Coastal Plain Deposits Research Articles

Coal petrographic genetic units in deltaic-plain deposits of the Campanian Mesa Verde Group (New Mexico, USA)

The Campanian rocks of the Mesa Verde Group in the San Juan Basin, New Mexico, USA, form a littoral wedge composed of offshore, shoreface and onshore facies. This siliciclastic wedge was interpreted as a landward-to-seaward stepping of grouped genetic units, i.e. intermediate term cycles. The continental facies consist of coastal-plain deposits (coals, shales, and sandstones) represented by three main domains, progressively distant from the palaeoshoreline: the deltaic-plain, the intermediate-plain, and the alluvial-plain domains. In the deltaic-plain, grouped aggradational–retrogradational genetic units consist of preserved coal-shale doublets alternating with thick shales. Although previous works have identified genetic units in the shoreface facies, the existence of the latter has not been proven in the coastal-plain deposits. As coal-shale doublets may represent such genetic units, an organic petrography study was performed at high resolution on an 80-cm thick, 1.5-km long coal seam to demonstrate this hypothesis. In this work, the depositional environments of the initial peatlands were rebuilt utilizing two complementary methods: maceral and microlithotype analyses. The results reveal the existence of internal sequences in the coal seam, corresponding to recurrent patterns of a palaeogeographical model proposed for a littoral domain. The authors interpret this coal sequence as the record of successive progradational and aggradational events. Furthermore, a previous study of the organic content of the shales located above the coal demonstrated that the preservation of these facies is related to higher accommodation/peat production and accommodation/sedimentary supply ratios. Coal-shale doublets are then interpreted as elemental genetic units of the deltaic-plain formation. This study demonstrates that, contrary to original concepts, littoral coal seams are not just markers of stable shoreline conditions at a high time scale, but also record landscape migration.

Architecture of channel bodies and paleovalley fills in high-frequency Carboniferous sequences, Sydney Basin, Atlantic Canada

ABSTRACT Fluvial channel bodies in the Pennsylvanian Sydney Mines Formation are contained within high-frequency sequences that represent relative sea-level fluctuations, linked to climate change, on a gently subsiding craton. Channel-body style within coastal-plain deposits was controlled by sea-level transit cycles, modulated by climate and substrate resistance. Coarse bed-load systems are deeply incised, multi-storey bodies up to 30 m thick. Some represent valleys backfilled during late lowstand and transgression, probably under a humid climate. Sinuous channel systems display well developed lateral accretion surfaces and ridge-and-swale topography. Distributary systems are narrow channel bodies that cut bayfill deposits. These two groups lie within highstand deposits, and represent the readvance of coastal rivers following maximum transgression. Sand-flat systems consist of plane-bedded sand sheets and downstream-accreting macroforms, laid down under ephemeral flow conditions, adjacent to deep sinuous channels. They are interpreted as channel and valley fills generated during late highstand, falling stage, and lowstand under a strongly seasonal climate. Calcrete caps on some sandflat bodies suggest that they filled prior to the main lowstand phase of paleosol development. A complex relationship is apparent between channel or valley fills and mature paleosols that bound sequences. Resistant substrates (coals, indurated limestones) influenced channel-body geometry by promoting lateral expansion and localising incision. 1 Present Address: Nova Scotia Community College, Institute of Technology Campus, P.O. Box 2210, Halifax, N S, Canade B3J 3C4; E-mail: batsonpA@it.nscc.ns.ca End_Page 138------------------------

Ancient shelf ridges-A potentially significant component of the transgressive systems tract: Case study from offshore northwest Java

Detailed stratigraphic evaluation of three-dimensional (3-D) seis mic volumes calibrated with well-log and core data from the Mio cene section of the offshore northwest Java shelf reveals the exten sive presence of preserved shelf ridge deposits. These features are long linear bodies ranging from 0.3 to 2.0 km wide, more than 20 km long, and up to 17 m high. On close inspection, these features appear to be asymmetric, characteristically sharp-edged and thicker on one side and gradually thinning with an irregular edge on the other side. Possible sand waves, smaller in scale, are observed super imposed on these ridges and oriented oblique to the long axes of the ridges. The observed shelf ridge deposits tend to be sand prone and overlie ravinement surfaces. The ridges appear to be oriented parallel with the axes of broad paleoembayments associated with the structural fabric of the basin. In addition to shelf ridges, shelf ribbons, possibly less than 5 m thick and less than 100 m wide, are also imaged. Sand ridges are common on modern shelves but significantly less commonly recognized in the subsurface or in outcrop. The features observed here represent examples of preserved ancient shelf ridges. These ridges are thought to have formed as a result of erosion and subsequent reworking of sand-prone deltaic and/or coastal-plain deposits by shelf tidal currents, which became active immediately after shoreline transgression. These deposits appear to have migrated across the ancient sea floor and represent an important component of the transgressive systems tract. These transgressive systems tract deposits have significant exploration potential because they are commonly sand prone and tend to be encased in shelf mudstone seal facies. Depending on the degree to which sand is present in interridge locations, these linear sand bodies can comprise potential stratigraphic traps. (Begin page 76)

