Freshwater Limestone Research Articles

Duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora, Mexico

Research Article| April 01, 2001 Duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora, Mexico Fred W. McDowell; Fred W. McDowell 1Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Jaime Roldán-Quintana; Jaime Roldán-Quintana 2Instituto de Geología, Universidad Nacional Autónoma de México, Estación Regional del Noroeste, Apartado Postal 1039, Hermosillo, 83000 Sonora, Mexico Search for other works by this author on: GSW Google Scholar James N. Connelly James N. Connelly 3Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Fred W. McDowell 1Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Jaime Roldán-Quintana 2Instituto de Geología, Universidad Nacional Autónoma de México, Estación Regional del Noroeste, Apartado Postal 1039, Hermosillo, 83000 Sonora, Mexico James N. Connelly 3Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Publisher: Geological Society of America Received: 21 Apr 1999 Revision Received: 04 May 2000 Accepted: 05 May 2000 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2001) 113 (4): 521–531. https://doi.org/10.1130/0016-7606(2001)113<0521:DOLCET>2.0.CO;2 Article history Received: 21 Apr 1999 Revision Received: 04 May 2000 Accepted: 05 May 2000 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Fred W. McDowell, Jaime Roldán-Quintana, James N. Connelly; Duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora, Mexico. GSA Bulletin 2001;; 113 (4): 521–531. doi: https://doi.org/10.1130/0016-7606(2001)113<0521:DOLCET>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Late Cretaceous–early Tertiary arc magmatism in east-central Sonora includes the Sonoran batholith and the volcanic rocks of the Tarahumara Formation. The Tarahumara Formation consists predominantly of propylitically altered andesitic to dacitic lava, agglomerate, and volcanic breccia, all of local derivation, along with subordinate felsic pyroclastic components. Relatively thin volcaniclastic intervals with intercalated freshwater limestone that contains Late Cretaceous plant fossils occur within the upper third of the formation. Six new U-Pb zircon ages from the Tarahumara Formation extend the known duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora. Four of the samples yield ages between 73 and 70 Ma, and the other two are 90 and 89 Ma (errors are generally <1 m.y.). All of these ages are older than 65 to 55 Ma K-Ar and U-Pb ages for plutons of the Sonoran batholith in east- central Sonora determined in other studies. Combined, the ages indicate arc magmatism over at least 35 m.y. Initiation of magmatism in eastern Sonora by 90 Ma is much earlier than predicted by regional trends, which are largely based on geochronology of plutons. It appears that a full history of the regional evolution of this magmatic arc will require substantial age information from its volcanic rocks.A component of inherited zircon was detected in five of the six dated samples from the Tarahumara Formation. Although ages calculated from upper concordia intercepts are mostly imprecise, all are consistent with the presence of one or more Proterozoic components. In one sample, a persistent inherited component provided a precise upper-intercept age of 1448 Ma. These small cores surrounded by new zircon growth must represent material incorporated into the magma chamber prior to eruption. The results record the presence of Laurentian basement 200 km south and east of known outcrops in Sonora. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Cranial remains of a new species of balbarine kangaroo (Marsupialia: Macropodoidea) from the Oligo-Miocene freshwater limestone deposits of Riversleigh World Heritage Area, northern Australia

A new species, Balbaroo fangaroo, of balbarine kangaroo is described from the freshwater limestone deposits at Riversleigh northern Australia. The type specimens include two partial skulls which reveal hitherto unknown characters of Balbarinae and provide new evidence relevant to the resolution of the phylogenetic affinities of Balbarinae. A number of the newly-revealed characters e.g., squamosal-frontal contact on the walls of the neurocranium, are argued as being plesiomorphic for Macropodoidea.Hypertrophied upper canines which occur in the paratype, have never previously been recorded in kangaroos and represent an example of evolutionary convergence between these herbivorous marsupials and ungulate eutherians.

