Siliceous Sponge Spicules Research Articles

Replacement of evaporites within the Permian Park City Formation, Bighorn Basin, Wyoming, USA

ABSTRACTThe Permian Park City Formation consists of cyclically bedded subtidal to supratidal carbonates, cherts and siltstones. Early diagenesis of Park City Formation carbonates occurred under the influence of waters ranging from evaporative brines to dilute meteoric solutions and resulted in evaporite emplacement (syndepositional nodules and cements), as well as dolomitization, silicification and leaching of carbonate grains.Major differences are seen, however, in the diagenetic patterns of subsurface and surface sections of Park City Formation rocks. Subsurface samples are characterized by extensively preserved evaporite crystals and nodules, and preserve evidence of significant silicification (chert, chalcedony and megaquartz) and minor calcitization of evaporites. In outcrop sections, the evaporites are more poorly preserved, and have been replaced by silica and calcite and also leached. The resultant mouldic porosity is filled with widespread, very coarse, blocky calcite spar.These replacements appear to be multistage phenomena. Field and petrographic evidence indicates that silicification involved direct replacement of evaporites and occurred during the early stages of burial prior to hydrocarbon migration. Siliceous sponge spicules provided a major source of silica, and the fluids involved in replacement were probably a mixture of marine and meteoric waters. A second period of replacement and minor calcitization is inferred to have occurred during deep burial (under the influence of thermochemical sulphate reduction), although the presence of hydrocarbons probably retarded most other diagenetic reactions during this time interval. The major period of evaporite diagenesis, however, occurred during late stage uplift. The late stage replacement and pore‐filling calcites have δ13C values ranging from 0·5 to ‐25·3%, and δ18O values of ‐16·1 to ‐24·30 (PDB), reflecting extensive modification by meteoric water. Vigorous groundwater flow, associated with mid‐Tertiary block faulting, led to migration of meteoric fluids through the porous carbonates to depths of several kilometres. These waters reacted with the in situ hydrocarbon‐rich pore fluids and evaporite minerals, and precipitated calcite cements.The Tosi Chert appears to have been an even more open system to fluid migration during its burial and has undergone a much more complex diagenetic history, as evidenced by multiple episodes of silicification, calcitization (ferroan and non‐ferroan), and hydrocarbon emplacement.The multistage replacement processes described here do not appear to be restricted to the Permian of Wyoming. Similarly complex patterns of alteration have been noted in the Permian of west Texas, New Mexico, Greenland and other areas, as well as in strata of other ages. Thus, multistage evaporite dissolution and replacement may well be the norm rather than the exception in the geological record.

Paleobiological and sedimentological evidence of Pleistocene/Holocene hiatuses and ironstone formation at the Pontian islands shelfbreak (Italy)

Iron-rich hardgrounds were grabbed near the shelfbreak NE Ventotene and SW Ponza, at water depths of 119 and 141 m, respectively. These 1 to 3 cm-thick ironstone layers formed at about the Pleistocene/Holocene boundary during rapid sea-level rise, which began about 16,000 years ago and within about 8000 years brought the bottom of the shelf from a water depth of less than 30–100 m or more. A rapid vertical transition from circalittoral deposits characterized by a coastal detritic community with calcareous algae to ironstones rich in iron-managanese pisoids or glaucony and containing planktonic foraminifera, siliceous sponge spicules and echinoderm remains, indicates sediment starvation during rapid drowning of the shelf. The crisis of the sedimentary system and the local ironstone formation at sites of favourable morphology were triggered by major paleogeographic changes during final deglaciation at the close of the Pleistocene, leading to modified circulation patterns and chemistry of sea-water, reduced carbonate productivity below the photic zone, and strong activity of northward-directed Tyrrhenian currents intruding onto the outer shelf. Abundance of organic matter transported from the drowned volcanic islands and diminished oxygenation, due to both increasing water-depth and sluggish vertical circulation, were responsible for local reducing micro-environments, as testified by the formation of pyrite, leaching of carbonate bioclasts, and growth of microbial mats. Offshore sedimentation did not resume until the last 2000–4000 years, when the deeper-water and finer-grained Ponza glauconitic ironstone was covered by a thin veneer of silty clay deposited on the uppermost slope, beneath the mudline. The shallower and coarser-grained Ventotene winnowed pisoidal hardground, instead, is probably still forming today under the action of strong northward directed marine currents sweeping the shelfbreak free of sediment.

