Senonian carbonate sediments rich in rudists are widespread throughout central-southern Italy. The Coniacian-Santonian series, analyzed in the Lattari Mountains (Sorrento Peninsula), are almost completely composed of limestones, with very subordinate dolomitic beds. On a field scale we can distinguish rudist-rich beds rhythmically alternating with finer-grained foraminiferal beds. The studied series testify to a deposition in shallow-sea environments. In the lower part of the series periodical, more or less prolonged emersions (subaqueous with fresh/brackish waters or subaerial exposure) are documented. The upper part of the series lacks emersion evidences; submarine exposition surfaces are testified by firmgrounds or hardgrounds. Wave- and cross-laminations, HCS and the lack of fine sediments document an overall deposition under influence of occasional high-energy water regimes with some storm-related events. The sedimentology and taphonomic signature of the rudist shell beds have been described in order to get a better understanding of depositional environment and the physical processes that controlled the Senonian sedimentation. Monospecific tabular beds mainly characterize the lower part of the series; more complex rudist concentrations, characterized by moderate species diversity, increase up-section. The recognized lithofacies are organized in shallowing-upward depositional cycles that show a gradual change from peritidal/shallow-subtidal cycles to dominantly subtidal cycles up-section; this change records a general deepening-upward trend as a possible result of an increase of the accommodation space provided by a relative sea-level rise, according to what suggested for other coeval Apennine and Sardinia series.

Lower Senonian rudist limestones in the Sorrento Peninsula sequences (southern Italy)

RUBERTI, Daniela;
1998

Abstract

Senonian carbonate sediments rich in rudists are widespread throughout central-southern Italy. The Coniacian-Santonian series, analyzed in the Lattari Mountains (Sorrento Peninsula), are almost completely composed of limestones, with very subordinate dolomitic beds. On a field scale we can distinguish rudist-rich beds rhythmically alternating with finer-grained foraminiferal beds. The studied series testify to a deposition in shallow-sea environments. In the lower part of the series periodical, more or less prolonged emersions (subaqueous with fresh/brackish waters or subaerial exposure) are documented. The upper part of the series lacks emersion evidences; submarine exposition surfaces are testified by firmgrounds or hardgrounds. Wave- and cross-laminations, HCS and the lack of fine sediments document an overall deposition under influence of occasional high-energy water regimes with some storm-related events. The sedimentology and taphonomic signature of the rudist shell beds have been described in order to get a better understanding of depositional environment and the physical processes that controlled the Senonian sedimentation. Monospecific tabular beds mainly characterize the lower part of the series; more complex rudist concentrations, characterized by moderate species diversity, increase up-section. The recognized lithofacies are organized in shallowing-upward depositional cycles that show a gradual change from peritidal/shallow-subtidal cycles to dominantly subtidal cycles up-section; this change records a general deepening-upward trend as a possible result of an increase of the accommodation space provided by a relative sea-level rise, according to what suggested for other coeval Apennine and Sardinia series.
Les sediments carbonatés sénoniens, riches en rudistes, sont très répandus dans l'Italie centro-meridionaux. Les séries du Coniacien-Santonien étudiées dans les Monts Lattari (Peninsule de Sorrento) sont principalement calcaires, les dolomies ètant très limitées. A l'échelle de l'affleurement on peut distinguer essentiellement des couches riches en rudistes s'alternant rythmiquement avec des couches de calcaires à granulométrie fine et riches en foraminifères benthoniques. Les séries étudiées témoignent un processus de dépôt dans un milieu marin de faible profondeur. Dans la portion basale de toutes les séquences il y a des caractères qui prouvent des phases d'émersion périodiques et plus ou moins prolongées (exposition sous-aérienne ou subaquatique en eaux douces ou saumâtres). Dans la portion supérieure manquent des évidences d'une émersion; au contraire, des surfaces d'exposition sous-marine, telles que firmground ou hardground, sont documentées. Finalement dans toutes les séquences il est possible reconnaître des laminations ondulées et obliques, des HCS et l'absence de sédiments fins qui témoignent une déposition sous l'influence de régimes occasionnels de haute énergie avec la présence d'évênements de tempête. La sedimentologie et la taphonomie des bancs à rudistes on été étudiees de maniere à mieux comprendre les processus physiques qui contrôlent la sedimentation pendant le Sénonien. Les couches monospécifique caractérisent surtout la portion inférieure de les successions; des concentrations à rudistes plus complexes, caractérisées par une différenciations spécifique plus grande, deviennent de plus en plus fréquentes vers la partie supérieure des séquences. Les lithofacies qui ont été reconnues sont organisées en cycles de dépôt du type shallowing-upward qui montrent un changement progressif, vers le haut, de cycles péricotidaux/bas-subcotidaux vers des cycles principalement subcotidaux. Ce changement fait enregistrer un trend général du type deepening-upward comme le résultat possible d'un accroissement de le accommodation space dû à un soulèvement relatif du niveau de la mer. Un trend de ce type semble être en accord avec ce qui a été suggéré par des autres séquences contemporaires étudiées dans les Apennins et en Sardaigne.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11591/216520
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