Pustaka Ilmiah Universitas Padjadjaran

Abstrak

The Tectonic Control on the Formation of Cleats in the Coalbeds of Sajau Formation, Berau Basin, Northeast Kalimantan

Some Pliocene lignite-sub bituminous seams are characterized by the presence of natural discontinuities, so-called cleats. Most often they are opening-mode fractures, consisting of two orthogonal sets (face and butt), both almost perpendicular to the bedding. This paper determines distributions of cleat orientation, spacing, and aperture from the Sajau lignite seams. All observations and measurements were conducted at macroscopic, mesoscopic and microscopic scale. The butt cleats’ mean orientations are NE–SW, NW-SE; whereas mean orientation of face cleats NNE-SSW and NE–SE, dipping at a high angle N75°. The angle between strikes of cleat sets is nearly 90°. The spacing of macro face cleats is from 9.52 to 14.46 cm (averaging 11.61 cm) and the spacing of butt cleats is from 2.3 to 11.3 cm (averaging 5.35 cm), and the aperture has a mean 0, 54 cm On the other hand, the mean spacing of microcleats 1.58 mm and aperture measurements of these cleats range from 0.021 to 0.029 mm (averaging 0.026 mm), respectively. The obtained results from outcrop and micro CT Scan Tomography clearly indicate that face cleat orientations NNE–SSW are strictly parallel to the elongation of the main tectonic structures in the study area. Their origin may be explained in at least there was relationship with local tectonic (the maximum principal stress, σ1, was horizontal). The Partial Least Square analysis, of cleat and faults data in this area indicate that a power-law distribution exists between cleats characteristics (spacing, density and aperture) with the distance of faults ( R2 = 0.56). The cleat formation in Sajau Formation was mainly controlled by mechanical in response to tectonic. Based on SEM photography; the origin of cleats in Sajau Formation area endogenic process and tectonic activity which indicated by change the shape of the cleats; from the straight line cleats to curved shape and branching.