James R. Staub

The Snuggedy Swamp of South Carolina: A Back-Barrier Estuarine Coal-Forming Environment

ABSTRACT The Snuggedy Swamp is a back-barrier estuarine depositional environment. Extensive peat deposits as much as 15 feet (450 cm) thick are underlain by kaolinite-rich clay similar to the underclay associated with coal seams. These peat and underclay deposits are underlain by silt and clay which coarsen upward and were deposited in lagoons; the peat deposits are surrounded by eroding sand areas that are the remains of Pleistocene barrier islands. At present the salt marsh is encroaching on the swamp, destroying the fresh water vegetation that forms the peat and covering the peat with clays and salts. The thickest peat deposits in this swamp are orientated parallel to the surface trends of the barriers or preexisting tidal inlets. Peat islands are hypothesized as the method by which peat was deposited in this swamp. Initially this region consisted of extensive salt marsh and probably some open water areas. Then fresh water vegetation began to colonize those areas of the salt marsh that were farthest removed from the areas of tidal creek submergence, and eventually fresh water vegetation covered the surface of the marsh. These coalescing fresh water peat islands resulted in an undulatory contact between the peat and the underclay. Two types of splay deposits are interbedded with the peat in this area, crevasse splays and fire splays. Both are composed mainly of clay, but fire splays are dintinguished by a dark fusinite (charcoal) zone at their base.

Peat-accumulating depositional systems of Sarawak, East Malaysia

Many coal deposits originate in deltaic, estuarine, and coastal plain settings and a knowledge of interrelationships between the tectonic and depositional elements active at the time of sediment deposition is necessary to formulate basin scale models. The prograding coastal depositional systems of Sarawak all contain domed peat-accumulating environments in which low-ash, low-sulfur peats are being deposited in areas of active clastic siliciclastic sedimentation. These depositional systems are as large as 11,400 km2 and individual peat deposits within systems are in excess of 20 m thick and 1000 km2 in area. The geographic positions and drainage basin areas of each depositional system are controlled by fault and fold systems. Although prograding into the same receiving basin, individual system geomorphology is variable and ranges from a wave-dominated microtidal delta, to a wave-dominated meso- to macro-tidal delta/coastal plain system, to a tide-dominated macrotidal estuarine embayment along a 450 km stretch of coastline. System variation is a function of sediment supply, shelf and embayment geometry, wave climate, and tidal range. These factors, which control depositional system geomorphology, also control the resulting long axis orientation of the thick, domed peat deposits. The surface vegetation and internal characteristics of most domed peat deposits, however, are similar. Internal characteristics consist of basal high-ash, high-sulfur, degraded peats overlain by low-ash, low-sulfur, well preserved peats in vertical profile. These systems demonstrate variable responses to late Pleistocene/Holocene sea-level rise and, in these instances, the variation is most attributable to local differences in siliciclastic sediment supply, which is a function of the drainage basin area.

Kaolinite-enrichment Beneath Coals; A Modern Analog, Snuggedy Swamp, South Carolina

ABSTRACT The Snuggedy swamp contains peat deposits up to 100 inches (250 cm.) thick underlain by about 10 inches (25 cm.) of rooted and unbedded clay. This clay has a kaolinite/montmorillonite ratio of more than 2/1 and a pH less than 5. On the other hand, the clay below this zone, or where the peat is absent, is bedded, contains no roots, has a kaolinite/montmorillonite ratio below 1, and a pH greater than 5. There is strong evidence to suggest that the clay zone immediately beneath the peat was not kaolinite-rich when deposited, but was enriched due to leaching by humic-acid solutions which filtered down from the peat. This phenomenon may be similar to the formation of underclays below certain Paleozoic coals.

A mechanism to explain the preservation of leaf litter lenses in coals derived from raised mires

Abstract Leaves and other non-woody canopy parts are rarely preserved in coals. Although the pH of pore waters within peat swamps is usually relatively low (≤3.5), providing geochemical conditions that would promote preservation after burial, shed canopy parts may remain at the air–soil interface for periods of up to several months prior to burial by additional organic detritus. Leaf half-life in tropical forests has been reported to range from several weeks to months, depending upon species histology. During this time of exposure on the forest floor, catabolic (internal enzymatic), fungal, bacterial and root degradation, as well as saprophagous scavenging, act upon the least resistant parts to promote decay into hemic and sapric macerals. It is unusual, then, to find well-preserved leaves in peats or coals. When such accumulations are encountered, either permineralized in coal balls or duripartically preserved in lignites, the bedded leaves generally are spatially isolated. Several explanations have been proposed to account for such fossil Lagerstatten that require temporal changes in accumulation or degradation rates. Neither of these mechanisms is required to account for such accumulations. Bedded leaves, showing minimal evidence of subaerial exposure and degradation, have been recovered at depth from a vibracore taken 1 km into the interior of a peat swamp in the Rajang River delta, Sarawak, East Malaysia. Evidence is provided to indicate that such accumulations form within peat substrate depressions resulting from the displacement of rootstocks as trees either die and fall over, or are blown down in severe storms. These localized, acidic water-filled pools act as a natural buffer to the degradation of fallen canopy parts that accumulate therein.

