Nautiloid septal strength: revisited and revised concepts

Hewitt, Roger A.; Westermann, Gerd E. G.

doi:10.1080/03115518808619000

Cited by 13 publications

(6 citation statements)

References 15 publications

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“…As is evident in Figure 4, longiconic orthocones are clearly the dominant morphotype present in the T. duseri shale assem blage with far fewer numbers of longiconic and breviconic cyr tocones, rare ascocerids, and no planispirally-coiled forms. This distribution of nautiloid morphologies is similar to that de scribed by Hewitt and Watkins (1980) for a sequence of terrig enous shelf facies of Late Silurian age in the Welsh borderland, and by Ward (1987) for the early Paleozoic in general. These longiconic shell morphologies were gradually replaced by in creasing numbers of planispirally-coiled taxa in the later Paleo zoic, with longiconic orthocones constituting only 12-15 percent of nautiloid faunas by the Permian.…”

Section: Early Paleozoic Nautiloid Assemblagessupporting

confidence: 84%

Paleoecology of a well-preserved nautiloid assemblage from a Late Ordovician shale unit, southwestern Ohio

Frey

1989

J. Paleontol.

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A diverse, well-preserved assemblage of nautiloid cephalopods was collected from the Treptoceras duseri shale, a 1.5-m-thick claystone within the Waynesville Formation (Late Ordovician, early Richmondian) exposed in southwest Ohio. The strata, the enclosed fauna, and its taphonomy indicate deposition in a low-energy, mud-bottom marine environment, in water depths of 20–25 m, below wave base but within the zone of storm-current reworking.Nautiloid specimens consist of complete conchs that have been replaced by calcite. Twelve species of nautiloids, belonging to eight genera, representative of four orders, have been collected from the shale in southwest Ohio. Longiconic orthocones are clearly the dominant nautiloid morphotype present, with the assemblage dominated by three species of the longiconic orthocerid Treptoceras and with fewer numbers of the endocerid Cameroceras and the slender orthocerid Isorthoceras?, the cyrtoconic oncocerids Oncoceras and Manitoulinoceras, and rare specimens of the orthocerid Gorbyoceras, the oncocerid Zittelloceras, and the ascocerid Schuchertoceras.Nautiloid taphonomy, the diversity of nautiloid taxa present, the lack of postmortem buoyancy in the shells of the more common taxa, the recurrent nature of this assemblage, and the restricted distribution of this Treptoceras–Cameroceras fauna to portions of eastern North America in the Late Ordovician suggest that this nautiloid assemblage represents an in-situ accumulation of nautiloids representative of a living assemblage. These nautiloids were important elements associated with benthic communities in these epeiric sea mud-bottom environments and not simply assemblages of drifted, necroplanktonic shells.

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Section: Early Paleozoic Nautiloid Assemblagessupporting

confidence: 84%

Paleoecology of a well-preserved nautiloid assemblage from a Late Ordovician shale unit, southwestern Ohio

Frey

1989

J. Paleontol.

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“…Maximum habitat depth calculations for cephalopod specimen of the Boda Limestone all Late Katian except * Hirnantian, Late Ordovician. Calculations afterHewitt & Westermann (1988).…”

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confidence: 99%

Palaeoecology and palaeogeography of Late Ordovician (Katian–Hirnantian) cephalopods of the Boda Limestone, Siljan district, Sweden

Kröger

Ebbestad

2014

LET

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The carbonates associated with the Late Ordovician (Katian-Hirnantian) Boda mounds of the Siljan district, Sweden, contain a rich cephalopod fauna. Cephalopods are rare in the micritic stromatactis facies of the Katian Boda Core Member, but are concentrated together with other molluscs and trilobites in synsedimentary fillings of caves and crevices of the lithified mound limestone. More than 60 cephalopod species are known from these fillings. The assemblage is dominated in richness and abundance by small orthoconic proteoceratids of the genus Isorthoceras and by curved barrandeocerids, and is considerably less endemic than the benthic fauna of the Boda mounds. Similarities are remarkable at the species level with assemblages from elsewhere in Baltica, with Avalonia and south-western Kazakhstan. A genus-level comparison reveals affinities with Laurentia. However, the genus-level similarities are interpreted as reflecting mainly similarities of the depositional environment and of physicochemical conditions. The presence of calcareous algae in the Boda Limestone and maximum hydrostatic septal strength of cephalopods indicate a depositional depth of <100 m, well within the euphotic zone. The dominance and diversity of cephalopods with vertical migrant lifestyle and the absence of actinocerids indicate a cool, nutrient-rich deeper neritic environment. The post-Katian sediments contain a drastically reduced diversity, dominated by orthocerids. The maximum hydrostatic septal strength of the Hirnantian cephalopods and sedimentological features indicate a shallowing during the Hirnantian, but a continuation of high food availability for cephalopods in the water column. □ Assemblage analysis, cephalopod diversity, Ordovician mud mounds.

