Field of Science

Two New Triassic Papers in Palaeo 3

Algeo, T. J., Kuwahara, K., Sano, H., Bates, S., Lyons, T., Elswick, E., Hinnov, L., Ellwood, B., Moser, J., and J. B. Maynard. 2010. Spatial variation in sediment fluxes, redox conditions, and productivity in the Permian-Triassic Panthalassic Ocean, Palaeogeography, Palaeoclimatology, Palaeoecology (2010), doi: 10.1016/j.palaeo.2010.07.007

Abstract - Two Permian/Triassic boundary sections in central Japan provide a rare window into environmental conditions within the Panthalassic Ocean, which encompassed more than half the Earth’s surface at 252 Ma. Integration of petrographic, geochemical, and time-series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site. The Ubara section was located in a high-productivity peri-equatorial location, whereas the Gujo-Hachiman section was located in a moderate-productivity location at some distance from the paleoequator. An upward transition from gray organic-poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity, intensified euxinia within the oxygen-minimum zone (OMZ), and decimation of the radiolarian zooplankton community. Euxinia in the OMZ of the equatorial Panthalassic Ocean developed episodically for a ~200-250 kyr interval during the Late Permian, followed by an abrupt intensification and lateral expansion of the OMZ around the Permian-Triassic boundary. Throughout the study interval, bottom waters at both sites remained mostly suboxic, a finding that counters hypotheses of development of a “superanoxic” Permo-Triassic deep ocean as a consequence of stagnation of oceanic overturning circulation.

Shukla, U. K., Bachmann, G. H., and I. B. Singh. 2010. Facies architecture of the Stuttgart Formation (Schilfsandstein, Upper Triassic), central Germany, and its comparison with modern Ganga system, India, Palaeogeography Palaeoclimatology, Palaeoecology (2010), doi: 10.1016/j.palaeo.2010.07.019

Abstract - The Stuttgart Formation (Schilfsandstein) is approximately 50 m thick in Thuringia, representing deposition during the “Mid-Carnian Wet Intermezzo”. Stratigraphically it occurs between the Grabfeld and Weser formations, which formed under arid conditions. It comprises NNE-SSW-trending elongate, anastomosing channelised sand-rich bodies with erosional bases (channel belts) that are several kilometres wide and pass laterally into predominantly mudstones deposited in interfluve areas. The source area of these clastics was the uplifted Norwegian Caledonides. Muddy interfluve facies is dominant in exposures in Thuringia, Central Germany. The Lower Stuttgart Formation has an unconformable base that is locally overlain by meter-thick “Basal Beds”. These consist of grey mudstones and thin sandstones deposited under humid conditions in predominantly shallow brackish water environments after a marine ingression via the Eastern Carpathian/Upper Silesian Gate. The following 30–40 m- grey, finegrained sandstones, siltstones and mudstones were deposited in fluvial environments in channel belts and interfluve areas under humid conditions. These are followed by predominantly reddish mudstones and sandstones of mainly fluvial origin, deposited under somewhat drier conditions with seasonal droughts. The Upper Stuttgart Formation may be more than 16 mthick; it comprises reddish and grey sandstones and mudstones that were mostly deposited in lake-delta settings by recurring flash floods. During the deposition of this unit climate was weakly humid with less prominent seasonal draughts. The modern Ganga Plain of India is an analogue for the depositional setting of the Stuttgart Formation. Climatic conditions in Ganga Plain are humid monsoonal with seasonal droughts and roughly comparable with those interpreted for Mid-Carnian times in Germany. The sandy deposits of incised channel belts and channels and muddy deposits of interfluve areas in the Ganga Plain are comparable with the sandstone-dominated channelized facies and mudstone-dominated interfluve facies of the Stuttgart Formation, respectively.

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