Mudflat Facies Research Articles

Diagenesis of the Sandflat and Mudflat Facies of the Upper Queen Formation, Midland Basin, Texas

The upper Queen Formation (Permian, Guadalupian) of the Midland basin, Texas, consists of cyclically interbedded clastics and evaporites that were deposited in a fluvial-dominated continental sabkha environment. Fluvial sandflat deposits, consisting of thin units (0.2-5.0 m) of very fine grained arkosic sandstones constitute reservoir horizons, whereas 0.1-1.3 m thick units of coarse siltstones and evaporites of playa-mudflat deposits are nonproductive. This study addresses the diagenetic histories of the reservoir and nonreservoir clastics. The primary porosity of the clastics was first reduced by pore-filling hematitic smectite clay, anhydrite, and dolomite during an early diagenetic phase. Subsequent dissolution of the anhydrite and dolomite by acidic pore-waters created high porosities (mean = 15%) and permeabilities (mean = 70 md) in the sandflat deposits, porosities which were only slightly occluded by later dissolution and reprecipitation of grain-lining smectite. Pore-water movement and subsequent hydrocarbon migration were both controlled by the coarser grain size and lower clay-matrix and silt content of these sandflat deposits. In contrast, the finer grain size and higher clay-matrix and silt content prevented similar dissolution of cements within the mudflat facies, which have significantly lower porosities (mean{lt}10%) and permeabilities (mean{lt}0.1 md). Fluids and gases used in enhanced recovery techniques will follow pathwaysmore » created by dissolution of anhydrite and dolomite cements within the sandflat facies. However, caution must be used with fluids that can cause swelling of the grain-lining smectite.« less

Depositional Environments and Reservoir Compartmentalization Within the Frio Zone 21-B Reservoir, Tijerina-Canales-Blucher Field, South Texas

Depositional Environments and Reservoir Compartmentalization Within the Frio Zone 21-B Reservoir, Tijerina-Canales-Blucher Field, South Texas

Depositional setting and geometric structure of the Beypazari lignite deposits, Central Anatolia, Turkey

The Neogene Beypazari basin is one of the important coal districts of Central Anatolia with approximately 600 million short tons lignite reserves. The coal-bearing Neogene sediments occurring in the Beypazari basin are divided into seven formations, in ascending order; Çoraklar, Hirka, Akpinar, Çayirhan, Bozbelen and Kirmir Formations with Sariyar Limestone and Teke volcanics. The Çoraklar Formation consists of cross-bedded sandstones, channel-fill conglomerates, mudstones, carbonaceous shales and volcanoclastic pebblestones, which are fluvial in origin. The lower lignite seam occurs in the lower part of the Çoraklar Formation. The upper lignite seam occurs in the uppermost part of the Çoraklar Formation and is overlain by the Hirka Formation with a sharp contact. The Hirka Formation consists mainly of alternating shale, mudstone, bituminous shale, claystone, tuffite and silicified limestone, and they all are apparently of lacustrine origin. The lignite deposite occur in the Çayirhan and Koyunaǧili parts of the Beypazari Neogene basin. The Çayirhan coal field consists of lower and upper lignite seams, but the Koyunaǧili field contains only an upper lignite seam. The lower lignite seam, which does not crop out at the surface, indicates a fluvial origin of the lignite deposits, based on the lateral discontinuity and the lower sulphur content of the lower lignite seam, and the sedimentologic and stratigraphic features of the associated sediments. But the uniform stratigraphic and sedimentologic features, high sulphur content and wide-spread distribution of the upper lignite seam indicate that the upper lignites were deposited probably in a mud-flat facies of playa-lake environment. The lower and upper lignites are completely different in relation to the depositional environment, the geometry and degree of rank in lateral directions. The lateral spreading and geometry of the lower lignite deposits were controlled by channel, floodplain and well-drained marshes of a fluvial system. On the basis of recent drillings and field investigations, the lower lignite deposit has been demonstrated to be a linear spreading parallel to the axis of the channel fills and throughcross beds in clastic sediments of fluvial facies. Therefore, the lower lignite deposits trend along a northeastern direction and is not expected to be as widely spread as the upper lignites.