Permian Cyclothem Development within the Onshore Canning Basin, Western Australia

Earth's climate during the latter part of the Permian has long been the subject of speculation and debate. Some studies suggest that Permo-Carboniferous glaciation persisted on parts of Gondwana up to at least the Permo-Triassic boundary. Other studies argue that deglaciation occurred as early as the late Sakmarian (lower Early Permian). Many such investigations have been based upon the sometimes ambiguous occurrence of direct glacial deposits (e.g. striated clasts, tillites). In contrast, this study evaluates the likelihood of post-Sakmarian glaciation by testing high-frequency, sedimentary cycles for a glacio-eustatic driving mechanism. The focus of this thesis is the Artinskian (upper Early Permian) Tuckfield Member of the Poole Sandstone. The Tuckfield Member is exposed around the periphery of the St George, Poole, and Grant Ranges of the Fitzroy Trough (onshore Canning Basin, Western Australia). In the St George and Poole Ranges, the Tuckfield Member outcrops as a 50 to 100 m thick package of vertically stacked, laterally continuous, coarsening- and thickening-upward cycles. In contrast, the Tuckfield Member outcrops in the Grant Range as a less than 50 m thick package of vertically stacked, laterally discontinuous, fining- and thinning-upward cycles. Primary sedimentary structures, trace fossils, and the vertical succession of facies suggest that the Tuckfield Member records shallow-marine, shorezone deposition in the St. George and Poole Ranges and non-marine, coastal plain deposition in the Grant Range. Gamma-ray and grainsize data, collected from 17 measured outcrops (11 in the St George Ranges; 4 in the Poole Range; 2 in the Grant Range), were analyzed for cyclicity. Spectral analyses identified several orders of meter- to decameter-scale cycles in both the shallow-marine and non-marine facies. The average periodicities of the identified cycles occur in the ratio of ~36:10:4:2 m. This ratio correlates strongly with the known mid-Permian orbital periodicities of elongated eccentricity, eccentricity, obliquity, and precession (~410:100:40:20 thousand years). Additionally, the Tuckfield Member is herein traced throughout the northern Fitzroy Trough and onto the adjacent Lennard Shelf via sub-surface data. Similar to outcrop, subsurface gamma-ray logs display several orders of meter- to decameter-scale cycles that correlate strongly with the orbital periodicities. This cyclicity is manifested by the systematic bundling of smaller-scale cycles into larger-scale cycles that can be traced laterally for more than 200 km. For comparison, correlative shallow-marine cycles from the Artinskian to Ufimian Pebbley Beach Formation (Sydney Basin, New South Wales) were also studied. Four outcrop sections were measured and correlated, giving a total stratigraphic column of approximately 45 m. Spectral analysis of gamma-ray data identified several orders of meter- to decameter-scale cycles. These cycles correlate strongly with the mid-Permian orbital periodicities and the identified Tuckfield Member cycles. The favorable comparison between the Tuckfield Member cycles and the orbital parameters indicates that Milankovitch-forcing of climate influenced the formation of depositional cyclicity. Furthermore, it is highly probable that these cycles are glacioeustatic in origin due to their laterally extensive nature and positive correlation with identified cyclicity in New South Wales. This suggests that Permo-Carboniferous glaciation must have persisted into at least the Ufimian stage of the Late Permian.

Nonmarine sequence stratigraphy: Updip expression of sequence boundaries and systems tracts in a high-resolution framework, Cenomanian Dunvegan Formation, Alberta foreland basin, Canada

Ten allomembers, labeled J-A, have been mapped in the deltaic Dunvegan Formation using 2340 wells and 63 outcrop sections. Each allomember spans about 200 k.y., is bounded by regional transgressive surfaces, and consists of 3-10 component shingles, apparently of autogenic origin. Allomembers H-E are discussed in this article. Their internal stacking patterns and bounding surfaces permit interpretation as depositional sequences. Sequences H-F have a sigmoidal-prismatic geometry, downlap to the southeast, and thin northwest onto the coastal plain. No differential thickening exists toward the orogen in the southwest. In contrast, sequence E thickens markedly toward the northwest. The tabular geometry of sequences H-F suggests accommodation was controlled by sea level change, whereas the wedge geometry of sequence E suggests significant tectonic tilting. Subaerial unconformities that bound valleys and extend onto adjacent interfluve paleosols can be traced 120-330 km updip into outcrop. The base of each sequence is characterized by shoreline backstep of 80-150 km. Transgressive and highstand shingles in each sequence comprise marine deltaic deposits that pass landward into coastal plain strata. Falling-stage shingles offlap seaward with little or no nonmarine equivalents updip, whereas lowstand shingles show renewed coastal onlap. In outcrop, three nonmarine systems tracts are recognized: (1) A channel-dominated, low-accommodation systems tract fills valleys up to 35 m deep and is equivalent to the early transgressive systems tract. (Begin page 1968) (2) A lacustrine-dominated, high-accommodation systems tract comprises mudstone enclosing ribbon channel sandstones, blankets interfluves, and forms the bulk of each sequence. It is equivalent to late transgressive and early highstand systems tracts. (3) A paleosol-dominated, low-accommodation systems tract occupies the upper part of each sequence and is capped by the sequence boundary. It is equivalent to the late highstand systems tract. Sequence-bounding interfluve paleosols represent tens of thousands of years of pedogenesis related to slow aggradation, followed by fluvial entrenchment and clastic bypass, and represent the late highstand, falling-stage, lowstand, and early transgressive systems tracts. Coastal plain deposits record only part (perhaps

