Psilonichnus upsilon Frey, Curran and Pemberton, 1984 burrows and their environmental significance in transgressive Albian (Lower Cretaceous) sands of Glanow-Stroniczki, Cracow Upland, southern Poland

A considerable Upper Albian sand lithosome, developed on the external margin of the Albian epicontinental sea in the Polish Jura Chain (Miechow Synclinorium, southern Poland), is recognized as a shallowing-up sequence within the generally transgressive Albian sands. In particular, burrows described as the ichnospecies Psilonichnus upsilon Frey Curran and Pemberton, 1984 have a particular ecologic and sedimentological significance, and constitute the primary focus of this paper. In the Glanow-Stroniczki section (Cracow Upland, southern Poland), such burrows seem to be a crucial tool in the interpretation of basin bathymetry, indicating a foreshore to backshore (beach) facies and probably recording a temporary break in sedimentation. They were infilled by sand with pebbles or pebble material, potentially during hurricane or strong storm action. Lithification of the burrow infillings and their enveloping concretionary halos should have progressed in a beachrock mode. The Glanow horst, composed of Jurassic biohermal limestones, was likely an emerged element that neigboured, or was surrounded by, a beach with active fauna. The Psilonichnus upsilon burrows in Glanow-Stroniczki closely resemble burrows of the modern ghost crab Ocypode. In modern settings, representatives of Ocypode are encountered in extremely shallow marine (foreshore/intratidal and backshore/supratidal) to dune environments. The ichnological data from Glanow-Stroniczki suggests that fauna behaviorally similar to Ocypode may have occupied the beach backshore (and to a lesser extent the foreshore) zone near the emerged Glanow horst.