EVOLUTION AND MARINE SEDIMENTS

MISH-MASH

Mish-mash is a title to accommodate comments with varied connections to the four main pages of this blog.   As may be evident from earlier posts, I am not as reluctant as I should be to talk about things I am not particularly well qualified to talk about.

Evolution, Invertebrates, And The Deep Sea 

Prior to the early 1980's it occurred to me that the conditions of much of the ocean bottom were so stable that a record of unusual disturbances is preserved for a long time in many locations.  Major disturbances show as unconformaties in rocks between periods of greater stability of deposition rates.  A study of deposition as it happens today makes interpretation of fossil deposition easier.  The gradual change in features of microfossils seems to be the rule when sediments are added without major disturbances such as those that characterize gaps separating major geologic times.  Disturbances were frequent enough during the sediment accumulation process that there is often a gap where transitional forms are not present; the concept of punctuated equilibrium is probably an artifact of those missing transitional sediments.  The opposite effect can be produced by action of bottom dwelling organisms or wave action mixing sediment above and below a gap and blurring the estimate of time of existence of a group.

Forams

A particularly useful group for dating sediments and seeing changes is the protozoan group known as the foraminiferans.  Microfossils of the planktonic ones are particularly useful because their skeletons can be carried by ocean currents to coat the sea bottom of an ocean.  The mixture of types can be a unique identifier of sediments that can span great distances on the ocean floor or continental rocks formed in past oceans.  Even climates of the past can be determined from isotope studies of their skeletons.

An introduction to some of the literature about bottom communities in the ocean can be found in the final few pages of the text I was working on at the time [Engemann, Joseph G., and Robert W. Hegner.  1981.  Invertebrate Zoology, 3^rd ed.  Macmillan Publishing Co., New York.  746 pp.].  The references at the end of the chapter include some such as Grassle (1977, Slow recolonization of deep-sea sediment.  Nature 265:618-619); and others about sedimentation rates and other topics pertinent to the topic.

An environmental consideration

The content of the last chapter made me aware the long term effects of ocean pollution could be much more severe and persistent than localized damage to communities.  The chapter was a step along the way to understanding the extreme age potential in the abyssal region organisms.  Marine sediment communities could have a sequence of animals recolonizing them that might yield an estimate of the time of major sediment disturbances.  Such actions might blur the clarity of community lines in the fossil record.  Are we in the process of leaving a major unconformity in sediments by our actions?  The widespread dispersal of chlorinated carbon pesticides shows the potential hazard of unlimited ocean dumping of wastes, either intentionally or by contaminated rivers and atmosphere.
  
Pogonophorans

Pogonophorans living in tubes in abyssal sediments are thought to have their tubes vertically oriented in the sediments.  One line of evidence is the lack of the posterior segmented region in most dredged specimens.  Such orientation indicates they could be getting nutrition from deeper sediments that are much older; that would make carbon dating of their age a near impossibility if fossil food in the sediments is a major source of their nutrients.

The complex of ideas involved in the topic were part of the preparation enabling me to make the pogonophoran connection of protostomes and deuterostomes.  Seeing that made understanding the tree of life correctly and the error needing correction in molecular proposals of Ecdysozoa and Lophotrochozoa possible.  That eureka moment began with my reading the paper of Gans and Northcutt, 1983, as described in earlier posts on evolution and creativity.

Joseph G. Engemann     November 6, 2014 (some editing on 10/18/2015)