Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support

Decay and Mineralization of Shrimps

Derek E. G. Briggs and Amanda J. Kear
PALAIOS
Vol. 9, No. 5 (Oct., 1994), pp. 431-456
DOI: 10.2307/3515135
Stable URL: http://www.jstor.org/stable/3515135
Page Count: 26
  • Read Online (Free)
  • Cite this Item
If you need an accessible version of this item please contact JSTOR User Support
Decay and Mineralization of Shrimps
Preview not available

Abstract

Experiments on decay and early diagenetic mineralization of shrimps in artificial sea water resulted, for the first time, in extensive mineralization in association with soft-tissues. The investigation focused on taxa with a cuticle which is not heavily mineralized in life: the shrimp Crangon, and the prawn Palaemon. A series of experiments was monitored in terms of morphological change, weight loss, change in chemical composition, and the formation of minerals. The major controls investigated were the amount of oxygen present at the outset, and whether the system was open or closed to diffusion. Decay resulted in a continuum of five morphological stages: 1. swollen, due to osmotic uptake, 2. ruptured, as the exoskeleton split, 3. hollow, as the muscles shrunk, 4. disarticulated, as the elements of the exoskeleton began to separate, and finally 5. fragmented. There was no indication that rate of decay (measured by weight loss) was strongly influenced by the availability of oxygen. Two categories of mineralization occurred, the precipitation of crystal bundles of calcium carbonate, and the replacement of soft-tissue in calcium phosphate. Where the system was open to diffusion, mineralization was dominated by the precipitation of crystal bundles in the shape of discs, hemispheres, rods and dumbbells; soft-tissue was rarely extensively mineralized. Where the system was closed, precipitation of crystal bundles was not as widespread, but mineralization of soft-tissue (muscle, hepatopancreas, eggs) in poorly crystalline calcium phosphate commonly occurred. The major source of phosphate was the carcass itself. In some specimens mineralized soft-tissue was subsequently overgrown by calcium carbonate crystal bundles. Crystal bundles began to precipitate within a few days; mineralization of soft-tissue started within two weeks but increased by four weeks. The main control was pH which decreases most where the system is closed, inhibiting the precipitation of calcium carbonate in favor of calcium phosphate. Where phosphate was added to the sea water the rate of morphological decay increased; soft-tissue was mineralized in a similar proportion of experiments but it was more extensive sooner. Doubling the content of bicarbonate resulted in an increase in the extent of crystal bundle formation, but the proportion of individuals in which they precipitated remained the same. The excess bicarbonate inhibited the phosphatization of soft-tissue. Control experiments showed that both types of mineralization also occurred when the shrimps were buried in sediment. Crystal bundles have not been reported from fossils (they would be very susceptible to diagenetic recrystallization). Phosphate minerals similar in texture and composition to those formed in the experiments preserve soft-tissues in exceptional preservations such as the Jurassic Cordillera de Domeyko of Chile and the Cretaceous Santana Formation of Brazil. The results of the experiments show that although the oxygen content of the sea water may not have a pronounced impact on rate of decay, the open or closed nature of the system influences pH and determines the type of early mineralization and hence the nature of preservation.

Page Thumbnails

  • Thumbnail: Page 
431
    431
  • Thumbnail: Page 
432
    432
  • Thumbnail: Page 
433
    433
  • Thumbnail: Page 
434
    434
  • Thumbnail: Page 
435
    435
  • Thumbnail: Page 
436
    436
  • Thumbnail: Page 
437
    437
  • Thumbnail: Page 
438
    438
  • Thumbnail: Page 
439
    439
  • Thumbnail: Page 
440
    440
  • Thumbnail: Page 
441
    441
  • Thumbnail: Page 
442
    442
  • Thumbnail: Page 
443
    443
  • Thumbnail: Page 
444
    444
  • Thumbnail: Page 
445
    445
  • Thumbnail: Page 
446
    446
  • Thumbnail: Page 
447
    447
  • Thumbnail: Page 
448
    448
  • Thumbnail: Page 
449
    449
  • Thumbnail: Page 
450
    450
  • Thumbnail: Page 
451
    451
  • Thumbnail: Page 
452
    452
  • Thumbnail: Page 
453
    453
  • Thumbnail: Page 
454
    454
  • Thumbnail: Page 
455
    455
  • Thumbnail: Page 
456
    456