ECOLOGY OF RECENT ORAMINIFERA
The distribution of foraminiferal taxa is influenced by many different factors. Although many authors consider water depth the most significant one, water depth specifically is not the main variable, the controlling factor being the various physical and chemical conditions associated with depth. Typical factors are temperature and temperature variability, light availability, sedimentation rate, bottom characters, energy conditions and pressure.
Studies of recent foraminiferal ecology have provided numerous distinct criteria by which many depositional environments can be characterized and which can be applied to fossil assemblages from sedimentary rocks. Some the main variables can be summarized as follows:
1. The total number of species and of individual increases away from the shoreline, and with increasing depth of water, to maximum values on the outer shelf and in the upper bathyal zone.
2. Porcellaneous forms show their present diversity in shallow, nearshore environment.
3. Arenaceous foraminifera with simple interior wall structure become dominant in shallow waters or in intertidal areas. The percentage occurrence of these arenaceous forms reaches a maximum near the effluence of rivers.
4. Calcareous foraminiferal tests become smaller and thinner near sources of fresh water. In carbonate rich environments, tests may reach a large size and be very robust
5. The percentage occurrence of the most common species in a foraminiferal population relates to the variability of the environment. As marginal marine conditions are approached, environmental parameters become more pronounced resulting in a tendency towards single species dominance in the most unfavorable environment.
6. Planktonic forms occur most abundantly within the outer neritic and deeper waters. Under ideal sedimentation conditions, especially in clastic deposits, planktonic foraminifera can show a more or less regular increase in abundance in depth.
7. Arenaceous taxa with labyrinthic wall structures occur most abundantly in bathyal or deeper waters. In sediments deposited below the calcium carbonate compensation depth (CCD) these forms may become dominant since the calcareous shells of other foraminifera are dissolved.
The distribution of foraminiferal taxa is influenced by many different factors. Although many authors consider water depth the most significant one, water depth specifically is not the main variable, the controlling factor being the various physical and chemical conditions associated with depth. Typical factors are temperature and temperature variability, light availability, sedimentation rate, bottom characters, energy conditions and pressure.
Studies of recent foraminiferal ecology have provided numerous distinct criteria by which many depositional environments can be characterized and which can be applied to fossil assemblages from sedimentary rocks. Some the main variables can be summarized as follows:
1. The total number of species and of individual increases away from the shoreline, and with increasing depth of water, to maximum values on the outer shelf and in the upper bathyal zone.
2. Porcellaneous forms show their present diversity in shallow, nearshore environment.
3. Arenaceous foraminifera with simple interior wall structure become dominant in shallow waters or in intertidal areas. The percentage occurrence of these arenaceous forms reaches a maximum near the effluence of rivers.
4. Calcareous foraminiferal tests become smaller and thinner near sources of fresh water. In carbonate rich environments, tests may reach a large size and be very robust
5. The percentage occurrence of the most common species in a foraminiferal population relates to the variability of the environment. As marginal marine conditions are approached, environmental parameters become more pronounced resulting in a tendency towards single species dominance in the most unfavorable environment.
6. Planktonic forms occur most abundantly within the outer neritic and deeper waters. Under ideal sedimentation conditions, especially in clastic deposits, planktonic foraminifera can show a more or less regular increase in abundance in depth.
7. Arenaceous taxa with labyrinthic wall structures occur most abundantly in bathyal or deeper waters. In sediments deposited below the calcium carbonate compensation depth (CCD) these forms may become dominant since the calcareous shells of other foraminifera are dissolved.