AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Facies and Fracture Distribution in the Miocene Cariatiz Reef Complex (Sorbas Basin, Southeast Spain)
(1) Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, Netherlands.
The Upper Miocene Cariatiz carbonate reef complex (CCR) is located at the northern side of the Sorbas basin in SE Spain The Sorbas Basin is one of a number of small Neogene basins that developed between emergent basement blocks during late phases of the Alpine orogeny in the Betic Cordillera. Bounded to the north by the Sierra de Filabres and to the south by the Sierra Alhamilla-Sierra Cabrera, which are metamorphic outcrops of the Internal Betic Zone, the narrow E-W elongate Sorbas Basin was infilled during the Middle Miocene. During the Late Neogene, it was marked by subsidence from the Tortonian to the Early Messinian, and exhumation from the Late Messinian until the present day.
The facies within the CCR consist of fine mud, marl and gypsum at the distal slope to coarse pack- to rudstone at the proximal slope. Latter deposits show a transition along well developed, steeply dipping clinoforms to coarse pack- to rudstones with occasional huge reef boulders at the upper slope. Colonies of Porites surrounded by algal mats tipify the reef frame work at the platform margin. The lagoonal facies is marked by smaller Porites colonies. The northern margin of the fringing reef system prograded over at least 1150 m.
The fractures show a distinct correlation between the sediment composition present along the CCR and the number of faults and their shape. The fractures were measured directly in the outcrop and georeferenced using a GIS Arcpad™ based measuring system. The majority of the fractures are oriented perpendicular to the strike of the platform margin. The main tendency in fracture development is an increase in the number of fractures in the coarser grained sediments. The ratio between mud and grains is a good indicator in this respect. Hence, a decrease in the number of fractures and an increase of fracture spacing occurs when moving from the reef framework facies to the distal slope facies, moving from to grain-supported sediments at the carbonate reef margin and upper slope to mud-supported sediments at the toe-of-slope and the basin. The fracture morphology also varies, especially within the reef, with straight fractures through well-layered sediments, the algal mats inbetween the Porites colonies, and curvy fractures along the outer borders of the Porites colonies, located at the reef rim.
The facies and fracture distribution within the CCR might help to understand the distribution and spacing of fractures within specific carbonate platform margins.