Abstract Presented here are cyclostratigraphic time-series data, using magnetic susceptibility (χ) results from Devonian Moroccan rocks to establish a floating-point age chronology, and a method that can be applied to any geological stage using geochemical or geophysical datasets as a climate proxy. The χ data are fit to an independent uniform climate model for the entire Eifelian Stage. The procedure used comprised: (a) definition of a uniform c. 405 kyr eccentricity climate model for the Eifelian, with a published duration for the Eifelian; and (b) graphical testing of the model using χ data derived from outcrop samples, here including data from the Global Boundary Stratotype Section and Point for the Emsian–Eifelian and Eifelian–Givetian stage boundaries, and an overlapping succession from Bou Tchrafine, Morocco. The time-series methods used here identify χ cycles that conform to the c. 405 kyr by graphically comparing the χ zonation with the climate model. Well-established conodont zonations developed using graphic correlation are then compared with this model, allowing time estimates for Eifelian conodont zone ranges. The time-series data indicate that the Eifelian Stage in the Middle Devonian lasted for c. 6.28 myr, the Lower Eifelian Choteč bio-event lasted for c. 600 kyr, and the Kačák bio-event in the Upper Eifelian lasted for c. 370 kyr.

Abstract Applying time-series analyses using Fourier transform and multi-taper methods to low-field, mass-specific magnetic susceptibility (χ) measurements on marine samples from well-studied shale and limestone outcrops of the Upper Ordovician (Edenian Stage; Upper Katian) Kope Formation, northern Kentucky, corroborates direct visual identification in outcrops of Milankovitch eccentricity ( c. 405 and 100 ka), obliquity and precessional climate cycles. Because individual outcrops were too short and deposition too chaotic to yield significant time-series results, it was necessary to build a c. 50 m thick composite sequence from three well-correlated outcrops to quantify the cyclicity. Time-series analysis was then performed using χ measured for 1004 closely spaced samples covering the section. Milankovitch bands are recorded in the time-series data from the composite. We tested this result by comparison of these bands to cyclic packages in outcrop, which correspond to thicknesses represented in the time-series datasets. This is particularly well defined for the eccentricity and obliquity cycles, with precessional bands being evident but as less well-defined packages of beds.

Abstract Here we establish a magnetostratigraphy susceptibility zonation for the three Middle Permian Global boundary Stratotype Sections and Points (GSSPs) that have recently been defined, located in Guadalupe Mountains National Park, West Texas, USA. These GSSPs, all within the Middle Permian Guadalupian Series, define (1) the base of the Roadian Stage (base of the Guadalupian Series), (2) the base of the Wordian Stage and (3) the base of the Capitanian Stage. Data from two additional stratigraphic successions in the region, equivalent in age to the Kungurian–Roadian and Wordian–Capitanian boundary intervals, are also reported. Based on low-field, mass specific magnetic susceptibility (χ) measurements of 706 closely spaced samples from these stratigraphic sections and time-series analysis of one of these sections, we (1) define the magnetostratigraphy susceptibility zonation for the three Guadalupian Series Global boundary Stratotype Sections and Points; (2) demonstrate that χ datasets provide a proxy for climate cyclicity; (3) give quantitative estimates of the time it took for some of these sediments to accumulate; (4) give the rates at which sediments were accumulated; (5) allow more precise correlation to equivalent sections in the region; (6) identify anomalous stratigraphic horizons; and (7) give estimates for timing and duration of geological events within sections.

Abstract Magnetic susceptibility (MS) measurements of marine rocks provide an underutilized but powerful high-resolution tool in stratigraphy. In ideal circumstances and when combined with other stratigraphic techniques, the method can yield resolution to 10,000 years or less. This paper applies the MS method to solving a Cretaceous global correlation problem. Because of the active global processes that drove significant evolutionary changes during this time, the Upper Cretaceous is important in Earth history. However, correlations among geological sequences are difficult, in part because Earth’s magnetic polarity was essentially non-varying from the Aptian to the Santonian. Here we present high-resolution correlations for Upper Cretaceous marine sedimentary successions spanning all or part of the Santonian Stage from the Western Interior Seaway (U.S.A.) and the Western Sinai Peninsula (Egypt). To do this we have integrated the results of magnetic susceptibility (MS) measurements of unoriented samples from lithified marine rocks (in outcrop and from core) and biostratigraphic data sets from these sequences. In this study a MS zonation for the Santonian Stage has been developed and graphic comparison has been used for correlation. In the main, correlation between the U.S. and Egyptian sequences is excellent. Third order T/ R cycles (> 100 kyr) observed in this high-resolution data set for the Santonian Stage indicate significant similarities between the U.S. and Egyptian sections and allow correlation among sequences. We interpret these correlations to result from cyclicities caused by climate-controlled continental erosion and deposition of detrital components, mainly clay, in the marine realm. Second-order cycles (> 1 Myr) are also observed in these data sets but show distinctive differences between the U.S. and Egyptian sequences. We interpret these second-order differences to result from local synsedimentary tectonic controls on sediment erosion and deposition. Also observed are two distinct, short-term MS marker events that can be correlated globally. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 155–166.

