Paleoecology of vegetation changes associated with a prehistoric earthquake at Serpentine Fen, southwestern British Columbia, Canada

Abstract

A sedimentary exposure near the mouth of Serpentine River, about 25 km southeast of Vancouver, British Columbia, records evidence of a large earthquake that happened about 2000 years ago. The evidence includes sand dykes injected into late Holocene peat and mud. Vegetation changes based on pollen analysis and radiocarbon-dated wood match sedimentary changes at the Serpentine Fen site. A shift from herbaceous to woody peat is matched by a dramatic peak (∼45%) in pollen of Myrica shrubs, indicating uplift and a vegetation shift to drier shrubland from fen, also incorporating detrital spruce wood (Picea). At the top of the woody peat, Myrica pollen disappears and intertidal mud with Triglochin-type pollen increases, indicating subsidence and establishment of an intertidal environment. The section above the woody peat shows increasing amounts of halophyte pollen, especially Chenopodiaceae (or Amaranthaceae) which reaches values up to 60%, and scattered dinoflagellate cysts, indicative of a continued tidal influence. The combined evidence of uplift and subsidence over a short interval is rare at most sites in south-coastal British Columbia.