Algal Blooms and “Marine Snow”: Mechanisms That Enhance Preservation of Organic Carbon in Ancient Fine-Grained Sediments

Abstract Combined petrographic and geochemical methods are used to investigate the microfabrics present in thin sections prepared from representative organic carbon-rich mudstones collected from three successions (the Kimmeridge Clay Formation, the Jet Rock Member of the Whitby Mudstone Formation, and the pebble shale and Hue Shale). This study was initiated to determine how organic carbon-rich materials were being delivered to the sediment–water interface, and what happened to them after deposition, prior to deep burial. Analyses of the fabrics present shows that they exhibit many common attributes. In particular they are all: (1) highly heterogeneous on the scale of a thin section, (2) organized into thin beds ( The organomineralic aggregates present in these mudstones are interpreted to be ancient examples of marine snow. This marine snow likely formed in the water column, particularly during phytoplankton blooms, and was then transported rapidly to the seafloor. The existence of the thin beds with homogenized tops and an in-situ infauna indicates that between blooms there was sufficient oxygen and time for a mixed layer to develop as a result of sediment colonization by diminutive organisms using either aerobic or dysaerobic metabolic pathways. These textures suggest that the constituents of these mudstones were delivered neither as a continuous rain of sediment nor were the bottom waters persistently anoxic. In addition, the presence of thin lags and sharp-based beds suggests that the seafloor was being episodically reworked during deposition. These fabrics indicate that conditions in the water columns and at the seafloors while these rocks were being deposited were very dynamic, and episodic fluxes of high concentrations of organic carbon to the seafloor, during phytoplankton blooms, likely enhanced preservation of organic carbon.

[1]  W. Dean,et al.  Depletion of 13C in Cretaceous marine organic matter: Source, diagenetic, or environmental sigal? , 1986 .

[2]  A. Alldredge,et al.  Can Microscale Chemical Patches Persist in the Sea? Microelectrode Study of Marine Snow, Fecal Pellets , 1987, Science.

[3]  D. Z. Piper,et al.  Molybdenum accumulation in Cariaco basin sediment over the past 24 k.y.: A record of water-column anoxia and climate , 1999 .

[4]  K. Pye,et al.  Microfabric, mineralogy and early diagenetic history of the Whitby Mudstone Formation (Toarcian), Cleveland Basin, U.K. , 1986, Geological Magazine.

[5]  R. Lampitt.  Evidence for the seasonal deposition of detritus to the deep-sea floor and its subsequent resuspension , 1985 .

[6]  A. Coe,et al.  Integrated stratigraphy of the Kimmeridge Clay Formation (Upper Jurassic) based on exposures and boreholes in south Dorset, UK , 2001, Geological Magazine.

[7]  Maurice E. Tucker,et al.  The Field Description of Sedimentary Rocks , 1982 .

[8]  J. Macquaker,et al.  A sequence-stratigraphic interpretation of a mudstone-dominated succession: the Lower Jurassic Cleveland Ironstone Formation, UK , 1996, Journal of the Geological Society.

[9]  N. Blair,et al.  Carbon remineralization in the Amazon–Guianas tropical mobile mudbelt: A sedimentary incinerator , 2006 .

[10]  C. Lange,et al.  Self-sedimentation of phytoplankton blooms in the geologic record , 1997 .

[11]  J. Schieber,et al.  Accretion of Mudstone Beds from Migrating Floccule Ripples , 2007, Science.

[12]  R. Bromley.  Trace Fossils: Biology, Taxonomy and Applications , 1996 .

[13]  I. N. McCave.  Size spectra and aggregation of suspended particles in the deep ocean , 1984 .

[14]  Q. Passey,et al.  Recurring Patterns of Total Organic Carbon and Source Rock Quality within a Sequence Stratigraphic Framework , 1993 .

[15]  Stefan Schouten,et al.  Sulfurized carbohydrates: an important sedimentary sink for organic carbon? , 1998 .

