Kentaro Izumi

MICROBE-MEDIATED PRESERVATION OF INVERTEBRATE FECAL PELLETS: EVIDENCE FROM THE ICHNOFOSSIL PHYMATODERMA BURKEI, PERMIAN SHALLOW-MARINE, TERESINA FORMATION, SOUTHERN BRAZIL

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 &mgr;m), 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.

Star-shaped trace fossil and Phymatoderma from Neogene deep-sea deposits in central Japan: probable echiuran feeding and fecal traces

Abstract. A co-occurrence of the ichnogenus Phymatoderma and a star-shaped horizontal trace fossil was discovered from Neogene deep-marine deposits (Misaki Formation, central Japan), and is described herein for the first time. Phymatoderma consists of a straight to slightly curved tunnel that shows first- or second-order branches. The tunnels are 5.30–27.25 mm in diameter and are filled with ellipsoidal pellets. The relatively well-preserved star-shaped trace fossil is a large horizontal structure (∼18 cm × 19 cm) that consists of at least 10 spokes with diameters ranging from 11.49–20.96 mm. As compared to modern analogous surface-feeding traces produced by abyssal echiuran worms and their burrow morphology, it is highly likely that the star-shaped trace fossil and Phymatoderma found from the Misaki Formation are feeding and fecal traces of ancient deep-sea echiurans, respectively. Difference in preservation potential between surface and subsurface traces may result in rare occurrence of star-shaped trace fossils as compared to Phymatoderma. Microscopic observation of the pelletal infill of Phymatoderma also reveals that the trace-maker fed on organic debris and microorganisms such as diatoms and radiolaria.