Chert appearance in the Cueva-Bedón carbonate platform (upper Cretaceous, northern Spain)

AbstractNodular chert from the Cueva-Bedón carbonate platform (late Turonian-earliest Coniacian) occurs above the type 1 sequence boundary and in association with a transgressive systems tract deposit. It formed by selective replacement of grainstones-packstones, and Thalassinoides burrow fillings. Other minor types of selective silicification include the replacement of anhydrite nodules, forming quartz geodes, and the partial or total replacement of oysters and inoceramids. The chert nodules consist predominantly of microquartz with volumetrically minor fibrous quartz (length-fast chalcedony) and megaquartz. The silica has a mainly biogenic source (siliceous sponge spicules and radiolarians). Lepisphere textures that are indicative of an intermediate opal-CT precursor are evident in chert nodules, which indicates the chert formed by a maturation process from opalA to opal-CT to quartz. The δ 18O values of microquartz suggest a precipitation from marine fluids. The fabric of quartz geodes consists of irregular bands of heterometric megaquartz, quartzine and lutecite spherulites, and a well developed band of petaloidal megaquartz that contains small anhydrite inclusions. Bivalve shells are replaced mainly by fibrousquartz (quartzine-lutecite), which forms extensive beekite rings. The silica source of the replaced fossils is also biogenic, but silicification couldhave occurred by direct quartz replacement without an opal-CT precursor. Field and petrographic evidence indicate that silicification was an early diagenetic process that affected both uncompacted and compacted sediments, andwas inhibited when the dolomitization began. There seems to exist a syncrony in age (late Turonian-earliest Coniacian) between the nodular chert in the Cueva-Bedón carbonate platform and the bedded and nodular chert ofthe Plentzia carbonate turbidites in the deeper Basque Arc.

Physical, geological and biological studies on four Pacific seamounts: introduction

SEAMOUNTS are prominent submerged volcanoes that rise above the surrounding sea floor and are distributed throughout the major basins of the World Ocean. Estimates of the abundance of these features continually increase with improvements in mapping and surveying technology (DE MOOSTIER, 1988). In the Pacific Ocean, the recorded number of seamounts greater than 1000 m in height has risen from 10,000 (MENARD, 1959) to over 30,000 (SMITH and JORDAN, 1988). Considering the abundance of seamounts and the unique conditions created by these features in a flow field, they have received little attention. The morphology of these topographic features varies greatly from steep-sided cones to complex truncated volcanoes (guyots) that were eroded during a period of emergence above sea level, prior to subsidence. Seamounts may possess complex topographic features such as summit calderas (LONSDALE and SFIESS, 1979; FORNAm et al., 1984) and drowned carbonate reef caps (ScHLANGER et al., 1987). Many features of seamounts may be masked by sedimentary deposits consisting of volcanic detritus, and biogenic and terrigenous sediment. Sediment supply and removal patterns are influenced by changes in surface water productivity, seamount depth, calcium carbonate dissolution rates (LEVIN and NITvI~OUER, 1987) and current flow. The most common type of sediment found on seamounts above the carbonate compensation depth is biogenic ooze composed of calcareous and siliceous microfossils and sponge spicules (KENNEa'r, 1982). Seamounts modify the large-scale dynamics of oceanic currents and alter the density stratification of the water column (GouLD et al., 1981; OWENS and HOGG, 1980). Despite the obvious geological evidence for active erosion (LONSDALE and SPIESS, 1977; HEEZEN and HOLLtSTER, 1971; ROBERTS et al., 1974; STANLEY and TAYLOR, 1977), only a few studies have directed attention toward the effects of currents on the surficial environment of seamounts (CAcCmONE et al., 1988; NOBLE et al., 1988). The interactions between seamounts and oceanic currents are governed by geographic location, water depth and the intensity of the flow field near the seamount. The intensity of this flow field generally decreases with increasing water depth and distance from continental margins.

