After picking up a rather interesting amber-in-matrix specimen, I decided to look into the geological history surrounding the deposition of Dominican Amber.
Mentally I had always pictured Dominican amber forming as sap oozed out of trees and deposited on the forest floor; resulting in burial in forest detritus.
The more interesting reality is that the ooze from the Hymenaea tree would get washed out to coastal sedimentary basins; such as coastal lagoons. Here the sap would settle and get fossilized into amber in siltstone. This is why large masses of amber, as can be seen in the picture, are present all as one layer while the rest of the rock is all siltstone; large storm events would wash the ooze out.
Usually the miners of this material remove the amber for easy transportation, which makes matrix pieces hard to come by. Rarely are pieces big enough to see the depositional layering effect.