Lithogenetic Units Research Articles

Prediction of CPTu static sounding parameters based on DPH dynamic probing heavy test on the example of “the Praski terrace” sands inWarsaw title

This paper attempts to relate the parameters obtained from CPTu static sounding and DPH dynamic test conducted in non-cohesive alluvial deposits of the Vistula River. The investigation was carried out in eight test stations located on the left bank of the Vistula River in Warsaw. The presented theses were based on the results of static CPTU and dynamic DPH tests obtained at 8 test stations. Additionally, in order to associate the obtained sounding results to the lithological type of the tested medium, drillings and grain size analyses were performed. The correlation of the different test methods stems from the need to identify and explain observed discrepancies against the background of different geological conditions, such as moisture content or grain size distribution. The comparative analysis of the parameters obtained from static and dynamic probing, is relevant to the alluvial sediments formed the lower over-flood terrace (called “the Praski terrace”) of Warsaw. Based on the comparison this paper proposes a correlation between the cone penetration resistance the sleeve friction and the number of blows, expressed by the functional relationship. Differences in the matching formulas were shown depending on the saturation of the tested sediments. Correlations were referred to a soil type, which enabled to specify the range of applicability of the proposed relationships. The results of the study were further used to show their diversity using statistical methods. This made it possible to assess the variability of the parameters of the non-cohesive soil, which forms a single lithogenetic unit.

A framework for the predictive mapping of forest soil properties in mountain areas

The modelling of forest ecosystems is a broad scientific field, encompassing species distribution, dynamic forest succession, growth and disturbance, and biogeochemical cycles. Soil information is frequently required for a holistic and spatially explicit modelling approach. Information on soil properties at sufficient resolution to be incorporated in spatially distributed models is rare however, in particular for mountain forest areas that are poorly accessible and where the required sampling effort is high. In order to bridge this gap, we aim to develop a concept for predicting spatially continuous forest soil properties in mountain areas and substantiate it by comparing different statistical approaches to digital soil mapping, namely Random Forests and Generalized Additive Models. Therefore, we used field descriptions of 1653 legacy soil profiles from a forest area of 5130 km2 in Tyrol and modelled a variety of soil properties that are essential for the characterisation of forest sites with respect to tree growth. A set of 23 spatially explicit predictor variables, grouped according to geological substrate information, topography, climate, biotic variables, and time–space, were included in the concept and tested. There was a special focus on the predictive relevance of the newly developed geological substrate information, which includes lithogenetic units, lithological composition, and the multilayering of sediments. As a physical soil property, it was possible to predict the plant-available water storage capacity with a significant degree of accuracy, with r2 = 0.49–0.56, while for the biologically driven state variable organic humus layer thickness, r2 = 0.22–0.27 was achieved. For describing soil reaction, Ellenberg’s indicator value of vegetation turned out to be a suitable proxy for soil pH value, and was modelled with a high degree of predictive power with r2 = 0.75–0.77. All model results were verified by different evaluation methods, ranging from cross-validation to comparison with independent datasets, tests for spatial autocorrelation, and considering ecological soundness in variable selection. We were able to show that in addition to variables derived from Digital Terrain Models and climate information, the new type of detailed geological substrate information is the most relevant predictor and is promising for digital soil mapping in mountain areas. This finding was independent of the applied statistical approaches and both Generalized Additive Models and Random Forests showed comparable accuracy and proved to be appropriate for these tasks. In addition, we were able to support the modelling results by interpreting the predictors’ mode of action with regard to the underlying processes controlling soil properties.

Geochemical mapping in polluted floodplains using in situ X-ray fluorescence analysis, geophysical imaging, and statistics: Surprising complexity of floodplain pollution hotspot

This study is focused on a pollution hotspot in a floodplain impacted by uranium mining in the second half of the 20th century. To image the internal structure of the hotspot, we performed surface gamma activity mapping, in situ X-ray fluorescence spectroscopic analysis (XRF) using a portable instrument and manually obtained sediment cores, and electric resistivity imaging of the shallow subsurface with the help of electric resistivity tomography (ERT) and dipole electromagnetic profiling (DEMP). We used two approaches aimed at deciphering the origin of the pollution hotspot: (i) surface pollution mapping and (ii) identification of the deeper lying lithogenetic units. The description of the floodplain subsurface was supported by optically stimulated luminescence (OSL) dating. The surface mapping approach was found insufficient to visualise the hotspot and understand its origin. We recognised deposition non-linear in time (or temporally independent) of younger overbank fines, including mining pollutants over considerably older channel sediments. Our work documents the value of dense geochemical mapping for documentation of fluvial pollution (accessible by portable XRF) as well as the need to understand the structure of the floodplain subsurface (accessible by electric resistivity imaging) and thereby rationalise the hotspot internal structure.

