Green Marine Clays: Oolitic Ironstone Facies, Verdine Facies, Glaucony Facies and Celadonite-Bearing

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Alert me when this article is cited: Sign up for e-alerts. Looking for a job? Visit the BioOne Career Center and apply to open positions across the sciences. Log in Admin Help. April 6, ; Published: Abstract This study documents the association of glauconitic pellets and trace fossils at two Cambrian sites: Current Trends in Geology-X: Geological Society of America Bulletin, v. Journal of the Geological Society, v. Biology, Taphonomy and Applications: Chapman and Hall , London , p.

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Miscellaneous Publication 9, p. MGB clay pellets, for the most part, are low in K 2 O, with an average of 1. The few glauconitic grains encountered were small and fractured. Raw data for glauconitic minerals and other clays are presented in Table S2. Several clay types were characterized in a study of Claiborne Group iron-rich authigenic clays by Huggett et al. The average chemistry of clay pellets from the MGB is very similar to the average of 53 analyses for pellets from the upper 8 m of the Crockett Formation, which includes the MGB, from the same locality as this study [11].

All MGB clay pellet analyses from this study, including glauconitic grains, are displayed as total Fe 2 O 3 plotted against Al 2 O 3 together with the published results Figure The compositional variation of MGB clay pellets is evident, where they are seen to lie within the compositional field of authigenic iron-rich clays from other Claiborne Group clays [11]. Also shown are published analyses of other clays including nontronite, berthierine, Fe-smectite, vermiculite and kaolinite.

These, along with the MGB clay pellets, tend to lie along a general trend between nontronite and kaolinite, and are distinctly lower in Al 2 O 3 than berthierine Figure 13 [11]. Open circles are published analyses of odinite [16] , [24]. The range of compositions of clay in pellets from the Claiborne Group is indicated by the large oval [11] , [61]. The field of berthierine is from Brindley [61].

Figure 14 shows a plot of isomer shift vs. A Clays from the MGB this study.

Green Marine Clays: Oolitic Ironstone Facies, Verdine by G. S. Odin PDF - ROMANOVA PICTURES E-books

B MGB clays compared to published analyses of glauconite. The difference in the average of the quadrupole splitting between the two sites, 0. However, Rancourt and co-workers [52] — [54] have argued that these sites may not be positively delineated, and that the spectral data may be recording local distortion environments. Dyar [55] suggested that hydrogen content may be responsible for variation around octahedral sites because of the difference in the location of hydroxyls around M1 and M2 sites. We do not have direct determination of H 2 O contents of MGB clays, but they do have measureable F and Cl, and both vary in concentration.

Substitution of F and Cl, and possibly O in OH sites could change the geometry of the adjacent trans and cis sites and be responsible for the bimodal behavior of MGB clays. A similar ratio of The biogenic nature of the pellets provides micro-reducing environments on the seafloor favorable for the formation of verdine minerals. Textural and compositional variation in the central MGB Figure15 shows that clay matrix is predominantly odinite and illite, while clay pellets are predominantly odinite and smectite. Figure 16 demonstrates that odinite is dominant in both the matrix and clay pellets with minor amounts of illite, smectite and glauconitic minerals.

Concretionary burrow fill at the top of the MGB is predominantly siderite and apatite cement, in various quantities. Other concretionary burrows are dominated by siderite.

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False color pink represents the P 2 O 5 -rich mineral, apatite. Clay pellets remain unaltered even though they are incorporated in the concretionary burrow fill. The identification of odinite, a key verdine mineral, is supported by all of the above analytical results.


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The unit cell calculation shows lattice parameters that are uniquely odinite. It is the dominant clay type in the MGB clay pellets. The structural formula calculated from EMPA data is consistent with that of odinite. X-ray diffraction results suggest an odinite, smectite, illite clay mixture. Concretions at the top of the MGB are composed of a fine-grained apatite-silicate mixture.

