Fossils reveal ancient shorelines
September 3, 2020
Retired biology teacher and geology aficionado John Norton recently sent out clay containing fossil samples from three areas in the Chilkat Valley to get radiocarbon dated. The results help paint a picture of what the local landscape looked like between 11,250 to 13,450 years ago when the fjord reached up to what is now 25 Mile Haines Highway and when what we know as the Chilkat Valley was at the bottom of the sea.
Norton tested samples from the old homestead of Dennis and Mary Miles just past 25 Mile, a subdivision around 9 Mile Haines Highway, and near 4 Mile Haines Highway. The fossil remains in the layer of glacial sediment from each area reveal a greater diversity of life as he moved closer to town-reflecting more than 2,000 years of retreating ice, sedimentation and rising land.
The area he sampled near 25 Mile was about 250 feet above today's sea level. The clay contained single-celled marine organism fossils, called Foraminifera, and other shells such as mussels and barnacles that a Florida lab radiocarbon dated to about 13,000 to 13,425 years ago.
"The area would have been a seashore," Norton said. "You can take a topographic map and draw a line around the 250-foot elevation on a topo map and it will give you a fair idea of the area that was once covered by marine waters throughout the valley. They would have gone up the Chilkat River Valley, the Klehini, the Tsirku, all of our major river valleys of our area."
Life in the area would have appeared similar to the landscape that appears today that has only recently been revealed by melting glaciers, said Tongass National Forest geologist Jim Baichtal.
"As that landscape was flooding, it would have been willow and alder choked lower valleys with tundra dominated higher elevations at ridge tops at the time that John's deposit was being laid down there at 25 Mile."
Baichtal and Norton have worked together trying to piece together the geologic history of Southeast Alaska. Both likened the data to pieces of a jigsaw puzzle that creates a picture of the region's geologic history. Norton's samples are among the scant data studied in the Chilkat Valley, Baichtal said, but he'll use the samples for a paper he's working on that includes more than 700 records of shell-bearing strata across Southeast that will help give scientists a better idea about sea levels and ice thicknesses through geologic time.
Norton's snapshot of time from 25 Mile occurred after what's known as the Wisconsin Ice Age, which lasted until about 18,000 years ago. During the peak of glaciation, ice covered Haines and continued all the way out to the continental shelf in front of Icy Bay.
Cathy Connor, former University of Alaska Southeast geology professor, said Juneau was covered by ice about a mile thick, and Haines was covered by at least that much if not more. When the global climate warmed, the Wisconsin ice beat a fast retreat and the land, thinner than larger continental crusts, rose rapidly relative to geologic time-at least 625 feet over 15,000 years. The crust of Southeast Alaska was formed after shards of other continents slammed together, like a demolition derby of terranes-what Baichtal described as "the great terrane wreck."
"It's huge changes in a really dynamic landscape," Baichtal said. "It's incredibly hard to wrap your head around. This thing we call terra firma, this earth we live on, being that flexible."
At 25 Mile, organisms got a small foothold but as the land continued to rise the environment was no longer suitable. And like local snowbirds avoiding unpleasant conditions, life flew south-about a dozen miles south across a few centuries.
The site Norton sampled at 9 Mile was about 160 feet above sea level. Those samples were dated to about 12,500 years ago. The third site, about 100 feet above sea level, came from a pit on Roger Schnabel's Southeast Roadbuilders property at 4 Mile Haines Highway. The clay he sampled from the area had larger clam shells that dated approximately 11,250 years old.
"By the time you get there, life's starting to stabilize and you're (seeing) more diversity, different clams and sea urchins and stuff like that," Baichtal said. "You have this changing habitat. By the time you get to 10,000 years ago the clam species would not look appreciably different than what we would find in a very productive intertidal clam bed today."
Norton said part of his interest in learning about how the landscape changed includes theorizing about places suitable to human habitation.
"Interestingly, on the backside of the Southeast Roadbuilders site on the downhill side is Yandeistkya, the old native village," Norton said. "Whether or not Yandeistkya goes back to the time of great antiquity, it would be hard for me to say. There's never been a kind of effort to date that site to see how far back occupation goes. If one were to look at our area and ask is there a candidate site where food is plentiful, that early inhabitants would be drawn to, that would definitely be on my list."
Baichtal and colleagues have used sea level models to predict shorelines suitable for human habitation. In 2009, there were five cultural sites known to scientists older than 7,000 years old. Using their model of shorelines, researchers have now found more than 30 sites across Southeast-the oldest dated at 10,600 years before present. Scientists have found stone tools made from rocks found in isolated areas dispersed through the Southeast, indicating that people were likely here longer than 10,600 years ago.
As the glacial uplift continued, the sea was also rising from melting ice and the land was flooded. Significant flooding was believed to have occurred from 17,000 to 12,900 years ago, Baichtal said. Daa_x_koowdein (Tommy Jimmie), a former Haines resident, retired teacher, and Tlingit Native, said his peoples' stories tell about a time of darkness and a flood that lasted for eight generations.
"While the world was flooding, Raven flew up and stuck his beak in the cloud and he hung there until the water started to go down and he saw the mountains of our country and that's when he let go of the cloud," he said.
Daa_x_koowdein said Raven stories have traditionally been associated with creation, but he believes they have more to do with restoration and repair after the floods receded.
"Most of our people, they think (we) begin with Raven. They give Raven the credit for being the creator. Baloney. That's not what the story is about, it's about survival," he said. "When people came back, that's the time of restoration. All of the damage that was caused because of flood was restored."
Daa_x_koowdein said Tlingit stories indicate that his distant ancestors go as far back as the ice age. He said there are stories about "a girl who was feeding the glacier," which caused the advancing ice to force his people to flee the region. His clan, he said, lived as far south as South America.
He said he's spent a lifetime reading what he described as disparate stories in an attempt to put them back together-all in an attempt to add context to Tlingit history. He, like Baichtal and Norton, likens the stories to pieces of a puzzle.
"When I go and read those stories it's like someone took them and cut them into all kinds of jigsaw puzzles and threw them up into the air," he said.
For his part, Baichtal said learning about the region's geologic history makes living there more meaningful, and the more data they can collect, the sharper the image will become. "It makes our experience on the landscape richer if we have a basic understanding of why the landscape looks the way it does."
Both Norton and Baichtal asked the public to inform them of anything they find that might add another piece to the puzzle.
"Maybe when they're digging in their backyard or fly fishing up a stream or hiking some place, they might take a second to look at a grey mud bank and if they see something let John or I know about it," Baichtal said.
Baichtal can be reached at email@example.com and Norton can be reached at firstname.lastname@example.org.