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Although numerous studies have examined the influence of external forcing factors (climate, tectonics, and eustasy) on fluvial systems, relatively little is known about the changes is fluvial geometry and architecture that may result from natural geomorphic variability in the ancient landscape.  A fuller understanding of the role of paleogeomorphology and depositional environment in determining channel body geometry, architecture, and reservoir properties is necessary in order to fully exploit these important hydrocarbon reservoirs.  During the summer of 2008, I worked with three SUNY Potsdam undergraduates to construct detailed measured sections through the Pennsylvanian Springhill Mines and Ragged Reef formations.  Although these coastal sections are widely regarded as the world’s best exposures of Pennsylvanian strata (the study area is part of the newly designated “Joggins Fossil Cliffs” UNESCO World Heritage site), this is the first detailed study of these units. 

The 714-m-thick type section of the Springhill Mines Formation can be subdivided into three cycles, each of which records the transition from lacustrine/wetland deposits to redbeds deposited in a seasonally-oxidizing floodplain.  Cycle 1 (0- 240 m) consists of 17 m of lacustrine deposits overlain by redbeds with scattered drab mudrocks and thin coals.  Fluvial deposits within this interval consist of fixed channel bodies (9-16 m thick with width: thickness (W:T) ratios of ~5) and meandering channel bodies with pronounced lateral accretion surfaces (3-7 m thick and W:T ratios  of ~35).    Cycle 2 (240-417 m) commences with 75 m of dominantly drab mudrock, thin coals, and rare channel bodies.  The overlying 100 m of redbeds contain fixed channel bodies (4.5-9 m thick, W:T ratios of ~24) which overlain by sheet channel bodies (4.5- 18 m thick, W:T ratios of ~38) with a complex internal architecture dominated by low-angle, cross-cutting erosional surfaces.  The basal 52 m of Cycle 3 (471-714 m) contains thin packages of drab floodplain deposits with scattered, poorly exposed channel bodies.  The upper part of this cycle consists of redbeds with meandering channel bodies (3-10 m thick, W:T ratios of ~40) that increase in thickness and abundance toward the top of the cycle.  These poorly developed cycles may record a glacioeustatic signature muted by high subsidence rate and sediment supply.  Coarsening upwards via an increase in the abundance of channel bodies occurs within individual cycles and at the formation-scale.

The 864-m-thick type section of the overlying Ragged Reef Formation consists of 47 channel bodies (57%) separated by red (42%) and drab (2%) floodplain deposits.  Channel bodies range from 1.6 to 27.9 m thick and are composed of medium-grained sandstone organized into lateral accretion deposits, trough cross-beds, and ripple cross-laminae.  Channel bodies near the base of the formation have erosional surfaces lined with coarse-grained sandstone and quartz pebbles; maximum grain size and relative abundance of lag deposits increases upwards through the formation (cobbles in upper half of the formation).  Sheet sandstones deposited adjacent to channel bodies range in thickness from 0.5 to 2.2 m (11.7 m total, 1% formation thickness). Grayish to dusky red mudstones and thin, interbedded sheet sandstones make up the majority of the overbank deposits (290 m total, 33% of formation thickness).  These facies are interpreted to represent distal floodplain sediments deposited under seasonally oxidizing conditions. Gray to grayish green mudstones and thin, interbedded sheet sandstones are common in the bottom 200 m of the formation (14 m total, 2% of formation thickness).  These drab facies are interpreted as distal floodplain or wetland deposits.  The type section of the Ragged Reef Formation contains no obvious cyclicity, no coal, and significantly less wetland deposits than the underlying Springhill Mines and Joggins formations. These progressive changes record aggradation of the alluvial surface above local base level via clastic input from the basin margin.      

This sedimentological framework provides new information about the depositional environments, relative sea-level history, and stratigraphic architecture of the Springhill Mines and Ragged Reef Formations.  During the summer of 2009, I returned with four undergraduates to examine the geometry, architecture, and reservoir characteristics of the superbly exposed channel bodies that occur within these units and to extend our study to coeval basin margin facies.  When completed, the second phase of this study will provide a comprehensive account of the significance of natural variability within ancient fluvial systems and will provide a basin-scale framework that links channel body geometry, architecture, and petrography to geomorphic position on the floodplain and depositional environment.