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