Oxygen-isotope fractionation between marine biogenic silica and seawater

A stepwise fluorination technique has been used to selectively react away the water component of hydrous silica in order to better investigate the oxygen-isotope fractionation between biogenic opal and seawater, and to determine whether all taxa produce opal which is suitable for oxygen isotope paleothermometry. δ 18O of the tetrahedrally coordinated silicate oxygen of siliceous sponge spicules grown at a wide variety of temperatures varies independently of temperature. δ 18O from an Eocene radiolarian ooze sample is much more enriched than would be expected from any reasonable isotopic temperature curve, given the probable growing temperature of the sample. δ 18O of diatom samples seems to vary systematically with temperature and to conform approximately to the isotopic temperature curve for diatom frustules obtained by Labeyrie and coworkers using an entirely different analytical technique. Sponges appear to precipitate silica in isotopic disequilibrium with seawater oxygen, and old radiolarian silica may exchange readily with cold oceanic bottom water. Neither will apparently be useful for paleo-climate reconstructions. Diatoms may be useful in deducing ancient surface-water temperatures, but the systematic variation of α with temperature for diatoms may not be related to the quartz-H 2O equilibrium isotope fractionation.

Chertification histories of some Late Mesozoic and Middle Palaeozoic platform carbonates

ABSTRACTA consistent pattern for the silica sources, depositional environments and timing of chertification was observed in a diverse suite of five Late Mesozoic and Middle Palaeozoic carbonate sequences; the (1) Upper Greensand (Cretaceous) and (2) Portland Limestone (Jurassic) of southern England, (3) the Ramp Creek Formation (Mississippian) of southern Indiana, and the (4) lower Helderberg Group (Devonian) and (5) Onondaga Limestone (Devonian) of New York State. Nodular chert formation in all five limestone sequences occurred in sediments that were largely uncemented. Ghosts of pre‐chertification carbonate cements are present in some chert nodules but are volumetrically minor. In every limestone sequence except the Upper Greensand, chertification occurred after burial to a depth sufficient for intergranular pressure solution and mechanical grain deformation of carbonate sand.Nodular chert is most abundant in subtidal, normal marine wackestones and mudstones that were deposited at or below fair‐weather wave base, and is absent or rare in supratidal, intertidal and high‐energy subtidal limestones and dolomites. An intraformational sponge spicule silica source for chert nodules is suggested by direct evidence, such as calcitized sponge spicules in the host limestone, and circumstantial evidence, such as ghosts of sponge spicules in chert nodules and a correlation of chert abundance with depositional environment. Most molds of siliceous sponge spicules were apparently obliterated by post‐chertification intergranular compaction. We propose that these general trends for the depositional environments, silica sources and timing of chertification are representative of most Mesozoic to Middle Palaeozoic platform limestones.

SHADE ADAPTED BENTHIC DIATOMS BENEATH ANTARCTIC SEA ICE1

ABSTRACTA dense community of shade adapted microalgae dominated by the diatom Trachyneis aspera is associated with a siliceous sponge spicule mat in McMurdo Sound, Antarctica. Diatoms at a depth of 20 to 30 m were found attached to spicule surfaces and in the interstitial water between spicules. Ambient irradiance was less than 0.6 μE · m−2· s−1 due to light attenuation by surface snow, sea ice, ice algae, and the water column. Photosynthesis‐irradiance relationships determined by the uptake of NaH14CO3 revealed that benthic diatoms beneath annual sea ice were light‐saturated at only 11 μE·m−2·s−1, putting them among the most shade adapted microalgae reported. Unlike most shade adapted microalgae, however, they were not photoinhibited even at irradiances of 300 μE·m−2·s−1. Although in situ primary production by benthic diatoms was low, it may provide a source of fixed carbon to the abundant benthic invertebrates when phytoplankton or ice algal carbon is unavailable.

CHERTS AND GEOCHEMISTRY OF STRATABOUND URANIUM ORE DEPOSIT OF CHERT TYPE

In this paper, the characteristics of various types of cherts are described, and the clas-sification and origin of bedded cherts are discussed. The author suggests that most of thebedded cherts are generated from the accumulation of died organism, such as radiolarians,diatoms and siliceous sponge spicules, which have imbibed silica from sea water before dy-ing. Concerning the geological and geochemical features and the origin of the strata-bounduranium ore deposit of chert type, a special emphasis is put on the discussions about the for-mation of ore-source beds and the relationship between uranium deposits and crustal move-ment.

