The conditions for preservation of organic matter affected by the rate of deposition of sediments as well as grain size of sediments. The high rate of depositing sediments give rise to rapid burial of organic matter and  the preservation will be good. The rapid burial of organic matter may lead to anoxic condition, in such condition decaying microbes can not survive and chances of preservation will increase. The grain size is also affect on the preservation of  organic matter. The good preservation of the any organic matter is found in the fine gained sediments while the comparatively poor preservation occurred in the coarse grain sediments.

Dear Tripathi

It is very interesting to have a 1000 m long sediment core sample! Such sample can bring out many interesting findings. I would suggest you to measure Al or even Fe through out the core length (at any interval that could represent the whole history) and simultaneously measure the organic content. Subsequently you may carry out some statistical analysis to find out the correlation between the two parameters. This may provide you with some useful information about the role of lithology in governing the organic contents.

Wish you all the best

karbassi 

Major and trace element analyses can bring out some information about the lithology and burial. Preservation can actually be correlated. 

Dear Shubham Tripathi,

Preservation in fine grained or mud mound levels is normally better than coarser grained materials.  The other point is pressure or weight of overburden of levels on a bed. Sometimes leaching process can clean organic materials. Please control your sequence with nearby logs or sedimentation condition.   

Dear Karbassi sir

Thank you very much for the response, I will try to look for parameters you suggested. 

Thanks 

PROCESSES FOR ENHANCED ORGANIC RICHNESS

BIOLOGIC PRODUCTIVITY

(Nutrient Concentrating Processes and Settings)

A.        Enhanced Nutrient Concentrations

1) Terrestrial Input of Nutrients

2) Coastal Upwelling

3) Open Water Upwelling

B.        Evaporitic Settings

1) Silled Basins

2) Shelf/Platform Depressions

3) Rifts on Flooded Continental Platforms

4) Mid and High Latitude Deserts

C.        Restricted Geographic Configuration

D.        Terrestrial Kerogen Influx

E.        High Latitude Effect (Oceanic Convergence)

DEPOSITIONAL PRESERVATION

(of Organic Material in Depositional Environment)

A.        Actively Subsiding Depocenter at Time of Deposition

B.        Maintenance of Anoxia

1) Positive Water Bal­ance (Fresh-Water Influx)

2) Salinity Stratification

3) Thermal Stratification

4) High Productivity

5) Restricted Circulation (Deep, Narrow Trough or Silled Basin)

C.        Isolation Factor

1) Distance of Basin from Paleo‑Shoreline

(Coastlines, Shelves, Epeiric Seaways)

2) Local Uplift Deflecting Drainage away from Basin (Rifts)

NON-DILUTION OF SEDIMENTED ORGANIC MATTER

(Low Sedimentation Rate)

A.        Proximity to Orogenic Belts during Interval of Source Rock Deposition

B.        Drainage Conduits into Depocenter from Uplifted Areas

C.        Rate Influence by Climatic Belts, e.g. Wet Zones

The preservation Organic matter is mainly controlled by lithological characters.

Hello,

the lithology may have several roles. The first influences regard OM sedimentation and preservation as mentioned by other colleagues before me (dilution of organic fraction by mineral fraction, which lowers the TOC; permeability+porosity which will condition the oxidant resupply (that's why OM is better preserved in fine-grained sediments). Diagenesis can have an impact, through mineral transformation, releasing reactive iron during, for instance, diagenetic transformation of clay minerals. The reactive iron may in turn fuel OM remineralization through iron reducing bacterial activity. If the lithology facilitates or hampers the circulation of diagenetic fluids (e.g., methane), it may also have impacts. If you have more specific questions, please ask me directly if I may help.

nt

Hi,

I would also add that the correlation between grain size and OM preservation is more a consequence than a cause. Environments of deposition of coarse material are directly related to high(er) energy and thus to zone where we have a good water renewal that favors OM degradation at the sea/sediments interface (that's why we do not find OM rich sands) . On the contrary, finer sediments are more likely associated to lower energy and thus to possible zone of low water renewal.

