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Enigma of the missing time; are storm events on carbonate shelves the key to gaps in the geologic record or an indicatio

Kendall ? Time

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Enigma of the missing time; are storm events on carbonate shelves the key to gaps in the geologic record or an indicatio

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    1. Kendall Time & Events Enigma of the missing time; are storm events on carbonate shelves the key to gaps in the geologic record or an indication of indecipherable noise in layered rock? Christopher G. St. C. Kendall Geological Science University of South Carolina

    2. Kendall Time & Events Paradoxical Statement!

    3. Kendall Time & Events Sedimentary evidence of Missing Time!

    4. Kendall Time & Events Continuum of Sedimentary Processes

    5. Kendall Time & Events Walthers Law "Facies adjacent to one another in a continuous vertical sequence also accumulated adjacent to one another laterally". Applies only to a section with no unconformities. Applies to a section without subdividing diachronous boundaries, including transgressive surfaces (TS) and the maximum flooding surfaces (mfs). The interpretation of depositional setting for a section cut by diachronous surfaces must contravene Walthers Law but does not? An oversimplification that works!!!

    6. Kendall Time & Events Introduction to subdividing surfaces Range from: Lowest frequency major subdivisions in sedimentary section - the sequence Lower frequency surfaces that define cycles {parasequences} (genetically related cycles or packages of sediment) High frequency surfaces that define beds

    7. Kendall Time & Events Link between time, surfaces & layers Each layer no matter its dimension and whatever the time involved in its deposition, is bounded by surfaces that transgress time The interpretation of depositional setting for a section cut by diachronous surfaces must contravene Walthers Law

    8. Kendall Time & Events Link between time, surfaces & layers Application of Steno's principles and Walthers Law provide powerful and useful simplifications that assume the sediments packaged by surfaces accumulated within discrete moments of time. If one thinks about this, these simplifications dont contravene logic (which is literally Fuzzy) and it aids in the interpretation of the sedimentary section.

    9. Kendall Time & Events Basis of sequence stratigraphic interpretations of carbonates Lower frequency Sequence Boundaries Transgressive surfaces (TS) Maximum flooding surfaces (mfs)

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    11. Kendall Time & Events Lst Sequence Stratigraphic Hierarchies

    12. Kendall Time & Events Lst Sequence Stratigraphic Hierarchies

    13. Kendall Time & Events Controls on Carbonate Surfaces

    14. Kendall Time & Events Bounding surfaces - Defined by origin Internal and external surfaces of any Stratigraphic sequence Cycle (Parasequence) Bed Products of unique associations of processes.

    15. Kendall Time & Events Bounding surfaces - Defined by origin Internal and external surfaces of any Stratigraphic sequence Cycle (Parasequence) Bed Products of unique associations of processes.

    16. Kendall Time & Events Bedding Planes Beds are enclosed or bounded by sharply defined upper & lower surfaces or bedding planes. These surfaces are easiest physical features of sedimentary rocks to identify in outcrop Subdivide successions of sedimentary rock into beds Used to determine relative order & timing of accumulation of sediments forming beds Character of bedding planes, be they eroded, cemented, bored, bioturbated, or depositional surfaces used to aid in interpretation of sedimentary rocks.

    17. Kendall Time & Events Bedding Planes Most probably formed by erosion of unconsolidated sediment collected at sediment surface. Weight of sediment, just beneath sediment surface, causes sediment to dewater, compact & become cohesive Less cohesive sediment of surface truncated & expose surface of firmer cohesive sediment below at bedding plane surface in response to: Storm waves Fast flowing currents of water (say in tidal or fluvial channels) Turbid flow of a density current

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    19. Kendall Time & Events Bedding Planes

    20. Kendall Time & Events Link of Time to Bedding Planes Curtailed or no sediment accumulation on surface can lead to Burrowing by Glossifungites Cementation at or close to sediment water interface by Exposure to photosynthetic effects of cyanobacteria Elevated salinities or upwelling ground waters If surfaces are exposed any length of time they may be colonized & bored by marine organisms; e.g.: Miocene of Murray Basin, Devonian of Canning Basin & Jurassic of the Arabian Gulf. Paradoxically Ordovician often not.

