Lake deposits as high-resolution archives of mid-Cretaceous equatorial climate variability: A combined approach including organic geochemistry and palynology
Final Report Abstract
The Araripe Basin of NE Brasil is world-famous for its exceptionally well-preserved and taxonomically diverse fossil fauna and flora located in two different fossil lagerstätten. Whereas the fossil biota received considerable attention, few studies have been carried out with focus on the sedimentary characteristics and palaeoenvironmental conditions, which prevailed during formation of the Crato fossil beds and Santana concretions. In the course of this project, numerous stratigraphie sections covering the Crato as well as the Santana formations have been logged and sampled along the flanks of the Chapada do Araripe. The sedimentary rocks have been studied intensively with a combined approach including optical organic matter analysis as well as stable isotope and organic geochemistry. The most important results of this project are summarized: (1) An improved biostratigraphie framework for the entire late Early Cretaceous succession based on new palynostratigraphic findings; (2) The organic-geochemical characterization of the Santana black shale, which represents the host rock for the fossiliferous concretions. Based on specific molecular markers, evidence for photic-zone euxinia during deposition of the organic-rich strata is provided. (3) The detailed inspection of the carbonate and of the lamination pattern observed in the Crato Formation provides a better understanding of the palaeoenvironmental conditions during formation of this fossil lagerstätte. (4) Finally, the succession provides a well-preserved and taxonomically diverse record of early angiosperm pollen grains from a low palaeolatitude. Considering the limited amount of stratigraphically well-constrained pollen data from equatorial areas, a continuous record of early angiosperm pollen from this latitude represents an important contribution for our understanding on early angiosperm evolution and radiation. The project on the fossil-rich deposits of the Araripe Basin initiated a follow-up research proposal which will focus on the carbonate concretions from the Santana Formation and on the role of microbial processes in carbonate precipitation. In addition, a detailed study of the early angiosperm pollen flora including SEM imaging and a comparison with time-equivalent floras from Portugal is planned.
Publications
- Evidence for photic-zone euxinia in Early Cretaceous lacustrine and marginal marine deposits from North-Eastern Brazil. 7th Cretaceous Symposium, Neuchâtel, Switzerland, 2005
Heimhofer, U., Hesselbo, S., Pancost, R. D., Hochuli, P. A., Guzzo, J. V., Rios-Netto, A. M.
- Aptian greenhouse climate: its impact on physical and chemical oceanography and on marine ecology. IAS Meeting, Fucojama, Japan, 2006
Weissert, H., Burla, S., Heimhofer, U., Hochuli, P. A.
- High-resolution multiproxy records from Early Cretaceous lacustrine deposits (Aptian-Albian, Araripe Basin, NE Brazil) and their palaeoenvironmental significance. EGU General Assembly, Vienna, Austria, 2006
Heimhofer, U., Ariztegui, D., Hesselbo, S., Pancost, R. D., Hochuli, P. A.
- (2007): Halite pseudomorphs in the Crato Formation (Early Cretaceous, Late Aptian-Early Albian), Araripe Basin, northeast Brazil: further evidence for hypersalinity. Cretaceous Research, 28, 613-620
Martill, D. M., Loveridge, R. F. and Heimhofer, U.
- (2007): Stratigraphy of the Crato Formation. In: Martill, D. M., Bechly, G. and Loveridge, R. F. (Eds.) The Crato Fossil Beds of Brazil: Window into an Ancient World, Cambridge University Press, United Kingdom, 624 pp
Martill, D. M. and Heimhofer, U.
- (2007): The sedimentology and depositional environment of the Crato Formation. In: Martill, D. M., Bechly, G. and Loveridge, R. F. (Eds.) The Crato Fossil Beds of Brazil: Window into an Ancient World, Cambridge University Press, United Kingdom, 624 pp
Heimhofer, U. and Martill, D. M.
- Response of continental environments to mid-Cretaceous carbon cycle perturbations: Evidence from terrestrial δ13C records and palynology. Joint workshop on IGCP 555 and ICDP, Daqing, China, 2007
Heimhofer, U., Erbacher, J and Hinderer, M
- The early evolution of angiosperms - a stratigraphic perspective. EGU General Assembly, Vienna, Austria, 2007
Heimhofer, U., Hochuli, P. A., Burla, S., Weissert, H.
- (2008): Dolomite pipes in the Crato Formation fossil lagerstätte (Lower Cretaceous, Aptian), of northeastern Brazil. Cretaceous Research, 29, 78-86
Martill, D. M., Loveridge, R. F. and Heimhofer, U.
- (2008): Evidence for photic-zone euxinia in the Early Albian Santana Formation (Araripe Basin, NE Brazil). Terra Nova, 20, 347-354
Heimhofer, U., Hesselbo, S. P., Pancost, R. D., Martill, D. M., Hochuli, P. A. and Guzzo, J. V. P.
- Sedimentary organic matter from the Early Cretaceous Araripe Basin (NE Brazil) - An optical and geochemical characterization. IPC XII & IOPC Vlll Joint Congress, Bonn, Germany, 2008
Heimhofer, U., Hochuli, P. A., Guzzo, J. V. P., Hesselbo, S.P. and Martill, D. M.
- The laminated Crato fossil beds of Brazil - High-resolution stable isotope and elemental geochemistry. IAS Meeting, Bochum, Germany, 2008
Heimhofer, U., Lenniger, M., Ariztegui, D., Hesselbo, S.P. and Martill, D. M.
