Sediment supply versus storm winnowing in the development of muddy and shelly interbeds from the Upper Ordovician of the Cincinnati region, USAThis article is one of a series of papers published in this Special Issue on the theme The dynamic reef and shelly communities of the Paleozoic. This Special is in honour of our colleague and friend Paul Copper.

2008 ◽  
Vol 45 (2) ◽  
pp. 243-265 ◽  
Author(s):  
Benjamin F. Dattilo ◽  
Carlton E. Brett ◽  
Cameron J. Tsujita ◽  
Robert Fairhurst
Keyword(s):  
Sediment Supply ◽  
Special Issue ◽  
Biological Factors ◽  
Upper Ordovician ◽  
Complex Interplay ◽  
Shell Beds ◽  
High Sedimentation ◽  
Discontinuity Surfaces ◽  
Carbonate Concretion ◽  
Shell Bed

Shell-bed development can be a product of complex sedimentological and biological factors. The Upper Ordovician sediments near Cincinnati, Ohio constitute a succession of thinly interbedded shelly carbonates and mudrocks. Despite years of study, the development of Cincinnatian shell beds and metre-scale cycles has, until recently, been attributed solely to storm reworking. This “storm-winnowing model” treats shells as passive sedimentary clasts, ignoring other factors of shell-bed development. A recently proposed alternative is Brett and Algeo’s idea that these shell beds grew during long periods of normally low sedimentation, while most mud accumulated during brief periods of high sedimentation. Under this “episodic starvation model,” any storms would winnow pre-existing muds and shell beds alike. We tested both models in the Edenian–Maysvillian (early to mid Katian) strata of the Cincinnati region by compiling observations on their petrologic, taphonomic, and paleoecologic characteristics. The storm-winnowing model does not explain several observed features that the episodic starvation model does, including (i) storm-related sedimentary structures in mudrocks and limestones; (ii) lack of a sufficiently fossiliferous precursor deposit to winnow; (iii) deep-water faunas in grainstones; (iv) mixed taphonomic conditions of shell-bed fossils; (v) ubiquitous discontinuity surfaces; (vi) carbonate concretion horizons; (vii) unwinnowed shell beds; and (viii) micrite in packstones. Episodic starvation is a superior explanation because it explains all of these features and allows for the complex interplay of other environmental and biological factors that contribute to shell-bed growth. It may also be applicable to other deposits, previously interpreted as tempestites.

scholarly journals Shell beds from the Low Head Member (Polonez Cove Formation, early Oligocene) at King George Island, west Antarctica: new insights on facies analysis, taphonomy and environmental significance

2014 ◽  
Vol 26 (4) ◽  
pp. 400-412 ◽  
Author(s):  
Fernanda Quaglio ◽  
Lucas Veríssimo Warren ◽  
Luiz Eduardo Anelli ◽  
Paulo Roberto Dos Santos ◽  
Antonio Carlos Rocha-Campos ◽  
...  
Keyword(s):  
King George Island ◽  
West Antarctica ◽  
Delta Front ◽  
Early Oligocene ◽  
Fan Delta ◽  
Shell Beds ◽  
The Matrix ◽  
Low Head ◽  
New Interpretation ◽  
Shell Bed

AbstractShell bed levels in the Low Head Member of the early Oligocene Polonez Cove Formation at King George Island, West Antarctica, are re-interpreted based on sedimentological and taphonomic data. The highly fossiliferous Polonez Cove Formation is characterized by basal coastal marine sandstones, overlain by conglomerates and breccias deposited in fan-delta systems. The shell beds are mainly composed of pectinid bivalve shells of Leoclunipecten gazdzickii and occur in the basal portion of the Low Head Member. Three main episodes of bioclastic deposition are recorded. Although these shell beds were previously interpreted as shelly tempestites, we present an alternative explanation: the low fragmentation rates and low size sorting of the bioclasts resulted from winnowing due to tidal currents (background or diurnal condition) in the original bivalve habitat. The final deposition (episodic condition) was associated with subaqueous gravity driven flows. This new interpretation fits with the scenario of a prograding fan-delta front, which transported shell accumulations for short distances near the depositional site, possibly between fair-weather and storm wave bases. This work raises the notion that not every shell bed with similar sedimentological and taphonomic features (such as geometry, basal contact, degree of packing and shell orientation in the matrix) is made in the same way.

Paleocommunity information retrieval vs. shell accumulation mode in Paleozoic carbonates: examples from the Lebanon Limestone (Middle Ordovician), Tennessee, U.S.A.