    21. Kendall Time & Events Characteristics of Transgressive Surface [TS) Inferred from presence of Glossifungites that burrows this surface

    22. Kendall Time & Events Link of Time to Bedding Planes Though we see facies changes across bedding planes, the vertical succession more often than not contains no apparent unconformities or major breaks. These usually occur at: Sequence boundaries Transgressive surfaces Maximum flooding surfaces.

    23. Kendall Time & Events Guadalupe Shelf Slaughter Canyon

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    25. Kendall Time & Events Carbonate Shelf Jurassic - Morocco

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    27. Kendall Time & Events Basin Moroccan High Atlas

    28. Kendall Time & Events Alternating Mcrite & Marl - Basin Moroccan High Atlas

    29. Kendall Time & Events Link between time, surfaces & layers Sedimentary layering of a stratigraphic section has a vast array of dimensional hierarchies Range from units millimeters thick, formed over seconds, to thousands of feet thick, formed of millions of years Each layer, no matter its dimension and the time involved in its deposition, is bounded by surfaces that transgress time

    30. Kendall Time & Events Link between time, surfaces & layers

    31. Kendall Time & Events Paradox of Time 40 Mile wide transgressive regressive shelf sequences of late Albian Georgetown in Pecos Valley are equated with 800,000 years Modern rates of accumulation would produce same sedimentary fill in 80,000 years Similar set of values calculated for Seven Rivers Formation of Permian basin

    32. Kendall Time & Events Paradox of Time - Albian Tx

    33. Kendall Time & Events Continuum of Sedimentary Processes Stream Migration Coastal progradation

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    37. Kendall Time & Events Clear Events in Time Spectra Storms Turbidites

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    39. Kendall Time & Events Storm Events Product - Tempestites Common during changes in base level Storm waves and currents extend to and just below wave base in shallow shelf settings Cause sediment deposition and reworking Produce coarsening up cycles in shallow water settings In deeper water sedimentary cycles of both tempestites and turbidites tend to be composed of graded beds that fine upward

    40. Kendall Time & Events

    41. Kendall Time & Events Carbonates Storm Deposits Represented by cycles of carbonate that are coarse at base & fine up to shale Coarser portion of each cycle is interpreted to be result of water being shallow enough for storms to sort sea floor, while fines represent water deep enough to afford protection from effects of similar storms

    42. Kendall Time & Events Setting of Storm Deposits Carbonate storm deposits associated with ramp margins lacking organic binding or cementation, enabling sediment dispersal Presence of storm deposits are indices of lack of cementation and/or organic binding Occurrence of larger metazoan skeletons enhances capacity for surface of ramp to build above a shelf equilibrium profile

    43. Kendall Time & Events

    44. Kendall Time & Events Examples of Storm Deposits Oligocene/Miocene of the Murray Basin Upper Ordovician of Kentucky & Ohio Upper Jurassic Hanifa & Jubaila Fms of Arabian cratonic margin basin Lower Cretaceous of Arabian Gulf

    45. Kendall Time & Events Examples of Storm Deposits Oligocene/Miocene of the Murray Basin Upper Ordovician of Kentucky & Ohio Upper Jurassic Hanifa & Jubaila Fms of Arabian cratonic margin basin Lower Cretaceous of Arabian Gulf

    46. Kendall Time & Events Cycles on temperate-water epeiric ramp: Part A-biotically depauperate carbonates of relatively shallow-water, restricted, variably stressed highly mesotrophic settings Part B-increasingly diverse biotic lst. with progressively more physical energy & less mesotrophic conditions upward OM1- hardground to firmground surface of late transgression to stillstand wave swept & reworked causing omission & lithification Part Crelatively diverse, epifauna-dominant sediments highly abraded during periods of oligotrophic condensed sedimentation OM2 (cycle boundary)a rarely conspicuous surface of arrested sedimentation & variable cementation as trophic resources increased & conditions for carbonate production deteriorated

