Lecture 13 - Sedimentary notes PDF

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Lecture 13: Sequence stratigraphy- Starts with large scale unconformity - bound packages and works down to smaller- Normally found at continental margins- If use remote sensing can find sediment packagesTerminology: Basin fill secession — entire pile of sediment in a basin Accommodation space — pote...

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Lecture 13: Sequence stratigraphy

- Starts with large scale unconformity - bound packages and works down to smaller - Normally found at continental margins - If use remote sensing can find sediment packages Terminology: Basin fill secession — entire pile of sediment in a basin Accommodation space — potential for sediment to accumulate — factors that affect it is basin subsidence and eustatic sea level change - there is very much less of it on the continental crust - where you are offshore theres more chance of accommodation space

- None in aeolian deserts as sediment is moving all the time. - Estuaries you don't need much space as tide is carrying the sediment - Most seen at continental margins.! Parasequence — a low amplitude short-term oscillation between sediment supply and accommodation space - Coarsening upwards if the parasequence progrades a) Aggradation - when vertical build up of parasequence is uniform — occurs if sediment supply and accommodation space are equal. - Sea levels fluctuate pretty often so doesn't often happen - Rarely long lived - Basically is perfect vertical stacking b) Progradation — occurs when the sedimentation rate exceeds the accommodation space - progrades outwards — build forwards into the basin - Sediment builds outwards as well as upwards. Also termed a regression. - Familiar in upward-coarsening deltaic sequences. c) Retrogradation — occurs when the accommodation space increases faster than the generation of sediment. This is also termed a transgression - Sediment steps backwards from the basin

Transgressive facies shift: - As ocean levels rises - the sediment shifts - get a dipping gently towards the ocean basin Depositional sequences: - a package of sediment deposited in a distinct time period in the history of a basin, i.e 1 cycle in the same balance between accommodation and sediment supply. - If add subsidence to eustatic sea level you get relative sea level - Can divide this relative sea level curve into 4 different system tracts - Each of these tracts represents part of the cyclic change in the balance between accommodation space and sediment supply - Usually systems tract must be made up of at least one parasequence

Clastic shelf and ramp are two different environments where these tracts can occur: Highstand system tract (HST) — accommodation space is decreasing through time and sediment supply is the same — must prograde into the basin Sequence boundary (SB) — surface created by falling sea level, on land see an unconformity Falling stage systems Tract (FSST) — where the sea level falls — causes erosion and sedimentation Lowstand system tract (LST) — accommodation space reappears when coastal sediments start to step landwards again Shelf — sedimentation on land, base level of rivers are rising, sea level rising, less erosion, deposition on floodplains Ramp — have no submarine fans, channels become straighter, rivers may turn into an estuary Transgressive system tract (TST) — accommodation space continues to rise, sea levels still rise - transgressive surface occurs on the continental surface - in filling of valleys from sediment

Maximum flooding surface (MFS) — can point out at top of transgressive sequence, where sediment is the furthest inland...