Silicified Fossils Research Articles

Silicified tubular microfossils from the Upper Doushantuo Formation (Ediacaran) in the Yangtze Gorges area, South China

The ediacaran Doushantuo Formation in the Yangtze Gorges area (Fig. 1.2) contains abundant silicified cyanobacterial coccoids and filaments (Y. Zhang et al., 1998), acanthomorphic acritarchs (Zhou et al., 2007), multicellular algae (Xiao, 2004), and possible animal embryos (L. Yin et al., 2007). These silicified fossils are taxonomically similar to the phosphatized fossils in the Doushantuo Formation of the Weng'an area, South China (Y. Zhang et al., 1998). However, the Weng'an assemblage contains tubular microfossils that have not been previously documented in the Yangtze Gorges area. Here we report the occurrence of secondarily silicified tubular microfossils—Sinocyclocyclicus guizhouensis(Xue et al., 1992) andYangtzitubus semiteresnew genus and species—from lenticular cherts in the upper Doushantuo Formation in the Yangtze Gorges area. Of the two named taxa,Sinocyclocyclicus guizhouensiswas previously known from the Weng'an area (Liu et al., 2008). The new data extend the geographic, taphonomic, and environmental distribution of Doushantuo tubular microfossils. A fuller documentation of the Doushantuo biodiversity is also important to the evaluation of possible taphonomic or environmental biases among the three exceptional taphonomic windows—carbonaceous compression (Xiao et al., 2002), phosphatization (Xiao and Knoll, 1999), and silicification (Y. Zhang et al., 1998)—in Doushantuo black shales, phosphorites, and cherts, respectively.

The most ancient terrestrial lichen Winfrenatia reticulata: A new find and new interpretation

Silicified fossils from Rhynie cherts in Scotland are studied. A lichen belonging to the genus Winfrenatia is detected and studied. This oldest terrestrial lichen is dated to the Pragian (=Siegenian) of the Early Devonian. New characters of the lichen are described, and their new interpretation is given. The main component of the lichen thallus is a filamentous cyanobacterium (Nostocales). Structures which were interpreted as fungal hyphae are probably hollow sheaths of this cyanobacterium. Mycobiont hyphae develop at the base of the thallus and symbiose with a coccoid cyanobacterium. Thus, Winfrenatia reticulata is a three-parted organism, constituted of a mycobiont and filamentous and coccoid cyanobacteria.

Woods of a Miocene Petrified Forest near Ankara, Turkey

The taxonomic composition of a recently discovered silicified fossil forest, preserved by volcanic activity 18.2-16.9 million years ago in Çamlıdere near Ankara (Turkey), is investigated. Many samples collected were divided into 2 groups as CAM1 and CAM2. Thin sections from transversal, radial, and tangential directions were cut to identify the woods. Wood identifications were performed using standard techniques and fossil wood features. The preserved wood indicates that the forest was composed almost exclusively of Taxodium (CAM1) and Sequoia (CAM2). These genera were extinct from Anatolia and Europe during late Miocene.

Acid digestion of silicified shells

Many fossils can be extracted from their host rock by using acid digestion. Whether this technique is suitable depends upon the mode of preservation. Very good results can be achieved for silicified fossils within a carbonate-rich host rock. However, incomplete silicification may lead to partial loss of fossils in the laboratory. Therefore, prior to commencing acid treatment it is helpful to have some knowledge of the taphonomy of the sample and its ambient depositional environment, as there are important geological factors that have a significant influence on the preparation process.

