Stratigraphy, amino acid geochronology, and correlation of Quaternary sea-level and glacial events, Broughton Island, arctic Canada

Abstract

Raised marine and glaciomarine terraces on Broughton Island record regional isostatic adjustments and eustatic sea-level changes. Previous workers proposed three alternative glacial and sea-level chronologies of the region. These conflicts are resolved by the stratigraphic control provided by amino acid ratios (D-allo-isoleucine/L-isoleucine) in marine molluscs collected form cliff exposures. Amino acid ratios, radiometric dates, and relative weathering measurements on geomorphological features provide a basis for regional correlations.Based upon amino acid ratios, the coastal sedimentary sequences, all part of the Broughton Island Formation, can be subdivided into six units to which informal member names have been assigned. These units delimit at least four glacial episodes during which local ice advanced around Broughton Island to the outer coast. The youngest advance is correlative with deposits that are dated > 54 000 BP, and the absolute ages of older events have been estimated from minimum uranium-series dates and amino acid data. Glacial events previously recognized as the Foxe Glaciation represent a much greater portion of the Quaternary than was previously realized.The Tuneek member, the oldest sedimentary unit on Broughton Island, consists of a bouldery, sandy clay diamicton deposited by a major pre-Foxe glacial advance(s) that occurred possibly > 500 000 years BP when ice traversed the island. Subsequent advances were deflected along the southern coast of the island through Broughton Channel. The Anigatalik member, estimated to be between 300 000 and 500 000 years old, consists of a variety of sediment types including bouldery clay diamictons and bedded, coarse sands and gravels. The Platform member represents a subsequent and extensive pre-Foxe glacial advance. It consists of a bouldery, shelly till deposited over a wave-cut platform at the north end of Broughton Island between 250 000 and 350 000 years BP. Correlative tills were deposited along the east coast by glacial ice extending around the southeast corner of the island. Relative sea level was at least 72 m asl during this time.The Cape Broughton member consists of ice-proximal sediments deposited when fiord ice was retreating from Broughton Channel approximately 150 000 – 200 000 years BP. The macrofauna and microfauna within these sediments suggest that subarctic water masses, warmer than present, were adjacent to the northeastern Baffin coast subsequent to the glacial maximum. These deposits may be correlative with a prominent moraine system on either side of Broughton Channel.The Harbour member represents the beginning of the Foxe Glaciation (as it is redefined) and delineates the last major advance of ice to the outer coast. The current best estimate for the age of these sediments is 70 000 – 130 000 years BP. At one locale, Harbour sediments overlie an organic-rich, oxidized horizon containing a pollen assemblage strongly indicative of interglacial conditions. The stratigraphy suggests that a major interglacial period preceded the Harbour advance. Organic horizons near the top of the Harbour member contain a pollen assemblage that suggests a terrestrial climate similar to that of today.The Matsaja member consists of nearshore marine sands and beach facies deposited by an early Holocene transgression to between 7 and 8 m asl that occurred approximately 8000 – 10 000 years BP. A minor transgression of 1–2 m commenced approximately 1000 years BP.