Digging into paleosol - trace fossil relationships

BELLOSI, E.; KRAUSE, J. M.; BEDATOU, E.

Santa Rosa

Simposio; Segundo Simposio Latinoamericano de Icnología SLIC 2013; 2013

INCITAP-FCEyN UNLPam

Integrated analysis of paleosols and trace fossils, helped with neoichnological studies, are making good progress in the interpretation of environmental and ecological conditions of ancient terrestrial ecosystems. Paleosol development reflects ecological succession, whereas trace fossil assemblages can record ecological preferences and organismal behaviors of soil biota. In order to recognize recurrent patterns, paleosols and invertebrate trace fossils were analyzed in a hundred, mostly Cenozoic, cases. Paleosols were arranged taxonomically into ten soil orders (U.S. Depart. of Agriculture). Entisols and Gelisols were excluded because uncertain or insufficient information. Raw data include 55 invertebrate traces, mostly (36) insect ichnogenera (termites, beetles, solitary/social bees, wasps, ants, cicadas, sphinx moths), earth worms (4), crustaceans (6) and undetermined (9) traces. Rhizoliths (rhizohaloes, rhizocretions, rhizotubules, rhizospheres) are grouped into small/fine (< 5 mm in diameter) and large or tree stumps, because they are not taxonomically studied. Preliminary results show particular relationships between most soil orders, ichnofossils and trace makers. Oxysols and Spodosols have very scarce ichnological information because they are uncommon paleosols in the stratigraphic record. The remaining soil orders contain on average13different trace fossils(range 9-18). Four of them are exclusive for each paleosol (range 2-7). On average, each trace fossil occurs in two soil orders, but not more than in five. More than half (29) of traces are present in only one paleosol type. Ultisols (7) and Inceptisols (6) show the greatest number of exclusive traces. Ichnodiversity is maximum in Andisols, clayey paleosols and Inceptisols; and minimum in oxic, carbonaceous and calcic paleosols. Ichnologically, the more similar paleosols are Andisols and Mollisols, with nine traces in common. Beetle and earth worm traces are the most ubiquitous (in all soil orders), followed by bee, termite and crustacean, and finally ant, cicada and sphinx moth traces. Alfisols exhibit the highest diversity in trace makers inhabiting soils from subhumid-semiarid, open forests or wooded grasslands. They include beetle (Coprinisphaera, Pallichnus, Rebuffoichnus, fecal pellets), bee (Celliforma, Celicalichnus), crustacean (Loloichnus), termite (Termitichnus, clay micro aggregates), earth worm (Lazaichnus, fecal pellets: fp), sphinx moth (Teisseirei) and ants traces. Ultisols present abundant traces developed in soils from temperate-warm, humid-subhumid forests or wooded grasslands: bees (Palmiraichnus, Uruguay, Ellipsoideichnus, Corimbatichnus), termites (Krausichnus, clay micro aggregates), beetles (Rebuffoichnus, Coprinisphaera), sphinx moths (Teisseirei), cicadas (Monesichnus), earth worms (Lazaichnus) and crustaceans (Guerraichnus). Mollisols originate in semiarid-subhumid grasslands, and also include traces from numerous producers: beetles (Coprinisphaera, Pallichnus, Quirogaichnus, fp), earth worms (Edaphichnium, Castrichnus, fp), small roots, and subordinately from termites (Syntermesichnus, unnamed nests), bees (Celliforma, Palmiraichnus), ants (Attaichnus) and cicadas. Aridisols develop in dry climates with desert scrub or sparse vegetation. They show a low-diversity ichnological assemblage with bee (Celliforma, Rebuffoichnus, Roselichnus), beetle (Pallichnus, Fictovichnus, Rebuffoichnus) and termite (Termitichnus, unnamed nests) traces. Vertisols evidence marked seasonal variations in humidity. They bear earth worm (Edaphichnium), beetle (Scaphichnium), crustacean (Camborygma) and cicada (Naktodemasis) traces, but abundant undetermined ones. Peaty soils such as Histosols, support bog, swamp and marsh in cool, humid-subhumid conditions. They contain earth worm (fp) and beetle (Eatonichnus) traces, along with Macanopsis, Planolites, Steinichnus and Fuersichnus. Earlier successional communities are represented by Andisols and Inceptisols. Unlike previous views and lack of time, these weakly-developed paleosols show high ichnological diversity. Andisols, developed on volcanic ash, show traces of beetles (Coprinisphaera, Pallichnus, Eatonichnus, Chubutolithes, Rebuffoichnus, Scaphichnium),crustaceans (Loloichnus, Dagnichnus, Cellicalichnus, Taenidium, Beaconites) and earth worms (Edaphichnium, Castrichnus, Lazaichnus, fp), subordinately traces of cicadas (Feoichnus, burrows) and bees (Celliforma), and only one undetermined trace. Inceptisols include numerous termite (Socialites, Fleaglellius, Vondrichnus, other nests), beetle (Pallichnus, Fictovichnus, Scaphichnium), ant (Parowanichnus), crustacean (Katbergia) and earth worm (Edaphichnium, fp) traces.