Sedimentalogical and stratigraphic analyses of the Lagoa Feia Formation, rift phase of Campos Basin, offshore Brazil

The Campos Basin is located offshore the State of Rio de Janeiro along the Southeast Brazilian Continental Margin. It comprises an approximate area of 100,00 km 2 up to 3,400 m Isobath. The Lagoa Feia Formation comprises mainly the rift phase sediments of the basin. Intense tectonic activity generated normal faulting with a preferential northeastern direction and great vertical displacement. Large basalt flows, with ages varying between 120 Ma and 130 Ma, represent the onset of the rift system forming the basement upon which Lagoa Feia formation sediments were deposited. The lack of marine fossils indicates non-marine depositional environments for this formation. The formation can be subdivided into four deposition sequences: Basal Clastic Sequence, Talc-Srevensltic Sequence, Coquinas Sequence, and Clastic-Evaporitic Sequence. Sediments of the three basal sequences are indicative of typical lacustrine environments. The presence of talc and stevensite clay-minerals, and the diagenetic assemblage of the Coquinas Sequence suggest that this lake had alkaline brackish to saline waters. Alluvial fans and their associated facies deve loped on the western border and adjacent to other highs of the basin. Sand flat and mud flat facies compose the marginal portions of the lake, while in deeper waters hydrocarbon generating shales were deposited. The Coquinas Sequence represents an expressive amount of pelecipod calcirudites, and calcarenites deposits, which now are important hydrocarbon reservoirs. An important and regionally widespread erosional unconformity separates the Coquinas Sequence of the overlying Clastic-Evaporitic Sequence, which is characterized by shallow water sedimentation defined through stromatolitic and nodular limestones associated with extensive deposition of alluvial fans. The top of the Lagoa Feia Formation is marked by a thick evaporitic layer deposited under hot arid to semi-arid climate and relative ly stable tectonic conditions, connected with the ocean at the south.

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.

Holocene sedimentology of hypersaline Lake Urmia, Northwestern Iran

A limnogeological expedition examined the sedimentary record of Lake Urmia, one of the world's largest saline lakes, located in a tectonically active, arid, intermontane plateau in northwestern Iran, near the cradle of western civilization. Lake Urmia resembles the Great Salt Lake, U.S.A. in many respects of morphology, water chemistry, and sediments. The present lake area is about 5000 km 2, shallow (8–12 m), and a perennial sodium chloride—sulfate system (22% salts). High resolution (3.5 kHz) seismic profiles show morphological relicts from a desiccation playa phase buried below only a few meters of sediments from lacustral phases. In places, around the deeper areas, the lake floor is not smooth but covered with mounds aligned in prevailing current directions. These are erosional relicts rather than bioherms. Sediments comprise aragonite chemical precipitates, fecal-pellet sands, detrital clayey muds, thin aragonite crusts, oolites, various gypsum types and occurrences of dolomite in peripheral areas. Organic matter, characteristic of the present shorelines, is not preserved at depth in basinal areas. Piston cores up to 6 m long penetrated a Holocene sequence of hypersaline facies with laminated aragonite—fecal-pellet muds and bottomed in a playa—mudflat facies with central gypsiferous muds and marginal terrigenous to dolomitic muds. Preliminary radiocarbon and pollen analyses suggest a playa stage prior to 9000 yr B.P. with saline lake deposition in a cool arid climate. From 9000 to 7500 yr B.P., higher-energy facies prevailed in a shallow saline lake and, since then, present-day saline environments have persisted with evidence of numerous second-order water-level fluctuations. The preliminary results suggest a lake system out-of-phase with North African and some other Middle Eastern lakes.

The sedimentology of the Lower Old Red Sandstone near New Aberdour, Grampian Region

Synopsis The Lower Old Red Sandstone exposed on the coast near New Aberdour can be divided into a lower sandstone and conglomerate formation and an upper sandy mudstone formation which contains several sandstone lenses in its upper part. The lower formation can be further subdivided into four lithofacies assemblages (Facies 1A to 1D) consisting of, respectively, debris flow conglomerates, stream channel deposits, proximal alluvial fan deposits, and distal fan/sandflat deposits. Facies 2A of Formation 2 consists of a mud flat (playa) facies, containing evidence for pedogenesis (calcretization), and bioturbation, whereas Facies 2B, the sandstone lenses, reflect a return to higher energy, probably alluvial fan, deposition. The sediments were laid down in a small fault-bounded basin. The influence of tectonic activity and fan sedimentary processes are reflected in fining upwards ‘megasequences’ and ‘sequences’ respectively. Periods during which some fan segments and the adjacent playa received little sediment are reflected in the occurrence of numerous calcrete layers in the mudflat/playa facies.

