ABSTRACT: The Upper Devonian Grosmont reservoir in Alberta, Canada, is the world’s largest heavy oil/bitumen reservoir hosted in carbonates, with an estimated 400 to 500 billion barrels of “Initial Oil In Place” at average depths of about 250 to 400 m. Our study is part of a more comprehensive effort to evaluate the Grosmont reservoir through geological, geophysical, and petrophysical methods in order to determine the most advantageous method(s) of exploitation. The reservoir is a carbonate–evaporite system. The carbonates of the Grosmont were deposited during the Late Devonian on an extensive platform and/or a ramp in five or six cycles. Evaporites are interbedded with the carbonates at several stratigraphic levels. These evaporites, informally referred to as the “Hondo Formation,” have received scant attention or were ignored in most earlier studies. However, they may play a crucial role regarding the distribution of the most porous and/or permeable reservoir intervals via dissolution, as permeability barriers to compartmentalize the reservoir during or after hydrocarbon migration, and as a source of dissolved sulfate for microbial hydrocarbon degradation. Most Hondo primary evaporites are anhydrite that formed subaqueously as well as displacively and/or replacively very close to the depositional surface. Secondary/diagenetic sulfates were formed from primary sulfates much later and under considerable burial. The locations of primary evaporite deposition were controlled by a shift from carbonate platform or ramp deposition over time. At present the primary sulfates occur in a number of relatively small areas of about 10 by 20 km to 20 by 30 km, with thicknesses of a few meters each. If these areas represent the depositional distribution, the primary evaporites were deposited in a series of large, shallow subaqueous ponds (salinas). Alternatively, the primary evaporites were deposited in a more extensive lagoon, and their present distribution represents the remnants after postdepositional, mainly karstic dissolution. The evaporites would have acted as intraformational flow barriers up until the time of dissolution, which may be a factor in the development of compositional differences of the bitumens contained at various stratigraphic levels. In the eastern part of the Grosmont reservoir the evaporites appear to be dissolved and replaced by solution-collapse breccias and bitumen-supported intervals of dolomite powder. In the western part of the reservoir the sulfates may form effective reservoir seals on the scale of the sizes of former brine ponds. However, it is likely that hydrocarbons bypassed them wherever the carbonates had sufficient permeability and/or where the marls were breached by faults and/or karstification.

Abstract: Detailed analysis of a sedimentary sequence of the Lorca basin (Upper Miocene, southeast Spain), employing stratigraphy, sedimentary petrology, paleontology and organic geochemistry, permitted the establishment of sediment-biomarker relationships of deposits formed under highly variable conditions. The conditions of sedimentation in this sequence range from open marine to strongly hypersaline (both marine and non-marine), as well as a number of marked variations in circulation, water-body chemistry and salinity. Most of the sectíon formed under marine conditions, but the upper part of the sequence is the product of increasingly non-marine waters, suggesting that the basin sporadically may have become a non-marine, hypersaline lake. Sedimentologically, many details of water circulation and the increasing amount of non-marine input are not particularly apparent, but the distribution of n -alkanes and isoprenoids permit these changes to be evaluated in a more convincing fashion.

Abstract Deposits from the modern highstand lacustrine deltas in Lake Malawi offer an excellent opportunity to test models of deltaic sedimentation in a tectonically active setting and to examine variations in sand-body geometry along the axis of a large lake that has significant gradients in physical processes. In 1991 we initiated a coring project in five of the largest deltas in the lake to describe, for the first time, the shallow-water environments of deposition and processes of sedimentation. Percussion drill holes through the lower delta plain in the Linthipe and Dwangwa (shoaling margin) deltas revealed moderate to extreme lithologic variability with sand units up to 15 m thick. Deposited in an alluvial or shallow subaqueous deltaic setting, the sediments ranged from clay to gravel, dark green to brown to orange in color, and contained sections with significant amounts of organic material. Units of gravel up to 1 cm in diameter were recovered, and 60 to 70 percent of the recovered sediments consisted of at least 75 percent sand and gravel. Silts and clays occurred in units up to about 1 m thick, usually in the middle section of each sequence. Although the age, and thus the sediment accumulation rate, is unknown, it is likely that the cored sections (20-26 m deep) represent a few hundred to a few thousand years of accumulation.