CRANIAL REMAINS OF A NEW SPECIES OF BALBARINE KANGAROO (MARSUPIALIA: MACROPODOIDEA) FROM THE OLIGO-MIOCENE FRESHWATER LIMESTONE DEPOSITS OF RIVERSLEIGH WORLD HERITAGE AREA, NORTHERN AUSTRALIA

Abstract A new species, Balbaroo fangaroo, of balbarine kangaroo is described from the freshwater limestone deposits at Riversleigh, northern Australia. The type specimens include two partial skulls which reveal hitherto unknown characters of Balbarinae and provide new evidence relevant to the resolution of the phylogenetic affinities of Balbarinae. A number of the newly-revealed characters, e.g., squamosal-frontal contact on the walls of the neurocranium, are argued as being plesiomorphic for Macropodoidea. Hypertrophied upper canines which occur in the paratype, have never previously been recorded in kangaroos and represent an example of evolutionary convergence between these herbivorous marsupials and ungulate eutherians.

Charles Darwin's field notes on the geology of Hobart Town- a modern appraisal

A transcription of unpublished field notes made by Charles Darwin details the observations and initial deductions he made on the geology of Hobart, Tasmania, and comments thereon place his work in a modern context. The field notes enable the routes of his excursions while in Hobart to be inferred in considerable detail and confirm earlier ideas about the site from which important fossils were collected. They also allow some appreciation of Darwin's style of geological study. Darwin's field notes reveal that he thought of the possibility of the influence of earthquakes on Tertiary beds at Sandy Bay. Several of his ideas on the geology, shown by these notes, some of them also in his publications (e.g. the origin of a Tertiary freshwater limestone, and relative movement of the land and sea in the area), remain topics for further study. His work in the Hobart area and his understanding of the geology of Van Diemen's Land were enhanced by contact with George Frankland, Surveyor-General, who had a long-term and systematic interest in the topic. The notes formed the basis ofa geological Memo on Hobart Town and, later, two publications, each work having a different purpose and emphasis. His work near Hobart did not produce enough information for the construction of a stratigraphic framework (imperfect sketches of the Geology). The imperfections, with other considerations, may have influenced him not to publish the memo which rendered subsequent publications less clear and less useful than had the memo been published. Darwin recognised the influence of glaciation on the Permian sedimentary rocks in the area but did not publish his observations and interpretation

Mystacinid bats (Microchiroptera) from the Australian Tertiary

A new genus and three new species of the microchiropteran family Mystacinidae are described from Miocene freshwater limestones in northern Australia. The type species,Icarops brevicepsnew genus and species, is from the middle Miocene Bullock Creek deposit, Northern Territory;I. aenaenew species andI. paradoxnew species are from the slightly older (early Miocene) Wayne's Wok and Neville's Garden Sites at Riversleigh, northwestern Queensland. Fossil mystacinids are rare in each deposit and represented so far only by lower teeth and dentary fragments. They are characterized by a suite of apomorphies shared only with Quaternary mystacinids endemic to New Zealand. The family Mystacinidae has no pre-Pleistocene record and its relationships to other groups of bats remain unclear. Possible sister-groups include South American noctilionoids and the cosmopolitan molossoids and/or vespertilionoids. The presence of plesiomorphic mystacinids in the Australian Tertiary suggests an Australian origin for the family.

