Tectonic and climatic controls on the sequential arrangement of an alluvial fan/fan‐delta complex (Montserrat, Eocene, Ebro Basin, NE Spain)

Abstract

A magnetostratigraphy‐based chronological framework has been constructed in the Eocene sediments of the Montserrat alluvial fan/fan‐delta complex (southeast Ebro Basin), in order to unravel forcing controls on their sequential arrangement and to revise the tectonosedimentary history of the region. The palaeomagnetic study is based on 403 sites distributed along an 1880‐m‐thick composite section, and provides improved temporal constraints based on an independent correlation to the geomagnetic polarity time scale. The new chronological framework together with sequence stratigraphy and geohistory analysis allow us to investigate the interplay between factors controlling the sequential arrangement of the Montserrat complex at the different temporal scales and to test for orbitally driven climate forcing. The results suggest that the internal stacking pattern in transgressive and regressive sequences sets within the more than 1000‐m‐thick Milany Composite Megasequence can be explained as the result of subsidence‐driven accommodation changes under a general increase of sediment supply. Composite sequences (tens to hundreds of metres thick) likely reflect orbitally forced cyclicity related to the 400‐kyr eccentricity cycle, possibly controlled by climatically induced sea‐level fluctuations. This study also provides new insights on the deformational history of the area, and shows a correlation between (tectonic) subsidence and forelimb rotation measured on basin‐margin deformed strata. Integration of subsidence curves from different sectors of the eastern Ebro Basin allows us to estimate the variable contribution of tectonic loads from the two active basin margins: the Catalan Coastal Ranges and the Pyrenees. The results support the presence of a double flexure from Late Lutetian to Late Bartonian, associated with the two tectonically active margins. From Late Bartonian to Early Priabonian the homogenization of subsidence values is interpreted as the result of the coupling of the two sources of tectonic load.

Orbital forcing as principal driver for fine-grained deep-marine siliciclastic sedimentation, Middle-Eocene Ainsa Basin, Spanish Pyrenees

“…In the Western Pyrenees, Payros and Martínez-Braceras (2014) studied deep-marine fan-fringe/ basin-plain turbidite deposits of the Gorrondatxe section and deduced orbitally-forced fluctuations in seasonal rainfall and riverine runoff. Also, Gómez-Paccard et al (2011) documented composite sequences in the Montserrat alluvial fan/fan-delta complex of the Ebro Basin, which they interpreted as 400-kyr long eccentricity cycles, possibly controlled by sea-level fluctuations.…”

Insights Into the Crustal‐Scale Dynamics of a Doubly Vergent Orogen From a Quantitative Analysis of Its Forelands: A Case Study of the Eastern Pyrenees

“…Tectonic subsidence in the south (Montserrat section) sees a brief acceleration to 0.21 mm/yr at 41.5 Ma that can be correlated to activity of the Catalan Coastal Ranges (Vergés et al, ). After ~36 Ma, tectonic subsidence slowed down throughout the southern foreland basin (Figures a and b; Gómez‐Paccard et al, ).…”

Rotational Kinematics of Basement Antiformal Stacks: Paleomagnetic Study of the Western Nogueras Zone (Central Pyrenees)

“…The Early Triassic reference is 345°/14° ( N = 5, α 95 = 5.8°, k = 138.3), calculated from paleopole data by Parés et al (), Schott and Perés (), and Osete et al (, compiled in Osete & Palencia‐Ortas, ). The Eocene‐Oligocene reference, chosen in accordance to known alpine deformation ages in the region, is 000°/47° ( N = 7, α 95 = 7°, k = 66), calculated from data in Taberner et al () and from normal average components in four different magnetostratigraphic profiles (Maians‐Rubió, Costa et al, ; Miralles‐La Tossa, Costa et al, ; Montserrat, Gómez‐Paccard et al, ; and Moia‐Santpedor, Costa et al, ), all located in the northeastern part of the south Pyrenean Ebro foreland basin.…”