Eathie Fishing Station

[NH 779 635]

Introduction

This site has yielded a well-preserved Kimmeridgian (Late Jurassic) assemblage of conifers, bennettites and cycads. Significantly, the fossils are preserved as permineralizations, showing fine detail of their internal cell structure. They include some of the best examples of bennettite flowers ever to have been found as well as some finely preserved conifer cones. Remarkably the flora has not been studied since the early 20th century and is in serious need of revision.

Miller (1857) first described the plant petrifactions at Eathie and his specimens are now nearly all in the collections of the Royal Scottish Museum, Edinburgh. Richards (1884) published a short account on Miller's cycadean species, but it was not until early in the 20th century that they were looked at again by Seward (1911, 1912) and Seward and Bancroft (1913). There has been little attempt to re-examine this site and its fossils, which is rather remarkable in view of the small number of petrifaction sites that exist in rocks of this age.

Description

Stratigraphy

The exposed succession here is summarized in (Figure 5.8). Cope et al. (1980a) dated it as Kimmeridgian, based on the work of Waterstone (1951) and Ziegler (1962). There are green mudstones at the base with some thin limestone nodules and bands that belong to the Rasenia cymodoce Zone. The plant petrifactions most probably come from this part of the succession. The higher beds yield a fauna of Amoebites and raseniids characteristic of the upper part of the R. cymodoce Zone and the basal Aulacostephanoides mutabilis Zone. Fossiliferous nodules, containing the ammonite Pictonia baylei, have also been found 10 km to the north of Eathie, indicating that the basal Kimmeridgian strata are preserved offshore in this region.

Palaeobotany

The plant fossils are preserved as petrifactions and reveal a considerable degree of anatomical detail (Figure 5.9). Miller considered that he had three species of conifer cones and a number of different conifer shoots. Seward (1911) named the shoots as his new species Taxites jeffryi. Others Seward named as Elatides curvifolia (Dunker) Nathorst, and Sphenolepidium cf. kurrianum Dunker, although it is not clear if these come from Eathie. He also named isolated cone scales as Araucarites milleri after Miller. Miller's imbricated stem (Miller, 1857, fig. 149) was described by Seward and Bancroft (1913) as a new species, Brachyphyllum eathiense. In the same paper, they named Miller's conifer cones as two new species, Masculostrobus woodwardii and Conites juddii (the latter in four forms).

Miller described cycad-like foliage under the name of Zamites pectinata and figured two cones that he thought might belong to a cycad intermediate between the fertile apices of Cycas revoluta and the cones of Zamia pungens. One of his leaves (Miller, 1857, fig. 133) was named Zamites eathiensis by Richards (1884) and then Pseudoctenis eatbiensis by Seward (1911). The other (fig. 134) was named Nilssonia orientalis Heer by Seward (1911). The cycad-like cones were described in another paper by Seward (1912) as Williamsonia pecten (Phillips), which is in fact a bennettite fructification.

Interpretation

The site has yielded a well-preserved assemblage of Kimmeridgian (Late Jurassic) plant petrifactions, consisting of the remains of conifers, bennettites and cycads. They preserve fine detail of the internal cell structure. Of particular interest are the bennettite flowers known as Williamsonia scotica Seward, which are among the best-preserved examples of such organs. Well-preserved conifer cones have also been described from here, including Maculastrobus woodwardii and Conites juddii. The flora has not been studied since the early 20th century and is in serious need of revision. It is a site of considerable potential for understanding the detailed structure of the Mesozoic gymnosperms.

The permineralized plants at Eathie must have been fragments that were carried into the sediments now represented by the green mudstones. Carbonates forming the limestone in bands within the mudstones would also have penetrated and preserved the plant fragments and formed nodules around them.

The flora is difficult to compare directly with the other Scottish Jurassic assemblages because it has been preserved in a different way. The only other locality where there are permineralized plants is at Helmsdale. Unlike the other localities, Eathie is dominated by both bennettites and conifers.

Conclusion

Eathie Fishing Station is an outstanding site for Kimmeridgian permineralized plants with four species of gymnosperms having been named from here. The presence of permineralized Williamsonia flowers and bennettite leaves, as well as conifer shoots, and cones makes it an extremely valuable succession for the study of these plants and is a site worthy of future investigation, especially for understanding the detailed structure of the Mesozoic gymnosperms.

References