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, (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.*.pdf file

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 km thick cont. granite 2.7 g/cc oceanic- basaltic >2.8 g/cc mantle Mantle peridotite >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 short- term 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 asthenosphere lithosphere RIGID DUCTILE

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 crust mantle Mantle asthenosphere lithosphere RIGID DUCTILE

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