Evolution of the Galicia Interior Basin over the last 60 ka: sedimentary processes and palaeoceanographic implications

Abstract

The Galicia Interior Basin (GIB; NW Iberian Peninsula) is located near a critical transition between the subtropical (temperate) and subpolar (cold) gyres of the North Atlantic. It therefore witnesses oceanographic changes driven by global climatic events. This study reports on the recent (latest Pleistocene) sedimentary, palaeoceanographic and palaeoclimatic history of the basin. We integrated analysis of deep-sea sediment cores retrieved from an E-W transect across the GIB. The analysis indicated three types of sedimentary processes recording glacial (Marine Isotope Stage 2-4) and deglacial events: along-slope bottom currents (forming contourite deposits), pelagic and hemipelagic sedimentation, and gravitational dislocation. Variation in depositional patterns and sedimentation rates indicate distinctive transport (along-slope and down-slope) and depositional processes. These in turn reflect climatic and oceanographic drivers. We interpret changes in sea level from core evidence showing changes in sediment supply. The cores exhibited conspicuous sedimentary evidence of Heinrich events (HEs). The stratigraphic intervals associated with HEs showed significant lateral variation. We suggest that the lateral variation may result from the development of an oceanographic boundary between surface water masses with different temperature and salinity parameters or changes in surface currents which may have introduced relatively warmer water into the GIB during the last glacial period.

Lateral variability of ichnological content in muddy contourites: Weak bottom currents affecting organisms’ behavior

“…As outlined above, established interpretations of ichnological shifts attribute them to variations in sedimentation rate, organic matter availability, and oxygenation. Deposits from Galicia Interior Basin show clear spatiotemporal domains and associated sedimentation processes which themselves document the paleoenvironmental changes 12 . The westernmost FSG09-10 core was collected along the east flank of the Galicia Bank, in the so-called Transitional Zone 30 .…”

“…Five gravity cores were collected during ForSaGal 09 in 2009 from the GIB, a narrow basin (around 100 km width; 2500–3000 m water depth) along the NW Iberian margin 17 . Sedimentary facies (i.e., Pelagic, Hemipelagic, Contouritic, Turbitidic and IRD layers) were previously characterized based on grain size, composition, sedimentary features and Computed Tomography (CT) scanning 12,17 . Contourite deposits, concretely muddy contourites, were identified in three cores.…”

“…Age was calculated using the age model based on XRF data and AMS- 14 C ages for the cores material analyzed 12 .…”

“…The present study investigated core material collected from about 3,000 m water depth 12 during the ForSaGal 09 research cruise around the Galicia Interior Basin (GIB; Fig. 1).…”

“…This dome-like elevation is strongly influenced by bottom current activity that generates abraded surfaces 31 . Cores FSG09-09 and FSG09-16 were collected from the central part of the basin, between the Transitional Zone 31 and lower slope 12,14 , which are dominated by pelagic and hemipelagic sedimentation 12 . Core FSG09-07, and especially the easternmost core FSG09-17, correspond to a contouritic and hemipelagic depositional setting developed on the lower continental slope 14 .…”