Recognition and Hydrologic Significance of Passive-Margin Updip Sequences: An Example from Eocene Coastal-Plain Deposits, U.S.A.

ABSTRACT Sequence-stratigraphic interpretations are extended to a passive-margin updip setting using sedimentological observations from cores and well-to-well correlations in Eocene coastal-plain strata of South Carolina. In the succession studied, formation contacts tend to follow sequence boundaries even as lithologies vary within individual sequences. Sequence boundaries at the base of the Congaree Formation and near the top of the Tinker Formation formed during relative sea-level fall associated with second-order global cycles. These boundaries can be recognized clearly in both downdip and updip areas of the passive margin. Three other sequence boundaries, which occur at the base and top of the Warley Hill Formation and within the Tinker Formation, are interpreted as formed during relative sea-level fall associated with third-order global cycles. Hydrostratigraphic units in the strata studied conform to depositional patterns that were controlled by changes in sea level and sediment influx. Sand of the Gordon aquifer comprises a thick aggradational succession deposited predominantly in the nearshore-shelf environment as accommodation increased during relative rise in sea level. Because of high rates of sedimentation in the proximal setting, aggradational stacking of nearshore sands may be common to other updip marine strata in accommodation-dominated regimes. The overlying Gordon confining unit consists of marine-shelf clay and carbonate sediment deposited in response to maximum transgression. During subsequent relative sea-level fall, accumulation of shoreface deposits produced a progradational succession that is represented by the lower part of the Upper Three Runs aquifer. Unlike formation contacts, boundaries between the clastic aquifers and confining units do not follow the third-order sequence boundaries because of lithologic variations within the sequences. An increasing degree of breaching through the Gordon confining unit, which results in downward contaminant migration into the Gordon aquifer, occurs in the updip direction because of nearly continuous sand deposition. Near the base of the interval studied, contaminants migrate locally through the Crouch Branch confining unit because of erosional breaches formed by scour during sea-level lowstand. In this example and in other strata deposited in an updip passive-margin setting, the extent to which confining units are breached at sequence boundaries decreases in the downdip direction, resulting in better protection of the adjacent aquifer.

Osmium Isotopes Demonstrate Distal Transport of Contaminated Sediments in Chesapeake Bay

Because the isotopic composition of anthropogenic Os is normally distinctive in comparison to continental crust and is precisely measurable, this platinum-group element is attractive as a tracer of transport pathways for contaminated sediments in estuaries. Evidence herein and elsewhere suggest that biomedical research institutions are the chief source of anthropogenic Os. In the Chesapeake Bay region, uncontaminated sediments bear a crustal 187Os/188Os signature of 0.73 ± 0.10. Slightly higher 187Os/188Os ratios occur in Re-rich Coastal Plain deposits due to post-Miocene 187Re decay. The upper Susquehanna Basin yields sediments also with higher 187Os/188Os. Beginning in the late 1970s, this signal was overprinted by a low 187Os/188Os (anthropogenic) source in the lower Susquehanna Basin. In the vicinity of Baltimore, which is a major center of heavy industry as well as biomedical research, anthropogenic Os has been found only in sediments impacted by the principal wastewater treatment plant. Surprisingly...

Forest Fires, Climate, and Sea-Level Changes in a Coastal Plain-Shallow Marine Succession (Early-Middle Oxfordian Jakobsstigen Formation, North-East Greenland)