Abstract Bottom sediments of the largest lake of the East African Rift system, Lake Tanganyika (length 650 km; maximum depth 1470 m; volume 18,800 km 3 ) (Fig. 1), were extensively studied between 1983 and 1986 by Project PROBE of Duke University (U.S.A.) and Project GEORIFT (1984-1985) of Elf Aquitaine (France), using a wide range of methods such as reflection seismology, piston coring, and dredging. Interpretation of multifold reflection seismic profiles collected by Project PROBE suggests up to 4 km of sediment has accumulated within local depocenters. In addition, seismic profiles exhibit several seismic discontinuities and associated sequences, interpreted to have resulted from large-scale, temporal changes in local tectonics and/or climate (Burgess and others, 1988; Scholz and Rosendahl, 1988). Our interpretation of Recent and Modern profundal sediments in Lake Tanganyika is based on high-resolution, 5-kHz seismic surveys, along with multiple Kullenberg cores from the north and south basins of the lake collected during the GEORIFT project, and our interpretation of littoral clastic and biogenic sedimentation is based on grab sampling, observations from SCUBA, and gravity cores collected by the University of Arizona (Cohen, 1990; Soreghan and Cohen, 1991). These previous studies were supplemented by gravity cores collected in the Burundian part of the northern basin during a 1992 joint field operation by the University of Arizona (U.S.A.), the INSU-CNRS (France), and the CASIMIR project (Belgium). In this paper, our goal is to illustrate fundamental differences in facies associations within Lake Tanganyika that are, to a large degree, controlled by the basin structure.

Abstract Badwater Basin salt pan, Death Valley, California, occupies the bottom of a large, enclosed basin and is the lowest elevation land surface in the Western Hemisphere. Its location, at the end point of regional drainage, makes the sediments collected in the valley of special interest for long-term paleoclimate study. This paper describes the bottom half of a 185 m-long core taken from the salt pan in 1993. Four facies, deposited in a changing saline lacustrine system, appear in the core. (1) Massive black mud and layered, mostly cumulate-textured, halite settled to the bottom of a perennial lake. (2) Layered halite, with distinctive vertical and horizontal dissolution and cementation fabrics, is similar to salt layers that form in the modern salt pan/shallow ephemeral saline lake cycles at Badwater Basin and is interpreted to represent the same or a very similar environment. (3) Brown silty mud with displacively grown salts was deposited in a saline mudflat. (4) Laminated silty mud displays sedimentary structures that reflect desiccation and exposure on a dry mudflat. The succession of facies in the lower 90+ m of the Death Valley core is dominated by the development and eventual desiccation of a perennial lake, which was saline during all or most of its long existence. The oldest sediments in the core record a saline mudflat in transition upward to a salt pan/shallow ephemeral saline lake, probably in response to increased inflow to the basin. After accumulating more than 20 m of halite and mud, the salt pan/ephemeral saline lake system experienced another period of increased inflow and made the transition to a more persistent shallow saline lake. The lake deepened and freshened, and more than 30 m of black mud accumulated at the quiet bottom. The lake occasionally evaporated to halite supersaturation and experienced one longer episode of halite precipitation. The top 18 m of perennial lake sediments record increased halite precipitation, probably during a period of increasing regional aridity. Dry mudflat sediments that cap the perennial lake sequence may record the most arid time, and they are overlain by saline mudflat sediments that signal the beginning of another episode of increasing inflow.

Abstract Continuous core from the Marsing No. 16 well in the southwestern portion of the Uinta Basin, Utah, contains both siliciclastic and carbonate marginal lacustrine and nearshore open lacustrine lithologies. Overall, a long-term stratigraphic record of lake evolution, characterized by an expanding lake, is recorded upward from deltaic through open lacustrine deposits. Coincident with this overall trend of lake expansion is an apparent reduction in supply of siliciclastics to the depositional site and a marked delta retreat. Two contrasting suites of related environments that alternate in concert with changes in climate are postulated to explain the lithofacies recognized in the core. A "wet-climate model," distinguished by evidence for high lake levels combined with high fluvial discharge, is envisioned with a siliciclastic strand plain, lacking in dolomite, and containing channels that served as throughgoing delivery systems for clastics spewing out into the open lake. A "dry-climate model," with evidence for low lake levels combined with low fluvial discharge, consists of a dolomitic mud flat in which clastics are almost entirely lacking and practically the only limestone present occurs as shell-rich and coaly "lags" that represent brief lake-water incursions. Superimposed on a long-term, wet-dry-wet trend, are a succession of finer-scale depositional cycles that are best expressed in the dry part of the trend, in the marginal lacustrine sediment, as limestone-dolomite couplets, but may also be expressed in deltaic and open lacustrine deposits. The typical cycle begins with interspersed shelly limestone and coal deposited with the rise in lake level. This is succeeded by burrowed pelecypod- and ostracod-rich limestone, and is locally capped by strand plain-deposited, laminated, ostracod grainstone, or exposed mudflat-deposited dolomite. The counterpart in the deltaic environment is a coarsening-upward cycle, beginning with interspersed shelly limestone and coal, which is succeeded by burrowed and rippled siltstone and mudstone, and eventually root-mottled siltstone or massive sandstone. The black shale facies contains both oil-prone Type I and gas-prone Type III organic matter, with Type I volumetrically the more important. The open lacustrine limestones have the highest source potential, are oil-prone and immature, with total organic carbon averaging 3.1 percent. The vitrinitic coals within the basal portions of the lacustrine cycles are gas-prone, whereas the marginal lacustrine dolomites and clastics are lean.

