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Stable isotopic analysis reveals evidence for groundwater-sediment-animal interactions in a marginal-marine setting

Marilyn E. Zorn, Karlis Muehlenbachs, Murray K. Gingras, Kurt O. Konhauser, S. George Pemberton and Richard Evoy
Stable isotopic analysis reveals evidence for groundwater-sediment-animal interactions in a marginal-marine setting
Palaios (September 2007) 22 (5): 546-553

Abstract

We use isotopic analyses of authigenic siderite and calcite cements within Rosselia socialis burrows from shoreface deposits in the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada, to reveal the early cementation history of the burrow and geochemical conditions of the initial sedimentary environment. Within the Horseshoe Canyon Formation, two forms of the Rosselia burrows are present: bulbous in situ burrows, and transported, spindlelike burrows, which display similar internal shaft diameters but smaller overall size compared to in situ forms. Transverse, incremental sampling of calcite and siderite cements in the Rosselia burrows reveals symmetrical isotopic deviation in delta (super 13) C and delta (super 18) O around the burrow core, representing accretionary records of evolving pore-water conditions. The number of isotopic deviations recorded in bulbous specimens is equal to those observed in spindle-shaped burrows, suggesting that in situ and transported burrows underwent similar periods of cementation. Cementation, however, was limited during each accretionary event in the spindle-shaped burrows, making them more susceptible to transport by storm waves because of their small size. Early cementation of Rosselia, thus, took place very close to the sediment-water interface at depths where storm waves could rework sediments (i.e., less than 1 m sediment depth). The enriched delta (super 13) C values for calcite and siderite (3.06-9.45 per mil PDB [Peedee belemnite]) suggest that cement precipitation followed bacterially mediated decomposition of the organic matter concentrated within Rosselia in the zone of methanogenesis. Oxygen isotope compositions are enriched also, ranging in siderite from 17.5 per mil to 29.4 per mil SMOW (standard mean ocean water) and in calcite from 16.8 per mil to 23.0 per mil SMOW, and are more akin to the composition of subsurface groundwater than marine waters. Freshwater discharging through shoreface sediments explains the delta (super 18) O isotopic signature of calcite and accounts for the early diagenetic precipitation of siderite in shallow marine sediments. In addition, the coexistence of authigenic calcite and siderite cements was most likely controlled by variation in the mixing ratio of meteoric and marine fluids related to variable discharge rates for the freshwater aquifer.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 22
Serial Issue: 5
Title: Stable isotopic analysis reveals evidence for groundwater-sediment-animal interactions in a marginal-marine setting
Affiliation: University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada
Pages: 546-553
Published: 20070901
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 35
Accession Number: 2007-101996
Categories: StratigraphyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch map
N51°16'60" - N51°16'60", W112°19'00" - W112°19'00"
Secondary Affiliation: PetroCanada, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 200744
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