Abstract The magnetostratigraphy susceptibility technique is used to establish high-resolution correlation among Paleocene–Eocene boundary sequences in Egypt, Spain, and the U.S.A. This work initially focuses on the Global boundary Stratotype Section and Point (GSSP), defining the base of the Ypresian Stage (lowest Eocene), located in the Dababiya Quarry near Luxor in Upper Egypt. The base of the Eocene represents the beginning of the Paleocene–Eocene Thermal Maximum (PETM) identified by a negative carbon isotope (δ 13 C) excursion. While onset of the CIE is somewhat gradual in most reported Paleocene–Eocene (P–E) sections, at the GSSP it is very abrupt and begins immediately after an unusual lithologic change that magnetic susceptibility (MS) and other data indicate represents a short erosional or nondepositional hiatus. Comparison of MS zones from five well-studied marine sequences (the Dababiya Quarry GSSP, Jebal El Qreiya, also in Upper Egypt, Zumaia in northern Spain, Alamedilla in southern Spain, and the MGS-1 Harrell Core from southeastern Mississippi, U.S.A.) with that from the GSSP site shows a period of reduced sedimentation and nondeposition through the boundary interval in the GSSP. This interval, estimated to have lasted for ~ 10,000 years, is less than the biostratigraphic resolution for the site. Due to the hiatus in the GSSP, we have chosen the P–E section in Zumaia as the MS reference section for the P–E boundary interval. Because the correlation between the Zumaia section in Spain and the MGS-1 Core from the U.S.A. is excellent, and because the MGS-1 data set represents a longer interval of time than does the Zumaia data set, we use the MS data from the MGS-1 Core to extend the MS zones from Zumaia and establish a MS composite reference section (MS CRS) for the P–E boundary interval sampled. Orbital-forcing frequencies for the Zumaia reference section are then identified, via spectral analysis. Extending the MS zones into the MS CRS allows age assignment to MS zones for all five sections with a resolution of ~ 26,000 years. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 167–179.

High resolution stratigraphy is important in understanding sedimentary systems in the Gulf of Mexico basin. We have been using magnetic susceptibility measurements, a relatively new, abiotic method, to characterize global stratotype sections defined for the Paleogene and projecting that work into the Gulf Coast. When magnetic susceptibility is combined with chronostratigraphically calibrated biostratigraphic data, such as that provided by our ongoing multi-well Gulf of Mexico basin-wide graphic correlation project, very high resolution is possible. Here we show preliminary data for the Paleocene, including the Paleocene-Eocene boundary stratotype in Egypt, and use characteristic in that data to identify the boundary location in the Gulf Coast. The MGS-1 Harrell core (southeastern Mississippi) and the OSM-2 Wahalak core (southwestern Alabama) penetrate Wilcox “type” section, sampling member beds of the Clayton, Porters Creek, Naheola, Nanafalaya, Tuscahoma, and Hatchetigbee formations. Results of this investigation illustrate the potential utility of the methods for detailed stratigraphic studies in the Gulf Basin. We plan to extend our Gulf Basin magnetic susceptibility chronology through the Eocene in an effort to clarify unresolved stratigraphic problems in ultra deep-water Gulf of Mexico sediments of Paleocene and Eocene age that are important targets of the petroleum exploration industry. Of particular interest will be examination of the age and duration of the Eocene foraminiferal and calcareous nannofossil “barren interval” and the radiolarian zones identified within it.

Abstract The magnetic susceptibility of soils has been studied at a sanitary landfill site, where upward-fluxing methane gas has caused changes in the magnetic mineralogy of the capping soils. Soil used as a cap on the Hillsboro, Texas, sanitary landfill was put into place 1,10, and 20 years before sampling for this study. After 1 year in place, the susceptibility of the capping soil dropped below that of control samples not exposed to methane flux. Magnetic susceptibilities increased progressively from the control soils to the 10- and 20-year-old samples, with the highest values at depths of -40 cm below the soil surface. New authigenic minerals accumulated in landfill caps, with longer exposure to infiltration during reducing conditions producing greater magnetic effects. Calcite along with maghemite, the principal authigenic magnetic mineral, accumulated below the 40-cm level, iron and calcium having dissolved from the upper soil of the landfill cap. Calcite also accumulated during times of soil desiccation, forming a barrier to fluid transfer. Landfill caps that have distinct zonation of Fe(II) minerals beneath those of Fe(III) are likely to have a well-established CaCO 3 barrier that separates redox environments. Magnetic anomalies appear in capping soils exposed to high upward flux of methane and periodic infiltration of water, which produce a reducing environment favorable to the growth of magnetotactic bacteria. When the level of microbial catalysis is high, Fe(II) dissolved from the upper levels is transported deeper into the soil where it can reprecipitate as magnetic oxide or sulfide. Precipitation of nonmagnetic Fe(II) phases during wet winters followed by oxidation to magnetic phases during dry summers may take place, as observed in normal soils. Our study demonstrates that sanitary landfills can be used as convenient laboratories for studies of natural soil magnetism and are effective model systems for the study of magnetic effects in soils above areas of light hydrocarbon flux, such as petroleum reservoirs.