View source for Facies map

{{publication 
 | image   = exploring-for-oil-and-gas-traps.png
 | width   = 120px
 | series  = Treatise in Petroleum Geology
 | title   = Exploring for Oil and Gas Traps
 | part    = Critical elements of the petroleum system
 | chapter = Sedimentary basin analysis
 | frompg  = 4-1
 | topg    = 4-123
 | author  = John M. Armentrout
 | link    = http://archives.datapages.com/data/specpubs/beaumont/ch04/ch04.htm
 | pdf     = 
 | store   = http://store.aapg.org/detail.aspx?id=545
 | isbn    = 0-89181-602-X
}}
[[file:FG11.JPG|thumb|400px|Facies map depicting Middle Jurassic paleogeography. 1 = deep-water deposits of the Lombardian Basin; 2 = Friuli and Bagnolo carbonate platforms; 3 = resedimented oolitic deposits of the Vajont Limestone (the arrow indicates the sense of direction of the gravity flows); 4 = deep-water deposits of the northern Adriatic Basin; 5 = condensed deposits of the Rosso Ammonitico Veronese (lower member). From Masetti et al.<ref name=Masettietal_2012>Masetti, Daniele, Roberto Fantoni, Roberta Romano, Dario Sartorio, and Enrico Trevisani, [http://archives.datapages.com/data/bulletns/2012/11nov/BLTN11087/BLTN11087.HTM Tectonostratigraphic evolution of the Jurassic extensional basins of the eastern southern Alps and Adriatic foreland based on an integrated study of surface and subsurface data]: AAPG Bulletin, v. 96, no. 11, p. 2065-2089.</ref>]]
==Purpose and procedure==

The purpose of a facies map is to reconstruct [[paleogeography]], from which we can predict [[reservoir]], [[seal]], and [[source rock]] distribution. Facies maps are made at an [http://en.wiktionary.org/wiki/isochronous isochronous] surface or within a coeval interval.<ref name=ch04r94>Tearpock, D., J., Bischke, R., E., 1991, Applied Subsurface Geologic Mapping: Prentice-Hall, 648 p.</ref><ref name=ch04r107>Visher, G., S., 1984, Exploration Stratigraphy: Tulsa, PennWell Books, 334 p.</ref> We map [[reservoir system]] thickness (1) to compare the distribution of reservoir-system thickness and field location and (2) to identify or predict locations with thick reservoirs and trapping conditions that are undrilled. A procedure for mapping facies is outlined in the table below.

{| class = "wikitable"
|-
! Step
! Action
|-
| 1
| Identify and correlate significant [[Isochron|isochronous]] surfaces throughout the [[depocenter]], integrating well data, [[Wikipedia:Bioevent|bioevents]], and [[Seismic interpretation|seismic reflection profile grids]].
|-
| 2
| Map areas of potential [[reservoir]] and [[seal]] [[Lithofacies|facies]] that occur between two isochronous surfaces.
|-
| 3
| Map [[Seismic facies mapping|seismic facies]] associated with that interval.
|-
| 4
| Plot important physiographic features, such as the [[shelf]]-[http://www.thefreedictionary.com/continental+slope slope] break or structurally controlled bathymetric highs.
|-
| 5
| Integrate all data into a depositional facies map.
|}

==Seismic facies profile==
<gallery mode=packed heights=200px widths=200px>
file:sedimentary-basin-analysis_fig4-36.png|{{figure number|1}}Interpreted seismic facies pattern for part of one seismic reflection profile down the axis of the High Island-East Breaks depocenter. After Armentrout.<ref name=ch04r6>Armentrout, J., M., 1987, Integration of biostratigraphy and seismic stratigraphy: Pliocene–Pleistocene, Gulf of Mexico: Proceedings, Gulf Coast Section SEPM 8th Annual Research Conference, p. 6–14.</ref> Copyright: Gulf Coast SEPM.
file:sedimentary-basin-analysis_fig4-27.png|{{figure number|2}}Seismic reflection profile schematic. From Armentrout<ref name=ch04r6 />; courtesy Gulf Coast SEPM.
file:sedimentary-basin-analysis_fig4-29.png|{{figure number|3}}Biofacies maps of the study area in the Gulf of Mexico. After Armentrout.<ref name=ch04r7 /><ref name=ch04r9 /> Copyright: Springer-Verlag, Geological Society of London.
file:sedimentary-basin-analysis_fig4-37.png|{{figure number|4}}Map of the seismic facies of ''Glob alt'' low stand interval.
file:sedimentary-basin-analysis_fig4-38.png|{{figure number|5}}Net sand distribution of shelf areas contoured parallel to the shelf edge and slope areas contoured parallel to the depositional dip of the slope valleys down which the sand was transported.
</gallery>