Lyell: the man and his times

Abstract Born in Scotland at the end of the eighteenth century, Charles Lyell spent his early life in Hampshire in the midst of the kind of comfortable rural society described in Jane Austen’s novels. Influenced by his father, who was a keen botanist, the young Lyell collected butterflies and studied natural hisory. As a student at Oxford, he attended the Revd William Buckland’s lectures on geology and continued to pursue geology while studying for the bar at Lincoln’s Inn. In 1824 Lyell wrote his first scientific paper on the freshwater limestones and marls of Scottish lakes, demonstrating their detailed similarity to ancient freshwater formations among the Tertiary strata of the Paris Basin. Throughout his life Lyell remained an active field geologist, travelling throughout Europe from Sicily to Scandinavia. He made repeated geological tours through the Swiss and Austrian Alps and studied intensely the Tertiary strata of France, Belgium and England. He examined the geology of North America from Nova Scotia to the Mississippi Delta, working in the field in all weather. In 1853–1854 he spent several months studying the volcanic geology of Madeira and the Canary Islands and in 1857 and 1858 revisited Sicily to spend arduous weeks studying Mount Etna. In his seventy-fifth year and nearly blind, he travelled to the south of France to examine the caves of Aurignac and the Dordogne. In 1830 in the Principles of Geology Lyell challenged the assumption of a cooling Earth and of the greater former intensity of volcanic action and other geological forces. He separated geology from cosmology, pointing out that the crust of the Earth told nothing of its origin. What geology did reveal was an unending cycle of changes such as were still going on. In his metamorphic theory developed in the Elements of Geology , Lyell showed how the various classes of igneous and metamorphic rocks were formed in the gradual elevation of mountains. Lyell’s theories brought about a revolution in geology, changing the meaning of geological data. In successive editions of the Principles and the Elements , two books of American travel, and the Antiquity of Man , Lyell’s stature as an author and as a scientist grew steadily throughout his lifetime, the sale of his books often exceeding the publisher’s expectations. Liberal in his sympathies, Lyell worked effectively for the reform of English university education and during the American Civil War defended the Union against its British critics.

97/04684 Chemical characterization of solid graphitic carbonaceous matter associated with the Oklo natural fission reactors and uranium ore deposits, Gabon (West Africa) (radioactive waste storage): Rigali, M. J. 1997, 188 pp. Avail. UMI, Order No. DA9729437. From Diss. Abstr. Int., B., 1998, 58, (58), 1756

The boundary between the Arabian and African plates, is marked in the Middle East by one of the most prominent deep-seated lineamentary structures, called the Dead-Sea-Transform Fault System (DSTFS). Structural and mineralogical processes related to the DSTFS were correlated with equivalent processes leading to the alteration of pyroclastic deposits of alkali-olivine basaltic to nepheline basaltic composition which formed during a time span of less than 0.5 Ma. The large deposit of Tell Rimah, Jordan, is operated for the exploitation of zeolites, tuffs, and as pozzolana raw material. Four discrete stages of mineralizations have been distinguished from each other within these volcanic-hosted mineral deposits.(1) Hypogene syneruptive alteration of pyroclastic rocks produced siliceous gels (“allophane”), smectite, analcime, and phillipsite in vesicles when the groundwater level was low in the rift basin of the DSTFS. The lake-level lowstand caused the fluid system in the pyroclastic cone to become self-sufficient and it has been considered as a closed hydrothermal system. (2) Periods of tectonic and magmatic quiescence grinded the detrital sedimentation in the rift basin to a halt, while triggering a supergene alteration in the eruptive cones on the adjacent Arabian Plate. (3) Epigenetic alteration affected the pyroclastic rocks in the distal part of the DSTFS as a result of a rising water level. The water gradually filled the pore space of the permeable pyroclastic deposits almost to completeness and caused meniscus and blocky cements of calcite, phillipsite and chabazite to develop. In the rift basin, contemporaneously with the alteration of the pyroclastic rocks, freshwater limestones formed on calcareous bedrocks. Ba and Mn minerals in these freshwater limestones were supplied by subaquatic brines. Subsequently, a drastic lowering of the lake water level in the DSTFS converted the system of subaquatic freshwater limestones into subaerial tufa and travertine. As long as the basal parts of the pyroclastic units at Tell Rimah were in the reaches of the saline groundwaters, calcite and faujasite developed in the pyroclastic host rocks. (4) Another lake level lowstand within the rift basin caused the pyroclastic host rocks to get emerged and forced zeolite–carbonate mineralization in the tuffs to a complete stillstand. Hypogene and supergene alteration in these phreatomagmatic–strombolian pyroclastic cones of the Pleistocene x were correlated with lake high- and lowstands in the adjacent rift basin along the DSTFS.The results obtained by current tectono-morphological studies of the rift-related alteration of pyroclastic rocks along the DSTFS may also be applied to basin-and-swell-topographies elsewhere in the world. The current studies involved microscopy supplemented by SEM-EDX, X-ray diffraction analysis, mid (MIR) and far (FIR) infrared spectroscopy. Major and trace elements were analyzed by X-ray fluorescence spectrometry (XRF). C- and O isotope analyses were conducted on carbonate minerals, which were also targeted on by radiocarbon dating.

