Lime mud factory and Carbonate slopes (19, 20 ,21)

Where doe slime mud come from?

Maceration

Whitings

Bioerosion

Microbial carbonates

Mud mounds

Lie mud in cool cold water carbonates

What is maceration

• The breakdown of skeletons of organisms into micritic particles which accumulate on the sea floor and create lime mud on the floor

What are whitings

• Clouds of white fine grained suspended carbonate particles and appear in open marine water

What is the dominant theory for whitings form

• Carbonate percipitates in the water coloum with the aid of cyanobacteria

What is the abiotic explanation for whitings

• resedimentation of the caco3, but whitings are still present in calm water

• storms turbulence, upwelling

• Primary mechanics is an increase in salinity, increase in temp, increase in pH

Why does increasing pH temp and increasing salinity lead to whitings?

• increasing the salinity may lead to nucleation of carbonate due to removal of Co2 from the water

• removal of Co2 sheifts reaction to the left and favours precipiation of Caco3

What is the biotic explanation for carbonate whitings

• The cyanobacteria synechococcus

• An envelope of water surrounds each bacteria

• creating an envirobnment that has a higher pH and higher calcium ion concentration than outside or inside the cell

• these cells are photosynthetic

How does cyanobacteria synechococcus result in whitings

• they raise pH due to photosynthesis and decreases Co2 concentration which causes Caco3 to precipitate

• favours exchnage of bicaronate across the cell

• then cell breaks off falls onto the sea floor and leaves the carbonate to settle as micrite

How does Bioerosion cause whitings

• The parrot fish eats the reef, poops it out and causes calcite (carbonate mud)

How does micrite form from Microbial carbonates?

• Microbial calcification that directly precipitates on microbial filaments

What are the 4 steps for microbial calcification

• Formation

• Calcification

• Degradation

• Sedimentation then into biomicrite (peliodal texture)

When do majority of mud moudns occur in the geological record

• From the cambrain to mid cretaceous

What is a mud mound

• Buildup of pelodal mud, or micrite can be very tall

• presence of stromatactise]

• deep quiet waters

What is the origin for mud mound micrite

• needs rising sea level to accomodate growth

• Requires organic baffle around the mud mound to contain it

• Need microbes to calficy and organimineralization

Where does lime mud come from in cool water carbonates

• breakdown of skeletal grains

• Major macceration along planes of weakness between structural elements (major)

• Boring into previpous Caco3 structures (minor)

What are three main organic sources of Caco3 mud

• Breakdown of rigid skeletal fragments (bivalves forams)

• Planktonic organism settling (Diatoms coccoliths)

• Whole spicule release from decay of tissue (sponge)

What are the types of carbonate slope grains?

• Debris

• Grains

• Mud

What is an escarpment margin in carbonates

• Carbonate edge, steep often vertical (cliff like)

• seperates shallow from deep and has a drop off

• Usually caused by tectonics which create the steep drop off

The cathedral escarpment

• Int he rocky mounts (Castle mountain)

• cambrian carbonate platform

• With a very big drop off

What was the geological setting of the cathedral escarpment

• Western edge of laurentia

• Passive margin deposition

• Overlying rift deposits

What are the three proposed models for escarpment formation?

• Growth escaprment

• Accretionary margin

• Platform collapse

Model 1: growth escarpment

• Vertically accretionary reef

• Pulses of growth from abrupt sea level rise

• Drastic SL rise drowned the reef

• harsh slope and facies break

• Resulted in the preservation of the burgess shale

Model 2: accretionary margin

• Facies along a ramp with storm events and erosion

• maybe it wasnt as steep of a slope and the ramp didnt grow as high, but then accelerated in growth creating the steep slope

• Model is completley dismissed

Model 3: Syndepositional platform collapse

• Megatruncation surfaces create deep seated faulting with escarpment surfaces along the reef platform

• The is the most likely model scenario

• agrees with geology

When was there an example of an accretionary margin?

• Carboniferous sverdrup basin

• Relatively cool shallow water temp

• warm water

• Photozoan heterozoan carbonates

• Proximal debris slopes

• distal carbonate grains

• Mud in outerslope

Where is the abyssal plain in bathymetry

• Deeper than 4.5 km, near flat except near tectonic structures

Near the equator why is the water less saline?

There is more evaporation in comparison to precipitation because there is more rainfall

At the poles, why is there more saline water?

• This area has more evaporation than precipiation, meaning salinity is concentrated in this part of the ocean

Where in the world has the warmest oceans?

• Near the equator as it has the most radiation from the sun

What is the corriolis effect

• Influences trade winds gyres and surface currents

• nutrient delivery, water temp, sediment transport

• Displaces to the RIGHT in N

• LEFT in SOUTH

  So RN and LS

How does upwelling and productivity effect carbonate formation?

Why is the coast of californa have such cold water?

• Constant upwelling of cold water, brings up nutrient rich cold water, cycling warm water underneath

What creates the O2 deflect along the thermocline?

• Organisms die, rain down OM which requires oxidation, and in the shallow sea lots of organisms use O2

Why do carbonate zones need no upwelling?

Theres already a low nutrient concentration so upwelling would only bring up cold water, not nutrientd

What is earths conveyor belt

• Global thermohaline

• aka heat salt transport

• water that is deeper is colder is more dense than surface water

• Cold water sinks near greenland

• Becomes warm in the indian and pacific oceans from upwelling

What is the calcite compensation depth?

• The depth where calcite is no longer stable and dissolves

• No carbonate precipiation and all dissolution

• due to high CO2 accumulation which lowers pH and dissolves Caco3

• Cold water also dissolves CaCO3 (warm water precips)

Chalk oceanic carbonates

• Made up of cocoliths

• Greenhouse climate

• SHallow seas with high biological productivity, cocoliths die and leave behidn their skeleton and then create large accumulations (hundreds of meters tall)

• all accumulates above the CCD, indicating shallow seas

Closed basins and anoxia conditions

• Closed basins have much less ocean circulation

• seperation of water creates anoxic black shales

• High salinity, high evaporation probably low precipiation