PowerPoint PresentationGianluca Frijia 2020-2021
Reference Books and course material
• Leeder, M. (2015) 2nd edition. Sedimentology and Sedimentary
basins. 768 p. Wiley-Blackwell.
• Tucker, M.E.(2010). Geologia del Sedimentario. Dario
Flaccovio
Editore.Palermo.
• Nichols, G. (2009). Sedimentology and Stratigraphy.
Wiley-Blackwell, 355 pp.
• Tucker, M.E. (2001). Sedimentary Petrology: An Introduction to
the Origin of Sedimentary Rocks. Blackwell, 262 pp.
Extra material provided by the instructor
Struttura del corso e esami
Teoria: 2h (Tutti)
Lab: 2h (Gruppi ??)
Martedi, Mercoledi,giovedi
Data esami: esame intercorso (data da stabilire) e esame orale
finale.
Orario di ricevimento: Martedi, Mercoledi 12-13
Contatti:
[email protected]
2. Principles of Hydrodinamics and trasport
3. Sedimentary structures
4. Depositional environments
Two disciplines often considered separately in the past. Now
increasingly combined in textbooks, research and economic
applications.
Sedimentology is primarily concerned with formation of sedimentary
rocks but as soon beds of rocks are seen in terms of spatial and
temporal relationships, we talk about Stratigraphy
Similarly, if a Stratigrapher wishes to interpret layers of rocks
in terms or environments, the study is considered as
Sedimentological.
Sedimentation – scientific study of only modern
sediments and sedimentary processes that excludes
subjects of diagenesis (fluids dynamic,sed transport,sed
structures)
(climate,paleoceanography, diagenesis,
organization, paleogeography, paleoecology, and the
sequence of geologic events
dep.environments, predictive models, sea-level
of sedimentary strata;
make up the strata; and
both the mechanisms of transport
and the environment of deposition
Ability to predict the depositional
environments evolution through time
Enable the geologist (YOU) to interpret
• classification of rocks
• describe sedimentary strata
• spatial and temporal patterns in sediment deposition
Goals of the course Learn the bases for interpreting sedimentary
deposits in terms of
So..let s get started:
What is a sediment?
What is a sediment?
Any kind of particle that was in suspension in a fluid (air,
water) and that was deposited to form a geological layer, a
rock, after compaction
A sediment is thus formed of particles that are not
cemented: it can ‘flow’
Sedimentary deposits are the final result of weathering, erosion
and deposition of particles which differ in origin, size, shape
and
composition.
Processes of formation of a Sedimentary Clastic Rock:
Weathering and Erosion – mechanical & chemical
Transport – by gravity, water, air, ice, sediment-water
mixtures.
Sedimentation –Different environments (beaches, dunes, basins,
etc)
Burial and Diagenesis (Lithification) – loose sediment turns to
solid rock
Sedimentary rocks
2) Material originated by volcanic eruptions (e.g. ash)
3) Supersatured solutions (chemical precipitation)
4) Action of organisms (direct or indirect)
Erosion and Weathering
Weathering: reaction of minerals to conditions at the Earth’s
surface
gravitational forces (wind, ice, water)
Denudation: sum of mobilization and transport processes of
material at the Earth’s surface
Erosion and Weathering
chemical equilibrium with their conditions of formation) as a
response to new surface conditions
Dense, fresh, massive rocks are transformed in lighter, less
dense and massive material with a lower mechanical
resistance
• Slow, continuous process
Two Types
smaller pieces but their chemical
makeup does not change
Mechanical Weathering
exfoliation
and expand which enlarge cracks
Abrasion: wearing away of rocks by particles carried
by wind water etc.
roots)
change of +9%. Cryofracturing or gelifraction
is important if the rock is totally water
saturated and compressible air is absent
www.kesgrave.suffolk.sch.uk
http://www.alexstrekeisen.it/english/sedi/weathering.php
Mechanical weathering: Decompression, dilatation and
exfoliation
Erosion and Weathering
Weathering: Biological activity
process known as root wedging
Animal attack
gophers, push open cracks and move rock
fragments. in the past century, humans have
become perhaps the most energetic agent of
physical weathering on the planet.
Chemical Weathering
Water: Chemical weathering refers to the many chemical
reactions that alter or destroy minerals when rock comes in
contact
with water solutions and/or air. Common reactions involved in
chemical weathering include the following:it dissolves minerals
that
hold rocks together, forms acids when mixed with gases or
acid
compounds, combines with minerals to make new minerals
(combine with feldspar to make clay)
(Bio-) chemical alteration
• Water as solvent
organic complexes (chelation)
• Surface of reaction: 1m3-> 6m2 but if divided into cubes
of
1mm3 -> 6000m2
• Life: appearance of terrestrial plants in the Devonian may
have
speeded up biochemical alteration by 7 times (R. Berner, Yale
Uni, pers. com to K. B. Föllmi)
• Mineral stability: olivine, anorthite, pyroxene, amphibole,
albite,
biotite, orthose, muscovite, clays, oxydes (Si, Al, Ti, Zr, Fe,
Mg)
What affects Weathering?
weathering
Climate: ex. Limestone Ok in warm/dry climate, when wet-weak acids
weather
Time exposed on surface: old,, unexposed rocks no big changes
New exposed rocks weather quickly
Surface area: when rock is a small pieces more surface area is
available for
weathering
Ph: Hydrolysis requires hydrogen ions. Thus pH, is a limiting
factor for them.
Note: Whereas rain water (and consequently fresh water) is slightly
acidic (pH
between 4 and 6.5), ocean water is slightly alkaline (roughly pH
8). Thus
chemical weathering is more prevalent on land.
Allen, 1997
FASTSLOW weathering rate
Weathering? To sum up:
Weathering? To sum up:
Process by which weathered rock and soil particles are moved
from one place to another. Erosion carries away the products
of
weathering
The final stage in the erosion process is when sediments are
laid
down in the new location (Deposition)
Erosion moves material, Deposition builds new features
Agents of Erosion
Landslides,Avalanches)
Wind (major agent in hot,dry climate or little vegetation)
Running water (more powerful than wind to move
particles.faster
it moves greater is erosion. Erosion in small channels on slide
of
slope is called rill erosion, when channel become deep it
becomes
gully erosion)
Waves
Transport:
• Gravity
• Fluids
• Wind
Sedimentary rocks cycle
Upstream: mainly production
(a) Global Rainfall Erosivity map (spatial resolution 30
arc-seconds). Erosivity classes correspond to quantiles.
Map generated with ESRI ArcGIS ver. 10.4 (http://www.esri.com); (b)
number and cumulative percentage of
GloREDa stations grouped by erosivity; (c) mean erosivity by
continent; (d) mean erosivity by climate zone.
global Water erosion map and a global population density map.
U.S. Dpt of Agriculture
