Molecular indicators of redox and marine photoautotroph composition in the late Middle Ordovician of Iowa, U.S.A.
Introduction
The late Middle Ordovician (P. undatus zone) of the eastern United States contains significant evidence for macrofaunal turnover (Patzkowsky and Holland, 1993, Patzkowsky and Holland, 1996, Patzkowsky and Holland, 1997; Frey, 1995). These authors suggested that a tectonically driven change in basin circulation and/or increased upwelling caused cool, oxygen-poor waters to spread through the Taconic foreland basin, resulting in the extinction of fauna in the eastern United States (Patzkowsky and Holland, 1996). Evidence for profound variation in basin circulation in this interval includes a transition from tropical- to temperate-type carbonates, a decline in the abundances of calcareous green algae and cyanobacterial mats and an increase in phosphorite deposits (Patzkowsky and Holland, 1993; Holland and Patzkowsky, 1996, Holland and Patzkowsky, 1997). A pronounced positive carbon-isotope excursion in both carbonate (∼3‰) and bulk organic matter (3–7‰) spans the interval of faunal change (Hatch et al., 1987; Ludvigson et al., 1996; Patzkowsky et al., 1997) and offers further evidence of regional and possibly global changes in carbon cycling.
During the same interval, a significant local extinction occurs in strata from the upper Mississippi valley (Sloan, 1987, Sloan and Alexander, 1997), suggesting that oceanographic processes similar to those of the eastern United States affected biota in the central United States. Indeed, in correlative units in eastern Wisconson Saylor et al. (1997)find a lithofacies shift to cool-water-type carbonates similar to those observed in the eastern U.S. However, Sloan (1987)invoked deposition of a widespread volcanic ash (the Deicke K-bentonite) rather than paleoceanographic processes as the cause of extinction.
Here, we use molecular indicators to examine the timing and magnitude of redox variations related to these oceanographic changes in a single continuous core from Iowa.
Specifically, we evaluate whether redox variations are associated with published evidence for bioturbation, lithofacies variations and inferred water depth. A second goal is to evaluate changes in the organic materials derived from photosynthetic organisms using molecular markers and to determine if those changes track sedimentological evidence for redox or water-depth variations. In particular, the contributions from cyanobacteria, anoxygenic photosynthetic bacteria, and Gloeocapsomorpha prisca are evaluated using lipid biomarkers. To achieve these goals, we performed molecular and isotopic analyses on saturated and aromatic hydrocarbons isolated from a continuous core of the upper Platteville and Decorah Formations.
Section snippets
Sample preparation
Approximately 50 g of rock were collected from thirty horizons in the Cominco SS-9 core from Millbrook Farms in Jackson County, IA (currently archived at the Iowa State Geological Survey). The sampled interval spans the upper Platteville Formation through the lower Ion Member of the Decorah Formation (Fig. 1). Samples were gently washed with methanol to remove handling and storage contamination, ground with mortar and pestle and powdered with a ball mill device. The powdered samples were Soxhlet
Lithology and paleobathymetry
The Platteville Formation is predominantly carbonate mudstone with interbedded fossiliferous packstone lenses. These lenses are similar to those observed in overlying formations, that have been attributed to tempestites (Ludvigson et al., 1996). In general, the Platteville Formation is bioturbated and contains abundant Planolites, Chondrites and Thalassinoides burrows (Byers, 1983; Dokken, 1987). CaCO3 contents range from 70 to 90% in the Platteville Formation (Table 1 and Fig. 1), and TOC
Biomarker redox indicators
Many biomarker redox proxies are affected by thermal maturity and clay contents of the mineral matrix (Peters and Moldowan, 1993). Because sampling is confined to a narrow stratigraphic interval from a single core, maturity variations are unlikely to influence biomarker proxies. However, the relative abundance of clay varies significantly in this interval (the noncarbonate fractions are composed predominantly of illite and kaolinite clays; Ludvigson et al., 1996), and some molecular
Green sulfur bacteria
Aryl isoprenoids are presumed degradation products of isorenieratene (Summons and Powell, 1987), a diaromatic carotenoid present in green sulfur bacteria (Chlorobiaceae, Liaaen-Jensen, 1978). Recent work indicates that in some depositional environments, aromatization of β-carotane can also be a significant source of aryl isoprenoids (Koopmans et al., 1996b). Compound-specific isotope analyses are therefore required to verify green sulfur bacteria as the exclusive source of aryl isoprenoids,
Redox variations
The presence of benthic macrofossils and bioturbation indicates that deposition throughout the Middle Caradocian of IA occurred under a relatively oxidizing water column. Ludvigson et al. (1996)argued that the lack of deep burrowing fabrics (i.e. Thalassinoides) in the Spechts Ferry and Guttenberg Members indicated that bottom waters were intermittently dysoxic during deposition of those units. Biomarker data do not entirely support this interpretation, and these apparently conflicting
Conclusions
We examined molecular indicators for organic-matter sources and depositional redox conditions during the Middle Caradocian from a single, continuous core from Jackson County, IA. Our molecular data and published sedimentological, ichnofossil and benthic macrofaunal data indicate oxic conditions prevailed throughout deposition of the Platteville Formation and the Ion Member of the Decorah Formation. Trace fossils are more restricted in the Spechts Ferry and Guttenburg Members of the Decorah
Note added in proof
Methylhopane identifications were confirmed by GC-MS/MS analyses performed at the Netherlands Institute for Sea Reseach.
