Depositional Environment
Of the
Astoria Formation
Resented by: Greg Helstrom
Miocene
Generally warmer temperatures than today
Elevated Ocean Levels
Todays coastline was located on the Continental Shelf
Continental Uplift + Decreasing Oceanic Levels results in Oregons Modern Coast line
Nye Formation
Formation that underlays the Astoria Formation
Deposition occurred 22 Million Years ago (Early Miocene)
Deep Crustal Forces resulted in deeper seas covering Western Oregon
Composed of predominately massive mudstone and siltstone fragments
Astoria Formation
Deposioin occurred 18 – 20 Million Years Ago (Middle Miocene)
Period of Uplift and Erosion, resulting in Shallower seas covering Western Oregon
Astoria Formation consists of Sandstone and Carbonacous Siltstone that were deposited in shallow low energy seas.
Deposition of the Astoria Formation was brought to a close by a period of uplift and volcanic activity from
ancient volcanoes along Ogegons Coast
Astoria Formation Today
Poorly Lithified alternating beds of sandstone and siltstone
Sediments contain high volumes of Shallow Marine Fossils
(Need specific type) Contacts are poorly joined with water continually leaking from these Contacts
Interpretation of Findings
Shallow Marine depositional environment lead to the deposition of sandstone and carbonaceous siltstone
Shallow burial resulting in Low pressure and heat conditions during Lithification
Lithification conditions resulting in poorly lithified sidements
Contacts between (A&B) are weak now and continue to weaken as they continually perculate water through the voids
within the contact
Conclusion
Based on the findings it is my conclusion that the Depositional Environment of the Astoria Formation Ditectly relates
to landslides associated with Beverly Beach Oregon.
Low energy small particulate sediments experienced low levels of lithification, resulting in a poorly lithified and
structurally weak rock.
Contact between (A+B) are inherent weak point in the Astoria Formation, and these recurring contacts represent …
which can be directly tied to the Miocene aged environment found in Western Oregon