Dynamic Processes of Abyssal Sedimentation: Erosion, Transportation, and Redeposition on the Deep-sea floor

Abstract

The concept of a quiet, nearly motionless, and certainly currentless deep-sea floor lacking the processes of erosion so prevalent in shallower seas was well ingrained in scientific thought until discoveries of the past decade revised this serene and static picture. The new concept is a more dynamic one in which submarine landslides, raging turbidity currents, internal tides, deep-sea current scour, and submarine postdepositional solution and alteration play a part in shaping the sea floor, in disturbing and nurturing its fauna and which produce sedimentary structures and distributions formerly thought to be the exclusive mark of shallow water deposits. The concepts involved are still in a critical state of flux with many conflicting viewpoints as to the processes involved and their relative importance. The development of the major concepts is traced and the principal variant viewpoints are briefly reviewed. Part I. Early ideasThe Naked Abyss. "The geological clock may strike new periods; its hands may point to era after era; but, so long as the ocean remains in its basin-so long as its bottom is covered with blue water-so long must the deep furrows and strong contrasts in the solid crust below stand out bold, ragged, and grand. Nothing can fill up the hollows there; no agent now at work, that we know of, can descend into its depths, and level off the floors of the sea." (Maury 1855.) Thus M. F. Maury eloquently summed up the view generally held a century ago. Remembering the then newly discovered deep-sea oozes he added:"But it now seems that we forgot the oceans of animalculae . . . whose remains in vast multitudes sink down and settle upon the bottom."The Unremitting Snowfall. The concept of the great unremitting snowfall which modified and then replaced the original picture of a naked abyss was stated clearly by Rachel Carson:"When I think of the floor of the deep sea, the single overwhelming fact that possesses my imagination is the accumulation of sediments. I see the steady, unremitting, downward drift of material from above, flake upon flake, layer upon layer-a drift that has continued for hundreds of millions of years, that will go on as long as there are seas and continents.'' Dynamic processes of abyssal sedimentation 143 Large elements of truth are found in both of these seemingly contradictory concepts which is why both have so long endured. To be sure, sedimentation is so slow over vast areas of the ocean floor that the original "grand and imposing'' relief mentioned by Maury is, over broad areas of the sea floor, still to be observed only slightly modified by subsequent deposition (Heezen, Tharp & Ewing 1959). Furthermore, the success which students of sediments have had in reading that "epic poem of earth history" contained in the successive layers of sediment further attests to the general validity of the concept of the unremitting snowfall (Phleger 1952, Ericson et al., in press, Broecker, Turekian & Heezen 1958. However, neither of these concepts tells the complete story; nature is considerably ...

Deep-water fine-grained sediments; history, methodology and terminology

“…Heezen 1959;Heezen & Johnson 1963;Hubert 1964). Finally, it was the compilation of evidence by Heezen et al (1966) on Shaping of the continental rise by deep geostrophic contour currents that caught the imagination of many more geologists. Stow & Lovell (1979) suggested that this paper marked the beginning of a revolution in sedimentology comparable to the turbidite revolution.…”

“…Marine geologists were documenting many other kinds of evidence that indicated an important role for bottom currents flowing alongslope in deep water (e.g. Heezen 1959;Heezen & Johnson 1963;Hubert 1964). Finally, it was the compilation of evidence by Heezen et al (1966) on Shaping of the continental rise by deep geostrophic contour currents that caught the imagination of many more geologists.…”

Sedimentary Evolution of Rifted Continental Margins

“…Piston cores collected by the Lamont-Doherty Geological Observatory, and cores drilled on Legs 1 and 11 of the JOIDES Deep-Sea Drilling project (JOIDES, 1968(JOIDES, , 1970 in the western North Atlantic, contain middle and lowermost Cretaceous sediments rich in unoxidized organic clays, JOIDES Core 105 (from Leg 11, 1970) includes a sequence of Lower Cretaceous clays so rich in carbonaceous material that some samples will actually burn (JOIDES, 1970). The present-day Red Sea, then, appears to be not only a tectonic analog to the proto-Atlantic (Heezen, 1960), but a sedimentary analog as well.…”

“…Since introduction of the theory of ocean basins widening by growth of new crust at the mid-ocean ridges (Heezen, 1959;Hess, 1962;Dietz, 1961), exciting new findings have been presented describing: (1) rates of sea-floor spreading using sea-floor magnetic data (Vine and Mathews, 1963;Heirtzler and others, 1968); (2) ages of prominent seismic reflectors within the ocean floor (Ewing and others, 1966); and (3) deep-ocean sedimentary processes (Heezen and others, 1966;Schneider and others, 1967). With this background, one can attempt to reconstruct the history of sedimentation in a widening and deepening ocean environment.…”

“…With this background, one can attempt to reconstruct the history of sedimentation in a widening and deepening ocean environment. Heezen (1960) suggested a tectonic history of such growing ocean basins. He envisioned an ocean initiating as a rift valley, widening with accretion of new crust along a ridge to a stage similar to the present-day Red Sea, then spreading to the width of a major ocean basin such as the Atlantic.…”