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Towards a quantitative paleogeography calculator
Abstract
Studies of paleoclimatology, paleoceanography, paleobiology, and other studies of paleoenvironment require paleogeographic reconstructions that display the past distribution of land and sea, and of bathymetry and altimetry. Quantitative reconstructions of past positions of continents and oceans have been available for decades, and have become easy to access and develop with the advance of GPlates software. Quantitative estimates of bathymetry and especially altimetry and topography, however, are considerably more challenging to develop. First attempts towards a global, quantitative approach towards paleotopography reconstruction were made in recent years. However these models are largely based on present day topography and require extensive manual adjustment for local modification that is subjective and precludes reproducibility. In this project, we attempt to overcome this subjectivity, and develop a quantitative methodology to calculate paleogeography based on kinematic input parameters.
Our aim is to develop ‘Paleogeography.org’, a free, online paleogeography calculator. This project calculates oceanic bathymetry and continental altitude and topography from plate tectonic reconstructions for various geodynamic settings. The algorithms are based on simple and straightforward dynamic principles: bathymetry of the ocean floor is at first order inferred from its age, and altimetry is based on computing crustal thickness based on shortening or extension reconstructions, assuming isostacy. Distinctions are made between undisturbed ocean floor, oceanic plateaus, trenches, continental rifts and back-arc basins, oceanic and continental volcanic arcs, upper plate orogens (e.g., Andes, Tibet) vs accretionary orogens (Zagros, Himalaya, Apennines, Alps), etc. This allows to calculate a global geography for any given time slice for which underlying kinematic reconstructions are available. These reconstructions are subsequently tested against independent quantitative estimates of e.g., altimetry and bathymetry and iterated where necessary. This approach provides a reproducible, global estimate of paleogeography without input from paleobiological or paleoclimatic indicators, enabling an independent platform for paleo-environmental study. The iteration between prediction and observation, moreover, will provide novel constraints on 4D geodynamic processes.
Code is written mainly in Python, especially using pyGPlates. The calculator will be available as open source code for scientists and other professionals. They can use it to make reproducible paleogeographic reconstructions based on their own plate tectonic reconstructions or on specific moments in time. In addition the output makes appealing pictures of plate tectonic reconstructions for both scientists and a wider audience.
... Furthermore, rather than modifying modern DEMs, topographic features may be fully generated based on geodynamic setting and surface processes, in turn constrained by geologic data (e.g. Frigola et al., 2018;Sewall and Sloan, 2006;van der Linden et al., 2020). ...
... As part of a continuous collaborative effort building paleogeographies and associated databases, we foresee that the addition and consideration of more and new data reconstructed to its past position with dedicated reconstruction tools (Baatsen et al., 2016;Ruiz et al., 2020;van der Linden et al., 2020) will certainly help to define more comprehensive, accurate and reliable paleoDEMs. The development and comparison of more reconstructions at different time slices, increasing the resolution in the Cenozoic and going further back in time, will necessarily add relevant data for a continuous and integrative overview of paleotopographies. ...
Paleogeographic maps are essential tools for understanding Earth system dynamics. They provide boundary conditions for climate and geodynamic modelling, for analysing surface processes and biotic interactions. However, the temporal and spatial distribution of key features such as seaways and mountain belts that govern climate changes and biotic interchange differ between various paleogeographies that require regular updates with new data and models. We developed a reproducible and systematic approach to paleogeographic reconstruction and provide a set of worldwide Cenozoic paleogeographic maps at 60, 40 and 20 Ma. We followed a six-stage methodology that integrates an extensive review of geological data into a coherent plate tectonic model using the open source software GPlates. (1) We generated a global plate kinematic model, and reconstructed intensely-deformed plate boundaries using a review of structural, paleomagnetic and other geologic data in six key regions: the Andes, the North American Cordillera, the Scotia Arc, Africa, the Mediterranean region and the Tibetan-Himalayan collision zone. (2) We modified previously published paleobathymetry in several regions where continental and oceanic crust overlap due to differences in the plate models. (3) We then defined paleoshorelines using updated fossil and geologic databases to locate the terrestrial to marine transition. (4) We applied isostatic compensation in polar regions and global eustatic sea level adjustments. (5) Paleoelevations were estimated using a broad range of data including thermochronology and stable isotopes, combined with paleobotanical (mostly pollen and leaf physiognomy), structural and geomorphological data. We address ongoing controversies on the mechanisms and chronology of India-Asia collision by providing alternate reconstructions for each time slice. We finally discuss the implications of our reconstructions on the Cenozoic evolution of continental weatherability and review methodological limitations and potential improvements. Future addition of new data, tools and reconstructions can be accommodated through a dedicated interactive website tool (https://map.paleoenvironment.eu/) that enables users to interactively upload and download data and compare with other models, and generate their own plots. Our aim is to regularly update the models presented here with new data as they become available.
Mountain building in the Andes, the longest continental mountain range on Earth, started in the Late Cretaceous but was highly diachronous. Reconstructing the timing of surface uplift for each of the different Andean regions is of crucial importance for our understanding of continental-scale moisture transport and atmospheric circulation, the origin and evolution of the Amazon River and Rainforest, and ultimately, the origin and evolution of species on the world most biodiverse continent. Here, I present (1) a compilation of estimates of paleoelevation for 36 geomorphological domains of the Andes from the literature, and (2) a paleoelevation reconstruction of the Andes since 80 Ma. In the northern Andes, uplift started in the Late Cretaceous (~70 Ma) in the Western and Central Cordilleras of Ecuador, while the northwestern corner of the continent was still covered by shallow seas. Mountain building migrated progressively northwards, with the Perija Range and Santander Massif uplifting since the Oligocene and the Eastern Cordillera, Garzon Massif and Mérida Andes since the Miocene. In the central Andes, uplift migrated from west to east, whereby the main phase of uplift in the Western Cordillera took place during the Late Cretaceous-Paleocene, in the western Puna plateau during the Paleocene, in the eastern Puna plateau during the early-mid Miocene, and in the Altiplano and Eastern Cordillera during the mid-late Miocene. In the southern Patagonian Andes, significant elevation was already in place at 80 Ma and in western Patagonia, modern elevations were reached in the early Eocene. A second pulse of uplift and eastward migration of the orogenic front occurred during the early-mid Miocene. The reconstruction developed here is made available as a series of raster files, so that it can be used as input for a variety of studies in the solid Earth, climate, and biological sciences, thereby being a stepping stone on the path towards a better understanding of the coevolution of the solid Earth, landscapes, climate, and life in South America.
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