Wednesday, June 27, 2012

After the Cretaceous: The Lincoln Creek Formation

Written May 7, 2012, published June 2014

Following the end-Cretaceous asteroid impact and subsequent dying off of dinosaurs and many large reptiles, 65.5 ma (million years ago), this area was a large shallow warm sea, dotted with volcanic islands, and filled with coral and oyster reefs. Along the east side of the sea, swamps grew on low slopes near the water, near present-day Centralia and Chehalis, WA. Plants grew in these swamps that later formed layers of coal.  In fossil-speak these are called coal swamps. This sea persisted for 50 my (million years), to around 20 ma, in the early Miocene. 

Many marine fossils are found in rocks from this period, including: snails, clams, corals, crinoids, brachiopods, barnacles, sharks’ teeth, fish, whales, seals and turtles. Burrowing shrimp from 45 ma were found in marine sediments; similar shrimp species live in Willapa Bay today.  

These geologic periods had wet warm climates and considerable volcanic activity due to a nearby subduction zone. Water-washed ash mixed with marine silts and sands makes a very good fossil-preserving combination. 

Three concretions and a fossil crab (inside a fourth concretion), were loaned by Karla Nelson for this article. She found these several decades ago while camping on Lincoln Creek in the east Willapa Hills with her family. Photo by Kathleen Sayce
A distinctive round rock called a ‘concretion’ often forms in marine sediments, where as fossilization proceeds, sediments cement together to make round rocks, with the fossil at the center. Concretions form easily with small shells and crustaceans, such as shrimp, barnacles and crabs. 

An outstanding sedimentary rock formation, the Lincoln Creek Formation, is from this period. The Lincoln Creek Formation is 2,000 to 9,000 feet thick, composed of tuffaceous (ashy) siltstone to fine-grained sandstone, and formed 37 ma.  It was originally described from a site on Lincoln Creek, off the Chehalis River in the Grays River Basin, Lewis County, WA, and covers about 1500 square miles in southwest Washington, including areas of Pacific and Wahkiakum Counties. This formation has a good exposure along the Willapa River east of Raymond.  

Mollusks and crustaceans are common in the Lincoln Creek Formation, as are microscopic foraminifera. Crabs are particularly common. Karla Nelson, Time Enough Books, and her family often camped on Lincoln Creek when she was a child, and collected concretions. When opened, these concretions typically contain fossilized crabs. 

Swampy shorelines persisted in lowlands along the west side of the Cascades during the Paleocene to early Miocene Period.  Trees in these swamps included palms and many conifers, mallows, species in the rose family (hawthorn, spiraea, amelanchier, sorbus, prunus, rubus), also gingko, banana, magnolia, and grasses. Specimens of many plant and animal fossils from this period can be seen at the Burke Museum ( HYPERLINK "" ), Seattle, WA. 

The most similar modern analog to those ancient coal swamps is mangrove thickets in the tropics. For an analog of that ancient tropical shallow sea, the most similar area today is Indonesia, including earthquakes, tsunamis and active volcanoes. 

Wednesday, June 20, 2012

Lost Landscapes: Coastal prairies before beach grass 

Written May 31, 2012, published June 2012

One of these days I’m going to write a book about all the lost views and vanished landscapes in this area. Until that day comes, here’s a start on the changes:  Simply put, the plants that live on the dunes today are different from those of the past. This change in species also changed the appearance of the dunes.

Barbara Minard, Columbia-Pacific Heritage Museum, proffered this image of the Breakers Hotel in north Long Beach; the date is between December 1900 and 1904. This is a winter or early spring photograph, showing abundant driftwood on the beach, and on the dune, very low vegetation. There’s bare sand in the foreground, and some of it may be black sand. 

Image loaned from Columbia-Pacific Heritage Museum, of the Breakers Hotel, looking north. Note the extensive driftwood on the west (left side of the image), the fence near the middle left, and the treeline, well to the east of the beach and fore dune. 

The Breakers Hotel stood on the dune that formed after the last subduction zone earthquake, which was in 1700. When this photo was taken the dune was 200 years old.  Today, a row of houses stands in this spot, more than one thousand feet east of the present beach. Note that the vegetation is very low and like a patchy turf. American dunegrass is native here, and was growing in the dunes in 1900. It goes dormant in fall and dies back to the ground. Many other dune plants are also perennial and also die back to the ground in winter, so the ground would look partially bare in winter. 

In spring, an image taken at this same location would show wildflowers, including beach lupine, footsteps-of-spring, sea thrift, early blue violet, harsh paintbrush, western buttercup, checkered lily and gray beachpea. By midsummer, dune goldenrod and white brodiaea would be flowering. There may have been patches of tough-leaf iris and nodding onion. Two orchids, hooded maiden’s-tresses and coast piperia, flower in mid to late summer. Beach morning glory, yellow and pink sandverbena and beach carrot thrive in open sandy dunes.  Several other native grasses grew in small tufts and clumps. 

Today, many of these species have all but vanished from the dunes due to the arrival of introduced beachgrasses.  Pink sandverbena is so rare today that when it appeared at Leadbetter Point a few years ago, it had not been seen in Washington for more than 60 years.  Snowy Plovers, Streaked Horned Larks and Oregon Silverspot butterflies were among the animal species that thrived in these open sandy, wildflower-rich coastal prairies. 

Not all dune species have suffered. Still flowering on today’s dunes are beach strawberry, purple beachpea, and patches of yarrow, pearly everlasting and silver bursage.  Sandbur is doing very well, having made a transition from dunes to lawns, to the dismay of bare feet.  Kinnikinnick grows among shore pines, and is a good groundcover for home gardens, in both full sun and partial shade.  As for animals, native voles, shrews, and thatch ants thrive in the beachgrass dominated dunes. 

There are small fragments of coastal prairie scattered along the peninsula; they are no longer on the outer dune line, but well inland, usually more than one thousand feet from the present beach. The diversity of wildflowers in these small remnant patches is amazing.

The vanished landscape that this image hints at is a diverse coastal prairie, rich in colorful flowers, which thrived on summer drought, fire, salt, winter rain and strong winds. In comparison, today’s dunes are very nearly monocultures, dominated by two species of beachgrass.  Someone probably has summer pictures of the dunes from a century or more ago, showing those now-vanished wildflowers. I’d love to see the images of the wildflower prairie that used to flower along the ocean beach.  As for the introduced beachgrasses, these species make gorgeous green grasslands in the dunes, but these grasslands are completely different from the colorful dunes of past millennia. 

Photo courtesy Columbia-Pacific Heritage Museum