Permian marine paleoecology and its implications for large-scale decoupling of brachiopod and bivalve abundance and diversity during the Lopingian (Late Permian)

The transition during the Permian–Triassic interval from brachiopod-rich benthic marine assemblages to communities with diverse molluscs has been well constrained by measures of global taxonomic richness but its ecological context has not been studied using quantitative relative abundance data. New relative abundance data from Early, Middle, and Late Permian silicified fossil assemblages from offshore shelf carbonate environments indicate that molluscs increased significantly in relative abundance, from 0.8% in the Middle Permian (Guadalupian) to 65.4% in the Late Permian (Lopingian). These numerical changes are accompanied by increases in the abundance of infaunal bivalves and motile gastropods in the Late Permian. Although this ecological change was coincident with the end-Guadalupian extinction, a new global diversity compilation indicates that the overall genus-level severity of that biotic crisis was substantially lower than previous estimates. The pronounced ecological shift was instead concurrent with the onset of deep-marine anoxic or euxinic conditions around the Guadalupian–Lopingian boundary, suggesting that increased environmental variability in proximity to the deep water mass may have given eurytopic molluscs a competitive advantage over more stenotopic brachiopods. However, the lack of global changes in relative genus richness implies dramatic decoupling of global taxonomic and local ecological processes. The pronounced increase in molluscan abundance and alpha diversity in the silicified assemblages contrasts with their unchanged global taxonomic richness and may also have resulted from increased environmental stress in offshore shelf environments. These results demonstrate that the ecological transition from the brachiopods to molluscs was more complex than inferred from global measures of taxonomic richness and imply that initial stages of Permo–Triassic environmental deterioration may have been responsible for the decoupling of local ecological from global taxonomic processes during the dramatic Late Permian rise of the Modern Fauna.

Nondestructive, in situ, cellular-scale mapping of elemental abundances including organic carbon in permineralized fossils.

The electron microprobe allows elemental abundances to be mapped at the microm scale, but until now high resolution mapping of light elements has been challenging. Modifications of electron microprobe procedure permit fine-scale mapping of carbon. When applied to permineralized fossils, this technique allows simultaneous mapping of organic material, major matrix-forming elements, and trace elements with microm-scale resolution. The resulting data make it possible to test taphonomic hypotheses for the formation of anatomically preserved silicified fossils, including the role of trace elements in the initiation of silica precipitation and in the prevention of organic degradation. The technique allows one to understand the localization of preserved organic matter before undertaking destructive chemical analyses and, because it is nondestructive, offers a potentially important tool for astrobiological investigations of samples returned from Mars or other solar system bodies.

Silurian (Llandovery/Wenlock) foraminiferida in carbonate environments of southeastern Wisconsin

This note presents the first stratigraphic, paleoenvironmental, and systematic account of Silurian foraminifers in Wisconsin, which include nine previously described species of Ammodiscus, Glomospirella, Hemisphaerammina, Hyperammina, Lagenammina, Psammosphaera, Stomasphaera, Thurammina, and Webbinelloidea (Appendix 1). Early Silurian carbonates in this area (Fig. 1) were deposited in shelf and ramp environments in the western part of the Michigan Basin (Harris et al., 1998), and the foraminifers are associated with macrofaunal communities that represent Benthic Assemblages BA3 to BA5 of Brett et al. (1993).Silicified agglutinated foraminifers were obtained from acidinsoluble residues processed for conodonts, sponge spicules, and macrofauna (Watkins et al., 1994; Kuglitsch, 1996; Watkins and Kuglitsch, 1997; Watkins and Coorough 1997a, 1997b). Silicification of the specimens, rather than a composition of agglutinated siliceous grains, is indicated by lack of detrital silica in enclosing dolostones, variable detail of preservation, and association with other silicified fossils.

