PALAIOS, 2015, v. 30, 771–778 Research Article DOI: http://dx.doi.org/10.2110/palo.2015.012 MICROBE-MEDIATED PRESERVATION OF INVERTEBRATE FECAL PELLETS: EVIDENCE FROM THE ICHNOFOSSIL PHYMATODERMA BURKEI, PERMIAN SHALLOW-MARINE, TERESINA FORMATION, SOUTHERN BRAZIL KENTARO IZUMI, 1 RENATA GUIMARA ˜ ES NETTO, 2 AND JOA ˜ O HENRIQUE DOBLER LIMA 2 1 Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan 2 Geology Graduation Program, UNISINOS University, Av. Unisinos, 950, 93022-000 Sa ˜o Leopoldo RS, Brazil e-mail: izumi.kentaro@nies.go.jp ABSTRACT: Fecal pellet-filled trace fossil Phymatoderma burkei from the Permian shallow-marine Teresina Formation (southern Brazil) was microscopically and geochemically investigated to reveal the significance of physicochemical processes in the preservation of invertebrate fecal pellets. Scanning electron microscope (SEM) analysis shows micron-sized spherules only in the pelletal infill of P. burkei, but not within the surrounding host sandstone. These spherules show highly uniform morphology and size (approximately 1 mm), and generally have hollow structures occasionally occurring as aggregates. Geochemically, such spherules are characterized by presence of Fe and Mn, occasionally with Ba. The evidence suggests that the spherules are mineral-replaced or mineral-encrusted microbial cells, which are most likely coccoid bacteria based on their morphological similarity. Within the fecal pellets excreted by the trace-maker of P. burkei, microbially mediated precipitation of Fe and Mn minerals probably occurred on or just near the outer surface of coccoid bacterial cells. Such microbial processes are important in the preservation of invertebrate fecal pellets excreted in shallow tiers, especially under wave- or current- influenced shallow-marine sedimentary conditions. INTRODUCTION Recent studies have shown that microbes and/or organic matter play a physicochemically significant role in the preservation and alteration of invertebrate burrows, trails, and tubes (Schieber 2002; Ahn and Babcock 2012; Georgieva et al. 2014). In particular, organic material and mucus secreted by infaunal invertebrate trace-makers are inferred to have formed the substrate for a biofilm that facilitated bacterial biominer- alization under localized anaerobic/dysaerobic conditions (Schieber 2002; Ahn and Babcock 2012). Rapid (i.e., a few weeks or months), microbe- mediated biomineralization of mucus-lined biogenic structures (i.e., burrow walls, trails) is suggested to have enhanced preservation of trace fossils and bacterial remains within/around such trace fossils (Fu ¨ rsich 1972; Schieber 2002; Gong et al. 2008; Virtasalo et al. 2010; Mazumdar et al. 2011; Ahn and Babcock 2012). In a similar way, microcrystalline apatite precipitation is promoted by bacteria (Hirschler et al. 1990; Lucas and Pre ´vo ˆt 1991; Jehl and Rougerie 1995), which enhances the preservation potential of feces excreted by vertebrates (i.e., coprolites) (Chin et al. 2003; Hollocher et al. 2010; Nakajima and Izumi 2014). Most works that discuss physicochemical processes in fossil preservation focus on invertebrate burrows, trails, and tubes, or vertebrate coprolites (Fu ¨ rsich 1972; Schieber 2002; Chin et al. 2003; Gong et al. 2008; Hollocher et al. 2010; Virtasalo et al. 2010; Ahn and Babcock 2012). Invertebrate fecal pellets have received much less attention. However, some studies reveal that sediment ingestion, digestion, and excretion by marine worms may accelerate early diagenetic processes such as weathering and mineral authigenesis (McIlroy et al. 2003; Needham et al. 2004, 2005, 2006). Considering that most marine sediments are believed to pass through the guts of deposit feeders at least once before final burial (Jumars et al. 1990), invertebrate fecal material is an important research topic in both ichnology as well as sedimentology. The present study found the evidence of microbially induced biominer- alization in fecal pellets of the ichnofossil Phymatoderma burkei Miller (1991) from Permian deposits of the Parana ´ Basin (Rio Grande do Sul, southern Brazil; Fig. 1), which provides data for evaluating the significance of physicochemical processes in preservation of invertebrate fecal pellets. The ichnogenus Phymatoderma is composed of clusters of radiating tunnels filled with elongated pellets, which have been interpreted as fecal pellets excreted by a surface deposit feeder (Fu 1991; Miller and Aalto, 1998; Miller and Vokes, 1998; Seilacher 2007; Miller 2011; Izumi 2012). Although the trace-maker of P. burkei from the Parana ´ Basin has not been identified, the study of Phymatoderma from the Neogene of central Japan, suggested an echiuran worm as its possible trace-maker (Izumi and Yoshizawa in press). In the present study, we conducted microscopic observation and geochemical analysis of P. burkei specimen for discussing the microbe-mediated processes involved in preservation of invertebrate fecal pellets and its paleoecological implications. GEOLOGIC SETTING The specimen studied herein came from a sandstone bed of the Teresina Formation (upper Kungurian–lower Wordian/Roadian; Neregato et al. 2008), which comprises part of the Permian infill of the Parana ´ Basin that are now exposed in Rio Grande do Sul State, southernmost Brazil (Fig. 1). This study focused on the Cerro Caveiras outcrop, which is located towards the northwest of Dom Pedrito City (Netto 1992; Lima and Netto 2012; Fig. 1). The Teresina Formation includes shallow-marine deposits (Lavina 1991; Klein et al. 1999; Neregato et al. 2008) that characterize the regressive phase of the Gondwana I Supersequence (Milani et al. 2007). The sedimentary succession is mainly composed of a thick layer of purple shale at the base, overlaid by an equally thick layer of intercalated sandstone Published Online: October 2015 Copyright E 2015, SEPM (Society for Sedimentary Geology) 0883-1351/15/030-771/$03.00