The Paleocene Chance Member of the Fort Union Formation, northern Bighorn Basin, Montana and Wyoming: aperiodic cyclothems in a tectonically dominated lake basin

A 400 m-thick sequence characterized by prominent tabular sandstone beds and a significant amount of marl and limestone occurs in Paleocene strata of the northern part of the Bighorn Basin (Clarks Fork Basin) of Wyoming and Montana. These strata, currently designated as the Belfry Member of the Fort Union Formation, actually consist of two separate but related lithogenetic units. The lower unit, which includes the Belfry Member stratotype, shows a gradual upward increase in tabular sandstone and marl or limestone and is inferred to have been deposited on a drowning flood plain under paralacustrine conditions. The upper unit, here proposed as the Chance Member, is characterized by the presence of six asymmetrical, basin-wide cyclothems. Each cycle begins abruptly with a transgressive surface overlain by laterally extensive tabular sandstone, followed by a micrite-dominated interval that together represent the lacustrine phase of the cycle. These are succeeded by lenticular interbeds of mudstone and sandstone inferred to have been deposited as a prograding fluvio-deltaic and flood plain sequence. The cyclothems are of variable thickness, ranging from ∼30m in the lowest cycle to ∼10 m in the uppermost cycles. Detailed stratigraphic mapping and correlation with the paleomagnetic and vertebrate biostratigraphic framework for the Bighorn Basin places the entire Chance Member within a portion of one vertebrate zone, Ti4, of the middle Tiffanian Provincial Age (59.2 to 58.5 Ma). The variable thickness of the cycles points toward deposition during unequal time intervals and suggests a tectonic origin most likely related to episodic movement of faults bounding the Bighorn Basin.

Geochemical characterisation of Early Cretaceous lacustrine sediments of Bima Formation, Yola Sub-basin, Northern Benue Trough, NE Nigeria: Organic matter input, preservation, paleoenvironment and palaeoclimatic conditions

The Bima Formation is the oldest lithogenetic unit occupying the base of the Cretaceous successions in the Yola Sub-basin of the Northern Benue Trough. It is differentiated into Lower (B1), Middle (B2) and Upper (B3) Bima Members. Integrated organic and inorganic geochemical studies were applied on the lacustrine sediments of the Bima Formation with the aim of reconstructing the palaeodepositional environment and organic matter input in response to climate and tectonism. The analysed sediments were deposited in a freshwater lacustrine environment with a low-salinity stratified water column and suboxic to relatively anoxic conditions, as indicated by the bulk geochemical parameters. The biomarkers provide evidence for a contribution of aquatic algae and microorganisms, with a significant amount of terrigenous organic matter input. The preservation of the organic matter is possibly attributed to the stratified water column with low salinity and suboxic to relatively anoxic conditions. Based on the geochemistry of major and trace elements, the sediments were deposited during semi-arid climatic conditions within passive continental margin setting. This agrees with the tectonic events in the West and Central African Rift System (WCARS) during the Early Cretaceous period.

Facies analysis, palaeoenvironmental reconstruction and stratigraphic development of the Early Cretaceous sediments (Lower Bima Member) in the Yola Sub-basin, Northern Benue Trough, NE Nigeria

The Benue Trough of Nigeria is a major rift basin formed from the tension generated by the separation of African and South American plates in the Early Cretaceous. It is geographically sub-divided into Southern, Central and Northern Benue portions. The Northern Benue Trough comprises two sub-basins; the N–S trending Gongola Sub-basin and the E–W trending Yola Sub-basin. The Bima Formation is the oldest lithogenetic unit occupying the base of the Cretaceous successions in the Northern Benue Trough. It is differentiated into three members; the Lower Bima (B1), the Middle Bima (B2) and the Upper Bima (B3). Facies and their stratigraphical distribution analyses were conducted on the Lower Bima Member exposed mainly at the core of the NE–SW axially trending Lamurde Anticline in the Yola Sub-basin, with an objective to interpret the paleodepositional environments, and to reconstruct the depositional model and the stratigraphical architecture. Ten (10) lithofacies were identified on the basis of lithology, grain size, sedimentary structures and paleocurrent analysis. The facies constitute three (3) major facies associations; the gravelly dominated, the sandy dominated and the fine grain dominated. These facies and facies associations were interpreted and three facies successions were recognized; the alluvial–proximal braided river, the braided river and the lacustrine–marginal lacustrine. The stratigraphic architecture indicates a rifted (?pull-apart) origin as the facies distribution shows a progradational succession from a shallow lacustrine/marginal lacustrine (at the axial part of the basin) to alluvial fan (sediment gravity flow)–proximal braided river (gravel bed braided river) and braided river (channel and overbank) depositional systems. The facies stacking patterns depict sedimentation mainly controlled by allogenic factors of climate and tectonism.