1992 ◽  
Vol 6 ◽  
pp. 81-81
Author(s):  
David J. Davies ◽  
Molly F. Miller
Keyword(s):  
Information Retrieval ◽  
High Energy ◽  
Sediment Surface ◽  
Time Averaging ◽  
Short Term ◽  
Diagenetic Alteration ◽  
Shell Beds ◽  
Carbonate Shell ◽  
Shell Bed

Compared to their terrigenous counterparts, carbonate shell accumulations have until recently been relatively little studied to determine either descriptive or genetic classifications of shell bed types, the preservation potential of each type, or their relative ability to preserve community-level information. A partial classification of Paleozoic carbonate shell-rich soft sediment accumulations is proposed using sedimentation patterns in the Lebanon limestone of the Stones River Group. Paleoecological information preserved therein is then contrasted by shell bed type. The Lebanon represents typical Ordovician shallow to moderate subtidal carbonate shelf deposits in outcrops flanking the Nashville Dome and peritidal deposits in the Sequatchie Anticline of Eastern Tennessee; shell beds alternate with shell poor sediments (micrites, wackestones and diagenetically enhanced dolomites and clay-rich partings).None of the analyzed shell beds was strictly biological in origin; most are sedimentological although >10% are combined sedimentological/diagenetic. While the majority are single simple shell beds, >20% are amalgamated. All are thin (1 shell to 15 cm) stringers that pinch and swell showing poor lateral continuity (outcrop scale, tens to hundreds of meters) likely enhanced by burial dissolution. These shell beds differ greatly in fabric (packing/sorting), clast composition, taphonomic signature, and intensity of time averaging; thus community information retrieval is biased in predictable patterns. Virtually no shell beds show common shell dissolution or encrustation from long-term sediment surface exposure or hardground formation. Five major categories of accumulation are herein proposed using a DESCRIPTIVE, non-genetic terminology modified from previous works of DJD, as well as a Genetic interpretation for each. These are easily distinguished in the field and are also discriminated by Q-mode cluster analysis.Categories include, in decreasing frequency of occurrence: 1. SHELL GRAVELS; Storm/“event” beds: Sharp bases; poorly sorted coarse basal bioclasts and/or intraclasts, often with no preferred orientation; clasts fine upward to comminuted shell material and micrite. Horizontal platy brachiopods often cap the beds. High diversity and a wide range in shell alteration is represented, from whole unaltered brachiopods to minor abraded fragments, indicating extreme time averaging and poor resolution of short-term community dynamics. 2. COMMINUTED SHELLY LS; Current/ripple concentrations: Small tidal channel fill and discrete ripple trough accumulations are composed of cross-stratified bioclastic deposits with local concentrations of rip-ups. Beds are not graded; typically clasts are abraded, rounded and concordant with cross-beds. Intense time averaging and mixing of discrete communities is inferred due to continual reworking in these background deposits. 3. SHELL/CEMENT LS; Early cementation beds: Intense early diagenetic alteration is inferred due to red discoloration and rapid intergranular cementation; some beds show diagenetic micritic rinds. Beds may be brecciated and show deep burial stylolitization cutting bioclasts and cement. They may represent zones of preferred early cementation rather than a change in shell accumulation rate. Many shells from some beds show little postmortem alteration; these units may preserve much of the original community structure. 4. DENSE SHELL PAVEMENTS; Subtidal surficial pavements: Single layers of shells, commonly concave down, overlie mudstones/wackestones with no basal erosion. No obrution deposits were noted. Bioclasts are typically disarticulated and reoriented, but are not substantially abraded, broken, or dissolved. Diversity is low. Only minor temporal and lateral community mixing with small environmental fluctuation is indicated. 5. VERTICALLY IMBRICATE SHELLY LS; High energy beach zones: Platy whole and major fragments of brachiopods are deposited in low diversity, high angle imbricate beds. Less postmortem reworking and time averaging is evident compared to types 1 and 2.Thus, the most common (physically reworked) shell bed types show the most intense loss of short-term paleocommunity information. There are surprisingly few insitu community pavements or obligate long-term accumulations. This pattern differs from some described Ordovician carbonates, which may contain common community beds or hardgrounds/hiatal accumulations. This implies a relatively low rate of net sediment accumulation on a shallow, periodically wave swept shelf, and no major flooding surfaces or other indications of significant sea level change. Delineation of the sequence stratigraphic position of these carbonates is enhanced from this type of integrated community/biostratinomic analysis.

scholarly journals Origin and alteration of organic matter of the Oxford Clay Formation (U.K.) determined from bulk geochemical analyses

1992 ◽  
Vol 6 ◽  
pp. 163-163
Author(s):  
Fabien Kenig ◽  
Brian Popp ◽  
Roger Summons
Keyword(s):  
Organic Matter ◽  
Isotopic Composition ◽  
Water Column ◽  
Sedimentation Rate ◽  
Carbon Isotopic Composition ◽  
Deposit Feeder ◽  
High Sedimentation Rate ◽  
Carbon Isotopic ◽  
Shell Beds ◽  
High Sedimentation

