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The trace fossil Lepidenteron lewesiensis (Mantell, 1822) from the Upper Cretaceous of southern Poland

Jurkowska A., Uchman A.

Acta Geologica Polonica

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2013

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Vol. 63, no. 4

611--623

EN

Lepidenteron lewesiensis (Mantell, 1822) is an unbranched trace fossil lined with small fish scales and bones, without a constructed wall. It is characteristic of the Upper Cretaceous epicontinental, mostly marly sediments in Europe. In the Miechów Segment of the Szczecin-Miechów Synclinorium in southern Poland, it occurs in the Upper Campanian–Lower Maastrichtian deeper shelf sediments, which were deposited below wave base and are characterized by total bioturbation and a trace fossil assemblage comprising Planolites, Palaeophycus, Thalassinoides, Trichichnus, Phycosiphon, Zoophycos and Helicodromites that is typical of the transition from the distal Cruziana to the Zoophycos ichnofacies. L. lewesiensis was produced by a burrowing predator or scavenger of fishes. The tracemaker candidates could be eunicid polychaetes or anguillid fishes.

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Palaeoenvironmental significance of iron carbonate concretions from the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland

Witkowska M.

Acta Geologica Polonica

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2012

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Vol. 62, no. 3

307-324

EN

Iron carbonate concretion horizons are characteristic features of the Bathonian (Middle Jurassic) claystone-mudstone succession at Gnaszyn. They occur in single horizons, which generally represent the same genetic type. The siderite concretions are the main type of iron carbonate concretions at Gnaszyn; a second type is represented by phosphate-siderite concretions. On the basis of the fieldwork, and their petrographical and mineralogical characteristics, the genesis of the concretions and their palaeoenvironmental significance is discussed. The results of this study (based on the localization, mode of occurrence, mineralogy of iron carbonate concretions and also the textural relationship between the concretions and host sediment layers) suggest an early diagenetic origin of the concretions. The preferential occurrence of the concretion horizons in single layers in the ambient sediments was associated with particular conditions of their deposition and early diagenesis, favored by a slower sedimentation rate and more intense bioturbation, and related primarily to the greater availability of reactive iron ions. From the viewpoint of physicochemical conditions the horizons with iron carbonate concretions in the study area reflect the redox boundary between oxic/bioturbated and anoxic/non-bioturbated zones. The conditions favoring the formation of such horizons was possibly due to longer periods of diminished sedimentation rate when the redox boundary remained in the same position within the sediment.

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

Wetzel A.

Acta Geologica Polonica

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2010

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Vol. 60, no. 1

125-138

EN

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.