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'''Geometrical analysis''' is simply dividing a basin's sedimentary section into three-dimensional bodies of strata using regionally correlative surfaces or features as boundaries. The [[sequence stratigraphy|sequence stratigraphi]]c approach uses unconformities or other genetically significant features to divide the section into [[depositional sequences]], [[Systems_tracts_and_trap_types|systems tracts]], and/or [[Hierarchy of sequences|parasequence]]s. Recognizing these correlation features is key to identifying depositional sequences properly.

'''Geometrical analysis''' is simply dividing a basin's sedimentary section into three-dimensional bodies of strata using regionally correlative surfaces or features as boundaries. The [[sequence stratigraphy|sequence stratigraphi]]c approach uses [[Unconformity|unconformities]] or other genetically significant features to divide the section into [[depositional sequences]], [[Systems_tracts_and_trap_types|systems tracts]], and/or [[Hierarchy of sequences|parasequence]]s. Recognizing these correlation features is key to identifying depositional sequences properly.

==Procedure==

==Procedure==

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| Identify unconformities (third-order sequence boundaries) in seismic sections, outcrop sections, and regional well log sections.

| Identify [[Unconformity|unconformities]] (third-order sequence boundaries) in seismic sections, outcrop sections, and regional well log sections.

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==Identifying unconformities==

==Identifying unconformities==

Unconformities are [[Hierarchy of sequences|third-order]] sequence boundaries. They are generally regional onlap surfaces. In ''basinal settings'', they are characterized by onlap of [[allochthon]]ous deposits (i.e., debris flows, slump deposits, turbidites), [[Well_log_sequence_analysis#Parasequence_stacking_patterns|prograding]] deltas, carbonate platform deposits, or evaporites. In ''shallow-water or nonmarine settings'', they are characterized by onlap of strata deposited in fluvial, deltaic, or nearshore marine or peritidal environments.<ref name=ch21r48>Weber, L., J., Sarg, J., F., Wright, F., M., 1995, Sequence stratigraphy and reservoir delineation of the middle Pennsylvanian (Desmoinesian), Paradox basin and Aneth field, southwestern U., S., A., in Read, J., F., Weber, L., J., Sarg, J., F., Wright, F., M., eds., Milankovitch Sea-Level Changes, Cycles, and Reservoirs on Carbonate Platforms in Greenhouse and Ice-House Worlds: SEPM Short Course No. 35, 79 p.</ref> We can identify unconformities using stratigraphic evidence and individual well evidence.

[[Unconformity|Unconformities]] are [[Hierarchy of sequences|third-order]] sequence boundaries. They are generally regional onlap surfaces. In ''basinal settings'', they are characterized by onlap of [[allochthon]]ous deposits (i.e., debris flows, slump deposits, turbidites), [[Well_log_sequence_analysis#Parasequence_stacking_patterns|prograding]] deltas, carbonate platform deposits, or evaporites. In ''shallow-water or nonmarine settings'', they are characterized by onlap of strata deposited in fluvial, deltaic, or nearshore marine or peritidal environments.<ref name=ch21r48>Weber, L., J., Sarg, J., F., Wright, F., M., 1995, Sequence stratigraphy and reservoir delineation of the middle Pennsylvanian (Desmoinesian), Paradox basin and Aneth field, southwestern U., S., A., in Read, J., F., Weber, L., J., Sarg, J., F., Wright, F., M., eds., Milankovitch Sea-Level Changes, Cycles, and Reservoirs on Carbonate Platforms in Greenhouse and Ice-House Worlds: SEPM Short Course No. 35, 79 p.</ref> We can identify unconformities using stratigraphic evidence and individual well evidence.

===Stratigraphic evidence===

===Stratigraphic evidence===

[[file:exploring-for-stratigraphic-traps_fig21-16.png|300px|thumb|{{figure number|1}}. Copyright: Dolson and Piombino, 1994; courtesy Rocky Mountain Assoc. of Geologists.]]

[[file:exploring-for-stratigraphic-traps_fig21-16.png|300px|thumb|{{figure number|1}}. Copyright: Dolson and Piombino, 1994; courtesy Rocky Mountain Assoc. of Geologists.]]

Cores and samples should be examined for evidence of unconformities. These unconformity surfaces should then be calibrated to logs. Logs can then be used to correlate the surfaces to seismic and to other wells. [[:file:exploring-for-stratigraphic-traps_fig21-16.png|Figure 1]]<ref name=ch21r12>DolsonMuller, D., S., 1994, Stratigraphic evolution of the Lower Cretaceous Dakota Group, Western Interior, U., S., A., in Caputo, M., V., Peterson, J., A., Franczyk, K., J., eds., Mesozoic Systems of the Rocky Mountain Region, U., S., A.: SEPM Rocky Mountain Section, p. 441–456.</ref> shows an example of calibrating unconformity evidence from cores to logs. The Lower Cretaceous Cutbank Sandstone unconformably overlies the Jurassic Swift Formation. A major lowstand surface of erosion (LSE) is shown at [[depth::2957 ft]] (901 m) and was identified using the following criteria:

Cores and samples should be examined for evidence of [[Unconformity|unconformities]]. These unconformity surfaces should then be calibrated to logs. Logs can then be used to correlate the surfaces to seismic and to other wells. [[:file:exploring-for-stratigraphic-traps_fig21-16.png|Figure 1]]<ref name=ch21r12>DolsonMuller, D., S., 1994, Stratigraphic evolution of the Lower Cretaceous Dakota Group, Western Interior, U., S., A., in Caputo, M., V., Peterson, J., A., Franczyk, K., J., eds., Mesozoic Systems of the Rocky Mountain Region, U., S., A.: SEPM Rocky Mountain Section, p. 441–456.</ref> shows an example of calibrating unconformity evidence from cores to logs. The Lower Cretaceous Cutbank Sandstone unconformably overlies the Jurassic Swift Formation. A major lowstand surface of erosion (LSE) is shown at [[depth::2957 ft]] (901 m) and was identified using the following criteria:

* Missing [[Biostratigraphic correlation and age determination|biostratigraphic]] horizons

* Missing [[Biostratigraphic correlation and age determination|biostratigraphic]] horizons