Lacustrine-Humate Model for Primary Uranium Ore Deposits, Grants Uranium Region, New Mexico

Two generations of uranium ore, primary and redistributed, occur in fluvial sandstones of the Upper Jurassic Morrison Formation in the San Juan basin; the two stages of ore formation can be related to the hydrologic history of the basin. Primary ore formed soon after Morrison deposition, in the Late Jurassic to Early Cretaceous, and a model, the lacustrine-humate model, is offered that views primary mineralization as a diagenetic event related to early pore fluid evolution. The basic premise is that the humate, a pore-filling organic material closely associated with primary ore, originated as humic acids dissolved in pore waters of greenish-gray lacustrine mudstones deposited in the mud-flat facies of the Brushy Basin Member and similar K shale beds in the Westwater Can on Member. During compaction associated with early burial, formation water expelled from lacustrine mudstone units carried these humic acids into adjacent sandstone beds where the organics precipitated, forming the humate deposits that concentrated uranium. During the Tertiary, much later in the hydrologic history of the basin, when Jurassic sediments were largely compacted, oxygenated ground water flowed basinward from uplifted basin margins. This invasion of Morrison sandstone beds by oxidizing ground waters redistributed uranium from primary ores along redox boundaries, forming ore deposits that resemble roll-front-type uranium ores.

Alteration of Magnetite and Ilmenite in Upper Jurassic Morrison Formation, San Juan Basin, New Mexico: Relationship to Facies and Primary Uranium Mineralization: ABSTRACT

Petrographic studies of outcrop and drill core samples in the Westwater Canyon Member of the Morrison Formation along the southern and western margins of the San Juan basin reveal a close spatial relationship among altered (iron-leached) detrital magnetite and ilmenite (FeTi oxides), depositional facies in the overlying Brushy Basin Member, and distribution of primary uranium deposits. Iron leaching of FeTi oxides resulted from passage of solutions containing soluble organic material; concentrations of this organic material are the sites of the primary uranium orebodies. Along the southern and western parts of the basin, FeTi oxides typically have been leached in the upper Westwater Member, but are unaltered in the lower Westwater; however, locally, leaching occurred thro ghout the Westwater. This zone of leaching systematically thins northward to zero, where unleached FeTi oxides occur throughout the Westwater. Regional patterns of alteration of FeTi oxides correspond to regional facies distribution in the overlying Brushy Basin Member. Extensive FeTi oxide leaching characterizes the Westwater beneath the smectite-rich mud-flat facies of the Brushy Basin, whereas negligible leaching characterizes the Westwater beneath the zeolite-rich playa facies of the Brushy Basin. This correspondence between facies and alteration patterns suggests that solutions responsible for solubilization of organic material, which in turn leached FeTi oxides in the Westwater, originated from the mud-flat facies of the Brushy Basin. Organic material that precipitated from these solutions concentrated uranium to form primary uranium orebodies; therefore, distribution of the Brushy Basin mud-flat facies may define, and restrict, distribution of primary orebodies in the Westwater. End_of_Article - Last_Page 937------------

Holocene Infilling of Coastal Lagoons by Mixed Terrigenous Siliciclastic and Marine Carbonate Sediments, Vieques, Puerto Rico: ABSTRACT

Infilling of coastal lagoons along the southern coast of Vieques, Puerto Rico, during the Holocene transgression is the result of contributions from both terrigenous siliciclastic and marine carbonate sources. Four lagoons displaying varying infilling and interaction with open marine waters were chosen for detailed stratigraphic study. Cores taken perpendicular to modern lithotope trends show a well-defined sequence that is similar throughout the lagoons. The stratigraphy also defines two distinct origins of the lagoonal basins: those resulting from sheltering provided by Oligocene-Miocene limestones and those developed by accretion of beach ridges seaward of shallow embayments. Sedimentation in both types of lagoons began with deposition of terrigenous colluvium. Rising sea level was accompanied by storm-generated marine derived gravels that accumulated above the colluvium. Intertidal mud-flat facies and subsequent Diplanthera peat deposits denote the existence of restricted intertidal and subtidal environments respectively. These facies were overlain by molluscan gravel and Halimeda sand indicating increased water depth and improved circulation with the open marine environment. Mangrove peats are prominent in cores from the lagoonal margins. They show seaward migration of this environment as terrigenous sediment continued to prograde into the lagoons. Lagoonal margins display a terrigenous, siliciclastic-dominated progradational sequence, whereas the central and seaward portions display a mixed siliciclastic and carbonate transgressive sequence. These sequences occur in close geographic proximity and could provide problems of interpretation for the geologist concerned with the ancient record if detailed stratigraphic data were not available. End_of_Article - Last_Page 446------------

