Thanks guys.

Eliathen, here's a picture showing what I took from Diamond maps (approximately). The southern land on the occidens side is inspired from the paleo north american continent (can't remember the period).
Click image for larger version.  Name: Sources.jpg  Views: 535  Size: 2.74 MB  ID: 51307
Max, about the colors and the mountains : the idea was indeed to get something chaotic and harsh. This world is completely alien and unstable : moving deserts of colored sands, strange forests, hard rocky mountains, etc.
About the coastlines and the sea texture... it's probably due to my lack of skills. I tend to use always the same techniques, even if I try new ones on this map. I liked the sea texture though. I must precise that I have reduced the map (and its quality) because the file was too big for being uploaded...
Maybe you could give me some advices or leads?

And yes, you're right for the last point. I didn't really get it, but it's quite clear now. I'm gonna see what I can do about it.