Discriminating intra-parasequence stratigraphic units from two-dimensional quantitative parameters

ISLA, MANUEL F.; SCHWARZ, ERNESTO; VEIGA, GONZALO D.; ZUAZO, JERÓNIMO J.; REMIREZ M.

JOURNAL OF SEDIMENTARY RESEARCH - (Print)

SEPM-SOC SEDIMENTARY GEOLOGY

Lugar: Lawrence; Año: 2021

1527-1404

The intra-parasequence scale is still a relative unexplored territory within the highresolution sequence stratigraphy. Much knowledge has been produced regarding thestratigraphic architecture and bounding surfaces of parasequences, which led totrustworthy conceptual models about their evolution. However, the analysis of theinternal genetic units conforming parasequences has been commonly simplified to thedefinition of bedsets. Such simplification seems to be insufficient to cover thecomplexity involved in the wide timespan estimated for building individualparasequences (10 3 to 10 5 yrs.). Through an exhaustive architectural analysis,several types of intra-parasequence minor units were identified and characterizedwithin successive wave-dominated shoreface-shelf parasequences in the LowerCretaceous Pilmatué Member of the Agrio Formation in central Neuquén Basin. Thisintra-parasequence scale was established parting from the definition of parasequencesfollowed in previous contributions. Sedimentary attributes such as extension ofbounding surfaces, deepening degree registered across these boundaries, thickness,proportions of facies associations within the regressive interval and associatedtransgressive deposits were quantitatively analysed. Three different scales of geneticunits were defined based on this analysis: (1) sub-bedsets; (2) bedsets; (3) bedsetcomplexes. Each scale exhibits their own ranges of quantified attributes responding tothe hierarchy of processes during its evolution. Independently from how many scaleswere defined, the individual analysis and combination of sedimentary/stratigraphicattributes demonstrated being a consistent method for the recognition of intraparasequence genetic units. Obtained results indicate that the internal architecture ofparasequences may be highly complex, with more than one order of hierarchy and thecharacterization of contained genetic units require the exhaustive analysis of verticaland lateral variations. Also, the improvement on the understanding of the highresolution stratigraphy of wave-dominated shoreface-shelf systems offer the possibilityto compare them with modern shorelines.