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Carbonate Grains
Carbaonate vs Clastic Rks
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Clastic rocks form from fragments of preexisting rocks
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Form outside the basin
Carbonate rocks form through biochemical
processes
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Form within the basin
Depends on chemistry of water
And temperature of water
And biological activity
Introduction
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Carbonate rocks Occur from Cambrian on
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PreC mostly dolomite w/ algae/stromatolite
Past deposition= epeiric seas
Economically important
Good for environmental interpretations
Form in basin of deposition
Skeletal grains in rks depend on age
Controls on Carbonate Deposition
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Carbonate Depositon controlled by:
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Shell producing organisms require warm waters
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most CO3 seds in trop-subtrop belt (30-40N&S)
So/oo--require normal salinities
Water depth--shallow photic zone, agitated, deeper=CCD
siliclastic imput--dilute accumulating CO3 sed
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MINERALOGY
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recent & subrecent = 2
CO3 minerals predominate
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aragonite (orthorhombic)
low Mg
calcite (trigonal)
mineralogy depends on
grains
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Mineralogy
Organism = specific
mineralogy or mixture
Mg content in part
depends on water temp
Non-CO3 mineral in LS
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terrigenous quartz & clay
pyrite
hematite
chert & phosphate of
diagenetic origin
pengellytrust.org
Non-skeletal
grains --Ooids
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Spherical-concentric lamellae
around nucleus
Nucleus=CO3 particle or qtz
grain
Sed composed of ooids=oolite
< 2mm diam; Pisolite=>2mm
Water depth generally <5m,
may reach 10-15m
Composite ooid=>1 ooid
enveloped by lamella
Most aragonitic, may get high
Mg or arag/Hi Mg
Ancient ooids=lowMg, unless
silicified or dolomitized
www.nhm.ac.uk/hosted_sites/quekett/island.html
Ooid Place of Formation
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Lakes, lagoons, rivers,
tidal flats, fresh &
hypersaline waters
Some ooids micritic-endolithic algae
Shallow tropical
supersaturated water
Saturation, agitation,
elevated temp, then
prec on
nuclei
031 Joulters Cay Ooids Offshore Bahamas, note
Batophera algae clumps (Kendall Photo)
1 Bahamas Ooids
Non skeletal grains-Pisolites
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Greater than 2 mm
in size
Pisolites
Non skeletal grains –
Peloids
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Spherical, cylindrical of microxlln
CO3-- no internal structure
Mostly .1-.5 mm –mostly fecal
pellets
Common in ls and micritic l.s
Intraclasts
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CO3 rip-ups lithified or partially lithified sediment
SKELETAL GRAINS
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skeletal components controlled by
invertebrates through time & space
controlling environmental factors:
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depth
temp
S o/oo
substrate
turbulence
I.D. skeletal grains
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Shape/size
Internal microstructure--diagenesis may
destroy
Mineralogy
Spines or spores
Mollusca
Mollusca (bivalves, gastropods,
cephalopod, found lower
Paleozoic onward)
 Bivalves
 marine, fresh, brackish
waters
 import since Tert
w/decline of brachs
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mode of life
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infuanal-in seds
epifauanal-attached
to substrate
vagil—crawler
calcite bivalves will
retain structure
Gastropods
Common in
shallow marine
Vast numbers
Hypersaline,
brackish-tolerate
fluctuations and
salinity extremes
Most benthic &
vagile
Look to i.d. by
shape
Clams
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Nautiloids, aminoid, Paleoz &
Meso, belemnoids in Meso l.s.