ABSTRACT The Lower-Middle Oxfordian Jakobsstigen Formation of North-East Greenland was deposited in a semi-enclosed marine embayment along the western margin of the rifted seaway between Greenland and Norway. It consists of rhythmically interbedded coastal-plain and shallow marine deposits, reflecting repeated alternation of two markedly different environments. The formation is 128 m thick and forms an overall coarsening-upward unit. The basic motif is a high-order sequence, 0.1-10 m thick, consisting of a thin, laterally extensive carbonaceous mudstone overlain by coarsening-upward offshore-transition-zone and shoreface heteroliths and sandstones. The mudstone was deposited during early base-level rise in a shallow, flat-bottomed lake or lagoon on a flat, low-lying coastal plain. The plain was subsequently flooded during maximum rise in sea level, followed by shoreface progradation during late rise, stillstand, and early fall. The boundary between coastal-plain and shallow-marine deposits represents the maximum flooding surface, separating the transgressive and highstand systems tracts. The organic material of the carbonaceous coastal-plain mudstones is dominated by inertinite macerals resulting from wildfires. In the shallow-marine sediments the organic material contains a high proportion of huminite and a significantly lower proportion of inertinite macerals, indicating wetter conditions and a lower frequency of wildfires in the hinterland during times of shoreface deposition. The different climatic regimes may reflect high-order sea-level fluctuations that exerted an important influence on the areal extent of the marine environments in large areas of the rifted seaway between Greenland and Norway due to the flat, low-gradient basin floor and overall shallow-water conditions. Periods of late rise and highstand were characterized by a humid climate, possibly caused by higher precipitation in the nearby source areas related to evaporation over the extensive sea. During lowstands only the topographically deeper parts of the rift complex remained submerged and a drier continental climate prevailed. The carbonaceous mudstones were deposited in the transitional period from the drier to the more humid climate corresponding to early sea-level rise. This was the time of large seasonal variations with optimum conditions for wildfires in the vegetated hinterland. This time interval was also characterized by onset of base-level rise in the low-lying coastal plain, where the wildfire-derived inertinite was trapped in shallow lakes and lagoons.

New sauropod dinosaur prints from the Saltwick Formation (Middle Jurassic) of the Cleveland Basin, Yorkshire

SUMMARY Undoubted sauropod prints are recorded for the first time from the Aalenian, Middle Jurassic, of the Cleveland Basin. This is only the third site known from which sauropod prints of this age have been reported. Eight pes and manus prints from the Saltwick Formation, near Whitby, Yorkshire are described and interpreted, and include prints up to nearly 1 m in length. The prints show features in common with those of the ichnospecies of Brontopodus and Breviparopus. The Saltwick Formation is a coastal plain deposit and indicates the print producers inhabited a humid, subtropical environment.

Some new and rarely documented Late Cretaceous calcareous nannofossils from subsurface sediments in South Carolina

One new calcareous nannofossil genusSenilatus; four new calcareous nannofossil speciesCalculites favosus, Lithraphidites?charactozorroSelf-Trail and Pospichal,Rucinolithus oriens,andWatznaueria bybelliae; and one new combination,Senilatus zipperumn. gen. and comb., are described from Upper Cretaceous (upper Campanian to Maastrichtian) sediments of east-central South Carolina. These new species were described from five coreholes located in marine coastal plain deposits. There is evidence that the presence of one species,Senilatus zipperum,is indicative of nearshore, restricted environments. Scanning electron and light microscope pictures are provided for two species,Cretarhabdus multicavusBukry, 1969 andRetemediaformis teneraretisVarol, 1991, that have previously been documented only with the transmission electron microscope. The ranges of these two species have been extended beyond those stated in the original descriptions.

Occupation horizons found in the search for the ancient Greek city of Helike

In 373 B.C. an earthquake and seismic sea wave destroyed and submerged Helike, the principal Greek city on the southwestern shore of the Gulf of Corinth. Our sonar survey of the seafloor in the area where ancient sources located Helike, southeast of Aigion, showed no evidence of a submerged city. We concluded that the site must now lie in the alluvial deposits of the adjacent coastal plain. Accordingly, we used bore hole drilling and geophysical techniques to look for buried occupation horizons on land. The bore hole cores yielded numerous ceramic fragments and remains of walls, ranging from near the surface to about 15 m deep, concentrated in an area of some 2 km2 on the upper part of the delta between the Selinous and Kerynites Rivers. Ceramic and organic samples from the cores yielded ages ranging from Byzantine to Early Helladic times. A shallow auger hole brought to light a superb fragment of an architectural terracotta statue from an Archaic building, ca. 600 B.C. Near the center of the ceramic-bearing area, we discovered by magnetometry a large Roman building and began its excavation. It may belong to a Roman settlement that Pausanias visited at the site of Classical Helike. The deeper layers of the excavation yielded black-glazed vase fragments from the 5th century B.C. and potsherds from Protogeometric and Mycenaean times. The overall results suggest that most of the Roman to Classical horizons lie within about 6 m of the surface, whereas Bronze Age horizons range down to 15 m. While we have yet to determine by excavation whether the occupation horizons include the center of a city, this area appears to be a strong candidate for the site of ancient Helike. © 1999 John Wiley & Sons, Inc.