Sedimentology and evaporite genesis in a Holocene continental‐sabkha playa basin—Bristol Dry Lake, California

ABSTRACTBristol Dry Lake, a 155 km2 continental‐sabkha playa basin in the Mojave Desert of south eastern California, is filled with at least 300 m of interbedded terrigenous clastics, gypsum, anhydrite, and halite. Evaporite facies conform approximately to a bull's eye pattern with gypsum and anhydrite surrounding a basin centre accumulation of halite. Transects through Bristol Dry Lake, from the alluvial fan to the centre of the playa, reveal: (1) crudely‐bedded, alluvial fan clastics interfingering with (2) playa‐margin sand flat and wadi sand and silt, followed by (3) gypsum, anhydrite, chaotic mud halite, and clay of the saline mud flat, and (4) salt‐pan halite beds.Terrigenous clastics were deposited in Bristol Dry Lake by sheetflow and by suspension settling from ponded floodwater. Some sediment has been reworked by aeolian processes to form barchan dunes around the playa margin. Thin nodular‐like beds of anhydrite and several types of gypsum occur across most of the playa. Giant hopper‐shaped halite cubes are suspended in saline mud flat facies, suggesting that they grew displacively in brine soaked sediment just below the surface. Thick beds (4 m) of halite, in the playa centre, may have formed through a complex alternating history of subaqueous and intrasedimentary precipitation under the influence of periodic floods, intense evaporation and brine‐level lowering, and capillary discharge of brines.The stratigraphy in the playa centre is cyclic. An ideal cycle consists of: (1) chaotic mud halite at the base overlain by (2) green to red clay with abundant, giant hoppers, and at the top (3) red clay, gypsum, and anhydrite with flaser‐ to wavy‐bedded sand and silt. This type of cycle probably records a gradual progradation of mud‐flat facies over salt pans.Bristol Dry Lake sediments are nearly identical to some of the Permian evaporites of the Permian Basin region, U.S.A. and they can serve as modern analogues for ancient‐sabkha facies analysis.

Facies Anatomy of Modern Continental Sabkha, Bristol Dry Lake, California: ABSTRACT

Bristol Dry Lake is a 155-sq km fluvial-lacustrine dominated, continental sabkha, or playa, in the Mojave Desert of southeastern California, and is filled with at least 300 m of interbedded terrigenous clastics, gypsum, anhydrite, and halite. The evaporite facies roughly form a bull's-eye pattern with abundnat gypsum and anhydrite surrounding a basin center accumulation of halite. Transects through Bristol Dry Lake, from the alluvial fan and sand flat to the center of the playa, reveal (1) crudely bedded, coarse-grained clastics prograding over and interfingering with either (2) wadi (alluvial/eolian) sand and silt, or (3) mud-flat facies of nodular to enterolithic gypsum or anhydrite and blades of gypsum in red-brown silt and clay, followed by (4) saline mud-flat facies f red-brown silt and clay crowded with giant (15 cm diameter), displacive, hopper-shaped crystals of halite, and (5) salt-pan beds of chaotic mud-halite up to 4 m thick in the center of the playa. Deposition of terrigenous clastics was by fluvial-sheetflood processes around the toes of alluvial fans, fluvial flow through very shallow rills and suspension settling in the mud-flat environments. Much of the sediment is reworked by eolian processes. Evaporites are precipitated at or just below the sabkha surface from discharging brines. Lithofacies of this modern continental sabkha are nearly identical to those comprising the Middle-Upper Permian evaporites of the Texas and Oklahoma panhandles, and they are excellent process analogs for ancient facies analysis. End_of_Article - Last_Page 934------------

Definition of Depositional Facies of Parachute Creek Member of Green River Formation, Colorado--Evidence from Sulfur Isotopes and Whole-Rock Mineralogic Data: ABSTRACT

