Calcareous Mud Research Articles

Petrology and Structure of Some Lower Carboniferous Reefs in Northwestern Ireland

Some Carboniferous knoll-reefs in Ireland have been mapped in detail. The reef bodies are 30-500 feet in thickness and several miles in diameter. All reefs contain many small-scale unconformities which dip in the same way as the sedimentary bedding, radially outward from the reef centers. No distinct core facies has been found. Paleocurrent directions run parallel with the length of the reefs. The reef limestone was found to be a clotted fine-grained calcareous mud (bahamite) which commonly contains larger mud pebbles. The only organic remains which might have petrological significance are bryozoans; their bulk contribution to the rock however is small. Early during diagenesis a cavity system was formed probably due to sliding movements on the reef slope. This was soon filled with calcite and dolomite crystals. It can be demonstrated that the dolomite formed at a stage when the reef was still a mound on the sea floor. Lithification set in at a later stage, it led to a preferred orientation of calcite grains and is tentatively explained by solubility gradients in the migrating pore solutions. An inorganic origin for the reefs seems likely; algae may have helped precipitating the calcite mud, but there is no evidence of this.

Marine Bank Development in Plattsburg Limestone (Upper Pennsylvanian) in Neodesha-Fredonia Area, Southeastern Kansas: ABSTRACT

The Plattsburg limestone is anomalously thick in the Neodesha-Fredonia area, swelling from less than 10 feet to maximum thickness of 115 feet. Thickening is due to large increases in thickness of two of the three members into which the Plattsburg has been divided. The Merriam limestone (lower member) varies only slightly in thickness, ranging from 1 to 3 feet, but the Hickory Creek shale (middle member) ranges from 1 to 45 feet, and the Spring Hill limestone (upper member) ranges from 3 to 88 feet in thickness. The principal cause of thickening of the Plattsburg limestone is interpreted to be due to deposition of an extensive, lens-shaped shallow marine bank which rose above the general level of the surrounding sea floor. The shape of the bank is thought to be partly reflected by present thickness variations in the Plattsburg limestone. The bank was at least 14 miles long northwest and southeast, and about 12 miles wide northeast and southwest. End_Page 127------------------------------ Two smaller, detached thickened parts of the Plattsburg limestone are also present in the area and probably represent small banks. A second cause of thickness variations in the Plattsburg limestone is local structural warping during deposition, which permitted greater thicknesses to accumulate over downwarps and less thicknesses over upwarps. Thickness of the Vilas shale also has been affected by this cause. Thickness of the Vilas shale has been observed to be inversely related to thickness of the Plattsburg limestone at most localities where the two formations are exposed. Where the Plattsburg limestone is thick, the Vilas shale tends to be thin, and vice versa. The Vilas shale has been interpreted to be an off-bank lateral time equivalent of the thickened Spring Hill member. Deposition of the bank is interpreted to have been strongly influenced by carbonate-secreting organisms, including crinoids, bryozoans, brachiopods, mollusks, and algae, which flourished over the bank. The organisms may have influenced deposition of silt and clay (Hickory Creek shale member) by exerting a sediment-binding effect, and probably helped stabilize slopes at least as great as 7° on the sides of the bank. In addition, the carbonate-secreting organism contributed large quantities of calcareous material to form the upper part (Spring Hill limestone member) of the bank. Where thick, the Spring Hill limestone member of the Plattsburg may be divided into three tabular lithologic subdivisions which occur in regular vertical sequence. The lower subdivision has been termed the fragment-pellet subdivision because of the abundance of irregular-shaped fragments and pellets. Much of the fragmental and pelletal material appears to be of algal origin. The middle subdivision is termed the crystalline subdivision because of the abundance of sparry calcite which is closely associated with fragments of carbonate encrusted blades of various forms of calcareous algae. Some of the algal forms resemble the alga Anchicodium, although positive identifications have not been made because of the lack of preservation of essential details. The upper subdivision is termed the alcarenite subdivision because of the abundance of calcarenite composed of grains with varying degrees of rounding and sorting. During deposition of the crystalline limestone subdivision of the Spring Hill member, carbonate-secreting algae may have imparted sufficient rigidity to the bank to cause it to be wave-resistant and thus allowing it to be classed as a reef. However, during deposition of most of the other parts of the Plattsburg bank, the deposits probably did not possess sufficient coherence to be wave-resistant. Porosity in the Spring Hill member in outcrops is closely related to limestone lithology. Highest porosity occurs in the crystalline limestone subdivision, where conspicuous pores and vugs occur in visibly crystalline calcite. Some of the crystalline calcite is interpreted to have formed through precipitation in open spaces which were not filled with calcareous mud during deposition because of the sheltering effect of individual fragments of carbonate-encrusted calcareous algae. Other crystalline calcite appears to have been produced through recrystallization of calcareous algae. It seems possible that favorable oil reservoir conditions in certain Pennsylvanian limestone in central and western Kansas may be provided by porous zones in thickened limestones lenses similar in origin to t e thickened Plattsburg in the Neodesha-Fredonia area. End_of_Article - Last_Page 128------------