An elasmobranch assemblage from the terrestrial-marine transitional Lethbridge Coal Zone (Dinosaur Park Formation: Upper Campanian), Alberta, Canada

The change in depositional environments observed in the Cretaceous (Upper Campanian) strata in the region of Dinosaur Provincial Park, Alberta, from the proximal coastal plain deposits of the Oldman Formation to the lowland coastal plain deposits of the Dinosaur Park Formation, reveals an associated change in faunal composition. An assemblage collected from a microvertebrate site in the paralic deposits of the Lethbridge Coal Zone (uppermost Dinosaur Park Formation) reflects an increasing marine influence. Elasmobranch (sharks and rays) remains are the most abundant, both in terms of number of overall taxa and number of elements, and they are the best-preserved specimens. However, several brackish-water-tolerant osteichthyan taxa, and four reptile taxa (two marine and two terrestrial), were also recovered, although they exhibited evidence of extensive taphonomic reworking.The elasmobranch fauna collected from the Dinosaur Park locality is uncommon for vertebrate microfossil assemblages in the Dinosaur Park Formation of Alberta and in equivalent beds in Montana. Seven of the 10 taxa collected from this site [Cretorectolobus olsoni Case, 1978; Eucrossorhinus microcuspidatus Case, 1978; Odontaspis aculeatus (Cappetta and Case, 1975); Archaeolamna kopingensis judithensis Siverson, 1992; Protoplatyrhina renae Case, 1978; Ischyrhiza mira Leidy, 1856; and Ptychotrygon blainensis Case, 1978] are recorded for the first time from the uppermost section of the Judith River Group in Alberta; Carcharias steineri (Case, 1987), represents the first occurrence within the upper Judith River Group from either Alberta or Montana.

Architecture and trace-fossil characteristics of a 10,000-20,000 year, fluvial-to-marine sequence, SE Ebro Basin, Spain

ABSTRACT The Eocene Sant Llorenc del Munt fan-delta complex lies on the southeastern edge of the Ebro Basin in NE Spain. Alluvial fans and fan deltas prograded northwestwards from the Catalan Coastal Range to form a series of clastic wedges that were interrupted by marine transgressions of period varying from 60,000 to a few hundred years, resulting in a highly cyclic succession. The cyclicity of the succession was controlled by a combination of syndepositional basin-margin tectonics, high sediment supply, and eustatic sea-level changes. Analysis of one of the component (25-40 m thick) transgressive-to-regressive sequences (10,000-20,000 year duration) shows that within its transgressive part the alluvial and coastal-plain deposits are extensive and thickly developed whereas shoreline lithosomes are narrow and thin. In the overlying regressive part the opposite relationship is documented. The transgressive and regressive tracts thus have an overall landward-expanding and seaward-expanding geometry, respectively. Six ichnofabrics have been documented in the succession, ranging from nonmarine to offshore-transition in origin. These ichnofabrics are used to help define sequence boundaries, flooding surfaces, and maximum flooding surfaces, as well as to increase the resolution of the stratigraphic analysis. Within the transgressive tract of the main sequence, nonmarine deposits are separated from marine deposits by a steep, landward-inclined complex of wave-ravinement surfaces. Successive ravinement surfaces have a vertical spacing of about a meter, are offset landwards from each other by less than 100 m, and diverge slightly from each other as they climb through the section. These same erosion surfaces merge with each other basinwards, causing the transgressive tract to thin significantly. Five high-frequency sequences are recognized within the main sequence. The middle one is nearly symmetrical, the lower two are asymmetric and dominated by their transgressive tract, and the upper two are asymmetric but dominated by their regressive tract.

Pre-drill predictions versus post-drill results: use of sequence stratigraphic methods in reduction of exploration risk, Sarawak Deep-water Blocks, Malaysia

Limited well control, great distances from age-equivalent producing fields, and a largely unknown stratigraphy necessitated use of sequence stratigraphic methods to assess exploration risk associated with reservoir, source and seal distribution in the Mobil-operated Deep-water Blocks of Sarawak, Malaysia. These methods allowed predictions to be made and reservoir risks to be halved in each of the locations drilled in 1995. Predictions regarding reservoir and stratigraphy proved correct, as the Mulu-1 and Bako-1 wells penetrated numerous high-quality, thick sandstone reservoirs in the Middle to Lower Miocene section. Shallow marine sandstones dominate the vertical succession in both wells, with characteristic aggradational, upward-coarsening log motifs. Cores display classic wave-generated stratification and hummocky cross-bedding. Evidence, such as marginal–marine to neritic microfauna in cuttings of both wells, supports these interpretations. Lack of hydrocarbon charge in the two wells may be due to their position relative to coaly hydrocarbon source beds. These prospects have high trap and seal integrity, being well defined on seismics as high relief horst blocks covered by a very thick shale-prone section. The Mulu-1 well, for example, is located at least 20–30 km down stratigraphic dip from mapped coeval lower coastal-plain deposits. Amplitude anomalies on the flank of the Mulu horst are probably derived from transported organics buried in deep Plio–Pleistocene kitchens in the northwest portion of the Mobil blocks. Remaining potential of mapped prospects is high and efforts continue at characterizing the petroleum system of the Deep-water Blocks. Seismic attribute and interval velocity analyses provide new clues to the location of probable coaly source rocks, especially when viewed in their regional and sequence stratigraphic context. Future work is planned and will serve to reduce risk to acceptable levels and support further drilling in this prospective hydrocarbon province.

