Yes, it is certainly marigold. But there's a whole range of marigold "effects" on Carnival Glass and they are often misunderstood. In a nutshell, marigold is an orange (ferric chloride) iridescence on clear base glass, but a range of variables (such as temperature of the glass) can alter the appearance. There's a middle of the road marigold that is most often seen. It can be flat and often shiny and not too interesting. But there are also some STUNNING marigold effects that really can blow your mind.
Northwood and Inwald (in my opinion) produced the very best marigolds. If you go to this page on my website and mouse over the images you will see two very different marigolds. http://www.thistlewoods.net/Northwood-Gallery.html
Second from the left is a pastel marigold Good Luck, while 4th in from the right is a pumpkin marigold Poppy Show plate. Click the images and they will open up a little bigger. These two effects are ones that are really sought after but are not seen too often. Inwald made some amazing marigold that was consistently breathtaking.
But it has to be said that an awful lot of marigold was not quite so mind blowing - and it was, of course, the most popular Carnival colour in its day (it really must have glowed against the dark furniture). Your punch bowl base isn't opalescent, it's marigold - and yes, sometimes there are clear sections on the glass where the flint glass base can be seen. Northwood made very little peach opalescent Carnival (which is the name for opalescence on marigold) - the masters of that colour were Dugan/Diamond and Fenton (imho).
Hope this helps a bit. I think your piece is marigold that goes somewhat "satiny" toward the bottom. Very pretty.
Here's a pic of a pastel marigold bowl that is one of my favourites - just to show you how amazing marigold really can be.