Skeletal and Nonskeletal

Ooids

spherical grains composed of thin concentric layers of precipitated aragonite. Develops in shallow agitated warm water.

Biochemical formation of ooids

bacterial activity within the organic matter creates a microenvironment conducive to carbonate precipitation

inorganic formation of ooids

shallow tropical seas saturated with CaCO3 together with water agitation, CO2 degassing and elevated temperature might be sufficient to bring about carbonate precipitation on nuclei

Peloids

fecal matter excreted by benthic organisms. Composed of packed lime-mud

intraclasts

Composed of semi-lithified lime mud

Aggregates

peloids, ooids, intraclasts, etc. cemented together

skeletal grains or bioclasts are…

whole fragmented parts of carbonate producing organisms

What affects the distribution and development of carbonate secreting organisms

• depth

• temperature

• salinity

• substrate

• turbulence

Mollusks

these refer to bivalves, gastropods, and cephalopods. Present in marine, brackish, and freshwater.

what is a rudist

coral-like bivalves formed reefs in cretaceous

describe the structure of mollusk layers

prismatic layer of aragonite prisms and nacreous layer consisting of sheets of aragonite tablets.

how are bioclasts categorized based on the organism’s life habit

Infaunal, epifaunal, agile, nektonic, planktonic

What is infaunal

organisms that live within the sediment ex. bivalves (clams), worms, etc.

what is epifaunal

organisms that live on the surface of the seafloor (oysters, brachiopods, corals, etc.)

what is agile

organisms that are mobile and can move actively across the seafloor

what is necktonic

organisms that swim actively

what is planktonic

organisms that float or drift with the ocean current

characteristics of gastropods

• present in shallow marine and hypersaline backish waters

• more are benthic and agile

• majority have shells of aragonite with similar internal microstructures to bivalves

What are nautiloids and ammonoids

a type of cephalopod that is common in limestones of the Paleozoic and Mesozoic

What are Belemnites

A type of cephalopod in the mesozoic made of calcite with a strong radial-fibrous fabric in cross-section

What is the life habit of cephalopods?

marine, dominantly necktonic or nektoplanktonic

Where do cephalopods occur?

pelagic, relatively deep water deposits

Where are brachiopods common?

common in Paleozoic and Mesozoic limestone of shallow-marine origin

What is the structure of Brachiopods

• Composed of low-Mg calcite

• Commonly very thin, outer layer of calcite fibers oriented normal to the shell surface with a thicker inner layer of oblique fibers

what are the different types of corals

hermatypic, ahermatypic, rugose, and tabulate

hermatypic corals

contain symbiotic dinoflagellate algae in their polyps

Ahermatypic corals

w/o algae, forms in deeper environments and can tolerate colder waters. Locally form build-ups and barriers

Rugose and tabulate corals

corals that are important in silurian and devonian reefs

Scleractinian corals

present in many triassic reefs, composition: aragonitic

what are echinoderms

Wholly marine, includes echinoids and crinoids. Their skeletons are calcitic.

where do echinoids and crinoids occur?

echinoids inhabit reef environments while crinoids are restricted to deeper waters

What type of organisms are bryozoans

Bryozoans are colonial organisms. Presently, they are only locally significant as suppliers of carbonate sediment.

During which geological era were bryozoans major contributors to reef and limestone formation?

Paleozoic

What are the mineral compositions of modern bryozoan skeletons?

Aragonite, Calcite (High-Mg calcite), a mixture of both

Describe the fenestrate form of Bryozoans

commonly seen in Paleozoic limestones. Skeleton consist of foliaceous calcite with round holes filled with sparite.

what type of environment do foraminifera primarily inhabit

planktonic: float in water, dominate some pelagic limestones

benthic: warm shallow seas. Live on seafloor sediments

what minerals make up foraminifera tests

mostly low or high Mg calcite, rarely aragonite

what is the shape of foraminifera tests

circular to subcircular with chambers

How does the test wall structure differ between thin-walled and thick-walled foraminifera?

• Thin-walled species: Microgranular texture.

• Thick-walled species (e.g., rotaliids, nummulites, orbitolinids): Fibrous texture.

what is a spicule (sponges)

small needle like structure that forms part of the sponge’s skeleton. Made of silica or calcite and occur in sediments from Cambrian.

What are Stromatoporoids

marine, spherical to laminar shape, major reef organism in the Silurian and Devonian.

What are Ostracods?

Type of small arthropods, 1mm length, with bivalved shells, found in marine, brackish, and freshwater environments, typically at shallow depths.

Rhodophyta (Red algae)

Skeletons of cryptocrystalline calcite precipitated within and between cell walls. Encrustations may be massive and rounded, or delicately branched.

what are the three types of Green Algae

Codiaceae, Dasycladaceae, and Characeae

Describe Dasyclad Algae

occurs in marine, shallow, and lagoonal areas of the tropics. Occur due to incomplete calcification where aragonitic crust precipitate around the stem and branches of the plant.

What are the two common genera of Codiacean Algae

Halimeda and Penicillus

Halimeda

a segmented plant which

disintegrates into sand sized particles.

Penicillus

algal consisting of a bundle of filaments coated in needles of aragonite. Disintegrates into find grained carbonate sediment.

What are coccolithophorids

planktonic algae with low-Mg calcite skeletons. From Jurassic to recent

what is micrite

consists of mirocrystalline calcite or aragonite. In modern time it is dervied from disaggregation of calcareous green algae.

Possible sources of micrite or lime mud

• inorganic precipitation

• Bioerosion

• mechanical breakdown of skeletal grains

• Biochemical precipitation through microbial photosynthesis

what is sparry calcite

large crystals of Low-Mg calcite that form cement in limestones. Commonly form from recrystallization.

Carbonate grains can be divided into (___-chem)

allochems and orthochems

allochems are…

transported grains

orthochems

deposited in place

differentiation micrite, sparite, and microspar

micrite: <4mm lime mud, analogous to matrix in siliciclastics

spar: larger, clean interlocking carbonate crystals

microspar: 4-20 microns