Abstract The Lower Cretaceous Viodo Carbonate, a lacustrine carbonate in the Congo Basin, was deposited in the evolving South Atlantic rift basin between Africa and South America. Extensive cores and cuttings permit analysis of the complex relations between carbonate facies and the coeval organic-rich shale of the Marnes Noires Formation. Carbonate deposition was primarily controlled by water depth, initiated by falls in lake level, and terminated by rises. During the most pronounced low stand, mollusc coquinas formed a reef-like margin on the platform margin. During lowstands of lesser magnitude, gastropods and oncolite shoals prograded to the platform edge. The Viodo Carbonate can be divided into three lithostratigraphic members designated the Lower Viodo Carbonate, the Mid-Viodo Shale, and the Upper Viodo Carbonate. Deposition of the Lower Viodo Carbonate began with a major fall in lake level; it consists of limestone and dolomite grainstone beds with characteristics of a Bouma sequence, deposited as a series of turbidite flows. Most clasts originated on a nearby shallow-water platform, but the presence of organic-rich interbeds between the grainstones and shale rip-ups implies anoxic, relatively deep water depositional conditions. The Mid-Viodo Shale is largely calcareous shale with thin beds of carbonate grainstone, interpreted as distal turbidites. It represents submergence of the nearby shallow-water platform. With a second fall in lake level, a shallow-water platform redeveloped basinward of the earlier platform. The Upper Viodo Carbonate includes both shallow-water platform and deep water basinal deposits. An inner platform section is divisible into a lower gastropod zone and an upper oncolite zone. Outer platform facies consist almost entirely of mollusc coquina. Coarse coquina conglomerate is the dominant basinal lithofacies adjacent to the platform, with subordinate oncolite and ostracod grainstones and dark, laminated, organic-rich calcareous shale. The conglomerates were deposited entirely in a relatively deep lake as subaqueous debris flows triggered by collapse of the bank margin. Shales accumulated under anoxic conditions during pauses in carbonate sedimentation. Above both platform and basinal facies, the section consists of shale with beds of carbonate conglomerate, reflecting resubmergence of the platform and displacement of the shoreline landward.

Abstract During the Early Cretaceous, the Lucula Sandstone was deposited along the platform margin of the Malongo Subbasin in offshore Cabinda, Angola. This subbasin is one of a series of lake-filled syn-rift basins that formed along the West African continental margin at an early stage of the opening of the Atlantic Ocean. The Lucula Sandstone is subdivided into a shallow-water facies association, deep-water facies association, and dolostone facies. The shallow-water facies association has beach and nearshore facies and fluvio-deltaic facies. Beach and nearshore facies are characterized by fossiliferous, planar- to cross-laminated sandstones arranged in cyclic, upward-fining packages. Fluvio-deltaic facies are characterized by large-scale cross-bedding and deformed, well-sorted sandstones. The deep-water facies association has turbidite- and slump-dominated facies. Turbidite-dominated facies consist of shales and fine-grained, planar-laminated turbidite sandstones. Slump-dominated facies consist of highly bioturbated, very fine-grained sandstones and siltstone with slump structures. Dolostone facies contain sandy, highly recrystallized dolomite. Two orders of cycle frequency occur in the Lucula Sandstone. Low-frequency cycles are represented by the interstratification of shallow- and deep-water cycles. These cycles are generated by longer-term, climate-forced lake-level changes. High-frequency cycles are represented by the cyclic pattern of beach and nearshore facies. Cycles are produced by low-amplitude lake-level changes caused by short-term climatic changes. Sandstones of the beach-nearshore and fluvio-deltaic facies have the best reservoir quality in the Lucula Sandstone. The distribution of potential shoreline and deltaic reservoirs like the Lucula Sandstone is generally predictable with use of depositional models of rift lake systems. But because of the complex nature of rift systems, stratigraphic prediction will always be somewhat problematic.

