MYERS, JEFFREY. Department of Earth and Physical Sciences, Western Oregon University, Monmouth, OR 97361 myersj@wou.edu. - Coastal Vegetation from the Middle Eocene of San Diego, California.
Impression macrofloras recovered from two localities in the ~43-44 Ma
Friars and lower Mission Valley Formations, San Diego County
California, were deposited in a fresh or brackish water coastal lagoon
during the middle Eocene sea level maximum. The newly recovered
assemblages further constrain the timing and magnitude of vegetational
and climatic change established from previously known middle Eocene
macro and microfloras of the San Diego region. Preliminary
identifications of taxa in the newly discovered floras include
Acrostichum, Polypodiaceae?, Sabalites,
Flacourtiaceae(?), Juglandaceae (Pterocarya?),
Macclintockia, Myrtaceae, Nelumbo(?), Phytocrene
sordida, Rhus, Rhizophoraceae(?), Ternstroemites,
and numerous unidentified forms. Nearest living relatives and leaf
physiognomy of plants in the assemblages suggest dense evergreen
broadleaved forest growing under humid paratropical climatic
conditions, similar to conditions interpreted from previously
described floras of the 45.5 Ma Torrey Sandstone, San Diego. Overlying
~ 42-43 Ma pollen and macroflora assemblages from floodplain and
fluvial facies of the Mission Valley Formation are interpreted to
record open woodland vegetation growing under seasonally dry climatic
conditions. The timing of the development of seasonally dry climate
and corresponding vegetational change in the San Diego sequence
correlates with comparable events recognized in the Clarno Formation,
Central Oregon, and the Gulf Coast sequence of the southeastern US.
Because middle Eocene floras from the San Diego sequence co-occur with
terrestrial vertebrate faunas and are interbedded with marine macro
and microfossil-bearing strata, they provide a precise benchmark for
the timing and magnitude of continent-wide climatic and vegetational
trends.
Key words: Macclintockia, mangrove, middle Eocene, paleobotany, paleoclimate, San Diego