Thus at a first order, OM will only have a chance to bury where fine sediments can deposit (more precisely in low energy environments). Then occur all the other processes already mentioned by our colleagues here above.

Mathieu

Fine-grained, low permeability, unburrowed sediments (like shale) will preserve organic matter better than high-energy, coarser sediments that allow oxygenated water to pass through.  My experience shows the richest organic shale form from slow clay sedimentation rates in an anoxic silled or stratified basin where the surface water are normal marine (or at least allow lots of algal production) and the organic matter settles in an anoxic bottom waters.  If sedimentation rates are to great the organic matter gets diluted with to much clay.  Being near shelf edge upwellings really helps organic matter production and can be associated with phosphates and glauconite.  TOC measurements are the cheapest way to document organic-richness (more reliable than trace element evaluation).

There is a lot of literature about mineral-organic associations.  Certain minerals, especially clays, can protect organic material from degradation during transport prior to deposition.  After deposition, organic matter is fundamentally protected by limiting porewater transport and oxygen exposure, as Paul Grover has answered.  In shallow burial, the most important factors in diagenesis of organic matter is water flow and oxygen availability.  So grain size, permeability, compactibility, and cementation all play a role post-depositionally.

A good summary of transport processes and organic carbon preservation can be found in Bianchi, 2011 (PNAS - www.pnas.org/cgi/doi/10.1073/pnas.1017982108).  Hedges and Kiel (1995 - Marine Chemistry) is a synthesis on organic matter preservation - it is dated, but still very pertinent. 

In the Middle-East, excellent source rocks deposited in marine strictly euxinic conditions are made of the repetition of marls and argillaceous limestone layers. The organic content of the limestone is systematically lower that those of the adjacent marls. This could be explained by the ability of clays to adsorb the organic matter and to protect it from bacterial degradation.

Marine organic-rich layers are deposited in low-energy layers. Therefore sand layers are generally organic leaner than associated clay layers.

Dilution of organic matter could explain that TOC content is inversely proportional with the deposition ratio.

We may suggest the reading of the excellent paper published by Demaison in the AAPG bulletin (1970)

I confirm what is already documented by other researchers . Lithology do have a significant effect on organic matter preservation. Excellent source rocks are in shales as exemplified in the Sargelu of Iran documented in my book : " le bitume dans l'antiquité " page 163-175. Best jacques Connan

Dear Brad E. Rosenheim and Paul Grover 

So as you mentioned various factors/Diagenesis affecting Preservation ..... actually as mentioned the core is >1000m long so I am worried whether pressure or temprature has affected it considrebly.    

of course, finer sediments such as shale and mudstones preserve organic matter from oxidation and biogenic degradation

Lithology controls the preservation of organic matter. So, fine sediments like as marls, clay, shale are the best for the preservation of the organic matter. By their permeability, they  protect the organic matter from oxidation and bacterial degradation.

Not only lithology control the organic matter preservation but also events such as turbidites and tempestites are more controlling factors for preservation of organic matter. When rich organic matters are covered by turbidites they will be preserved from oxidant conditions and oxidized waters.

I totally agree with the comment  of Mr kavoosi

Pressure and temperature effect the organic phase of the organic matter from carbohydrates/kerogen/bitumen (live oil/gas)/asphaltines/pyrobitumen.  Again the cheapest way to determine the organic richness, organic type (1,2,3,4), bitumen to kerogen ratios and thermal maturity is TOC/RockEval.  If your sediments are hotter than the oil maturation and migration window the TOC values will start to decrease once the oil and gas begins to migrate out.  You should know the thermal gradient of your basin.  Average values of some sedimentary basins are 20 to 40 degrees C per kilometer but that does not account for overburden that has been removed or past geothermal gradients.  Unlike Mr. Kavoosi I would suggest high organic sedimentation rates, the degree of anoxia, and low clay sedimentation rates will affect organic-richness more than high amounts of turbidite and tempestite deposits which can be fairly coarse grained.

Organic matter preservation is a function of several factors including lithology, environmental conditions during deposition and tectonic activities during deposition. For the marine environment, organic matter preservation depends on the anoxic condition of the environment and fine grain size of the muddy facies.