Charles F. Kahle

Morphology, Relationship, and Origin of Fiber and Dendrite Calcite Crystals

ABSTRACT Fiber and dendrite calcite crystals, formed by abnormal growth conditions, are minor but important components of many limestones that have undergone vadose meteoric diagenesis. Fiber crystals, which have a length: width ratio of greater than 6:1, are divided into hexagonal fibers, rectangular fibers, composite fibers, and rhomb chains according to their crystal form. Dendrite crystals are formed of a main stem, primary branches, and secondary branches. Random and tangential fiber crystals refer to masses of fibers that have a random distribution or tangentially coat a substrate, respectively. Such crystals may be tightly or loosely packed. The shape of fiber and dendrite crystals can be substantially modified by destructive or constructive diagenetic processes. Destructive modification includes physical breakdown, dissolution, or micritization. Constructive modification, which usually involves epitaxial growth around the original fiber or dendrite crystal, may proceed to the point where the original crystals are completely disguised. In extreme cases fiber crystals can be cemented together to form lattices that look like dendrite crystals. Fiber and dendrite calcite crystals generally form from fluids that are supersaturated with respect to calcium carbonate. Although experimental data suggest that both types of crystal can form from the same parent fluid, there are only rare examples where both are present together in nature. Such crystals form through biogenically and abiogenically mediated processes. The common association of these crystals with plant roots or microorganisms suggests that the organisms can produce conditions suitable for growth of the crystals.

Ooids from Great Salt Lake, Utah, as an analogue for the genesis and diagenesis of ooids in marine limestones

Study of 13 oolite samples from Great Salt Lake, Utah by means of X-ray analysis, staining for aragonite with Feigls solution, and the use of scanning and petrographic microscopes show that aragonite makes up all or more than 90% of the carbonate mineralogy of the samples. This new evidence, combined with the high degree of allochem recrystallization, indicates that the aragonite in the allochems typically undergoes recrystallization to aragonite and not to calcite as interpreted by Eardley (1938) and Carozzi (1962). Failure to take note that the original grain orientation in the rim of Great Salt Lake ooids is radial (Eardley, 1938), along with confusion about the meaning of the term structure as applied to ooids, has conceivably retarded a better understanding of ooid genesis and diagenesis. Radial grain orientation is demonstrably not developed in many initially aragonitic Pleistocene marine ooids as a result of their partial to complete conversion to calcite. Many ooids in marine limestone probably formed initially with an entirely radial grain orientation in their rims under a variety of environmental conditions. This hypothesis provides an alternative to the popularly accepted hypotheses that all ooids in marine limestone were initially like those that occur today in the Bahamas and Persian Gulf, and that radial grain orientation in ooids is invariably a product of diagenesis.

Possible Roles of Clay Minerals in the Formation of Dolomite

ABSTRACT Evidence is accumulating which strongly suggests that clay minerals effect the formation of some dolomites. Clays may behave somewhat as catalysts by providing a source of magnesium ions or by serving as membranes which effect ionic migration. Alternately, clays may assume a more active role in dolomitization by serving as centers of nucleation, or by entering into chemical reactions which involve dolomite as one of the products.

Seismogenic Deformation Structures in Microbialites and Mudstones, Silurian Lockport Dolomite, Northwestern Ohio, U.S.A.

Syndepositional deformation structures are present at two different stratigraphic levels in the Silurian Lockport Dolomite at a quarry in Maumee, Ohio. Such structures are absent in this unit at twelve other quarries in northwestern Ohio. The structures at Maumee, present within stromatolites, thrombolites, and variably bedded mudstones, include convolute layers, homogenization of bedding and breccia clasts, clasts of stromatolites, boudinage structures, normal, reverse, and thrust faults, and discordant and concordant breccias. The distribution of deformation structures within beds suggests substantial control from substrate rheology, possibly resulting from differences in degrees of lithification and from variations in water content. The extensive variety of syndepositional deformation structures, juxtaposed evidence for nearly synchronous compression and dilation, proximity (4.5 km) of the structures to the largest fault in northwestern Ohio (the Bowling Green fault), and the restricted geographic distribution of the deformation structures suggest seismic shaking as a probable mode of genesis. Similarities between features produced by seismogenic deformation of siliciclastic sediments and deformation features in the Lockport Dolomite provide additional evidence that the latter features are seismogenic. It is postulated that two earthquakes, one with a magnitude 5, caused the formation of the syndepositional deformation structures present in the youngest facies in the Lockport Dolomite at Maumee quarry. The Bowling Green fault, 4.5 km west of Maumee, was a growth fault during formation of the Lockport Dolomite, and is considered to have been the source of earthquakes that created the syndepositonal deformation structures in this unit at Maumee quarry. Evidence from the Lockport Dolomite in northwestern Ohio suggests that seismogenic deformation structures created by two earthquakes along the Bowling Green fault with magnitudes of 5 did not form in this unit over large areas (i.e., all of northwestern Ohio). This evidence challenges the suggestion that syndepositional seismogenic deformation structures are always formed over a large area.