Abstract The Newark Basin Coring Project (NBCP) has recovered over 6730 m of continuous core from 7 coring sites. Cores spanning the 4800 m of Lockatong and Passaic formations are characterized by cyclic lacustrine mudstone and shale, which reflect rise and fall of lake level in response to climatic fluctuations at intervals of 20,000 years and larger patterns of 100,000- and 400,000-year intervals. Sedimentary structures in the mudstones include: 1. Organic-rich laminites with thin, flat, continuous lamination; thick lamination with diffuse or irregular boundaries; silty or sandy laminae; or crystal-rich lamination. 2. Mudcracked, thin-bedded mudstone with lenticular sandstone layers; graded sandstone layers; mudstone layers with sharp contacts; muddy siltstone curls; or crystal-rich layers. 3. Massive mudstones with angular breccia fabric; vesicular fabric; rounded breccia fabric; root-disrupted fabric; or crystal-rich fabrics. These structures define five types of cycles: 1. Cycles dominated by thick, organic-rich laminites deposited in deep lakes and rounded breccias, reflecting deflated, salt-encrusted mudflats. 2. Cycles similar to the previous, but with more thin-bedded mudstone and massive mudstone with upward-fining crystal sequences reflecting saline mudflats. 3. Cycles with mudcracked thin beds grading to brecciated mudstone, then vesicular fabric reflecting shallow lakes drying up to dry playa mudflats. 4. Cycles similar to the previous, but with more organic-rich laminites or thin beds and root-disrupted mudstone at top, indicating wetter conditions and vegetation growth before lake transgressions. 5. Cycles dominated by root-disrupted mudstone and thin, organic-poor laminites or thin beds reflecting thick soils superimposed on shallow lake deposits. The abundance of each cycle type changes through the stratigraphic section, reflecting the change from arid conditions in a narrow basin upward to semi-arid to subhumid conditions in a broad basin. The use of climatic patterns and tectonic setting can provide important information toward modeling source and reservoir rocks in rift basin lacustrine deposits.

Abstract The Lockatong Formation lacustrine sequences are the most extensive Upper Triassic deep-lake deposits exposed in eastern North America. Sedimentation took place within tropical lakes in a developing rift basin. These lacustrine deposits and their sedimentary structures exhibit a generally upward-shallowing sedimentary pattern and follow an internal repetitive pattern of cyclicity. The sequences suggest that lake depth responded to continuing changes in climatic conditions, although the basinal bounding faults were also active during sedimentation and may have had some general control. The identified lithologies formed in these lakes are black and gray shales, carbonate-rich mudstones, siltstones, and evaporite-bearing mudstones. The authigenic minerals present are analcime, dolomite, and calcite. Petrographic and electron microprobe investigations suggest that (1) analcime formed both as a direct chemical precipitate from lake and groundwaters and as an early diagenetic mineral, due to the early alteration of original clay minerals by the increasingly concentrated alkaline waters; (2) the lacustrine calcites are primary and/or early diagenetic; and (3) dolomite also was formed penecontemporaneously during evaporative concentration of shallow groundwaters. These observations are supported by carbon and oxygen isotopic ratios of the carbonates taken from major sections of the Lockatong Formation, and show that variations in the stable isotope ratios closely match the lithological alternations of the Lockatong Formation. The sedimentary succession shows an overall upward trend of increased evaporation, upsection increase in evaporite development, and, with this, a concomitant enrichment in δ 18 O. The δ 13 C isotope ratio, on the other hand, remains quite constant throughout the section, having a value appropriate to lacustrine deposition.