From river valley to estuary: the evolution of the Rhine mouth in the early to middle Holocene (western Netherlands, Rhine-Meuse delta)

AbstractThe aim of this paper is to reconstruct the evolution of the early to middle Holocene Rhine-Meuse river mouths in the western Netherlands and to understand the observed spatial and temporal changes in facies. This is achieved by constructing three delta wide cross-sections using a newly accumulated database with thousands of core descriptions and cone penetration test results, together with a large set of pollen/diatom analyses and OSL/14C-dates. Most of the studied deposits accumulated in the fluvial-to-marine transition zone, a highly complex area due to the interaction of terrestrial and marine processes. Understanding how the facies change within this zone, is necessary to make correct palaeogeographic interpretations.We find a well preserved early to middle Holocene coastal prism resting on lowstand valley floors. Aggradation started after 9 ka cal BP as a result of rapid sea-level rise. Around 8 ka most parts of the study area were permanently flooded and under tidal influence. After 8 ka a bay-head delta was formed near Delft, meaning that little sand could reach the North Sea. Several subsequent avulsions resulted in a shift from the constantly retreating Rhine river mouth to the north. When after 6.5 ka the most northerly river course was formed (Oude Rijn), the central part of the palaeovalley was quickly transgressed and transformed into a large tidal basin. Shortly before 6 ka retrogradation of the coastline halted and tidal inlets began to close, marking the end of the early-middle Holocene transgression.This paper describes the transition from a fluvial valley to an estuary in unprecedented detail and enables more precise palaeo-reconstructions, evaluation of relative importance of fluvial and coastal processes in rapid transgressed river mouths, and more accurate sediment-budget calculations. The described and well illustrated (changes in) facies are coupled to lithogenetic units. This will aid detailed palaeogeographic interpretations from sedimentary successions, not only in the Netherlands, but also in other estuarine and deltaic regions.

A provisional Quaternary and Neogene lithostratigraphical framework for Great Britain

AbstractThis paper presents an overview of a provisional lithostratigraphical framework for the Quaternary and Neogene deposits of Great Britain (England, Scotland and Wales) (onshore). The objective is to provide a workable framework to aid future Quaternary mapping and research, and a stratigraphical scheme capable of use in a wide variety of applications. Using the full hierarchy, a supergroup, group and subgroup lithostratigraphy, based upon the primary mapping unit, the formation, is proposed. It is recommended that some classes of lithogenetically-defined deposits which, at present cannot be accorded formational status, should be assigned informally to one of the proposed groups or subgroups. The framework distinguishes one superficial deposits supergroup within which seven groups are defined: i) Crag Group, marine deposits (Late Pliocene to Early Pleistocene); ii), Dunwich Group, fluvial deposits (pre-Anglian/pre-Elsterian); iii) Residual Deposits Group; iv) British Coastal Deposits Group, coastal and marine deposits (Anglian to Holocene); v) Britannia Catchments Group, fluvial, organic and mass movement deposits (Anglian to Holocene) within broadly defined catchment areas related to Late Devensian to present-day physiography; vi) Albion Glacigenic Group, glacigenic deposits (pre-Devensian/pre-Weichselian), and vii) Caledonia Glacigenic Group, glacigenic deposits (Devensian/Weichselian). North of the Devensian (Weichselian) ice-sheet limit, a series of glacigenic subgroups are defined geographically for the two glacigenic groups on the basis of mappable formations of till. The subgroups include associated formations of glaciofluvial and glaciolacustrine deposits. Consequently some of the glacigenic water-lain units may extend beyond the Devensian limit. Catchment subgroups of the Britannia Catchments Group are proposed for formations and lithogenetic units defined within broad present-day physiographic regions by major river drainage systems that have developed since Middle Pleistocene time. Lithostratigraphical description and correlation of formations will aid the refinement of the proposed framework and enable the development of lithostratigraphical maps and three-dimensional models. As well as offering a unified framework for onshore Quaternary and Neogene deposits the proposed supergroup, group and subgroup structure may prove useful for a wide range of regional applications (e.g. hydrological, hydrogeological, engineering).

