Graptolites from glacial erratics of the Laerheide area, northern Germany

Jörg Maletz,Heinrich Schöning

doi:10.1007/s12542-017-0345-9

Abstract

Ordovician and Silurian glacial erratics of the Laerheide area (Lower Saxony, north-western Germany) bear well-preserved graptolites. The faunas provide important information on the origin and transport direction of the sediments preserved in a kame, representing the Drenthe stadial of the Saalian glaciation. The faunas even include species not commonly encountered in the successions of mainland Sweden, from where the erratics presumably originated. The most common graptolites are from Upper Ordovician (Sandbian to Katian) limestones and from Katian black shales. More common, however, are greenish limestones, sand- and siltstones, often combined in the term ‘Grünlich-Graues Graptolithengestein’, in which upper Wenlock to Ludlow (upper Silurian) graptolites are common.

Highlights

Fossil-bearing glacial erratics have long been used to document transport and flow directions of glacial ice sheets from the place of origin of the material (e.g. Roemer 1862, 1885), even though modern methods like satellite imaging are superseding this seemingly ‘old-fashioned’ method (e.g. Boulton et al 2001)
These identify unambiguously the age of the sedimentary rocks and their origin if the sedimentary rock types are still exposed in the area of their origin. Spectacular fossils such as Xenusion auerswaldae Pompeckj, 1927 have been found in glacial erratics, and new taxa are even being described from glacial(?) erratics originating from the Palaeozoic succession of Scandinavia (e.g. Botting and Rhebergen 2011)
Kowalski (1964, 1966a, b, 1968a, b, 1969, 1984) provided overviews on the graptolites found in glacial erratics in a number of short review papers

Summary

Introduction

Fossil-bearing glacial erratics have long been used to document transport and flow directions of glacial ice sheets from the place of origin of the material (e.g. Roemer 1862, 1885), even though modern methods like satellite imaging are superseding this seemingly ‘old-fashioned’ method (e.g. Boulton et al 2001). Kowalski (1964, 1966a, b, 1968a, b, 1969, 1984) provided overviews on the graptolites found in glacial erratics in a number of short review papers These show the most important taxa encountered, but the illustrated material is often not specimens of glacial origin, but based on available published illustrations from various sources, and may be misleading. Glacial erratics with Ordovician graptolites are either rarely encountered or have not attracted much attention, even though they may bear excellently preserved faunas and even provide information on taxa not known from other sources This is shown by the descriptions of Archiretiolites regimontanus by Eisenack (1935) and Corynites wyszogrodensis by Kozłowski (1956) (Fig. 1d), species that have been found only once or twice and are unknown from successions in situ. Monograptids from chemically isolated material, and Eisenack (1942) named the sinus and lacuna stages of this development based on specimens he identified as Monograptus ( Pristiograptus) frequens Jaekel, 1889

The Laerheide locality

Ordovician graptolites

Silurian graptolites

Saetograptus chimaera