[[:file:sedimentary-basin-analysis_fig4-36.png|Figure 1]] is the interpreted [[Seismic facies mapping|seismic facies]] pattern for part of one [[Seismic interpretation|seismic reflection profile]] down the axis of the High Island-East Breaks [[depocenter]].<ref name=ch04r7>Armentrout, J., M., 1991, Paleontological constraints on depositional modeling: examples of integration of biostratigraphy and seismic stratigraphy, Pliocene–Pleistocene, Gulf of Mexico, in Weimer, P., Link, M., H., eds., Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems: New York, Springer-Verlag, p. 137–170.</ref> This is the same seismic profile shown in [[:file:sedimentary-basin-analysis_fig4-27.png|Figure 2]].

Each [[Well_log_sequence_analysis#Parasequence_stacking_patterns|prograding]] [http://unterm.un.org/DGAACS/unterm.nsf/8fa942046ff7601c85256983007ca4d8/6d701a3f58b3c00d852570d70052c711?OpenDocument clinoform] contains a rotated package of chaotic facies within the upper and steepest part of the clinoform facies and basinward of the tabular facies. The clinoform facies is [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=onlap onlapped] by parallel, moderate-amplitude, onlapping reflections of the onlap-fill facies, which are subsequently [http://www.glossary.oilfield.slb.com/en/Terms/d/downlap.aspx downlapped] onto by the next overlying prograding clinoform. In a broader sense, the drape facies below these clinoforms and the ''Glob N'' datum represent basinal deposits; the clinoform and onlapping-fill facies represent [http://www.thefreedictionary.com/continental+slope slope] deposits; and the overlying tabular facies above the clinoforms and the ''Glob M'' datum represent shelf deposits—all part of a basin-filling succession.

Associated foraminiferal [[Fossil assemblage|biofacies]] shown in [[:file:sedimentary-basin-analysis_fig4-27.png|Figure 2]] and [[:file:sedimentary-basin-analysis_fig4-29.png|Figure 3]] support this analysis. The ''Glob alt'' sequence is the fourth clinoform from the right, the fourth-most basinward of five oblique clinoforms that toplap along a common horizon. Superjacent clinoforms show progressively more topset deposition forming sigmoidal clinoforms, suggesting relative rise of sea level (with consistent widespread increase in accommodation space). Observations of seismic facies from a single phase of deposition, such as lowstand or highstand, are recorded on a map and contoured to convey the distribution of each seismic facies ([[:file:sedimentary-basin-analysis_fig4-37.png|Figures 4]] and [[:file:sedimentary-basin-analysis_fig4-38.png|5]]).

==Seismic facies map==
<gallery mode=packed heights=300px widths=300px>
sedimentary-basin-analysis_fig4-28.png|{{figure number|6}}Map of the seismic facies of the ''Glob alt'' low stand interval. After Armentrout.<ref name=ch04r7 /><ref name=ch04r9>Armentrout, J., M., 1996, [http://sp.lyellcollection.org/content/104/1/65.abstract High-resolution sequence biostratigraphy: examples from the Gulf of Mexico Plio–Pleistocene], in Howell, J., Aiken, J., eds., High Resolution Sequence stratigraphy: Innovations and Applications: The Geological Society of London Special Publication 104, p. 65–86.</ref> Copyright: Springer-Verlag, Geological Society of London.
sedimentary-basin-analysis_fig4-39.png|{{figure number|7}}An integrated data base for interpreting depositional environments. After Armentrout.<ref name=ch04r7 /> Copyright: Springer-Verlag.
</gallery>

[[:file:sedimentary-basin-analysis_fig4-37.png|Figure 4]] is a map of the seismic facies of the ''Glob alt'' lowstand interval ([[:file:sedimentary-basin-analysis_fig4-29.png|Figures 3]] and [[:file:sedimentary-basin-analysis_fig4-28.png|6]]). The mapped facies are observed in the interval immediately above the sequence boundary at the base of the ''Glob alt'' sequence in [[:file:sedimentary-basin-analysis_fig4-36.png|Figure 1]]. In the basin setting, the sequence boundary is, at seismic scale, essentially coincident with the underlying condensed section. The mapped facies are within the lowstand systems tract. Each observed facies is plotted along the transect of the seismic reflection profile, profile by profile. The area of shelf/slope inflection is plotted, based on the location of the inflection point between foreset and topset elements of the clinoform. [[Fossil assemblage|Biofacies]] information ([[:file:sedimentary-basin-analysis_fig4-29.png|Figure 3]]) and sediment type ([[:file:sedimentary-basin-analysis_fig4-38.png|Figure 5]]) can then be overlain on the seismic facies map to provide an integrated data base for interpreting depositional environments ([[:file:sedimentary-basin-analysis_fig4-39.png|Figure 7]]).

