Hi Karla,
The short answer is yes, but it’s going to require some careful planning.
You’ll want to use the Resin Obsession deep pour resin. It mixes clear and releases bubbles easily. Plus you can pour it up to two inches thick at once. You can buy it in a couple sizes in our store here: https://shop.resinobsession.com/collections/resin/resin-obsession-deep-pour-resin
But, your seashells are going to sink. You’ll need to pour in layers to make the seashells ‘float’ if you want that effect. This article shows you how to do that: https://resinobsession.com/resin-tutorials/how-to-suspend-objects-in-resin/
You can minimize the lines between layers by pouring the next layer when the previous layer starts to thicken, like jelly. This article explains when that happens: https://resinobsession.com/resin-frequently-asked-questions/resin-gel-time/
Most importantly, you’re going to have to find a way to control the heat as your resin cures. The glass is a relatively good insulator and will help the resin stay extra warm, which can lead to cracking. This article talks about the ways you can control that heat when doing thick pours like this one: https://resinobsession.com/resin-resin-resin/epoxy-table/
Good luck!