Peridital and cold water carbonates

What is the bahamian tidal flat environment

• Ooidic sands with tidal channels that erode into the limstone basement

• Bidirectional flow

• Channels may never be subaerially exposed

• Has storm lags

Tidal Flats modern processes and products

• persian gulf

• Can be ahrid or humid

When does most peritidal accumulation of carbonates occur?

• During high sea level rise rates

What is a simple beach profile defined as

• Offshore

• Shoreface

• Foreshore (affecte dby tides)

• Backshpre (not affected by water on a normal basis)

Eolian carbonates

• IS a carbonate that has been transported by wind

• Dunes, Beach and subtidal environment

How do you recognize eo9lian carbonates in the rock record

• Very difficult

• sediments look identical to beach and shoal deposits

• Shoreface erosion destroys lithified dunes

Cold water carbonates

• Heterozoan association

• Slow growth rates

• Mainly bryozoan echinoderm

Open ocean shelf cold water carbonate

• Very strong winds and storms and waves that crash against the coast with no protection, very high energy active environment

• Carbonates act like clinoforms in a silisclastic basin

Interior basin margin ramp

• Poor in oxygen, low carbonate production

• Oxygen depleted water flows into the basin with high nutrient load

Interior basin margin ramp estuarine va anti estuarine model

• Estuarine has fresh water flowing in vs anti estuarine has evaporation which creates saltier and denser water

What is a sea way ocean model

• Closed of carbonate ramp, has wave dominated and tide dominated environments, mainly clastics

• Modern english channel

Thermocline stratified ramp

• Warm from radiation from the sun develops a good thermocline

• is above the FWWB

• Most heterozoan below thermocline

What does the occurence of cool water carbonates indicate

• Shallow water, mid to high latitude settings

• area of upwelling

• sedimentation below thermocline

• area affected by cool water currents

• an icehouse climate

What are the cold water carbonate smokign guns

• Ikaite (hydrated calcite)

• glendonite

What is ikaite

• A metastable form of hydrated calcite at very low temps

• doe snot percipoitate and just dissolves

• very hard to see in the rock record

• Needs high alkalinity environment

• Inhibitor of anhydrite calcium carbonate (low mg-ca)

• Cold temp percipitating solution

• Has many pseudomorphs (same shape diff composition)

How do we know ikaite = glendonite

• Monoclinic

• pyramidal terminations

• quasi square

What are 5 criteria for recognition of cool water carbonates

1. Carbonates have drop stones and glacicene sediments

2. situated in appropriate paleolatitudes

3. Glenonite and pseudomorphs in heterozoan association

4. Heterozoan association of facies

5. Trace elements and isotope geochemistry indicates

Early Permian Warm Tropical carbonates in the asselian

• Panthalasa sea connected to the tethys ocean and allwoed for warm water to enter the svedrup basin

• deep thermocline with a deep photozoan assemblage

What happened in the Artinskian?

The panthalasa sea way is now closed and in the svedrup basin there are only cool carbonates and bryanoderm assemblages

• Heterozoan extended carbonate factories

What happened in the Wordian in the svedrup basin

• Clastic influence

• sharp transition between warm and cool water

• prograding basin

What happened in the late permian (tempreate cold glass ramp)

• Rapid growth of spiculite cherts and hyalosponges expand onto the ramp

• Pangea nears completion

How does one explain the progressive eradication of carbonate factories for the onset of siliceous factories

• Carbonates were no lonegr preserved

• it was very cold which does not prevent the accumulation of sponges as they can live anywhere

• anoxic waters favoured biogenic chert preservation

What are the conditions for production accumulation and preservation of chert?

1. Adequate supply of silica

2. Transport of silica

3. Biota to grow chert

4. Favourable environment

5. Post death preservation

6. minimal clastic and carbonate dilution

What was the ideal silica environment for a silica ramp?

• Nutrient rich water with zones of upwelling

• Lack of light

• Low sedimentation rates

• Low carbonate input

• anoxic basinal conditions to prevent carbonate percipitation

What events caused the rapid spread of glass ramps

What happeend in the middle permian extinction of western pangea

• Complete domination of the silica ramps

• heterozoan carbonate factories eradicated

• Phosphatic brachiopods go crazy

• accumulation of glauconite

Late carboniferous early permian silicate buffering

• Little to no silicate weathering with high Co2 accumulation results in low pH leads to ocean acidification

• There is no bicarbonate so there is no buffering

• Results in very high CCD and narrow lysocline with no Caco3 accumulation

What time in the permian resulted in runaway greenhouse gases from breakdown of silicate buffering

• early to late permian

• with no CO2 being removed from the atmosphere

What happened to the late permian glass ramps

• Sponge spicules werent affected by pH an dlysoclines

What happened to the ocean along NW pangea

• Active upwelling brings cool water onto the platform that is acidic

• there was widesprea docean acidification at this time