Production of lime mud by breakdown of foraminiferal tests

Many sources of lime mud have been discussed in the literature. However, fo raminifers, despite their abundance and importance in recent as well as in ancient sediments, have been generally disregarded. This study is based on stereo microscope observations and on a detailed SEM study of modern carbon ate sediments from New Caledonia and French Polynesia, and of foraminiferal tests. Many particles of the mud fraction have a morphology and compositio n similar to particles observed in benthic foraminiferal tests. The particl es are calcitic or Mg-calcitic needles, or are columns composed of crystall ites less than 0.5 mu m in size. In tropical environments, foraminifers can produce as much as 1 kg m(-2) of carbonate annually, and their tests may f orm more than 80% of the sediment. These observations show the genetic link from mud back to foraminiferal tests and show that at least a noticeable p art of the carbonate mud can result from the breakdown of foraminiferal tes ts. The role of foraminifers for the production of calcitic mud may be as i mportant as the role of Halimeda for the production of biogenic aragonite. (C) 1999 Elsevier Science B.V. All rights reserved.