Sequence stratigraphic model of a fluvio-lacustrine system in the Guadix Basin (Betic Cordillera, Spain)

Sequence-stratigraphic depositional models for fluvial and lacustrine basins have established that climate and tectonics work in tandem to control sediment supply, subsidence, and water input (hydrology) as sedimentation evolves through time. Using two pre-existent continental sequence-stratigraphic models, the influence of allogenic factors during the last 3.5Ma on the sedimentary evolution of a fluvio-lacustrine system in the Guadix Basin (Betic Cordillera, southern Spain) is outlined.
The Guadix Basin hosts a complete succession of continental sediments dated from the end of the Miocene to the Late Pleistocene, when the basin changed its drainage regime from endoreic to exoreic, resulting in a deep incision of the Holocene drainage network into the sedimentary infilling of the basin. The sedimentary record of the basin can be divided into six genetic units with the continental infill stages (Late Tortonian-Late Pleistocene) corresponding to the three youngest units (IV, V and VI). For the considered time span, the paleogeography of the basin consisted of three main drainage systems: an axial fluvio-lacustrine system and two transverse alluvial fan systems.
In order to establish a sequence-stratigraphic model for units V and VI, the stratigraphy and origin of the architectural elements formed by the siliciclastic and carbonate sediments of the axial fluvio-lacustrine system have been characterized.
The integration of two models (proposed respectively by Martinsen et al., 1999 and Alonso-Zarza, 2003) based on nonmarine sequence stratigraphy has been used to interpret the last two units of the basin fill in terms of climate, tectonism, and stratigraphic base level. One of the models deals with siliciclastic sediments, while the other is focused on carbonate sedimentary patterns.
Unit V presents a facies distribution in which isolated high sinuosity channels are embedded in thick floodplain fines. Some thin beds of palustrine carbonates and immature paleosols can also be found in association with the floodplain deposits. This unit can be interpreted as a high accommodation systems tract (HAS), according to both models.
On the other hand, unit VI presents a different facies distribution in each zone of the study area. In the western zone, carbonate sedimentation prevails, with vertically stacked palustrine sequences representing a protected area of the floodplain. In the eastern zone, sedimentation is dominated by siliciclastic floodplain lutites, some isolated channels, as well as a multistorey channel in the upper part. This unit is interpreted as a low accommodation systems tract (LAS), according to the second model. An integrated sequence-stratigraphy model involving both siliciclastic and carbonate, nonmarine sedimentation sequences is needed to connect the eastern and western zones of the basin.
This study has been financed by research projects CGL2005-06224/BTE (MEC, FEDER), IGME 2001-016, IGME 2005-009, and the Working Group RNM-022JA.