Facies Analysis of Upper Devonian Wabamun Group in West-Central Alberta, Canada

The Wabamun group, consisting mainly of carbonate rocks and anhydrite, increases in thickness westward from less than 500 feet in the Leduc and Stettler areas to approximately 1,800 feet in part of the Rocky Mountains of Alberta. East of Leduc and north of Stettler, the Wabamun has been irregularly truncated by pre-Cretaceous erosion. For purposes of facies analysis the Wabamun is subdivided into four units: (1) basal unit including the lowermost evaporitic interval and lateral marine carbonate equivalents; (2) lower middle Wabamun representing the overlying interval to the top of the Crossfield dolomite in the Calgary area; (3) upper middle Wabamun including post-Crossfield and pre-Big Valley beds; and (4) upper Wabamun representing the Big Valley formation and approximate lateral equivalents. The evaporites and dolomites are dominant in the southeastern part of the map area, limestones in the northwestern part (and locally at the southwest), and fine to coarse crystalline dolomite in the intervening area. Evaporites and associated extremely fine-textured dolomites exhibit most widespread distribution in the basal Wabamun. The main evaporites extend northwest through Stettler to Leduc whereas the extremely fine-textured dolomites also occur farther northwest. In the middle Wabamun, the evaporites terminate a relatively short distance northwest and north of Stettler because of probable removal by solution and pre-Cretaceous erosion. Presumably middle Wabamun evaporites originally extended north beyond their present limit. During deposition of the basal and upper Wabamun units, a subsidiary evaporite province occurred in the foothills belt west of Calgary and may have extended north as far as the Clearwater River. Limestones range from calcilutites to calcarenites and exhibit incipient dolomitization that commonly imparts a mottled appearance to the rock. The calcarenites are generally of the pseudo-oolitic or pelletoid type, although bioclastic limestone is characteristic of the uppermost, and locally, of lower beds. The pelletoid limestones and calcilutites were deposited on a widespread bank on which slight restriction of the shallow waters promoted precipitation of calcium carbonate. Anhydrites and cryptocrystalline dolomite were precipitated in the Stettler-Drumheller area near the bank margin at the east, and the associated calcareous muds were diagenetically dolomitized to microsucrosic dolomite. Coarser (very fine to medium crystalline) dolomites are characteristic of a belt between the limestone province at the northwest and evaporites at the southeast. Local vuggy dolomite sections in this belt are interpreted to be possible reefs. Petroleum has accumulated in two main types of stratigraphically controlled traps within the Wabamun group. Facies change from porous secondary dolomites to relatively non-permeable equivalents approximately up regional dip (mainly eastward) is responsible for gas entrapment in the Okotoks-East Calgary-Olds trend of fields. In the Edmonton area, oil or gas has been localized in erosional hills made up of porous Wabamun dolomites at the pre-Cretaceous unconformity.

