Transcript Slide 1

Basin Analysis
Chapter1: Basins and their plate
tectonic environment
This presentation contains illustrations
from Allen and Allen (2005 ) as well as
illustrations from Press et al. (2004)
Basins
• INTRODUCTION
– Definition and examples
(What is a basin?)
– How are basins classified?
– Essay (due next Tuesday)
• MAKEUP of the EARTH
– Compositional division
– Rheological division
• BASIN FORMING MECHANISMS
–
–
–
–
Plate Tectonics
Thermal
Thermo-mechanical
Mechanical
Basins
• Definition and examples
Basins
• Definition
Areas of the earth where there is a net sedimentation,
or in the fossil (ancient) record of such areas
Zones of pronounced subsidence where sediment can
accumulate. The larger the thickness of sediments and
longer the accumulation has taken place, the more
interesting to the oil companies the basin becomes.
• Examples
Gulf of Mexico (today and ancient)
Pyrenees (ancient)
Oman (oil from 650 Ma stromatolites still in living
position)
Basins
• INTRODUCTION
– Definition and examples
(What is a basin?)
– How are basins classified?
– Homework # 1.A (due next Tuesday)
• MAKEUP of the EARTH
– Compositional division
– Rheological division
• BASIN FORMING MECHANISMS
–
–
–
–
Plate Tectonics
Thermal
Thermo-mechanical
Mechanical
How are basins classified?
Basin can be classified according to many priorities of the individual. A
classification scheme should not just create "order from the chaos", but
highlight patterns that are useful for predicting stratigraphy, and
faulting.
Dickinson's (1974) classification scheme is based on tectonic history:
(a) lithospheric substratum: oceanic versus continental
(b) proximity of the basin to a plate margin
(c) type of plate margin nearest the basin i.e., convergent, divergent,
conservative (similar to Bally and Snelson, 1980)
Other factors used are: hydrocarbon characteristics, types of sedimentary
sequences filling the basin, and the tectonics that modify the sediment
infill
If on the other hand one is interested in WHERE they are to be found with
respect to PLATE TECTONIC boundaries we might also get a hint about
the mechanism of formation. Fossil basins may no longer be in the plate
tectonic setting in which they were originally formed.
.
How are basins classified?
If one is interested in HOW Basins are formed then it is very natural that
we break up the basin types according to their mechanism of formation.
E.g., mechanical, thermal or thermal-mechanical.
Basins
• INTRODUCTION
– Definition and examples
(What is a basin?)
– How are basins classified?
– Homework # 1.A (due next Tuesday)
• MAKEUP of the EARTH
– Compositional division
– Rheological division
• BASIN FORMING MECHANISMS
–
–
–
–
Plate Tectonics
Thermal
Thermo-mechanical
Mechanical
Homework due next
Tuesday
Essay
• For the basin you have chosen to write a proposal in this class write an
essay (1 page or 300 words at most, including figures). In the essay
you will classify your basin according to Kingston et al., (1983a) scheme
(4-5 sentences). If you wish you may read the original paper to get a
detailed understanding of their classification scheme. This scheme was
devised to help predict hydrocarbon potential. Write a brief sentence
or two about your opinion of this classification scheme? Does it help
you? Does it make it more difficult to understand the basin? Please
justify your answer with a reason. Think honestly and write clearly in
your own words.
•
Kingston, D.R. Dishroon,C.P. and Williams,P.A. (1983) Global basin
classification. Bull AM. Assoc. Petrol. Geol. 67, 2175-2193 (A copy of
this paper will be available for xeroxing outside my office. Please
borrow and return ASAP so everyone can use it. A copy of the main
table is given as a handout as well). There is also a *.pdf file of this
paper available from my website.
Basins
• INTRODUCTION
– Definition and examples
(What is a basin?)
– How are basins classified?
– Homework # 1.A (due next Tuesday)
• MAKEUP of the EARTH
– Compositional division
– Rheological division
• BASIN FORMING MECHANISMS
–
–
–
–
Plate Tectonics
Thermal
Thermo-mechanical
Mechanical
Basins
•
MAKEUP of the EARTH
– Compositional subdivision
Crust
10-70 km
thick
Mantle
cont. granite
2.7 g/cc
oceanic- basaltic
>2.8 g/cc
peridotite
mantle
>3.1 g/cc
down to
2900 km
depth
Where is the Moho
deepest?
Where is the Moho the
shallowest?
Where are there basins?
Allen and Allen (2005)
Compositional zonation
• Based only on the composition, which affects density, and shortterm rigidity (and hence seismic velocities) the shallow portions
of the earth (0-80 km) can have one of three flavors:
• oceanic composition, i.e. gabbroic melt and all its cooling
derivatives- mafic rocks, density ~ 2,800 kg/m3, Vaverage
Vp=5km/s
• continental composition, i.e. granitic melt and all its cooling
derivatives - felsic rocks, density ~ 2,700 kg/m3, average Vp =
6.5 km/s
• mantle i.e. peridotite and high temperatures and pressures,
density = 3,300 kg/m3, average Vp>=8.1 km/s
Basins
• MAKEUP of the EARTH
– Rheological divisions
RIGID
lithosphere
DUCTILE
asthenosphere
Key parts of Plate Tectonics
Lithosphere or rigid lid that holds both
crust and cold mantle together as one
solid block (0-100km)
asthenoshphere or plastic,ductile, layer also
within the mantle (100km depth to 300
km depth??)
Comparison of views earth
structure
RIGID
crust
lithosphere
mantle
Mantle
DUCTILE
asthenosphere
Plates
• Group of rocks all moving in the same
direction
• Can have both oceanic and continental
crust or just one kind.
Earth Divisions
What type of subdivisions are being used in these diagrams from Allen
and Allen (2005)?
Basins
• Definition and examples
• INTRODUCTION
– What is a basin?
– How are basins classified?
– Essay (due next Tuesday)
• MAKEUP of the EARTH
– Compositional zonation
– Rheological zonation
• BASIN FORMING MECHANISMS
–
–
–
–
Plate Tectonics
Thermal
Thermo-mechanical
Mechanical
Plate Tectonics
What drives plate tectonics?
Driving Mechanism of
Plate Tectonics
• GRAVITY
• Convection may have overturned asthenosphere 4–6
times.
• Convection may initiate process but cooling leads to
densification and plate movement?
• A cold planet is a dead planet. Is there oil on Mars?
Ridge Push and Trench Pull
Press et al., 2005
Two Models of Mantle
Convection
Press et al. 2004
Divergent Plate Boundary
Usually start within continents—
grows to become ocean basin
Press et al. 2004
Basins
• BASIN FORMING MECHANISMS
– Thermal
– Thermo-mechanical
– Mechanical
The Rock
Cycle
Press et al. 2004
Rock Cycle
Igneous rocks from magma. These rocks are subsequently eroded
to form sediments that are transported and deposited in basins
and can be preserved within continents
… Why is there a rock cycle?
Allen and Allen, 2005