Existencia de estructuras nodulosas de celestina afectadas por silicificación en el Valle de Losa (N. de Burgos )

The present work describes sorne nodules of celestite, which appear in a marly clay level of the Upper Cretaceous (Santonian) in Losa Valley (North of Burgos). A great number of nodules have been in some extent, or totally pseudomorphized by quartzine and lutecite (length-slow chalcedony). These nodules have not been mentioned up to now in the research works carried out in the Basque Cantabric Basin; some nodules present elongated shapes, while some others are subspherical, In the inside, the radial arrangement shows pyramidal shapes with rhombic sections, emerging from a compact nucleus. These nodules are diagenetic structures growing expansively from the nucleus towards the periphery. In this action echinoid spines, pelecypods fragments, bryozoans, etc., are enclosed. Celestite here is highly pure; there is no barite at all. For the celestite ions the following origin in proposed. The sulphate was supplied by fluids which laterally migrate from the Triassic gypsum (Keuper). Sr seems to have been released along the transformation process of aragonite sediments to calcite. Although it can't be forgotten the amount of Sr furnished in the parcial dolomitization process suffered by the sedimentary sequence, In the same level, irregular cherts appear associated to celestite nodules. These cherts have a considerable amount of siliceous sponge spicules (litisteids?) replaced by sparry carbonate what doubtless shows the biogenic origin of the silica. The silicification process has allowed the preservation of the nodules, in spite of the strong celestite solution which afterwards originated a great loss celestite.

Some Permian (Leonardian) Radiolarians from Bone Spring Limestone, Delaware Basin, West Texas: ABSTRACT

A sample of the deep basinal Bone Spring Limestone (Leonardian) has yielded a diverse and superbly preserved assemblage of spumellarian radiolarians, associated with siliceous sponge spicules and conodonts. Radiolarians include typically Paleozoic paleoactinommids, entactiniids, and rotasphaerids; Permian albaillellids and parafollicucullids; and triradiate spongodiscids or hagiastrids. Triradiate forms, which include approximately 60% of the shells in the sample, have not previously been reported to be abundant in pre-Mesozoic rocks. Albaillellids and parafollicucullids are similar to forms reported from the Permian strata of Japan, but the Bone Spring forms do not fit in the biostratigraphic zonation proposed by Japanese workers. This may be due to gaps in the Japanese tratigraphic sections or to provincialism in radiolarian faunas. Diversity in the Bone Spring assemblage is higher than in other Permian assemblages. Most reported Permian radiolarians have been recovered by HF extraction of cherts, while the Bone Spring specimens were extracted from limestone with acetic acid. Thus, diversity differences can be partly attributed to fortuitous preservation. End_of_Article - Last_Page 444------------

Characteristics of Peat Deposits in Mississippi River Delta Plain: ABSTRACT

Variations in organic-rich sediment (peat) from the Mississippi River delta plain can be explained by differences in three interrelated parameters: (a) depositional setting, (b) balance between subsidence and detrital influx, and (c) marine inundation. Variations are observed in geometry of the overall deposits, organic matter content, and the mineralogy of peats and related ashes. Using a vibracorer, samples were collected from two brackish areas (Avery Island/Sale-Cypremort and Barataria basin) and one freshwater area (Gueydan). Geometries of the deposits are different for the two brackish settings; interdistributary peats of Barataria basin tend to be discontinuous and somewhat thicker than blanket peats of Avery Island/Sale-Cypremort. The freshwater peat is an elongate body in a Pleistocene channel cut. Peats in all areas average 90% moisture content. Dried peat averages 81.3% organic matter with a bulk density of 0.12 g/cm3. Holocene differential compaction has been minimal (< 4%). Conventional ash values indicate different distributions of organic material for the two brackish areas. For the area containing interdistributary peats, approximately 5% of the subsurface contains more than 70% End_Page 1466------------------------------ organic matter, whereas for blanket peats, 14% of the section has more than 70% organic matter. Mineralogic data collected on low-temperature ashes indicate that major minerals in brackish peat consist of kaolinite, quartz, and water-soluble salts, whereas minerals from freshwater samples are primarily kaolinite and quartz. X-ray diffraction and electron microscopy show the presence of smectite, illite, abundant siliceous spicules, framboidal pyrite, biotite, pyroxene, and rutile in the insoluble fraction. Suitability of these deposits as coal precursors has been discussed by several workers. Superficial examination of data generated so far suggests that only thin coal seams with high ash would be produced. However, the presence of decomposing siliceous sponge spicules in the ash and the possibility of ash being leached by fresh ground water, suggest that much ash may be lost during early diagenesis. Hence, this environment may have more potential as a modern coal-forming model than it first appeared. End_of_Article - Last_Page 1467------------

