Abstract
AbstractArumberia is an enigmatic sedimentary surface texture that consists of parallel, sub-parallel or radiating ridges and grooves, most commonly reported from upper Neoproterozoic – lower Palaeozoic strata. It has variably been interpreted as the impression of a small metazoan, a ‘vendobiont’, a physical sedimentary structure formed on a substrate with or without a microbial mat covering, or a non-actualistic microbial community. In this paper we contribute new insights into the origin of Arumberia, resulting from the discovery of the largest contiguous bedding plane occurrence of the texture reported to date: a 300 m2 surface in the lower Cambrian Port Lazo Formation of Brittany, NW France. We compare the characteristic features of Arumberia at this locality with 38 other global records, revealing four defining characteristics: (1) the three-dimensional (3D) morphology of exposed Arumberia lines (either positive relief ‘ridges’ or negative relief ‘grooves’) records fully preserved cords within clay laminae; (2) lines may transition laterally into reticulated patterns; (3) characteristic parallel and sub-parallel Arumberia lines can become modified by desiccation on emergent substrates prior to interment; and (4) Arumberia are streamlined with palaeoflow in successions showing evidence of unidirectional currents, but are organized parallel to ripple crests where strata were sculpted by oscillatory flows. These characteristics indicate that Arumberia records a 3D entity, distinct in material properties from its host sediment, which occurred in very shallow water settings where it was prone to passive reorganization in moving water, and desiccation when water drained. A literature survey of all known Arumberia occurrences reveals that the most reliable examples of the form are stratigraphically restricted to a 40 Ma interval straddling the Ediacaran–Cambrian boundary (560–520 Ma). Together these characteristics suggest that Arumberia records the remains of extinct, sessile filamentous organisms (microbial or algal?) that occupied very shallow water and emergent environments across the globe at the dawn of the Phanerozoic Eon.
Highlights
Arumberia is a sedimentary surface texture comprising a series of low-relief, sharply defined sub-parallel lines (Fig. 1), which is often recognized on Precambrian and lower Palaeozoic bedding planes
It was originally reported from the Ediacaran Arumbera Sandstone of Australia by Glaessner & Walter (1975), who interpreted it as an impression fossil of a small cup-shaped metazoan
While we agree that there is the potential for a microbial role in the formation of this surface structure, we argue that the 3D morphology of individual lines indicates that they preserve casts of fossil organisms, rather than modifications of sedimentary surfaces
Summary
Arumberia is a sedimentary surface texture comprising a series of low-relief, sharply defined sub-parallel lines (Fig. 1), which is often recognized on Precambrian and lower Palaeozoic bedding planes It was originally reported from the Ediacaran Arumbera Sandstone of Australia by Glaessner & Walter (1975), who interpreted it as an impression fossil of a small cup-shaped metazoan. Our literature survey has been groundtruthed by field visits to six of these Arumberia-bearing formations (Table 1; the Arumbera Sandstone of Northern Territory, Australia; the Crown Hill, Ferryland Head, Gibbett Hill and Maturin Ponds formations of Newfoundland, Canada; and the Synalds Formation of Shropshire, England)
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