The Parachute Creek Member of the Green River Formation in the southern Piceance Creek basin displays four major lacustrine and marginal-lacustrine facies: deltaic-interdeltaic mudflat, carbonate mudflat, proximal open lacustrine, and distal open lacustrine. These facies are strongly gradational across the basin and their definition is not clearly evident from study of the physical characteristics of each facies. Additional evidence from whole-rock mineralogy (defined by X-ray diffraction) and sulfur isotopes, however, help to clarify each facies. The deltaic-interdeltaic mudflat facies contains channel-form cross-stratified sandstone intercalated with pyritic mudrock and marlstone. Detrital quartz, K-feldspar, Na-plagioclase, and rock fragments characterize the sandstone. The mudrock and marlstone contain both calcite and dolomite plus detrital silicate minerals; ^dgr34S values of pyrite from this facies range from 2 to 26 per mill and average 12 per mill. The carbonate mudflat facies is dominated by dolomitic algal stromatolite, oolite, pisolite, and interclastic carbonate rock, and interbedded green to gray pyritic marlstone. The marlstone contains both calcite and dolomite and considerable authigenic analcime; ^dgr34S values range from 5 to 40 per mill and average 16 per mill. End_Page 824------------------------------ Proximal open-lacustrine deposition produced well-stratified marlstone and lean oil shale, and rare algal stromatolite. Detrital silicate minerals become less abundant and are volumetrically replaced by dolomite, Fe-dolomite, excess-Ca ankerite, analcime, and rare dawsonite. The ^dgr34S values of pyrite from this facies range from 22 to 54 per mill and average about 30 per mill. The distal open-lacustrine facies is represented by richer grades of oil shale (greater than 15 gal/ton) and saline minerals (nahcolite and halite). The oil shale contains abundant Ca-Fe-Mg-carbonate phases, authigenic quartz, K-feldspar, Na-plagioclase, and dawsonite. Analcime is rare. The ^dgr34S values of pyrite and marcasite range from 18 to 66 per mill and average 35 per mill. Overall, the Parachute Creek Member shows that detrital silicate minerals and calcite are concentrated in the marginal-lacustrine facies but authigenic silicate minerals, complex Mg-Ca-Fe-carbonate minerals, and saline minerals are concentrated in the open-lacustrine facies. Sulfur-isotope data show that iron sulfide minerals become progressively enriched in 34S toward the open-lacustrine environment of deposition. End_of_Article - Last_Page 825------------

Green River Formation, Wyoming: A Playa-Lake Complex

Recent observations in the Green River Formation suggest that ancient “Lake Gosiute” was a playa-lake complex (Eugster and Surdam, 1973). In this paper, the new playa-lake model is tested in a basin-wide study of surface and subsurface observations. The rocks deposited in and around “Lake Gosiute” can be divided into three distinct facies: (1) marginal silt and sand, (2) carbonate mud flat, and (3) lacustrine. Each lithologic facies has a characteristic carbonate mineral assemblage. The marginal facies is characterized by calcite concretions and calcareous cements. The mud-flat facies is characterized by calcite and (or) dolomite. The lacustrine facies is characterized either by trona (sodium carbonate) or by oil shale (either calcitic or dolomitic). The regional distribution pattern of lithologic facies and mineral zones in the Green River Formation of Wyoming is identical with that of modern playa-lake complexes. Moreover, in the Tipton Shale Member, once supposed to have been deposited in a large, deep, open, fresh-water lake (Bradley, 1963), there is strong evidence demonstrating large fluctuations in the position of the shoreline and progressive increases in salinity and alkalinity of the lake water. By mapping the regional distribution and types of lateral changes characterizing individual stromatolite units, the fluctuations in shoreline position can be quantified. The vertical distribution of fossils and ooliths in the Green River Formation allows an evaluation of water chemistry. In addition, the assemblage of sedimentary structures in the Tipton Shale Member is compatible only with a sedimentologic model characterized by shallow-water deposition and frequent subaerial exposure. Thus, the deep-water stratified-lake model is untenable not only for the Wilkins Peak Member but also for the Tipton Shale Member of the Green River Formation. In contrast, the playa-lake model is consistent with the physical, chemical, and paleontologic aspects of the Green River Formation of Wyoming.

CRYSTAL CASTS IN UPPER TRIASSIC LOCKATONG AND BRUNSWICK FORMATIONS

SUMMARYUpper Triassic Lockatong argillite (lacustrine facies) and reddish‐brown Brunswick mudstone (mudflat facies) contain numerous pseudomorphs after glauberite. Those in the Brunswick Formation are large calcite casts of complete crystals both isolated and in bunches in beds a few inches thick, or are slender skeletal crystal casts forming open‐work rosettes in massive mudstone. Those in analcime‐rich dolomitic Lockatong argillite are smaller, more slender, skeletal crystal‐casts filled with dolomite and analcime; most of them are scattered through the rock but locally arranged in vague geometric patterns; less commonly they form conspicuous rosettes and downward‐ diverging conical sprays.Many glauberite crystals (and rarely halite in the Brunswick mudstone) grew in soft mud during Late Triassic time, thus emphasizing dryness and the role of saline water in the later history of the closed carbonate‐sulphate Lockatong lake. Early extraction of calcium and magnesium carbonates and later of sodium and silica during each chemical cycle left the lake enriched in calcium, sodium, and sulphate. These crystallized as glauberite and possibly anhydrite in lake‐bottom mud and in surface mudcracks during the waning of a chemical cycle.Crystals of the soluble salts in the Lockatong mud were then replaced by dolomite and analcime from solutions released during dewatering of the mud.

