The organic production related to minerogene salt marsh deposits represents a challenge to all attempts to model the development of these areas, and evaluate their chances of survival under different sea level scenarios. Salt marsh deposits on a typical temperate backbarrier saltmarsh area at the Skallingen barrierspit (Denmark) were investigated for autochthonous or below ground organic production, which was found to have a mean value of 0.14 kg m− 2 y− 1 or about 0.1 mm y− 1. This production is concentrated in the upper approximately 5 cm of the salt marsh. Below this level the organic material decomposes with a decreasing organic content until about 15 cm below the surface. Hereunder the decomposition of organic material seems to stabilize at a very low level. The constant rate of the below ground organic production results in a larger concentration of this type of organic matter in the slowest accreting salt marsh deposits. The root activity is the primary reason for differences in the bulk dry density of salt marsh surface layers, therefore the surface layers of slowly accreting salt marshes have the lowest bulk dry density. During autocompaction, the bulk dry density increases down core. This process is only to a small degree (< 10%) directly affected by the space loss due to decomposition of organic matter. The decay of organic matter, however, is most likely indirectly part of the autocompaction process by weakening the internal strength of the root fabric and thus the capability of resistance against compaction from the overburden of depositing sediments.