Petroleum potential and depositional environments of Middle Jurassic coals and non-marine deposits, Danish Central Graben, with special reference to the Søgne Basin

New data from five wells in the Søgne Basin, Danish Central Graben of the North Sea - West Lulu-1, West Lulu-3, Lulu-1, Amalie-1 and Cleo-1 - together with previously released data from the West Lulu-2 well, show that the cumulative thickness of the Bryne Formation coal seams decreases towards the palaeo-shoreline from 5.05 m to 0.60 m, and that the seams have varying extents. Their overall organic petrographic and geochemical composition reflects the palaeoenvironmental conditions in the precursor mires, in particular the rate of rise in the water table, principally related to the relative rise in sea level, and the degree of marine influence. Laterally towards the palaeo-shoreline, all coal seams have increased proportions of C27 steranes and higher C35-homohopane indices suggesting stronger marine influence on the coastal reaches of the ancient mires. In each well it is also observed that coal seams formed during accelerated relative sea-level rise (T-seams) are characterised by higher contents of sterane C27 and higher C35-homohopane indices than seams formed during slower rates of base-level rise (R-seams). The most landward and freshwater-influenced parts of the seams have higher proportions of sterane C29 and the highest Pr/Ph ratios.
 The coals, with respect to thermal maturity, are well within the oil window, except in the Amalie-1 well where they are more mature. The largest average hydrogen indices and thermally extracted and generated bitumen yields are obtained from the T-seams. However, generally an increase in the hydrogen index is recorded in a seaward direction for all seams. Multivariate regression analysis demonstrates that collotelinite, telinite, the vitrinite maceral group, vitrinite-rich microlithotypes and the TOC content have a significant positive influence on the remaining generative potential represented by S2. Pyrolysis-gas chromatography reveals that during maturation the coals will generate from 72.4 to 82.0% oil-like components and only 18.0 to 27.6% gas. However, this does not necessarily imply that all of these oil-like components can be expelled to form a crude oil accumulation. Distribution of C27–29 regular steranes shows good correlation between extracts of Bryne Formation coals and oils/condensates present in Bryne Formation sandstones.
 The sum of evidence indicates that the coals in the Søgne Basin have generated and are still capable of generating liquid and gaseous petroleum, but with respect to petroleum generation potential, they are not as good as the documented oil-prone Middle Jurassic coals from North-East Greenland and Tertiary coals from Asia. Mudstones intercalated with the Bryne Formation coals have a similar or lower generative potential as the coals.
 In areas outside the Søgne Basin, the coastal plain deposits of the Central Graben Group contain predominantly terrestrial-derived kerogen type III or IIb. The thermal maturity of the organic matter ranges from close to or within the peak oil generation range in the oil window (Alma-1x, Anne-3a and M-8 well) to the late oil window (Elly-3 and Falk-1 wells) or close to the end of the oil window (Skjold Flank-1 well). Only a limited generative potential remains in Elly-3, but the kerogen may initially have possessed a good petroleum potential. In the Falk-1 well, a good generative capacity still remains. The kerogen in Skjold Flank-1 may possess the capability to generate condensate and gas, whereas the organic matter in the Alma-1x, Anne-3a and M-8 wells generally exhibits a poor petroleum generative potential.

Mechanisms Controlling Release of Colloids to Groundwater in a Southeastern Coastal Plain Aquifer Sand

The release of colloids from a shallow Southeastern Coastal Plain deposit, in response to treatment with solutions that perturbed electrostatic and cementitious associations among the clay-size constituents, suggested that these constituents are predominantly chemically bound within the interstitial matrix. Sediment-packed columns subjected to a sequence of high/low ionic strength solutions, acidic pH (2.6) solutions, and anionic surfactant solutions yielded undetectable colloid releases. Treatment with elevated pH (8.8) solutions and solutions containing phosphate resulted in mobilization of colloids only partially representative of the bulk matrix. Organic acids, which both (i) initiated dissolution of the amorphous iron oxyhydroxide intermediaries among kaolinite books and (ii) imparted negative charge to the iron oxyhydroxide surfaces to generate sufficiently repulsive forces among the juxtaposed matrix constituents, appeared to induce mobilization of colloids compositionally representative of the ent...

