Stanisław Leszczyński

Trace-fossil tiering in flysch sediments: examples from the Guipúzcoan flysch (Cretaceous-Paleogene), northern Spain

Abstract Distribution of trace fossils in flysch sediments is in great part conditioned by tiering; that is, the vertical partitioning of trace-producing organisms below the sediment-water interface. Ichnologic studies in the Guipuzcoan flysch (Upper Albian-Lower Eocene), northern Spain, show that tiering in flysch sediments is strongly controlled by sediment character, mode and rate of deposition, and degree of oxygenation of pore waters. Depending on the mode of deposition, trace-fossil tiering in flysch developed and was preserved in two radically different styles: (1) In event layers (chiefly turbidites), tiering is preserved without secondary distortion, owing to synchronous colonization and the lack of vertical ascent through time. Vertical tiering structure depends primarily on sediment composition, sequence and thicknesses of structural divisions, and oxygen profile. Variations in tiering are interpreted to reflect the particular oxygen tolerances, penetration potentials, and nutritional requirements of tracemakers; (2) In background sediments (hemipelagites and pelagites), tiering resulted from successive colonizations that were influenced by background sedimentation rates, sediment composition, and oxygen levels of pore waters. Tiering of actively or passively filled burrows is reflected by complex ichnofabrics and the superposition of different tiers by ascension. Tiering structure was frozen upon deposition of superjacent event layers. The original tiering of graphoglyptids (open burrows) may be reconstructed from their cross-cutting relationships on turbidite soles. These contrasting styles of tiering development are characteristic of flysch and other sediments composed of alternating event and background deposits.

Ichnocoenoses of a turbidite sole

Specimens of 13 ichnospecies and their spatial distributions were analyzed on a spectacular cast of a turbidite sole surface (2.9 m2), from Eocene flysch of Spain. The distribution tends to be patchy. Except for postturbidite Granularia, no intraspecies overcrossing was observed. Overlapping and intersecting graphoglyptids indicate that they were formed at different times. This difference may result from (1) ecologic succession of their producers, (2) upward migration of a tiered community following sediment accretion, or (3) synchronous burrowing on the whole area, the specific places of occupation shifting with time.

Biogenic structures of organics‐poor siliciclastic sediments: Examples from Paleogene variegated shales, Polish Carpathians

The chiefly red and green (variegated), muddy to clayey sediments of the Polish Carpathian flysch display low diversity assemblages of macroscopic biogenic sedimentary structures (trace fossils). Plano‐lites and Chondrites are the most common distinctive traces in these sediments. A restricted food supply for tracemakers and low shear strength of sediments inhabited by them are suggested as the chief factors responsible for the low diversity of biogenic structures. Because of temporal fluctuations in rates of sediment accretion and/or changes in food supply some bioturbation occurred cyclically in what we are now the variegated shales.

Ichnocoenosis versus sediment colour in Upper Albian to Lower Eocene turbidites, Guipúzcoa province, northern Spain

Abstract Relative frequencies and penetration depth of distinctive trace fossils were examined in turbidites differing in colour. Distributional differences between particular sediment groups are interpreted to reflect primarily distinct nutritional and oxygen requirements of individual tracemaker taxa. The more tolerant a species was to oxygen deficiency the more distinct is the increase of its trace frequency towards deeper sediment levels. Traces produced by less tolerant species show a frequency increase down to certain depth levels, followed by a decrease toward still deeper levels. In turbidites containing dark gray to black fine-grained divisions, frequencies of all trace fossil taxa decrease towards deeper sediment levels, starting from about 1 cm below the turbidite top.

Trace fossils indicating bottom aeration changes: Folusz Limestone, Oligocene, Outer Carpathians, Poland

Abstract Bioturbation sequences in the pelagic Folusz limestone indicate deposition under decreasing bottom aeration, possibly in association with the development of microbial mats. U-shaped burrows Diplocraterion and Arenicolites exclusively were produced in the laminated limestone, and they represent the only colonizers (sessile suspension feeders) of the oxygen-deficient sediment.

A generalized model for the development of ichnocoenoses in flysch deposits

A systematic survey of intrastratal trace fossil distribution in flysch deposits shows that the ichnocoenoses form along two radically different modes: 1. Post‐turbidite ichnocoenoses begin with synchronous colonization. Further development of the tiered structure depends primarily on sediment composition, textural profile and oxygen levels. Different species respond to these factors according to their oxygen tolerances, penetration potentials and nutritional requirements. 2. Pre‐turbidite ichnocoenoses result from successional colonization, depending on the duration of background sedimentation. The depth of subsequent turbidite erosion determines which tier becomes preserved.

Origin and resedimentation of rhodoliths in the Late Paleocene flysch of the Polish Outer Carpathians

This study analyses the rhodolith-bearing deposits in the largest and most rhodolith-rich outcrop of the Polish Outer Carpathian flysch, located in the Silesian Nappe, at the village of Melsztyn. The rhodoliths and sparse associated biota occur as resedimented components in a deep-marine succession of siliciclastic conglomerates and coarse-grained sandstones, deposited by high-density turbidity currents and debris flows. The sediment was derived from a fan-delta system located at the southern margin of the Silesian flysch basin. Stratigraphic data indicate that the succession represents the Upper Istebna Sandstone deposited during the Late Paleocene. The rhodoliths are composed mostly of coralline red algae with seven genera and eight species representing the family Sporolithaceae and the subfamilies Mastophoroideae and Melobesioideae. Rhodoliths show sub-spheroidal and sub-ellipsoidal shapes with encrusting, warty and lumpy growth forms. Lumpy growth forms show massive inner arrangements, whereas the encrusting growth forms are usually made of thin thalli and show more loosely packed inner arrangements. The rhodoliths grew on a moderately mobile siliciclastic substrate in a shallow-marine environment with a low net sedimentation rate. It is inferred that the growth of rhodoliths was favored during a relative sea-level rise. During the subsequent sea-level fall, the rhodoliths and associated siliciclastic deposits were resedimented by gravity flows into the deep-sea setting. The analyzed deposits, like other Paleocene–Eocene deposits of the Polish Outer Carpathians, provide no evidence of coeval widespread shallow-marine carbonate sedimentation along the margins of the Outer Carpathian flysch basins.