To understand the processes controlling production, accumulation, and preservation of organic matter in the Lower Oxford Clay (LOC), we determined the hydrogen index (HI), the oxygen index (OI), the Tmax (from Rock-Eval), the content of total organic carbon (TOC), total carbon and total sulfur, and the carbon isotopic composition of bulk organic matter from 160 samples collected from 6 different quarries and one continuous core. With concentrations of TOC varying between 0.5% and 16.6%, the LOC is an organic-rich shale. For samples dominated by organic matter of phytoplanktonic origin, the hydrogen and oxygen indices and the Tmax (~418°) indicate low levels of maturity, and, thus, the shallow burial of the LOC through geologic time.Two main sources of organic matter can be distinguished: a major phytoplanktonic source with high HI and low OI and a minor terrestrial source with low HI and high OI. A third group, represented by samples with low HI and low OI, consists mainly of altered materials from the Middle Oxford Clay and the LOC. Selection of samples for chemical analysis was based on the macrofaunal assemblages defined by Duff (1975). These various biofacies are characterized by specific organic geochemical features indicating the relationship between conditions affecting faunal assemblages and those controlling accumulation and preservation of organic matter. For example, Duff's ‘deposit feeder shales', which are dominated by epifaunal bivalves and are depleted in infaunal organisms, exhibit the highest concentration and best preservation of marine organic matter, with an average TOC of 6.8% for 56 samples analyzed. The preservation of such organic matter requires a dysaerobic water column and a high sedimentation rate.Carbon isotopic compositions within the ‘deposit feeder shale’ biofacies (−27.6 to −23.2±) appear to have been controlled by the intensity of primary productivity. The highest-TOC, marine-dominated, 13C-rich samples reflect photosynthetic drawdown of dissolved-CO2 level, and, thus, originated in highly productive environments. On the other hand, variations in the carbon isotopic composition of organic matter in shell beds (−27.5 to −26±) probably reflect heterotrophic reworking of the organic matter, winnowing of the sediments, and mixing with a source of organic matter enriched in 13C, such as wood (δ13C from −25 to −23±). Such mixing phenomena may also explain the high variability of the carbon isotopic compositions of TOC-depleted and altered samples from the Middle and Upper Oxford Clay.The environment of deposition of the LOC would be characterized by the alternation of two major conditions: 1) periods of high productivity, dysoxic water column and high sedimentation rate leading to the development of organic-rich shales dominated by phytoplanktonic organic matter, and 2) periods of low productivity, oxic water column and high current activity implying winnowing and alteration of organic matter, and leading to the formation of shell beds where marine and terrestrial organic matter are mixed.

INTEGRATED SEDIMENTOLOGICAL ANALYSIS: THE EOCENE OF THE BASS BASIN

1989 ◽  
Vol 29 (1) ◽  
pp. 312
Author(s):  
Peter W. Baillie ◽  
Carol A. Bacon
Keyword(s):  
Sea Level ◽  
Sequence Stratigraphy ◽  
Complex Mixture ◽  
Sediment Supply ◽  
Log Analysis ◽  
Core Analysis ◽  
Anaerobic Conditions ◽  
Complex Interplay ◽  
Maximum Thickness ◽  
Sand Bars

The Eocene section in the Bass Basin comprises the upper part of the siliciclastic coal- bearing Eastern View Group and the thin but regionally extensive Demons Bluff Formation.An integrated sedimentological study utilising core analysis, log analysis, palynology, coal maceral studies and geochemistry, together with sequence stratigraphy, has been used to determine Eocene sedimentation styles in the basin.The most likely environment during deposition of the Upper Eastern View Group was a tide- dominated delta consisting of a complex mixture of distributary channels, strandline sand bars, peat swamps and shallow lagoons, the sedimentary successions resulting from a complex interplay between sea- level, tectonics and sediment supply. A major coal- forming episode occurring in the interval 48- 51.5 m.y. is related to oscillations of sea- level following a major highstand.A locally developed progradational unit, Konkon Sandstone, comprising two sandy parasequences separated by a very thin shaly interval is recognised at the top of the Eastern View Group in the northwestern sector of the basin and reaches a maximum thickness of 140 m.The Demons Bluff Formation is a diachronous unit consisting dominantly of siltstone probably deposited in a barred basin with anaerobic conditions.

scholarly journals Discriminating signal from noise in the fossil record of early vertebrates reveals cryptic evolutionary history

2015 ◽  
Vol 282 (1800) ◽  
pp. 20142245 ◽  
Author(s):  
Robert S. Sansom ◽  
Emma Randle ◽  
Philip C. J. Donoghue
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
Biological Factors ◽  
Sea Level Changes ◽  
Upper Ordovician ◽  
Recovery Potential ◽  
Random Models ◽  
Rock Record ◽  
Early Vertebrates ◽  
Fossil Records

