COMPILATION OF A DEVONIAN BIOSTRATIGRAPHIC COMPOSITE STANDARD SECTION AND ITS USE AS A CALIBRATION TOOL FOR MAGNETOSUSCEPTIBILITY EVENT AND CYCLOSTRATIGRAPHY DATA FROM MOROCCO, NORTH AFRICA

Using published biostratigraphic data for several Devonian stratigraphic sections in North Africa, Europe, and Asia; we have used graphic correlation to compile a Devonian composite standard section (CSS). The CSS has been used to calibrate Devonian magnetosusceptibility event and cyclostratigraphy (MSEC) data obtained from the Bou Tchrafine (BT), Jebel Amelane (JA), and Jebel Issimour (JI) sections of Morocco. The calibration process demonstrates the refined correlation potential of the MSEC data.

Magnetic susceptibility (MS) is a measure of the degree to which a substance can acquire a magnetization when placed in a weak magnetic field, and the MSEC method is based on vertical MS variations in stratigraphic sections. Typically, for a given section, the section's biostratigraphic data supplies the calibration framework for zonation of the section's MSEC curve.

The CSS was constructed using a modified version of Shaw's (1964) graphic correlation technique. Among the study sections, the Igaroldy section, Tajikistan, Central Asia was selected as the standard reference section (SRS- section into which the biostratigraphic data from the other study sections are compiled) because it has a diverse and abundant marine fauna, the thickest stratigraphic interval, and strata representative of all Devonian stages. Forty five Devonian sections from North Africa, Europe, and Asia were compiled into the SRS to give a CSS containing range data for approximately 2,000 taxa.

Projection of key biostratigraphic horizons from the CSS into the BT, JA, and JI MSEC curves provides an improved calibration framework on which MSEC zones can be defined. A critical aspect of this process is that, for a given section, the fossil appearance determining a horizon need not be present for the horizon to be placed in the section's MSEC curve. In most cases, the MSEC zonation supplies a refined correlation potential relative to the biostratigraphy of each section. Also, it is important to note that CSS horizons have a degree of uncertainty. This uncertainty results from the fact that, in some cases, the position of lines of correlation are not tightly constrained.