Jurassic ammonites from Patagonia

Jurassic sediments of hydrocarbon seeps from La Elina Ranch (northern Patagonia) are the only source of information on this kind of environment in South America. Apart from gastropods and bivalves typical of hydrocarbon seeps and usually deep-water, this site provided also numerous ammonoids, which suggest rather shallow water character of this seep. The absence of shallow water gastropods and bivalves might be related to unusual environmental conditions in the basin, most likely oxygen depletion of surrounding bottom waters.