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SUMMARY:Late Miocene Uplift of the Lesser Himalaya Recorded by Clumped Iso
 tope Compositions of Detrital Carbonate - Dr Uri Ryb\, Hebrew University o
 f Jerusalem
DTSTART:20251014T110000Z
DTEND:20251014T120000Z
UID:TALK237106@talks.cam.ac.uk
CONTACT:David Hodell
DESCRIPTION:Variations in the composition and texture of detrital records 
 preserved in the Himalayan foreland basin and the Indus and Bengal fans li
 kely track stages in the evolution of the orogen\, the Indian Summer Monso
 on\, and regional ecology. Yet\, interpreting these records remains challe
 nging\, as sediment characteristics are shaped by shifting provenance\, hy
 drological sorting\, weathering intensity\, incorporation of mineral and o
 rganic matter\, and post-depositional alteration. To address some of these
  complexities\, we examined the mineralogy and clumped isotope composition
 s of detrital carbonates from modern Ganga River sediments and from early 
 Miocene to Holocene Bengal Fan turbidites. Our results show that variation
 s in clumped and oxygen isotope values of detrital calcite in Himalayan ri
 vers reflect mixing between lithic carbonates and authigenic calcite preci
 pitated within the river system. In Bengal Fan turbidites\, clumped isotop
 e temperatures and calcite-to-dolomite ratios decline during the Late Mioc
 ene\, marking an increase in the relative contribution of authigenic calci
 te. This trend cannot be explained by decreasing source temperatures\, whi
 ch would imply unrealistically high-temperature calcite formation\, nor by
  intensified weathering\, as K/Si* values (a weathering proxy) remain stab
 le since the mid-Miocene. Instead\, we argue that the shift primarily refl
 ects a change in the relative abundances of calcite and dolomite in Himala
 yan-derived sediments\, specifically a Late Miocene\, Himalaya-wide proven
 ance shift from calcite-rich (dolomite-poor) Tethyan and Greater Himalaya 
 terrains to calcite-poor (dolomite-rich) Lesser Himalaya sources.
LOCATION:Department of Earth Sciences\, Tilley Lecture Theatre
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