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SUMMARY:Modern versus ancient controls on sedimentary systems\; the presen
 t is not always the key to the past  - Prof. Poppe de Boer\, Utrecht Unive
 rsity
DTSTART:20180116T120000Z
DTEND:20180116T130000Z
UID:TALK97093@talks.cam.ac.uk
CONTACT:37221
DESCRIPTION:The concept of uniformitarianism dates back to the late 18th c
 entury. The idea is that physical and chemical laws have not changed\, and
  that also in the distant geological past sedimentary processes have acted
  as they do today. However\, various types of sedimentary processes and de
 posits\, e.g. large-scale black-shale deposition during the middle Cretace
 ous\, the absence of terrestrial vegetation in the pre-Ordovician\, the de
 position of up to 4 km thick evaporites in large basins\, the rise and fal
 l of dinosaurs during the Mesozoic\, testify changes in the controls of se
 dimentary processes in the course of geological time. \nThe Black Sea is c
 onsidered one of the end members of marine systems with black shale deposi
 tion\, the other one being upwelling zones along continental margins. Why 
 is the Black Sea the only example of the “black-sea model” today\, and
  when and where did such situation occur in the past? Why is extensive ano
 xia\, as in the North Atlantic and Tethys Oceans during the middle Cretace
 ous\, not encountered in present-day oceans? \n\nOrbital (Milankovitch) fo
 rcing\, that is forcing of climate and oceanography by varying eccentricit
 y\, obliquity and precession\, has been active throughout geological histo
 ry. Orbital cyclicity in marine and terrestrial sediments is reported\, ho
 wever\, much more frequently from certain stratigraphical periods (e.g. Cr
 etaceous and Jurassic) than from others. Is this due to variations of the 
 orbital parameters and their influence on climate and oceanography\, or ar
 e other factors involved? The transfer of orbital signals is generally con
 sidered to be mediated by orbitally forced climate (change). In addition\,
  variations in the distance between celestial bodies affect their mutual g
 ravitational attraction which\, in turn\, should be of influence on the oc
 ean tide. May we expect such tidal effects\, in addition to orbital climat
 e signals\, to be recorded in sedimentary successions?\nSaline Giants\, ac
 cumulations of evaporitic salts of up to several kilometres thick\, have b
 een intermittently deposited in sedimentary basins during some few 100\,00
 0 years\, on average about once every 5 million years. There are no recent
  examples of such large basins with evaporite salt accumulation. The Mioce
 ne Mediterranean example\, formed during the Messinian Salinity Crisis\, s
 ome 5.5 million years ago\, is the most recent one. Is the absence of pres
 ent-day saline giants accidental or are conditions different from the past
 ? Can we expect other saline giants in the future\, and where?\n\nThe pres
 ent-day Earth’s surface with high mountains (Himalaya\, Andes) is not re
 presentative for various other parts of the geological record. For example
 \, after the break-up of Pangea major plate collisions were largely absent
 \, with consequences for the continental relief and the character and exte
 nt of terrestrial and shallow marine environments. In addition to catastro
 phic events\, the decline of dinosaurs may be related to the gradually cha
 nging face of the Earth during the Mesozoic.\n
LOCATION:Tilley Lecture Theatre\, Department of Earth Sciences\, Downing S
 ite
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