Plate tectonics, Reconstruction and Reservoirs Flashcards
How does isostasy create basins?
Compensation of mantle, it’s denser which creates subsidence.
When we thin the crust, the mantle will compensate causing the formation of a basin
What 3 overall things create total subsidence?
Thinning, Thermal and Load
What is McKenzie’s Model?
A model of isostacy which involves a thermal gradient.
Cooling of Mid Oceanic Ridge = Dense crust which leads to subsidence
Initial thinning –> the cooling of asthenosphere –> subsidence
Involves pure sheer –> symmetry in rifting
Definition of Basin / Depositional Basin
A bounded area where thick layers of sediment is deposited, often by gradual subsidence of the surface.
Definition of reservoir
A porous and permeable rock (Often sediment) that can produce fluids from it
Fluids: Oil gas or water
Describe the Wilson cycle
A continuous cycle where a continent rifts, forms an ocean and converges with the continent again with sedimentary accretion
1: Continental rift
2: Spreading continues, passive margin cools and sediments accumulate
3:Convergance begins and one plate subducts
4: Accretion of sedimentary wedge happens
5: Collision between the two continents
6: Erosion thinning the crust
What is important about the early rifting in the wilson cycle
It is very rarely symmetrical, which leads to differing sediment accumulation over time
Subsidence
Downward vertical movement of the Earth’s surface
Synrift & postrift phase?
Synrift: Extension controlled subsidence
Postrift: Cooling and load controlled subsidence
What is an example of a strike-slip basin (Pull apart basin) in Denmark?
Sorgenfrei-Tornquist zone (Bornholm)
What is an example of a strike-slip basin in other places in the world?
The dead sea
Death Valley (San Andreas)
Foreland Basin
A structural basin that develops adjacent and parallel to a mountain belt.
The four main basin types
Rift basin
Passive margins
Pull apart basin
Foreland basin
What are the differing types of subsidence that make up total subsidence (M)?
Tectonic (T) + Isostatic (I) subsidence and compaction of underlying succession (K)
M=T+I+K
Porosity
Describes the fraction of space between the particles (matrix) in percentage
Phi= (V_v*100) / V_T
V_v = volume of void-space
V_T = total or bulk volume of material
Porosity is dependent on packing, which is affected by depositional and diagenetic history
