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TROELS- SMITH SCHEME

 

Sediments are naturally occurring materials that is broken down by processes of weathering and erosion, and is subsequently transported by the action of water, wind, ice or by the force of gravity acting on the particle its self. (en.wikipedia.org)  On the other hand sedimentation is a tendency of particles in suspension to settle out of the fluid (Water, air) in which they are entrained, and come to rest against a barrier.

There are lots of processes and schemes to describe the sediments according to their characteristics.  These schemes are used and developed by the agriculturists, Engineers, geographers. From them a universally accepted and used scheme is essential as one method is not similar to other and one method is important for one group of professionals and not for other group. So Troels-Smith in 1955 attempted to devise a scheme for recording the physical characteristics of unconsolidated sediment.

TROELS- SMITH SCHEME

Troels- Smith (1955) developed a comprehensive classification for sediments from organic- rich. North temperate lakes and wetlands. The classification was originally designed primarily as a field based classification but could be expanded to include laboratory study. This classification has been widely applied by European paleoecologists but only rarely outside ofEurope, despite the urging of several handbooks of paleoecological techniques (Birks and Birks 1980; Faegri and Iversen 1964).

Troels-Smith’s scheme defines three elements that should be specified for each layer of stratigraphy identified, these are:

  • Composition or The Components
  • The Degree of Humification
  • The Physical properties of Sediment layer.

The components:

The main components recognized are trufa, detritus, limus, argilla and grana. There are several accessory elements such as molloscorum, stripes and rudimenta culturae.These elements are described below.

Trufa:

Turfa is define as the roots of woody and herbaceous plants and the stumps strunks, branches and stems it connected to the roots. It also includes mosses. The different types of trufa may be recognized: T.bryophytica includes the remains of sphagnum and hypnum for example; T.ligonosa includes the rots and stumps of woody plants and their trunks, branches and twigs. The most common type of turfa in Bengal Basin is the T. herbaceous (th.).

Detritus:

Detritus is made of plant fragments that are unconnected to root system. It includes fragments of wood, bark, branches and trunks, stems and leaves, fruits and seeds. All of these have either been rained down onto the forest floor of have been washed into the site and then deposited. Three types of detritus D. Lignosus (DI), D. herbosus (DH) and D. Granosus (Dg).

Limus:

Limus is a mud like, homogenous non – plastic deposit made up essentially of small organic particles arising from the productivity of macro organisms in lakes and swamps common types are limus detritus’s (LD) and substantia humosa (Sh).

Argilla:

Argilla consists of minerogenic sediments (Silt, Clay) and is characteristically sticky and plastic. Two types of Argilla can be recognized in the field. A steatodes (AS) with grain sizes <0.002 mm (clay), and A. graviosa (Ag) with grain size 0.06 – 0.02 mm (silt)

Grana:

Grana is made up of macroscopic particles (Sand) gravel etc) that can be seen with naked eye.grana lacks coherence, cannot be rolled when wet and crumbles when dry.

The Class Limit of Grana and Argilla:

The class limits for argilla and grana size fractions are the same as those used for established the particle size distribution of a sediment specified by British standards Institution (1961).

 Degree of Humification:

It indicates the degree of decomposition of the macro fossils that can be observed. It is estimated on a five point scale and refers to the degree of breakdown of the macrofossils that can be observed.

Hence, 0 on the scale indicates that the plant structure is humified and squeezing yields clear, colorless, water; 4 indicates more or less complete humification and peat may be squeezed through the fingers.

