THE LAKE IZABAL BASIN – A POSSIBLE ICDP DRILLING SITE

The Lake Izabal Basin in eastern Guatemala is a pull-apart basin that developed along the strike-slip North American and Caribbean plate boundary. The basin is deep and asymmetric, with more than 4 km of sediment. The thickness of the sedimentary cover, its tectonic setting along a major transform, and its location along the tropics make this basin an ideal location for an ICDP drilling project. However, very little is known about the basin, especially its age of inception and initial infill history. We report here preliminary interpretations from outcrop observations along the eastern side of the basin, description of drill cutting from an industry well, and interpretation of industry seismic reflection profiles to better understand the evolution of this basin. Outcrop observations suggest that the initial infill of the basin is characterized by fluvial and lacustrine deposits, with abundant sandstone, shale, mudstone, limestone, tephra, and coal. CA-TIMS ages of the tephra indicate that the basin developed close to 12.01 Ma. Cuttings from the Colorado-1 well are dominated by mudstone, with a coal interval ~ 100 m thick and an interval ~ 200 m thick with abundant conglomerate. Correlation between datasets indicate that the conglomerate was deposited around 4 Ma during the uplift of the Mico Mountains. In contrast to the eastern side, the western side of the basin is structurally simpler, with minor faults and with concordant and parallel seismic reflections. Some of the faults appear to be active today, evidenced by the presence of fault scarps along the northwestern side of the basin. Time-depth correlation between the Colorado-1 well and seismic profiles indicate that the western side contain more than 1000 m of continuous sedimentation spanning the entire Quaternary and possibly extending into the Pliocene-Miocene. This study provides a comprehensive examination of a diverse dataset that can help understand the evolution of the Lake Izabal pull-apart basin. Such work is needed to constrain the tectonic and structural history of an understudied continental strike-slip plate boundary and the deep basin that formed along a segment of the fault in Guatemala.