New ichnospecies of the medusiform burrows Gyrophyllites from the Eocene of Marambio (Seymour) Island, Antarctica

GELFO J. N.; ACOSTA HOSPITALECHE, CAROLINA

Hobart OSC

Congreso; SCAR Open Science Conferences; 2020

Scientific Committee on Antarctic Research

Ichnofossils are structures produced by the activity of organisms, which modified the depositional fabric of the sedimentary rocks. Burrows, borings, and traces ichnogenera were recognized for the Eocene outcrops of Seymour Island. Here we describe the first record of Gyrophyllites usually interpreted as the result of worm-like organisms that mined the unconsolidated sediment in search for food. More than a hundred of specimens with an average diameter of 40 mm were collected from surficial levels of the Submeseta Allomember II of the Submeseta Formation that crops out in the locality DPV 13/84 of Bartonian age. They were found associated with Planolites, penguins and fish bones, in a flat sandstone surface of less than 50 mm thickness. Most of them were preserved as epirelief, although a minor number of specimens were found as complete relief, enclosed in ellipsoid concretions. They preserve a different number of non-overlapping concave petaloid lobes radiating from a shaft. Some of the specimens are preserved as a radial structure with six oval to subcircular deep lobes. In others, the petaloids are less excavated and defined, increasing the number of lobes up to nine. A third type are kidney-like structures in outline with five or less lobes. Despite these new specimens differ from all known Gyrophyllites ichnospecies, the main resemblance is with G. cristinae (Ordovician from Argentina), interpreted as the result of the colonization of a storm bed by worm-like organisms, favored by an increase of sea-floor oxygenation and the supply of fresh organic detritus.