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Transcript of Ench week05
1
Week 5
Review of week 4o context of geologic description within basin analysis
o stratigraphy: differing stratigraphic units and their use
o modern contributions to stratigraphy
Topics for Week 5o facies analysis
Website URL for course materials
Reading and reference:
2
Course Schedule and Content: Ver 2Class Topic
Sept 14
Week 1
Introduction to Course and Material
Review and discussion of concepts
Sept 21
Week 2
Example of basin analysis: Gulf of Suez Rift Basin
Basins I: description of basins, plate tectonics, basin classification and
tectonic setting, basin setting of oil and gas fields
Sept 28
Week 3
Basins II: basin classification (continued), basin models of subsidence
and sedimentation, Wilson Cycle
Oct 5
Week 4
Basin Fill I: Stratigraphy and sedimentology; tools used, dating and
correlation
Oct 12
Week 5
Basin Fill II: Facies models, basin mapping; sequence s tratigraphy
Oct 19
Week 6
Basin Fill III: Sequence stratigraphy (continued), seismic stratigraphy
Oct 26
Week 7
Due Today: Selection of basin/petroleum system for main class
project
Basins III: Regional and global stratigraphic cycles
Nov 2
Week 8
Mid Term Exam (tentative)
Nov 9
Week 9
Petroleum System I: The petroleum system
Nov 16
Week 10
Student seminars
Petroleum System II: Field size distribution, exploration risk
Nov 23
Week 11
Student seminars
Reservoir quality and preservation of quality with burial and
diagene sis, carbonate and c lastic pore systems in basin settings
Nov 30
Week 12
Student seminars
Case studies in basin analysis
Dec 7
Week 13
Student seminars
Review, Basin modeling software demonstration
3
Magnetic Anomalies and Spreading Rates
Magnetic anomalies near the crest
of Reykjanes Ridge, Iceland. Dark
bands: normal polarity; light bands:
reverse polarity.
Calculation of rate of seafloor
spreading from age of ocean
sediment and distance from
spreading center.
4
Age of Oceanic Crust Away From Ocean Ridges (magnetic “stripes”)
5
6
7
Basin Fill In Context of Basin Analysis
Basin Analysis
Tectonic Setting
Basin FillPetroleum
System
Geological methods
Stratigraphy
Facies models
8
Categories of Stratigraphic Classification
Rock bodies may be classified according to many
different inherent properties. Each classification needs
its own distinctive nomenclature. The following kinds
of formal units are best known and most widely used:o 1. Lithostratigraphic units - units based on the lithologic properties of the rock
bodies.
o 2. Biostratigraphic units - units based on the fossil content of the rock bodies.
o 3. Magnetostratigraphic polarity units - units based on changes in the
orientation of the remanent magnetization of the rock bodies.
o 4. Unconformity-bounded units - bodies of rock bounded above and below by
significant discontinuities in the stratigraphic succession.
o 5. Chronostratigraphic units - units based on the time of formation of the rock
bodies.
9
Modern Developments
Traditional methods:o lithostratigraphy
o biostratigraphy
Modern contributions:o Chronostratigraphy
o Sedimentology
o Depositional systems
o Plate Tectonics/Geodynamics
o Seismic Stratigraphy
o Sequence Stratigraphy
10
Categories of Stratigraphic Classification
stratigraphic units
lithostratigraphic
biostratigraphic
allotstratrigraphic
chronostratigraphic
magnetostratigraphic
chemostratigraphic
specific rock attributes must be
present to be observed or
measured
11
Categories of Stratigraphic Classification
used in chronostratigraphy
defined using
stratigraphic units
lithostratigraphic
biostratigraphic
allotstratrigraphic
chronostratigraphic
Group Formation
MemberTongue
Bed
Allogroup AlloformationAllomember
EonothemErathemSystemSeriesStage
Chronozone
biozonesradiometric dating
magnetostratigraphychemostratigraphyseismic reflectors
magnetostratigraphic
chemostratigraphic
Biozone
12
Summary of Categories and Unit Terms
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
13
Rock vs Time Descriptions
Chronostratigraphy (rocks) Geochronometric (time) Examples
Eonothem Eon Phanerozoic
Erathem Era Mesozoic
System Period Cretaceous
Series Epoch Upper (late) Cretaceous
Stage Age Campanian
Chronozone Chron Orbitoides tissoti
14
Stratigraphic Completeness (Miall Text, p. 127)
Assumption in stratigraphy: rocks are correlatable given that
they formed at the same time in different places under
differing depositional environments
The stratigraphic record of time is discontinuous on several
time scales (seconds to 100,000+ years)
Rates of sedimentation are highly variable (11 orders of
magnitude!)
Estimate 1/30th of elapsed time is represented by sediment
Are we correlating time equivalent strata?
15
Geologic Time and Stratigraphic Units
Each lithostratigraphic unit was formed during a specific interval of geologic time, it has chronostratigraphic
significance. The concept of time, however, plays little part in establishing or identifying lithostratigraphic
units and their boundaries.
