Evolutionary trend of Zoophycos morphotypes from the Upper Cretaceous–Lower Miocene in the type pelagic sections of Gubbio, Italy

Abstract

About 200 Zoophycos specimens, including 90 specimens studied in detail, have been analysed in the continuous Upper Cretaceous–Lower Miocene pelagic sedimentary type sections of the Gubbio area (the Contessa Highway, Contessa Quarry and Bottaccione sections, Northern Apennines). The sediments are reddish to grey limestones and marls of the Scaglia Group and marls with volcaniclastic deposits of the Bisciaro Formation. The aim was to examine the evolutionary trend of what is probably the most debated trace fossil of all time, from the Upper Cretaceous to Lower Miocene. Despite having been found in beds ranging from the Cambrian to the present, no consensus has been reached regarding mode of construction, tracemaker or ethological explanation for Zoophycos. Four Zoophycos morphotypes are recognized at Gubbio showing variations of major and minor lamellae, apex, lobes and whorls: the Cretaceous–Eocene cone‐shaped type 1, the Upper Eocene–Middle Oligocene helicoidal type 2, the Oligocene lobate type 3 and the Upper Oligocene–Lower Miocene flat type 4. The very high ichnodensity in some beds (hundreds of specimens in discrete levels of the Bisciaro Formation, now destroyed by quarrying) seems to find explanation in abnormal concentrations of phytodetritus and organic matter on the seafloor in some periods. This very high abundance in discrete levels reflects a change in sedimentation and seafloor conditions at pre‐flysch deposition. Due to such high ichnodensity, many adjacent specimens display deformed outer margins. Taphonomic analysis shows a variation of whorls, laminae and U‐shaped lobes, reflecting ontogenetic development of the tracemaker(s) (?sipunculid worms).

Zoophycosin storm-affected environments: a case study from lower Maastrichtian deposits of the Mateur-Beja area (Northern Tunisia)

“…Zoophycos represents a multilobate spreite burrow usually composed of several elementary or "basic lobes". The latter were evaluated to distinguish and to classify the various Zoophycos morphotypes while considering morphology of lobes, major lamellae, minor lamellae, and marginal tubes as main structural elements (Zhang, Fan, et al 2015;Zhang, Shi, and Gong 2015;Monaco et al 2017).…”

“…Most of these traces are multilobate and are composed of several lobes that are connected to a shaft. Four main structural elements were used to differentiate the burrow morpholoy;  basic lobe -a protrusive spreite extending beyond the apex that is repeatedly produced to construct the burrow (e.g., Monaco et al 2017);  marginal tube -remnant of the spreite causative tube outlining a lobe externally (e.g., Wetzel and Werner, 1980);  major (or primary) lamellae -elongated ribs extending from the apex to the marginal tube (e.g., Zhang, Shi, et al 2015), and major interspaces -elongated concave groove-like structures, parallel to the major lamellae and extending from the apex to the marginal tube;  minor lamellae -crescent-shaped, obliquely oriented laminae between the major lamellae (e.g., Olivero and Gaillard 2007).…”

“…The conspicuous trace fossil Zoophycos is reported from ancient and modern marine environments (Seilacher 1967;Simpson 1970;Wetzel and Werner 1980;Kotake 1989;Bromley, Ekdale, and Asgaard 1999;Bromley and Hanken 2003;Ekdale and Lewis 1991;Gaillard and Olivero 1993;Olivero 1996;Miller and d'Alberto 2001;Löwemark et al 2004;Löwemark 2015;Richiano 2015;Zhang, Fan, and Gong 2015;Monaco et al 2017, and references herein). However, the architecture of the burrow system described in publications is commonly interpretative, while only some characteristic parts of Zoophycos were observed, but not the complete trace (e.g., Olivero 1996;Miller and d'Alberto 2001;Monaco et al 2017). Due to their high morphological variability and complexity the traces are ascribed to the Zoophycos group (Uchman and Demírcan 1999).…”