The Lake Izabal Basin (LIB) in eastern Guatemala, located along the active strike-slip North American–Caribbean plate boundary, contains an extensive sedimentary record extending over 4 kilometers and spanning the last 12 million years. This archive offers an opportunity to investigate the dynamic interplay between tectonics, climate, and sedimentary processes shaping basin evolution through time. We integrate seismic sequence mapping, reflection terminations, seismic facies analysis, and well cuttings X-ray fluorescence (XRF) data from a 1,400 m deep industry well. Using seismic data, elemental concentrations, principal component analysis (PCA), and an age–depth model, we reconstructed the LIB’s history and its sedimentary response to sea level, temperature, and atmospheric CO₂ since the mid-Miocene. Seismic stratigraphic analysis along the basin’s eastern margin identifies six seismic sequences and five seismic facies, reflecting distinct phases of basin filling and environmental change. The sedimentary architecture shows a progression from subparallel, low-amplitude, semicontinuous reflections indicative of fluvial deposition during mid-Miocene basin initiation and deepening, to late Miocene subparallel, high-amplitude, basinward prograding clinoforms indicative of deltaic deposition. Mid-Pliocene subparallel, semicontinuous, variable amplitude reflections appear linked to a fluvial-lacustrine setting while Late Pliocene moderate to high amplitude, sigmoidal to oblique clinoforms signal a shift to deltaic environments during increased sediment supply. Finally, the Quaternary fill is dominated by subparallel, high-amplitude, semicontinuous reflections likely linked to lacustrine deposition. Comparison of XRF results with global sea level, temperature, and atmospheric CO₂ time series indicates three principal phases in the basin’s history, supporting our seismic interpretations. From the late Miocene to early Pliocene, proxies indicate increased erosion corresponding to deltaic progradation, while carbonate production varied, likely influenced by rising global atmospheric CO₂. The early to late Pliocene increased erosion reflects a fluvio-deltaic transition, likely linked to early Pliocene warming, the regional uplift of the Mico Mountains, and moisture availability from the Caribbean Sea. Carbonate deposition during this interval coincides with peak sea level and atmospheric CO₂, underscoring a complex interplay between tectonics and climate. During the Quaternary, decreased erosion and lacustrine facies reflect reduced tectonic activity and sediment supply, potentially linked to the onset of Northern Hemisphere glaciation. These results provide insights into strike-slip basin fill dynamics to long-term changes in sediment supply, regional tectonics, climate, and sea level change.

Keywords: Strike-slip basin, Seismic stratigraphy, Geochemistry, Tectonics, Climate.