CHALLENGES TO STUDYING DIFFERENTIAL TAPHONOMIC DESTRUCTION OF CALCAREOUS FORAMINIFERS IN MARGINAL-MARINE ENVIRONMENTS

The original protocol developed for studying the differential rates of dissolution of foraminifers from marginal-marine environments along Onslow Bay, North Carolina, included collecting 100 specimens of three different taxa and exposing the tests to slightly acidic water (pH ~ 5.5) for increasing periods of time. We collected 300 specimens of Quinqueloculina, Elphidium, and Ammonia. A taphonomic scale was developed to quantify the rate of test destruction and we predicted that the rate of dissolution would be variable between the three foraminifers.

Microfossil samples were wet-picked from sediments taken from the marshes and the back-barrier shallow estuary around Fort Fisher and Alligator Bay. These marginal-marine environments have a pH of 7.3 and 7.0, respectively. As samples were being collected they were temporarily stored in what was thought to be purified water. Upon completion of the microfossil collection it was discovered that all specimens had dissolved. Exploration of the sampling protocol revealed that the storage water was actually deionized water which had been exposed to atmospheric carbon dioxide for approximately nine months and had a pH of < 5.

A smaller subsample of Elphidium was collected a second time to study the dissolution process in the deionized water. Three sets of ten specimens were submerged in the deionized water and their taphonomic condition was assessed every 24 hours for three weeks. Most specimens showed etching and surface dissolution to the test within 48 hours and 90% of the foraminifers had dissolved completely within twelve days. The longest duration any test survived was twenty days. In contrast, Elphidium tests stored in the original waters from the sampling sites for three weeks showed no taphonomic degradation.