Ammonite shell form and transgression in the British lower Jurassic

摘要: The early Jurassic transgression has been traced in detail southern England. Shell forms Ammonitina have classed eight groups, and the occurrence of these groups is related to progress transgression. Unkeeled shells are replaced by with carinate, bisulcate venters as proceeds, diversity increases; this interrupted regression during Oxynotum Zone, which oxycones dominant. Renewed again shows unkeeled followed shells, then Eoderocerataceae at beginning Pliensbachian. Regression late Pliensbachian brings oxycones.