Makah Formation — A deep-marginal-basin sequence of late Eocene and Oligocene age in the northwestern Olympic Peninsula, Washington

Abstract

The Makah Formation of the Twin River Group crops out in a northwest-trending linear belt in the northwesternmost part of the Olympic Peninsula, Wash. This marine sequence consists of 2800 meters of predominantly thin-bedded siltstone and sandstone that encloses six distinctive newly named members four thick-bedded amalgamated turbidite sandstone members, an olistostromal shallow-water marine sandstone and conglomerate member, and a thin-bedded water-laid tuff member. A local unconformity of submarine origin occurs within the lower part of the Makah Formation except in the central part of the study area, where it forms the contact between the older Hoko River Formation and the Makah. Foraminiferal faunas indicate that the Makah Formation ranges in age from late Eocene (late Narizian) to late Oligocene (Zemorrian) and was deposited in a predominantly lower to middle bathyal environment. The Makah Formation is part of a deep-marginalbasin facies that crops out in the western part of the Olympic Peninsula, in southwesternmost Washington and coastal embayments in northwestern Oregon, and along the central part of the coast of western Vancouver Island. On the basis of limited subsurface data from exploratory wells, correlative deep-marginal-basin deposits underlie the inner continental shelf of Oregon and the continental shelf (Tofino basin) along the southwestern side of Vancouver Island. Directional structures in the Makah Formation indicate that the predominantly lithic arkosic sandstone that forms the turbidite packets was derived from the northwest. A possible source of the clastic material is the dioritic, granitic, and volcanic terranes in the vicinity of the Hesquiat Peninsula and Barkley Sound on the west coast of Vancouver Island. Vertical and lateral variations of turbidite facies suggest that the four packets of sandstone were formed as depositional lobes on an outer submarine fan. The thin-bedded strata between the turbidite packets have characteristics of basin-plain and outer-fan fringe deposits.

Deep-sea food bonanzas: early Cenozoic whale-fall communities resemble wood-fall rather than seep communities

“…These sediments were deposited in bathyal depths and for the last 35 Myr have been accreted to the accretionary wedge and uplifted by the ongoing subduction of the Juan de Fuca plate under the North American continent (Rau 1966;Snavely et al 1978;Snavely et al 1980;Batt et al 2001;Stewart & Brandon 2004). These thick sediment sequences are generally fossilpoor, monotonous, thick-bedded silt-and mudstones, but contain also calcareous concretions with whale bones and wood associated with fossil mollusc assemblages that resemble those of modern whale-and wood-falls.…”

Paleoecology of whale-fall habitats from deep-water Oligocene rocks, Olympic Peninsula, Washington state

“…The lower Oligocene to lowermost Miocene Pysht Formation directly overlies the Makah Formation on the north side of the Olympic Peninsula (Snavely et al, 1980). Like the Makah Formation examples, four fossil cetaceans collected from the Pysht Formation also have unusual invertebrate associations (Table 1).…”

“…Rare allochthonous masses of limestone contain an invertebrate assemblage that indicates cold-methane seeps supported localized chemosymbiotic molluscan communities on the shelf/slope near the basin that contained the whale carcasses (Goedert and Campbell, 1995). Benthic foraminifers from this part of the formation indicate an age ranging from late Eocene to late Oligocene (Snavely et al, 1980;Armentrout et al, 1983); however, mollusks support a late early to early late Oligocene age assignment (Squires and Goedert, 1994).…”

“…Rocks in this part of the formation are hemipelagic siltstones and sandstones that were deposited at lower to middle-bathyal depths (Snavely et al, 1980) and are nearly barren of megafossils. Megafossils from these basin-plain and outer fan-fringe deposits include wood fragments, deep-water gastropods Squires and Goedert, 1994), the deep-water bivalve My oner a (Goedert, in press), and large isopods (Wieder and Feldmann, 1989).…”

Magnetostratigraphy and Tectonic Rotation of the Eocene-Oligocene Makah and Hoko River Formations, Northwest Washington, USA

“…Not only is the Makah Formation fossiliferous with mollusks [8,28], crustaceans [8,[29][30][31][32][33][34][35], and benthic foraminifera [8], but it also yields it also yields birds [36], terrestrial plants [37][38][39], and some of the earliest known fossils of baleen and toothed whales [23]. Some of these fossils come from apparent chemosymbiotic communities [40][41][42], including communities that are apparently associated with decaying whale carcasses and sunken wood [22,[43][44][45].…”