K-strategy and adaptative specialization in Steneofiber from Montaigu-le-Blin (dept. Allier, France; Lower Miocene, MN 2a, ±23 Ma): first evidence of fossil life-history strategies in castorid rodents

Abstract The fresh-water limestone deposits of Montaigu-le-Blin yielded a small pocket containing almost exclusively cranial and post-cranial elements of the castorid Steneofiber . A full inventory of these skeletal remains makes it possible to recognize an assemblage of two adults and eight juveniles of two different ages. It corresponds well to a family group of the extant beaver, usually consisting of an adult breeding pair together with a variable number of yearlings and kits; consequently this pocket is interpreted as a fossil burrow containing the catastrophic death-assemblage of a Steneofiber family, and we infer a K-strategy model of reproductive pattern for this genus. Moreover, a minute fossil ungual phalanx corresponds well to the “combing-claw” of the extant beaver and suggests the development of nonwettable fur, an important adaptation to a semiaquatic way of life. The shape of the fossil caudal vertebrae, without the wing-like transverse processes of Castor , indicates that the tail of Steneofiber was cylindrical, however.

Scottish Carboniferous fresh-water limestones in their regional setting

ABSTRACTThe East Kirkton Limestone is one of a number of horizons within the Scottish Carboniferous sequence which have commonly been referred to as ‘fresh-water’ limestones. The stratigraphy and distribution of these non-marine carbonates is reviewed and discussed in terms both of Carboniferous palaeogeography and of the interaction between sedimentation, volcanism and tectonics within the Midland Valley graben. Particular attention is given to late Viséan horizons of broadly similar age to the East Kirkton Limestone. The range of carbonate facies and faunas found in these limestones is described and their environmental significance is discussed.

A sedimentological and stable isotopic study of travertines and associated sediments within Upper Triassic lacustrine limestones, South Wales, UK

ABSTRACTThe Upper Triassic in South Wales is composed of up to 100 m of red, dolomitic mudstones of the Mercia Mudstone Group which overlie and are laterally equivalent to basin margin coarse clastic deposits. In the Sully Island and Dinas Powys areas, a series of carbonate deposits was laid down within small basins adjacent to the main Bristol Channel Basin. The rocks consist of dolomites containing replaced evaporites, overlain by perilittoral freshwater limestones. The limestones are fenestral intrasparites and contain abundant pedogenic and stromatolitic horizons, as well as locally developed travertines. Evidence for vadose diagenesis within the limestones is common. The travertines consist of sheets of fibrous calcite (flowstone) associated with pisoids and flöe calcite. Most of the travertines consist of single sheets several millimetres in thickness although ‘mounds’up to 1 m in height and 5 m in diameter are also present. The topmost metre of the limestones, which has been dolomitized, is deformed into tepee and megapolygonal structures.The carbon and oxygen stable isotopic composition of the limestones suggests that they were precipitated in low salinity waters. Successive samples from individual bands of flowstone show a covariance of δ18C and δ13C which is consistent with the mixing of resurgent groundwaters with pools of more evolved waters at the surface. The sedimentological and geochemical evidence suggests that the limestones were deposited in a small, enclosed basin fed by upwelling meteoric groundwaters in an environment distinct from that in which the laterally equivalent gypsiferous red mudstones were formed.

