Abstract

The Gualdalquivir–Gulf of Cádiz Neogene Basin started to form at the end of the Early Miocene compressional phase in the Betic System. Seven stratigraphic sequences are identified in the Basin: 1–3. Preolistostromic sequences (Atlantida Group), Al, A2 and A3; 4. Synolistostromic sequence (Betica Sequence); 5. Andalucia sequence; and 6–7. Post-erosional phase sequences (Marismas and Odiel).

Introduction

After the Early Miocene Betic compressional phase, an extensional period began, affecting the Guadalquivir Valley and the Gulf of Cadiz area (Fig. 1) and forming a Neogene foreland basin with the following general characteristics:

1. – Langhian to Quaternary sediments infilling a WSWENE basin widening and deepening to the west.

2. – A passive margin to the north, resting on a Paleozoic basement and a residual Mesozoic platform.

3. – An active margin to the south, which is compressional and gravitational, with a large olistostromic mass infilling this side of the basin during Late Tortonian times, partly destroying and masking the previous sediments of this margin. Some olistostromic events have been reported before that time, but they are less important than the Late Tortonian gravitational advance.

The main tectonic phase affecting the basin shape occurred during the Late Miocene, when downwarping of the basement took place in the south followed by the extension of a system of faults. These processes created an important trough where a thick sedimentary sequence quickly accumulated.