THE NEOPROTEROZOIC SQUANTUM MEMBER, BOSTON BASIN; GLACIAL OR NON-GLACIAL?

The Neoproterozoic (c.580 Ma) diamictite-bearing and volcanically-influenced Squantum Member of the Boston Bay Group of the Boston Basin has been the focus of contrasting interpretations since the early 20th century. Some consider it to be glacial and recent work correlates it to the volcanically-influenced Gaskiers Formation of eastern Newfoundland as part of a putative snowball Earth (Gaskiers Glaciation). The Gaskiers was deposited in a back arc basin and contains clear evidence of ice in the form of striated clasts and dropstones. To others, the Squantum is a non-glacial deposit. This continuing uncertainty requires detailed assessment of the sedimentology and basinal setting of the Squantum and its related strata. This study presents a detailed analysis of sedimentary and volcanic facies of the Squantum based on consideration of more than twenty sites. This work indicates a deep marine basin dominated by mass flow processes that resedimented volcanic and fluvial sediment downslope, possibly on a submarine fan. Diamictites are the product of mixing of coarse conglomeratic and fine sediments. Lonestones (dropstones of earlier work) were produced as conglomerate clasts ‘foundered' down into soft fine grained facies. We report new evidence of a strong volcanic influence on sedimentation in the form of hitherto unrecognised ash flows indicating an active volcanic arc setting. There are strong similarities with the Gaskiers in terms of overall depositional setting but to date, no clear evidence of a glacial influence can be identified for the Squantum.