The stratigraphy and history of Groenvlei, a South African coastal fen

Borings on the fen at Groenvlei show that the earliest sediment was a diatomaceous nekron mud in a small freshwater lake. This filled in and fen peat formed over it. Subsequently, marine mud was spread over almost the whole basin, the course of the transgression being followed by diatom analysis. A change in composition of the marine diatom flora, apparently due to an unexplained change of temperature of the sea, is recorded. The marine incursion graded into brackish lagoon stages, towards the end of which conditions were rather unfavourable to diatom growth, followed by increasingly freshwater conditions, during which calcareous muds were laid down. The eastern basin of the lake became more or less separated from the main lake by a sand bar. The calcareous lake mud was overgrown by the latest reedswamp and sedge fen. Radiocarbon dating gave an age of 6870 years for a sample from the upper part of the submerged peat bed at Groenvlei, and a lapse of little under 5000 years before freshwater deposits again occupied the eastern basin of the lake (14C age of gyttja sample, 1905 years). This dating of the Groenvlei transgression is compatible both with the main post-Glacial eustatic rise of sea-level in the North Temperate latitudes, and with similar transgressions on the coasts of south-eastern Australia, New Zealand, and Fuego–Patagonia. The maximum height of the sea-level is considered to have been about 1.5 m higher than at present.

Biostratigraphic and Paleologic Study of Midway Foraminifera Along Tehuacana Creek, Limestone County, Texas: ABSTRACT

The Midway group of Texas, a predominantly shale, sandy shale, and sandy limestone section of Paleocene age, was deposited in an open sea whose depth fluctuated between very shallow and deep. This concept is based on a study of samples form Tehuacana Creek, Limestone County, in east-central Texas. The interval sampled extends upward for 278 feet from the Cretaceous-Paleocene contact. Lithologic examination revealed a complete cycle of deposition, with a basal glauconitic sand overlain successively by sandy shale, sandy limestone or calcareous sandstone, glauconitic sand, and shale. The foraminiferal content indicates that the very lowest beds of the Midway (Littig member of Kincaid formation) are marine, not littoral, probably mid-neritic to outer neritic. Seemingly the unconformity between this section and the Cretaceous developed without the latter being exposed subaerially. Biostratigraphic and paleoecologic interpretation demonstrates that the shales and sandy shales of the lower part of the succeeding Pisgah member were deposited in water deeper than 200 meters. As the water became more shallow, sands and calcareous muds interbedded with sands of the upper Pisgah and Tehuacana member were deposited. This shallow-water environment favored an abundant growth of a few species of Foraminifera. The Mexia member (lower unit of Wills Point formation) represents a radual return to a deeper-water environment characterized initially by a glauconitic sand followed by glauconitic muds and a rich fauna of both deep and shallow-water species. The dark pyritic muds of the upper part of the Mexia member were deposited in deep water (more than 200 meters). The fauna was rich in variety of genera and species of Foraminifera but poor in number of individuals. The Midway group of Texas (Danian) has been included in the Globigerina compressa-daubjergensis zone by Loeblich and Tappan. An analysis of the distribution of Foraminifera showed that 4 zonules can be established at this locality. They are, from the base upward: 4. Marginulina tuberculata (Plummer) zonule 3. Polymorphina cushmani Plummer zonule 2. Discorbis newmanae Plummer zonule 1. Alabamina midwayensis Brotzen limbata (Plummer) zonule. End_of_Article - Last_Page 2517------------

Statistical Analysis of Regional Facies Change in Ordovician Cobourg Limestone in Northwestern New York and Southern Ontario

Multiple regression analysis is applied to the study of facies change in the Ordovician lower Cobourg limestone in northwestern New York and southern Ontario. A linear surface is fitted to the scattered outcrop data. The results indicate an increase in the lower Cobourg calcilutites north-northeastward along the outcrop east and north of Lake Ontario and an accompanying decrease in the calcarenite texture. This is interpreted as a winnowing-out of the calcareous muds into the deeper water on the north-northeast. Preferred orientation of lower Cobourg pararipples indicates that northeast-southwest currents predominated. Progressive change in mean pararipple wavelength tends to support the northward increase in depth of water obtained from the texture analysis. A synthesis of the linear regression results for Shoreham, early Denmark, and lower Cobourg textural data in the northwestern New York area denotes maximum submergence in early Shoreham and minimum submergence around early Denmark. Lower Cobourg seas were slightly deeper than early Denmark.