Abstract The Redstone limestone of Platt and Platt (1877) is one of five nonmarine limestone beds in the Upper Pennsylvanian Monongahela Group. The Redstone limestone lies within the lower member (Berryhill and Swanson, 1962) of the Pittsburgh Formation between the thick, economically significant Pittsburgh coal bed (below) and the Redstone coal bed (above), and reaches a thickness of 12 m in some places. In addition to the autochthonous coal and limestone, beds of clay, shale, mudstone, siltstone, and sandstone also occur in the interval between the Pittsburgh and Redstone coal beds. The limestone occurs over at least 10,000 km 2 in the northern Appalachian Basin. The mineralogy of the Redstone limestone is predominantly calcite, ankerite, and quartz. In addition, dolomite, pyrite, feldspar, and clay minerals are present in smaller amounts. The carbonate minerals are most commonly micritic, but spar frequently fills voids in the limestone. Five carbonate facies were identified within the Redstone limestone beds: (1) desiccation breccia with paleosol characteristics, (2) nodular limestone composed of rounded limestone clasts, (3) fossiliferous limestone that is usually organic-rich, with plant debris, pyrite blebs, and nonmarine ostracods, gastropods, and bivalves, (4) massive micritic limestone, and (5) laminated limestone composed of dark and light gray micrite laminae 5 mm or less in thickness. Results of this study indicate that the Redstone limestone beds probably formed in a large, shallow, freshwater lake, or series of lakes, with regular influx of fresh water and fine-grained clastic material. Seasonal changes in rainfall caused wetting and drying of sediment along the shoreline and consequent paleosol development. These seasonal changes were also responsible for at least some of the lamination observed. There was enough wave and current activity to rip up, round, and redeposit intraclasts, and to cause breakage of many of the bivalves, gastropods, and crustaceans.

Abstract The Upper Freeport Formation (Upper Allegheny Group, Middle Pennsylvanian) is one of the earliest nonmarine cyclothems in the Appalachian Basin and contains carbonates, siliciclastics, and coal. A detailed facies analysis of 25 limestone cores, along with detailed subsurface data from the Upper Freeport Formation in western Pennsylvania (Armstrong and Indiana counties), identified a large lacustrine/alluvial complex. The complex was drained by an anastomosed fluvial system containing a mosaic of subenvironments including extensive wetlands, densely vegetated swamp areas, and freshwater, carbonate-producing lakes. These lakes were small in size (several square kilometers), shallow, stratified, and connected by surface and groundwaters. Carbonate production was not triggered by evaporative concentration but by biogenic algal production in a sediment-starved system. Carbonates were continually being recycled, both physico-chemically and biologically. Siliciclastic wedges and predominance of reworked and traction-deposited carbonates favor a current-dominated, open lacustrine environment. Small-scale lake-level changes may have been controlled by climatic or depositional dynamics of the river system. The northern Appalachian Basin was an active foreland basin situated in the wet equatorial zone during Allegheny time. Through the use of modern analogs for carbonate lacustrine systems, as well as for anastomosed river systems, a model for the generation of nonmarine sequences within cyclothems was proposed. Tectonics (subsidence) may have been the driving force that controlled river drainage patterns. The evolution from an anastomosed to a single-channel system between tectonic pulses produced a mosaic of subenvironments that culminated in soil and swamp formation. This culmination explains the great lateral continuity of coal and underclay deposits. The low depositional gradient and unique combination of climate, tectonics, and eustatic level simply created a place where lake sediments and plant material could collect for a limited period of time.

Abstract Lacustrine depositional systems are intriguing from sedimentologic, stratigraphic, and paleoclimatic perspectives. In localizing hydrocarbon source and reservoir rocks and also valuable evaporate minerals, they are also extremely important from an economic viewpoint. Lakes are dynamic systems that are susceptible to fluctuations in climate. They are also highly variable in their tectonic and depositional settings. The papers included in this volume, although not a comprehensive collection, provide coverage of a broad spectrum of modern and ancient lacustrine examples.

Abstract Evaporites were classified by Krumbein and Sloss (1963) on the basis of their environmental relationships, particularly with respect to the under-and over-lying sedimentary sequences. The scope of knowledge that went into establishing this classification was limited to deposits developed in cratonic (continental crust) areas of the world. The advent of the concept of sea-floor spreading, together with new data collected by the Deep Sea Drilling Project and extensive submarine seismic surveys, both on the continental margins and in the deep-sea, enables us to classify evaporitic sediments on the basis of tectonic setting as well as sediment affinities. The various divisions are in a sense artificial; the one classification readily overlaps with the other, and each of the groupings may grade through time and space into another.