Analyses of siderite are presented in Table 5. Despite attempts with the electron microprobe to locate regions without a phosphorus X-ray signal, when measured, phosphorus was always detected, ranging in three samples from 0. A small amount of Al 2 O 3 was also recorded, and probably represents a minor amount of clay. Mole percent carbonate end-members are calculated with CaCO 3 adjusted for the Ca-equivalent of apatite as determined from P 2 O 5 concentrations when measured Table 5. Analyses of concretions consisting of a fine-grained mixture of apatite and one or more alumino-silicates are provided in Table 6.

Assuming that all P is contained in apatite, and accounting for the equivalent CaO, the composition of the silicate component neglecting halogens can be estimated. The calculated silicate component is similar in composition to MGB clays with respect to total Fe 2 O 3 and Al 2 O 3 , although with slightly lower SiO 2, suggesting that the silicate in the phosphate-bearing cement is the same or very similar to the clay in the pellets and the matrix of the MGB. The detailed mineralogy and geochemistry of the MGB determined in this study relate to paleoecology, sedimentology and stratigraphic findings from previous studies.

When integrated with the ichnology of the MGB, a coordinated approach to understanding the depositional environment in a sequence stratigraphic context is possible. Verdine minerals, specifically odinite, were identified in the clay pellets. Whether the MGB is comprised of odinite or authigenic verdine minerals that were altered, the paleoenvironmental implications are the same.

It is presumed that the present-day verdinization environment is key to understanding the Middle Eocene continental shelf green marine clay environments. The mineralogy of the clay pellets and their occurrence in the central MGB and in concretionary burrow fill at the top of the MGB has implications for understanding depositional processes. Odinite-rich clay pellets are abundant in the central MGB.

They are interpreted as fecal pellets based on their consistent shape, varied size, appearance and iron oxidation state. Their varied size is attributed to multiple producers, which reflects a diverse faunal community. Fecal pellets originally must have contained organic matter, resulting in locally more reducing conditions than the surrounding environment [24]. The pellets provided a favorable site for verdinization, because verdine minerals tend to form within sheltered, reducing, granular microenvironments. Clay pellets occur in both the central bed and in the concretionary burrow fill at top of the MGB.

In the central bed, pellets are not evenly distributed throughout, suggesting that they may have been reworked by gentle winnowing and episodic storms. Clay pellets at the top of the MGB could have been introduced into the open burrows along with other detritus, possibly reworked from the central MGB, or they could have been left behind by occupants in the burrow fill. The clay pellets do not show characteristics of those produced by decapod crustacean burrowers.

The larger, heterogeneous pellets composed primarily of the apatite-cementing agent, can be seen in both the photomicrographs and the QEMSCAN mineral images of concretionary burrow fill. In comparison with the clay pellets, the apatite pellets are larger and more mineralogically heterogeneous Figure 9. These pellets also occur in the central MGB as a loosely compacted unaltered mixture of clay and tiny clasts. At top of the MGB, these pellets were incorporated into the apatite and siderite-cementing agents of the concretionary burrow fill.

Based on their affinity for phosphate minerals and their shape, they are interpreted as fecal in origin. Like the clay pellets, the apatite pellets could have been left behind by occupants in the burrow fill. They do not show the morphologic characteristics typical of pellets produced by decapod crustacean burrowers. The fragmented nature of the grains lends support to the hypothesis that some winnowing and reworking of sediments may have occurred, and that glauconitic minerals were transported from deeper environments where they originated.

Glauconitic minerals, once formed, are very stable in the marine environment, and they may well survive transport of appreciable distance. The glauconitic grains may be more brittle than the non-glauconitic clay pellets, and so they tend to fracture more readily. Glauconitic grains found in the concretions were likely added with clastics in the burrow fill.

