MEIOFAUNAL BIOTURBATION OF LATE PLEISTOCENE–HOLOCENE GLACIOMARINE MUD IN THE CHAMPLAIN SEA BASIN, EASTERN CANADA: ORIGIN OF BURROWS, THEIR GEOCHEMICAL IMPLICATIONS, AND PALEOENVIRONMENTAL CONTROLS

Abstract

Meiofaunal traces in cored Pleistocene to Holocene silt-clay glaciogenic rhythmites consist of four types: clay-rich fill (type A) representing feeding structures, and a silt-rich fill with a clay-rich lining (type B) representing dwelling structures. A third burrow type (type C) is filled with framboidal pyrite suggestive of microbially mediated early diagenesis under anoxic and circumneutral pH conditions. A variant of type C is filled with framboidal pyrite overgrown by poorly crystalline pyrite indicating at least two stages of iron sulphide growth within earlier formed burrows. Higher in the cored succession a bed thickness increase to about ~ 14 cm is marked by an absence of meiofaunal traces. Since each bed represents deposition during a single year, it suggests that sustained sedimentation rates of ~ 14 cm yr21 represents a threshold for endobenthic activity. A fourth burrow type (type D) is filled mostly with clay and a lining with a distinctive parallel-aligned fabric of clay and dispersed silt grains, which occurs in slump blocks resedimented downslope from a shallower water setting. The absence of type A, B, or C burrows in these silt-rich slump blocks suggests that prior to slope failure, the silt-rich sediment substrate, and likely brackish pore fluid conditions, were not conducive to these tracemakers and/or trace-making behaviors. These differences illustrate the first-order control of physico-chemical factors, specifically, sedimentation rate, salinity, and substrate composition on the behavior of burrowing meiofauna in a glaciomarine basin plus the significance of meiobenthic activity on controlling early, shallow burial diagenesis.