Sequence mapping of Holocene coastal lowlands: the application of the Streif classification system in the Belgian coastal plain

A geological map of the Holocene deposits of a portion of the western Belgian coastal plain is presented. The map differs from a conventional geological map which is of little use for coastal lowlands because of the high lateral and vertical variability in lithology in the subsoil. The method of sequence maps was chosen because these maps allow the representation of the entire vertical sequence of the Holocene deposits. A sequence map is constructed on the basis of profile types consisting of the vertical succession of the various mapping units. In order to produce a user-friendly map, preference was given to lithogenetic units instead of formal lithostratigraphic units for the determination of mapping units. The organisation of the mapping units was established according to the Streif classification system. The application of the system is demonstrated with two different sequence maps each constructed on a different level of the hierarchic system: a general sequence map and a special sequence map showing further differentiation.

Chronohorizons Based on Resistivity Curve Variations - Upper Miocene Sediments of the Ivanić Grad Formation in the Sava Depression (NW Croatia)

Regional definition of chronohorizons represents a fundamental andmost difficult problem in geology. Adequate precision of dating canonly be obtained from biological evolution, radioactive decay andfrom the key surfaces of the sequence stratigraphic concept (MFS,TSE, and LSE). It is concluded in this paper that the variation of formation resistivity values (Ra curve), as measured in wells located inthe Croatian part of the Pannonian Basin System, is also a criterion for the stratigraphic definition of concurrently deposited sediments. This enables the construction of a sequence of lithogenetic units related to very small time-intervals. The morphology of the resistivity curve measured in well sections composed of massive marls (that were deposited in a quiet environment of moderate water depth), is regionally exceptionally well defined. This pattern consists of a succession of peaks of lower and higher resistivity values that are in the same relative position regionally, which results in similar form of the resistivity curves of the wells in the study area. On the curve, one peak of higher values together with the next (overlying) peak of lower ones composes a single cycle(SC). Marls of a single cycle were regionally deposited at the same time, thus enabling the points of both the maximal and minimal resistivity values of each SC to be considered as time-markers (chronohorizons). Variation of the resistivity reflects fine changes of petrographicand granulometric composition which can be associated with cyclic water-level fluctuations (Milankovitch cycles). For future exploration of the remaining, potential hydrocarbon accumulations in the sandstone reservoirs of the Ivanić Grad Formationin the Sava Depression, spatial modelling of the distribution, geometry, facies and palaeocurrent structure of separated depositional episodes and genetic units is suggested. This should be done with special emphasis on the spatial definition of channel sandstones thatare the most important hydrocarbon reservoirs (according to current interpretations).

Well Log-Seismic Sequence Stratigraphy Analysis: An Integrated Approach to Exploration and Development

Well log-seismic sequence stratigraphy analysis is a new technology that integrates high-resolution biostratigraphic and paleobathymetric data and the characteristics of the well log signatures with seismic reflection profiles. This methodology permits the biostratigrapher, geologist, and geophysicist to work together to subdivide a stratigraphic section into packages of sediments bounded by chronostratigraphically significant condensed sections and their associated maximum flooding surfaces and sequences boundaries using well logs and seismic profiles. Each sequence is subdivided into smaller lithogenetic (facies linked) units called systems tracts on the basis of characteristic well log patterns. Faunal and floral abundance and diversity data provide critical information to make reproducible chronostratigraphic correlations. The paleobathymetric interpretations permit the identification of rock types in relation to the depositional environment and systems tracts. The high resolution biostratigraphically is critical in integrated well log-seismic sequence stratigraphic analysis because it provides information for identifying fossil abundance and diversity peaks that are important for recognizing and correlating condensed sections. Added to the well log and seismic data set, it now provides a integrated data package that permits the inexperienced person to use the concepts of seismic well log-sequence stratigraphy to develop expertise and confidence in its practice. In order to obtain consistently reliablemore » results in well log-seismic sequence stratigraphy, a particular procedure must be followed and specific data sets must be used.« less

An Integrated Approach to Exploration and Development in the '90s: Well Log/Seismic Sequence Stratigraphy Analysis

