From what I've read, the "fountains of the deep" notion and the idea that the oceans used to be a lot smaller a few thousand years ago have their own significant problems, but we don't need to argue that here.
I doubt that I've read anything more on the dating of sedimentary rock than you have. As far as I know, it's inferred from the dates of the igneous rock in and around the sedimentary rock. Most of the quibbles with the accuracy of radiometric dating that I know of have been addressed to my satisfaction; I look forward to reading about the issues with the Mt. St. Helens rock.
Where we (me the creationist and what I understand to be the typical Macor-Evolutionist) disagree is in the arrival of the different kinds, e.g. frogs, cats, dogs, ducks, finches, camels, etc. I believe they were created from dust on the 5th & 6th days, the Macro Evo believe they all descended from a common ancestor. Whenever I do the research, if one ignores the dating of rocks, the whole hierarchal tree of life system, IMHO, is completely arbitrary and circular, based on the premise that evolution occured. I am not questioning taxonomy per se, but rather the arrangement of "ancestor" and "offsrping" genus'. Amphibians are a good exampl of that.
The lack of a coghesive gelogic column in one place, the overthrusting of "older" layers on top of "younger", and the discovery of "living fossils" (amongst other things) gives me serious concerns about the validity of said system. Hence, my desire to research this whole dating methodology for myself.