Genesis, composition, and properties of sapropel sediments

Abstract

Holocene Black Sea basin sediments were formed in happened geocatastrofic event on the border Pleistocene - Holocene (8 - 9 thousand years ago). As a result of the catastrophic event on the Upper Pleistocene lake sediments occur organogenic - mineral (sapropel diatoms and coccolith) marine sediments. The characteristic features of happened catastrophe is the occurrence of hydrogen sulfide charging that conserved the organic matter and protect it from decomposition (Dimitrov, 2010).
Unfortunately most of the Black Sea researches deny geocatastrofic nature sapropel mud, claiming that they are the result of a gradual salinization Black Sea Lake.
Chemical composition and properties of deep-water organogenic - mineral deposits give us reason to Tip of the raw material as an integrated multi-purpose and most notably in agriculture.
The Kalamitian – Vityazevian, Oldchernomorian, unit 2 (Ib) layers in the deep parts of the sea are represented by the so called sapropelic sediments. The term sapropel comes from the Greek sapros – rotten and pelos – ooze and was first used by R. Lauternborn in 1901 to designate sediments from lakes rich in organic material and smell of hydrogen sulfide. Lithologically they are very well separated along the contrasting erosive lower and transitional upper boundary with unit 1a (fig. 1). Sometimes they make a transition from the Neoeuxine Ic through a thin “intermediate” layer but in most cases they lie on the erosive surface of unit 3 (Iс) – carbonate ooze of the seekreide type (Degens, Ross, 1972; Dimitrov, 1982).
The sapropels form a single horizon with constant thickness typical of the Black Sea basin. Analogues of the sapropels on the shelf and the upper part of the continental slope are the green aleurite-pelitic oozes with accumulation of plant detritus and decomposed shells of Mytilus galloprovincialis. The transition from aleurite-pelitic oozes to sapropels is facial. The organic matter in the sapropels is of heterogenous origin. They are composed primarily of planktogenic organisms (about 80%) and continental organic matter (20%). The planktonic organisms are well preserved in most cases under the conditions of the hydrogen sulfide zone. The main components of the sapropels are the dinoflagellate cysts, diatom algae, coccolithophorids, peridinea.
The accumulation of sapropels testifies to a biogenous sedimentation with catastrophic parameters. The paleogeographic picture of the formation of biogenous sediments of such exceptional scale would look like as follows:
• The climate warmed up sharply after a prolonged Würmian glaciations fixed within the interval of 10–70 thousand years.
• The level of the World Ocean that was lower by 120–130 m than the modern level 18–20 thousand years ago rose and the inflow of Mediterranean water with salinity of 36–38‰ began through the Bosphorus threshold about 8 thousand years.
At that time the Black Sea was a lake with brackish to freshwater with salinity of about 5–6 ‰ within the boundaries of the Neoeuxinian basin at present-day depths of 90–120 m. The inflowing Mediterranean water about 8 thousand years ago (this event was fixed in С-544) were more saline and heavier, rich in biogenous components, filled the deep water valley and mixed with the substantially less saline Black Sea water. The consequences of this event were catastrophic for the flora and fauna and this triggered the sedimentation of organogenic mineral oozes with thickness from 45–50 cm to 1–2 m. The sapropels have different thickness in the different morpholithological zones. They are often absent from the continental slope, the slopes and axes of the underwater valleys due to active sliding processes. They are better preserved in the flat places where their thickness reaches 45–60 cm. The thickness of the sapropels is most substantial at the foot of the continental slope, where they reach up to 2 m.
The mineral component of sapropel mud is represented by a polycomponent mixture of clayey minerals. It is dominated by illite and montmorillonite and smaller amounts of chlorites and kaolinite.
The micro- and macrocomponents of the sapropels are very specific and are a product of the interaction marine environment - hydrogen sulfide contamination – organic and terrigenous component.
What is typical of the sapropels in the western part of the Black Sea is the dilution by clayey matter and the leading role of the pelite fraction. In conclusion, it should be noted that the mineral composition of the clay component of the sapropels is determined both by the type of the rocks feeding the western part of the Black Sea and by the material delivered to the bottom by the mud volcanoes.
There are also cases where the content of Сorg. in the upper part of the cross-section is higher than in the middle or in the base. In such cases samples are also taken from the common terrigenous interbeds. The analysis of the current data of content of Сorg. in the cross-section of the sapropelic ooze s shows stable high content of Сorg. in the typical dense stratified sapropels. The sapropel horizon is steadily distributed throughout the water area of the basin as shown on the lithofacial map of the Oldchernomorian sediments in unit Ib according to Khrischev et al. (1988) where the facial diversity in the sapropels is well reflected.

Acknowledgements:

Project: No 02 – 35.
NATIONAL SCIENCE FUND
Ministry of Education and Science. Bulgaria – Ukraine. “Non-traditional resources from Black sea bottom and their possibilities to use as complex raw material”.
Project: No 02 – 337.
NATIONAL SCIENCE FUND
Ministry of Education and Science. “Ancient coastlines of the Black Sea and conditions for human presence”.