Summary of the Origin and Occurrence of 

 Microreiief 



The summarized information in this section is 

 arranged to correspond with the five microreiief types of 

 table 2. 



I. ROCK OUTCROPS AND BURIED BOULDERS 



These usually occur on shoaler and irregular under- 

 water topographic features such as banks, island shelves, 

 sides of troughs, seamounts, mountains, cliffs, ridges, 

 canyons, marine terraces, and shelf breaks. Medium-to- 

 coarse sands are usually present near the outcrops and 

 show ripple marks, scour, banking, and other signs of 

 water activity. Fine-grained materials other than fine- 

 grained sands, such as silts and clays, have usually been 

 washed into deeper water leaving the rock outcrops and 

 gravel deposits exposed. A variety of benthonic organisms, 

 together with a few fish, live in or near the shallow rocky 

 environments, whereas finer sediments, manganese coatings 

 and crusts, and infrequent benthonic organisms occur in 

 the deeper rocky environments. Rock outcrops usually 

 consist of volcanics (including basalt flows and pumice 

 slabs), coral boulders, and conglomeratic aggregates, and 

 they are normally coated with manganese and iron oxides. 



II. CHEMICAL DISTURBANCES 



Manganese nodules are the most prominent free 

 chemical precipitate on the sea floor. They occur over a 

 wide range of depths, but are most noticeable on topograph- 

 ical highs, on red clays below 5000 meters, and on shoaler 

 calcareous oozes. They are present in high concentrations 

 on extended abyssal areas and in deep-sea basins of all 

 major oceans, constitute strong microreiief, and represent 

 a mineral resource of great potential economic value. 

 Phosphorite slabs are found in high concentrations on 

 coastal banks where they are localized. Both manganese 



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