1. Changes in Sediment Supply:
* Increased sediment input: A sudden influx of sand, silt, or clay can bury and smother the organic matter before it has a chance to decompose properly. This can result in the formation of clastic sedimentary rocks rather than organic ones.
* Reduced sediment input: Without a constant supply of sediment to bury and preserve organic matter, it will be exposed to oxygen and decomposition. This can happen in environments that are prone to erosion.
2. Changes in Water Chemistry:
* Increased oxygen levels: Organic matter needs an anoxic (oxygen-poor) environment to accumulate and form sedimentary rocks. Increased oxygen levels, often due to changes in water currents or the influx of oxygenated water, will lead to decomposition.
* Changes in salinity: High salinity levels can inhibit the growth of microorganisms responsible for decomposing organic matter. Conversely, freshwater influx can also change the chemistry, making the environment unsuitable.
3. Changes in Biological Activity:
* Changes in species composition: The types of organisms present can significantly impact organic matter accumulation. If the dominant species change, the type and abundance of organic matter will be affected, altering the potential for sedimentary rock formation.
* Increased bioturbation: This refers to the disturbance of sediments by burrowing organisms like worms and clams. Bioturbation can mix sediments, allowing oxygen to penetrate and decompose organic matter.
4. Changes in Climate:
* Drought or excessive rainfall: Both can disrupt the delicate balance of conditions needed for organic matter accumulation. Droughts can lead to a decrease in organic production, while excessive rainfall can flush away organic matter.
* Temperature changes: Extreme temperature fluctuations can lead to changes in the types of organisms present and their decomposition rates.
5. Tectonic Activity:
* Uplift or subsidence: Uplift can expose organic-rich sediments to erosion, while subsidence can create environments that are too deep or oxygenated for organic matter accumulation.
It's important to note that these changes don't necessarily mean organic sedimentary rock formation will cease entirely. Instead, they can cause changes in the type of organic rock formed, its composition, or the rate of formation. The process of organic sedimentary rock development is highly influenced by the interplay of many factors.