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    50. Kendall Time & Events Examples of Storm Deposits Oligocene/Miocene of the Murray Basin Upper Ordovician of Kentucky & Ohio Upper Jurassic Hanifa & Jubaila Fms of Arabian cratonic margin basin Lower Cretaceous of Arabian Gulf

    51. Kendall Time & Events Storm Events Ordovician Kentucky Epicontinental ramp exposed to periodic storms Succession of carbonates, siltstones & shales Cyclic character of each cycle becomes coarser & contains less shale upward Coarser portion of each cycle when water shallow enough for storms to sort sea floor Finer portions of the section represent water deep enough to protect from similar storms Low stands in sea level more likely to affect floor with storms Highs the section likely to starve sediment & cause surfaces of condensation Each cycle has a storm sorted base produced by last major event, & a cap from quieter water conditions

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    53. Kendall Time & Events Graded Beds

    54. Kendall Time & Events Graded Beds

    55. Kendall Time & Events Graded Beds

    56. Kendall Time & Events Waves Modify Surface of Tempestite as with Turbidites

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    63. Kendall Time & Events Paradoxes of Storm Deposits? Wide spread storm events have been identified on ramps explaining occurrence of shallow water cycles that do not make it to sea level Surface of ramps on which storm deposits occur related to: An ecological base level that does not match hydrodynamic base level but is connected to it ( Pomar(2001) Lack of local cementation Ramp response to increase of accommodation is ascribed to Eustasy Tectonic events Storm deposits can be sorted, rounded, & incorporate several generations of sediment component that are product of Single large storms at sea level low? Multiple storms? Cannibalism supports lack of cementation & binding on ramp? Micritization of the surfaces of gravels grains can be common but more often it is not: Time spent exposed on sea floor insufficient for cyanobacteria colonization?

    64. Kendall Time & Events Preliminary Conclusions Wide spread sea level events matched to storm prone portions of geological section Accommodation controls carbonate productivity Lows favor carbonate production and storm sorting Highs reduce carbonate productivity and induce condensation of section This response explains the lack of tidal flat fill on ramps Suggest a continuum of processes applied to section but no time gaps or lost sediment!

    65. Kendall Time & Events Turbiditic Events Product - Turbidites Common during changes in base level Sudden sediment mobilization on shelf margin by over-steepening of sea floor & sudden movement downslope triggered by Too much sediment Storms Earthquakes Form cyclic bundles of fining up graded beds Symmetric or asymmetric of sequences Complete and incomplete cycles Latter reflect non-deposition &/or erosion during depositional cycle

    66. Kendall Time & Events

    67. Kendall Time & Events Storm & Turbiditic Events Often mark changes in base level Recurring processes associated with depositional regime (autocyclic) generate successions of symmetric or asymmetric bundles cyclic beds Complete & incomplete cycles, latter reflecting non-deposition &/or erosion during depositional cycle Varying magnitudes, larger rarer events wipe out signatures of earlier smaller Non-periodic sequences caused by irregular stratigraphic events Storms & turbidite currents are unpredictable, sudden, & catastrophic but sediments deposited by them are very clear time markers

    68. Kendall Time & Events Storm & Turbiditic Events Juxtaposition of similar vertical facies in sedimentary record appears complete No extensive erosion, so lacks evidence of missing time Even fauna exposed on seafloor may be unaltered & unbored in Ordovician despite apparently long periods on seafloor In Jurassic and Miocene these grains show clear evidence of boring, and alteration. Storms & turbidite currents are unpredictable, sudden, & catastrophic but sediments deposited by them are very clear time markers

    69. Kendall Time & Events Paradoxical Conclusion

    70. Kendall Time & Events Where is sedimentary evidence of Missing Time!

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