The Eocene/Oligocene boundary and the psychrospheric event in the Tethys as recorded by deep-sea ostracods from the Massignano Global Boundary Stratotype Section and Point, Central Italy
- 標題
- The Eocene/Oligocene boundary and the psychrospheric event in the Tethys as recorded by deep-sea ostracods from the Massignano Global Boundary Stratotype Section and Point, Central Italy
- 作者
- Barbara Dall’Antonia, Alessandro Bossio, Claude Guernet
- 文件屬性
- 國外期刊
- 知識分類
- 基礎研究
- 出版年
- 2003
- 刊名
- Marine Micropaleontology
- 關鍵字
- Ostracoda; Palaeoecology; Eocene/Oligocene boundary GSSP; Tethys (Central Italy)
- 點閱數
- 3243
摘要
Latest Eocene–earliest Oligocene deep water ostracods from the Massignano Global Boundary Stratotype Section and Point (GSSP), Central Italy, were studied from a palaeoecological perspective to investigate the psychrospheric event in the Tethys. Although quantitative analyses were hampered by the low incidence of fauna, the high-resolution sampling used in this study (148 samples distributed over a 23-m-thick succession spanning 3 m.y.) allowed the following inferences: (1) overall features (e.g. abundance, diversity, composition) of the assemblages suggest a middle–lower bathyal environment with no significant palaeobathymetrical changes; (2) today a similar fauna, notably characterised by the common occurrence of the genus Agrenocythere, would likely be encountered in upper psychrospheric conditions (water masses beneath the permanent thermocline with a temperature range of 4–10°C); (3) although no noticeable faunal turnover has been recognised throughout the succession, minor faunal changes seem to occur in the first part of the section (probable appearance of Legitimocythere presequenta) and to a lesser extent also across the Eocene/Oligocene boundary. The presumed appearance of L. presequenta (latest Eocene) correlates quite well in timing and possible significance with the faunal changes observed in other microfossil groups (foraminifers and dinocysts). This event is possibly linked to a cooling pulse, which might have been caused by the arrival, or increasing advection, of cold bottom waters in the study area. Faunal evolution across the Eocene/Oligocene boundary is thought to be consistent with an intensification of the cooling trend and an increase of primary productivity, which fits fairly well with the δ13C record. Relationships between the subtle ostracod faunal changes observed in the Massignano GSSP and the main Late Eocene–Early Oligocene psychrospheric event can be only speculative. Nevertheless, we found no evidence that precludes the possibility of interpreting the Massignano ostracod pattern as a subdued, local expression of this major event. Although speculative, this is a reasonable hypothesis, because the investigated area is situated in Western Tethys, far from the main circulation of deep ocean waters.