A numerical analysis of grain-size and colour variations of a fan-lake transition, Upper Carboniferous Bechtsrieth Formation (Southern Germany)

The Upper Carboniferous Bechtsrieth Formation of the Weiden Basin (Southern Germany) shows a depositional evolution from an alluvial fan to a lake. The sedimentary record of the probably Westphalian GC-member reflects gravity slides and waterlaid deposition of braided streams; the younger GSC-member is dominated by floodplain and sheetflood deposition, locally hosting abundant freshwater limestone and clastic sediments deposited by meandering streams. They grade into the nearshore and offshore lacustrine sediments of the VC-member laid down during the Late Stephanian. These subfacies-types have been numerically coded as “fan ratios”, which normalized to a 10 m drill interval, resulted from the “sand-mud ratio” multiplied by the “degree of contrast” and “maximum clast size”. Supplemented by rock colour, which indicates oxidizing and reducing conditions of these strata, and carbonate content, a discrimination of these continental environments is possible and also makes the procedure amenable to cutting examinations. Because these terrigenous rocks have attracted the attention of exploration geologists for their coal, hydrocarbon, uranium and precious metal contents, the source and host environments have tentatively been described in terms of these facies codes. Low fan ratios between 0 and 0.75 are indicative of predominantly offshore and nearshore lacustrine environments and seem most prospective for hydrocarbons, uranium and gold. This approach is a rapid method to improve environmental analysis and facilitate well-log correlations.

The Occurrence of Freshwater Limestones in the Upper Pennsylvanian and Lower Permian of the Northern Appalachian Basin: ABSTRACT

Freshwater limestones comprise a significant portion of the Upper Pennsylvanian and Lower Permian strata of the northern Appalachian basin. In some areas, the Monogahela Group consists of as much as 50% freshwater limestones. These limestones are clayey to silty, iron-bearing, sparsely fossiliferous, micritic, and thinly bedded or nodular and are presumed to be lacustrine in origin. They are part of a recurring sequence of beds that include coal, sandstone, shale/clay, and marine limestone. The initial goals of this study are to develop a stratigraphic framework for these freshwater limestones and to determine, their lateral continuity, thickness variability, and relation to other beds in this section, in particular the coals, on a regional scale. The Pittsburgh coal and Ames limestone are very persistent regionally and are used as a datum. Regional correlations show that possibly 20 freshwater limestone beds are persistent and widespread; some cover at least 5,000 mi{sup 2} in eastern Ohio, western Pennsylvania, northern West Virginia and western Maryland. Cross sections and fence diagrams constructed from drill logs and measured sections indicate that the thickness of these limestone beds varies laterally and between beds, ranging from less than 1 to 150 ft thick. Correlations also show stratigraphic and paleogeographicmore » relationships between the coals and freshwater limestones. Many of the limestones underlie coal beds, directly in some places. The coals and limestones are better developed in the northern part of the Appalachian basin. These associations may hold significant clues to the depositional and the paleoclimatic setting of the freshwater limestones and the coals.« less

Dissolution kinetics of Carrera marble, Portland stone and several limestones in acid waters

The rate of dissolution (at 25 °C), in acidic waters (dilute hydrochloric acid, pH 3), of six calcium carbonate containing rocks (Carrera marble, Portland stone, Abbeytown limestone, freshwater limestone, chalk and Connemara marble) has been studied using the channel flow cell method. For the first three of these the dissolution rate was found to be first order with respect to the surface concentration of H+ at the solid/liquid interface and the following heterogeneous rate constants were measured: 0.099 cm s–1(Carrera marble); 0.039 cm s–1(Portland Stone); 4.5 × 10–3 cm s–1(Abbeytown limestone). In contrast, the reaction of freshwater limestone and chalk with H+ was found to be mass transport controlled, whereas Connemara marble was too heterogeneous for meaningful results to be obtained. Chemical analyses of all the rock specimens studied are reported.

Tufa: a freshwater limestone

Tufa, or travertine, is a deposit of calcium carbonate precipitated with the loss of carbon dioxide from springs or streams saturated with calcium bicarbonate. Algae or bacteria may assist in this process, which is favoured by raised temperatures. British and overseas examples of tufa deposits show various features including their role in damming up lakes.