ABSTRACT Well Log-Seismic Sequence Stratigraphy Analysis is a new technology that integrates high resolution biostratigraphic and paleobathymetric data and the characteristics of the well log signatures with seismic reflection profiles. This methodology permits the biostratigrapher, geologist and geophysicist to work together to subdivide a stratigraphic section into packages of sediments bounded by chronostratigraphically significant condensed sections and their associated maximum flooding surfaces and sequence boundaries using well logs and seismic profiles. Each sequence is subdivided into smaller lithogenetic (facies linked) units called systems tracts on the basis of characteristic well-log patterns. The systems tract boundaries, are identified on well logs, marked on two-way time logs or synthetic seismograms and correlated with corresponding systems tracts that have been independently identified on the seismic profiles using seismic-stratigraphic interpretation procedures (Vail and Wornardt, 1990). Faunal and floral abundance and diversity histograms provide critical information to make reproducible chronostratigraphic correlations (Huang and Wornardt, 1986; Shaffer, 1987; Wornardt, 1989; and Shaffer, 1990). The paleobathymetric interpretations permit the identification of rock types in relation to the depositional environment and systems tracts. The high resolution biostratigraphy is critical in integrated well log-seismic sequence stratigraphic analysis because it provides information for identifying fossil abundance and diversity peaks that are important for recognizing and correlating condensed sections and maximum flooding surfaces on well logs and seismic profiles. High resolution biostratigraphy and paleobathymetry data provides the additional data package that has heretofore been missing in seismic sequence stratigraphy. Added to the well log and seismic data set, they provide an integrated data package that permits the inexperienced person to use the concepts of seismic well log-sequence stratigraphy to develop expertise and confidence in its practice. In order to obtain consistently reliable results in well log-seismic sequence stratigraphy, a particular procedure must be fo lowed and specific data sets must be used.

Stratigraphic and Structural Relationships of Strawn Group, Brown, Coleman, and Runnels Counties, Texas: ABSTRACT

The Strawn Group (Atokan-Missourian) is exposed in two approximately triangular areas in north-central Texas: the Brazos River valley and the Colorado River valley. The exposures in the Brazos River valley are relatively well understood and are represented by cycles of fluvial-deltaic and transgressive shallow marine facies. These exposures have been traced into the subsurface, and grade laterally into a mostly carbonate shelf succession. The Strawn Group in the Colorado River valley has not been extensively studied, but recent work is increasing their knowledge of this significant area. In the Colorado River valley, the Strawn Group is subdivided into two lithogenetic units which accumulated in at least two depositional settings. The lower Strawn Group constitutes basin-fill sediments, and represents outer shelf, slope, and submarine-fan depositional environments. The upper Strawn, although exhibiting significant differences, is essentially correlatable to the Strawn Group known in the Brazos River valley and westward into the subsurface. Subsurface mapping westward from the Colorado River valley demonstrates the general applicability of published cyclic interpretations based on surface and subsurface work in north-central Texas. However, in the Colorado River valley and westward into the subsurface, mapping reveals a system of faults presumed to be related to the horst andmore » graben structural development in the Llano uplift area. In addition, the Concho arch, a feature closely related to the Llano uplift, was a positive area which resisted subsidence and acted as a buttress to terrigenous clastic deposition. It thus became a core for a persistent algal buildup.« less

Evolution of Permian Evaporite Basin in Texas Panhandle

Permian (Leonardian to Ochoan) evaporites in the Texas Panhandle were deposited in a range of marine shelf to supratidal environments along an arid coastline. Carbonates in these strata generally were deposited in inner shelf systems and include subtidal to supratidal facies. Landward of shelf environments, evaporites were deposited in brine pans and salt flats. Brine-pan facies are laminated anhydrite and banded salt that formed in shallow, hypersaline waters such as restricted lagoons or supratidal salines. Salt-flat facies are mainly chaotic mixtures of mudstone and halite possibly formed by salt deposition on and within mud flats that bordered brine pans, or in brine-soaked mud-flat depressions. Periodically, mud flats built across the evaporite systems and were suppl ed with red terrestrial clastics, mainly mud and silt. These facies occur together in at least three different types of lithogenetic units. Strata in the Clear Fork Group (Leonardian) are considered deposits of a coastal evaporite basin that was progressively filled by terrestrial clastics. These rocks exhibit regressive cycles of brine-pan, salt-flat, and mud-flat facies. In contrast, San Andres strata (Guadalupian) were deposited in a broad marine embayment with persistent brine-pan conditions, and contain cycles of inner shelf and brine-pan facies. Post-San Andres strata (late Guadalupian and Ochoan) were deposited in the inner reaches of a broad interior salt basin and are composed mainly of mud-flat, salt-flat, and halite-rich brine-pan facies.

