Sediment provenance from coastal and offshore northern Colombia: Detrital zircon U-Pb geochronology of the Magdalena River Delta and La Aguja Canyon

Understanding the provenance and transport pathways of sediments is crucial for reconstructing the geological history of source-to-sink systems. Northern Colombia, with its complex tectonic and geomorphological settings, provides an ideal framework to study the connectivity between coastal and offshore sedimentary systems. The Magdalena River Delta (MRD) and La Aguja Canyon (LAC), two prominent features in the Caribbean Sea, serve as major conduits for sediment transport from continental to deep marine environments. This study analyzes detrital zircon U-Pb geochronology data from four coastal sediment samples collected near the MRD and LAC, along with ten offshore samples retrieved during a research expedition aboard RV Maria S. Merian, using a Giant Box Corer at ~50–4000 m depths.  A total of 1550 extracted zircon grains were analyzed by LA-ICP-MS to determine U-Pb ages and trace element compositions, enabling sediment provenance identification.

Zircon U-Pb ages range from <1 to 2620 Ma in the MRD and 50 to 1798 Ma in the inner LAC, with younger ages down to 2.7 Ma in the outer offshore regions. Coastal zircons from LAC are generally larger (>200 µm) than those from the MRD (~50–150 µm), reflecting differences in sediment transport and source rock characteristics. Offshore zircons show more consistent sizes (~50–200 µm) across both regions. The morphology of the grains varied from equant and elongated grains to broken grains with rounded terminations. Cathodoluminescence (CL) imaging reveals oscillatory zoning typical of magmatic zircons, homogeneous or rim-core zoning indicative of metamorphic origins, and grains with no CL response, suggesting prolonged surface exposure.

The youngest age clusters in the MRD, spanning 0.1 to 8 Ma, 75 Ma, 155 Ma, and 275 Ma, indicate contributions from the Central Cordillera of Colombia, highlighting recent contributions from this tectonic unit. Ages from 459–682 Ma suggest additional input from the Santander Massif and San Lucas Range, while older clusters (916–2232 Ma, largest peak at 991 Ma) reflect influences from the Eastern Cordillera. These age distributions underscore the interplay of tectonic uplift and fluvial transport in shaping sediment deposition in the MRD. Coastal samples near the MRD show age distributions that correlate well with offshore samples, particularly for peaks below 300 Ma and above 860 Ma. However, coastal samples lack significant ages in the intermediate range (~300–860 Ma), contrasting with the offshore spectrum, which exhibits a more continuous distribution with only a minor gap between 700 and 800 Ma. In LAC, prominent U-Pb age peaks at ~50 Ma, ~180–265 Ma, and ~1000 Ma denote provenance from the Santa Marta Batholith and its adjacent units, including gneisses, metasediments, and the Santa Marta and San Lorenzo Schist. Coastal samples near LAC display comparable provenance signals, with dominant contributions from the Santa Marta Massif. These findings highlight the influence of tectonic activity in the Santa Marta region on sediment delivery to both coastal and deep marine environments.

Keywords: detrital zircon U-Pb geochronology, source-to-sink, Magdalena River Delta, La Aguja Canyon, marine sediment provenance