Lecture 2: Geomorphic Systems Flashcards
What to polar wander paths act as historical evidence for, and how?
The opening of the Atlantic ocean. By documenting a seemingly systematic change in the position of the magnetic pole, which reveals continents have moved differentially with respect to the (actually fixed) pole.
Magnetic reversal is found where, and reflected where? What does this show?
Found along either side of an ocean spreading ridge, and reflected in the vertical sequence of rocks on continents. Shows the age of rocks recorded by the magnetism of the basalts in the crust.
What provides evidence that the pacific ocean has been migrating northwards?
Chalky deposits from plankton, that would usually only form in warm, up-welling regions found north of the equator.
Palaeoclimatic evidence of continental drift is largely in the form of what?
Mapping of striations and grooves, and deposits from ancient glaciers cover large portions of the continents in the south hemisphere - it would have been impossible for glaciers to have developed from what is now ocean, to land, so continents must have existed in places other than their present formation.
Palaeontological evidence of continental drift is…
fossil remains spread over different continents.
Geological evidence of continental drift largely occurs in two forms -
ancient orogenic belts and cratons
Hotspot doming may produce areas of hot asthenosphere up to 2000km across, but how much thermal uplift might they cause?
2km
Which two processes are they associated with?
Rifting and basaltic volcanism.
Describe the process and outcome of rifting on a dome.
Grabens form, dome fractures, two pieces form new oceanic crust, whilst third is a failed rift arm, draining to new ocean.
Drainage on tilted normal fault blocks deposits sediment as which four types of fan?
Alluvial, scree, small foot wall and large transfer fans.
Where do large alluvial fans form in relation to small foot-wall fans?
Large alluvial - on hanging wall dip slope Small foot-wall on fault scarps.
Regional uplift and erosion of horizontal sediments to expose old, folded rocks changes a dendritic (branch like) pattern of drainage to what? Via?
A trellis pattern, by superimposing drainage on old rocks, so streams cut both resistant and non-resistant rock, as well as stream capture from headward erosion of exposed weak rock.
What are the four mechanisms of drainage system formation?
Antecedence, superimposition, piracy and overflow.
Lithospheric flexure occurs by which two processes and how do they operate?
Isostacy - crust thickness changes and compensates for topographic height if loads have equal density. (The gravitational adjustment of the earths crust to maintain balance) Glacial loading - melting of ice causes rebound as density of load reduced/removed.
Moho depth is greatest in the Gulf of Bothnia, Pyrenees, Alps and Carpathians, but what is it?
The depth at which the base of the earth’s crust lies. Marks the compositional change from feldspar rich crust to olivine rich mantle. Lies at 5-8km under deep ocean basins and 20-70km for continental crust. Can be offset and respond to tectonic and magnetic perturbations.
