Sequential colonization of muddy turbidites in the Eocene Belovez Ïa Formation, Carpathians, Poland A. Wetzel a, * , A. Uchman b a Geologisch-Pala Èontologisches Institut der Universita Èt, Bernoullistrasse 32, CH-4056 Basel, Switzerland b Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, PL 30-063 Krako Âw, Poland Received 23 February 2000; received in revised form 12 September 2000; accepted for publication 23 October 2000 Abstract A 100±350-m- thick succession of centimeter-thick ®ne-grained turbidites form the lower, mud-dominated part of a prograd- ing deep-sea fan in the Eocene Belovez Ïa Formation in the Carpathian Mountains of Poland. These strata contain over 50 ichnotaxa, only six of which are common (Phycosiphon, Nereites, Chondrites, Scolicia, Halopoa, Ophiomorpha). Polished slabs and examination of cross-cutting relationships show that post-event colonization was sequential. Using modern analogues, it can be shown that the colonization of different depth levels in the sediment at different times re¯ects changing geochemical conditions, especially the re-adjustment and re-establishment of the redox boundary. Modern analogues allow an assessment of the timing of each colonization phase. The Phycosiphon producers entered ®rst and occupied the well-oxyge- nated muds, 5±40 mm below the sediment surface. As the redox boundary reformed, Nereites producers entered and probably utilized microbial matter just above the redox boundary, about 15±30 mm below the sediment surface. Subsequently, Chon- drites producers penetrated down to the oxygen-de®cient layers of the event bed or even deeper levels. The Halopoa producers entered with Phycosiphon, but reworked coarser layers. Contemporaneously with this sequential colonization, deep permanent bioturbators, which were unaffected by the event, cross-cut the post-depositional suite. The variability of the resultant ichno- fabrics can be attributed in part to a patchy distribution of the benthos and the relative frequency of turbidite events. Five ichnofabrics, which re¯ect the successive colonization episodes, are recognized; each was modi®ed by elements of the permanent infauna. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Ichnofabrics; Turbidites; Colonization; Eocene; Poland 1. Introduction Thick turbidite successions deposited on active continental margins have long attracted paleontolo- gists because of their wide variety of trace fossils, in particular the very highly organized and patterned trace fossils that are called graphoglyptids (Fuchs, 1895) and are typically preserved on the base of sandy turbidites. Interest in the trace fossils rapidly grew when the origin of turbidites became clear, and ichnological research revealed the utility of trace fossils in recognizing various sub-environments of deep-sea fans (Seilacher, 1962, 1974, 1977; Crimes, 1973, 1976; Crimes et al., 1974; Ksia Îz Çkiewicz, 1977). Crimes and Fedonkin (1994) noted that submarine canyons and the inner parts of fans commonly contain a low-diversity ichnofauna with a preponderance of shallow-water types; middle fan sub-environments have a mixed ichnofauna of shallow-water and Palaeogeography, Palaeoclimatology, Palaeoecology 168 (2001) 171±186 0031-0182/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0031-0182(00)00254-6 www.elsevier.nl/locate/palaeo * Corresponding author. E-mail address: andreas.wetzel@unibas.ch (A. Wetzel).