Digital outcrop mo deling using "structure-from-motion" photogrammetry: applications to analyze Neogene? Quaternary environmental signals preserved in the Andean Foreland, Argentina

BILMES, ANDRÉS; D'ELIA, LEANDRO; LUCIANO LOPEZ; AUGUSTO N. VARELA; MARÍA DEL PILAR ALVAREZ; EYMARD, INES; ARIZTEGUI, DANIEL; FRANZESE, JUAN R.

Toulouse

Congreso; International Meeting of Sedimentology 2017. 33rd IAS & 16th ASF; 2017

IAS

In the last years, the progressive technological and geomatic revolution made it possible to obtaindigital outcrop models (DOM) and high-resolution digital terrain models (DTMs) , using a novelphotogrammetric technique named ?Structure from Motion?Multi‐View Stereo (SfM‐MVS)?. Thisphotogrammetric method produces 3D point clouds or mesh models using multiple overlappingoffset images. The major success of this technique is that allows constructing 3D models similar thatobtained with more sophisticates techniques (e.g., LIDAR, Terrestrial Laser Scanning), although witha greatly enhanced ease-of-use and the advantage of being low-cost. A typical complete workflow todevelop this technique involves: (i) field work component to establish ground control points andacquire the photoset, either taking terrestrial photos or using unnamed aerial vehicle; (ii) a computerprocessing for the 3-D scene reconstruction; (iii) a post-processing stage to scaleand geo-reference the model; and (iv) a 3D analysis using a 3D visualization & interpretationsoftware for geological data (e.g. VRGS ®). The objective of this work is to illustrate the effectivenessof the SfM‐MVS technique for the resolution of quantitative case studies devised in the context ofsedimentary systems influenced by tectonics and climate changes. Two case studies located in theSouthern Andean Foreland, Argentina, previously analyzed with traditional fieldwork, were selectedand re-analyzed. For each case study the aim was to solve questions that were not possible to carryout without the using of DOM and DTMs, such as: (a) determining of tilting phases related tocontractional tectonic deformation based on the analysis of progressive discordances in the Neogeneinfill of the Andean Foreland (i.e. Piedra del Aguila Basin); and (b) the quantification of lake level fallduring the past 10 years of a closed basin evaluating the geomorphological impact over the exposurelandforms (i.e., the Laguna Carri Laufquen Grande in the Maquinchao Basin). Related to the first case,the results suggest that four deformation phases occurred, two of them involving a inter-tectonicsedimentation and the others syn-tectonic sedimentation. In addition, the analysis of progressivediscordances allows to establish different tilting phases. The accurate statistical analysis of strike anddip directions determined variations of the tilting axis, which were related to different scale ofstructures, such as local fault-propagation fold and regional rotation of fault blocks. Related to thesecond case, the analysis and interpretation of the DEMs and satellite images of the last decade (i.e.,2002-2016) allow to constrain the ages and topographic position of the different modern lakeshorelines, showing lake level variations up to 8.5m. In addition, the analysis of lake level fluctuationstogether with meteorological dataset of the region suggest that water lake levels have different timeof response to climate variations.The outcome of the investigations of this work shows the potential of the SfM‐MVS approachto solve cases studies with different spatial and temporal resolution. This increasingly populartechnique allows not only to improve the analysis of sedimentary forms, but also to move forward inunanswered questions related to environmental signals preserved in sedimentary systems.