GEOL 340 Sedimentology and Stratigraphy
Lecture 33
1. Sea Level Reconstructions: Problems and Trends
2. Sea Level Change: Definitions
3. Sea Level Change Rates
1. Sea Level Reconstructions
Problems and Trends
a. Exxon model built for extensional continental margins, not good for other settings
b. Genesis of unconformities
regional versus global
environment of formation
c. Impact of changes in sediment supply on stratal geometries
d. Chronostratigraphic correlations
Are sedimentary cycles regional or global in their distribution?
2. Sea Level Change: Definitions and Rates
BIG PICTURE
a. What was the timing, rate, and magnitude of sea level change
through geologic time?
b. What will be the timing, rate, and magnitude of sea level change in the future?
Eustasy and Eustatic Sea Level Changes (Seus, 1906)
a. original: synchronous changes in the strandline elevation on
a worldwide basis
b. current: globally synchronous changes in the mean elevation of the sea surface
Definitions of "Sea Surface"
a. distance from stationary datum at center of the Earth to
the sea surface
impossible to precisely measure from the center of the Earth
b. distance from seafloor (sediment-water interface) to the
sea surface
any process that causes sediments to move and accumulate would
create a SL change
i.e. burrows, slumps, gravity flows, etc.
c. distance from the base of unconsolidated sediments on the
seafloor to the sea surface
sediment consolidation on the seafloor is a diagenetic process
as a result, not at consistent depths everywhere
1. Rates of Sea Level Change
Definition of a sea level change cycle - one wavelength, generally
one low to the next low
CAUTION - these hierarchical abstractions in grouping sea
level changes may not reflect actual natural groupings, thus not
reflecting scaled natural processes
a. First Order - 200 to 300 million years
plate tectonic reorganization
b. Second Order - 10 to 50 million years
tectonics and some ice volume
c. Third Order - 0.5 to 5 million years
eustatic ice volume changes
d. High Frequency (Fourth and Fifth Order) - 20,000 to 40,000
years
linked to climate changes
2. Mechanisms of Sea Level Change
Changes in the Volume of Water
a. Oceanic Steric (thermohaline)
shallow
deep
b. Glacial Accretion and Wastage
mountain glaciers
continental-oceanic ice sheets
c. Liquid Water on the Land
groundwater
lakes and reservoirs
Changes in the Volume of the Ocean Basins
a. Crustal Deformation
lithosphere formation and subduction
glacial isostatic rebound
continental collision
seafloor and continental epirogeny
3. Mechanisms Driving Sea Level Change
Overview of processes and events handout