Lithostratigraphy, sedimentary evolution and sequence stratigraphy of the Upper Proterozoic Lyell Land Group (Eleonore Bay Supergroup) of East and North-East Greenland

The Late Proterozoic Lyell Land Group is an approximately 3 km thick succession of siliciclastic shelf deposits, within the upper part of the Eleonore Bay Supergroup. It is widely exposed in the region between Ardencaple Fjord in the north and Canning Land in the south. In this paper the seven formations named by Sønderholm & Tirsgaard (1993) are formally described. These are from base to top: the Kempe Fjord Formation (400-600 m thick), the Sandertop Formation (200-405 m thick), the Berzelius Bjerg Formation (250-450 m thick), the Kap Alfred Formation (500-640 m thick), the Vibeke Sø Formation (290-325 m thick), the Skjoldungebrae Formation (205-240 m thick) and the Teufelsschloss Formation (35-110 m thick).
 Five facies associations have been recognised. Outer shelf deposits dominated by dark green, brown to dark red mudstones with thin sandstone lenses are mainly found in the Sandertop, Kap Alfred and Skjoldungebræ Formations. Storm- and wave-dominated inner shelf deposits comprising fine-grained sandstones and dark heterolithic mudstones are common in the Sandertop, Kap Alfred, Vibeke Sø and Skjoldungebrae Formations and are also found in southern outcrops of the Teufelsschloss Formation. Tidally influenced shoreface deposits form stacks of laterally extensive sandstone bodies separated by heterolithic mudstones and are only found in the middle part of the Kap Alfred Formation. Storm- and wave-dominated shoreface deposits comprise highly mature, thick and laterally very extensive sandstone bodies of which a few may be traced for distances exceeding 150 km. This association is present in several intervals within all formations of the Lyell Land Group. Tidally dominated coastal plain deposits consist of stacked sandstone sheets forming laterally extensive, multistorey units separated by heterolithic mudstones and sandstones. These sediments form part of the Kempe Fjord and Berzelius Bjerg Formations and are also found in northern outcrops of the Teufelsschloss Formation. Evidence from palaeocurrent data combined with regional lithological variations suggest a consistent general N-S coastline with the basin deepening in an eastward direction. Deflection of geostrophic currents suggest a palaeolatitude on the southern hemisphere.
 The deposits of the Lyell Land Group are subdivided into four, large-scale sequences which overall show the same general sedimentary evolution through time reflecting large-scale, cyclic changes in relative sea-level. The sequences vary in thickness from 400-1000 m and are all readily traceable 300 km parallel and 100 km perpendicular to inferred palaeocoastline. The development of all sequences indicates that major regional translation of facies are related to large-scale forced regressions. Sequence stratigraphic considerations suggest that correlation of formations of the Lyell Land Group with units of the Petermann Bjerg Group some 75 km to the west may be very difficult to carry out.
 Citation: Tirsgaard, H. & Sønderholm, M. 1997: Lithostratigraphy, sedimentary evolution and sequence stratigraphy of the Upper Proterozoic Lyell Land Group (Eleonore Bay Supergroup) of East and North-East Greenland. Geology of Greenland Survey Bulletin 178, 60 pp.

Palynology of the Bryn Mawr Formation (Miocene): insights on the age and genesis of middle atlantic margin fluvial deposits

The ages of fluvial deposits at the head of Chesapeake Bay, thought to be the updip, chronostratigraphic equivalents of a well-dated late Oligocene to Quaternary marine sequence in the Salisbury Embayment, are poorly known. We present data regarding a new occurrence of a palynoflora recovered from the Bryn Mawr Formation in Cecil County, Maryland. The floral assemblage for the Bryn Mawr Formation includes at least 40 taxa at the generic level where Quercus, Cupuliferae, Ilex, Carya, Taxodium, and Pinus are important elements. Most of the taxa identified from the Bryn Mawr Formation palynoflora are extant and occur within the modern middle Atlantic Coastal Plain; however, several important taxa such as Alangium, Engelhardia, Sciadopitys, Tricolporopollenites sp., and Cupuliferoidaepollenites sp. are at present either extinct or exotic to the middle Atlantic Coastal Plain. Comparison of the Bryn Mawr Formation palynoflora to well-dated marine deposits of the Salisbury Embayment suggests a late middle to early late Miocene age (late Serravallian-early Tortonian) for Bryn Mawr Formation phase-2 deposition, supporting previously proposed genetic links to the marine deposits of the Choptank Formation in the subsurface of the Delmarva Peninsula. Relative abundances of common, extant taxa such as Quercus, Carya, Pinus, and NAP (the total non-arboreal pollen) vary considerably throughout late Cenozoic deposits of the middle Atlantic Coastal Plain. We present data for common, extant taxa in a ternary diagram to define discrete palynofacies that discriminate among middle Miocene, late Miocene, Pliocene, and Pleistocene palynofloras. These results show that relative abunances of common, easily identifiable extant pollen may be as diagnostic as exotic taxa in assigning ages to middle Atlantic Coastal Plain deposits. The Bryn Mawr Formation palynoflora, like other middle to late Miocene palynofloras of the middle Atlantic Coastal Plain, suggests terrestrial climatic cooling. In the larger temporal scale of climate change throughout the Cenozoic, this change in Miocene climate is one of three major events that may have had a significant impact on the rate of sediment yield from the Appalachians as recorded in the volume of offshore basin sediments.

