Abstract
Meteoric alteration of marine delta (super 13) C (sub carb) below subaerial unconformities; Paleozoic examples across a range of spatial and temporal scales
Abstracts with programs - Geological Society of America, Vol.51(5)
Geological Society of America, 2019 annual meeting & exposition
09/2019
DOI: 10.1130/abs/2019AM-340553
Abstract
Despite decades of study, the interpretation of the carbon isotope record preserved in carbonate successions continues to be highly debated, particularly in regard to the effects of meteoric diagenesis on primary marine delta (super 13) C (sub carb) . Studies of Recent carbonates that show substantial modification of fabrics and chemical composition through processes related to subaerial exposure and shallow burial have introduced varying levels of uncertainty as to how delta (super 13) C (sub carb) values measured from ancient stratigraphic sequences should be interpreted. To better understand the signal origin of delta (super 13) C (sub carb) in ancient carbonates, we evaluate successions containing unconformities of varying scales, focusing on evidence for the modification of primary delta (super 13) C (sub carb) values by meteoric processes. Subhorizontal, shallowly buried Paleozoic carbonates along structural arches in the U.S. Midcontinent contain infilled paleokarst cavities and locally thick paleosols preserved at unconformity surfaces, that range between a few hundred thousand to millions of years in duration. Here we present multiple high-resolution delta (super 13) C (sub carb) and delta (super 18) O (sub carb) profiles across several unconformities to evaluate the resetting of primary values. While we document distinct negative shifts in the range of -2 to -10 ppm, cements bearing these values are generally minor and highly localized. In an extreme example, delta (super 13) C (sub carb) negative shifts below the high-relief, 40 million-year-duration Walbridge Unconformity are relatively minor and generally restricted to rock clearly affected by paleo-weathering. Surprisingly, shorter duration subaerial surfaces associated with low-relief 3rd and 4th order depositional sequences show little evidence of delta (super 13) C (sub carb) modification. In fact, the largest delta (super 13) C (sub carb) shifts appear to be produced by marine diagenesis below unconformity surfaces through infilling of secondary porosity with younger marine cements and plugging of paleokarst features with transgressive sediments. Also noteworthy is the preservation of primary values and trends despite post-deposition dolomitization of some of these stratigraphic sections. Together, our extensive evaluation of subaerial unconformity surfaces testifies to the robust preservation of primary delta (super 13) C (sub carb) signatures in Paleozoic whole-rock carbonates.
Details
- Title: Subtitle
- Meteoric alteration of marine delta (super 13) C (sub carb) below subaerial unconformities; Paleozoic examples across a range of spatial and temporal scales
- Creators
- James J. Zambito - Beloit CollegePatrick I. McLaughlinAlyssa M. BancroftPoul Emsbo
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.51(5)
- Conference
- Geological Society of America, 2019 annual meeting & exposition
- Publisher
- Geological Society of America (GSA)
- DOI
- 10.1130/abs/2019AM-340553
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2019 annual meeting & exposition
- Language
- English
- Date published
- 09/2019
- Academic Unit
- Earth and Environmental Sciences; Iowa Geological Survey; IIHR--Hydroscience and Engineering
- Record Identifier
- 9984702715702771
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