Deep-Sea Floor and the History of the Earth

During Leg 48 of the IPOD phase of the Deep Sea Drilling Project, seven holes were drilled on the margins of the Bay of Biscay and Rockall Plateau to compare the evolution of passive margins of contrasting age and structural development. The geological setting and principal results of the drilling are outlined for each margin. We discuss the history of rifting and subsidence on these margins in relation to the sea floor spreading history of the adjacent ocean basins. Implications of the results for the nature of unconformities at passive margins and anoxic episodes during the Lower Cretaceous are discussed briefly.

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Tectonic Escalator

The Earth After Us ◽

10.1093/oso/9780199214976.003.0009 ◽

2008 ◽

Author(s):

Jan Zalasiewicz

Keyword(s):

Solar System ◽

Deep Sea ◽

Planetary Systems ◽

Original Order ◽

The Earth ◽

Long Time ◽

History Of

How does it work, this engine that produces the world’s strata, those storehouses of an almost infinite history? Our future explorers might be sorely puzzled, for the Earth’s motor is quite specific in its mechanism. There is nothing else like it in the solar system, and even reasonably close duplicates of it may be rare among planetary systems generally. A problem is immediately encountered in any attempt to construct a history of the Earth’s life and environments from the stratal archives. For the question will extend beyond simply explaining why the strata that formed on ancient sea floors happen to be present high up on land. Any explorer, in trying to construct a coherent history of the Earth, will find anything but coherence in those rock layers, once they try to put them back into their original order. For in many regions of the earth the strata are tilted, or are upside down, or are crumpled into huge folds, or have been sliced into segments in which the primary stratal layers are markedly off set from one another. Some layers show signs of having been recrystallized by heat and pressure, showing that they must have somehow been carried down to great depths below the Earth’s surface, and then carried back up again to lie exposed at the surface. The strata of neighbouring Mars, by contrast, have nothing like the richness of the Earth’s—but neither do they possess such formidable structural complications. These crazy Earthly stratal geometries, just as much as earthquakes or volcanoes, are indisputable signs of an active planet, in which the seemingly solid and stable crustal surface is, in reality, highly mobile. Our future explorers should take it for granted that strata are essentially made of sediment that was eroded from topographic highs (say, mountains) and was carried down to topographic lows (say, the floor of a lake or of a deep sea). This is straightforward. It has happened, say, on Mars. But on Mars it essentially happened as one cycle, a long time ago, where the highlands represent the eroded areas and the flatlands are an accumulation of the sediment derived from them.

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