The deposit that contains pollen grains and spores suitable for identification and analysis include peats, lake sediments, soil and mor humus.
Peats:
Peats are the early stage of coalification which are formed due to accumulations of organic detritus largely of plant origin. Peats are developed into a stratified sequence due to the successive deposition of plant parts containing pollen and litter for several hundred years.
Thus, several successive deposits become stratified into horizons within the developing peat profile. Peats are generally classified into three major types in terms of the nutrient regime under which they were formed (Table 13.1).
Lake Sediments:
Lake sediments are made up of either autochthonous (in situ) or allochthonous (transported from other sites) materials. The autochthonous materials are composed of bulk of peats develop from the lake vegetation. The most of the lake sediments contain a large proportion of allochthonous materials derived from the plants outside the lake basin.
So the lake sediments consist of inorganic and organic allochthonous detritus including microfossils, organic materials of local vegetation and an input of local pollen direct from the air via drainage water. Lake sediments are classified into three types in terms of their nutrient status (Table 13.2).
Soils:
Soils are also good source of pollen and spores. Many works have been done on the different strata of soil profile. It is evident that soil having pH less than 5 contain very considerable quantities of pollen, up to half a million per gram, or 1.5 million per gram of dry soil. Soil above a pH level of 6, generally devoid of pollen grains.
A good quantities of pollen grains are also recovered from surface and sub-surface soil sediments So the analysis of soils has frequently revealed a distinct stratification of pollen assemblages.
Mor Humus:
Generally in temperate vegetation litters with a high polyphenol content are incorporated very slowly into the mineral soil following a low rate of breakdown by microorganisms. These litters get accumulated on the surface of soil. The reconstruction of vegetation change based on mor humus sample has got limitation as these humus layers are very thin to interpret the changes.