An exceptionally preserved conulariid from Ordovician erratics of Northern European Lowlands

Consuelo Sendino,Martin M Bochmann

doi:10.1007/s12542-020-00534-7

Abstract

A conulariid preserved in three dimensions from Ordovician fluvioglacial erratics of the Northern European Lowlands (North German Plain) is described under open nomenclature. It is assigned to the genus Conularia with similarities to Baltoscandian conulariids. The lithology of the erratic boulder and fauna contained in it provide important information on the origin and transport direction of the sediment preserved in a kame from the Saalian glaciation. This paper deals with the site of origin of the boulder in Baltoscandia analysing the comprised palaeofauna, from a palaeostratigraphic and palaeogeographic point of view, from its deposition in Ordovician times until its arrival at its current location in the Late Pleistocene. It also reveals for the first time the internal structure of the conulariid aperture.

Highlights

This article deals with a new conulariid form from an Ordovician erratic boulder collected in the Northern European Lowlands, NE Germany
A conulariid form from the Late Ordovician erratics of Brandenburg is described with a plicated closure allowing us to see, for first time, most of the internal part of the closure with rib continuation inwards
The detail of its exceptional preservation in the Baltoscandian epicontinental sea may imply a swift burial after an episode of relatively high energy in warm waters

Summary

Introduction

This article deals with a new conulariid form from an Ordovician erratic boulder collected in the Northern European Lowlands, NE Germany. There is a site on the island, Böda harbour (Böda Hamn), where abundant fossils preserved as internal moulds have been found These include conulariids and other palaeofauna such as Chasmops and illaenids, that are found as internal moulds in the erratic boulder found in the Brandenburg area. The Macrourus Limestone palaeofauna inhabited shallow pericontinental seas with an approximate latitude of 25°–28° S, close to the limit between temperate and tropical water faunal assemblages, and was associated with stormgenerated sedimentation This is confirmed by the calcareous lithology (Bergström and Ahlberg 2004), abundant chasmopine trilobite fauna characteristic of shallow-water platform deposits (McNamara 1980), the conulariid with semi-closed aperture preserved (see discussion below) and the different orientation of the organisms inside the boulder. Apical angle—is the angle formed by the corners of each face; intercostal angle—is the angle formed by a pair of ribs at the midline; rib inclination—is the complementary angle of a rib with the corresponding corner; length—is the distance from the apertural margin (at the midline if measurement possible) to the apex; face width—is the distance between the corners that border a face; transverse ribs density—is the number of ribs per 5 mm; node density—is the number of nodes per 1 mm on the ribs; longitudinal bar density—is the number of nodes per 1 mm on the ribs; ratio of the face width—at the apertural margin to the length of the specimen; and ratio of the shortest to the longest cross-section diameter

Material and methods

Findings

Conclusion