Journal Article

Trace fossil tiering within event beds and preservation of frozen profiles; an example from the Lower Carboniferous of Menorca

Orr, Patrick J

1994

Overview

The recognition of habitat partitioning in ancient marine sedimentary sequences, via the development of a tiering profile, is an important part of the reconstruction of paleocommunities. Such tiering profiles are often established on the basis of either the cross-cutting relationships displayed by ichnofauna, or, the maximum, or characteristic, depths of their occurrence. However, a complete tiering profile may be preserved as a frozen profile. A change in the environmental conditions, for example upon rapid deoxygenation of the sediment profile, may result in the evacuation of the profile by the infauna and thus the production of a frozen profile. An alternative method of producing a frozen profile within event beds as a result of the nature of the depositional regime is proposed. The paleoichnocoenosis preserved in a sequence of inter-channel deposits from a middle-fan environment in the Lower Carboniferous of eastern Menorca provides an example of this latter method; a simple, two-tiered profile is preserved as a frozen profile. The upper tier is a thoroughly bioturbated layer, dominated by Nereites delpeyi Bourrouilh, 1973; this is underlain by a partially bioturbated layer characterized by Dictyodora liebeana (Geinitz, 1867), and Arthrophycus minoricensis (Bourrouilh, 1973). After initial colonization of the event bed and establishment of a tiering profile by the infauna, no succession of tiers occurred because the thickness of inter-event bed deposits was minimal. Deposition of the succeeding event bed resulted in rapid relocation of the infauna, leaving the previous tiering profile preserved as a frozen profile. This frozen profile is preserved intact because the thickness of the succeeding event bed was greater than the depth from the sediment/water interface to the base of the lower tier.

• Publisher: Society of Economic Paleontologists and Mineralogists,SEPM
• Subject: Arthrophycus minoricensis / Balearic Islands / Bedding / biogenic structures / Bioturbation / buried channels / burrows / Cabo de Favaritz Minorca / Carboniferous / case studies / communities / cross-stratification / deposition / Dinantian / Earth sciences / Earth, ocean, space / Europe / Exact sciences and technology / fluvial features / Geological facies / Geology / Grain size / Gravel / habitat / Iberian Peninsula / ichnofabrics / ichnofossils / interpretation / invertebrate / Invertebrate paleontology / lithofacies / Lithology / lithostratigraphy / Mediterranean region / Minorca / Nereites / Nereites delpeyi / Paleontology / Paleozoic / planar bedding structures / preservation / Research Letters / sed rocks, sediments / sediment-water interface / Sedimentary petrology / Sedimentary structures / sedimentation / Sediments / Southern Europe / Spain / Stratigraphy / submarine fans / Trace fossils