The significance of hiatal surfaces in coal seams

Abstract

A widespread misconception is that coals correspond to single palaeo-peat bodies, which represent continuous and time-invariant records of peat accumulation. Evidence for the occurrence of intra-seam hiatal surfaces within datasets from bituminous coals, lignites and modern peats suggests that existing depositional models for peat and coal require modification. Recognition that coals may represent a succession of stacked mires separated by hiatal surfaces has implications for palaeoenvironmental and sequence stratigraphic studies that assume a continuous record of peat accumulation, as well as for the prediction of whole-seam composition and thickness trends.

Genetically Related Incised Valleys and Deltas: Sequence and Modern Analogue Modeling From the Nonmarine Santa Barbara Coalfield, Late Pliocene, Italy

“…This process was then followed by a sudden clastic shutdown (Cattaneo and Steel 2003), which promoted the expansion of a peat-forming environment (McCabe 1987;Jerrett et al 2011b). Minor anabranching channel bodies are encased within the coal, indicating that the seam may represent stacking of several peat-forming mires (Jerrett et al 2011a). Despite the major shutdown of clastic input from the valley system, the lacustrine domain records short-lived, wavedominated deltaic deposition atop the coal, before the final reestablishment of open lacustrine sedimentation.…”

Use of carbon accumulation rates to estimate the duration of coal seams and the influence of atmospheric dust deposition on coal composition

“…Given the uncertainties, it is remarkable that the volumetric approach to rates of peat growth underpins some of the most important literature on the stratigraphy of coal and coal-bearing sequences including many key papers on the sequence stratigraphy of coal-bearing strata (Bohacs & Suter 1997;Diessel et al 2000;Jerrett et al 2011a). The volumetric approach, which considers only growth and compaction, not only ignores mass loss during coalification but is based on a weak and incomplete understanding of peat compaction.…”

“…For example Jerrett et al (2011a) argue on a sequence stratigraphic basis that 2 m of coal in the Cretaceous Blackhawk Formation, USA would have accumulated over periods in the order of 100 -400 kyr which assuming 10:1 compaction would correspond to a peat accumulation rate of 0.05 -0.2 mm yr 21 . These authors argue that such rates are too low when compared to typical volumetric rates (Diessel et al 2000) at the mid-palaeolatitude of deposition.…”

“…Due to the considerable uncertainty inherent in this wide range, a compaction factor of 10 is commonly used (e.g. Jerrett et al 2011a) implying that typical coal densities of 1.2 -1.4 g cm 23 correspond to precursor peat densities of 0.12 -0.14 g cm 23 . Uncertainty in the degree of compaction is not surprising as, due to its virtually neutral buoyancy in water, organic matter exercises very little force with which to drive compaction.…”

Sedimentology and stratigraphy of an intra-cratonic basin coal seam gas play: Walloon Subgroup of the Surat Basin, eastern Australia

“…c. 80 km) and an inability to confidently correlate between them, it is impossible to determine how laterally extensive the brightening-and dulling-upward trends are. In paralic coals these trends can be correlated over tens to hundreds of kilometres (Jerrett et al 2011b). The WSG coal units (rather than their internal trends) can be correlated over several kilometres (Leblang et al 1981).…”