The erratic rocks of the Upper Cretaceous Chalk of England: how did they get there, ice transport or other means?
نویسندگان
چکیده
Rare erratic clasts – extraneous rock types occur in the Upper Cretaceous Chalk, including a local basal facies, Cambridge Greensand. The underlying Albian Gault Clay and Hunstanton Red Chalk Formations have also yielded erratics. discovery of these erratics, their description development hypotheses to explain origins significance are reviewed. They became subject scientific interest with interpretation particularly large example “The Purley Boulder” by Godwin-Austen (1858) as having been transported its depositional site Sea drifting coastal ice. Thin section petrography (1930–1951) extended knowledge diverse provenance. At same time had become interpreted warm, so ice was considered out context, preferred agents transport were entanglement roots trees, holdfasts floating marine algae, or stomach stones reptiles fish. Reconsideration occurrence, variable nature sedimentary setting suggests that there three zones English where erratics may be less rare (1) near base Cenomanian area, (2) Cenomanian–Middle Turonian Surrey, (3) Coniacian Lower Santonian Kent. assemblage from each level is subtly different. Present evidence found Albian–Lower represent shallow water shoreline rocks into (fast-ice) enclosed sediments it froze. from Rochester Gravesend Kent gastroliths.
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ژورنال
عنوان ژورنال: Acta Geologica Polonica
سال: 2023
ISSN: ['0001-5709', '2300-1887']
DOI: https://doi.org/10.24425/agp.2020.134555