PaleoBotany_Fossils - Identification of Miocene Fossil...

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Identification of Miocene Fossil Flora  from Cape Blanco, Oregon Jordan Anderson Abstract - The Cape Blanco flora is located on the southern Oregon coast, just south of Cape Blanco point. Fossil flora is Miocene in age and comprised mostly of angiosperm leaf compressions, some charcoal and a few conifer needles. The fossils are typically well preserved, showing clear venation and/or general shape. The fossils are found in a fine- grained tuff layer no more than 42 cm thick, 0.5 m below a 6 m thick section of thinly bedded fine to coarse-grained tuff. This tuff was deposited from a fluvial source and is part of the 153-m-thick sandstone of Floras Lake, consisting of fine to medium grained sandstone and inter-bedded conglomerate. Within the section of sandstone containing fossil flora, over 300 leaf compressions have been collected, ranging in at least 25 morphotypes. From this collection I have chosen five distinct leaf compressions to identify, each with a unique set of characteristics that seem to distinguish each fossil as a separate species. Some have very well preserved venation. The tertiary, quaternary and subsequent veins are visible and useful in the identification process. Others will need to be diagnosed based more on their general shape (leaf base, apex, leaf margin) because the lack of venation. Geology
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The Oregon coast in has one of the most unique geological formations on the planet with many diverse regions consisting of different layers of rock form different sources. The constant submerging of the oceanic plate and the uplifting of the continental plate provide for the steady change in the land. At Cape Blanco and the surrounding region the oldest rocks are quite dark and run from the base of the cape to the sea stacks and southward on. It is part of the Otter Point Formation, a Jurassic age conglomerate dating to 180 million years old. The rocks of this formation are also part of the Gold Beach terrane and form some of the younger rocks in the Klamath Mountain range. It is also highly faulted, with strip-slip faults measuring tens of miles. Just above the Jurassic age rocks are gray sediments which seem to be part of the Eocene Tyee Group, 45 million years in age. The sands and clay of this group are a result of the Klamath microcontinent, an island arc, colliding with North America. The erosion from the uplifting and creation of the Klamath Mountains deposited the sediments in this layer. Above this level, fine-grained sands and silts of the Empire Formation are present, embedded with many fossil clams, dating from 10 to 7 million years old. (Morris 2004) The fossil site we visited is middle Miocene in age and from a fluvial source. The fossils are present in a light gray tuff about 40 centimeters thick, 2 or 3 meters above the actual surface of the beach. 527,528
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This note was uploaded on 04/18/2008 for the course GEOL 433 taught by Professor Retallack during the Winter '06 term at University of Oregon.

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PaleoBotany_Fossils - Identification of Miocene Fossil...

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