Mississippian Sedimentation and Oil Fields in Southeastern Saskatchewan

Marked facies changes occur in the Mission Canyon and lower part of the Charles formation (Mississippian) in southeastern Saskatchewan. Northeastward from the basinal area, four successive environments of deposition with characteristic rock types and fossils may be mapped as follows. 1. Basin: dark brown-gray argillaceous limestone containing scattered white crinoid columnals, black bituminous shale partings, and brownish gray chert. 2. Open marine shelf: cream-white fossiliferous-fragmental and chalky limestones containing crinoids, bryozoans, brachiopods, and zaphrentid corals. 3. Barrier bank: cream-white precipitated limestones including pisolitic, oolitic, pseudo-oolitic, and lithographic types. Fossils include abundant algae and few scattered gastropods. 4. Lagoon: cream-white chalky argillaceous limestone containing ostracods, earthy to sucrosic secondary dolomite and anhydrite. Evaporitic (primary?) dolomites occur in the upper Charles as a result of basin-wide evaporitic conditions. These typically dense (cryptocrystalline) and non-porous dolomites are closely associated with anhydrite. Factors which control porosity in the limestones include sorting of fossil debris or precipitated calcareous grains, submarine erosion and re-deposition of partially lithified calcareous muds, solution, dolomitization (?), fractures, compaction, and infilling of pores by calcite, anhydrite, or chert. Stratigraphic trap oil accumulations occur where permeable units of the Mission Canyon and Charles are truncated and overlain by pre-middle Jurassic redbeds. Factors affecting oil accumulation include the presence of the following. a. Permeable reservoir beds at or near the unconformity. b. Anhydrite filling pores where the permeable reservoir beds are truncated by the pre-Jurassic erosion. c. Anhydrite beds conformably overlying and underlying the permeable units and thus form a roof and floor for the reservoir beds. d. Topography of the Mississippian erosion surface. Mississippian strata in the oil-producing area of southeastern Saskatchewan are characterized by the following. 1. Relatively steep dips (40-60 feet per mile) as compared with dips of 10-20 feet per mile in much of southwestern Saskatchewan. 2. Relatively rapid truncation (15-40 feet per mile) as compared with an average of approximately 5 feet per mile in southwestern Saskatchewan. 3. Relatively saline waters (50,000-150,000 parts per million of chloride ion content) as compared with 100-8,000 parts per million in southwestern Saskatchewan. In exploration for new trends or extensions of known producing areas, important consideration should be given to the distribution of permeable rock facies within individual stratigraphic units. In addition, it is possible to predict the location of topographically high trends as the various lithologic types are differentially resistant to erosion. For example, the precipitated barrier bank limestones End_Page 94------------------------------ are relatively resistant to weathering and form topographic ridges in the Nottingham field. The lower limit of oil accumulation within reservoir beds may be determined by the location of a spill point, in turn controlled by the downdip limit of lagoonal anhydrite floors.

Une tourbiere littorale, Colleville-s-Mer (Calvados)

Abstract Pollen analysis of a coastal peat deposit at Colleville-sur-Mer, Normandy, France, and examination of the molluscan fauna of interstratified beds, shows that the peat is postglacial in age. Discontinuity of the peat and interbedded layers is due to slumping and sliding of calcareous mud derived by alteration of Jurassic Bradfordian deposits overlying Vesulian clays.

An Intraformational Conglomerate by Mixed Sedimentation in the Upper Cretaceous of the Roc-de-chere, Autochthonous Chains of High Savoy, France

ABSTRACT The glauconitic and sandy limestone sequence, which in most places represents the Upper Cretaceous transgression throughout the High Calcareous Alps of the High Savoy, gives way in the Roc-de-Chere region to a 3- to 4-feet bed of conglomerate containing curiously shaped pebbles of fine-grained limestone scattered in a glauconitic matrix. Three distinct limestone types may be distinguished in the conglomerate on the basis of shape, dimension, and induced flow structures (from base to top): (1) contorted streaks, (2) larger irregular pebbles with highly deformed matrix inclusions, and (3) still larger subrectangular chunks with slightly deformed matrix inclusions. Well-developed flow structures are shown by the orientation of quartz grains and by the arrangement of deformed Globotruncana tests in both the pebbles and the matrix. A tentative explanation might suggest a mixed sedimentation in which beds of plastic calcareous muds and glauconitic sands were alternately deposited. Reworking phenomena intensively stretched and mixed the freshly deposited beds. However, intensity of deformation decreases upward as depth of water increased during transgression. Such a sediment may be classified as a special type of intraformational conglomerate formed under wave action when beds were still plastic.

