An Eldorado for Paleontologists: The Cenozoic Seeps of Western Washington State, USA

Abstract

Most seep communities occur in deep water and it requires certain geologic processes – particularly their preservation within carbonates and their uplift above sea-level – before paleontologists can study them. Just like their modern analogs fossil seeps are highly localized and finding them requires walking through endless meters of strata that are usually barren of megafossils. The outcrop situation in western Washington is far from being ideal because most of the area is covered in thick forest. Many seep deposits are exposed along, sometimes even in, river beds Plate 31 and can be sampled only at certain times of the year when water levels are low. Sites at coastal outcrops may only be reached by kayak or canoe, during low tide or only early in the year before they are covered by algal growth. Nevertheless, extensive searching over the past 20 years produced seep fossils that are unrivaled world-wide in their diversity and the quality of their preservation Plate 32, and they are now probably the best-studied fossil seep faunas on Earth. A particular appeal is the fact that the seep-bearing sediment also revealed diverse whale-fall (Squires et al. 1991; Goedert et al. 1995) and wood-fall communities (Lindberg and Hedegaard 1996; Kiel and Goedert 2006b) so that evolutionary interactions between these ecosystems can be traced through nearly 45 million years of time (e.g., Kiel and Goedert 2006a). Furthermore, the seep carbonates preserve a wide range of molecular fossils (biomarkers) that reveal past fluid compositions, and the biochemical processes and microbial consortia involved in the precipitation of the carbonates, even on very small spatial scales (Peckmann et al. 2002, 2003; Goedert et al. 2003; Hoffmann 2006).