I ran the same model in Mechanical and got similar results than in Fluent (i.e., conduction is the main heat transfer mechanism).
Now, I added another geometry (circle) to deliver heat to the sediment body. I compared the temperature profiles in the two heat sources and observed that they differed significantly (image below). The circle-shape source in the 2D represents heat injection/propagation perpendicular to the line heat source (heating tape), whereas the thin bar represents heat injection/propagation longitudinal to the heating tape.
Wonder why the shape of temperature profiles are so different??
Note: in my experiments, the heating and cooling profiles (observed data) resembles those resulted from the circle heating source in the 2D model.