Abstract It has just been within the past 15 years that intensive studies of in situ evaporite deposits have been carried out and the first working models formulated for the origin of such deposits. These studies have focused on deposition along supratidal margins of normal marine basins. However, examination of evidence from the geologic record has long suggested that many evaporite bodies were also deposited within previously existing, open marine basins. These basins apparently had become constricted and developed hypersaline conditions within the water which they enclosed. Recently, data obtained from the latest Miocene (Messinian) sediments of the Mediterranean Basin and from modern salinas have shown that specific submarine evaporites do indeed exist and their facies are demonstrable. The primary composition, texture, and form that comprise these subaqueous deposits are only partly understood. Incomplete understanding arises, in part, because there are so few hypersaline water bodies existing in the world today in which environments may be observed that serve as an analogy to those which formed evaporites. It seems that another problem in interpretation of any marine evaporite, whether modern or ancient, lies within the materials themselves because they are exceedingly prone to alteration both while on the surface and after burial. Because of this ease of alteration, the ancient record left to us can be totally misleading. The range of environments under which evaporites can form and accumulate is as diverse as that for carbonates, and, in a general way, for every type of carbonate sediment, there is an equivalent evaporite.

Abstract Two approaches have been followed to determine which minerals will precipitate by evaporation of seawater. The first, and most intuitive approach is to take a bucket of seawater and evaporate it under controlled conditions of temperature and humidity, noting how much of which minerals form at certain salinities. The second approach is to start with a simple theoretical or experimental system, apply rigorous principles of physical chemistry, and attempt to relate results to what is actually found in nature. The first approach was attempted by Usiglio (in Clarke, 1924), who took a container of seawater from the Mediterranean Sea and evaporated it. Results of Usiglio’s experiment are given in table 4.1. Usiglio’s results show that calcium carbonate begins to precipitate when seawater has been evaporated to about half of its original volume. The most common carbonate mineral to form from normal seawater is aragonite, although low-Mg calcite, high-Mg calcite, and dolomite may also form if conditions are right. However, what is meant by “right conditions” could be the subject of a whole separate short course. Suffice it to say that the key factors that control which carbonate minerals will form are the total ionic strength and Mg:Ca ratio of the solution, and the presence of other complexing ions such as sulfate and phosphate. The fact that aragonite is the most common carbonate mineral to form from seawater points out a common problem, metastability, in applying physical chemistry to low temperature chemical systems. That aragonite should form at all is still

Abstract Evaporite minerals can be some of the purest chemical compounds, in terms of lack of trace contaminants, manufactured by any geologic process. For example, some natural gypsum deposits contain lower trace-element concentrations than reagent grade calcium sulfate. There are relatively few published analyses of evaporite minerals, and most of these are whole rock analyses rather than analyses of single mineral phases. Fortunately, most evaporite rocks contain one dominant mineral so that comparison of analyses of a particular evaporite lithology (e.g. halite rocks from several localities) is usually more meaningful than a comparison of analyses of other sedimentary rock types that have more complex and variable mineral compositions (e.g. sandstone from several localities). Most published chemical analyses of evaporites consist of only one analysis of a particular lithology from a given formation or subunit within a formation; there are few systematic studies available where the investigators have tried to determine the compositional variability of a particular evaporite lithology within one formation. The study of bromine geochemistry is an outstanding example of the application of systematic chemical analyses applied to evaporite units in order to determine compositional variability and to try and solve geologic problems involving correlation, paleosalinity, and diagenesis (see discussion by Raup and Hite later in these notes). In this section, we will examine the ways in which trace and minor elements are incorporated into evaporite minerals, summarize some published and unpublished chemical analyses of the more common evaporite minerals (gypsum, anhydrite, and halite), and discuss several other examples in

Abstract Establishing the distribution of bromine in the chloride facies of marine evaporites aids in the reconstruction of the paleosalinities in evaporite basins and provides an important geochemical tool in the exploration for potash deposits. Detailed stratigraphic profiles of bromine distribution are also useful in resolving problems in correlation and in understanding some of the post-depositional processes that have occurred in the evaporitic rocks. Much work has been done on the geochemistry of bromine in the German Zechstein. A few of these workers are: Baar (1954, 1955, 1963), Boeke (1908), Braitsch (1962, translation 1971), Braitsch and Herrmann (1 963), D’Ans and Kühn (1940-1944), Herrmann ( 1 958), Kühn (1 955, 1968), Schulze (1960), and Schulze and Seyfert (1959). Examples of work done in Russia are by Ogienko (1959) and Valyashko (1956). In recent years, bromine geochemical work has been done by Baar (1966), Schwerdtner (1964), Schwerdtner and Wardlaw (1963), and Wardlaw (1964) in Canada; Holser (1966), Raup (1966), and Raup and others (1970) in the United States; and Hite (1974) in Thailand.