Five days after leaving Hong Kong, the JOIDES Resolution is on site and drilling into the muds and silts of the South China Sea. The expedition’s main objectives are tectonic in nature, and I’m not really a tectonicist (I’m on board for the borehole logging), so for me this cruise is a crash course in the geological history of this area.
The origin of the ocean crust under the South China Sea is enigmatic, and there is ongoing scientific debate about which tectonic forces pulled apart the crust here to form the basin. In one hypothesis, the collision of India into Asia that built the Himalayas and pushed out Indochina to the southeast had the collateral effect of causing extension to form the South China Sea. The leading rival hypothesis says that the extension resulted from slab-pull from subduction at the southern edge of the basin (Borneo and Padawan). Of course, there are theories that mix the two, as well as minor-party candidates (plumes!).
The expedition aims to test the competing hypotheses by dating the earliest ocean crust (at the northern edge of the basin) and the youngest ocean crust (close to the now-inactive spreading center). If the age interval of sea floor spreading matches the age of the extrusion of Indochina (lets say 35 to 16 million years ago), then the Indochina extrusion hypothesis gains support; but if we find different ages, other hypotheses will move up the leader board. The debate and this expedition add to our understanding of the basic forces that shape the Earth’s surface.
Until now, the dating and interpretations rely on magnetic sea floor anomalies and other geophysical surveys. We will date the rocks directly for the first time, by argon-argon dating of the basalt that forms the ocean crust, and by the age of the sediments sitting on the basalt. The tricky part is that the basalt lies under 950 meters of sediments at the first site, and under 1850 meters at the second. To drill to this depth and bring back 100 meters of basalt is challenging to say the least, but there is a highly experienced drilling crew on board, so we are in with a shot. I’ll let you know how we get on!
Just imagine: one fine day, a fish revealed to you …
With proto-limbs, a monstrous face, all tinged with silver-blue!
Huge and strange and other-worldly, long thought to be lost,
In the flesh (starting to smell!) so many epochs crossed.
The coelacanth! Good Old Four Legs, to some, the “Living Fossil,”
The animal itself is big, its history colossal!
Ms. Latimer, she recognized its weirdness and allure;
Decades later, of its story some things were not sure.
But now we have its genome clear and plain for all to see,
Shedding light on autopods, immune systems, and pee!
More closely tied to humans than to tuna or to trout,
Holding secrets of the beasts who from the sea, climbed out.
Living fossil genome unlocked, Nature News
African coelacanth genome provides insights into tetrapod evolution, Amemiya et al., Nature 2013
First posted 4/19/13 at Katherine Allen’s website.
Behold! New treasures from the Burgess Shale,
In black and silent strata long held firm.
From features soft, a bold ancestral tale …
Be proud, descendants of the noble worm!
Oh, glorious the hemichordate line,
Spartobranchus tenuis among them,
On slime and mud they heartily do dine;
History has surely under-sung them.
From which deep root, vertebral creatures grew?
A scarcity of fossils long obscured;
Into this question we can dive anew,
With gorgeous, detailed imprints that endured.
A wondrous time, the Cambrian Explosion …
Move over, Eve; my roots are in the ocean!
- Tubular worms from the Burgess Shale, Nature / News & Views by Henry Gee:
- Tubicolous enteropneusts from the Cambrian period, Caron et al., Nature 2013
First posted on 3/29/13 at Katherine Allen’s website.