Chasing the 400 kyr pacing of deep-marine sandy submarine fans: Middle Eocene Aínsa Basin, Spanish Pyrenees

Abstract

In an attempt to understand the relative importance of climate and tectonics in modulating coarse-grained sediment flux to a tectonically-active basin during what many researchers believe to be a greenhouse period, we have studied the Middle Eocene deep-marine Aínsa Basin, Spanish Pyrenees. We use orbital tuning of many spectral gamma-ray logged fine-grained siliciclastic sections, already shown to contain Milankovitch frequencies, in conjunction with a new high-resolution palaeomagnetic study through the basin sediments, to identify polarity reversals in the basin as anchor points to allow the conversion of a depth-stratigraphy to a chronostratigraphy. We use these data, in conjunction with a new age model incorporating new biostratigraphic data, to pace the development of the deep-marine sandy submarine fans over ∼8 million years. Timing for the sandy submarine fans shows that, unlike for the fine-grained interfan sediments, coarse-grained delivery to the basin was more complex. Approximately 72% of the sandy fans are potentially coincident with the long-eccentricity (400-kyr) minima and, therefore, potentially recording changing climate. The stratigraphic position of some sandy fans is at variance with this, specifically those that likely coincide with a period of known increased tectonic activity within the Aínsa Basin, which we propose represents the time when the basin was converted into a thrust-top basin (Gavarnie thrust sheet), presumably associated with rapid uplift and redeposition of coarse clastics into deep-marine environments. We also identify sub-Milankovitch climate signals such as the ∼41.5 Ma Late Lutetian Thermal Maximum (LLTM). This study demonstrates the complex nature of drivers on deep-marine sandy fans in a tectonically-active basin over ∼8 Myr. Findings of this study suggest that even during greenhouse periods, sandy submarine fans are more likely linked with times of eccentricity minima and climate change, broadly consistent with the concept of lowstand fans. However, hysteresis effects in orogenic processes of mountain uplift, erosion and delivery of coarse siliciclastics via fluvial systems to coastal (deltaic) and shallow-marine environments, likely contributed to the complex signals that we recognise, including the 2–3 Myr time gap between the onset of deep-marine fine-grained sediments in the early development of the Aínsa Basin and the arrival of the first sandy fans.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5132975

Water discharge and sediment flux intermittency in the fluvial Escanilla Formation, Spain: Implications for changes in stratigraphic architecture

“…Black vertical bars denote the average value in HA intervals while grey bars denote the average value in LA intervals. cyclical variations relatively coarser and finer-grained reflect a strong relationship to the 400 eccentricity cycles (Cantalejo & Pickering, 2014;Cantalejo et al, 2021). In the continental Escanilla Formation, 400 kyr eccentricity cycles have recently been proposed to influence sediment depositional patterns from the HA to LA intervals due to cyclical variations in sediment flux and water discharge (Sharma et al, 2023a(Sharma et al, , 2023b.…”

“…This particular latitude is recognised to be sensitive to climate changes induced by astronomical factors with some studies suggesting that orbital variations could impact precipitation and evaporation patterns at such latitudes (Cantalejo & Pickering, 2014). For instance, in the Middle Eocene (Late Lutetian) Ainsa System submarine fan deposits, cyclical variations in relatively coarser and finer‐grained sediments reflect a strong relationship to the 400 kyr eccentricity cycles (Cantalejo & Pickering, 2014; Cantalejo et al., 2021). In the continental Escanilla Formation, 400 kyr eccentricity cycles have recently been proposed to influence sediment depositional patterns from the HA to LA intervals due to cyclical variations in sediment flux and water discharge (Sharma et al., 2023a, 2023b).…”

Water discharge variations control fluvial stratigraphic architecture in the Middle Eocene Escanilla formation, Spain

“…Cyclical oscillations of the orbital configuration of the Earth-Sun system over so-called Milankovitch periodicities constitute a plausible mechanism to account for the observed cyclic changes in water discharge in the Escanilla fluvial succession. Milankovitch cyclicity is known to have played a major role in driving climate change during Earth’s history [e.g., 65 , 66 ], in the Cenozoic [e.g., 67 ], and has also been invoked in several studies in the Spanish Pyrenees as an important factor controlling depositional sequences [e.g., 68 ].…”

Orbitally‐driven Palaeogene to Neogene deposition in the western South Atlantic (Espírito Santo Basin) and its correlation with global sea level

“…Cantalejo et al . (2021) demonstrate that 72% of the sand fans in a siliciclastic section of the mid‐Eocene deep‐marine Aínsa Basin (Spanish Pyrenees) coincide with 405 kyr long eccentricity minima and could be attributed to climate change. The preferential deposition of abrupt mass‐flow coarse‐grained turbidites at lowstand sea‐level times could give these random events some sort of periodicity.…”