Sedimentology of IODP 302 ACEX lithologic subunit 1/5 (the zebra interval) and implications for Arctic sediment source and deposition
Abstract
Sediment cores recovered from the Lomonosov Ridge on IODP Expedition 302, the Arctic Coring Expedition (ACEX), provided the first major insights into long-term Cenozoic history of climate and ocean conditions in the central Arctic. However, the ACEX record is hampered by a major hiatus or severely condense interval (depending on age-model interpretations) at 198.7 mcd separating the middle Eocene and Miocene records. Lithologic subunit 1/5 lies above this depth horizon, and is informally called the zebra interval because of distinctive stripes - black and gray tilted and cross-banded silty-clay layers, up to 3 cm thick that characterize the lower 2.5 m of the subunit. Prior studies provide strong micropaleontological evidence for a brackish, shallow water depositional environment below and across the hiatus, continuing into subunit 1/5; and the cross-banding suggest a high-energy shallow water setting conducive to reworking and erosion. In addition, prior studies place the hiatus and subunit 1/5 within an overall up-section transition from warmer to cooler temperatures with more persistent ice-rafting, and from restricted to more open water circulation. Given the paleoclimatic and paleoceaographic difference above and below this interval and its unique lithologic pattern, this study aims to better characterize the sedimentology of the black and gray couplets. 24 samples from the black and gray layers and 11 samples from above and below the zebra interval are being analyzed to characterize the XRF elemental composition, XRD bulk and clay mineral composition, coarse sand composition and abundance, and surface textures of quartz grains. These factors will be used to hypothesize about potential changes in source, transport, and depositional environment. On average, the black layers have more Fe, Co, Ni, K, P, As, Sr, and Mn, whereas gray layers have more Ti, but differences are not statistically significant. Preliminary XRD results show that the gray layers are more enriched in quartz, plagioclase, and muscovite, which may point to a difference in source. Results from our ongoing work on clay mineralogy, coarse sand composition and abundance, and quartz surface textures, will also be presented to further the comparison between the layers and infer source areas and patterns of deposition.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP23E1528H
- Keywords:
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- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICSDE: 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4926 Glacial;
- PALEOCEANOGRAPHYDE: 4954 Sea surface temperature;
- PALEOCEANOGRAPHY