Only sparse data sets, if any, are available to constrain the age attribution of ancient fluvial deposits. In this respect, Quaternary stratigraphy may provide an important chronostratigraphic framework within which to develop a generalized model of channel belt formation and evolution. Detailed stratigraphic analysis of middle-late Quaternary fluvial deposits from the Po River Basin, in Northern Italy, reveals distinctive cyclic changes in lithofacies and channel stacking patterns, falling in the Milankovitch (100 kyr) band . Stratigraphic correlations with the coeval nearshore successions document that the lower portions of fluvial cycles, characterized by isolated sand bodies, were deposited during phases of relatively high-accommodation (episodes of sea-level rise under interglacial conditions). In contrast, accumulation of laterally amalgamated fluvial bodies (channel belts) took place during phases of relatively low accommodation, marking the “regressive” maxima (i.e., OIS 2 and OIS 6). A well constrained chronostratigraphic framework indicates that eight major channel belts (aquifer systems), separated by thick mud-prone floodplain successions, were deposited during the last 870 ka, while development of the youngest (LGM) channel-belt took place during an interval of time of about 20 ka. Comparison of the late Quaternary succession of the Po Basin with the fluvial analogue Escanilla Formation, an Eocene formation commonly applied for reservoir studies, documents striking analogies in terms of both tectonic setting and fluvial architecture. These include: i) sedimentation in a highly subsiding, actively folded basin; ii) overall thickness of about 800 m; iii) similar cyclic architecture (100 m-thick cycles), with development of 6-8 laterally extensive channel belts. Whilst new data are increasingly capable of providing a refined stratigraphic framework for the Escanilla Formation, no direct dating is available, and duration of its deposition (1.5 or 7 Ma?) is still problematic. Based upon similarities with modern channel belts, we suggest that most of the Escanilla Formation (i.e., the 550 m-thick Olson Member) is likely to span less than 1 My, and that the unconformities with both underlying Mondot Member and overlying Collegats Formation could account for major stratigraphic hiatuses. This interpretation is consistent with the remarkable homogeneity in terms of both lithology and facies architecture observed across the Olson member, along with lack of highly mature palaeosols throughout the formation.
Development and evolution of a Late Quaternary fluvial channel belt: implicationsfor the interpretation of ancient analogues
SARTI, GIOVANNI
2009-01-01
Abstract
Only sparse data sets, if any, are available to constrain the age attribution of ancient fluvial deposits. In this respect, Quaternary stratigraphy may provide an important chronostratigraphic framework within which to develop a generalized model of channel belt formation and evolution. Detailed stratigraphic analysis of middle-late Quaternary fluvial deposits from the Po River Basin, in Northern Italy, reveals distinctive cyclic changes in lithofacies and channel stacking patterns, falling in the Milankovitch (100 kyr) band . Stratigraphic correlations with the coeval nearshore successions document that the lower portions of fluvial cycles, characterized by isolated sand bodies, were deposited during phases of relatively high-accommodation (episodes of sea-level rise under interglacial conditions). In contrast, accumulation of laterally amalgamated fluvial bodies (channel belts) took place during phases of relatively low accommodation, marking the “regressive” maxima (i.e., OIS 2 and OIS 6). A well constrained chronostratigraphic framework indicates that eight major channel belts (aquifer systems), separated by thick mud-prone floodplain successions, were deposited during the last 870 ka, while development of the youngest (LGM) channel-belt took place during an interval of time of about 20 ka. Comparison of the late Quaternary succession of the Po Basin with the fluvial analogue Escanilla Formation, an Eocene formation commonly applied for reservoir studies, documents striking analogies in terms of both tectonic setting and fluvial architecture. These include: i) sedimentation in a highly subsiding, actively folded basin; ii) overall thickness of about 800 m; iii) similar cyclic architecture (100 m-thick cycles), with development of 6-8 laterally extensive channel belts. Whilst new data are increasingly capable of providing a refined stratigraphic framework for the Escanilla Formation, no direct dating is available, and duration of its deposition (1.5 or 7 Ma?) is still problematic. Based upon similarities with modern channel belts, we suggest that most of the Escanilla Formation (i.e., the 550 m-thick Olson Member) is likely to span less than 1 My, and that the unconformities with both underlying Mondot Member and overlying Collegats Formation could account for major stratigraphic hiatuses. This interpretation is consistent with the remarkable homogeneity in terms of both lithology and facies architecture observed across the Olson member, along with lack of highly mature palaeosols throughout the formation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