Silica-replaced fossils through the Phanerozoic

A systematic survey of 1863 papers on macrobenthic assemblages reveals that an average of 21% of published Paleozoic papers concern silicified fossils, but that average drops to just 4% for post-Paleozoic papers. During the Paleozoic, silicified fossil occurrences do not significantly correlate with the amount of shelf chert, outcrop area, time, duration of geologic intervals, or carbonate rock volume. This substantial drop in numbers of silicified fossils coincides temporally with increased importance of aragonite faunas following the end-Permian extinctions. However, qualitative measurements of secular changes in abundance and diversity of siliceous sponges are consistent not only with the post-Paleozoic decline in fossil silicification, but also with fluctuations in the amount of silicified fossils throughout the Paleozoic. The facies distribution of silicified fossils in the Permian of West Texas also suggests that the distribution of silicified fossils may reflect the occurrence of siliceous sponges. The decline in silicified fossils after the Permian may be related to a concomitant rise in offshore bedded chert deposition and movement of the locus of biogenic silica formation from nearshore to offshore regions beginning in the Triassic, rather than with the expansion of diatoms in the Cretaceous.

Pennsylvanian Fossils Replaced by Red Chert: Early Oxidation of Pyritic Precursors

ABSTRACT Upper Pennsylvanian cyclothems of western Nebraska and southeastern Utah contain abundant brachiopods and crinoids replaced by red quartzine (length-slow chalcedony). Red fossils typically occur within silty wackestones that were deposited below fair-weather wave base during eustatic high stands. Within the D zone cyclothem of the Lansing-Kansas City Group (Nebraska), a well-documented paleosol recording an episode of subaerial exposure lies several meters above the chert-bearing rocks. The upper member of the Hermosa Formation (Utah) contains large-scale cross-stratified eolianites resting directly upon three red-chert-bearing limestones. Petrographic study of the silicified fossils from these two sequences shows that although fossils are presently hematitic, iron was initially con entrated within the skeletal material as scattered pyrite framboids and euhedra. Anaerobic decay of the organic material within shells during their replacement by quartzine may have led to the precipitation of pyrite. During a subsequent event, acid generated by the oxidation of pyrite inclusions allowed migration of dissolved iron through the quartzine. Buffering of these solutions by surrounding, unreplaced skeletal material caused preferential accumulation of iron oxide at the perimeters of the silicified zones. Silicification, pyrite precipitation, and pyrite oxidation all predated the crushing of shells during mechanical compaction of the matrix. We hypothesize that oxidation took place when the regional groundwater table dropped as the sea regressed and overlying beds were subaeria ly exposed. Cherts with similar histories should be present in other strata that bear internal sources of silica, iron, and organic material, and record large-scale, rapid changes of sea level.

Wood Decay in Silicified Gymnosperms from Antarctica

Gymnospermous secondary xylem degraded by wood-decaying fungi was examined in silicified fossils from Antarctica. Araucarioxylon-type wood from the Triassic and specimens of Vertebraria from the Permian demonstrate similar patterns of decay. Specimens are characterized by irregularly shaped areas lacking cells and are infected with branched, septate hyphae with clamp connections. The decay in these fossils is comparable in appearance to present-day rots caused by basidiomycetes. Two patterns of decay are evident: (1) A wall component, presumably lignin, is removed from the wall and middle lamella of infected tracheids, leaving a considerably thinner cellulose framework; and (2) the primary and secondary walls typically separate, and all wall layers are progressively reduced in thickness and eventually removed. The middle lamella, particularly where it is thickest in the corners between cells, persists longer than other layers. Indications of host response to fungal attack include the production of possibl...

Preservation of shell microstructure in silicified brachiopods from the Upper Cretaceous Wilmington Sands of Devon

SummaryFrom a study of silicified fossils, and in particular the microstructure of brachiopods, from the Wilmington Sands (Upper Cretaceous) of Devon, a model of skeletal silicification is proposed. Three distinct morphologies of silica were formed, controlled by the relative rates of silica supply and carbonate dissolution: (a) a fine-scale replacement of the original shell microstructure where silica was abundant; (b) a concentric ring morphology called ‘beekite’ where silica supply was limited, and (c) a granular white crust formed where carbonate dissolution was restricted. Silicification occurred during early diagenesis as a result of bacterial decay of organic matter intimately associated with skeletal fragments, within a sediment of restricted permeability. A build-up of CO2probably caused dissolution of skeletal carbonate, and bicarbonate released from this caused local precipitation of silica. The proposed mechanism is belived to be of general applicability to micrite-rich carbonate sediments.

