Radialimbricatus, a new ichnogenus from the lacustrine sandstone facies of the Lower Cretaceous Jinju Formation, South Korea

Abstract

Lee, D.-C. February 2017. Radialimbricatus, a new ichnogenus from the lacustrine sandstone facies of the Lower Cretaceous Jinju Formation, South Korea. Alcheringa XX, XXX–XXX.

The trace fossil Radialimbricatus igen. nov. with type species of R. bitoensis isp. nov. occurs in river-mouth-bar sandstone beds of a lacustrine sequence of the Lower Cretaceous Jinju Formation in South Korea. Radialimbricatus is a horseshoe-shaped or elliptical, convex hyporelief structure characterized by imbrication of traces with radial ridges and a median furrow. These features differentiate Radialimbricatus from arthropod ichnofossils such as Rusophycus and Cruziana, possibly cnidarian ichnofossils such as Astropolichnus and vermiform organism ichnofossils such as Oldhamia. Cross-sectional features of R. bitoensis, including upward mud protrusions at lateral margins, demonstrate that R. bitoensis can be formed as an open epigenic furrow at the water/mud interface or an endogenic burrow along the sand/mud interface at the same time. Analysis of discrete and imbricating horseshoe-shaped traces indicates that the tracemaker maintained an obligate inclined posture even when forming trails. The radial ridges and pit along the median furrow are interpreted to reflect feeding behaviour, and the imbrication to result from unidirectional and more or less regular movements to next feeding sites. The tracemaker is thought to have been an organism with an elliptical body outline, radially arranged body parts at the base of or around the body (probably for collecting and transporting foods and moving to feeding sites) and a mouth near the centre of the body, which is consistent with body plan features of arthropods, cnidarians and annelids.

Dong-Chan Lee [[email protected]], Department of Earth Sciences Education, Chungbuk National University, Cheongju, 28644, South Korea.

Key words:

• Radialimbricatus
• Lower Cretaceous
• lacustrine sandstone
• open furrow
• endogenic structure
• feeding

Acknowledgements

The author wishes to thank Radek Mikuláš and two anonymous reviewers for their constructive comments on the manuscript. The author also thanks Seong-Yeon Lee and Jeong-Seon Hwang in Chungbuk National University for assisting in specimen collection and thin-section preparation. This work was supported by the research grant of the Chungbuk National University in 2014.