Paleobathymetry of a Silurian shelf based on brachiopod assemblages: an oxygen isotope test

Abstract

Primary δ18 O signals of 97 brachiopod shells from the Lower Silurian (Llandovery) carbonate succession of Anticosti Island were used to test the hypothesis of water-depth and water-temperature gradient for the Silurian onshoreoffshore benthic assemblages (BA1-BA5 O differentiation in their shell composition; and (3) that the Pentamerus, Stricklandia, and Triplesia communities need to be investigated at the species level, as both taphonomic and oxygen isotopic data indicate that the Stricklandia planirostrata Community most likely lived in a notably warmer, shallower water than the Pentamerus palaformis Community and that Triplesia anticostiensis (BA5) lived at water temperature comparable to that of the Pentamerus habitat (BA3). This may suggest either that, at the generic level, the Pentamerus, Stricklandia, and Triplesia (Clorinda equivalent) communities may have had substantial overlap in their spatial distribution in the BA3-BA4 paleobathymetric settings or that the isotope signals are too faint to record water depth differences on a tropical shelf.

Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era

“…lived at depths significantly below the surface (~20-90 meters) 9 . We suggest, therefore, that the temperatures we present here provide minimum estimates of the actual sea surface temperatures.…”

“…The Silurian brachiopods and mid-Pennsylvanian molluscs analyzed in this study were collected from sedimentary rocks which were originally deposited in tropical, shallow-marine environments 9,10 . Although the exact growth depths of the analyzed samples are not known for certain, a study involving the Lower Silurian (Llandovery) carbonate succession of Anticosti…”

“…Early Silurian brachiopod samples were visually examined under a binocular microscope to determine their extent of preservation 9 . Our suite includes equal numbers of samples that appear to have excellent preservation and samples that appear to be moderately altered (i.e., so we can systematically examine the effects of alteration on the isotopic record).…”

Bathymetry and productivity of the southern Great Basin seaway, Nevada, USA: An evaluation of isotope and trace element chemistry in mid-Carboniferous and modern brachiopods

“…Few studies have attempted to resolve the issue of identifying bathymetry from the geochemical results of fossil brachiopods (e.g., Adlis et al, 1988;Bates and Brand, 1991;Brenchley et al, 1994;Azmy et al, 2006). However few, the studies on modern brachiopods may explicitly demonstrate a relationship between water depth (temperature) and oxygen isotopes (e.g., Lowenstam, 1961;James et al, 1997;Brand et al, 2003).…”

“…Furthermore, bathymetric interpretations of fossil brachiopods rely on paleoecologic, faunal associations and/or sedimentologic indicators in deciphering their depth habitat, which may be lacking for some sites or difficult to discern from the available information and/or reconcile with the isotopic information (e.g., Azmy et al, 2006). The importance and impacts of these parameters were addressed by some authors in their studies and evaluation of fossil brachiopod chemistry but many issues remain unresolved or unsatisfactorily explained by the results (e.g., Bates and Brand, 1991;Grossman, 1994;Azmy et al, 2006). In contrast, the influence of seawater productivity on brachiopod abundance and distribution is essentially unstudied, and its application to studies of fossil and paleo-ocean chemistry remains unexplored.…”