Bahaman Calcareous Sands

The major part of the Bahama Banks is covered with a mantle of sands composed of calcium carbonate. They rest on a basement of similar sediment which has been consolidated into limestone by the subaerial deposition of calcite cement. Along the extreme edges of the Banks, the sand consists of the debris of neritic organic skeletons; elsewhere it is predominantly non-skeletal, and composed of grains of cryptocrystalline aragonite. These non-skeletal sand grains have hitherto been regarded as a break-down product of the limestones, but the present study, based on the Ragged Island area in the southeast part of the Great Bahama Bank, disproves this, and shows that such derived grains are rare in the recent bottom sediment. The sand grains are instead considered to be primary: they have formed, and are now forming, by the physico-chemical and bio-chemical extraction of aragonite from the sea water, which is saturated or supersaturated with calcium carbonate. The grains develop by the progressive aragonitic cementation of friable aggregates of calcareous silt particles. Further cementation tends to join the grains into lumps, in which an outer dense cryptocrystalline layer commonly allows the slower growth of larger aragonite prisms in the interior parts. The habit and surface texture of the lumps undergo a sequence of changes when traced from the ocean edge toward the interior of the Banks. Corrasion prevents excessive lump growth, and the typical bottom sediment is a well sorted medium-grade sand. The traces of calcareous mud in the sands contain no evidence of drewite needles, which are restricted to the protected shelf lagoons west of Andros and Abaco Islands. The controlling factor in the formation and distribution of the sands is the tidal currents of cooler oceanic water which sweep onto the Banks with velocities diminishing toward the interior, precipitating calcium carbonate as the water warms and evaporates. Sedimentation is therefore most rapid along the borders of the Banks. Aided by sea-level changes, this has led to the building of lines of elongate cays, parallel, and close to the ocean edge, making each Bank a gigantic atoll. Superficial aragonite ooliths develop on the protected beaches of the cays, and in the track of currents through the inter-cay channels. East of the Tongue of the Ocean and elsewhere close to End_Page 1------------------------------ the borders of the Banks, there are extensive areas where the sand is swept into a curvilinear pattern-work of submarine dunes, which occasionally adopt barchan shape. These have not been sampled, but are considered favorable for the formation of true, as opposed to superficial, ooliths. Evidence from the well drilled to a depth of 14,587 feet on Andros Island suggests that calcareous sands, similar to the recent deposits, have played a large part in building the Bahama Banks.

Sevy Dolomite in East-Central Nevada: ABSTRACT

Nolan first described the Sevy in the Gold Hill district of western Utah in 1935. His evidence pointed to Middle Devonian age for the non-fossiliferous formation. In east-central Nevada and adjacent Utah the Sevy consists of 500-1,600 feet of aphanic, homogeneous, End_Page 954------------------------------ white-weathering dolomite. It unconformably overlies the Laketown dolomite (Silurian) and grades upward into the Simonson dolomite (Middle Devonian). Halysites, found in the lower part, indicates at least part of the Sevy is Silurian; the upper part is probably Devonian. The Sevy is tentatively correlated with the Lone Mountain formation of central Nevada. A widespread, persistent dolomitic quartz sandstone at the top of the Sevy was derived from sources on the southeast. Evidence of this is based on geographic distribution of sorting, proportion of quartz sand, cross-lamination, and regional relationships. The slowly deposited Sevy represents a calcareous mud which was dolomitized and reworked on a tidal flat or very shallow bay. The provenance, peripheral to the miogeosyncline, was a lowland underlain by Silurian and Upper Ordovician dolomites. These were removed by erosion, and the Middle Ordovician Eureka sands were exposed to provide the quartz in the sandy phase of the Sevy. End_of_Article - Last_Page 955------------

The natural moisture‐content, voids (porosity) and compaction of unconsolidated clayey rocks

AbstractData relating to the natural moisture‐content of samples of saturated fine‐grained sediments, ranging from Devonian to Recent, are assembled and discussed. They indicate that the voids occupy volumes proportionally much greater than those shown by published figures for porosity obtained by standard displacement methods. Void‐ratio/pressure (depth) relationships and formulae devised to facilitate prediction are thus likely to need revision.The natural moisture‐content varies with the predominance of particular clay‐minerals, as well as with grading. The special cases of calcareous muds, organic muds, varves and boulder clays (tills), are discussed, together with geological implications of the further study of moisture‐contents.

