The term "saturation horizon" isn't a standard geological or hydrological term. It's possible you're referring to something else, or it's a term used within a specific context.

Here are some possibilities for what you might be looking for:

* Water Table: This is the upper surface of the zone of saturation in the ground. The zone of saturation is the area where all the pore spaces in the soil and rock are filled with water.

* Capillary Fringe: This is the zone above the water table where water is drawn upwards by capillary action. It's essentially a transition zone between the saturated zone and the unsaturated zone.

* Saturated Zone: This is the region beneath the water table where groundwater resides and all the pore spaces are filled with water.

* Unsaturated Zone: This is the region above the water table where the pore spaces are only partially filled with water. Air and water co-exist in this zone.

To help me understand what you're looking for, please provide more context:

* Where did you encounter the term "saturation horizon"?

* What is the topic you are researching?

* Can you provide any additional information or details?

With more information, I can provide a more accurate and relevant answer.