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“…The lateral trend is interpreted to result from a combination of basin geometry and relative sea-level changes, and displays a deep, oxygen-stressed environment in the southern area, and diversified benthic fauna northward, indicating shallowing to the north. (Westermann, 1973(Westermann, , 1977(Westermann, , 1985Hewitt and Westermann, 1988) and whole-rock δ 13 C isotope stratigraphy.…”

Section: Paleobathymetrymentioning

confidence: 99%

“…Westermann (1973) detailed procedures and methods for measuring and calculating septal strength as follows: Strength = (septal thickness/septal radius) × 1000, and supplied conversions for translating strengths into absolute depths of implosion. Hewitt and Westermann (1988) offered a revised equation:…”

Section: Paleobathymetrymentioning

confidence: 99%

“…In all but two cases (83938A and 83939B, Table 2), the analyzed samples for depth Figure 8. Absolute water depths can be quantified by measuring depth-dependent nautiloid septal implosions (methodology after Westermann, 1973Westermann, , 1977Westermann, , 1985Hewitt and Westermann, 1988). Isorthoceras sociale nautiloids from Graf, Iowa, exhibit partially imploded septa.…”

Section: Paleobathymetrymentioning

confidence: 99%

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Depositional environments and sequence stratigraphy of Upper Ordovician epicontinental deep water deposits, eastern Iowa and southern Minnesota

Raatz¹,

Ludvigson²

1996

Paleozoic Sequence Stratigraphy; Views From the North American Craton

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This study examines depositional environments, stratigraphy, paleontology, and petrology of the Upper Ordovician upper Dubuque Formation and Elgin Member (basal Maquoketa Formation) in eastern Iowa and southern Minnesota within a sequence stratigraphic framework. Dubuque-Elgin deposition occurred within a subcycle of the Maquoketa depositional cycle and records a single transgressive-regressive event; the Dubuque Formation and lowermost Elgin Member deposits are transgressive, lower Elgin deposits are highstand, and middle and upper Elgin deposits are regressive. The transgressive Dubuque Formation grades from an open marine benthic environment in its lower portions, to slightly oxygen stressed environments in its upper portions, with an associated loss of calcareous algae and tempestites, and increase in trilobite grain frequency and mud matrix. The Dubuque-Elgin contact is marked at all but the northernmost localities by a regional condensed section consisting of transgressive phosphatic hardgrounds and overlying highstand dark brown pelagic shale. The nature of overlying regressive Elgin Member deposits is dependent upon geographic location, with thick carbonates (~25 m [~82 ft]) present in the north and north-central areas, mixed carbonates and shales in the south-central area (~15 m [~48 ft]), and thin shales in the southern area (~8 m [~25.6 ft]). Depositionally, this wedge represents shelf (thick carbonates), shelf-slope boundary (mixed carbonates and shales), and slope-basin (shales) environments. The epicontinental Maquoketa seaway is interpreted to have had significant maximum depths (>200 m [650 ft]), and to have contained a density-stratified water mass. Upwelling and associated phosphate deposition resulted from a gyre circulation pattern driven by Taconic freshwater runoff and surface winds, with net surface currents in the study area flowing basinward, replaced by deep upflowing waters. Depths are estimated from regional facies associations, depth-dependent nautiloid septal implosion measurements, and whole-rock carbonate δ 13 C isotopic trends indicating increasing burial of organic carbon.

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Nautiloid septal strength: revisited and revised concepts

Cited by 13 publications

References 15 publications

Paleoecology of a well-preserved nautiloid assemblage from a Late Ordovician shale unit, southwestern Ohio

Paleoecology of a well-preserved nautiloid assemblage from a Late Ordovician shale unit, southwestern Ohio

Palaeoecology and palaeogeography of Late Ordovician (Katian–Hirnantian) cephalopods of the Boda Limestone, Siljan district, Sweden

Depositional environments and sequence stratigraphy of Upper Ordovician epicontinental deep water deposits, eastern Iowa and southern Minnesota

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