Sedimentary Architecture, Structural Setting, and Late Cenozoic Depocentre Migration of an Asymmetric Transtensional Basin: Lake Izabal, Eastern Guatemala


Lake Izabal, located in eastern Guatemala, lies in an EW-trending basin located along the transform margin between the North American and Caribbean plates. This plate boundary consists of two main left-lateral, strike-slip faults known as the Polochic and Motagua Fault System (PMFS). The basin is a 100 x 20 km lens-shaped depression in which the lake occupies its eastern half. To the north, the basin is confined by a Principal Deformation Zone (PDZ) which is recognized in this area as the most important upper-crustal branch of the Polochic Fault. The eastern part of the basin has been uplifted and dissected, exposing the basin infill along the slopes of the Montana del Mico. Analysis of a set of multichannel seismic reflection profiles, most of them acquired within the lake, combined with well and outcrop information, allowed to outline the structure and evolution of the basin and its stratigraphic architecture. The basin is strongly asymmetrical, both in cross and along-strike directions, and is filled up by Neogene to Quaternary sediments, with the deepest side of the basin being to the north, close and parallel to the PDZ. The base of the infill is a mid-Tertiary unconformity whose differential subsidence through time brought the basin to its present structural setting. Five main evolutionary stages are recognized based on seismo-stratigraphic and structural features, which are related to the development and activity of the bordering faults. Development of the basin began in its easternmost sector. A small half graben, tilted to the south, developed in response to the activity of an Oligocene (?) or Early-Middle Miocene growth fault. In the second stage (Late Miocene), the basin tilts to the north, causing the sedimentary sequences to thicken towards the northern PDZ. This stage is dominated by oblique extension, and by progressive migration of the basin depocenter towards the west. The third stage (Early Pliocene) records a strong acceleration of the strike-slip activity which causes a rapid westward migration of the depocenter. The fourth stage (Late Pliocene), although still dominated by regional transtension, is related to the development of a transpressional event along the eastern side of the basin, as evidenced by the occurrence of folds and reverse faults parallel to the northern bend of the Polochic Fault. During the fifth stage (Quaternary), the eastern part of the basin remains relatively quiescent while the western part undergoes subsidence with localized transtension, still related to the activity in this sector of the Polochic Fault. Left-lateral movement along the Polochic Fault caused the depocenter to migrate 75-80 km at different velocities, with slip rates ranging between 2.1 and 16.3 mm/yr. This study suggests that the Polochic Fault developed in the Early-Middle Miocene in connection to the deposition of the early sediments of the Izabal Basin, even though an older age (Oligocene?) could also be possible. To our knowledge, this is one of the best examples of sedimentary architecture documenting depocentre migration due to fault movement along a transform system.


Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Basin asymmetry; Depocentre migration; Eastern Guatemala; Izabal pull-apart/strike-slip basin; Seismic profiles; Tertiary evolution

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Article - Journal

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