My data includes X,Y,Z. I also have the thickness of each geologic layer. I can create TIN of each geologic layer but I don't know how can I fill the gap between these layers.
How can I create 3d solid geologic model in ArcGIS?
This is normally done by extruding between 2 surfaces which created a multipatch geological layer. You will need 2 TIN surfaces (top surface and bottom surface) and a polygon layer containing input features that defines the area you wish to extrude. See Toolbox -> 3D Analyst Tools -> TIN Surface -> Extrude Between