Acknowledgements
This research was supported by a fellowship from the Earth System Science Center, Pennsylvania State University and a student grant from the Geological Society of America. We also thank Dr A. Davis and Dr G. Mitchell for assistance in petrographic analysis, Mr. D. Walizer for technical support, Dr G. Ludvigson and Dr B. Witzke at the Iowa Geological Survey for assistance in procuring samples from the SS-9 core, and Dr J. S. Sinninghe Damsté of the Netherlands Institute for Sea Research for
References (68)
- et al.
An isotopic bio-geochemical study of the Green River oil shale
Organic Geochemistry
(1992) - et al.
δ13C compositions of saturate and aromatic fractions of lacustrine oils and bitumens: evidence for water column stratification
Organic Geochemistry
(1996) - et al.
Characterization of Estonian Kukersite by spectroscopy and pyrolysis: evidence for abundant alkyl phenolic moieties in an Ordovician, marine, type II/I kerogen
Organic Geochemistry
(1990) - et al.
Similar morphological and chemical variations of Gloeocapsomorpha prisca in Ordovician sediments and cultured Botryococcus braunii as a response to changes in salinity
Organic Geochemistry
(1992) - et al.
Gloeocapsomorpha prisca Zalessky, 1917: a new study. Part I: taxonomy, geochemistry and paleoecology
Geobios
(1989) Biological and carbon isotopic analysis of individual biological markers: evidence for sources of organic matter and paleoenvironmental conditions in the Upper Ordovician Maquoketa Group, Illinois Basin, U.S.A.
Organic Geochemistry
(1996)- et al.
The ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks
Geochimica et Cosmochimica Acta
(1995) - et al.
Molecular indicators for paleoenvironmental change in a Messinian evaporitic sequence (Vena del Gesso, Italy). II. High-resolution variations in abundances and 13C contents of free and sulphur-bound carbon skeletons in a single marl bed
Organic Geochemistry
(1995) - et al.
Diagenetic and catagenetic products of isorenieratene: molecular indicators for photic zone anoxia
Geochimica et Cosmochimica Acta
(1996) - et al.
Restricted utility of aryl isoprenoids as indicators for photic zone anoxia
Geochimica et Cosmochimica Acta
(1996)
Effects of source, thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum
Organic Geochemistry
Acquisition and processing of data for isotope-ratio-monitoring mass spectrometry
Organic Geochemistry
Carbon isotopic compositions of individual biomarkers in gilsonites (Utah)
Organic Geochemistry
Reflected light microscopy and micro-FTIR of Upper Ordovician Gloeocapsomorpha prisca alginite in relation to paleoenvironment and petroleum generation, Saskatchewan, Canada
Organic Geochemistry
Identification of aryl isoprenoids in source rocks and crude oils: biological markers for green photosynthetic bacteria
Geochimica et Cosmochimica Acta
Identification of methylhopanes in sediments and petroleum
Geochimica et Cosmochimica Acta
Carbon isotopic fractionation in lipids from methanotrophic bacteria: relevance for interpretation of the geochemical record of biomarkers
Geochimica et Cosmochimica Acta
The microplankton organisms at the oxic-anoxic interface in the pelagial of the Black Sea
FEMS Microbiology Ecology
Marine black shales: depositional mechanisms and environments of ancient deposits
Annual Review of Earth and Planetary Sciences
Primary production, sulfate reduction and sulfur isotope fractionation in algal mats and sediments of Hamelin Pool, Shark Bay, WA
Australian Journal of Marine and Freshwater Resources
Prokaryotic triterpenoids 2. 2β-Methylhopanoids from Methylobacterium organophilum and Nostoc muscorum, a new series of prokaryotic triterpenoids
European Journal of Biochemistry
Chondrites: a trace fossil indicator of anoxia in sediments
Science
Polar lipids of of archaebacteria in sediments and petroleum
Science
Organic geochemical indicators of palaeoenvironmental conditions of sedimentation
Nature
Water column anoxia: vertical zonation of planktonic protozoa
Marine Ecology Progress Series
Evidence from carbon isotope measurements for diverse origins of sedimentary hydrocarbons
Nature
Tocopherols as likely precursors of pristane in ancient sediments and crude oils
Nature
Possible Late Middle Ordovician organic carbon isotope excursion: evidence from Ordovician oils and hydrocarbon source rocks, Mid-Continent and east-central United States
Bulletin of the American Association of Petroleum Geologists
Restricted utility of the pristane/phytane ratio as a paleoenvironmental indicator
Nature
Cited by (72)
Occurrence, distribution and sources of petroleum contamination in reef-associated sediments of the Gulf of Mannar, India
2023, Marine Pollution BulletinFrom cyanobacteria to kerogen: A model of organic carbon burial
2023, Precambrian ResearchApplication of chemometrics to quantitative source assessment of crude oils from the Zhanhua Depression, Bohai Bay Basin, northeast China
2021, Journal of Asian Earth SciencesCarbon and oxygen isotope variations in shell beds from the Upper Ordovician (mid-Cincinnatian: Maysvillian to early Richmondian) of Ontario: Evaluation of the Warm Saline Deep Ocean hypothesis, paleoceanographic changes, and Milankovitch orbital cycles in the transition to the Hirnantian glaciation
2021, Palaeogeography, Palaeoclimatology, PalaeoecologyCitation Excerpt :The Collingwood, in particular, has significant amounts of the algal or cyanobacterial Gloeocapsomorpha prisca, as well as other algae and especially bacteria, which produced very negative δ13Corg values of −30‰ (Fowler, 1992). G. prisca also occurs in the Mohawkian to Cincinnatian of eastern North America where its relative abundance can reduce bulk δ13Corg by several ‰ (Pancost et al., 1998). G. prisca may be a related to the planktonic green microalga B. braunii, which can adapt to large salinity variations (Sinninghe Damsté et al., 1992).