Late-Glacial deposits at Nazeing in the Lea Valley, North London

At Nazeing, Essex, in the valley of the River Lea, a series of deposits has been investigated which extends back in time from the Post-Glacial climatic optimum to Late-Glacial times in the widest sense of that term. They are of special importance as bridging the time gap between the well-known ‘Arctic Plant Bed’ of the Ponder’s End stage (which occurs also at Nazeing), and the established Post-Glacial vegetational and climatic sequence. Pollen analysis of the main organic beds has permitted a general dating to be given to the various stages of formation of the deposits and this has been supplemented by a radio-carbon assay. Through the gravel sheet of the Ponder’s End stage a wide channel was cut which persisted with vicissitudes until Boreal time. At first this channel and the surrounding gravel plain were covered with organic muds and marls of a shallow lake containing stunted Mollusca of close affinity with those of Ponder’s End, and pollen indicative of rich herbaceous vegetation and an unwooded countryside. The channel was re-cut and the mere drained, and in the bed of the new channel, above an infilling of gravel, there began deposition of organic muds and then peats, a process which continued without interruption until, after a third short phase of erosion and drying in MidBoreal time (zone VI), the whole valley of the Lea was converted to fen. The later Boreal and succeeding Atlantic peats (zone VII) are sealed in by river flood clay. The Mollusca (whose determination is largely that of the late Santer Kennard) retain the general character of the Ponder’s End aggregate through the mere deposits, and the channel deposits up to the third erosion stage. The progress of drying of the mere is shown by the increasing proportion of land- to fresh-water shells. From the base of the channel which is referred to zone III, the close of the Late-Glacial period, the calcareous muds have yielded an extensive collection of plant remains, chiefly fruits and seeds belonging to ‘arctic-alpine’, ‘marsh’ and ‘ruderal’ species. Some of the species recognized have hitherto been regarded as weeds and introductions by man to the British flora; others have now a very restricted range. The pollen analyses of both the mere and channel-bottom deposits show great abundance and range of pollen of herbaceous plants, including many familiar already as Late-Glacial species and some, such asPolemonium coeruleum, newly recognized as such. It is apparent that conditions of the Late-Glacial period greatly favoured the spread of certain categories of plants, and that knowledge of this period is of the utmost importance in establishing the history of the British Flora. In the calcareous muds of the channel (zone III) and in the earlier muds beneath the lake marl the remains have been identified of four mammals of late Pleistocene character (including two species of lemming). At the close of zone III the calcareous muds yielded abundant bones ofBufoandRanatogether withLacerta vivipara. At the Early Boreal drying surface (Mx) of the channel there are also abundant land shells, and at this stage the molluscan fauna has a new and characteristic Holocene stamp, although small mammals of Late Pleistocene type survive, notablyOchotona spelaea(pika) andMicrotus anglicus. A general correlation is attempted for all the phenomena described, geological, floristic and faunistic, and they are tentatively related to corresponding phenomena in Britain and north-western Europe.