Seasonal sediment transport and deposition in the Rajang River delta, Sarawak, East Malaysia

The Holocene Rajang River delta plain, which covers an area of 6500 km 2 , has developed in a tropical, ever-wet climatic setting. Peat deposits, up to 15 m thick, occur in this delta plain. The tributary system to the delta is about 50,000 km 2 in area. Elevations exceed 2000 m in the drainage basin and hill slopes are steep. Rainfall in the region exceeds 370 cm/year, with highest rainfall levels or the “wet” season being coincident with the December‐March monsoon. The monthly drainage-basin discharge is calculated to average about 3600 m 3 /s, and the discharge normally ranges from 1000 to 6000 m 3 /s. Spring tides in coastal areas range from 2.9 to 5.8 m. Tide data indicate that the tides are semidiurnal with a noticeable diurnal inequality. Vibracores recovered from bar forms in tidally influenced distributary channels contain laminated silts and sand-silt couplets that show evidence of rhythmic heterolithic stratification. Grain-size data indicate that these preserved delta plain siliciclastic sediments are the result of estuarine depositional processes that occur during intervals of reduced rainfall or the “dry” season (April‐November). The number of laminae preserved per neap‐spring cycle is the highest (o18‐20), and the average thickness is the greatest in the middle part of the delta plain. Distributary channels in this region normally contain low-salinity brackish water to freshwater. Vibracores recovered from delta front and prodelta sediments show evidence of heterolithic stratification, but rhythmicity is absent. Grain-size data indicate that preserved delta front and prodelta sediments are implaced by “wet” season processes (December‐March) when fluvial flux and delta-plain erosion are at their maxima. Individual silt laminae and/or silt and sand interbeds are sometimes many centimeters thick, but average about 1 cm. These silt laminae and silt and sand interbeds or varves represent annual sedimentation events. These varves demonstrate that about 24 million MT of sediment produced by the drainage basin is deposited in the delta front and prodelta region annually. q 2000 Elsevier Science B.V. All rights reserved.

Provenance and sediment dispersal in the Rajang River delta/coastal plain system, Sarawak, East Malaysia

Preliminary sedimentologic investigations were conducted in the Rajang River delta/coastal plain system in Sarawak, East Malaysia, to determine the processes and timing of siliciclastic transport and sedimentation in tropical, peat-dominated systems. Methods involved depth profiling and collection and analysis of bottom and suspended sediment load samples from channels and offshore areas, and coring and trenching of subaerial channel, shoreline, and backswamp features. The Rajang delta occurs in an embayment formed by the folded Mesozoic and Cenozoic sediments of the Central Borneo Massif. It covers an area of 11,000 km2 and is physiographically separated into an alluvial valley floodplain, an abandoned tidally flushed delta plain, and an actively accreting rectilinear delta/coastal plain. From 50 to 80% of the surface area is covered by peat 1 to 20 m thick. During the dry season of July/August, 1992, river channels varying from 2 to 45 m deep with discharge rates from < 100 to approximately 3550 m3/s were carrying suspended sediment loads ranging from 0 to 2281 mg/l. At present, approximately 8.2 x 10(10) kg/yr of fine-grained sediment is supplied to the system and areal accretion rates are over 1.0 km2/yr. The structural configuration of the uplands/receiving basin and subsequent drainage patterns and tidal influence results in a contradictory distribution of mature, fine-grained sediments in the channels of the active delta/coastal plain, and immature. coarse-grained angular sands and gravels in the channels of the abandoned delta lobe. The contemporaneity of the peat and clastic accumulation is evidenced by the margins of the thick, domed, low ash peat deposits interfingering with and being overlain by root-penetrated siliciclastic sediments. Much of the fine-grained sediment, however, bypasses the delta plain due to in-channel density gradients. Delta/coastal plain accretion occurs by distributary mouth bar buildup, sand bar welding, and ridge and runnel accretion. All subaerially exposed surfaces are quickly vegetated. The aberrant depth and configuration of some channels suggest that drainage is, in part, controlled by contemporaneous faulting.

Comparisons of central Appalachian Carboniferous coal beds by benches and a raised Holocene peat deposit

Abstract Three Carboniferous age coals from southern West Virginia, U.S.A., were examined at bench level and compared to a Holocene peat deposit, the Snuggedy Swamp, South Carolina, U.S.A. Data for all deposits consisted of coal or peat thickness, ash content and petrographic composition as well as parting or overlying clastic sediment thickness. Comparison of coal and parting thickness showed an inverse relationship in all cases. Bimodal distribution patterns for coal/peat thickness versus area indicate that the transition between areas of extensive, thick coal/peat and extensive, thin coal/peat was rapid. In the coal deposits at bench level, both ash and organic inert content increased toward the transition to thin coal. The areas of thick coal contained the highest vitrinite/reactive contents and lowest ash values volumetrically. This is similar to the distribution of low-ash, well-preserved, thick peat occurring in the central, raised areas of the Snuggedy Swamp, surrounded by areas of high-ash, decomposed peat subject to flooding. Although the depositional environments interpreted for each of the three coal beds and the Snuggedy peat deposit differ widely, the deposits themselves show similar distribution trends in thickness, ash content and petrographic composition.

