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SUMMARY:Driving mechanisms for globally correlatable Phanerozoic eustatic 
 sequences? - Mike Simmons (Netflex Petroleum\, Oxford)
DTSTART:20081028T163000Z
DTEND:20081028T173000Z
UID:TALK14280@talks.cam.ac.uk
CONTACT:Francis Rowland
DESCRIPTION:Large-scale changes in stratigraphic architecture and facies t
 hat are brought about by changes in relative sea-level have been the focus
  of much academic and industry study over the last few decades. Within ind
 ustry in particular\, the prediction of hydrocarbon play elements using se
 quence stratigraphic techniques is now well established. Six years ago we 
 demonstrated the veracity of a sequence stratigraphic model for the Arabia
 n Plate based on the recognition of 63 major stratal surfaces (maximum flo
 oding surfaces (MFS) and sequence boundaries (SB)). Ongoing work\, incorpo
 rating the stratigraphy of nearly all sedimentary basins on Earth\, can no
 w demonstrate the occurrence of >200 MFS and SB that are both synchronous 
 and global in extent. These sequences are thus eustatic in origin.\n\nThis
  then raises the question - what causes globally synchronous eustatic sea-
 level change? To answer this question requires an understanding of the bot
 h the pace and amplitude of the observed eustatic sea-level change. In suc
 cessions where duration can be deduced from orbital forcing cycles\, our o
 bserved sea-level changes appear to be relatively rapid - less than 500\,0
 00 years\, for example\, for sea-level rises in the Late Jurassic. The amp
 litude of such rises is in the order of tens of metres.  Such rates and am
 plitudes as inferred from our global model preclude tectonism as a primary
  driver and implicate glacio-eustacy as a key driving mechanism\, even in 
 supposed "greenhouse times".\n\nGiven the clear economic importance of und
 erstanding the underlying mechanisms driving this eustatic change we have 
 compiled records of key isotopic proxies through the entire Phanerozoic in
  an effort to explore the relationship between global sea-level and palaeo
 climate. Our research reveals a clear link between the timing of some of o
 ur large-scale MFS events with known episodes of palaeoclimatic warming\, 
 as well as a similar link between our SB and climatic cooling.\n\nFurther\
 , in addition to isotopic proxy evidence for polar ice presence\, we have 
 compiled direct evidence for the occurrence of polar ice sheets in the Pha
 nerozoic (tillites\, glendonites\, etc). Both isotopic and direct evidence
  suggest the presence of polar ice sheets for periods previously supposed 
 as ice free and that glacio-eustacy can be suggested as the major driver o
 f Phanerozoic eustatic sea-level change. 
LOCATION:Tilley Lecture Theatre\, Department of Earth Sciences
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