In a sequence stratigraphic context, green minerals often are associated with condensed sections and transgressive-systems-tracts. A transgressive phase on a sediment-starved sea floor offers favorable conditions for the glauconitization or verdinization process. A regressive phase, on the other hand, may introduce a more energetic, oxidizing environment of higher sediment influx, which would inhibit clay authigenesis [25] , [29].

Green minerals of the verdine facies suggest the shallow inner shelf, more proximal zone of the transgressive surface and transgressive-systems-tract. The siliciclastic depositional center was associated with the Houston Embayment Figure 1 [57]. Deposition occurred during an interval of fluctuating sea level in sediment-starved conditions, interfingering with episodes of higher sedimentation rate. The basal contact of the MGB is sharp, irregular and burrowed. The central MGB has verdine facies clays that indicate shallow marine conditions with transgressive characteristics in proximity to river mouth influx Figure 7.

The upper contact of the MGB marks a boundary between two contrasting facies. It is irregular due to burrowing [2] , [13]. The burrows are interpreted as firmground trace fossils that often occur in temporarily dewatered and compacted sediment. The top of the MGB may highlight a coplanar transgressive surface—sequence boundary in a parasequence. It is possible that the top of the MGB could have been exposed in an intertidal environment. Then the open burrows were filled with detritus during renewed submergence.

Subsequent apatite and siderite cementation of the firmground would have occurred in a subaqueous setting. The Crockett Formation was deposited in a complex marginal marine environment with dynamic sea level fluctuation. It represents a shallow-water transition zone in an overall upward deepening sequence. While odinite formed in situ associated with the fecal pellets of the central MGB, the few glauconitic mineral grains in the MGB may be explained by detrital reworking.

Grains can be transported widely in transgressive systems, and glauconite is stable geochemically in the marine environment. The paucity of glauconitic minerals indicates that seafloor conditions during deposition of the MGB were unsuitable for their formation, or that the glauconitization process was incomplete or arrested.

This might mean a number of things. For example, perhaps sea-floor conditions were not consistently marine, too close to river mouth influx, too close to shore, or too shallow water depth. Sediment influx can inhibit the glauconitization process by not allowing enough time for glauconitic minerals to mature. The few, small glauconitic mineral grains in the MGB were often fractured, which indicates they may be of allochthonous origin, so it appears that the glauconitization process did not occur during deposition of the MGB. On the other hand, verdinization apparently did occur.

The presence of odinite, especially in the clay pellets, indicates a set of sea-floor environmental conditions pertaining to geochemistry, temperature, oxidation state, energy and latitude. The central MGB reflects depositional processes in a low energy, somewhat sheltered, shallow, warm, mostly marine environment. Sedimentation rate was sufficiently slow in proximity of continental input of iron and gentle winnowing currents to provide Eh and pH conditions suitable for verdine mineral authigenesis [16] , [24] , [32]. The change in mineralogy from the central bed to the top of bed indicates a change in the sea-floor environment.

The central MGB was deposited in a near shore, subaqueous setting, while it is possible that the top of the MGB, with its concretionary burrow fill comprised of pellets and detritus, may have been in an intertidal environment. This interpretation is supported by characteristic burrowing patterns at top of the MGB. It represents an interval of non-deposition, dewatering, compaction and burrowing. Ultimately, the open burrows excavated by infaunal crustaceans were filled with sediment and bioclasts, indicating return to a subaqueous environment in moderate energy where precipitation of siderite and apatite cementing agents occurred.

A coordinated approach to understanding the paleoenvironment of the MGB incorporates verdine facie characteristics, ichnological signature, and findings from previous MGB studies. During a period of regional transgression, relatively high sea level, and some lateral continuity of facies, several coastal siliciclastic environments may apply.

These include protected shoreface settings, large scale normal marine lagoons, interdeltaic bays, sounds, or embayments.

