A grain started journey from a source area and in the way it become weathered, eroded, transported and finally deposited. It is a gross geologic description of grain's journey.

1. Introduction:
Earth surface processes are indeed a growing field. Part of this growing appreciation and interest
in the entire Earth surface system, especially with regards to erosion, transportation, and
deposition of sediment, is an approach that has been termed source-to-sink (Allen, P. (2008),
Nature).
Researchers have certainly been investigating and discussing source­to­sink (or less
alliteratively, source­to­basin) aspects of modern and ancient sedimentary systems for a long
time. The term Source refers to the net­erosional part of the system and the term sink is the net­
depositional part of the system and the process transportation is the joining component of the
system.
Sediment is moved from source to sink — from the erosional engine of mountainous regions to
its eventual deposition — by the sediment­routing system (Allen, P. (2008), Nature).
The mass fluxes associated with the physical, biological and chemical processes acting across the
landscape involve the transport of particulate sediment and solutes (Allen, P. (2008), Nature).
The selective long­term preservation of elements of the sediment­routing system to produce the
narrative of the geological record is dictated by processes operating in Earth’s lithosphere (Allen,
P. (2008), Nature).
Journey of a Grain from Source to Sink:
Journey of a grain from source to sink is the changes of grain along the path from liberation to
ultimate deposition. Geomorphologists primarily look at the net­erosional parts of the system
(the ‘source’) and try to get clues from the landscape about tectonics and getting the answers of
what is the rate of erosion, how does that relate to rates of uplift, how does the climate affect
patterns of denudation, where, when, and why does that grain come loose and start making its
way down system.
Sedimentary geologists are primarily concerned with the net­depositional parts of the system, or
the ‘sink’ and concern with how many times was that grain deposited along the way, how long
did the whole journey take, how long did it remain in an intermediary location, where is the final
site of deposition before it’s buried and put into the stratigraphic record – in a river or a delta or
the deep sea, why that location for that system, what does that tell about the system as a whole,
and so on, and so forth.
The term source indicates uplifted areas such as Himalayans, Mountain belts, Hilly regions and
others from where a grain used to disintegrate or decomposed which is termed as weathering
process then the grain would transport due to some transporting agent like wind, water or glacier

2. and would have got changes in shape, size, composition and texture and at last by falling the
energy it will deposit on a lower land (lower than the source area) which could be a depressed
area such as river, delta or deep sea and this depositional zone is referred to the term sink.
Figure: Journey of a grain from source to sink.

3. Weathering and Erosion:
Sedimentary rocks form through a complex set of processes that begins with weathering, the
physical disintegration and chemical decomposition of older rock to produce solid particulate
residues (resistant minerals and rock fragments) and dissolved chemical substances (Sam
Bogg,1995). Some solid products of weathering may accumulate in situ to form soils that
can be preserved in the geologic record (paleosols or ancient soil).
When the preexisting rock disintegrated or decomposed and transported by transporting agent
like wind, water, glacier and others, then the process is termed as Erosion. Weathering never
involves transportation whereas erosion always involves transportation.
Ultimately , most weathering residues are removed from weathering sites by erosion and
subsequently transported, possibly along with fragmental products of explosive volcanism, to
more distant depositional sites.
Weathering is mainly two types (1) Physical weathering and (2) Chemical Weathering.
Physical breakdown of rock without changing the internal arrangements of molecules is termed
as physical weathering and chemically change of rock body or grain is termed as chemical
weathering such as Calcite grains turns into clay by chemical weathering. By compacting and
solidification of grains sedimentary rocks form.
Weathering is the breakdown of older rocks exposed in upland areas to yield soluble ions,
which are transported to the ocean in solution, and insoluble ions may accumulate at the
weathering site for a time as soils. Soil formation, like weathering, is intimately related to
climatic conditions. Some soils, called paleosols, are preserved to become part of the
sedimentary record.
Transportation:
Transport of grain to depositional basins can involve a variety of processes. Mass­transport
processes such as slumps, debris flows, and mud flows are important agents in the initial
stages of sediment transport from weathering sites to valley floors. Fluid­flow processes,
which include moving water , glacial, ice, and wind, move sediment from valley floors to
depositional basins at lower elevations.
Wind can be considered a very low density , low viscosity "fluid" that is capable of flowing
and bringing about sediment transport. The principals involved in entrainment and
transport of particles by wind (eolian transport) are similar to those for water; however, wind's
low density and viscosity cause the threshold values for wind entrainment and transport to be
quite different ( Nickling,1994). Entrainment of grains by wind action can be strongly affected
by the impact of moving grains hitting the bed.

