ABSTRACT

An understanding of taphonomic processes including diagenesis would enhance the usefulness of fossils such as the foraminifera. In this study, shells of five modern species of calcareous foraminifera were subjected to temperatures and pressures (T-P) that simulated burial. One kilometer increments were used with a maximum simulated depth of ten kilometers in wet sediment.

There was increased alteration of shells at each higher T-P in each sediment type (quartz, illite or calcite). Shells in quartz were more altered than those treated in either illite or calcite. Compared to untreated shells, in quartz at 5 kilometers pores were enlarged by 15% and tiny hillocks were visible at higher magnification (2000X). At 6 kilometers, high sharp pinnacles were formed and pores were enlarged 30-50%. At 7 kilometers, long narrow solution channels developed while pores were increased by 40-60% in diameter. The next T-P increment (8 kilometers) caused even greater pore solution, while at 9 kilometers sutures were obliterated and the previously formed pinnacles were removed. At the highest T-P (10 kilometers), chambers and shell outlines were highly altered and newly formed crystals appeared. There were platelets oriented perpendicular to the shell surface; often they were arranged as rosettes.

Under experimental conditions alteration features of foraminifera shells appear to be diagnostic of certain T-P levels. If such features develop on shells in natural sediments they may be useful to reconstruct some conditions of diagenesis.