Pyrite framboids interpreted as microbial colonies within the PermianZoophycosspreiten from southeastern Australia

Abstract

AbstractTwo types of pyrite framboids (PF, probably sulphate-reducing bacteria) have been found within theZoophycosspreiten, hosted in the Guadalupian (Middle Permian) glaciomarine greywacke of the Westley Park Sandstone Member within the Broughton Formation from the southern Sydney Basin of southeastern Australia. They are composed of non-sheathed (PF1) and sheathed (PF2) sub-micron balls, respectively. Chemically, the sub-micron balls consist of iron, sulphur, carbon and oxygen. Both PF1 and PF2 occur in rhythmic alternation within the thick, light-grey and thin, dark-grey minor lamellae ofZoophycosspreiten. The framboids from the minor lamellae are highly abundant and occur in an orderly arrangement of equal density and in a good state of preservation. WithinZoophycosspreiten no homogeneous filling, fecal pellets, or any sign of re-exploitation of the minor lamellae have been recognized. No similar framboids have been observed outsideZoophycosspreiten. Therefore, the framboids are interpreted as the pyritized remains of microbial colonies withinZoophycosspreiten. The traceZoophycoswould be a multifunctional garden that may have been carefully constructed by theZoophycosmaker, where different microbial colonies were orderly and carefully planted and cultured within different minor lamellae. Further, it is proposed that theZoophycosmaker had a symbiotic relationship with microbial colonies on the mutual basis of food supply and redox conditions. The fact that the overlying spreiten cut the underlying ones indicates that theZoophycosfrom the study area is of an upward construction. The rhythmic alternation of both the thick, light-grey and thin, dark-grey minor lamellae withinZoophycosspreiten may be suggestive of a gardening manner of theZoophycosmaker responding to the warm and cold changes, food supply in pulses and variations of sedimentation rate for planting and culturing microbial colonies under the conditions of a glaciomarine environment at the high latitudes.