1 Basin Classification
and Depositional Environments (Overview)
1.1 Introduction
1.2 Tectonic Basin Classification
1.3 Tectonics and Basin Filling
1.4 Basin Morphology and Depositional Environments
1.4.1 General Aspects
1.4.2 Different Methods in the Study ofModem
and Ancient Sediments
1.4.3 Depositional Environments (Overview)
1.4.4 Elementary Principles for Basin Filling
1.4.5 Some General Trends for Sediment
Accumulation and Facies
1.4.6 Facies Architecture
1.4.7 Summary (Basin Classification)
1.1 Introduction
Sedimentary basins are, in a very broad sense, all those
areas in which sediments can accumulate to considerable thickness and be preserved for long geologie al
time periods. In addition, there also exist areas of longpersisting denudation, as well as regions where erosional and depositional processes more or less neutralize each other (creating what is known as non-deposition or omission).
In plan view sedimentary basins can have numerous
different shapes; they may be approximately circular
or, more frequently, elongate depressions, troughs, or
embayments, but often they have quite irregular boundaries. As will be shown later, even areas without any
topographie depression, such as alluvial plains, may act
as sediment traps. The size of sedimentary basins is
highly variable, though they are usually at least 100 km
long and tens of km wide.
We can distinguish between (1) active sedimentary
basins still accumulating sediments, (2) inactive, but
little deformed sedimentary basins showing more or
less their original shape and sedimentary fill, and (3)
strongly deformed and incomplete former sedimentary
basins, where the original fill has been partly lost to
erosion, for example in a mountain belt.
As many workers have pointed out, the regional deposition of sediments, non-deposition, or denudation of.
older rocks are controlled mainly by tectonic movements. Hence, most of the recent attempts to c1assify
sedimentary basins have been based on concepts of
global and regional tectonics which will be briefly discussed below. In spite of obvious advantages, however,
this approach has some serious shortcomings if it is not
supplemented by additional criteria. One ought always
bear in mind that the characteristics of sediments filling
a basin of a certain tectonic type are pre-dominantly
controlled by other factors and can be extremely variable. With few exceptions (also discussed later), there
is hardly such a phenomenon as a "tectonic sedimentary facies". For example, the broad concept of "geosync1inal sediments", often postulated in the past, was
more misleading than helpful.
In addition to tectonic movements in the basinal area
itself, sedimentary processes and facies are controlled
by the paleogeography of the regions around the basin
(peri-basin morphology and c1imate, rock types and
tectonic activity in the source area) , the depositional
environment, the evolution of sediment-producing organisms, etc. Many sedimentologists therefore prefer a
c1assification scheme based mainly on criteria which
can be recognized in the field, i.e., the facies concept
and the definition of the depositional environment (fluvial sediments, shelf deposits etc.). A further approach
is the subdivision of sediments into important lithologic
groups, such as silicic1astic sediments of various granulometries and composition, carbonate rocks, evaporites, etc. Having established the facies, succession,
and geometries of such lithologic groups, one can proceed to defme the tectonic nature of the basin investigated.
In this book an attempt is made to combine some
principal points of these different c1assification systems
and to show the interaction between tectonic and environmental characteristics of depositional areas.
1.2 Tectonic Basin Classification
Basin-generating tectonics is the most irnportant prerequisite for the accumulation of sediments. Therefore,
a tectonic basin c1assification system is briefly introduced at the beginning of this chapter. Such a c1assification must be in accordance with the modem concept
of global plate tectonics and hence will differ from
older c1assifications and terminology.
and Depositional Environments (Overview)
1.1 Introduction
1.2 Tectonic Basin Classification
1.3 Tectonics and Basin Filling
1.4 Basin Morphology and Depositional Environments
1.4.1 General Aspects
1.4.2 Different Methods in the Study ofModem
and Ancient Sediments
1.4.3 Depositional Environments (Overview)
1.4.4 Elementary Principles for Basin Filling
1.4.5 Some General Trends for Sediment
Accumulation and Facies
1.4.6 Facies Architecture
1.4.7 Summary (Basin Classification)
1.1 Introduction
Sedimentary basins are, in a very broad sense, all those
areas in which sediments can accumulate to considerable thickness and be preserved for long geologie al
time periods. In addition, there also exist areas of longpersisting denudation, as well as regions where erosional and depositional processes more or less neutralize each other (creating what is known as non-deposition or omission).
In plan view sedimentary basins can have numerous
different shapes; they may be approximately circular
or, more frequently, elongate depressions, troughs, or
embayments, but often they have quite irregular boundaries. As will be shown later, even areas without any
topographie depression, such as alluvial plains, may act
as sediment traps. The size of sedimentary basins is
highly variable, though they are usually at least 100 km
long and tens of km wide.
We can distinguish between (1) active sedimentary
basins still accumulating sediments, (2) inactive, but
little deformed sedimentary basins showing more or
less their original shape and sedimentary fill, and (3)
strongly deformed and incomplete former sedimentary
basins, where the original fill has been partly lost to
erosion, for example in a mountain belt.
As many workers have pointed out, the regional deposition of sediments, non-deposition, or denudation of.
older rocks are controlled mainly by tectonic movements. Hence, most of the recent attempts to c1assify
sedimentary basins have been based on concepts of
global and regional tectonics which will be briefly discussed below. In spite of obvious advantages, however,
this approach has some serious shortcomings if it is not
supplemented by additional criteria. One ought always
bear in mind that the characteristics of sediments filling
a basin of a certain tectonic type are pre-dominantly
controlled by other factors and can be extremely variable. With few exceptions (also discussed later), there
is hardly such a phenomenon as a "tectonic sedimentary facies". For example, the broad concept of "geosync1inal sediments", often postulated in the past, was
more misleading than helpful.
In addition to tectonic movements in the basinal area
itself, sedimentary processes and facies are controlled
by the paleogeography of the regions around the basin
(peri-basin morphology and c1imate, rock types and
tectonic activity in the source area) , the depositional
environment, the evolution of sediment-producing organisms, etc. Many sedimentologists therefore prefer a
c1assification scheme based mainly on criteria which
can be recognized in the field, i.e., the facies concept
and the definition of the depositional environment (fluvial sediments, shelf deposits etc.). A further approach
is the subdivision of sediments into important lithologic
groups, such as silicic1astic sediments of various granulometries and composition, carbonate rocks, evaporites, etc. Having established the facies, succession,
and geometries of such lithologic groups, one can proceed to defme the tectonic nature of the basin investigated.
In this book an attempt is made to combine some
principal points of these different c1assification systems
and to show the interaction between tectonic and environmental characteristics of depositional areas.
1.2 Tectonic Basin Classification
Basin-generating tectonics is the most irnportant prerequisite for the accumulation of sediments. Therefore,
a tectonic basin c1assification system is briefly introduced at the beginning of this chapter. Such a c1assification must be in accordance with the modem concept
of global plate tectonics and hence will differ from
older c1assifications and terminology.