D.M. Davis’s Theory: on Origin of Coral Reefs and Atolls
D.M. Davis revisited Darwin’s Subsidence Theory and attempted to strengthen it with additional physiographic evidence. His theory reinforces the idea that coral reefs grow along subsiding land, but he also focuses on sediment deposition as a key factor in shaping reef features.
Key Arguments of Davis’s Theory
- Corals Grow Along Subsiding Land 🌊
- Davis supported Darwin’s idea that coral reefs form due to the gradual sinking (subsidence) of land.
- The existence of highly indented coastlines was seen as proof of this process, indicating that land had been slowly submerged over time.
- Flat Lagoon Bottoms & Uniform Depth 📏
- He argued that marine sediments accumulate in lagoons, leading to flat bottoms and uniform depths.
- This sedimentation prevents deepening of the lagoons, which aligns with Darwin’s idea that lagoons remain shallow.
- Shallowness of Lagoons Due to Debris Deposition
- According to Davis, lagoons remain shallow because of the constant deposition of coral debris and sediments.
- This contrasts with Murray’s theory, which suggests that lagoons are deepened by wave erosion.
- Rejecting the Standstill Theory 🚫
- If submarine platforms were stable (as Murray suggested), then continuous sedimentation would eventually fill up lagoons.
- This would cause water to overflow, killing corals and stopping reef growth.
- However, Darwin’s subsidence model allows lagoons to continuously accommodate debris, preventing them from being filled up completely.
Comparison with Other Theories
| Theory | Main Idea |
| Darwin’s Subsidence Theory | Coral reefs grow as land gradually sinks, leading to the formation of fringing reefs, barrier reefs, and atolls. |
| Murray’s Standstill Theory | Corals grow on stable submarine platforms, and lagoons are formed due to coral dissolution. |
| Daly’s Global Control Theory | Reefs were shaped by glacial sea-level changes, where submerged wave-cut platforms provided a foundation for coral growth. |
| Davis’s Theory | Supports Darwin’s subsidence theory, adding that lagoon depth is controlled by sediment deposition. |
Limitations & Criticism of Davis’s Theory
- Over-Reliance on Sedimentation
- Not all lagoons have perfectly flat bottoms—many show variations in depth, indicating that factors beyond sedimentation are at play.
- Lack of Direct Evidence for Indented Coastlines
- While Davis claimed that highly indented coastlines prove subsidence, this feature can also result from wave erosion, tectonic uplift, or river activity.
- Does Not Explain Coral Growth in Stable Regions
- If subsidence is the only driving factor, how do coral reefs exist in tectonically stable areas?
Final Thoughts
Davis’s theory reinforced Darwin’s ideas and highlighted the role of sedimentation in shaping coral lagoons. However, like other single-factor theories, it does not fully explain all types of coral reef formations. Today, we recognize that subsidence, sea-level changes, biological growth, and environmental conditions all interact to shape the diverse coral reef landscapes we see worldwide. 🌊🐠