Some lithostratigraphic units are excellent guides to approximate time correlation over large areas, as in the case
of volcanic ash beds, but they, like biostratigraphic units, are not chronostratigraphic units because they
are not bounded everywhere by synchronous surfaces.
The boundaries of almost all lithostratigraphic units cut across synchronous surfaces when traced laterally
Unconformity-bounded units may include a number of other kinds of stratigraphic units, both in vertical and lateral
succession. Similarly, an unconformity-bounded unit may represent all or parts of several
chronostratigraphic units. In special cases, the boundaries of an unconformity-bounded unit may coincide
with the boundaries of other kinds of stratigraphic units. However, the boundaries of unconformity-bounded
units are always diachronous to a lesser or greater extent, and so never correspond with the boundaries of
chronostratigraphic units.
Magnetostratigraphic polarity units are potentially recognizable globally and, in this respect, they are similar to
chronostratigraphic units.
The boundaries of magnetostratigraphic polarity units because they record the very rapid reversal of the Earth's
magnetic field, approach synchronous surfaces closer than any other kind of objective stratigraphic unit.
Chronostratigraphic units are defined as encompassing all rocks formed within certain time spans of Earth history
regardless of their compositions or properties.
Biostratigraphic units may approximate chronostratigraphic units even over wide areas, but the boundaries of
biostratigraphic units may diverge from those of a chronostratigraphic unit for many reasons. Principal
among these are changes in depositional facies, variations in conditions for fossilization and preservation
of fossils, vagaries of fossil discovery, and biogeographic differences. Biostratigraphic units cannot be
recognized in rocks where there are no fossils.
16
Geochronometry: Geologic Time Scale
17
18
Summary
The geological observations and methods in common
use to carry out stratigraphic analysis have been
reviewed.
Modern developments in stratigraphic work have
added significantly to the technique of basin analysis.
Developments in these areas as they relate to basin
analysis have been reviewed.
Main stratigraphic units have been described, with key
differences, scope of use.
19
Facies Analysis (Miall Text Chapter 4)
Place within framework of Basin Analysis
Fundamental use of facies and facies models
Relate facies to depositional processes and environments
modern facies-modeling vs ancient facies reconstructions
Scale of facies analysis:
the study and interpretation of the textures, sedimentary structures, fossils and lithologic associations of sedimentary rocks on the scale of an outcrop, well section or small segment of a basin
20
Facies Analysis within Basin Analysis
Goal is to get from facies analysis to a
paleogeographic synthesis depicting an interpretation
of the stratigraphic and geographic evolution of the
basin through time.
make use of large scale basin-fill patterns; these are
“depositional systems”
the difference between facies analysis and analysis of
depositional systems is one of scale
mapping is an essential tool to support the use of
facies analysis in interpretation of depositional
systems and sequences.
21
Facies and Sedimentology (Reading, 1986)
Sedimentology is concerned with the composition and genesis of sediments and sedimentary rocks. Processes of sedimentation are important. Matching processes with the corresponding sedimentary product is often difficult.
Sedimentary structures are used in basinal reconstruction
Physical processes of sedimentation create the sedimentary structures
Ancient environments are reconstructed by:
1. interpretation of processes that gave rise to facies
2. interpret the environment in which the process operated
22
Facies Definition and Use
facies: a body of rock with specified characteristics. A
distinctive rock that forms under certain conditions of
sedimentation, reflecting a particular process or
environment (lithofacies, biofacies, seismic facies).
lithofacies: rock unit defined on the basis of distinctive
lithologic features such as composition, grain size,
sedimentary structures, bedding characteristics. Each
lithofacies represents an individual depositional event.
lithofacies associations/assemblages: groups of
lithofacies characteristic of particular depositional
environments
23
Reconstruct Depositional Environments
Use geological tools and experience to
reconstruct environments:o field description
o depositional processes (think of flow regime)
o vertical and lateral relationships
o present day environments and processes
24
Correlation: Pembina Cardium Example
(Miall, Figure 3.5)
25
Application of Facies Concept
lithofacies model: use of lithofacies assemblages
to describe depositional models
facies term can be applied to groups of rock
formed under similar conditions:o depositional processes (turbidites) or depositional environment (fluvial)
lithostratigraphy vs lithofacies:o Lithostratigraphy: traditional descriptive approach
o lithofacies: basis for genetic study of sediments using facies models
26
Application of Facies Concept
Knowledge of the context of a facies must be known before proposing an environmental interpretation (relationship to other facies).
o Contacts: sharp, gradational or erosive
o Cycles: patterns of facies are repeated
o Facies associations: groups of facies that occur together and are considered to be genetically or environmentally related. Associations provide additional evidence for environmental interpretation
o Facies sequence: a series of facies which pass gradually from one into the other; typical sharp or erosive base at top and bottom
o Vertical transitions from one facies into another reveals patterns – random or cycles of sedimentation
o Facies sequences may reflect sedimentological controls, external controls or combination of both.
o A limited number of facies models have been developed, each representing a particular depositional environment
27
Facies Relationships (Reading, 1986)
Facies relationship diagram
Appotsham Formation deltaPictorial representation of
facies relationships
28
Other Uses of Facies: Seismic Facies
Seismic facies: a seismic facies is a mappable,
3-D seismic unit defined on the basis of
reflection configuration, continuity, amplitude,
frequency and interval velocity (Mitchum, Vail
and Sangree, 1977). Typically an order of
magnitude greater in thickness than rock units
described in the field.