Origin of endogenetic micrite in karst terrains; a case study from the Cayman Islands

ABSTRACT Cavities in the dolostones of the Cayman Formation (Miocene) on Grand Cayman and Cayman Brae commonly contain spar calcite cements and/or a variety of exogenetic (derived from sources external to the bedrock) and endogenetic (derived from sources in the bedrock) internal sediments. Micrite is a common component in many of these internal sediments. The exogenetic micrite, which is typically laminated and commonly contains fragments of marine biota, originated from the nearby shallow lagoons. The endogenetic micrite formed as a residue from the breakdown of spar calcite crystals by etching, as constructive and destructive envelopes developed around spar calcite crystals, by calcification of microbes, by breakdown of calcified filamentous microbes, and by precipitation from pore waters. nce produced, the endogenetic micrite may be transported from its place of origin by water flowing through the cavities. Endogenetic micrite can become mixed with the exogenetic micrite. Subsequently, it is impossible to recognize the origin of individual particles because the particles in endogenetic micrite are morphologically like the particles in exogenetic micrite. Formation of endogenetic micrite is controlled by numerous extrinsic and intrinsic parameters. In the Cayman Formation, for example, must endogenetic micrite is produced by etching of meteoric calcite crystals that formed as a cement in the cavities or by microbial calcification. As a result, the distribution of the endogenetic micrite is ultimately controlled by the distribution of the calcite cement and/or the microbes--factors controlled by numerous other extrinsic variables. Irrespective of the factors involved in its formation, it is apparent that endogenetic micrite can be produced by a variety of processes that are operating in the confines of cavities in karst terrains

Recurrent tectonics in a cratonic setting: An example from northwestern Ohio

Structural, stratigraphic, and sedimentologic relations in northwest Ohio indicate that this part of the craton was the site of recurring tectonic activity throughout much of the Paleozoic. The locus of much of this activity was the Bowling Green fault, a complex north-trending zone of diverse fault types. At least six episodes of displacement can be documented, most of which involved vertical displacement along steeply dipping faults. The youngest structures in the fault zone are southwest-directed thrusts. Faulting began as early as the Ordovician Period and continued possibly as late as the Cenozoic Era. Abrupt thickness changes, isopach and structure-contour trends, intraformational unconformities, and soft-sediment deformation structures in Ordovician and Silurian units are attributed to syn-depositional deformation associated with the Bowling Green and related faults. Silurian paleogeography in the region also was affected by ongoing tectonic activity. The location of the Bowling Green fault and the cause for its long history of displacement appear to be related to the underlying Grenville front. Stresses associated with orogenic activity in the Appalachians, lithospheric flow, or forebulge migration were localized by the front and resulted in displacements in the overlying Paleozoic strata along and adjacent to the Bowling Green fault.

Strontium in oolitic limestones

ABSTRACT An integrated study was made of the petrography and strontium content of sixty-two samples of oolitic limestones. The range in strontium content is from 230 parts per million for a sample of Cambrian oolite to 10,080 parts per million for a recent Bahaman oolite. Excepting Quaternary samples, the mean strontium content of the samples is 414 parts per million, a value nearly identical to the mean strontium content known to occur in other types of carbonate rocks. Diagenesis of ancient oolitic sediments could have involved a reduction in the strontium content as large as 10,000 parts per million and possibly more. Maximum loss of strontium occurs during early diagenesis before major cementation, when aragonite allochems change to calcite. Factors of secondary importance in the loss of s rontium may include changes brought about by solid-state recrystallization and decomposition of organic material. The overall loss of strontium is probably related most directly to the expulsion of fluids from individual allochems and thence from the entire sediment mass. Recrystallization of allochemical constituents in oolites is more common than recrystallization of cement and matrix material. No systematic relationship was detected between the amount of strontium and the degree of recrystallization on a bulk sample basis. Study of seven samples indicates that the carbonate cementing material contains, on the average, nearly twice as much strontium as the allochems. Diagenetic modifications of allochems probably continue after cementation.

Proposed origin of aragonite Bahaman and some Pleistocene marine ooids involving bacteria, nannobacteria(?), and biofilms

