How much crossover is there between "weird" and adventure fiction? I'm thinking of books like The Lost World (and others by Sir Arthur Conan Doyle featuring Professor Challenger) and King Solomon's Mines (Allan Quartermain). In those books, the main character often encounters something unusual, but eventually explainable. For example, Professor Challenger finds a place in South America where dinosaurs still exist.
This even fits into films like the Indiana Jones series. If Dr. Jones were looking for the Necronomicon instead of the Ark of the Covenant or the Grail, that would be one step from a Lovecraft story. Could even melt the faces off the bad guys at the end still. I hate to admit to its existence, but Crystal Skull definitely has some weirdness going on.
Now I want a story about Nazis looking for the Necronomicon and being stopped by a two-fisted archeologist.
"In those books, the main character often encounters something unusual, but eventually explainable."
I think what is weird in weird fiction is maybe explainable in some way, but isn't 'containable' for most people in the story (like the protagonists in many of weird tales). This feeling of 'this can't be / this should not be' is what makes weird weird in my opinion (and, as is said, can happen in almost all genres).
When dinosaurs are found and scientists say 'oh, ok, unexpected, but we just overlooked them apparantly' then it isn't weird to me. When you find a dinosaur in your (oversized) cellar and no one knows where it came from - then that's weird.
There's a massive overlap. I often try to bring up how the technothriller genre has moved away from the Clancy-esque political thrillers and into the realm of the weird. You can see this especially in James Rollins and Lincoln & Child. It's maybe always been this way on some level.
I totally count Raiders as weird fiction, for sure. Our operating principal is that weird-fiction isn't a genre, it's a mood. All stories, regardless of genre, can be plotted on a spectrum with weird on one end and wonder on the other, and we'll read anything that's even the tiniest bit on the weird side no matter which genre it's in. We have even (accidentally) done a rom-com on the show!
But, yeah, some of my favorite weird-fiction stories are these pulp adventure stories about discovering something weird in a strange location. That and occult detectives are really where I like to go most often.