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Unusual echinoid resting trace records change in the position of the redox boundary (Palaeogene of the Lesser Caucasus in Georgia)

Uchman Alfred, Lebanidze Zurab, Kobakhidze Nino, Beridze Tamar, Makadze Davit, Lobzhanidze Koba, Khutsishvili Sophio, Chagelishvili Rusudan, Koiava Kakha, Khundadze Nino

Acta Geologica Polonica

2022

Vol. 72, no. 3

317--330

The first recognition of a tracemaker responding to a temporary shift in the redox boundary is recognized. This is recorded by a new trace fossil, Sursumichnus orbicularis igen. et isp. nov., which is established for mound-like structures on the upper surfaces of sandstone beds from the Borjomi Flysch (upper Paleocene–lower Eocene) in the Lesser Caucasus (Georgia). It is connected with the spatangoid echinoid burrow Scolicia de Quatrefages, 1849 and interpreted as a resting trace of the same tracemaker produced after moving up from a deeper position within the sediment. The resting is caused by an episode of unfavourable conditions related to shallowing of the redox boundary. The trace fossil is a component of the Nereites ichnofacies.

Deep-sea ichnology : observations in modern sediments to interpret fossil counterparts

Wetzel A.

Acta Geologica Polonica

2010

Vol. 60, no. 1

125-138

Extensive areas of the abyss represent a dynamic environment experiencing seasonally strongly fluctuating organic-matter deposition that in turn affects the oxygen content of the pore water. At high organic-matter deposition, oxygenation of the pore water decreases and forces organisms respiring this water to move upward. Thus, times of benthic food richness on the seafloor affect the behaviour of endobenthic organisms; aside from deep-deposit feeding, temporary surface feeding (including unselective bulldozing) represents an additional nutritional strategy. This has been shown for the producers of Nereites and Scolicia as well as Thalassinoides and Zoophycos, the latter two have an open tube. Each of these activities leads to intense sediment mixing and prevents or disturbs the formation of near-surface burrows including graphoglyptids. The distribution of organic matter in the sediments is reflected by the orientation and geometry of Phycosiphon. Quantity and quality of food appear to be related to abundance and size of Scolicia. Food selectivity, the ability of selective feeding and organism mobility all appear to be important factors in benthic ecology, however, they are as yet little known. To use the full potential of uniformitarian studies relying on cores taken in soft sediments, they should be based on X-ray radiographs, contain information about the timing of burrow production and focus on ichnotaxonomically determinable burrows.

Abyssal epibenthic megafauna of the Clarion-Clipperton area (NE Pacific): Changes in time and space versus anthropogenic environmental disturbance

Radziejewska T., Stoyanova S.

Oceanological Studies

2000

Vol. 29, No. 2

83-101

Abyssal epibenthic megafauna was used as one of biological indicators of the effects of anthropo-genic sediment disturbance in the Benthic Impact Experiment (BIE) carried out within 1994-1997 by the Interoceanmetal Joint Organization (IOM) in the Clarion-Clipperton Fracture Zone (NE Pacific). Analysis of bottom photographs collected from 14 phototransects measuring about 2-10 km in length, made during three cruises, yielded data on the composition and abundance of the epi-benthic megafauna in nodule-bearing (N) and nodule-free (NF) areas of the bottom. The latter included a site at which experimental sediment disturbance, mimicking that produced by nodule mining, was induced. Megafauna was studied before (October 1994, July 1995) and immediately after the disturbance (July 1995), a follow-up survey being performed in April 1997, i.e., 22 months after the original disturbance. Characteristic differences in megafaunal composition and abundance between the two habitat types (N vs. NF) were recorded, the N bottom megafauna being consistently more abundant and dominated by sessile invertebrates (mainly sponges), while the NF megafauna showed a preponderance of mobile deposit feeders (holothurians). The megafaunal abundance in both habitat types showed differing patterns of temporal changes: while the abundance in the NF areas declined sharply immediately after the disturbance and markedly increased 22 months later, the N megafauna abundance was observed to increase from one survey to the next. Due to the fact that the sediment sampled in April 1997 showed evidence of a substantial phytodetritus input, the increase in the megafaunal abundance, recorded in both habitat types at that time, is assumed to reflect mainly the increase in the benthic food supply, superimposed in the NF transect sections on natural processes of recolonisation, proceeding in the disturbed areas of the bottom.