Re: Marine and Continental Sands/Shales
Although I usually do not tackle these issues myself I can remember some things on this topic from the old days at uni.
Basically there is no simple way to distinguish marine from terrestrial sandstone. Back in the days we used acid to look whether or not a sandstone would start "bubbling" indicating carbonate matrix (usually marine). Some continental sands and shales also have this characteristic though. You can also look at shell fragments (shells usually indicate marine). Other fossil indicators are usually only observable under the microscope and needs to be done in a (field) lab. One can also look at the depositional structures like sand bars, ripple marks, cross bedding, but these can form under a lot of different condition (marine and continental, eg lakes) and can often look very similar (also depending on the angle of view. The best practice remains to study any trace fossils you encounter and determine if they are marine or terrestrial.
Sometimes other sedimentary structures, smaller lateral extent of some features like clay deposits, or pebbly or larger grains can suggest fluvial environments. Finer sediments are usually associated with less energetic marine environments.
There is no definitive answer (other than Paleontology) and identifying marine or terrestrial deposits usually comes with experience. Even though you say books confuse you, there is no 'simple' answer to this and you need to study a lot of literature (or a single good book) before you get the idea. Probably the field work guide will also help you!
Hope this helped. Have fun on your field trip!