Quaternary stratigraphic stacking patterns on the continental shelves of the southern Iberian Peninsula: their relationship with global climate and palaeoceanographic changes

• Published in: Quaternary international Vol. 92; no. 1; pp. 5 - 23
• Main Authors: Hernández-Molina, F.J, Somoza, L, Vazquez, J.T, Lobo, F, Fernández-Puga, M.C, Llave, E, Dı́az-del Rı́o, V
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2002
• ISSN: 1040-6182; 1873-4553
• DOI: 10.1016/S1040-6182(01)00111-2

A Quaternary stratigraphic stacking pattern on the continental shelves of the southern Iberian Peninsula has been determined by analysing and comparing a dense network of low-, medium-, high- and very high-resolution mono-channel and multi-channel reflection seismic lines and well-log data. Four major low-resolution depositional sequences related to a 3rd-order cycle at 1.4–1.6 Ma have been recognised in the Pliocene–Quaternary sedimentary record (M/P1, P2, P3/Q-I and Q-II). They are separated by four discontinuities corresponding to the most drastic changes in climate and palaeoceanography affecting the Atlantic and Mediterranean linkage, and especially to the most prominent sea-level falls in the Messinian (M) at 5.5 Ma, in the Lower Pliocene at 4.2 Ma in the Upper Pliocene at 2.4 Ma and in the Mid-Pleistocene at 900–920 ka (MPR). These major sequences were built up by asymmetrical sea-level cycles. The regressive and lowstand system tracts are the best-developed deposits, controlling the main progradation of the shelf basinwards as well. The Quaternary shelf stratigraphy can be divided into asymmetric 3rd-order sequences of 800 ka (Q-I and Q-II), and into 4th-order asymmetric sequences of approximately 400 ka (Q1–Q4), 200 ka (A–H) and 100 ka. On low-, medium- and high-resolution seismics, the overall architectural stacking of the shelf shows a change after the MPR discontinuity, characterised by well-differentiated sequences of shelf-break wedges with progradational sigmoid configurations, assumed to be related to approximately 100 ka sea-level cycles. This change in the configuration of the shelf wedges during the Quaternary is attributed to the onset of the 100 ka eccentricity orbital cycles, which abruptly increased the amplitude of sea-level variations (100–120 m) during the last 900–920 ka.