It’s a turbidite’s life

A turbidite is a deposit formed under water by the gravity-driven flow of an unstable sediment. It can be triggered by a storm, earthquake or rapid sea-level change. Deepwater turbidite deposits now provide excellent reservoirs of oil and gas worldwide, and are being prospected for by major companies. This is the life story of one of them.

Conceived from the grains of aeolian sand
Fresh-eroded from rocks of an earlier land,
Fallopially river-flushed mile after mile,
A turbidite foetus implants for a while
On a continent’s shelf, where there’s little impediment
To the gradual accretion of thick sandy sediment.

But when its time comes, its cohesion can’t cope
And it’s born as it plummets at speed down the slope,
Carving canyons that reach to the deep ocean floor.
Its arrival is followed by more sand, and more. . .
But gravity keeps a firm grip on its child
As it flows o’er the depths in vast fan shapes restyled.

Maturing, the turbidite slows to a stop,
Then layers of silt form a mud seal on top.
And now, as it rests from a life helter-skelter,
This deep-water turbidite acts as a shelter
To oil or gas seeping from rocks down below
And contains it, arresting its high-pressure flow.

That’s why it is searched for by seismic surveys,
By drilling and coring and 3-D displays:
Its oil and gas content is needed by man,
Who’ll burn the stuff up just as fast as he can.
So a peaceful old age without worry or toil
Is not for a turbidite full up with oil.

[Diagram: Indiana University]
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