Introduction

Tropical seagrass beds demonstrate high molluscan diversity, such as that observed in the MGB. Seagrasses were present in the Gulf and Caribbean during the warmer climatic conditions of Middle Eocene [58]. Seagrass environments are recognized only rarely in the geological record due to the low preservation potential of soft plants, but they probably were much more abundant than is normally realized. Benthic foraminiferal evidence would be instructive, however that was outside the scope of this study.

In general, the setting of the MGB is characterized as shallow inner shelf, proximal to some terrestrial influence. It is the main constituent of the clay fecal pellets and matrix of the central MGB. Few occurrences of odinite, other than modern odinite, are described in the literature. The MGB provides an informative example of odinite in the geologic record. Odinite was established as the main constituent in clay pellets of the MGB through several analytical methods.

X-ray diffraction found a 7. Unit cell calculation indicated odinite-1M to be the most reliable interpretation.

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Thus, essential chemical data was obtained to calculate the average structural formula for clay pellets of the MGB as follows: Odin and Bailey [16] , [24] first described odinite in , and they calculated a similar mineral formula that was slightly more Mg rich and Fe, Al poor. Documentation of odinite and verdine facies clays in the MGB is an important finding of this report.

The environmental conditions associated with modern verdine facies clay occurrences include tropical latitudes, nearby runoff with iron influx, and water depth between 15 and 60 m locally in 5 m depth. The characteristic sea-floor conditions are normal to nearly normal salinity, positive Eh, elevated sea-floor temperature and common association with fecal pellets. Circulating, winnowing currents are required to stir the sediment slightly and provide oxygenation. It is presumed that paleoenvironmental conditions were comparable during the Middle Eocene accumulation of authigenic verdine clays in the MGB.

The contrasting mineralogy between the central and the top of the MGB reflects a change in environmental conditions during its deposition. The central MGB has abundant pellets, comprised mostly of odinite, with lenses of shell concentrations and laminated sand. In contrast, the top of the MGB is a zone of concretions that are filled burrows comprised of pellets and detritus with siderite and apatite that formed as cementing agents. Glauconitic minerals are very sparse in both the central and top of the MGB and are probably allochthonous. A change in environmental conditions is reflected in a composite ichnofabric where deeper water biogenic activity in the central MGB is replaced by shallow water to intertidal burrowers in a firmground at the top of the MGB.

The firmground was subsequently submerged and cemented. The paleoenvironmental interpretation for the geologic section at Stone City Bluff has been the subject of numerous studies. This contribution of detailed mineralogy and geochemistry, although focused on the fecal pellets of the MGB, offers key information about processes during its deposition. With the identification of authigenic odinite or its alteration products, this study complements findings of previous studies.

The MGB represents an ancient verdine facies paleoenvironment, which has implications for paleoecology, sedimentation rate, sequence stratigraphy and paleoclimate. It provides a coordinated approach to paleoenvironmental understanding of the dynamic depositional environment of the MGB at Stone City Bluff. Minerals of the verdine facies at the diffraction peak are between1. Quartz at the hkl peak is 1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. National Center for Biotechnology Information , U. Published online Feb 4.

Nash , 1 Erich U. Petersen , 1 A. Ekdale , 1 Christopher D. Bradbury , 1 and M. The authors have declared that no competing interests exist. Received May 6; Accepted Dec This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.

Introduction Green clay-rich sediment is recognized throughout the geologic record, and the paleoenvironmental implications of green clay facies are not always understood clearly. Open in a separate window. Stone City Bluff and Stone 1core located.

Green Marine Clays Oolitic Ironstone Facies Verdine Facies Glaucony Facies and Celadonite Bearing Ro

Wilcox Group Ewi ; Crockett Fm. Ecm ; and Caddell Fm. Stone City Bluff outcrop photos, the MGB is green and nearly vertical, A looking west, upstream the subject in this photograph has given written informed consent, as outlined in the PLOS consent form, to publication of their photograph , B looking east, downstream.