Petrography and Diagenesis of Silcrete from Kuwait, Arabian Gulf

ABSTRACT Silcretic duricrust is found capping scattered, isolated hills in the southern desert plain of Kuwait. It occurs in genetic association with surface and subsurface calcrete, dolocrete, and gypcrete deposits. Two main types of silcrete were found--quartzitic silcrete and massive silcrete. The first was developed by precipitation of microcrystalline drusy quartz cement in the intergranular pores of sandstones, whereas the second type was formed by replacement of calcrete, dolocrete, and freshwater limestone by microcrystalline quartz. Silica precipitation took place in two stages. In the first, primary silicification caused the development of the main silcrete mass which is usually composed of microcrystalline quartz, syntaxial quartz overgrowth, and quartzine spherulites. A second stag of secondary silicification was responsible for the precipitation of length-fast chalcedony and megaquartz in cavities. The field occurrence and the petrographic characteristics of the silcrete in Kuwait provide support for the Folk and Pittman (1971) hypothesis on the replacement of evaporite and carbonate by quartzine and lutecite. Calcretization of Kuwait Group clastic deposits, which resulted in complete or partial dissolution of siliciclastic grains and precipitation of carbonate minerals, is likely to have provided soluble silica for groundwater. A diagenetic model for the studied silcrete is proposed in which both vertical and lateral translocation of soluble silica in groundwater is considered. Silcrete has played an important role in the landscape development of the southern ar a of Kuwait.

Depositional Model for Freshwater Limestones of Upper Allegheny Group (Pennsylvanian System) of Western Pennsylvania: ABSTRACT

A depositional model is proposed for the freshwater limestones of the upper Allegheny Group of western Pennsylvania, specifically the Upper Freeport limestone. The model is based on a facies sequence analysis of core logs through the limestone-bearing interval, on isopachs of limestone and sandstone of the same coal-to-coal interval, and on microfacies analysis of the limestone itself.

Evidence for slowly changing [formula omitted] in runoff from freshwater limestones of southern France

87 Sr 86 Sr ratios have been determined in modern rivers and freshwater limestones dating from 65 Ma to the present over an area extending from the Pyrénées to the Massif Central (southern France). About 40 Ma ago, the Alpine mountain range of the Pyrénées was strongly uplifted by the Alpine orogenic activity and its pre-Hercynian basement dominated by schists, gneisses and granites was rapidly exposed from beneath its blanket of Mesozoic marine limestones. Meanwhile, the 87 Sr 86 Sr ratio of the rivers has remained remarkably constant in both space (with the exception of the very few northernmost samples) and time: in this area, extreme variations through the orogenic period are small with 87 Sr 86 Sr lying between 0.7073 and 0.7084 at 55–65 Ma and 0.7077–0.7096 for the last 30 Ma. River Sr is controlled by a nearly binary mixing of silicate ( ∼ 3 4 ) and ( ∼ 1 4 ) end-members with negligible influence of evaporites. It is inferred that the silicate/sediment contribution ratio of the world-average rivers to seawater Sr changes at a very slow rate. Even taking major basaltic events into account does not alter this conclusion as their contribution to the river Sr is very subordinated to other components. It is inferred that the seawater 87 Sr 86 Sr secular main trend over the Phanerozoic is controlled by hydrothermal alteration of oceanic basalts and slow variation of the limestone/silicate contribution ratio to the riverine Sr. Oceanic events [changes in organic productivity and carbonate compensation depth (CCD)] may produce intense, short-term variations but recovery of steady-state seawater 87 Sr 86 Sr is delayed by 40–80 Ma through diagenetic Sr remobilization in carbonate sediments.

Depositional Environment of Bullion Creek Formation (Paleocene) in Southern McKenzie County, North Dakota: ABSTRACT