The vast majority of laminae in the cortex of modern Bahaman ooids and ooids in the Pleistocene Miami Limestone in the Florida Keys are aragonite. The aragonite has two forms: rod-shaped batons (0.5–3.0 μm long and 0.17–0.7 μm in diameter), and nannoballs (0.025–0.3 μm in diameter). Nannoballs are always subordinate to batons and are much more common in Bahaman ooids than in ooids in the Miami Limestone.Variations in the size and shape of known rod-shaped bacteria correspond exactly or very closely to variations in the size and shape of batons. Accordingly, batons are interpreted as calcified rod-shaped bacteriaThe intimate association of batons and nannoballs suggests a formational link. Aggregates of nannoballs and aggregates of nannoballs and batons probably originated via the complete decay of original batons in the former cases, and the partial decay of original batons in the latter case. Nannoballs not in contact with one another may be bacterial spores that become separated from gram-positive bacterial vegetative cells as a result of a lack of nutrients or some other from of environmental pressure.Calcification of rod-shaped bacteria probably involved aragonite formation in the bulk phase external to individual bacteria. It is proposed that calcification of individual bacteria took place in biofilms that were adsorbed to the surface of a nucleus (such as a fecal pellet) and then to successive laminae as the ooids grew in size. Each lamina would initially, therefore, represent a single biofilm and, ultimately, a layer of calcified rod-shaped bacteria. Calcification of bacteria in biofilms probably took place rapidly so that successive biofilms were formed on mostly solid surfaces. Thus, the ooids lithified from the inside out.It is hypothesized that ooids stop growing as a result of termination of a nutrient supply necessary to create biofilms on the surface of developing ooids. The most likely cause is burial of older ooids by younger ooids so that biofilms in older ooids no longer have access to a nutrient source in the water column.

Stratigraphic and Environmental Significance of Sedimentary Structures in Cayugan (Silurian) Tidal Flat Carbonates, Northwestern Ohio

Detailed studies of outcropping rocks of Cayugan age in the Findlay arch area disclose numerous and diverse types of sedimentary structures, the majority of which have not been recognized or described previously in these strata. The recognition of these structures provides a new approach to the lithostratigraphic and environmental analysis of Cayugan rocks in the Findlay arch region. The 170-ft (52-m) sequence of Cayugan rocks which crops out in the Waterville, Ohio, area is the thickest sequence of Cayugan rocks exposed in Ohio along the southern margin of the Michigan basin. These rocks include the uppermost part of the Greenfield Formation, nearly all the Tymochtee Formation, and the lower part of the Put-in-Bay Formation. The 130-ft (40-m) section of the Tymochtee Formation is the thickest surface section of this unit and the only section in which both the upper and lower contacts are exposed in the Findlay arch region. The section of the Tymochtee Formation is designated as a principal reference section for the Findlay arch region; portions of this section can be correlated physically with the type section of the Tymochtee Formation. Sedimentary structures provide criteria for the recognition of four new members in the Tymochtee Formation, which are, in ascending Stratigraphic order, the Granger Island, Ovitt Road, Maumee River, and Roche de Boeuf Members. The principal types of rocks developed from Cayugan sedimentation in northwestern Ohio are fine-grained, mostly unfossiliferous dolomites and shaly dolomites, which contain algal stromatolites, shrinkage cracks, ripple marks, tidal channels, gypsum, pseudomorphs after gypsum, celestite, and molds and casts of halite. Collapse has occurred in some rocks due to the solution of evaporite minerals. By analogy with Holocene sediments, it is concluded that the Cayugan rocks were formed on an evaporite-carbonate tidal flat wherein the conditions of sedimentation were not unlike those found today in the Persian Gulf. Subenvironments in the Cayugan tidal flat were mainly intertidal, but ranged from subtidal to supratidal. During Cayugan time northwestern Ohio was an evaporite-carbonate tidal flat rather than a reef bank complex as has been suggested previously. Strandlines within the tidal flat were probably oriented mainly northwestward, in opposition to the present northeastward trend of the Findlay arch through northwestern Ohio. It is probable that the Findlay arch did not affect sedimentation in northwestern Ohio during Cayugan time.

Facies and evolution of Silurian coral-microbialite reef complex, Maumee, Ohio, USA

ABSTRACT Silurian dolomite that crops out in a quarry at Maumee, Ohio USA, forms a thick reef complex roughly 600 m in diameter and about 68 m thick. It is composed, in ascending stratigraphic order, of the Lockport Dolomite and the Greenfield Dolomite. The Lockport Dolomite at Maumee contains multistory stromatolite, thrombolite, and coral-microbialite reefs. Such reefs have never been reported previously in this unit in Ohio and Indiana. Thrombolite and stromatolite reefs are interpreted to have formed in a subtidal setting possibly within a hypersaline lagoon. Wave stress affected the coral-microbialite reefs by limiting the number of metazoans and promoting the formation of fibrous cement inferred to have been marine precipitates originally in the form of magnesian calcite. Thrombolites an stromatolites form 20-60% by volume of coral-microbialite reefs, and they contributed substantially to the syndepositional stabilization of these reefs by serving as binders and encrusters of metazoans, especially branching corals. Such stabilization sharply limited the amount of sediment available for the formation of flank beds next to coral-microbialite reefs. Evolution of the Maumee reef complex (MRC) involved two shallowing-upward sequences, each of which was terminated by subaerial exposure. The older interval of subaerial exposure is represented by an intraformational unconformity within the Lockport Dolomite. The younger unconformity at the top of the Lockport Dolomite is correlated with the base of the A-1 evaporite in the Michigan Basin. Parts or all of patterns shown by coral-microbialite reefs and microbialite reefs in the MRC may provide an analogue for better understanding the nature and evolution of pinnacle reefs and patch reefs in the Michigan Basin region and other reefs elsewhere.