Turfa Tb T. bryophytica Mosses +/- humus substance
Th T. lignosa Stumps, roots, intertwined rootlets, of ligneous plants
Tl T. herbacea Roots, intertwined rootlets, rhizomes of herbaceous plants
Detritus Dl D. lignosus Fragments of ligneous plants >2mm
Dh D. herbosus Fragments of herbaceous plants >2mm 
Dg D. granosus Fragments of ligneous and herbaceous plants <2mm >0.1mm
Limus Ld L. detrituosus Plants and animals or fragments of these <0.1mm +/- humus substance
Lc L. calcareus Marl, not hardened like calcareous trufa. Particles <0.1mm
Lf L. ferrugineus Rust, non-hardened. Particles <0.1mm
Argilla As A.steatodes  Particles of clay
Ag A. granosa Particles of silt
Grana Ga G. arenosa Mineral particles 0.6 to 0.2mm
Gs G. saburralia  Mineral particles 2.0 to 0.6mm
Gg(min) G. glareosa Mineral particles 6.0 to 2.0mm
Gg(Maj) G. glareosa majora Mineral particles 20.0 to 6.0mm

Table: Physical and sedimentary properties of deposits according to Troels-Smith (1955)

 

The Physical properties:

The Physical properties of any layer include –

 

The degree of darkness Nig=nigror
Stratification Strat = stratification
Elasticity Elas = elasticity
Dryness (Sice = siccitas)
Sharpness of upper boundary superior I.S. = Limes

 

Degree of Darkness
nig.4 Black
nig.3  
nig.2   
nig.1   
nig.0 white

 Table: Degree of Darkness

Degree of Stratification
strf.4 well stratified
strf.3
strf.2
strf.1
strf.0 no stratification

Table: Degree of Stratification

Degree of elasticity
elas.4 Very elastic
elas.3
elas.2
elas.1
Elas.0 Non elasticity

Table: Degree of Elasticity

Degree of Dryness
Sicc.4 Very Dry
sicc.3
sicc.2
sicc.1
Sicc.0 Water

Table: Degree of Dryness

 

Sharpness of Upper Boundary:

Sharpness of upper boundary ranges from 0.5 mm to 10 mm.

                                                      Sharpness of Upper Boundary
lim.4 < 0.5mm
lim.3 < 1.0 & > 0.5mm
lim.2 < 2.0 & > 1.0mm
lim.1 < 10.0 & > 2.0mm
lim.0 > 10.0mm

Table: Sharpness of Upper Boundary.

Scale:

The composition of a layer is recorded on the basis on a scale of 1 to 4, where 1 indicates 25% and 4 indicates 100% of the component. The trace amount of any component in a stratum are represented by the plus (+) sign where one plus (+) indicates 1% of the total components.

In a brief we can say

1                      = 25%

2                      = 50%

3                      = 75%

4                      = 100%

+          = 1%

 

Example of Using the Scheme:

We can use the above scheme to identify sediment. For example:

1)  Nig.4; strf.0; elas.0; sicc.2; lim.3.

Sh1; Ag 2; Ga1

This sign indicates Black –Organic rich soil.

 

2) Nig.2; strf.1; elas.1; sicc.2; lim.3.

Ag 3; Ga1

This sign indicates Light brown minerogenic sandy soil.

Advantages:

  • Until 1955 there had been no consistency among the workers in stratigraphic description. Troels- Smith helped to overcome this difficulty by his scheme for recording the physical characteristics of unconsolidated sediment.
  • This scheme gives importance on describing sediment components rather than attempting to force a small set of terms onto compositionally diverse sediments.
  • This scheme considers environmental and pale logical issues more than the other classification schemes. That’s why geographers, environmentalists can easily use it for their purposes.

Disadvantages:

  • The primary disadvantages of the scheme lie in its use of Latin terms.
  • The reliance on microscopic field description of extruded cores.
  • Its term “seekreide” is proposed for carbonate rich lacustrine sediment – a term preferable to “marl” which is widely used in North American limnology. (Dean, et.al.1985).

Despite its many advantages the system has been little used, probably as it was published only in the original German and not widely read. (Journal of Paleo Limnology, 29:/41-154, 2005)

Reference:

http:www.information of teknaf.blogspot.com Accessed on19/09/12

http:www.wikipedia.org/wiki/sediment Accessed on19/09/12

Tyrrel, G.W; 1928: The principle of petrology, B.I. Publications PVT LTD,India.

The environment of British Prehistory.

Schurrenberger, D; Russel, J; and Kelts, K; 2003: Classification of Lacustrine Sediments Based on Sedimentary Components.

 

 

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