A Nearshore Sponge Spicule Mat from the Pennsylvanian of West-Central Indiana

ABSTRACT A thin (3-6) cm) interval in the Perth Limestone Member of the Staunton Formation (Pennsylvanian, Desmoinesian) in Warren County, Indiana, contains abundant small siliceous sponge spicules that form a spicule mat. The limestone is a grain-supported packstone with a micritic matrix, the predominant grains being small sponge spicules that range down to a few micrometers in size. The intermeshed spicules helped support a wide variety of vagile and sessile benthonic marine invertebrates on a lime mud bottom. In contrast to other spiculites that are basinal deposits, the spiculite reported here developed in shallow water, probably no more than 90 feet deep, as part of a cyclothemic sequence that includes coals and fluviatile channel sandstones above and below the Perth.

Deposition and Diagenesis of Mississippian Pinnacle Reefs of Chappel Limestone, Fort Worth Basin, Texas: ABSTRACT

The Mississippian Chappel Limestone constitutes an important oil-bearing unit that occurs along the western margin of the Fort Worth basin in north-central Texas. It has long been assumed that the Chappel is productive from Stratigraphic relations of the Chester, which in part overlies the Chappel, and the Chappel have remained enigmatic. Study of cores reveals that the Chappel represents a mound-core facies consisting predominantly of fenestrate bryozoans which, soon after death, became rigidly stabilized by submarine aragonitic-fan druse cements; these provided sufficient wave resistance for the mounds to be termed reefs. The Chester represents a flank facies, consisting predominantly of crinozoan components and siliceous sponge spicules, that is time-equivalent to Chappel core facies. Flank dips range up to 35°. Thus the term pinnacle is no longer applicable to these reef complexes. The core facies consists predominantly of bryozoan boundstones and very coarse grainstones (slabstones); the flank facies contains grainstones, packstones, and wackestones. Slope instability precluded formation of submarine cements in grainstones of the flank facies. The reef complex was subjected to complex, multicyclic diagenesis which records several episodes of subaerial exposure and freshwater diagenesis followed by submergence, recolonization, and renewed reef growth. Nearly all preserved porosity is in the reef core and represents primary voids among erect and broken bryozoan fronds--voids which have been filled to varying degrees by submarine and vadose internal sediments, submarine cements, and meteoric vadose and phreatic cements. These materials were cyclically emplaced during submergent and emergent phases. End_of_Article - Last_Page 548------------

Origin of a Lower Pennsylvanian Depositional Cycle

ABSTRACT The Marble Falls Group, a Lower Pennsylvanian limestone exposed at the margins of the Llano uplift in central Texas, was deposited on a carbonate shelf bordered by the Fort Worth basin. Outcrops near the basinward margin of the shelf reveal a depositional cycle containing a regressive sequence, a low-relief unconformity, and a transgressive sequence. Minor cycles within the transgressive and regressive sequences include inner shelf successions of facies capped by thin intervals of the outer shelf facies. Vertical progressions of inner shelf facies, algal bank to calcarenite bank to tidal bar-tidal flat, were clearly the product of regression. Thin capping intervals of the outer shelf facies contain open marine clay and carbonaceous matter mixed with siliceous sponge spicules, micrite and pellets. Incursions of the outer shelf facies onto inner shelf facies are judged to be a product of transgression. The regressive sequence exhibits a striking down-to-basin shift of progressively younger minor cycles, interpreted to indicate net regression interrupted by minor transgressions. The transgressive sequence exhibits similar cyclic tendencies and is interpreted to represent net transgression interrupted by minor regressive episodes. There is striking similarity between the interrupted patterns of transgression and regression in the Marble Falls cycle, and the discontinuous nature of ice sheet advances and retreats in Pleistocene climatic cycles. Estimates of relative sea level changes necessary to account for Lower Pennsylvanian facies patterns are in the same range as those resulting from Pleistocene climatic cycles. After carefully considering all cycle-generating mechanisms it is concluded that the Marble Falls cycle was most likely produced by glacio-eustatic changes.

