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Geology Colloquium: Dan Lehrmann, Trinity University
November 8, 2018 @ 2:30 pm - 4:00 pmFree
Our KU Geology Colloquium guest on Thursday, November 8, will be Dan Lehrmann, Pyron Professor of Geoscience, Trinity University, and KU alumnus. He will present:
Basin-wide assessment of the factors controlling carbonate platform evolution: Triassic, Nanpanjiang Basin, South China
Colloquium will be held in the Beren Petroleum Center, Slawson Hall, with a reception at 2:30 p.m. followed by colloquium at 3:00 p.m. All are welcome to attend.
The Nanpanjiang Basin (NPJB) is a large, complex basin within the south China plate bordered by Precambrian uplifts on the northeast, southeast, and west and by a suture zone of possible Triassic convergence to the south. During the Permian and Triassic, the NPJB embayed the Yangtze Platform (YP) and contained several isolated carbonate platforms (IPs), including the Great Bank of Guizhou (GBG).
The NPJB presents an exceptional natural laboratory for evaluating controls on carbonate platform-margin and slope architecture. Multiple 2D transects through the YP and IPs provide exposure along spatial and temporal gradients in tectonic subsidence rate, siliciclastic input, and antecedent topography. Platform development across the end-Permian extinction allows assessment of the impact of global change from a basin-wide perspective.
The YP and IPs evolved from ramps to progressively steepening high-relief oolite margins in the Early Triassic and steep margins with prograding Tubiphytes slope reefs in the Middle Triassic. Development steepening high-relief oolite margins and giant ooids in the Early Triassic, prior to biotic recovery of reef building organisms, reflects high seawater carbonate saturation in the aftermath of the end-Permian mass extinction.
During the Middle Triassic, the YP developed extreme lateral variability exhibiting lateral change from prograded, aggraded, tectonically backstepped and collapsed margins. The GBG evolved a high-relief margin late in the Middle Triassic, with lateral variability in margin architecture akin to the YP. Differences in antecedent topography and timing of siliciclastic basin fill affected stability resulting in changes from broad aggrading to prograding margins vs. high-relief and collapsed margins. Timing and rates of subsidence largely controlled along-strike variability, timing of drowning, back-step geometries, and pinnacle development.
The western sector of the YP and the GBG drowned under pelagic carbonates followed by siliciclastic turbidites in the Carnian, while the eastern YP continued shallow-marine deposition until burial by shallow-marine siliciclastics in the late Carnian. Syndepositonal faulting and concentration of redox sensitive trace metals in the drowning horizon indicates tectonic subsidence into anoxic basin waters facilitated drowning of the western sector of the YP. The southerly IPs have backstepping geometries, terminal pinnacles, and earlier drowning and burial by siliciclastics.
About our guest:
Dan Lehrmann is the Pyron Professor of Geoscience at Trinity University where he teaches courses in paleontology and sedimentary geology. He is originally from Wisconsin where he received his bachelor’s degree in geology from the University of Wisconsin Oshkosh and his master’s degree in geology from the University of Wisconsin-Madison. He received his Ph.D. from the University of Kansas. He got his start conducting geological research in south China in 1991 during his Ph.D. research advised by Paul Enos. His research focuses the factors controlling the evolution of marine sedimentary basins, the evolution of carbonate platforms and major events in the history of life such as the end-Permian mass extinction.