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