Deep‐sea ostracods as indicators of palaeoceanographic changes: a case history from the middle–late Miocene of southern Italy (Central Mediterranean)

Abstract

The middle–late Miocene palaeoceanography of the Central Mediterranean was investigated using bio‐chronostratigraphically constrained (estimated ages are based on plancktonic foraminifers) ostracod faunas from the Tremiti Islands and the Hyblean Plateau (southern Italy). Specifically, differences and similarities between the hydrographical evolution of the two study areas, inferred from the ostracod record, are herein used to provide new insights into the evolution of the Mediterranean deep‐water circulation. Ostracod assemblage compositions suggest a simultaneous progressive trend from deep thermospheric towards psychrospheric conditions in both the areas during the Langhian. However, this trend seems to have developed fully only in the Hyblean Plateau. Notably, the first sign of an oceanic deep water‐mass supply is shown by the almost synchronous entry of the upper psychrospheric genus Agrenocythere in the middle Langhian. The youngest reliable evidence of deep oceanic influences (common occurrence of Agrenocythere) in the Central Mediterranean comes from the Tremiti Islands and dates back to the earliest Serravallian. Similarities between the two study areas suggest large‐scale modifications in the Central Mediterranean deep basins. This hypothesis is discussed in the context of the global middle Miocene oceanographic scenario.

Response of Mediterranean circulation to Miocene shoaling and closure of the Indian Gateway: A model study

“…8 the flow configurations consistent with the entrance of Atlantic waters at depth in the Atlantic Gateway for a shallow Indian Gateway, as well as the conditions under which these flow patterns arise, are summarized. Note that although estuarine exchange can also develop when the connection to the Atlantic is shallow, only with a relatively deep Atlantic Gateway (i.e., 900 m) does the temperature of the Atlantic inflow lie within the inferred from faunas (see Dall'Antonia, 2003). The possibility that the estuarine exchange was related to a positive Mediterranean water budget (i.e., precipitation and river runoff being greater than evaporation)-as indicated in Karami et al (2009)-cannot be excluded.…”

“…Observational evidence concerning the Atlantic exchange during the Early-Middle Miocene comes from faunal and isotopic studies performed at several sites of the western and central Mediterranean. These studies postulate the presence of cold Atlantic waters (4-10 °C) at depth in the Mediterranean basin during the Langhian (e.g., Benson, 1978;Vergnaud-Grazzini, 1983;Gebhardt, 1999;Dall'Antonia et al, 2001;Dall'Antonia, 2003). Given that most estimates of the time of closure of the Indian Gateway lie in the range from the Early to the Middle Miocene, we assume that deep Atlantic inflow was coeval, at least during some time, with a still open-but probably shallow-Indian Gateway.…”

Abordagens faunísticas e geoquímicas em microfósseis calcários e suas aplicações à paleoceanografia e paleoclimatologia

“…Steineck & Thomas (1996) e Speijer & Morsi (2002) discutem as mudanças oceanográficas decorrentes de aquecimento no período Paleoceno-Eoceno e sua influência nos ostracodes de Maud Rise (Mar de Weddell) e no norte da África, respectivamente. Dall'Antonia (2003), por sua vez, desenvolveu um estudo semelhante com faunas miocênicas do Mediterrâneo Central, onde observou a transição de uma fase termosférica para uma psicrosférica, com base na ocorrência do gênero criofílico Agrenocythere. Estudos similares foram também desenvolvidos com faunas cretáceas e, de forma análoga aos foraminíferos, Majoran et al (1997) propuseram o cálculo de taxas de acumulação de valvas (OVAR -'Ostracode Valve Accumulation Rates') como um indicador paleoceanográfico.…”

The influence of the geological setting on the morphogenetic evolution of the Tremiti Archipelago (Apulia, Southeastern Italy)

“…More recently high-resolution cyclostratigraphic (astrochronological calibration), biostratigraphic and palaecological studies have been carried out on the Miocene sediments of the Tremiti Islands, specifically on the middle Serravallian-basal Tortonian section of the Cretaccio Fm. outcropping at the Isle of San Nicola Foresi et al, 2002;Russo et al, 2002;Dall'Antonia, 2002;2003;.…”