Mineralogical and textural criteria for recognizing remnant Cenozoic deposits on the Piedmont: evidence from Sparta and Greene County, Georgia, U.S.A.

Two soil/saprolite profiles from ridge crest sites in central Georgia were investigated for mineralogical and textural trends to help elucidate the relationship between Cenozoic Coastal Plain deposits landward of the Fall Line and the Piedmont. Result from the study of a 10.5 m thick sequence in Sparta, Georgia reveal a deep lateritic profile showing complete loss of plagioclase, gradational loss of K-feldspar, vermiculitization of biotite and precipitation of kaolinite and halloysite within the lower 6 m. The middle section of the sequence is characterized by authigenic kaolinite, halloysite and goethite. The upper 1.35 m is quartz-rich, but also contains K-feldspar, hydroxy-interlayered vermiculite (HIV) and gibbsite. A comparison of grain shape and size indicates a slight textural difference between the upper and middle sections, with the fine sand grains of the upper section being more spherical and less angular. Preliminary results from the study of a 6.35 m sequence in Greene Country, Georgia also reveal a deep lateritic profile. A sharp soil fabric contact, from slightly mottled to highly mottled, occurs 3.1 m below the surface. This profile is characterized by a bimodal clay mineral abundance distribution as a function of depth. This includes an antithetical relationship between kaolinite and HIV, where HIV is abundant at the surface, decreases with depth, increases again at the fabric interface and then decreases with depth. It is suggested that the profiles contain paleosols that are a result of deep lateritic weathering, subsequent allochthonous deposition of a sedimentary cap and then further chemical weathering. The exact relationship between the depositional ages of the veneers and the age, duration and climatic conditions for past weathering events are currently poorly constrained. Recognition of paleo-weathering surfaces has potential importance for our understanding of the record of geologic and paleoclimatic change in the southeastern United States. Identification of such Cenozoic sedimentary veneers and paleosols on the Piedmont also has potential importance for land use practices from the standpoint of better understanding regional soil terrain properties.

Marine and nonmarine systems tracts in fourth-order sequences in the Early-Middle Cenomanian, Dunvegan Alloformation, northeastern British Columbia, Canada

Abstract The Early to Middle Cenomanian Dunvegan Alloformation is a 3rd-order clastic sequence that was deposited on the western margin of the Alberta foreland basin. The alloformation, comprising ten allomembers (A-J) has been mapped over 33 000 km 2 using 1500 well logs and 40 outcrops. Regional flooding surfaces are used to define allomembers because they are more reliably identified in well logs than are Exxon-type unconformities (although in many instances unconformities and flooding surfaces are coplanar). The Dunvegan records episodic deltaic progradation from NW to SE along the axis of the foreland basin. This paper focuses on an 800 km 2 study area in NE British Columbia where both shallow marine and coastal plain strata are exposed in the valleys of the Peace and Beatton rivers. Marine strata comprise sandier-upward successions that grade from platy mudstone through cm-scale interbeds of wave rippled fine sandstone to dm-scale beds of HCS, commonly including large gutter casts. Successions may be capped by SCS and cross-bedded, fine-grained sandstone, sometimes with a rooted top. The succession of facies suggests a strongly wave-influenced deltaic shoreline. Gutter casts are consistently orientated shore-normal and appear to have been formed by oscillatory wave scour during storms. Sandstone distribution varies between successive progradational packages (‘shingles’) in allomember J, suggesting that delta switching was an important control on depositional cyclicity. Coastal plain deposits include small-scale (few metres) coarsening-upward successions of carbonaceous mudstone, siltstone and fine sandstone interpreted as lake and bay-fill deposits. Decimetre scale sharp-based sandstones may represent crevasse splays whereas lenticular, rippled and crossbedded sandstones were probably deposited in distributary channels. Rooted palaeosols are abundant. Both coastal plain and marine strata are locally replaced by erosive-based bodies of cross-bedded sandstone up to 25 m thick and 0.5–3 km wide, interpreted as incised valley fills underlain by type 1 sequence boundaries. Additional evidence of relative sea-level fall is provided by regressive surfaces of marine erosion beneath sharp-based shoreface sandstones. If attached to highstand deposits, these sandstones are assigned to the falling stage systems tract, whereas detached sandstones are assigned to the lowstand systems tract. During the early part of the transgressive systems tract, sedimentation was confined to incised valleys but later, interfluves were buried by sediments that locally contain dense Thalassinoides burrow systems, Teredolites and well-developed mud drapes, suggestive of brackish, tidally-influenced conditions. Overlying coastal plain strata lack evidence of marine influence and are attributed to the highstand systems tract.