Changes

[[File:BLTN13190fig2.jpg|thumb|300px|{{figure number|2}}Examples of clinoforms produced by the clinoform-modeling algorithm conditioned to different bounding surfaces and clinoform geometries. (A) Bounding surfaces represent postdepositional compaction and folding of the original (depositional) geometries of the clinoform and the top and base bounding surfaces. (B) Bounding surfaces represent a clinoform within a volume truncated at its top, for example, by a channel ([[:File:BLTN13190fig1.jpg|Figure 1]]). (C) Bounding surfaces represent a clinoform downlapping onto irregular sea-floor topography. (D) Height function, ''h(r_c)'' (equation 1; see Table 1 for nomenclature). (E) Shape function, ''s(r_c)'' (equation 7; Table 1), demonstrating that increasing the exponent, ''P'', increases the dip angle of clinoforms.]]

[[File:BLTN13190fig2.jpg|thumb|300px|{{figure number|2}}Examples of clinoforms produced by the clinoform-modeling algorithm conditioned to different bounding surfaces and clinoform geometries. (A) Bounding surfaces represent postdepositional compaction and folding of the original (depositional) geometries of the clinoform and the top and base bounding surfaces. (B) Bounding surfaces represent a clinoform within a volume truncated at its top, for example, by a channel ([[:File:BLTN13190fig1.jpg|Figure 1]]). (C) Bounding surfaces represent a clinoform downlapping onto irregular sea-floor topography. (D) Height function, ''h(r_c)'' (equation 1; see Table 1 for nomenclature). (E) Shape function, ''s(r_c)'' (equation 7; Table 1), demonstrating that increasing the exponent, ''P'', increases the dip angle of clinoforms.]]

Clinoforms occur at a wide range of spatial scales, from large, basinward-dipping surfaces at the shelf-slope margin, to smaller surfaces associated with progradation of deltaic and shoreface systems across the shelf (e.g., Helland-Hansen and Hampson<ref name=HHH>Helland-Hansen, W., and G. J. Hampson, 2009, Trajectory analysis: Concepts and applications: Basin Research, v. 21, no. 5, p. 454–483, doi: 10.1111/j.1365-2117.2009.00425.x.</ref>). This study focuses on developing a surface-based approach to represent clinoforms at any lengthscale in reservoir models, with emphasis on clinoforms produced by the progradation of deltaic, barrier-island, and strandplain shorelines, which are typically up to a few tens of meters in height. The 3-D geometry and spatial arrangement of shoreline-scale clinoforms reflect in large part the process regime under which they were deposited (e.g., Galloway<ref name=Glwy>Galloway, W. E., 1975, Process framework for describing the morphological and stratigraphic evolution of deltaic depositional systems, in M. L. Broussard, ed., Deltas, models for exploration: Houston, Texas, Houston Geological Society, p. 87–98.</ref>). Fluvial-dominated deltas exhibit a hierarchy of point-sourced, teardrop-shaped sediment bodies that are fed via a downstream branching network of distributary channels. From small to large lengthscales, this hierarchy consists of mouth bars, mouth-bar assemblages, and delta lobes<ref name=Bhttchry2006>Bhattacharya, J. P., 2006, Deltas, inH. W. Posamentier, and R. Walker, eds., Facies models revisited: SEPM Special Publication 84, p. 237–292.</ref> (equivalent to the jet-plume deposits, jet-plume-complex deposits, and delta lobes of Wellner et al.<ref name=Wllnr2005>Wellner, R., R. Beaubouef, J. C. Van Wagoner, H. H. Roberts, and T. Sun, 2005, Jet-plume depositional bodies—The primary building blocks of Wax Lake delta: Transactions of the Gulf Coast Association of Geological Societies, v. 55, p. 867–909.