ABSTRACT

Detailed analysis of recent literature on glaucony and selected case studies (Eocene, Isle of Wight; Miocene, northern Apennines) shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence. A reliable sequence stratigraphic interpretation of glaucony-bearing units requires additional information on glaucony, including: (1) spatial distribution, (2) maturity (distinction between nascent, slightly evolved, evolved, and highly evolved glaucony), and (3) genetic attributes (differentiation of autochtonous from allochthonous, and intrasequential from extrasequential glaucony).

Autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract (TST) and the lower highstand systems tract (HST), showing an upward increase (TST) and then decrease (HST) in abundance and maturity. The condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony. Allochthonous intrasequential (parautochthonous) glaucony can be present in the entire TST, HST, and lowstand systems tract (LST), generally showing lower concentration and maturity than its autochthonous counterpart. Allochthonous extrasequential (detrital) glaucony is present mainly in the LST, its concentration and composition depending on the characteristics of the source horizon. The associa ion between autochthonous and allochthonous (intrasequential and extrasequential) glaucony commonly exists in the LST and in the lower TST.