Astronomically-Forced Sedimentary Record in the Late Turonian–Early Coniacian Shallow Platform Sediments of the Iberian Ranges (Spain)

During the late Cretaceous, the Iberian Basin was a Peri-Tethyan, shallow, intracratonic basin, located on the Iberian Microplate between two emerged massifs. Subsidence during these times was mainly thermal in origin.

The significant late Cretaceous, global, eustatic sea-level rise was the main factor controlling the sedimentary episodes in the Iberian Basin (Segura et al., 2002). This area was particularly sensitive to sea level oscillations, recording even those of high-frequency and smaller amplitude. Thus, its sedimentary record is especially appropriate to develop detailed cyclostratigraphic analysis.

The late Turonian–early Coniacian 3rd-order sequence is composed of a thin- and well-bedded, inner platform carbonate succession. Up to 27, meter-scale, 6th-order parasequences are recognized showing shallowing up trends. They are hierarchically grouped into 5th- and 4th-order parasequences. This stacking pattern suggests the existence of periodic, cyclic, sedimentary signals in the record. Spectral analysis of the lithofacies thickness, using the Lomb-Scargle algorithm, recognize three orders of cycles (12.76-14.05 m, 3.11-3.28 m and 1.32-1.53 m), very closely to the mean thickness of the 4th-, 5th- and 6th-order parasequences respectively. The linear correlation with the Milankovitch orbital periodicities for late Cretaceous shows that the spectral periodicities can be related to long eccentricity cycles of 400 ka, short eccentricity cycles of 95 ka and obliquity cycles of 39 or 50.6 ka respectively.

Thus, the Milankovitch orbital forcing acted as a major factor that controlled the rhythms of depositional events in the late Turonian-early Coniacian 3rd-order sequence of the Iberian Ranges. A precise floating astronomical time scale can be developed, assuming a 95 Ka orbital period for each 5th-order parasequence.

Segura, M.; García, A.; Carenas, B.; García-Hidalgo, J.F.; Gil, J. (2002): Upper Cretaceous of the Iberian Basin. In: Gibbons, W. & Moreno, T. (eds.), “The Geology of Spain”. Geological Society, London. 288-292.