Kaua'i limestone 315,000 years old
By Jan TenBruggencate
Advertiser Science Writer
MAHA'ULEPO, Kaua'i — The limestones of this windswept corner of Kaua'i provide evidence of four periods of global glaciation over the past 300,000 years or so.
Jan TenBruggencate • The Honolulu Advertiser
Kaua'i geologist Chuck Blay has studied the limestone deposits along several miles of southeastern shoreline. His findings add to other studies that show that even in tropical Hawai'i, science can find hard evidence of large-scale global climate processes.
Chuck Blay's studies of the Maha'ulepu deposits have helped provide a sense of Kaua'i's geological formation and development.
Blay, whose specialty is the study of sediments, said the Maha'ulepu limestone represents ancient sand dunes dating to successive periods when the sea level was roughly at the height it is now.
The most recent limestones are 5,000 to 6,000 years old, and they are fairly easily broken apart by hand into sand particles.
The next series is 125,000 years old. It is preceded by limestones 215,000 years old. The oldest and hardest limestones along the coast are roughly 315,000 years old, he said.
Ice and snow lock up water and can result in lower sea levels. Global cold spells and glaciation periods correspond to the periods between the Maha'ulepu deposits, Blay said.
Blay, along with Colorado geologist Mark Longman, published the Maha'ulepu findings in the Society of Sedimentary Geology publication, "Modern and Ancient Carbonate Eolianites: Sedimentology, Sequence Stratigraphy and Diagenesis." Eolianites are the components of windblown geological deposits such as sand dunes.
Blay said the Kaua'i limestone interglacial pattern mimics that on Mauna Kea, which has had glaciers during each of the Earth's recent cold spells.
Mauna Kea moraine deposits — the collars of rock debris pushed downslope by glaciers — have been dated and match the periods between the Kaua'i sand dune deposits.
Another piece of supporting evidence for these glacial periods is in ocean-floor core tests in the waters around the Islands. These tests show that periods when the oceanwater around Hawai'i was cooler coincide with the glacial times identified both at Maha'ulepu and Mauna Kea.
Hawai'i sand dunes become limestone over time as water seeps through the sand particles, using a chemical process to cement the sand particles together. The older the deposit, the harder the limestone.
Blay said his studies concluded in part that the contents of beach sand have not changed on Kaua'i in the past 315,000 years. The beach sand back then, as it is today, is made up of 40 percent to 60 percent coralline algae, 20 percent to 30 percent coral, roughly 10 percent foraminifera and the remainder the shells of clams, snails and other creatures.
Foraminifera are one-celled marine creatures that leave behind tiny shells when they die.
In related studies, Blay said he examined the dune deposit patterns and found that Hawai'i's trade winds have blown in generally the same direction for the past 300,000 years. By studying layering patterns of sand, he was able to identify the prevailing wind patterns in each of the limestone fields, he said. As they do today, the trade winds blew generally from the northeast, he said.
One of the fascinating things about the Maha'ulepu area is that sand dunes are still being formed there today.
"That makes it easy to interpret what you're seeing. The same processes are still at work," he said.
Blay first became interested in the dune systems and related limestone deposits when he walked around the island of Kaua'i in 1986.
"I recognized that they (the limestone deposits) were windblown deposits, and found that they've never been studied before. There's no previous literature on it," he said.
The limestone fields — some would call at least the more recent deposits sandstone — also contain fossils of plants, marine and coastal animals and birds.
Blay himself has not conducted studies into the fossils, but others have collected the fossilized bones of extinct bird species from the Maha'ulepu area.