[16]  W. Dean.  Sediment geochemical records of productivity and oxygen depletion along the margin of western North America during the past 60,000 years: teleconnections with Greenland Ice and the Cariaco Basin , 2007 .

[17]  J. Schieber.  Discovery of agglutinated benthic foraminifera in Devonian black shales and their relevance for the redox state of ancient seas , 2009 .

[18]  A. L. Rice,et al.  Seasonal sedimentation of phytoplankton to the deep-sea benthos , 1983, Nature.

[19]  J. Macquaker,et al.  On the Accumulation of Mud , 2007, Science.

[20]  R. Berner.  Sedimentary pyrite formation: An update , 1984 .

[21]  C. Nittrouer,et al.  Emplacement, modification, and preservation of event strata on a flood-dominated continental shelf: Eel shelf, Northern California , 2003 .

[22]  J. B. Maynard,et al.  Geochemistry of Sedimentary Ore Deposits , 1983 .

[23]  R. Baerwald,et al.  Comparison of pelagic and nepheloid layer marine snow: implications for carbon cycling , 1998 .

[24]  Charles A. Nittrouer,et al.  STRATAFORM: overview of its design and synthesis of its results , 1999 .

[25]  T. Algeo.  Can marine anoxic events draw down the trace element inventory of seawater , 2004 .

[26]  C. V. Campbell.  Lamina, Laminaset, Bed and Bedset , 1967 .

[27]  M. Allison,et al.  Carbon burial on river‐dominated continental shelves: Impact of historical changes in sediment loading adjacent to the Mississippi River , 2007 .

[28]  J. Macquaker,et al.  Mudstone Sedimentation at High Latitudes: Ice as a Transport Medium for Mud and Supplier of Nutrients , 2005 .

[29]  A. Shanks.  The abundance, vertical flux, and still-water and apparent sinking rates of marine snow in a shallow coastal water column , 2002 .

[30]  S. Audry,et al.  Effect of estuarine sediment resuspension on early diagenesis, sulfide oxidation and dissolved molybdenum and uranium distribution in the Gironde estuary, France , 2007 .

[31]  P. E. Potter,et al.  Mud and Mudstones: Introduction and Overview , 2004 .

[32]  G. Luther,et al.  Chemistry of iron sulfides. , 2007, Chemical reviews.

[33]  J. D. Hudson,et al.  Intermittent euxinia: Reconciliation of a Jurassic black shale with its biofacies , 2004 .

[34]  A. Shanks,et al.  Reducing microzones and sulfide production in marine snow , 1993 .

[35]  Yogesh C. Agrawal,et al.  Direct optical assessment of large amorphous aggregates (marine snow) in the deep ocean , 1984 .

[36]  R. Tyson,et al.  A stratified water column environmental model for the type Kimmeridge Clay , 1979, Nature.

[37]  T. Lyons,et al.  A tale of shales: the relative roles of production, decomposition, and dilution in the accumulation of organic-rich strata, Middle–Upper Devonian, Appalachian basin , 2003 .

[38]  W. Dean,et al.  Iron-sulfur-carbon relationships in organic-carbon-rich sequences I: Cretaceous Western Interior seaway , 1989 .

[39]  B. Jørgensen,et al.  Anoxic aggregates - an ephemeral phenomenon in the pelagic environment? , 1997 .

[40]  M. Boussafir,et al.  Accumulation of organic matter in the Kimmeridge Clay formation (KCF): an update fossilisation model for marine petroleum source-rocks , 1997 .

[41]  I. Tailleur,et al.  Pebble Shale (Early Cretaceous) Depositional Environments in National Petroleum Reserve in Alaska (NPRA): ABSTRACT , 1983 .

[42]  J. Schieber.  Facies and origin of shales from the mid‐Proterozoic Newland Formation, Belt Basin, Montana, USA , 1989 .

[43]  T. Lyons,et al.  Trace metals as paleoredox and paleoproductivity proxies: An update , 2006 .

