Diagenetic modeling of siliciclastic systems: Status report

Basin analysis (the reconstruction of the dynamics and history of sedimentary basins) has entered a quantitative stage that requires analytical lithologic data. These data must include geologic parameters that describe the characteristics of sediments and the diagenetic changes that they undergo through time. Diagenesis is controlled by eight geologic parameters: sediment composition, temperature history, rate of accommodation (subsidence + sea-level changes + sediment compaction), rate of sediment accumulation, age (time that sediments have been exposed to other variables), internal sediment-body architecture (sedimentary texture and structure), sediment-body external geometry, and fluid chemistry and flow history. Tectonic and paleogeographic settings determine the primary compositions of both chemical and siliciclastic sediments. Siliciclastic provenances are reflected by the mineralogy of sandstones. The source or sources of sediment in sandstone units within genetic sequences and the contribution of each source need to be evaluated in terms of quantitative effects on the various diagenetic styles observed. With the use of modern settings as partial analogues, stratigraphic, sedimentologic, and petrographic data can be used to reconstruct sandstone architecture and to draw inferences about original pore fluid chemistry. Subsidence histories, isotopic signatures, trace element compositions, and fluid inclusion studies combined with petrographic observations can be used to set constraints on the geologic parameters for sandstone bodies within a time-temperature-basin setting framework. As more insight is gained into the reaction kinetics within specific paleotectonic and depositional settings, diagenetic modeling will become increasingly more quantitative and precise

Diagenetic modeling of siliciclastic systems: Status report

Basin analysis (the reconstruction of the dynamics and history of sedimentary basins) has entered a quantitative stage that requires analytical lithologic data. These data must include geologic parameters that describe the characteristics of sediments and the diagenetic changes that they undergo through time. Diagenesis is controlled by eight geologic parameters: sediment composition, temperature history, rate of accommodation (subsidence + sea-level changes + sediment compaction), rate of sediment accumulation, age (time that sediments have been exposed to other variables), internal sediment-body architecture (sedimentary texture and structure), sediment-body external geometry, and fluid chemistry and flow history. Tectonic and paleogeographic settings determine the primary compositions of both chemical and siliciclastic sediments. Siliciclastic provenances are reflected by the mineralogy of sandstones. The source or sources of sediment in sandstone units within genetic sequences and the contribution of each source need to be evaluated in terms of quantitative effects on the various diagenetic styles observed. With the use of modern settings as partial analogues, stratigraphic, sedimentologic, and petrographic data can be used to reconstruct sandstone architecture and to draw inferences about original pore fluid chemistry. Subsidence histories, isotopic signatures, trace element compositions, and fluid inclusion studies combined with petrographic observations can be used to set constraints on the geologic parameters for sandstone bodies within a time-temperature-basin setting framework. As more insight is gained into the reaction kinetics within specific paleotectonic and depositional settings, diagenetic modeling will become increasingly more quantitative and precise

Using the factors of soil formation to assess stable carbon isotope disequilibrium in late Pleistocene (MIS 3) buried soils of the Great Plains, North America

The stable carbon isotope composition of both soil organic matter (SOM) and pedogenic carbonate are widely used as paleoenvironmental proxies. This study utilizes δ13C analyses to reconstruct bioclimatic change from a series of buried soils in the central Great Plains of North America that developed between ca. 44–24 ka. Results revealed a paradoxical isotopic disequilibrium between the isotopic composition of bulk SOM (δ13CSOM) and pedogenic carbonate (δ13Ccarb). Specifically, Δ13C values are 0.1 to 6.3 per mil greater than the highest expected equilibrium value of 17 per mil in the Bk horizons. In contrast, Δ13C values are 0.1 to 4.8 per mil lower than the lowest expected equilibrium value of 14 per mil in the Ak horizons. A soil-forming factor approach was utilized to establish multiple working hypotheses regarding the influence of climate, vegetation, parent material, and time on the observed isotopic disequilibrium. Of the various hypotheses presented, we suggest that the following most likely explain the observed isotopic disequilibrium. The greater-than-expected Δ13C values in the Bk horizons most likely reflects seasonal bias in pedogenic carbonate formation, resulting in an apparent C4-biased signal. The lower-than-expected Δ13C values in the Ak horizons remains perplexing. The most likely explanation is that detrital carbonate contributions affected the δ13Ccarb record or that the δ13Ccarb and δ13CSOM records are asynchronous. Overall, it appears that different factors have affected the δ13CSOM and δ13Ccarb records independently and therefore results of this study highlight the importance of assessing pedogenic carbonates for isotopic equilibrium as well as the need to understand past environmental conditions (i.e., soil-forming factors) when interpreting isotopic trends

Bedrock geology of southwest Iowa, Digital geologic map of Iowa, Phase 5: Southwest Iowa

https://ir.uiowa.edu/igs_ofm/1028/thumbnail.jp

Precambrian nomenclature in Kansas

The informal stratigraphic term “Precambrian” is replaced by formal nomenclature—Proterozoic and Archean Eonothems/Eons—and the informal term Hadean. The Phanerozoic Eonothem/Eon, representing all rocks younger than the Proterozoic, is added. The Proterozoic is further divided into Paleoproterozoic, Mesoproterozoic, and Neoproterozoic Erathems/Eras. The name Rice Formation (Scott, 1966) is abandoned, and the use of the informal term “Rice unit” is recommended. The proposed name Rice Series (Berendsen, 1994) is not accepted. These changes are adopted by the Kansas Geological Survey (KGS) and the stratigraphic nomenclature of Zeller (1968) has been revised accordingly

Clarification and Changes in Permian Stratigraphic Nomenclature in Kansas

This paper outlines Permian nomenclature changes to Zeller (1968) that have been adopted by the Kansas Geological Survey. The Permian System/Period, Cisuralian Series/Epoch, and Asselian Stage/Age are established at the base of the Bennett Shale Member of the Red Eagle Limestone. Series/epoch names Wolfcampian, Leonardian, and Guadalupian are retained and usage of Gearyan, Cimarronian, and Custerian is abandoned. The repositioned Carboniferous-Permian boundary divides the Council Grove Group into Carboniferous (Upper Pennsylvanian Series/Epoch; Virgilian Stage/Age) and Permian (Wolfcampian Series/Epoch) segments

New Stratigraphic Rank for the Carboniferous, Mississippian, and Pennsylvanian in Kansas

A new classification for the Carboniferous System/Period is formally adopted by the Kansas Geological Survey (KGS), and Zeller (1968) is modified accordingly. The Carboniferous is the system/period between the Devonian and Permian, and the Mississippian and Pennsylvanian are subsystems/subperiods of the Carboniferous. The Mississippian is subdivided into Lower, Middle, and Upper Mississippian Series and the Pennsylvanian is subdivided into Lower, Middle, and Upper Pennsylvanian Series. Regional stage names remain unchanged

Surficial geologic materials of the Marion Quadrangle, Iowa

https://ir.uiowa.edu/igs_ofm/1002/thumbnail.jp

Surficial geologic materials of Linn County, Iowa

https://ir.uiowa.edu/igs_ofm/1009/thumbnail.jp

Surficial geologic materials of the Bertram Quadrangle, Iowa

https://ir.uiowa.edu/igs_ofm/1008/thumbnail.jp