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The AAPG/Datapages Combined Publications Database
Sediments are delivered to continental margin basins via several paths. Major process types are mass movement, turbidity currents, discrete particle settling, and nepheloid flow. Some are episodic, others are continuous, and all vary in rate and magnitude depending on distance from source, variations in climate and oceanographic conditions, relief of source terranes, and trapping or storage within the basin systems which are commonly
important hydrocarbon reservoirs.
Based on detailed field sampling, simple models for the growth of both fine- and coarse-grained deposits can now be described. It is evident that contemporary field samplings will miss geologically significant events and are biased in their recovery owing to the rarity of major events on a human time scale and the dimensions and efficiency of the samplers. However, study of contemporary sediments and their modes of formation and later alteration show us much about the three-dimensional character of the deposits actively forming and, when combined with studies of the ancient analogs exposed in outcrop, can yield a very complete story of the typical history of a deep marine sedimentary basin.
Fine-grained sediments come from two dominant sources--the overlying waters and the adjacent land sources. The terrigenous contribution is usually the dominant contributor in all environments open to its influence. The biologic components raining from the overlying water masses yield information about environmental characteristics and oceanographic circulation patterns as well as time markers. Benthic faunas provide depth data and also add deep-water environmental data. All usually pass through the surficial zone of bioturbation active in all but the least aerated basins and so the record preserved tends to be smeared.
Where time dimension can be defined and the rates of individual component sedimentation defined the picture that emerges usually clearly defines the major sources and their regional influence. When we examine the recent sediments we can directly measure these factors and then check them against the patterns preserved in the basin floor materials. Simple first-order models have been developed that explain the major features of the continuously depositing fine basin sediments. Second-order models have also been described which add the influence of current action within and over the basin. These are described and their results compared to the actual sediments presently collecting.
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