Sequence Stratigraphy Flashcards
What does it mean to say that facies are retrogradational?
If sea level rises faster than sediment is supplied, the coastline shifts landward: this is known as transgression and the pattern in the sediments is retrogradational
What is progradational?
If sediment is supplied to a coast where there is no (or relatively slow) sea‐level rise the coastline moves seaward: this is regression and the sediment pattern is progradational.
What is aggradational
A situation where the coastline stays in the same position for long periods of time is relatively unusual and requires a balance between relative sea‐level rise and sediment supply producing a pattern of aggradation in the sediments.
What is the maximum flooding surface?
When transgression ceases and the shoreline initially remains static and then starts to move seawards. It can be identifies by the furthest point of landward extent of the shore line
The maximum flooding surface divides which two system tracts?
Highstand and transgressive
What is a ravinement surface? How does it form?
surfaces of erosion formed during transgression, they form because high wave energy in the shallow water that floods over the land surface can result in erosion
What is a parasequence?
packages of beds deposited as a consequence of the creation of a small amount of accommodation that is then filled up by sediment.
What triggers the start of new parasequence
a facies shift from shallower to deeper water deposition
What is the surface called that divides two parasequences
flooding surface
What is the facies pattern within an individual parasequence?
progradational
What is the definition of “sequence stratigraphy
The study of the relationships between sea level changes and sedimentation
What forms the upper and lower boundaries of a sequence
An unconformity caused by erosion called a sequence boundary
What is transgression
During a relative sea‐level rise, the shoreline will move landward
What is regression
Movement of the shoreline seawards as a result of sedimentation occurring at the coast
What is forced regression
seaward movement that is due to a relative sea‐level fall
What is accommodation space?
Places where sediment will accumulate
What three variables are responsible for changes in accommodation space?
tectonics, eustatic sea level (global level changes), and sediment supply
Why is this area called the “Book Cliffs”?
The layered sandstone and shale resemble book pages
What resource forms the basis for the local economy?
Coal
What sedimentary structure is used to deduce the storm wave base?
Hummucky beds that indicate they were made during storm waves
Describe what is meant by “sediment partitioning.
It is a method of sectioning off the various depositional systems present in an environment based off of water depth and sediment supply over time
When evaluating the unit called the “panther tongue”, what evidence was interpreted for the case of a river dominated delta vs a wave dominated delta
Lack of hummucky beds, instead being unilaterally deposited, having seaward dipping clinoforms, overall low-bay geometry, indicating river dominated delta
An incised (eroded) valley was discovered that indicated a sea level fall. The valley was
subsequently filled in with deposits from what environment? What geologic evidence supported the interpretation of this environment?
The valley was an estuary turned marine open conditions based on the wave patterns, bioturbation patterns, and and the sand sediments
Across the canyon, another erosional surface was identified. Was it another sequence boundary
It was a incied valley fill therefore a sequence boundry
What puts an end to the field work for the day
How does the flooding surface differ between the distal and proximal parts of the coastal
environment?
Its non linear and is above shoreline
How do we know that the plants that formed coal layers grew in situ?
Underlying beach deposits have pitted pot marks that indicate peat swamp
