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Integrated Digital Outcrop Modeling of a Large-Scale Carbonate Slope System: The Upper Cretaceous-Paleocene Ionian Basin of Albania

Abstract

Ancient carbonate platform-slope-basin systems may host important hydrocarbon reservoirs. This is demonstrated by current exploitation and ongoing industrial surveys of carbonate reservoirs in the Ionian Basin in Italy, Albania and Greece, where 25 fields and about 500 MMBOE were discovered to date in the Upper-Cretaceous-Paleocene play. The foreland evolution of the basin is recorded in a ca. 500-meter-thick carbonate succession exposed along the Albanian fold-and-thrust belt. This study focuses on the Kurveleshi belt, presenting an excellently exposed, unique example of a carbonate re-sedimentation system analogous to subsurface reservoirs. A high-resolution drone survey covering over 5 km² was conducted around Muzina town. The virtual model was integrated with detailed sedimentological field and laboratory data. A variety of deep-water deposits including gravity-flow deposits (turbidites, debrites), mass transport deposits (MTDs) and pelagites record the eastward sediment-shedding off the Apulian Platform during the Upper Cretaceous-Paleocene. The lower to middle part of the succession comprises graded 0.5 m to 2 m thick calcarenite beds. These calciturbidites are characterized by load-casts composed of coarse biogenic debris at the base, grading upward into planar-horizontal to low-angle lamination, convolute structures and calcilutites at the top. The beds adopt an overall sheet-like geometry without evidence of significant erosion. The upper part of the succession contains six seismic-scale stratigraphic intervals making up one third of the entire sediment stack. These intervals comprise reworked calcarenite beds and are interpreted as MTDs. Drone imaging allowed to accurately constrain the basal shear surface, top and internal architecture of each MTD. Internal folds and faults demonstrate intense syn-sedimentary deformation during the emplacement of each unit. Individual MTDs are overlain by healing-stage deposits that typically fill relict topography at their upper boundaries. The entire sequence shows the interplay between infrequent tectonic processes (MTDs) and normal sediment export patterns (calciturbidites) of prolific carbonate platforms. This study contributes to understanding the ‘big picture’ of ancient carbonate slope successions hosting hydrocarbon reservoirs in the subsurface. The integration of drone imaging and classical field observations of outcrop analogs can be the key to the challenge characterizing these sedimentary systems.