29
Controls on Facies
Factors controlling the nature and distribution of facies:o sedimentary processes: change to facies as a result of sedimentation; filling
basin, abandoning river course, changing fluvial gradient, delta switching,
changing erosive products
o sediment supply: sources of sediment (extrabasinal vs intrabasinal); balance
between sediment supply and base level; constant or episodic sedimentation
o climate: evaporites to limestone reefs to desert sand dunes
o tectonics: distribution of highlands and basins, location of depocentres
o sea-level changes: eustatic (global: volume of oceanic water, volume of oceanic
basins); relative changes within a basin (sedimentation, isostasy)
o biological activity: affect of plants on rate of erosion; reef growth
o water chemistry: ph and salinity and composition, preservation of organisms,
precipitation of carbonate and evaporites
o volcanism
30
Facies Models In Basin Analysis
Leads to description of depositional systems
End goal: paleogeographic synthesis depicting an
interpretation of the stratigraphic and geographic
evolution of the basin through time
31
Facies Analysis for Basin Analysis
(Catuneanu, 2002)
32
Facies Model
4 functions of a facies modelo 1. acts as a norm for purpose of comparison
o 2. acts as a framework and guide for future observation
o 3. acts as a predictor in new geological situations
o 4. act as a basis for environmental interpretation
33
Submarine Fan Facies Model (Walker, 1992)
34
Establishing a Facies Scheme: Fluvial system
Example: Facies scheme for description of braided river
(Miall, 1996)
35
Application of Braided River Facies Description
Sr: sand, very fine to coarse, ripple
cross lamination, lower flow regime
36
Establishing a Facies Scheme: Carbonate System
Example: Facies scheme for description of carbonate rocks
(Wilson, 1975)
37
Application to Describe Limestone Section
SMF-12: encrinite grainstone
38
Rock Descriptions
Main descriptive methods to define facies:o Grain size and texture
o Petrology (constituent classification)
o Bedding
o Sedimentary structures (hydrodynamic forms, erosion)
o Liquefaction, load and fluid loss structures
o Paleoecology
o Vertical profiles
o Architectural elements and bounding surfaces
Very few sedimentological criteria have unambiguous
interpretations!
39
Carbonate Grain Size and Texture
(Dunham, 1962)
(Folk, 1962)
40
Clastic vs Carbonate Grain Size and Texture
41
Structures From Hydrodynamic Molding
Variations in bedform morphology with depth and velocity.
Dependence of dune and ripple shape on water depth.
42
Facies Model for Point Bar Sedimentation
Decreasing water depth and velocity up slope lead to fining
upward sequence and well established profile of sedimentary
structures
43
Paleoecology: Carbonate Reefs
Fig 4.32 Lithofacies-biofacies composition of carbonate buildups
in the mid-Silurian shelf of the American Mid-west.
44
Paleoecology: Carbonate components
45
Paleoecology: Trace Fossil Assemblages
Fig 4.38 Six marine trace fossil ichnofacies shown in
representative environmental settings.
46
Vertical Profiles: Fining Upward Sequences
Fig 4.40
A sandy braided river
B,C point bars in high
sinuosity rivers
D degrading alluvial fan
E sandy tidal flat
F-I tidal creek point bars
careful facies and
paleocurrent studies
required to distinguish
environments of fining
upward cycles
47
Architectural Elements
Table 4.5 Hierarchy of architectural units in clastic deposits
48
Fluvial Facies Model
Figure 4.51 Dependency of channel style on sediment grain size
and other factors and the range of typical architectural elements.
49
Scales of Sedimentological Analysis
50
Facies Model: Shoreface Zone
(Einsele, 2000, Fig 3.1)
51
Facies Model: Beach profile, offshore sand bar
(Einsele, 2000, Fig 3.3a)
52
Facies Model: Beach profiles
(Einsele, 2000, Fig 3.3b,c)
53
Summary: Facies Analysis
Facies: a distinctive rock that forms under certain
conditions of sedimentation, reflecting a particular
process or environment (Reading, 1986, p. 4)
Facies term can be applied by geologists in differing
contexts:o observation sense for rock product (sandstone facies)
o genetic sense for the products of a process (turbidite facies)
o environmental sense for the environment in which the rock or suite of
mixed rocks was formed (fluvial facies)
o tectonic setting or tectofacies (post-orogenic facies)
In Basin Analysis: facies description are essential for
interpreting depositional systems used in sequence
stratigraphy