Mass-Transport Complexes as Markers of Deep-Water Fold-and-Thrust Belt Evolution; Insights from the Magdalena Fan, Offshore Colombia

Abstract

Abstract

Mass-wasting of tectonically active margins is an important process in the degradation of deep-water fold-and-thrust belts where structural traps are often exploration targets. Large volumes of sediment can be removed from anticlines, and understanding the relationship and relative timing of deformation and mass-wasting is important when assessing the presence and risk of the elements of the petroleum system. This detailed study is based on mapping of the near-seabed stratigraphy in a 3D seismic volume in the Magdalena Fan, offshore Colombia and investigates. The relationship between the growth of a deep-water fold-and-thrust belt (the southern Sinú Fold Belt) and the source, distribution, and size of MTCs is investigated.

The study area is located at the northern tip of the Southern Sinú Fold Belt where two anticlines form the updip and downdip limits of a syncline. The downdip anticline is thrust cored to the SW where it has higher structural relief and to the NE is not faulted; the updip anticline is thrust-cored along the entire study area. Basinward of these folds several MTCs associated with at least three separate updip-headwalls coalesce. Detailed mapping of the MTCs and interpreted flow directions based on kinematic indicators show that the oldest MTCs, which are relatively small (10-160 km²), are syn-tectonic and were sourced from the flanks of growing anticlines. Younger MTCs, which are considerably larger (200-400 km²), are sourced from the shelf and post-date the main phase of active thrusting and folding. The largest (c. 400 km²) post-tectonic MTC basal erosion surface occupies the syncline and traverses the downdip anticline. Breaching of the anticline resulted from several mass-flows that were initially confined in the syncline and progressively degraded the downdip anticline connecting the shelf break with the basin low basinward of the anticlines, enabling larger MTCs sourced from shelf to traverse the structural high.

The changes in source areas, distribution, and dimensions of the MTCs resulted from the combined effect of growth, and syn-tectonic and post-tectonic degradation of the deep-water fold-and-thrust belt. The characteristics of the MTCs, therefore, reflect the complex tectono-stratigraphic history and can be used to constrain the timing and style of deformation, and seascape evolution in time and space. This study serves as an analogue for exploration prospects at greater depths in tectonically-active basin margins.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016