Broken Jug Formation
The Broken Jug Formation is a geologic formation in southwestern New Mexico. It was likely deposited in the late Jurassic period.
Description
The formation consists of a variety of marine, deltaic, and volcanic rocks. It is divided into five informal members. The lowest of these is the dolomite member, which consists of about of thinly bedded dolomite and dolomitic sandstone. This rests disconformably on Paleozoic limestone, either the Escabrosa Limestone or the Horquilla Limestone. Above the dolomite member is the lower conglomerate member, which is about of calcareous conglomerate, mudstone, and sandstone interpreted as turbidite formations. The third member is the fine-grained member, consisting of varied sandstone, siltstone, and mudstone. Above this is the upper conglomerate member, which is of thickly bedded clast-supported conglomerate. A number of diabase dikes and sills intrude the lower part of this member. Finally, the formation is capped with the basalt member, which is of vesicular basalt in at least 11 separate flows.The formation is thought to have been deposited in a subsiding marine basin, which was subsequently filled in by delta deposits and capped by subaerial silica-poor lava flows. The formation is late Jurassic in age, based on fossils in the upper conglomerate member, the position of the formation in the stratigraphic column, and its similarity to nearby formations whose age is better constrained.