[44]  Stefan Schouten,et al.  Preservation of carbohydrates through sulfurization in a Jurassic euxinic shelf sea: Examination of the Blackstone Band TOC cycle in the Kimmeridge Clay Formation, UK , 2006 .

[45]  F. Kenig,et al.  Water column structure during deposition of Middle Devonian–Lower Mississippian black and green/gray shales of the Illinois and Michigan Basins: a biomarker approach , 2004 .

[46]  S. Fowler,et al.  Role of large particles in the transport of elements and organic compounds through the oceanic water column , 1986 .

[47]  S. Hesselbo,et al.  Carbon‐Cycle Perturbation in the Middle Jurassic and Accompanying Changes in the Terrestrial Paleoenvironment , 2003, The Journal of Geology.

[48]  T. Milligan,et al.  Macroflocs: Production of Marine Snow in the Laboratory , 1980 .

[49]  L. Schwark,et al.  The Posidonia Shale (Lower Toarcian) of SW-Germany: an oxygen-depleted ecosystem controlled by sea level and palaeoclimate , 2001 .

[50]  N. Fiet,et al.  Revisiting amorphous organic matter in Kimmeridgian laminites: what is the role of the vulcanization process in the amorphization of organic matter? , 2006 .

[51]  J. Syvitski,et al.  In situ characteristics of suspended particles as determined by the floc camera assembly FCA , 1996 .

[52]  D. Eisma,et al.  Flocculation and de-flocculation of suspended matter in estuaries , 1986 .

[53]  J. Bernhard,et al.  Benthic foraminiferal population fluctuations related to anoxia: Santa Barbara Basin , 1991 .

[54]  E. Wolanski,et al.  FLOCCULATION OF SUSPENDED SEDIMENT IN THE FLY RIVER ESTUARY, PAPUA-NEW-GUINEA , 1995 .

[55]  L. Balistrieri,et al.  Suboxic trace metal geochemistry in the Eastern Tropical North Pacific , 2002 .

[56]  H. Thiel.  Ocean cleaning and marine snow , 1995 .

[57]  H. Grossart,et al.  Microbial ecology of organic aggregates in aquatic ecosystems , 2002 .

[58]  C. Bjerrum,et al.  Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event , 2000, Nature.

[59]  Alice L. Alldredge,et al.  Discarded appendicularian houses as sources of food, surface habitats, and particulate organic matter in planktonic environments , 1976 .

[60]  R. Hill,et al.  Mineral Surface Control of Organic Carbon in Black Shale , 2002, Science.

[61]  J. B. Maynard,et al.  Trace-element behavior and redox facies in core shales of Upper Pennsylvanian Kansas-type cyclothems , 2004 .

[62]  Alice L. Alldredge,et al.  Characteristics, dynamics and significance of marine snow , 1988 .

[63]  H. Jenkyns,et al.  Lower Jurassic epicontinental carbonates and mudstones from England and Wales: chemostratigraphic signals and the early Toarcian anoxic event , 1997 .

[64]  L. Legendre,et al.  Climatic and biological forcing of the vertical flux of biogenic particles under seasonal Arctic sea ice , 2002 .

[65]  J. Trent,et al.  Marine snow: sinking rates and potential role in vertical flux , 1980 .

[66]  J. Schieber.  Distribution and deposition of mudstone facies in the Upper Devonian Sonyea Group of New York , 1999 .

[67]  T. Pedersen,et al.  The accumulation of silver in marine sediments: A link to biogenic Ba and marine productivity , 2008 .

[68]  H. Jenkyns.  The early Toarcian (Jurassic) anoxic event; stratigraphic, sedimentary and geochemical evidence , 1988 .

[69]  A. Sheremet,et al.  Event sedimentation, bioturbation, and preserved sedimentary fabric : Field and model comparisons in three contrasting marine settings , 2006 .

[70]  D. Thornton.  Diatom aggregation in the sea: mechanisms and ecological implications , 2002 .