4. Transport of sediment by fluid flow involves two fundamental steps: (1) erosion and
entrainment of sediment from the bed and (2) subsequent, sustained down current or
downwind movement of sediment along or above the bed. Mass­wasting processes such as
slides and slumps commonly play an initial role in moving sediment short distances down
steep slopes to sites where other transport processes take over.
Deposition:
When transport processes are no longer capable of moving the grain, deposition of grain
takes place, either sub aerially (e.g., in desert dune fields) or sub aqueous in river systems, lakes,
or the marginal ocean. Grain deposited at the ocean margin may be retrained and retransformed
tens to hundreds of kilometers into deeper water by turbidity currents or other transport
processes.
Grain that deposited in basins are eventually buried and undergo physical and chemical
changes (digenesis) resulting from increased temperature, pressure, and the presence of
chemically active fluids. Burial digenetic processes convert the grain composition. , deposition
of the material in continental or marine environments, and diagenetic alteration during
burial to ultimately produce sedimentary rock by lithification.
Figure: Journey of a grain from source to sink.

5. Changes of the Grain:
The grain shows changes in size, shape, composition and texture due to the processes that
discussed earlier. The grain would become well rounded, well sorted, with sphericity minimum
porosity due to long way transportation. By increasing the path of transportation the grain would
become smaller due to the effect of fraction.
Figure : The change of shapes of the grain due to long way transportation.
Particle shape is defined by three related but different aspects of grains. Form refers to
the gross, overall configuration (outline) of particles and reflects variations in their
proportions. The roundness of grains in a sedimentary deposit is a function of grain
compositional, grain size type of transport process, and distance of transport.
The term sphericity was introduced by Wadell (1932). If all three axes have about the
same length, a particle has high sphericity. If the axes differ markedly in length, the
particle has low sphericity. A formula for expressing this relationship mathematically was
developed by Krumbein (1941), which yields a mathematical value of 1 for a perfect
sphere; less spherical particles have lower, fractional values.
Figure: Equation that was given by Wadell and modified by Krumbein.

6. The sphericity of particles in sedimentary deposits is a function mainly of the original shapes
of the grains, although the shapes of gravel­size particles can be modified somewhat by
abrasion and breakage during transport. The form of some particles resembles that of a
sphere; other particles may have a platy or rod like form.
Sphericity affects the settling velocity of small particles. Well­rounded grains have smooth
corners and edges; poorly rounded grains have sharp or angular corners and edges. Surface
texture refers to small­scale, micro relief markings such as pits, scratches, and ridges that
occur on the surface of grains.
The three aspects of shape can be thought of as constituting a hierarchy , in which form is
a first­order property, roundness a second­order property superimposed on form, and surface
texture a third­order property superimposed on both the corners of a grain and the surfaces
between corners (Barrett, 1980).
Figure : Schematic representation of the principal aspects of particle(Sam Boggs).
The surface of pebbles and mineral grains may be polished, frosted (dull, matte, texture
like frosted glass), or marked by a variety of small­scale, low­relief features such as pits,
scratches, fractures, and ridges. These surface textures originate in diverse ways, including
mechanical abrasion during sediment transport; tectonic polishing during deformation; and
chemical corrosion, etching, and precipitation of antigenic growths on grain surfaces during
diagenesis and weathering.
Gross surface textural features such as polishing and frosting can be observed with an
ordinary binocular or petrographic microscope; however, detailed study of surface texture
requires high magnifications. Krinsley (1 962) pioneered use of the electron microscope for
studying grain surface texture at high magnifications.

7. Conclusion:
In summary, the origin of grain involves weathering of older or preexisting rock to generate
the materials that make up newer grain, erosion and transport of weathered debris and
soluble constituents to depositional basins, deposition of this material in continental
(terrigenous) or marine environments, and diagenetic alteration during burial to ultimately
produce lithified sedimentary rock.
Weathering brings about the breakdown of older rocks exposed in upland areas to yield
soluble ions, which are transported to the ocean in solution, and insoluble ions may
accumulate at the weathering site for a time as soil. However , most insoluble soil materials
are removed by erosion and transported by gravity processes, water, glaciers, or wind to basins
at lower elevations, where deposition takes place.

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