Ninth international conference on - Marum

74
Abstracts of posters
Controlling factors on the morphology and spatial distribution of hydrocarbon-related tubular
concretions – study of a Lower Eocene seep system
E. De Boever 1 , M. Huysmans 1 , R. Swennen 1 , P. Muchez 1 , L. Dimitrov 2
1 K.U.Leuven, Department of Earth and Environmental Sciences. 3001 Heverlee (Leuven), Belgium
2 Institute of Oceanology (IO-BAS), P.O. Box 152, 9000 Varna, Bulgaria
Tubular, calcite-cemented sandstone concretions, which are exceptionally well exposed in the Pobiti Kamani
area (Varna, Bulgaria) are the subsurface geological product of Lower Eocene methane-related fluid migration.
Tubular concretions were classified in five field-based morphological types and the position of individual tubular
concretions, together with their characteristics, were mapped in detail on a scale of several 100m² at three
selected locations. Concretion growth and morphology were primarily controlled by a buoyancy-driven,
vertically upward directed fluid flow through the rather homogeneous sandy host sediments. Their morphology
was additionally influenced by differences in the depositional/diagenetic fabric affecting the fluid path and
assumed changes in the fluid flux.
GPS-mapping of the positions of tubular concretions within individual clusters (fig. 1) strongly suggests that
focused fluid migration is controlled by the Paleogene structural framework whereby the detailed spatial
distribution of the tubes mimics the typical geometry of deformation structures in fault damage zones in loose
sediments. A geostatistical data analysis of tube contour data confirms the spatial cluster structure. The
directions of maximal spatial correlation of “tube contours” (m) (over distances >100m) are interpreted as an
indication for the continuity of fluid flow characteristics over a certain distance and time along specific
lineations.
Fig. 1: Strashimirovo group. (A) Cluster geometry and mapped tubular concretions with indication of tube
type. (B) Rose diagram of the strikes of connection lines between two distinct tubular concretions. (C)
Experimental and modelled omnidirectional variogram (n = 126; lag distance = 15m) demonstrates the
presence of a spatial structure in the distribution of tubular concretions.