Upper units of the Stone City Member, sample number and location modified after Stenzel [2]. Previous Work on the MGB The MGB and associated stratigraphy have been studied extensively by other workers who have offered various mineralogical and paleoenvironmental interpretations [1] — [9]. Background on Green Clay Minerals Green clay minerals Published research on green minerals in sedimentary rocks reveals a lack of consistency in use of mineralogic terms.


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Authigenesis Mineral authigenesis in sea-floor sediments can occur as glauconitization or verdinization, processes by which a sea-floor substrate is progressively modified to glauconitic minerals or to verdine minerals, respectively [16]. Diagrammatic verdine facies model depicting the idealized paleoenvironment at a tropical river mouth modified after Odin [16].


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Diagenesis and weathering Diagenesis refers to the physical and chemical reactions occurring in sediment after burial. Mineral Identification Petrography of each thin section was described using a polarizing light microscope, and a variety of analytical techniques were employed to ascertain mineral composition and texture. Electron microprobe analysis Thirty clay pellets from both the central MGB and the concretionary burrow fill at the top of the MGB, and 14 non-pellet, cement areas were analyzed with a Cameca SX electron microprobe equipped with four wavelength-dispersive spectrometers.

Pellets Two pellet types are recognized on the basis of size and composition: Color The central MGB appears olive gray in outcrop. Eleven peaks were indexed. Chemical analyses apfu , published [16] , [24] and MGB clay pellets, used to calculate mineral formula. Table 3 Maximum, minimum, mean and standard deviation of chemical analyses from MGB pellets and published odinite.

MGB clays plotted within the compositional field of iron-rich clays from the Claiborne Group. Plot of isomer shift vs. Siderite and apatite Concretions at the top of the MGB are composed of a fine-grained apatite-silicate mixture. Table 6 Concretionary burrow fill, MGB top, a fine-grained mixture of apatite and one or more alumino-silicates. Discussion The detailed mineralogy and geochemistry of the MGB determined in this study relate to paleoecology, sedimentology and stratigraphic findings from previous studies.

Pelleted Component The mineralogy of the clay pellets and their occurrence in the central MGB and in concretionary burrow fill at the top of the MGB has implications for understanding depositional processes. Sequence Stratigraphy In a sequence stratigraphic context, green minerals often are associated with condensed sections and transgressive-systems-tracts.

Paleoenvironment The paucity of glauconitic minerals indicates that seafloor conditions during deposition of the MGB were unsuitable for their formation, or that the glauconitization process was incomplete or arrested. TIF Click here for additional data file. XLSX Click here for additional data file. Journal of Paleontology 8: Bureau of Economic Geology, University of Texas. A field guide to selected localities in Pennsylvanian, Permian, Cretaceous and Tertiary rocks of Texas and related papers. Claiborne sediments of the Brazos Valley, southeast Texas: Davidoff AJ, Yancey TE Relating sequence stratigraphy to lithostratigraphy in siliciclastic-dominated shelf settings, Paleogene, central-east Texas.

A test of chemical taphofacies in the rock record [Master of Science]: Journal of Paleontology Lower Tertiary of the Brazos River Valley: Guidebook of the Houston Geological Society. Burst JF Mineral heterogeneity in glauconite pellets. Clays and clay minerals Triplehorn DM Morphology, internal structure, and origin of glauconite pellets. Useful Indicators of Paleoenvironment.

The Canadian Mineralogist Amorosi A Glaucony and sequence stratigraphy; a conceptual framework of distribution in siliciclastic sequences. Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies Journal of Sedimentary Research Upper Saddle RiverNew Jersey Evidence from the Abu Tartur Plateau, Egypt. Journal of Physics E Effects of fitting models on recoil-free fractions and redox ratios. Quaternary Science Reviews Geological Society of America Rock color chart with genuine Munsell color chips. Amorosi A Detecting compositional, spatial, and temporal attributes of glaucony: Clays and Clay Mineralogy Clays and Clay Minerals