Wagwater Trough, Jamaica: Model for Aulacogen Transgressive Sedimentation: ABSTRACT

The Wagwater Trough, Jamaica, tectonically and sedimentologically represents a failed rift arm of the Cayman Trough, a Tertiary extensional plate boundary zone between the North American and Caribbean plates. Integration of regional geologic-geophysical data with the geometrical relationships of the northern Wagwater Belt sediments and volcanics demonstrates that the trough has proceeded through the four major stages of development for failed rift arms outlined by Burke in 1977. Initial basement swelling, rifting, rupture (sedimentation/subsidence), and later convergent deformation stages were correlated to the Tertiary depositional and deformational history within the Wagwater Trough. The transgressive depositional package tectonically recorded these events and can be di ided into 4 lithogenetic units: (1) upper Paleocene-lower Eocene Wagwater alluvial fan conglomerates, (2) lower Eocene Nutfield pillow basalts, (3) lower Eocene Richmond fan delta/submarine fan conglomerates to mudstones, and (4) middle Eocene Font Hill deep marine limestones. The thermal doming and swelling stages occurred during the late Cretaceous-early Paleocene as evidenced by concordant ages of granodiorites (65 m.y.B.P.) in the Cayman and Wagwater Troughs and by the Paleocene unconformity at the base of the Wagwater Formation. This stage resulted in the eventual formation of an active triple junction within the Cayman Trough by late Paleocene. Initial rifting and deposition are recorded by the basal Wagwater Formation. The graded, boulder-cobble conglomeratic litharenites with granodiorite clasts were deposited in an alluvial fan environment adjacent to the fault scarps bounding the recently created Wagwater Trough. The volcanic activity associated with the triple junction is represented by the Nutfield spilitic pillow basalts, extruded in deep marine waters following the deposition of the terrestrial Wagwater Formation. These events together with the following indicate rapid deposition, subsidence, and ocean encroachment into the Wagwater Trough. Active rifting ensued between the North American and Caribbean plates along the east-west-trending Cayman Trough. This rupture stage is characterized by thick transgressive sedimentation and differential subsidence as the nonmarine Wagwater Formation grades into the marine Richmond Formation. This depositional transition is further manifested by both slope and shelf facies of litharenites within the Richmond. The slope facies consists of thick boulder conglomerates fining up into turbidite sequences and volcanic slide conglomerates overlying the Nutfield flows. The shelf facies include: (1) a pebble-cobble conglomeratic fan delta complex, (2) several sandstone feeder channel deposits radiating north from the fan delta to the shelf break, and (3) progradational mudstones and siltstones The interfingering of the Richmond and Wagwater lithogenetic units along a major east-west contact zone in the northern end of the belt is in direct contrast to the abrupt yet conformable slope facies contact between the two formations. These events indicate a much slower subsidence on the shelf in contrast to the rapid subsidence on the slope. By middle Eocene, clastic input was shut off, subsidence and marine transgression ensured, and a deep marine biomicrite, the Font Hill Limestone, capped the Richmond Formation within the Wagwater Trough. The final stage of aulacogen development began during middle Miocene associated with a change from north-south rifting to left lateral motion along the Cayman Trough. As a consequence of this change in plate motion, the Wagwater Trough was uplifted and wrenched by left lateral transcompression. Today, fluvial sedimentation along the Wagwater River, the largest in Jamaica, progresses down the ancient axis of the Wagwater Trough. End_of_Article - Last_Page 532------------

Coal Geology of Eastern McCreary and Western Whitley Counties, Kentucky: ABSTRACT

On the southern flank of the Pocahontas basin, Kentucky, Lower to Middle Pennsylvanian sedimentary rocks contain the coal-bearing strata of eastern McCreary and western Whitley Counties. These strata are divided into two major formations, the Lee and the Breathitt, each composed of quasi-cyclic sequences of sandstones, siltstone, coal, and shale, which have been interpreted as paralic lithogenetic units reflecting depositional environments that periodically intertongued laterally. Cores from six exploratory drill holes penetrating the formations are described, and analyses of basic lithologies in conjunction with geophysical logs are integrated into detailed stratigraphic columns. Correlation using key beds is established, producing geologic sections and a stratigraphic framework to End_Page 614------------------------------ which the coal beds could be referred for specific correlations. Isopach maps of the major coal seams and a structure contour map of the unconformity at the base of the Corbin sandstone were prepared. A fence diagram incorporating the six core holes illustrates a detailed interpretation of the subsurface stratigraphic record, including depositional sequences, distribution, and thickness of the strata. A brief review of the general geologic history of the coal zones is presented. End_of_Article - Last_Page 615------------