</ref>). Sediment-body geometry is modified by the action of waves and tides, which respectively tend to result in shoreline-parallel and shoreline-perpendicular sediment transport that suppresses branching and switching of distributary channels (e.g., Galloway;<ref name=Glwy /> Willis;<ref >Willis, B. J., 2005, Deposits of tide-influenced river deltas, in L. Giosan, and J. P. Bhattacharya, eds., River deltas—Concepts, models, and examples: SEPM Special Publication 83, p. 87–129.</ref> Bhattacharya;<ref name=Bhttchry2006 /> Plink-Björklund<ref>Plink-Björklund, P., 2012, Effects of tides on deltaic deposition: Causes and responses: Sedimentary Geology, v. 279, p. 107–133, doi: 10.1016/j.sedgeo.2011.07.006.</ref>). Clinoforms exist as a preserved record of sediment-body morphologies at each of these hierarchical lengthscales (e.g., Gani and Bhattacharya<ref name=GB07>Gani, M. R., and J. P. Bhattacharya, 2007, Basic building blocks and process variability of a Cretaceous delta: Internal facies architecture reveals a more dynamic interaction of river, wave, and tidal processes than is indicated by external shape: Journal of Sedimentary Research, v. 77, no. 4, p. 284–302, doi: 10.2110/jsr.2007.023.</ref>) but are most commonly described at the scale of delta lobes in outcrop and high-resolution, shallow seismic data. For example, in Pleistocene fluvial-dominated delta deposits imaged in shallow-seismic data, Roberts et al.<ref name=Rbrts2004>Roberts, H. H., R. H. Fillon, B. Kohl, J. M. Robalin, and J. C. Sydow, 2004, Depositional architecture of the Lagniappe delta; sediment characteristics, timing of depositional events, and temporal relationship with adjacent shelf-edge deltas, in J. B. Anderson, and R. H. Fillon, eds., Late Quaternary stratigraphic evolution of the northern Gulf of Mexico margin: Tulsa, Oklahoma, SEPM Special Publication 79, p. 143–188.</ref> comment that “each clinoform set represents rather continuous deposition from a distributary or related set of distributaries, resulting in the formation of a delta lobe.” Shale drapes and cemented concretionary layers occur along depositional surfaces at each hierarchical level but generally have greater continuity and extent at larger lengthscales of the hierarchy (e.g., Gani and Bhattacharya;<ref name=GB07 /> Lee et al.;<ref>Lee, K., M. D. Gani, G. A. McMechan, J. P. Bhattacharya, S. Nyman, and X. Zeng, 2007, [http://archives.datapages.com/data/bulletns/2007/02feb/BLTN05114/BLTN05114.HTM Three-dimensional facies architecture and three-dimensional calcite concretion distributions in a tide-influenced delta front, Wall Creek Member, Frontier Formation, Wyoming]: AAPG Bulletin, v. 91, no. 2, p. 191–214, doi: 10.1306/08310605114.</ref> Ahmed et al.<ref name=Ahmd2014>Ahmed, S., J. P. Bhattacharya, D. Garza, and L. Giosan, 2014, Facies architecture and stratigraphic evolution of a river-dominated delta front, Turonian Ferron Sandstone, Utah, USA: Journal of Sedimentary Research, v. 84, no. 2, p. 97–121, doi: 10.2110/jsr.2014.6.</ref>). Thus, delta lobes tend to be overlain across flooding surfaces by prodelta shales and distal-delta-front heteroliths, which may cause them to behave as distinct reservoir zones that can be correlated between wells, whereas clinoforms are associated with heterogeneity between wells and within reservoir zones (e.g., Ainsworth et al.,;<ref name=Answrth1999 /> Hampson et al.<ref name=Hmpsn2008 />).