A Fossil Wood of Dipterocarpaceae from Pliocene Deposit in the West Region of Java Island, Indonesia

Fossil woods in Java Island have been excavated and sold for outdoor ornaments or indoor decoration purposes since 30years ago. These fossils are in danger of being drained out without known identities, composition and history. This studywas aimed to find out the botanical identity and geographical aspect of a newly recovered silicified fossil wood from Bantenarea in the west region of Java Island. The fossil trunk 28 m in length and 105 cm in diameter was buried in a tuffaceoussandstone layer. The age of the stratum was thought to be Lower Pliocene. A small sample was cut from the outer part ofthe log and then ground to obtain thin section for anatomical observation. The main anatomical features of the fossil woodare as follows: wood diffuse porous; vessel almost exclusively solitary, vascicentric tracheid present; axial intercellular canalpresent, distributed in long tangential rows; fibers with distinctly bordered pit. These features show affinities of the fossilwood to the extant wood Dryobalanops of the family Dipterocarpaceae, regardless of the fact that this genus is no longer exists living in the natural forest of the present day Java Island. 2004 Jurusan Biologi FMIPA UNS SurakartaKeywords: fossil wood, Dipterocarpaceae, Dryobalanoxylon, Pliocene, Java Island

Ste. Genevieve (Mississippian) Formation at Its Type Locality in Missouri

A field and petrographic study of lithologic attributes and stratigraphic relations of the Ste. Genevieve Formation in its type locality area was made after reconnaissance showed these outcrops to be inadequately correlated by earlier workers. The objectives of this work were to describe in detail individual sections, determine persistent local marker beds, tie together isolated exposures, and redefine the type sections. North of Ste. Genevieve, Missouri, the type section consists mainly of cross-bedded, biocalcarenitic limestone beds comprising the lower 70 feet of the formation. South of town, the upper 60-foot section is exposed. These two intervals have been correlated by a distinctive marker bed characterized by a unique insoluble residue assemblage of silicified fossils, glauconite, and red chert fragments. About 25 feet of equivalent Ste. Genevieve beds, below a 10-23-foot-thick sandstone member, appears at the top of the type section on the north and in the lower part of the type section exposed on the south. Within the type locality area a composite section attains a maximum thickness of 122 feet, although the average is perhaps 15 feet less. The most common rock type consists of medium crystalline limestone composed of crinoid stem fragments, ooids, brachiopod shells, and bryozoan zoaria in a calcite mud matrix which in some beds has recrystallized to a sparry calcite. Sublithographic limestones make up about 10 per cent of the carbonate units. Argillaceous limestones and thin shaly beds and partings contain large amounts of fine quartz silt. The sandstone member is a fine-grained, well sorted massive unit cemented by carbonates and hydrated iron oxides. It is almost identical with the overlying Aux Vases Formation in physical character. A zone of algal pellets, mostly of genus Solenopora, is found near the base of the formation above a thin limestone conglomerate. Some question still exists regarding the nature of the St. Louis-Ste. Genevieve contact and the position of the sandstone member in the sequence at several outcrops south of the town. Alternative interpretations from those presented in previous studies are suggested but not proved.