Foraminiferal paleoecology of the Montpelier and lower coastal groups (eocene-miocene), Jamaica, West Indies

Two domains of carbonate deposition characterized mid-Tertiary Jamaica. After latest Cretaceous to Paleocene orogeny, submergence of insular paleo-Jamaica accompanied the strike-slip or extensional faulting associated with the formation of the Cayman Trench to the north. Differential subsidence along a series of peripheral subsea escarpments (Duanvale-Wagwater escarpment) produced relief in excess of 2000 m by the Late Eocene. Shoalwater limestones covered the slowly subsiding Cornwall-Middlesex platform, thus ending the supply of clastics to deep-sea bottoms north and east of the escarpment where contemporaneous planktonic-foraminiferal pelagites accumulated. Middle Eocene to Middle Miocene carbonate rocks deposited in the deep-sea represent a distinctive lithogenetic unit termed the Montpelier Group. A preponderance of globigerinacean and radiolarian tests characterizes lower Montpelier microfossil assemblages. Dominant benthonic forms include Melonis pompilioides, Fontbotia wuellerstorfi and species of Stilostomella and Pleurostomella. Available faunal criteria including the assemblage composition, depth preferences of extant species and recurrent morphologic-ecologic patterns suggest abyssal (2000 m) paleo-depths at the site of accumulation on a sediment apron near the base of the Duanvale-Wagwater escarpment. Computed from inferred paleodepth and estimated sedimentary thickness, Middle Eocene to Lower Miocene subsidence totals 2800 m. Biostratigraphic and paleoecologic data do not support the prevalent concept of a regional unconformity within the Montpelier. In the Middle Miocene, regional uplift led to the emergence of the Cornwall-Middlesex platform and to pronounced shoaling of marginal sea bottoms. Here, hemipelagic sedimentation resumed during the later Middle Miocene after the carbonate veneer on the adjacent platform was sufficiently eroded so as to expose noncarbonate rocks. See NAPS document No. 02395 for 67 pages of faunal reference lists, maps of sample locations and tables of foraminiferal occurrences. Order from ASIS/NAPS, c/o Microfiche Publications, 305 East 46th St., New York, N.Y., U.S.A. 10017. Remit with order $9.05 for photocopies or $5.55 for microfiche. Make checks payable to Microfiche Publications.

Paleogeography, Paleobathymetry, and Paleotectonism of Mid-Tertiary Jamaica: ABSTRACT

Two biologically and lithologically distinct realms of carbonate deposition characterized mid-Tertiary Jamaica. After a latest Cretaceous to Paleocene orogenic episode, complete submergence of insular paleo-Jamaica accompanied the strike-slip or extensional faulting associated with the formation of the Cayman Trench on the north. Differential subsidence along a series of peripheral subsea escarpments (Duanvale-Wagwater escarpment) produced relief of more than 2,000 m by the middle Eocene. The slowly subsiding Cornwall-Middlesex platform was covered by shoal-water limestones which ended the supply of clastics to sea-bottoms north and east of the escarpment, End_Page 806------------------------------ where contemporaneous planktonic-foraminiferal pelagites accumulated. Middle Eocene to middle Miocene carbonate rocks deposited in the deep-sea realm represent a distinctive lithogenetic unit herein united as the Montpelier Group. The preponderance of globigerinid and radiolarian tests typifies lower Montpelier (late Eocene to early Miocene) microfossil assemblages. Dominant benthic forms include Melonis pompilioides, Fontbontia wuellorstorfi, and species of Stilostomella and Pleurostomella. Available faunal criteria including assemblage parameters, depth preferences for extant species, and convergent-ecologic morphologies suggest that abyssal (below 2,000 m) paleodepths prevailed at the depositional site on a sediment apron at the base of the Duanvale-Wagwater escarpment. Middle Eocene to early Miocene subsidence computed from inferred paleodepth and estimated sedimentary thickness totals 2,800 m. Biostratigraphic and paleoecologic evidence does not support the concept of a regional unconformity within the Mon pelier, as has been proposed. End_of_Article - Last_Page 807------------

