Paper No. 42-2
Presentation Time: 9:15 AM
PALEOCLIMATIC AND PALEOENVIRONMENTAL RECONSTRUCTION OF THE LATE PALEOZOIC ICE AGE IN AN EQUATORIAL SETTING: INTERPRETATIONS FROM CARBONIFEROUS PALEOSOLS AT JOGGINS FOSSIL CLIFFS, NOVA SCOTIA, CANADA
The UNESCO World Heritage Joggins Fossil Cliffs of Nova Scotia are famous for exceptionally well-preserved fossil standing trees of Pennsylvanian Age, and constitute one of the best-known records of the Late Paleozoic Ice Age (LPIA) in an equatorial setting. Although the fluvial sedimentology and stratigraphy are well-known for this 5 km thick succession, which was deposited in 3-4 m.y. in a rapidly subsiding basin and now exposed along 20 km of coastline, modern research involving paleosols is currently lacking. Preliminary research results suggest major variations in soil drainage, which are either caused by episodic changes in tectonic subsidence or changes in the overall equatorial climate during this period of time. The four units examined (Boss Point Fm., Little River Fm., Joggins Fm., and Spring Hill Fm., in ascending stratigraphic order) show repetitive alternations of: (1) successively more poorly-drained soil conditions, with very gley, gray-green reduced mudstone/siltstone paleosols and abundant pedogenic and early diagenetic siderite nodules precipitating around remnant roots, and (2) better-drained soil conditions, with better-developed soils, including red, slickensided paleo-Vertisols and red siltstone paleosols, greater overall oxidation, and pedogenic calcium carbonate nodules. We favor the hypothesis that these cycles of successively more poorly-drained and better-drained soils are a high-resolution record of episodes of Gondwanan ice-sheet (GIS) expansion and contraction, respectively. During episodes of GIS expansion, the Inter-Tropical Convergence Zone (ITCZ) narrowed at the equator, bringing more precipitation and more permanent water saturation, and impeded drainage processes. During episodes of contraction of the GIS, the ITCZ had a much wider zone of influence, causing less water-saturated soil conditions, although the climate likely remained humid; soils thus experienced more episodes of aeration and drainage, which allowed for better development and effects of seasonal shrink-swell processes. We propose that the study of paleosols at Joggins will provide the first high-resolution record of the LPIA in an equatorial setting, and will help better constrain and understand climate evolution during this period of time in a very rapidly subsiding equatorial basin.