The fossil record of early vertebrates has been influential in elucidating the evolutionary assembly of the gnathostome bodyplan. Understanding of the timing and tempo of vertebrate innovations remains, however, mired in a literal reading of the fossil record. Early jawless vertebrates (ostracoderms) exhibit restriction to shallow-water environments. The distribution of their stratigraphic occurrences therefore reflects not only flux in diversity, but also secular variation in facies representation of the rock record. Using stratigraphic, phylogenetic and palaeoenvironmental data, we assessed the veracity of the fossil records of the jawless relatives of jawed vertebrates (Osteostraci, Galeaspida, Thelodonti, Heterostraci). Non-random models of fossil recovery potential using Palaeozoic sea-level changes were used to calculate confidence intervals of clade origins. These intervals extend the timescale for possible origins into the Upper Ordovician; these estimates ameliorate the long ghost lineages inferred for Osteostraci, Galeaspida and Heterostraci, given their known stratigraphic occurrences and stem–gnathostome phylogeny. Diversity changes through the Silurian and Devonian were found to lie within the expected limits predicted from estimates of fossil record quality indicating that it is geological, rather than biological factors, that are responsible for shifts in diversity. Environmental restriction also appears to belie ostracoderm extinction and demise rather than competition with jawed vertebrates.

scholarly journals Upper Middle to lower Upper Ordovician chitinozoans and conodonts from the Bliudziai-150 core, southern Lithuania

2016 ◽  
Vol 53 (8) ◽  
pp. 781-787
Author(s):  
Svend Stouge ◽  
Garmen Bauert ◽  
Heikki Bauert ◽  
Jaak Nõlvak ◽  
Jan A. Rasmussen
Keyword(s):  
Shallow Water ◽  
Carbonate Rocks ◽  
Upper Ordovician ◽  
Depositional Sequence ◽  
Lower Upper ◽  
Discontinuity Surfaces ◽  
Sedimentary Carbonate

Integration of chitinozoan and conodont biozones is based on detailed collections from the Bliudziai-150 well, southern Lithuania, that penetrated upper Darriwilian – lower Sandbian sedimentary carbonate rocks. The strata accumulated at the southeastern side of the Livonian Tongue and represent the transition from shallow shelf facies of the Lithuanian shallow-water shelf facies belt to the deeper-water shelf facies belt. Systematically collected and closely spaced samples of the carbonates from the Bliudziai-150 core yielded both chitinozoans and conodonts in abundance. The chitinozoans are assigned to the Laufeldochitina striata, Laufeldochitina stentor, Angochitina curvata – Armoricochitina granulifera, Lagenochitina dalbyensis, Belonechitina hirsuta, and Spinachitina cervicornis chitinozoan biozones, and the conodonts are assigned to the Pygodus serra Zone (with three subzones), Pygodus anserinus Zone (with two subzones), and the three subzones of the Amorphognathus tvaerensis Zone. The fossils are clearly of Baltoscandian affinity, and the integrated results support existing knowledge concerning the biostratigraphy of the two groups in Baltoscandia. Thus, the studied interval is confidently assigned to the Lasnamägi, Uhaku, Kukruse, and Haljala regional stages of the East Baltic regional chronostratigraphical scheme, corresponding to the global upper Darriwilian – lower Sandbian stages (Middle to Upper Ordovician). International correlation of the chitinozoan and conodont succession is presented, and the position of the base of the international Sandbian Stage is placed at 1380.00 m in the Bliudziai-150 core. A horizon marked by multiple discontinuity surfaces represents the base of Kegel depositional sequence and coincides with the appearance of Armoricochitina granulifera, Angochitina curvata, Lagenochitina dalbyensis, and Baltoniodus gerdae in the Bliudziai-150 core.

Remarkable preservation of shell microstructures from the Late Ordovician of the Cincinnati Arch region, USA, and the success of nacre among Ordovician mollusks

2019 ◽  
Vol 93 (04) ◽  
pp. 658-672
Author(s):  
Michael J. Vendrasco ◽  
Antonio G. Checa ◽  
William P. Heimbrock
Keyword(s):  
Late Ordovician ◽  
Shell Microstructure ◽  
Upper Ordovician ◽  
Shell Beds ◽  
Detailed Record ◽  
Mollusk Shell

AbstractExceptional sub-micrometer details of shell microstructure are preserved in phosphatic micro-steinkerns representing several phyla from shell beds of the Upper Ordovician of the Cincinnati Arch region, USA. These fossils provide the most detailed record of Ordovician mollusk shell microstructures, as well as exceptional details on the earliest cases of undisputed nacre. The trend towards nacre in the Mollusca is one aspect of the surge in escalation between mollusks and their predators during the Great Ordovician Biodiversification Event.

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