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nektonic or nektonic-planktonic
common pelagic, deep water l.s.
shell orig. arag--lose internal
stucture
large size, presence of speta &
siphuncle-keys
Cephalopods
Brachiopods
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Common Paleozoic &
Mesozoic, less so
today
shallow marine
now not prominent
marine invertebrate
similar to bivavles but
low to high Mg calcite,
internal structure
typically preserved
structure
blackriverfossils.org
Cnidaria (especially corals)
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include Anthozoa (corals)
2 types corals:
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mesa.edu.au
hermatypic-contain symbiotic dinoflagellate algae (zooanthellae) in polyps
ahermatypic--do not contain symbiotic dinoflagellate
because of algae, hermatypic must be in shallow warm & clear water
hermatypic corals are reef-formers
ahermatypic corals may occur at great depth & tolerate colder water, local
Paleozoic: Rugose & tabular corals= hi mg calcite-structure preserved
scelractinian corals (Triassic-Rec) aragonite skeleton: poorly preserved structure
Corals
Rugose
palaeos.com
Sceleractinian science.uva.nl
Tabulate
humboldt.edu
Echinodermata
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All marine, echinoids (sea
urchins) crinoids (sea
lillies)
Echinoids found in reef &
assoc, environ.
Crinoids in deep water,
not much sed. contrib.
Paleo & Meso crinoids
major component
Identified by large single
calcite xls
May find echinoderm
spines
science.jrank.org
Bryzoa
Small colonial marine organism
 In past, helped form reef & other
l.s esp in Paleozoic
 Formed of string of cells (zooecia
about 100 u in diam, joined by
stem of calcite
Foraminifera
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Composed of lo Mg calcite, rarely arag
Planktonic & benthic, planktonic dominate
Many forms, but in l.s most circular to subcircular
Algae
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major contrib. to carb.
seds
provide skeletal
grains, trap sed to
form laminated seds,
break down particles
by boring into them
many PreC carb.
formed in part by
algae
wetwebmedia.com
Algae Continued
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4 major types of
algae
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red algae
(rhodophyta)
green algae
(chlorphyta)
blue-grn algae
(cyanophyta-bore
into skeletal grain)
yellow green algae
(chrysophytacoccoliths)
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Bluegreen algae & algal
mats
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occur in lo lat. shallow subtidal
through supratidal
environments (just above high
tide)
also occur in hypersaline lakes
and marshes
bl grn is mucilagiinous &
filamentous—trap particles to
form stromatolite
stromatolite occur through out
but are especially important in
the PreC
stromatolite=variety of growth
patterns
morphologies depend on water
depth, tidal & wave energy,
sed rate, & frequency of
exposure
small columns & dome in less
agitated bay waters
low domes & planar mats in
protected tidal flats
Algae Continued
AlgaeFrom capping reef deposits of the w:Tabernas basin, S
Stromatolites &
Oncalites
Algae Continued
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endolithic alageborers
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fine micrite due to
endolithic algae
then dep. at depths
of 100-200 m=
photic zone--
Most of the microalgal borers associated with
corals are chlorophyes of the genus Ostreobium as
shown below (white arrow). The red arrows indicate
borings from endolithic worms or mussels to be
discussed later. www2.fiu.edu
Other CO3-forming organisms
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sponges: spicules may be silica
arthropods
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ostracods 1mm, Cam-recent
shallow marine, brakish or fresh env
 shell=calcite
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trilobite-Cam-Perm
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entirely marine
Micrite
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F gr dark matrix of carb called
micrite < 4 u
accumulates in tidal flats,
shallow lagoons to deep
ocean floor and on slopes
thought to accumulate
through breakdown of blgrn
algae
 algae breaks down and
release vast arag needles
other processes:
 bioerosion-boring algae &
sponges
 mechanical breakdown of
skeletal grainswaves/currents
 biochemical precip-photosynthesis &
decomposition
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geology.sfasu.edu
atlantisonline.smfforfree2.com
Aragonite Needles
AAPG
Micrite Continued
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inorganic precipitation in some areas e.g.
Arabian coast due to supersaturated
water--little calcareous algae is present
cannot discount inorganic precipt in past
also, micrite may be a cement
Carbonate Rocks
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Carbonate rocks - limestones composed of
calcite (CaCO3) or dolostones composed
of dolomite (CaMgCO3).