Mechanism of Internal Stratification of Siliceous Sponge Spicules

BECAUSE sponges constitute an important part of many fossil records, their fine structure should be of interest to palaeontologists. Internal fine structure in spicule fossils would provide a valuable comparison with present day spicules. Furthermore, changes in the fine structure of spicule fossils may offer clues as to climatological or ecological conditions in that period.

Dimple Limestone--A Turbidite Sequence: ABSTRACT

Recent work on the Dimple Limestone (Atokan) of the Marathon tectonic belt of West Texas indicates that it is predominantly a turbidite sequence deposited in relatively deep water below normal wave base. A narrow upperslope facies of nongraded, festoon cross-stratified grainstone, packstone, and chert conglomerate beds deposited in relatively shallow water occurs in the northwest part of the area. Wherever exposed, the formation is part of an overthrust complex which moved northwestward a distance of several miles or more. The basin facies to the southeast consists of interbedded pelagic and turbidite beds. The pelagic beds are dark gray to black terrigenous shale, calcilutite, and chert containing a sparse fauna of radiolaria and sponge spicules. The turbidite beds are graded lithoclastic fossiliferous limestones ranging in thickness from less than an inch to more than 9 feet. Lithoclasts are mostly angular fragments of Devonian and Ordovician cherts. The fauna is characteristic of shallow shelf and slightly deeper slope environments, and indicates redeposition by turbidity currents. Small quantities of ooliths, pellets, glauconite, and quartz sand grains occur commonly in the turbidite beds. The turbidite beds contain current direction features including aligned fossil fragments (particularly sponge spicules and brachiopod spines), cross laminae, ripple marks, and flame structures; and slope indicators such as convolutions and medium-scale slump structures. Sole markings are not evident. Delicate laminae in upper parts of graded beds commonly consist of siliceous sponge spicules aligned parallel with the current direction. Numerous measured sections of the basin facies indicate a record of continuous deposition from the flysch-like Tesnus Formation, through the Dimple Limestone, and into the overlying flysch-like Haymond Formation. Submarine slides containing large blocks of white Devonian chert locally produced erosional surfaces. A comparison of the Tesnus Formation, Dimple Limestone, and Haymond Formation with the Scaglia-Brecciola-Macigno sequence of the northern Apennines shows striking similarities. Current direction indicators, bed thickness, grain size, facies, and over-all formation thickness indicate that the Dimple Limestone was transported down a slope from the northwest. During early Atokan time, a carbonate shelf in the vicinity of the Glass Mountains provided shallow-water fossils and other carbonate debris for later redeposition in a relatively deep basin on the southeast. End_of_Article - Last_Page 372------------

Microfacies of Wabash Reef, Wabash, Indiana

ABSTRACT The microscopic statistical investigation of the Wabash reef has revealed five main microfacies ranging, in decreasing relative depth conditions, from highly dolomitic shales of the country-rock to dolomitic biocalcarenites and bioconstructed dolomitic limestones or dolomites belonging to the reef system. Among the microscopic parameters, the variation of the orientation of siliceous monoaxonic sponge spicules in the shales can be used as a criterion for predicting the position of the reef.