Origin of Sodium-Rich Triassic Lacustrine Deposits, New Jersey and Pennsylvania: ABSTRACT

Successive Stockton arkose, Lockatong argillite, and Brunswick mudstone, nonmarine basin deposits, contain abundant sodium derived from Na-feldspar-rich source rocks that lay to the east. Lockatong lacustrine deposits (3,750 feet thick), in cycles averaging 15 feet thick, accumulated at a rate of about 0.2 mm. a year. Detrital cycles consist mainly of mudstone containing abundant Na-feldspar, illite (and muscovite) and chlorite, and calcite, but very little quartz or K-feldspar. They are composed of abundant Na2O (4.0%), K2O (5.2%), and MgO (3.8%), and only about 49 per cent SiO2. They accumulated in an open lake with estimated low salinity, Eh 0 to -2.5, and pH 7 to 8. Chemical cycles consist mainly of colloidal-chemical mudstone containing abundant analcime, Na-feldspar, dolomite and calcite, and illite and chlorite; quartz is absent and K-feldspar is very rare. The rock is composed of K2O (3.3%), abundant MgO (4.0%), very abundant Na2O (6.4%), and only 49 per cent SiO2. Cr, V, Ni, and Co approach or exceed concentrations in marine mud. These cycles accumulated when the lake was closed; gray deposits in an environment of estimated moderate salinity, Eh -1 to -3, and pH 7.5 to 8.5, and grayish-red deposits in an environment of somewhat higher salinity, Eh -0.5 to 1.5, and pH 7.0-8.5. Lockatong detrital and chemical cycles shared a common physical (lacustrine) environment. But detrital cycles and fine-grained Stockton fluvial facies shared a rather similar geochemical environment, as did chemical cycles and lowermost Brunswick mudflat facies. End_of_Article - Last_Page 361------------

ESQUISSE ÉCOLOGIQUE DES COMTÉS DE L'ISLET ET DE KAMOURASKA

The vegetation of the region south of the St. Lawrence estuary, more specifically L'Islet and Kamouraska counties, is described in relation to soils and physiographic features.In the first part, a climatic, geologic, geomorphic, and phytogeographic approach is made, summarizing known data for the region. The second part is devoted to the natural vegetation, particularly in its primeval state.On the estuarian lowlands, in the southwest part, the dominant feature is a sugar maple forest which maintains itself in good condition along the coast as far as Saint-Roch-des-Aulnaies. Farther to the northeast, maples are restricted to the Champlain terraces, along the appalachian foothills. The perpetuation of the maple woods is relatively precarious on account of the cold climate. In many cases, maple woods seem to be a relic vegetation. White spruce often reclaims hills where maples have been cut down, especially when the parent-material of the soil has a low calcium content. In the northeast, spruce is the dominant feature of the landscape, on account of the siliceous rocks and a slightly colder climate.On the seashore, the sandy beach facies is characterized by a lyme-grass fringe, and the alluvial mud-flat facies is characterized by salt-water cord-grass. The latter constitutes the original phase of the silty clay soils of the lower plain. In the fresh-water section of the estuary, the alluvial muds, under tidal influence, are characterized by American bulrush and wild rice.Because of its fertile soils, the upper clay plain of the lowlands is entirely under an agricultural régime. Some reliquary fragments of forest allow us to reconstruct the primeval vegetation. In the southwest, a stand, of red maple, associated with American elm, possibly covered these flat and poorly drained soils. In the northeast, there might have been a spruce–sphagnum type of vegetation.The upper Appalachian Plateau has a rolling topography. A maple forest grows on the glacial till of the hills, where limestone delays podsolization. More often a mixed wood occurs, with white spruce, red maple, balsam fir, aspen, and white birch. The depressions are characterized by a black spruce forest, often associated with American larch and eastern white cedar. It seems that red pine and white pine have been characteristic elements of fluvioglacial soils. A coniferous forest is dominant on all sites in the northeastern part of the Plateau.