Form through biological and biochemical
processes and through inorganic
precipitation from seawater
Carbonate rocks widespread and in every
geological period beginning with Cambrian
Environment
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Most carbonate sediments form in
warm waters
E.g., corals and algae common in
carbonate rocks, and mostly found
tropical to subtropical latitudes or
from about 30o N and S latitudes
Most carbonate sediments
generated in photic zone
Unlike sandstones, most
carbonate grains formed in
environment in which they are
deposited
Detrital grains in sandstones
usually derived from outside the
environment in which they were
deposited
Environment Continued
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Carbonate sediments
do not usually occur
below depths of about
3500 -4000 meters in
the oceans
Below these depths
carbonate sediments
will dissolve
The depths at which
carbonate sediments
dissolve in the ocean
is called the carbonate
compensation depth
or CCD
Classification Scheme
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Two principal classification schemes are used for
limestones. One is Folk's classification scheme, named
after Robert Folk, and Dunham's classification scheme,
named after Robert Dunham
Folk's scheme based on presence or absence of
allochems (carbonate particles or grains), matrix
(limestone clay called micrite), and type of cement (spar
is a cement composed of coarse)
Dunham's scheme is based on texture of rock. i.e.
whether rock contains matrix, whether carbonate grains
float in matrix or whether they are in contact with each
other, and whether rock has carbonate grains
Dunham’s Classification
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Based on whether have
more or less that 10%
grains
Whether rock is mud or
grain supported.
Also if original
components were bound
together like coral.
Tells about transport
history.
Folk Classification
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Carbonate rocks consits
of:
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Allochems—grains
Intersitial material—micrite
or spar cement
Micrite is "lime mud", the
dense, dull-looking
sediment made of clay
sized crystals of CaCO3.
Spar—clear to translucent
carbonate cement.
Micrite and Spar
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Name is built up by stringing together
all the allochem names in order from
least to most abundant, and then
adding the interstitial material name
("matrix" below for short). For example,
a rock like this:
Folk Continued
Oolites + Fossils + Spar matrix =
Oo bio sparite
The name is written as one word,
Oobiosparite.
Another example (again allochems
from least to most abundant):
Pellets + Oolites + Fossils +
Micrite matrix = pel oo bio micrite
The name is written as one word,
Peloobiomicrite.
But what if there is both micrite and
spar matrix? The system is the same;
just list them from least to most
abundant.
Fossils + Spar matrix + Micrite
matrix = bio spar micrite
Carbonate Grains
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ooids--Ooids are
spherical grains formed
by calcite precipitation
around a nucleus such as
a shell fragment, a quartz
grain, etc. They are less
than 2mm in diameter
and typically form in
shallow, warm, agitated,
and carbonate-saturated
waters such as those
near the Bahamas.
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pisolites--Pisolites
are ooids greater than
2mm in size
Similar environments
as ooids
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stromatolites--Stromatolites are
laminated carbonate sediments
composed of mats of blue-green
algae and layers of sediment. The
algae, which forms the mats, is a
plant and plants require sunlight
to survive. Therefore,
stromatolites generally form in
warm shallow waters. The algae
is "sticky" and it grows filaments.
This sticky and filamentous algae
traps sediment brought in by the
currents. Consequently, a layer of
algae forms then a layer of
sediment is deposited on top of
the algae. Subsequently, the
algae grows through the sediment
to form another mat and the cycle
begins again. Ultimately, a
layered rock composed of
alternating algal mats and
sediments is produced.
Stromatolites form in quiet,
hypersaline waters with little
animal life around to destroy the
mats.
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oncolites-Oncolites are
stromatolites
rolled in a ball.
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corals--Corals have a
symbiotic relationship
with dinoflagellate
algae called
zooanthellae. Algae
are plants. Therefore,
in order for corals to
survive they generally
have to be within the
photic zone (the zone
of maximum light
penetration in the
ocean). Plants require
sunlight for
photosynthesis. In the
process of
photosynthesis, plants
produce oxygen and
consume CO2. Corals
are major reef formers
today and in the past.
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Intraclasts--Semiconsolidated
carbonate material
ripped-up and
incorporated in the
rock.
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dolostone--A
dolostone is a rock
compose of 90100% dolomite.
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