A NEW MIDDLE MIOCENE FLORA FROM CAPE BLANCO, OREGON

The Cape Blanco flora located on the southern Oregon coast south of Cape Blanco is a new Miocene fossil flora dominated by angiosperm leaf compressions.  The fossils are found in a massive fine-grained tuff layer with a maximum thickness of 42 cm located 0.5 m below the top of 6-m-thick section of thinly bedded fine to coarse-grained tuff.  The tuff was deposited in a near-shore or lacustrine environment from a fluvial source and is a unit within the sandstone of Floras Lake, a 153-m-thick fine to medium-grained sandstone with inter-bedded pebble and cobble conglomerate lenses.  Molluscan fauna from the sandstone of Floras Lake includes Mytilus middendorffi and Molopophorus matthewi, which constrain the age of the very shallow marine to intertidal sandstone to the late early to middle Miocene Newportian Molluscan Stage.  The sea-level elevation and coastal location of this flora expand the range of Miocene angiosperm biogeography west to the Pacific Ocean. Most of the fossils are moderately well preserved leaf fragments. There are at least 25 morphotypes and a preliminary species list includes Betula thor, Cercocarpus ovatifolius, Cornus ovalis, Lithocarpus nevadensis, Populus eotremuloides, and Quercus simulata.  No one species is represented by more than a few specimens, but the Betula and Quercus are most common. Numerous conifer needles were found, but Pinus ponderosoides was the only identifiable species from a bundle of three long needles.  Charcoal is found throughout the tuff unit and the largest piece is >100 cm².  This assemblage suggests a humid, summer dry climatic regime along the Pacific coast of Oregon during the middle Miocene.