THE BACKPIT SEAM, SYDNEY MINES FORMATION, NOVA-SCOTIA - A RECORD OF PEAT ACCUMULATION AND DROWNING IN A WESTPHALIAN COASTAL MIRE

Extensive Westphalian D to Stephanian coal seams divide the Sydney Min es Formation of Cape Breton Island into large-scale repetitive sedimen tary packages. The Backpit seam, one of the most continuous seams with in this formation, was studied in detail to establish compositional tr ends and relate these to paleomire development within an overall trans gressive setting. The seam is of high-volatile B to A bituminous rank and ranges in thickness from 0.6 to 1.5 m onshore. Agglutinated forami nifera occur in strata directly below and above the seam, indicating a coastal setting for the mire. Ash and sulphur contents average 15.3 /- 6 and 5.2 +/- 2 %, respectively. Sulphur, predominantly in the form of pyrite, increases near the roof of the seam, consistent with a bra ckish influence in the roof strata. The planar Backpit mire was subjec ted to widespread, periodic flooding, marked by thin dull to coaly sha le lithotype intervals. Some intervals can be correlated across the on shore portion of the basin for more than 45 km and this distribution s uggests regional controls on their formation. Seam lithology changes f requently in vertical section and banded lithotypes predominate. Vitri nite macerals and vitrinite-rich microlithotypes are abundant and thin discrete fusain bands, the remains of ancient fires, are also common. Coal facies patterns record a series of wetting upward pulses in the upper portion of the seam that culminated in the drowning and terminat ion of the mire. A broad, relatively shallow embayment subsequently fo rmed that supported a fresh- to brackish water fauna.