Preservation of Organic Matter

Preservation of Organic Matter

It is primarily the particulate remains of phytoplankton* that form organic matter in most marine and many aquatic sediments.

Factors that affect preservation of these remains include: (a) the flux of organic matter to the sediment, (b) bulk sediment accumulation rate, (c) grain size, and (d) availability of oxygen

The flux of organic matter to the sediment depends in turn on its rate of production in surface waters (biological productivity) and the depth of the overlying water column.

Productivity depends mainly on the availability of nutrients.

Organic matter falling though the water column from the upper photosynthetic zone (200 m) is rapidly remineralized by bacteria and animals. Hence the greater the water depth, the less organic matter reaches the sediment.

In marginal marine environments, that is, those adjacent to continents, such as river deltas, bays, estuaries, and marginal seas, the land-derived remains of higher plants constitute a significant fraction of the accumulating organic matter. Such material is said to be allochthonous (i.e., derived from sources external to the water body). Organic matter produced within the immediate water body is called autochthonous.

Small grains have higher surface area and, therefore, would have higher organic content being of low density.

Where the burial flux of organic carbon exceeds the downward flux of oxygen, the latter will ultimately be completely consumed and conditions will be reducing.