Sponge Spicules from the Lower Mississippian of Indiana and Kentucky

Siliceous sponge spicules belonging to the genus Hyalostelia have been found at several localities along the strikie outcrop of Lower Mississippian Borden group Floyds Knob-Edwardsville reef facies rocks from northem Indiana into Kentucky. It is believed that the presence of this unique form of spicule can be useful to recognize and trace the reef facies of this stratigraphic unit in both surface outcrops and subsurface samples. Shrock and Malott (1929, p. 222) described the stratigraphy of a quarry 5 miles south of Wolcott, Indiana. On the basis of a few fragmentary fossils observed, they erroneously correlated the strata with the Devonian. This error has been subsequently corrected on a later edition (1932) of the Geological Map of Indiana. A visit to the quarry in 1951 yielded the first spicules recovered from HCI residues made from the several limestone samples collected. Little attention was given to these few fragmental spicules until later, when an examination was made of a Borden reef being quarried near New Ross, Indiana. At this place the rock consists of a coarsely-crystalline crinoidal limestone irregularly interbedded with bright, light grayish-green shale. The simnilarity of the crinoidal rock to that in the Wolcott quarry prompted a study of residues which yielded anchor-shaped spicules identical with those found in the Wolcott quarry. Later, a cursory stop to qxamine rocks in the roadcut section where U. S. highway 31 W ascends the Muldraugh Hill escarpment in Kentucky revealed the same crinoidal facies and spicules. Finally, samples furnished by the Indiana Geological Survey from the Floyds Knob formation of the Stobo bioherm east of Bloomington, Indiana, also contained Hyalostelia spicules. In 1888, Hinde, pp. 158-162, identified two species of Hyalostelia (H. smithii and H. parallela) from the Lower Carboniferous rocks of England, Scotland, and Ireland. Ulrich (1890, p. 246, figs. 2-3) erected the species Hyalostelia delicatula for hexactinellid spicules found in Lower Pennsylvanian rocks of Illinois. Butts (1915, p. 159) mentioned white needle-like sponge spicules in the Borden rocks of the Muldraugh Hill area in Kentucky but did not describe them. Weller (1930, p. 242) described a sponge spicule assemblage including Hyalostelia diabola and Hexactinellida delicatula (Ulrich) from Lower Pennsylvanian rocks of Illinois apparently from the same horizon as the ones which Ulrich figured. Both Ulrich and Weller found large cylindrical shafts which undoubtedly came from spicules of the anchor type, but neither found the four recurved rays which are attached to these shafts in complete spicules. Some spicules described by Scott (1943) from the Lower Pennsylvanian of Montana appear to belong to Hyalostelia sp. namely the hexactinellids on plate 3 and the anchor spicules on plate 4, especially fig. 23. STRATIGRAPHY

Siliceous Sponge Spicules from the Lower Pennsylvanian of Montana

It is needless to dilate on the limitations imposed on one who undertakes to describe a collection of wrote Dr. H. V. Wilson, foremost authority on modern sponges, forty years ago when he described a collection from Porto Rico. The statement is equally true concerning the difficulties confronting the paleontologist who attempts to describe a group of fossil sponge spicules; indeed, the limitations are multiplied many fold. There are only a few papers describing sponge spicules from North America and this has led some workers to believe that spicules of Paleozoic age are rare. The apparent paucity, however, may be partially explained by the difficulties of classification.

Petrography and origin of the Rex chert

Research Article| August 01, 1941 Petrography and origin of the Rex chert W. D. KELLER W. D. KELLER Search for other works by this author on: GSW Google Scholar GSA Bulletin (1941) 52 (8): 1279–1298. https://doi.org/10.1130/GSAB-52-1279 Article history received: 09 Dec 1940 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation W. D. KELLER; Petrography and origin of the Rex chert. GSA Bulletin 1941;; 52 (8): 1279–1298. doi: https://doi.org/10.1130/GSAB-52-1279 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 The Rex chert member of the Phosphoria formation of Permian age was studied petrographically from specimens collected across the stratigraphic sections at five localities in Idaho, Wyoming, and Utah. The Rex is a fine-grained quartzite with chert in its upper part in the Big Hole Mountains of Idaho. Southward toward the Utah-Idaho lines much of the clastic character is lost, calcareous chert predominates, and the member increases in thickness. It becomes thinner again farther south toward the type locality.Microcrystalline quartz predominates in the chert, but some thin sections were studied in which three varieties of silica—clastic quartz grains, chalcedony, and microcrystalline quartz—all occurred in a single section. Petrographic evidence suggests that the chert of the Rex is primary with probably considerable diagenetic replacement of carbonate. It is inorganic in the main but contains some siliceous sponge spicules. Subsequent replacement is believed to be insignificant. 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.