Joint Spacing as a Consequence of Depositional Environments and Diagenetic History: An Example from Miocene Layered Carbonates (Granada Basin, Spain)

Rustichelli, Andrea ¹; Agosta, Fabrizio ²; Tondi, Emanuele ¹
(1)Geology Division, School of Science and Technology, University of Camerino, Camerino, Italy. (2) Department of Geology, Basilicata University, Potenza, Italy.

In the past, many studies have shown that, within relatively undeformed sedimentary rocks, the bed-perpendicular joint spacing is largely controlled by the bed thickness. This type of joints are usually contained within one or more beds, terminating against the bed surfaces. In literature, it has also been documented that, considering a linear elastic rock behaviour, the bed-perpendicular joint spacing is also affected by the mechanical rock properties such as the Young’s modulus and the Poisson’s ratio. Recently, a few articles addressed the control exerted by depositional and diagenetic features on the mechanical rock properties and, hence, on bed-perpendicular joint spacing.

In this contribution we present the results of an integrated sedimentological-structural study conducted on bryozoan-dominated, skeletal grainstones and rudstones cropping out in the Granada Basin, Spain. These Tortonian layered carbonates were deposited within different sectors of a beach-like environment, which were characterized by specific biological (e.g. flourishment of bryozoan colonies) and sedimentary processes (i.e. fair weather vs. storm wave action).

By means of stratigraphic/sedimentological field and laboratory analyses (i.e. optical microscopy and digital image analyses), we investigate the relationships among intrinsic rock parameters such as size, sorting and shape of grains and diagenetic processes such as cementation and dissolution, and identify the principal controls on the resulting rock petrophysical properties (porosity and Uniaxial Compressive Strength). After a quantitative fracture analysis, we also document the role exerted by the following variables: (i) depositional environment, (ii) biological and (iii) depositional processes, (iv) diagenesis, (v) petrophysical and (vi) mechanical properties of skeletal grainstones and rudstones on the bed-perpendicular joint spacing.

Depositional environment conditions such as water temperature, wave regime and siliciclastic input are inferred to be the main controlling factors for both flourishment and growth form of biota (i.e. bryozoans). On the other hand, the wave regimes are inferred to be responsible for both destruction of bryozoan colonies and subsequent selective redistribution of skeletal sediment along the beach floor and, subsequently, for the whole diagenetic evolution. All these factors affect the rock petrophysical properties and, consequently, the joint distribution within the layered carbonates.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.