MOLLUSCAN FAUNA FROM THE PERMIAN KAIBAB FORMATION, WALNUT CANYON, ARIZONA

During the summer of 1946, field investigations of the Alpha member of the Permian Kaibab formation were undertaken in the region of Walnut Canyon, south of Flagstaff, Arizona. Excellence of exposures greatly facilitated the measuring of sections and tracing of rock units along the canyon. Specimens were collected for lithologic analyses, and representative fossils secured from several zonules. More extensive fossil collections were made at three exposures several miles north of Walnut Canyon, and at a fourth some 35 miles north. The fauna is analyzed and described, and an attempt is made to interpret the environment in which it developed and the conditions under which it was preserved. Environmental factors such as depth, salinity, temperature, and turbidity of the water, presence or absence of currents and other agitation, intensity of light, and the nature of the bottom are discussed. Conclusions reached indicate that the fauna, composed largely of mollusks, developed in a warm, shallow, epeiric sea not very far from land. A gradual retreat of the sea probably did not modify the depth of the sea very greatly. From lowland to the northeast, fine sediments were brought into the sea, but it is believed that the water was not very brackish, except perhaps for short periods of time. The sea bottom was composed of a silty, clayey, calcareous mud containing abundant shells of dead organisms, and most of the smaller mollusks may well have lived attached to seaweeds and other marine growth, while larger and heavier forms crawled over or burrowed into the mud bottom. Periodic changes of conditions, probably due to oscillations in depth and a corresponding change in the nearness of the shore, brought about local extinction of the fauna and changes in the nature of the sediments.

The Origin of Stylolites

ABSTRACT The Origin of Stylolites is not clear. The writer's field observations in Southwestern Germany showed that the stylolites there most probably were formed by solution of precipitated calcareous mud during sedimentation.

On the Significance of Metamorphosed Calcareous Concretions in Lower Birrimian Schists of the Gold Goast

AbstractNodules of “pseudodiorite”, i.e. metamorphosed calcareous concretions, occur in the Lower Birrimian (Pre-Cambrian) quartz-biotite schists which are interpreted as having been calcareous muds and silts. The probable metamorphic history of these nodules is traced.

Interglacial deposits from the Histon road, Cambridge

Summary The paper describes the results of the examination of deep sewer trenches in the Middle Terrace of the Cam on the northern outskirts of Cambridge. Extensive aggradation of upwards of 20 feet is indicated by the sequence of organic shelly calcareous muds followed by silt, sand and gravel. The muds and silt yielded abundant molluscan remains and a few mammalian bones, as well as a rich flora. Abundant Corbicula fluminalis at one horizon is a noteworthy feature of the extensive faunal lists based on determinations by the late A. S. Kennard. From an analysis of the proportions of land and fresh-water shells (both numbers of individuals and of species) at several horizons an attempt is made to infer the changing flood-water conditions. Vegetable remains are recorded from several levels. Evidence from both macroscopic remains and from pollen-analysis results, notably the abundance of hornbeam pollen, demonstrates a clear correlation with Jessen's zones f and g associated with the Eemian transgression of the Last Interglacial of North-West Europe. There are indications of brackish water conditions in the flora at one level. There is a striking agreement between the climatic and ecological condition suggested by Kennard from the mollusca, the physical nature of the deposits and the inferences from the flora. It is concluded that this aggradation phase probably represents a marginal phase of the transgression of the Eem Sea in Britain. The implication of the new data on the age of the overlying gravel of the terrace is not discussed and no revision of the Cam sequence is attempted.