Stratigraphy and Paleogeography of Mabou Group and Related Middle Carboniferous Facies, Nova Scotia, Canada

Marine and nonmarine facies in Nova Scotia, Canada, of Visean through Westphalian A (middle Carboniferous) age are closely related to a tectonic framework that consists of a narrow region of highly mobile blocks surrounded by a broad region of stable blocks. Defining and mapping new lithogenetic units and a more precise method of time control (fossil microspores) supports this hypothesis. Middle Carboniferous units of previous workers, the Windsor, Canso, and Riversdale “groups,” are time-stratigraphic and hence inadequate for defining facies. New lithogenetic units of group rank were defined in a previous report (Belt, 1964) to include strata represented by those time-stratigraphic units. The new units are termed the Windsor Group (restricted Windsor “group”), the Mabou Group (previously a formation), and the Coarse Fluvial Facies (an informal term). Existing formations have, wherever possible, been regrouped into these new units. A new formation (Emery Brook Formation) and a tongue (Glengarry tongue of the Pomquet Formation) are herein proposed. Windsor, Canso, and Riversdale time-stratigraphic units are redefined as Windsorian, Cansoan and Riversdalian Stages. The term Mabou Group is applied to fine-grained “red” and “gray” fluvial and lacustrine strata that succeed the widespread marine and evaporite deposits of the Windsor Group. The Mabou facies represent basin-fill sediments that underlie and also are laterally equivalent to coarse marginal deposits of the Coarse Fluvial Facies. The major zone of mobility during middle Carboniferous time, the Fundy Basin, was irregular in shape and not entirely a region of subsidence. The Caledonia and Cobequid arches, narrow upthrown blocks within the basin, supplied much of the sediment. The New Brunswick and Meguma platforms, bordering the Fundy Basin on the northwest and south, respectively, do not represent a major source of sediment, although much sediment moved across them from outside the Maritime region. The platforms are distinguished from the basins by a thin veneer of relatively undeformed strata; they alternated between gentle uplift and gentle subsidence. In contrast, the subsiding portions of the Fundy Basin received up to 20,000 feet of middle Carboniferous sediment that was subsequently highly folded and faulted and locally mildly metamorphosed. The margin of the Fundy Basin is interpreted as a region of high-angle faults because the thickness of Carboniferous sediment decreases abruptly from the basin onto the platform, Mabou facies grade laterally from “gray” (lacustrine) to “red” (fluvial) facies toward the margin of the basin, and coarse alluvial fans were deposited on the basin side of long, sinuous faults. The margin is believed to parallel the area of long faults that today separate the area of pre-Carboniferous platform, with its thin, slightly deformed Carboniferous cover, from the area of the basin, with its thick, highly deformed Carboniferous strata.

Depositional Environments of Muddy Sandstone, Western Denver Basin, Colorado

In the area of Fort Collins, Colorado, the Lower Cretaceous Muddy (or J) Sandstone can be subdivided into two distinct lithogenetic units. These units, established as a result of detailed description and measurement of surface sections, and recognizable in cores and cuttings from wells in the adjacent subsurface, are herein named the Fort Collins and Horsetooth Members of the Muddy Sandstone. The lower unit, the Fort Collins Member, is a 12-50-foot-thick white, very fine- to fine-grained clayey sandstone, with sub-horizontal stratification and abundant tracks, trails, and burrows on the bedding planes. It grades downward and southward into the Skull Creek Shale, and is overlain, along a knife-edge contact, by the Horsetooth Member. The Fort Collins Member is interpreted as a near-shore marine sandstone deposited in a late stage of a shoaling begun during Skull Creek deposition. The upper unit, the Horsetooth Member, is a 1- 40+-foot-thick light gray, fine-grained, well sorted sandstone, with locally abundant carbonized wood fragments. High-angle cross-stratification is common. Ophiomorpha and other burrows are present only in the upper 3 feet; clam molds are present locally at the base. The Horsetooth Member is tentatively interpreted as part of a shoal-water delta (or possibly modified alluvial plain) assemblage, with a central facies consisting mainly of channel sandstones, and southern and northern facies each consisting of channel sands redistributed and reworked by wave action. Two characteristics of this and other similar ancient models pose somewhat serious interpretive problems: the existence of widespread disconformities separating sandstone members, and the scarcity of mudstone in supposed shoal-water deltaic complexes. Part of the difficulty may be that Recent models are too few in number to account for all the conditions represented in the ancient.