Silurian of Great Basin: ABSTRACT

The Silurian rocks in the Great Basin can be assigned to two distinct facies: an eastern carbonate facies and a western shale facies. The line separating the two facies, actually a narrow transition zone, trends northeast from Independence, California, through Beatty, Eureka, and Elko in Nevada. The rocks in the eastern carbonate facies are composed almost entirely of dolomite. The dolomite is heterogeneous, varying from fine- to coarse-grained, black to white, and from almost pure dolomite to very silty dolomite. The dolomite facies is one of the poorest systems for paleontological studies in the Great Basin. Fossils are scarce and where present are usually poorly preserved. A few localities yield silicified fossils that can be etched and studied in detail. Both Middle and Upper Silurian fossils are present in the dolomite. The faunas seem to be most closely allied to those of Australia and the Orient, and have little similarity to the Silurian forms in eastern North America. No Lower Silurian fossils have been End_Page 354------------------------------ recognized. Early references to Lower Silurian faunas in the Great Basin are Lower Silurian in the old European sense, that is, Ordovician. The rocks in the western facies are predominantly black shale with minor amounts of sandy and calcareous shale and rare interbeds of limestone. The fauna in the western shale facies is largely pelagic. Locally well preserved graptolites range from Middle to Late Silurian in age. The Upper Silurian shales locally contain eurypterids. End_of_Article - Last_Page 355------------

Dadoxylon (Araucarioxylon) boureaui n.sp., bois silicifie mesozoique de Nouvelle-Caledonie

Abstract Describes Dadoxylon (Araucarioxylon) boureaui n.sp. from a Triassic-Jurassic volcanic formation in New Caledonia, and discusses its affinities with Cordaioxylon, living Araucariaceae, and other silicified fossil woods.

Silurian Sea Balls

The Niagaran dolomite in the vicinity of Chicago is characterized by several kinds of nodules, one type consisting of an intimate mixture of silicified fossils in a matrix of calcium carbonate. The mode of origin of these nodules is compared with that of modern usea and lake balls, which are produced by wave action in shallow waters. The apparently dwarfed fauna of the Silurian sea balls comprises most of the common Paleozoic classes of invertebrates, with bryozoans, brachiopods, corals, and echinoderms most abundant. An extended storm period has been posulated to account both for the dwarfing of the fauna and for the genesis of the nodules.

Preliminary Study of Insoluble Residues of Kansas Pennsylvanian Rocks

Insoluble residues as here defined are the substances that remain on the complete digestion of calcareous rocks in commercial hydrochloric acid. Ordinarily 25 to 30 grams of the broken rock are placed in a beaker, covered with hydrochloric acid diluted to half strength and allowed to stand until all of the soluble material has been digested completely. Silica in one form or another, principally as fossil debris or in granular form, constitutes by far the greater part of most insoluble residues. The common types thus observed are the following: (1) silicified fossils and fossil debris, (2) chert, (3) granular silica, (4) silicified oolites and colloids, (5) sand, (6) ferruginous material, (7) mineral crystals such as those of quartz, pyrite, sphalerite, limonite, (8) casts or impressions of dolomite crystals (dolocasts) and miscellaneous objects as siliceous flakes, grains of glauconite, fragments of hematite, carbonaceous material, shale particles, clay, silt, mica flakes, etc. Although studies of insoluble residues at the present time are used primarily for purposes of correlation, such studies have a wide application in strictly scientific investigations (1). Insoluble residues show the character of the rocks and the different constituents, and thus indicate the character of the sediments that were deposited, the possible source of the material and the conditions under which they were laid down. In the process of preparation the presence of organic matter can be detected easily. According to McQueen (2) from a study of insoluble residues erosion surfaces and unconformities have been recognized. Areas in which sedimentation in basins has been a dominant process have been determined. Important overlaps also have been recognized. The residues also yield data regarding other processes affecting calcareous rocks. When and how did dolomitization or silicification take place? The residues included in this study were obtained from seventeen limestones cropping out in Douglas county, Kansas. The various limestones analyzed are members of limestone formations included between the Stanton limestone of the Lansing group, Missouri series, and the Hartford limestone member of the Topeka limestone of the Shawnee group, Virgil series. All of the rocks are of Pennsylvanian age. The stratigraphic relationship of these limestones is graphically represented by figure 1. The primary purpose of this preliminary investigation was to determine whether or not the various limestones could be differentiated on the basis of their insoluble residues.

