Elemental Chemostratigraphy, Isotopic Chemostratigraphy and Magnetic Susceptibility Stratigraphy of a Prograding Reef Complex Using Well Exposed Cliff Sections through the Upper Miocene Llucmajor Platform, Mallorca, as an Example

Carbonate reef complexes in the sub surface are stratigraphically challenging. Often, “traditional” stratigraphic methods employed in the petroleum industry, such as biostratigraphy, seismic stratigraphy and log correlation, do not provide the high-resolution, chronostratigraphically grounded correlation frameworks required for efficient reservoir exploitation. Therefore, “alternative” stratigraphic correlation methods are increasingly being used for subsurface stratigraphic correlation. However, using “alternative” methods in otherwise stratigraphically poorly constrained subsurface settings, presents a conundrum; since “traditional” methods cannot provide a correlation, there is no control on the significance of any “alternative” stratigraphic correlation. Therefore, a chemostratigraphic correlation, for example, may be correlating facies, or it may be recognizing temporal surfaces, but it is impossible to know which.

Here, two “alternative” stratigraphic methods that are being increasingly applied in the subsurface, elemental chemostratigraphy and magnetic susceptibility stratigraphy, together with the somewhat more established stable isotope stratigraphy are applied to Late Miocene-age reef complex deposits of the Llucmajor Platform, Mallorca. These reef complexes are well exposed along 4km of sea cliff sections at Cap Blanc in the south of Mallorca. Along the length of this exposure, slope and open shelf deposits are clearly prograded over by reefs and subsequently by mid to outer lagoon and inner lagoon sediments. A total of 280 samples from 8 measured sections through these sequences have been analysed for their elemental compositions (10 major elements, 23 trace elements and 13 rare earth elements), their carbon and oxygen isotope compositions and their magnetic susceptibility.

Due to the excellent exposure in the cliff sections, the response of each dataset to changes in depositional facies versus potential chronostratigraphically significant changes can be determined. Therefore, for the first time, it is possible to test the chronostratigraphic significance of “alternative” stratigraphic methods through a back reef, reef top, fore reef depositional sequence. The results of this work will provide an insight as to the applicability and stratigraphic significance of chemostratigraphy (elemental and isotopic) and magnetic susceptibility in subsurface reef complexes.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California