THE ROLE OF TECTONISM IN THE DEVELOPMENT OF STRATIGRAPHIC SURFACES IN THE COLOMBIAN LLANOS FORELAND BASIN

• Author / Creator

  Carvajal Torres, Juan Sebastian

• During the Campanian-Paleogene, a regional basin extended from the Magdalena Valley in the west to the Llanos Basin in the east. Subsequently, the Llanos Basin was separated from the Magdalena Valley and became an independent depocenter from the Oligocene to the present. This study combines the facies analysis from the late Campanian – early Oligocene rock units in the southern Llanos Basin, with a regional chronostratigraphic correlation to provide a better understanding of the stratigraphic response to the tectonic changes. Based on outcrop data from the Sagu creek and cores from three wells in the southern Llanos Basin this study identified four unconformities present at the limits between the Campanian-Maastrichtian, Cretaceous-Paleocene, Paleocene-Eocene, and Eocene-Oligocene. The oldest and youngest developed under subaqueous conditions, whereas the others developed under subaerial conditions. They control the distribution of the Maastrichtian to Eocene facies across the southern Llanos Basin. Indeed, the ±80 m of the Upper Guadalupe and Guaduas formations from the Sagu creek are absent in the sedimentary record of the studied wells. The early-middle Eocene Mirador Formation preserves the coarsest sediment along the area, which is truncated by a subaqueous unconformity and is overlain by shallow marine facies from the earliest Oligocene. Chronostratigraphic correlation with adjacent basins demonstrates the magnitude of these unconformities. The subaqueous unconformities are locally presented across the southern Llanos Basin, while the subaerial unconformities extend across the Colombian territory. Each of the latter indicates a hiatus ±16 My along the Southern Llanos Basin. The variations in magnitude, type, and correlatability of the surfaces unveil how the tectonic reorganization influenced the southern Llanos Basin from the Late Cretaceous to the Oligocene. Compared to other similar basins worldwide, the data reveals a complex depositional setting, where the type, magnitude, diachroneity, and complexity of the unconformities is the result of the compressional tectonism.
  The Magdalena Valley, Eastern Cordillera, and westernmost Llanos Basin comprised the major depocenters of the basin. However, the western flank of the Eastern Cordillera and most of the Llanos Basin were uplifting. A late Campanian first-order maximum regressive surface preserved at the base of the retrograding marine facies of the Upper Lidita, Buscavidas and Umir, Guadalupe, and Palmichal units, is the lower boundary of the retroarc foreland sequence. This surface does not extend across the whole basin. In the uplifting areas, subaerial unconformities truncate the middle Campanian rocks. These surfaces compound the lower first-order boundary and its diachroneity is controlled by the northward migration of the orogen. The Teruel, Hoyon, Bogota, Cacho, Socha, Barco, and Cuervos formations are truncated by a regional first-order subaerial unconformity formed during orogenic unloading that marks the termination of the foreland basin in the Eocene. Therefore, it is the upper boundary of the first-order sequence.
  Outcrop and well cores data from the southern Llanos Basin indicate the sedimentary record preserves four second-order sequences, formed during the under- and overfilled stages of the foreland basin. Tectonism controlled their development. The diachroneity of the surfaces and sequences is related to the northward migration of the orogen that influenced the tectonic stages and architecture of the basin. The southern Llanos Basin was at the marginal part of the foreland, where the role of the tectonism resulted in the formation of multiple unconformities. Their formation processes vary regarding the proximity of the shoreline and the tectonic stage. These unconformities reworked the boundaries of the sequences, so their connection towards the depocenter also varies. In the Sagu area, the three lowermost four second-order sequences deposited during the underfilled stage are incomplete and pinch out eastward as subaerial unconformities truncate them. The uppermost sequence was formed during the overfilled stage when fluvial deposition took place across the basin, and the eastward migration of the depocenter renewed the sedimentation along the basin margins. At this time, accommodation was outpaced by sedimentation due to the high sediment supply resulted from the uplifting orogen and forebulge. Albeit, the reduced amalgamation of the channels suggests the creation of accommodation during this stage. Their partial or total absence and the facies changes are the consequence of the basin architecture and tectonism.

• Subjects / Keywords

  • sequence stratigraphy
  • sedimentology
  • stratigraphy
  • foreland basin

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-thwh-n473

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.