Giant burrows in the Quaternary Limestones of Futaysi Island and Al Dabb'iya, Abu Dhabi Emirate

Pleistocene carbonates along the northern coasts of Futaysi Island and Al Dabb'iya tombolo, Abu Dhabi, U.A.E., contain unusual calcirudite-filled structures which are bowl- and funnel-shaped in vertical section; roughly circular in plan view; up to 1 m in diameter and 1 m deep. The calcirudite infill is dominated by clasts of reworked lithified smaller burrows and what appear to be fragments of beach rock or hardground. These structures were previously interpreted as marking the sites of former trees with holes, left behind by their root balls, infilled by a storm deposit and were considered to indicate an emergent event marking the boundary between two Pleistocene sedimentary sequences represented by the Futaisi (Futaysi) and Dabb’iya Members of the Fuwayrit Formation. However, they are here re-interpreted as giant burrows formed by some, as yet, unknown marine animal probably foraging for food or using them as dwelling sites which contained storm deposits emplaced in shallow water. Thin crusts on top of some giant burrow infills possibly suggest emergence and this would require a repositioning of the sequence boundary between the Futaysi and Dabb’iya Members. The burrows are believed to have been formed at approximately 75–125 Ka.