularly shaped while ooids are sub-spherical; pisoids have a range of grain sizes while ooids are well-sorted
What is a Pisolite?
the sedimentary rock composed mainly of pisoids
What are Oncoids? What is an Oncolite?
oncoid: biologically formed coated grains; oncolite: the sedimentary rock composed mainly of oncoids
Why does carbonate mud and sand stick to Oncoids?
bc the cyanobacteria (blue-green algae) creates a sticky surface
Do Oncoids need to roll around on the seafloor in order to grow?
yes