The environment of deposition of the Bullion Creek Formation in western North Dakota has been variously ascribed to lacustrine, meandering fluvial, and marginal marine deltaic environments with the latter three being favored by most workers. The purpose of the present study is to evaluate these previous models through careful field observations on a local scale, more specifically T145 and 146N, R102W of McKenzie County, North Dakota. The Bullion Creek Formation rests conformably atop the Slope Formation (nonmarine) in the southwest quarter of the state and is conformably overlain by the Sentinel Butte Formation. The Tongue River Member of the Fort Union Formation is the lateral equivalent of the Bullion End_Page 1359------------------------------ Creek Formation in Montana, Wyoming, and South Dakota. The Bullion Creek Formation is composed primarily of flood-plain sediments, including unconsolidated sands, silts, and clays. Freshwater limestones and thin, discontinuous lignites (with the exception of the thick and laterally extensive HT Butte lignite which has been defined as the upper contact of the Bullion Creek) are also present. The carbonates are of two types: most common are the discontinuous pods of laminated lime mud, which are mudcracked at the top and may indicate evaporative ponds; more rarely, a gastropod-pelecypod-fishscale wackestone occurs near the top of the formation, and represents a small (^approx 1 mi2, 3 km2) lacustrine deposit. Channeling in the Bullion Creek is of special interest. Paleochannels have a low width to depth ratio and appear laterally stable as evidenced by lack of lateral accretion or point bar deposits and vertical stacking. In map view, channels of equal stratigraphic position converge with and diverge from each other. The preponderant flood-plain sediments, lignites, and carbonates, as well as channel configuration would seem to indicate deltaic sedimentation; however, the deposits contain fauna which are strictly fresh water, thereby making this interpretation tenuous. A possible alternative to this deltaic interpretation is the anastamosing fluvial model. This model, proposed by Smith and Putnam in 1980, has a dominance of vertical accretion, producing channel deposits which are thick, narrow, and laterally stable, as well as extensive inter-channel wetlands and lakes. Hanley and Flores in 1983 proposed a similar depositional picture for part of the Tongue River Member in the Powder River basin in northeastern Wyoming. Anastamosis in the Williston basin is probably the result of greater relative ocal subsidence of the basin than in the downstream reaches. End_of_Article - Last_Page 1360------------

Brazilian continental cretaceous

Cretaceous deposits in Brazil are very well developed, chiefly in continental facies and in thick sequences. Sedimentation occurred essentially in rift-valleys inland and along the coast. Three different sequences can be distinguished: (1) a lower clastic non-marine section, (2) a middle evaporitic section, (3) an upper marine section with non-marine regressive lithosomes. Continental deposits have been laid down chiefly between the latest Jurassic and Albian. The lower lithostratigraphic unit is represented by red shales with occasional evaporites and fresh-water limestones, dated by ostracods. A series of thick sandstone lithosomes accumulated in the inland rift-valleys. In the coastal basins these sequences are often incompletely preserved. Uplift in the beginning of the Aptian produced a widespread unconformity. In many of the inland rift-valleys sedimentation ceased at that time. A later transgression penetrated far into northeastern Brazil, but shortly after continental sedimentation continued, with the deposition of fluvial sandstones which once covered large areas of the country and which have been preserved in many places. The continental Cretaceous sediments have been laid down in fluvial and lacustrine environments, under warm climatic conditions which were dry from time to time. The fossil record is fairly rich, including besides plants and invertebrates, also reptiles and fishes. As faulting tectonism was rather strong, chiefly during the beginning of the Cretaceous, intercalations of igneous rocks are frequent in some places. Irregular uplift and erosion caused sediments belonging to the remainder of this period to be preserved only in tectonic basins scattered across the country.

Etude palynologique (pollen et spores) du Lutétien continental de Bouxwiller (Bas-Rhin, France)

Freshwater limestones and the underlying Eocene clays and lignites were penetrated by a cored borehole drilled in the Bouxwiller area. Pollen analyses of the clays and lignites were carried out on 75 samples. The pollen diagram could be subdivided into 3 distinct vegetation periods : floral assemblage I occurs at the base of the lower sands at the Bathonian (Jurassic)/Eocene boundary, and floral assemblages II and III in the brown clays and lignites. The results indicate that the base of the Bouxwiller Formation belongs to the lower Lutetian and the lignite beds to the middle Lutetian. The floral assemblages are characterized by an abundance and variety of Pteridophyta, the progressive development of the Myricaceae and Juglandaceae, the disappearance of the Normapolles and the diversification of the whole flora. The flora clearly indicates the development of a freshwater lake phase which was followed by a swamp and bog phase, during which the climate was warm and humid.