The Chert Gravels of Lyon County, Kansas

The chert of these gravels is impure silica. This silica is evidently derived from an alkaline solution of the mineral occurring abundantly in the water of rivers, lakes and the ocean. Billions of diatoms, each with a skeleton of silica, are found, for example, in the water of the Cottonwood river, Kansas. Diatoms are also very abundant in the ocean, together with animals that use silica in their skeletons, such as the sponges and rhizopods. For some unexplained reason the waters contain and deposit, periodically, great quantities of silica in the limestones and sandstones. In this paper we will consider the deposits in certain limestones. There is an abundance of silicified honeycomb coral and chert in the Niagara limestone of the Wisconsin Silurian; the Onondaga limestone of the New York Devonian contains chert and silicified fossils in very great abundance; the Osage limestone of the Mississippian of Kansas and Missouri possesses quantities of chert packed in the zinc sulfid and lead sulfid togethed with silicified fossils; while the Wreford and Florence limestones of the Permian of eastern Kansas contain the chert and silicified fossils that are the subject of this paper. The chert gravel of Lyon county, Kansas, has been studied in three situations: I. These limestones have an average dip of twenty or twenty-five feet to the mile to the westward and are very resistant to erosive agencies, owing to the presence in them of great quantities of chert or impure flint. The Flint Hills, or Permian Mountains, as the early geologists named them, are being eroded more rapidly on their eastern face because the westerly dip exposes the underlying softer formations on this face to more rapid weathering. The chert debris is therefore distributed somewhat evenly for about fifty miles to the eastward of the present position of the Flint Hills. II. At the present time west and east of Emporia we find more than a dozen hills and mounds of chert gravel resting on the Pennsylvanian shales and limestones, at an elevation of about 100 feet above the beds of the Cottonwood and Upper Neosho rivers and mostly between these streams. A brief description of the Cottonwood valley to the sources of the streams which now drain it will help to understand the origin of these stratified deposits of water-worn chert so high above the present level of the rivers. Beginning at Delavan, west of Council Grove and near the Flint Hills, we follow a semicircular ridge with an altitude of about 1,500 feet, past Lost Springs, Canton east of McPherson, Walton west of Peabody, to near Matfield Green into the Flint Hills again, and have the sources of five or six small streams that unite at Florence, altitude 1,270 feet, to form the Cottonwood river. At Strong City the bed of the river has an altitude of about 1,150 feet, the Wreford limestone, 1,340 feet, and the bed of the Cottonwood river about 1,100 feet at Emporia. At McFarland, Kan., the core of a diamond drill prospect hole was interpreted by the Universtiy Geological Survey as to the formations penetrated belonging to the Pennsylvanian except the first 610 feet. This upper part of

V. Remarks on the Fossils collected by Mr. Phillips near Dover and Folkstone.

My object in the following remarks is to give a catalogue of the fossils collected by Mr. Phillips, and to offer at the same time such desultory observations as the fossils themselves may suggest. As the search for Organic remains was confined to the cliff, the following list must not be considered as a general catalogue of the numerous fossils which these strata are known to contain. Fossils of the Chalk with numerous Flints. Plagiostoma spinosa. Inoceramus Cuvieri . . in fragments. Terebratula carnea . . . Mineral Conchology, Tab. xv. fig. 5 & 6. . . . . . . semiglobosa . . . . . . . . . . . Tab. xv. fig. 9. . . . . . . subundata . . . . . . . . . . . . Tab. xv. fig. 7. Echini . . . . . . . . . Many of the common species of galeæ, spatangi, and cidares, with some of the cucumerine, clavated, and slender muricated spines. Sponges . . . . . . . . Various species, in a silicified state, sessile, ramose, or umbellate, and some attached to a pedicle. Traces of sponge were also perceptible in the chalk. In this bed were also found various silicified fossils, allied to sponge, but apparently of a more complex structure. That peculiar asperity of surface, by which the presence of silicified sponges and alcyonia may be detected, was observable in many of the flints of this bed.