Macroscopic Description

The collected samples are fragments (loose debris) of what are probably individual concretionary layers/lenses. The specimens vary in length from 2 to 10 cm and in thickness from 2 to 7 cm (Fig. 3-9). The cone-in-cone structures are dark brown to black in color and often display a strong luster. Individual cones range in size from a few millimeters to 6 cm. Apical angles are variable and range from 30° to 60°. Scales on cone cups are well developed and may be as wide as 0.5 cm (Fig. 4 and 5). In thin layers, the cones have a strong tendency to telescope out of the sample surface (Fig. 9), whereas relatively thicker layers have an uneven relief formed by interference of large cone tops that project out from the bedding plane by 1 to 2 mm (Fig. 6). The bedding plane relief, thus, has a step structure formed by intersecting and overlapping circular arcs separated by argillaceous films (Fig. 7 and 9). These circular arcs are segments of the nested conical surfaces forming the cone-in-cone structure, and the intersection and interference of these conical portions produce the striated appearance of the cone surfaces (Fig. 3 and 7). Striae are generally straight

Fig. 10. Photomicrograph of two separate silicified layers in cone-in-cone structures (top) grown on layers of dark ferruginous material including shell fragments and detrital quartz (bottom). Apices of cone structures point downward in photograph, but original orientation is unknown. Dark gray to black areas contain argillaceous material that defines the conical layering (black arrows) and outlines plumose aggregates of former fibrous calcite. Minute, disseminated, dark spots are pyrite framboids (white arrow). Erfoud (Morocco) sample. Round spots are thin sectioning artifacts (bubbles; in lower part of photograph). Section cut parallel to cone axes. Plane-polarized light; scale bar length: 0.5 mm.

Pyrite Framboids

Fig. 11. Photomicrograph of two separate silicified layers of minute cone-in-cone structures grown in opposite directions from two different substrate beds and meeting in the middle of the photograph. The substrates are layers of dark ferruginous material including shell fragments and detrital quartz (at top and bottom). Erfoud (Morocco) sample. Round spots are thin sectioning artifacts (bubbles; in bottom right corner). Section cut parallel to cone axes. Plane-polarized light; scale bar length: 0.5 mm.

but, especially in the case of prominently telescoped cones, show a fan-like arrangement and rapidly widen in major parts of cones (Fig. 8).

The cones are silicified and do not have the tendency to break apart along curved surfaces (so-called "leaves" - Franks 1969), as is common for cone-in-cone structures in carbonate.

Cone Cone Structures

Fig. 12. Photomicrograph of silicified cone-in-cone structures grown on an unknown substrate. Apices of cone structures point to the left in photograph, but original orientation is unknown. Black areas contain argillaceous material and abundant pyrite and Fe-oxide/hydroxide that outline interference of nested conical surfaces. Erfoud (Morocco) sample. Section cut parallel to cone axes. Plane-polarized light; scale bar length: 0.5 mm.

Fig. 12. Photomicrograph of silicified cone-in-cone structures grown on an unknown substrate. Apices of cone structures point to the left in photograph, but original orientation is unknown. Black areas contain argillaceous material and abundant pyrite and Fe-oxide/hydroxide that outline interference of nested conical surfaces. Erfoud (Morocco) sample. Section cut parallel to cone axes. Plane-polarized light; scale bar length: 0.5 mm.

Fig. 13. Photomicrograph of cone-in-cone structures grown on layer of dark ferruginous material (bottom). Apices of cone structures point downward in photograph, but original orientation is unknown. Dark gray to black areas consist of argillaceous material that is particularly concentrated in angular patches corresponding to fillings of annular rings (arrows). Erfoud (Morocco) sample. Section cut parallel to cone axes. Plane-polarized light; scale bar length: 0.5 mm.

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