Sedimentology Lecture 1. introduction to the course

Course of
DEPOSITIONAL SYSTEMS IN THE ROCK RECORD:
FROM STRATA TO SEDIMENTARY SUCCESSIONS
(5 days, 8 h/day including lab activity and practical exercises)
Course Instructor: Sergio G. Longhitano
University of Basilicata, Potenza, Italy

EDUCATIONAL GOALS AND EXPECTED LEARNING OUTCOMES
The prime purpose of this course is to show how ancient environments may be reconstructed by interpreting
first the processes which gave rise to sedimentary rocks and then the environment in which these processes
operated. To achieve this, an understanding of the elementary concepts, such as sedimentary facies, flow
hydrodynamics, changing base level, etc. that control the environment, both modern and ancient, is essential.
Course of

Course Program
1. Introduction to the Course: what is a depositional system?
1a. Modern depositional systems of the Earth; 1b. Most common types of subaerial, transitional and subaqueous systems (alluvial fans, rivers,
deltas, estuaries, submarine fans); 1c. Systems in terrigenous, carbonate and mixed supplying settings; 1d. Examples of less common depositional
systems (colluvial fans, marine straits, shelves and slopes);
2. Ancient depositional systems of the past Earth
2a. How systems are preserved in the rock record? 2b. Analysis of the rocks, from strata to sedimentary successions; 2c. Concept of Sedimentary
Facies and interpretation of sedimentary facies; 2d. Recall on the Walther Law; 2e. Facies dynamics and resulting successions; 2f. Sedimentary
environments and systems; 2g. How to describe sedimentary units based on their macroscopic features.
3. Traces of past processes: sedimentary structures in clastic sediments
3a. Primary inorganic; 3b. Secondary inorganic; 3c. Biogenic. 3d. Examples from modern and ancient settings; 3e. Corresponding sedimentary
processes (e.g., mass vs. selective; depositional vs. erosional, short- vs. long-lasting processes).
4. Strata and stratification and stratigraphic surfaces
4a. Concept of strata and main stratal geometries; 4b. Bedding (Stratification and lamination); 4c. Strata successions. 4d. Key-strata or key-beds; 4e.
Stratigraphic correlations; 4f. How to recognize bedding in well-core or outcrop samples. 4g. Stratigraphic continuity or conformity; 4h.
Discontinuities, paraconformities and unconformity. 4i. Time-transgressive and time-regressive surfaces. 4j. How to use stratigraphic surfaces to build
a geological reconstruction.
Course of

Course Program
5. Sedimentary successions
5a. Sedimentary successions: from seismic, to outcrop and well-core examples; 5b. Complete vs. condensed successions; 5c. Stratigraphic hiatuses
or gaps; 5d. How to describe/analyze a stratigraphic successions (use of the basic concepts of stratigraphic subdivision).
6. Laboratory practice: measurement of sedimentological data
6a. Logging on outcrops and well cores: practical exercise on a variety of sedimentary successions, acquisition of their main attributes and
vertical representation; 6b. Graphical representation of lithology, bedding, sedimentary structures, discontinuities and bioturbation; 6c. Interpretation
of sedimentary successions based on well-log datasets.
7. Virtual Field trips (3D projection of studied outcrop areas)
7a. Examples of continental successions, terrigenous in marginal-marine and deeper settings; 7b. Carbonate successions from shallow-marine
settings; 7c. Mixed successions.
Course of

Suggested readings
Course of

1. What is a depositional system?
1a. Modern depositional systems of the Earth;
1b. Most common types of subaerial, transitional and subaqueous systems
(alluvial fans, rivers, deltas, estuaries, submarine fans);
1c. Systems in terrigenous, carbonate and mixed supplying settings;
1d. Examples of less common depositional systems (colluvial fans, marine
straits, shelves and slopes).

1a. Modern depositional systems of the Earth; 1b. Most common types of subaerial, transitional and subaqueous
systems (alluvial fans, rivers, deltas, estuaries, submarine fans); 1c. Systems in terrigenous, carbonate and mixed
supplying settings; 1d. Examples of less common depositional systems (colluvial fans, marine straits, shelves and
slopes);

Sedimentology Lecture 1. introduction to the course

Sedimentary processes
and properties of the rocks
(constituting depositional systems)

The Rocks Display‘s (from Wilson, in Read, 1944), illustrating that the
sedimentary cycle is a small part of the whole crustal cycle of the dynamic earth.
Individual sedimentary grains of stable minerals, principally quartz, may be
recycled several times before being destroyed by metamorphism.