Marine flooding events and coal bed sequence architecture in southern West Virginia

Abstract Eight regional Lower to Middle Pennsylvanian coal beds (Namurian B/C to Westphalian C) in southern West Virginia were examined. Beds were divided into their component sedimentary parts or benches by identifying bounding surfaces and associated siliciclastic partings within beds. Bounding surfaces represent the cessation of peat accumulation. Paleo-peat mire morphology at the bench level was determined using shape analysis, petrographic indices and coal chemistry data. Planar and raised paleo-peat mire benches were identified. All gas coal and some splint coal benches were derived from raised mires. Heterolithic coal and the remaining splint coal benches were derived from planar mires. Most bounding surfaces are thin, composed of oxidized and degraded organic materials, high in ash and sulfur content, and contain clay minerals and silt-sized quartz. Vitrinite reflectance is suppressed in the upper part of some benches. The associated siliciclastic parting materials, when thick, show evidence of tidal influence and contain brackish water to marine trace fossil assemblages. Bounding surfaces and the associated sediments represent a sudden increase in water depth and the lateral continuity of these surfaces indicates regional to basinal extent. Bounding surfaces are the up-paleoslope expression of rapid (

Evidence for a Tidally Influenced Upper Carboniferous Ombrogenous Mire System: Upper Bench, Beckley Bed (Westphalian A), Southern West Virginia

A discontinuous portion of the upper bench of the Beckley bed (Westphalian A) in southern West Virginia was examined in regard to its areal distribution, horizontal and vertical trends in chemistry, horizontal trends in petrographic composition, and its facies relationships with encasing sediments. The results of this examination were compared to those of a process model for the development of ombrogenous mire systems in tidally influenced coastal areas of Sarawak, East Malaysia. The results of these comparisons suggest a strong parallel between the two areas. The ombrogenous mire system that formed the upper bench of the Beckley bed initially developed as small individual topogenous peat swamps in a tidal flat setting. With time, the small individual peat swamps coalesced into an ombrogenous mire system that resulted in a coal bench that covers about 65 sq km. The mire system was eventually covered by channel deposits from a deltaic distributary system. The mire system that developed for the coal bench shows distinct zonation of dull and bright macrolithotypes (dull on the margins and bright in the interior) and contains high concentrations of ash and sulfur in its margins and base. Coal thickness, chemistry and petrographic data allow differentiation of the raised interior from the more topogenous areas of the mire. The interior portions are interpreted as those areas of the bench that are > 65 cm thick and average > 85% vitrinite group macerals, 5.5% ash and 0.60% sulfur. The more topogenous areas of the mire system, which were subjected to flooding, oxidation and sediment influx are < 65 cm thick and average < 65% vitrinite group macerals, 15.1% ash and 1.81% sulfur. In addition, the amount of preserved cell structure, irrespective of maceral group, appears to increase toward the margins of the bench. These trends are consistent with observations in the peat deposits of Sarawak, East Malaysia.

Development of low-ash, planar peat swamps in an alluvial-plain setting: The no. 5 Block beds (westphalian D) of southern West Virginia

ABSTRACT Coals from the No. 5 Block coal beds (Westphalian D) of the central Appalachian basin are noted for their blocky, dull character and their low ash and low sulfur content. The beds are multiple benched, with rock partings separating benches. Individual benches have limited lateral extent and, where thick, are dominated by bright, high-ash coal at the base and dull, low-ash coal in the upper parts. The duller coals contain more exinite-group and inertinite-group macerals than the brighter coals. These coal beds are encased in sandstone units dominated by fining-upward sequences. The overall depositional setting is an alluvial-plain environment with northwest-flowing channels spaced approximately 20 km apart. The channels were flanked by clastic swamps about 7 km wide. Low-ash peat accum lated in areas of the flood plain most distant from the channels. These peat-accumulating swamps were about 8 km across. In a few instances low-frequency flood events introduced fine siliciclastic sediment into the peat swamps, depositing a thin layer of sediment on top of the peat. This sediment layer is thicker where the underlying coal is the thickest. These thick coal areas are topographically lower than surrounding coal areas. This relationship between coal thickness, parting thickness, and topography indicates that these peat swamps were planar at the time of deposition. Individual coal benches contain abundant preserved cellular tissue (telocollinite, semifusinite, and fusinite) at most locations, suggesting that robust vegetation was widespread in the swamps and that the morpholo y was planar. The high concentrations of exinite-group an inertinite-group macerals in the upper parts of benches resulted from selective decomposition and oxidation of the peat in subaerial and aquatic planar-swamp environments.