Shallow-water Globigerina sediments

Research Article| January 01, 1941 Shallow-water Globigerina sediments G. W. CRICKMAY; G. W. CRICKMAY Search for other works by this author on: GSW Google Scholar H. S. LADD; H. S. LADD Search for other works by this author on: GSW Google Scholar J. E. HOFFMEISTER J. E. HOFFMEISTER Search for other works by this author on: GSW Google Scholar Author and Article Information G. W. CRICKMAY H. S. LADD J. E. HOFFMEISTER Publisher: Geological Society of America Received: 03 Jun 1940 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 1941 Geological Society of America GSA Bulletin (1941) 52 (1): 79–106. https://doi.org/10.1130/GSAB-52-79 Article history Received: 03 Jun 1940 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation G. W. CRICKMAY, H. S. LADD, J. E. HOFFMEISTER; Shallow-water Globigerina sediments. GSA Bulletin 1941;; 52 (1): 79–106. doi: https://doi.org/10.1130/GSAB-52-79 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 On Katafanga, Vanua Vatu, and Avea, three small islands in the Lau group of Eastern Fiji, occur highly calcareous Neogene sediments in which the most abundant organic remains are Globigerinidae (about 20 per cent by volume). Less abundant are calcareous red algae (0—2.0 per cent), calcareous blue-green algae (0—5.5 per cent), benthonic Foraminifera (0—4.0 per cent), coral fragments (0—22.0 per cent), echinoid spines (1.0—2.0 per cent), and brachiopods and mollusks (0—6.0 per cent).An origin in water considerably shallower than that of most Globigerina deposits is indicated by both physical and biological evidence. Diagnostic features are: fragmental oölites; interbedding of thin oölitic layers containing few Globigerinidae with beds rich in Globigerinidae; abundant calcareous mud; and high calcium carbonate content and absence of volcanic material generally present in deep-sea oozes. Biological characters of significance are the presence of fragments of reef corals, blue-green algae, and Crustacea.The above features and other evidence suggest a depth of more than 40 fathoms—the limit of flourishing reef-coral growth—but a depth not greatly in excess of this figure. Apparently the pelagic shells were brought by surface currents to an area where there was little clastic deposition and a paucity of benthonic forms. Some limestones contain a high percentage of lithified calcareous mud which appears to be similar to muds now accumulating on submarine banks and in certain coral lagoons. It is suggested that the presence of this material inhibited benthonic growth.The Fiji sediments are compared with deep-sea ooze; the supposed deep-water Globigerina limestones of Barbados, the Solomon Islands, South America; deposits on submarine banks and in the lagoons of existing atolls; shallow-water Globigerina chalk of England; Globigerina “soapstone” of Vitilevu, Fiji; and foraminiferal dune limestone of the Arabian Sea. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Authigenic Albite from the Lowville Limestone at Bellefonte, Pennsylvania

ABSTRACT Insoluble residues, obtained from the Lowville limestone at Bellefonte, Pa., show appreciable quantities of authigenic albite of unusual purity. The mineral occurs as twinned idiomorphic crystals, the largest of which are about one-fourth millimeter along the major diameter. Inclusions of small rhombs and granules of calcite are commonly observed in the albite crystals. The authigenic character of the albite is suggested by the unusual chemical composition, idiomorphic habit, the dearth of associated clastic materials, and the manner of distribution in the limestone. The crystals do not appear to be confined to special horizons, nor are they related genetically to fracture zones which may be considered avenues of circulation for hydrothermal solutions. The enclosing rock shows no trac of metasomatic change or heat effects of any kind, nor do the crystals appear to show replacement features, but rather they suggest formation in the calcareous muds of the sea floor during deposition and compaction of the sediment. Complete chemical analyses of the feldspar collected at random from several different parts of the Lowville rock show no potash but an unusually high soda content.

Wisconsin Silurian Bioherms (Organic Reefs)

The Silurian of Wisconsin contains biohermal structures at several stratigraphic horizons. These bioherms are essentially cuboidal, domal, or ridgelike masses of porous and cavernous, crudely bedded and poorly jointed, barren to highly fossiliferous dolomites which grade peripherally outward and vertically upward and downward into well-bedded, dense to saccharoidal, relatively unfossiliferous dolomites. The approximately contemporaneous surrounding strata, which commonly are thin bedded, first dip away from the reefy mounds at relatively low angles, except where differential slumping has steepened the initial dip, and then become essentially horizontal and take on the lithological character of the normal stratigraphic sequence of the region. The complexity of the fauna on some of the bioherms shows clearly that no single phylum of organisms played the dominant role in the construction. On the contrary, it is usually obvious that many different classes of organisms made large and important contributions to the growing calcareous mounds. Chief among the bioherm builders were algae, hydrozooid stromatoporoids, tabulate corals, camerate crinoids, cryptostomatous bryozoans, protrematous and telotrematous brachiopods, pelecypods, gastropods and cephalopods, and trilobites. Biohermal sites, especially at Wauwatosa, Milwaukee, and in the vicinity of Cedarburg and Grafton, were the main sources of the several large Silurian collections made by local amateur collectors in the closing decades of the nineteenth century; they still remain among the best collecting sites. The interbiohermal strata may or may not be fossiliferous, but if they are their fauna tends to be small and somewhat different from the typical biohermal assemblage. The bioherms appear to have accumulated in fairly shallow water and to have stood as low mounds a few feet to a few tens of feet above the surrounding bottoms where fine calcareous muds were being deposited.