Clinoforms occur at a wide range of spatial scales, from large, basinward-dipping surfaces at the shelf-slope margin, to smaller surfaces associated with progradation of deltaic and shoreface systems across the shelf (e.g., Helland-Hansen and Hampson<ref name=HHH>Helland-Hansen, W., and G. J. Hampson, 2009, Trajectory analysis: Concepts and applications: Basin Research, v. 21, no. 5, p. 454–483, doi: 10.1111/j.1365-2117.2009.00425.x.</ref>). This study focuses on developing a surface-based approach to represent clinoforms at any lengthscale in reservoir models, with emphasis on clinoforms produced by the progradation of deltaic, barrier-island, and strandplain shorelines, which are typically up to a few tens of meters in height. The 3-D geometry and spatial arrangement of shoreline-scale clinoforms reflect in large part the process regime under which they were deposited (e.g., Galloway<ref name=Glwy>Galloway, W. E., 1975, Process framework for describing the morphological and stratigraphic evolution of deltaic depositional systems, in M. L. Broussard, ed., Deltas, models for exploration: Houston, Texas, Houston Geological Society, p. 87–98.</ref>). Fluvial-dominated deltas exhibit a hierarchy of point-sourced, teardrop-shaped sediment bodies that are fed via a downstream branching network of [[distributary channels]]. From small to large lengthscales, this hierarchy consists of mouth bars, mouth-bar assemblages, and delta lobes<ref name=Bhttchry2006>Bhattacharya, J. P., 2006, Deltas, inH. W. Posamentier, and R. Walker, eds., Facies models revisited: SEPM Special Publication 84, p. 237–292.</ref> (equivalent to the jet-plume deposits, jet-plume-complex deposits, and delta lobes of Wellner et al.<ref name=Wllnr2005>Wellner, R., R. Beaubouef, J. C. Van Wagoner, H. H. Roberts, and T. Sun, 2005, Jet-plume depositional bodies—The primary building blocks of Wax Lake delta: Transactions of the Gulf Coast Association of Geological Societies, v. 55, p. 867–909.</ref>). Sediment-body geometry is modified by the action of waves and tides, which respectively tend to result in shoreline-parallel and shoreline-perpendicular sediment transport that suppresses branching and switching of distributary channels (e.g., Galloway;<ref name=Glwy /> Willis;<ref >Willis, B. J., 2005, Deposits of tide-influenced river deltas, in L. Giosan, and J. P. Bhattacharya, eds., River deltas—Concepts, models, and examples: SEPM Special Publication 83, p. 87–129.</ref> Bhattacharya;<ref name=Bhttchry2006 /> Plink-Björklund<ref>Plink-Björklund, P., 2012, Effects of tides on deltaic deposition: Causes and responses: Sedimentary Geology, v. 279, p. 107–133, doi: 10.1016/j.sedgeo.2011.07.006.</ref>). Clinoforms exist as a preserved record of sediment-body morphologies at each of these hierarchical lengthscales (e.g., Gani and Bhattacharya<ref name=GB07>Gani, M. R., and J. P. Bhattacharya, 2007, Basic building blocks and process variability of a Cretaceous delta: Internal facies architecture reveals a more dynamic interaction of river, wave, and tidal processes than is indicated by external shape: Journal of Sedimentary Research, v. 77, no. 4, p. 284–302, doi: 10.2110/jsr.2007.023.</ref>) but are most commonly described at the scale of delta lobes in outcrop and high-resolution, shallow seismic data. For example, in Pleistocene fluvial-dominated delta deposits imaged in shallow-seismic data, Roberts et al.<ref name=Rbrts2004>Roberts, H. H., R. H. Fillon, B. Kohl, J. M. Robalin, and J. C. Sydow, 2004, Depositional architecture of the Lagniappe delta; sediment characteristics, timing of depositional events, and temporal relationship with adjacent shelf-edge deltas, in J. B. Anderson, and R. H. Fillon, eds., Late Quaternary stratigraphic evolution of the northern Gulf of Mexico margin: Tulsa, Oklahoma, SEPM Special Publication 79, p. 143–188.</ref> comment that “each clinoform set represents rather continuous deposition from a distributary or related set of distributaries, resulting in the formation of a delta lobe.” Shale drapes and cemented concretionary layers occur along depositional surfaces at each hierarchical level but generally have greater continuity and extent at larger lengthscales of the hierarchy (e.g., Gani and Bhattacharya;<ref name=GB07 /> Lee et al.;<ref>Lee, K., M. D. Gani, G. A. McMechan, J. P. Bhattacharya, S. Nyman, and X. Zeng, 2007, [http://archives.datapages.com/data/bulletns/2007/02feb/BLTN05114/BLTN05114.HTM Three-dimensional facies architecture and three-dimensional calcite concretion distributions in a tide-influenced delta front, Wall Creek Member, Frontier Formation, Wyoming]: AAPG Bulletin, v. 91, no. 2, p. 191–214, doi: 10.1306/08310605114.</ref> Ahmed et al.<ref name=Ahmd2014>Ahmed, S., J. P. Bhattacharya, D. Garza, and L. Giosan, 2014, Facies architecture and stratigraphic evolution of a river-dominated delta front, Turonian Ferron Sandstone, Utah, USA: Journal of Sedimentary Research, v. 84, no. 2, p. 97–121, doi: 10.2110/jsr.2014.6.</ref>). Thus, delta lobes tend to be overlain across flooding surfaces by prodelta shales and distal-delta-front heteroliths, which may cause them to behave as distinct reservoir zones that can be correlated between wells, whereas clinoforms are associated with heterogeneity between wells and within reservoir zones (e.g., Ainsworth et al.,;<ref name=Answrth1999 /> Hampson et al.<ref name=Hmpsn2008 />).

The clinoform-modeling algorithm developed here is simple to use, requiring specification of only a few input parameters: (1) the upper and lower surfaces that define the rock volume within which the clinoforms are to be modeled; (2) the plan-view geometry of clinoforms; (3) clinoform geometry in depositional-[[dip]]-oriented [[cross section]]; and (4) spacing and progradation direction of the clinoforms. The user can also use a stochastic component of the clinoform-modeling algorithm if there are uncertainties in the parameter values to be used.

The clinoform-modeling algorithm developed here is simple to use, requiring specification of only a few input parameters: (1) the upper and lower surfaces that define the rock volume within which the clinoforms are to be modeled; (2) the plan-view geometry of clinoforms; (3) clinoform geometry in depositional-[[dip]]-oriented [[cross section]]; and (4) spacing and progradation direction of the clinoforms. The user can also use a stochastic component of the clinoform-modeling algorithm if there are uncertainties in the parameter values to be used.