Sedimentary rocks represent ca. the 35-40% of the deposits ont eh Earth surface.
Their nature is a valuable source of information in the field of geological application.
SEDIMENTARY DEPOSIT:
Mineral (unorganic) material, forming non-consolidated accumulation of clasts
SEDIMENTARY ROCK:
Mineral (unorganic) material, forming consolidated accumulation of clasts

SEDIMENTARY DEPOSIT: Mineral (unorganic) material, forming non-consolidated accumulation of clasts

SEDIMENTARY DEPOSIT: Mineral (unorganic) material, forming non-consolidated accummulation of clasts

SEDIMENTARY ROCK: Mineral (unorganic) material, forming consolidated accumulation of clasts

Often, sedimentary rock and sediments occur
adjacently and they can, thus, be genetically
linked each other
DETRITUS
TALUS

Sediments change into rocks as consequence of a combined process of
BURIAL, COMPACTION and DIAGENESIS
The Diagenesis is the process of transformation
(lithification) of sediment from unconsolidated to
lithified rock, through the sum of physical and
chemical changes, which occur after the phases of
burial and compaction.
The Compaction occurs because
of the pressure exerted from the
lithostatic weight due to the
overlying sediment. A compaction
causes the decreasing of porosity,
influencing the internal circulation of
fluids and provoking possible
fragmentation among clasts.
The burial of a sedimentary deposit occurs
because even new sediment accumulates
over the previous, in absence of relevant
processes of erosion
1
2
3

After the transformation of a sediment into a rock, before or during the process of diagenesis, the sedimentary
rocks can be subject to relevant changes of their primary features, because of the burial and the consequent
compaction, specially concerning their POROSITY and PERMEABILITY

Sedimentary rocks can be characterised by a wide spectrum of different types of
S T R A T I F I C A T I O N

Sedimentary rocks can also be
DEFORMED and/or FAULTED

Sedimentary rocks subjcted to very low metamorphism can also exhibit
S C H I S T O S I T Y

27
The two properties that control the storage potential of fluid and gas at microscopic scale in a sedimentary rock are the
POROSITY and PERMEABILITY.
Together, these two features are often considered as fundamental in reservoir characterization studies.
The quality of a reservoir of a sedimentary rock depends upon the texture of a rock and the primary sediment composition.
The primary texture can often be modified after the burial, compaction and deformation.
P O R O S I T Y & P E R M E A B I L I T Y

28
Note: a rock has a good porosity if it is characterised by a high percentage of pores; it implies a high storage capacity of fluids or
gas.
However, if none of these pores are interconnected each other, fluids or gas cannot propagate and, consequently, a rock has a
scarce permeability. Contrarily, a better permeability derives from well-interconnected pores.
The POROSITY represents the percentage fo the total
volume of pores (space potentially filling by fluids or gas)
included within a rock (measurable in %).
rocky matrix
pores
The PERMEABILITY represents the capacity of a rock to
be passed through by a fluid (it is, thus, a velocity and it is
measured in milliDarcy - mD).
POROSITY
(storage capacity)
PERMEABILITY
(flux capacity)
FLUID INFLUID OUT
Hypothetic pathway of a
flux passing through the
pores of a sedimentary rock
P O R O S I T Y & P E R M E A B I L I T Y

POROSITY in sedimentary rocks can be of dual origin:
1. Primary Porosity and
2. Secondary Porosity

What is a depositional system?
Hierarchies of environments, examples of continental,
transitional, shallow and deep-marine depositional
systems

Definition:
A DEPOSITIONAL SYSTEM is an assemblage of multiple process-based sedimentary facies which
record genetically-related depositional environments
(e.g.: a RIVER DELTA is a depositional system; it can be subdivided into ‘components’
represented by constituent depositional environments, including: the delta plain, the delta
front, the delta slope, etc …
slopes);

slopes);
There are a pletora of different
types of DEPOSITIONAL
SYSTEMS in the Earth
surface.
We can distinguish them on
the basis of their genesis and
location: continental,
transitional or marine.
Continental systems
Transitional systems
Marine systems
alluvial fans
glaciers lakes
rivers
embayments
aeolian
dune fields
estuaries

34
A HIERARCHICAL RELATIOSHIP LINKS THE VARIOUS
PHYSICAL ELEMENTS WHICH DEFINE A
SEDIMENTARY FACIES, A DEPOSITIONAL
ENVIRONMENTS AND A DEPOSITIONAL SYSTEM
1. A FACIES, together with other genetically-related facies,
forms a FACIES ASSOCIATION [for example: cross-
laminated sands (A)];
2. A FACIES ASSOCIATION represents the sedimentary
product of a DEPOSITIONAL ENVIRONMENT [for
example: fluvial channel filled by gravels and sands (B)];
3. An ensemble of depositional environments forms a
DEPOSITIONAL SYSTEM (for example: braided fluvial
system (C)];
4. Two or more depositional systems coexist in a COMPLEX
of DEPOSITIONAL SYSTEMS [ for example: alluvial fans
with fluvial systems (D)];
5. Finally, an ensamble of complexes represent a part of a
SEDIMENTARY BASIN (E).
Miall, 1996
A
B
C
D
E
Facies
Depositional
Environments
Depositional
system
Complex of
Depositional
Systems
Sedimentary
Basin
Facies Association
What is a depositional system?

COLLUVIAL FANS ALLUVIAL FANS RIVERS & DELTAS
ESTUARIES TIDAL FLATS TIDAL STRAITS
SHOREFACES SHELVES DEEP-SEA FANS
There is a multitude of different types of depositional systems on the Earth’s surface

Sedimentology Lecture 1. introduction to the course

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