==Net sand map==
<gallery mode=packed heights=300px widths=300px>
file:sedimentary-basin-analysis_fig4-6.png|{{figure number|8}}Tectonic map of the GOM basin. Modified from Buffler;<ref name=Buffler1991>Buffler, R. T., 1991, Early evolution of the Gulf of Mexico basin, in D. Goldthwaite, ed., An Introduction to Central Gulf Coast Geology: New Orleans Geological Society, p. 1–16.</ref> courtesy New Orleans Geological Society.
file:sedimentary-basin-analysis_fig4-41.png|{{figure number|9}}Depositional strike seismic reflection profile across a valley.
</gallery>

Of the 240 wells used in the study area, 147 penetrated the ''Glob alt'' interval and provided information on the distribution of the net sand deposited within that interval. Using the net-sand values from the wells, we integrate the data with seismic facies maps within the ''Glob alt'' lowstand [[isochron]] and contour a net-sand isopach map ([[:file:sedimentary-basin-analysis_fig4-38.png|Figure 5]]). Contours are for areas with at least [[length::200 ft]] (60 m) of net sand. The sandstones occur mostly seaward of the age-equivalent physiographic shelf/slope break identified on the seismic-reflection profiles. Because most of the wells penetrated the ''Glob alt'' sequence basinward of the ''Glob alt'' shelf edge, the sandstones penetrated were most likely transported by gravityflow processes and deposited in environments on the slope and within intraslope basins.

The resulting map shows the net-sand distribution of shelf areas contoured parallel to the shelf edge and slope areas contoured parallel to the depositional dip of the slope valleys down which the sand was transported. The distribution of sand within the depositional dip-oriented isopachs is consistent with the regional pattern of downslope-oriented salt withdrawal valleys bounded by salt-cored anticlines ([[:file:sedimentary-basin-analysis_fig4-6.png|Figures 8]] and [[:file:sedimentary-basin-analysis_fig4-41.png|9]]). Note the lowstand position of the middle-to-outer neritic [[Fossil assemblage|biofacies]] boundary, below which few waves reach the sea floor. This results in downslope sand distribution being controlled by bottom currents alone.

==Depositional facies map==
The figure below is a depositional facies map for the ''Glob alt'' interval's basal sequence boundary, constructed by integrating the [[Fossil assemblage|biofacies]] map, the net sandstone map, and the seismic facies map ([[:file:sedimentary-basin-analysis_fig4-29.png|Figures 3]], [[:file:sedimentary-basin-analysis_fig4-38.png|5]], and [[:file:sedimentary-basin-analysis_fig4-37.png|4]], respectively).

The upper slope deposits consist of the clinoform facies and numerous areas of chaotic facies, including rotated-block packages deposited in middle neritic to upper bathyal water depths ([[:file:sedimentary-basin-analysis_fig4-36.png|Figures 1]], [[:file:sedimentary-basin-analysis_fig4-37.png|4]]). The shelf facies consist of a thin interval of tabular facies representing a mixed system of inner-to-middle neritic deposits, nonmarine coastal-plain deposits, and the erosional surface at the ''Glob alt'' sequence boundary. The basinal deposits consist of the drape and onlap-fill facies of bathyal hemipelagic mudstone that encase the sandstone-prone mounded facies of sediment gravity flow origin, indicated here by the > [[length::200 ft]] (> 60 m) sandstone isopach. The gravity-flow sandstones were deposited within slope valleys basinward of the physiographic shelf/slope break in deep middle neritic and deeper-water environments during falling and lowstand of sea level. The physiographic shelf/slope break is identified by the inflection point between the fore-set and the topset reflections of the clinoform.

==See also==
* [[Paleogeography]]
* [[Applying paleogeography to prospect identification]]
* [[Relating traps to paleogeography]]

==References==
{{reflist}}

==External links==
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* [http://archives.datapages.com/data/specpubs/beaumont/ch04/ch04.htm Original content in Datapages]
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[[Category:Critical elements of the petroleum system]] 
[[Category:Sedimentary basin analysis]]