RADIOLARIAN EVIDENCE FOR THE STRATIGRAPHY AND PALAEO-OCEANOGRAPHY OF THE DEEP-WATER PASSIVE MARGIN OF THE INDIAN PLATE (KARAMBA FORMATION, INDUS SUTURE ZONE, LADAKH HIMALAYA)
T. Danelian et Ahf. Robertson, RADIOLARIAN EVIDENCE FOR THE STRATIGRAPHY AND PALAEO-OCEANOGRAPHY OF THE DEEP-WATER PASSIVE MARGIN OF THE INDIAN PLATE (KARAMBA FORMATION, INDUS SUTURE ZONE, LADAKH HIMALAYA), Marine micropaleontology, 30(1-3), 1997, pp. 171-195
New radiolarian biostratigraphical information sheds light on the Meso
zoic sedimentary, tectonic and palaeoceanographic evolution of a south
-Tethyan margin in northern India. Radiolarian cherts studied here for
m part of deformed deep-water successions within the Indus Suture Zone
(Ladakh Himalaya); these are defined as the Karamba Formation and int
erpreted as the stratigraphically higher and palaeogeographically more
distal parts of a passive margin (Lamayuru Group). This formation inc
ludes radiolarites, pelagic carbonates, redeposited limestones, ferrug
inous shales, sandstones, and abundant mafic extrusive rocks. Radiolar
ian assemblages of early and late Middle Jurassic, mid-Cretaceous (mid
-Albian to Cenomanian) and Late Cretaceous (Santonian) age were obtain
ed from four measured sequences. Results indicate: (i) long, intact Ju
rassic-Cretaceous successions, rather than disrupted melange, are pres
ent in the Karamba Formation; (ii) extensive basic volcanism took plac
e during the Middle Jurassic and can be correlated with an extensional
phase affecting the NW Indian continental margin; (iii) non-calcareou
s radiolarian-rich sediments accumulated during the Middle Jurassic, r
eflecting the influence either of a broad Jurassic equatorial upwellin
g zone, or a more localised coastal upwelling system. After drowning o
f the Zanskar elastic shelf in the late Albian, sedimentation on the d
istal shelf and upper slope was restricted by bottom current activity.
Late Albian-Cenomanian radiolarites of the Karamba Formation are cont
emporaneous with stratigraphic gaps and glauconite-phosphorite deposit
ion on the Zanskar shelf. A well-developed eastward boundary current o
ff the northern margin of India may have persisted until near the end
of the Late Cretaceous. During the late Albian-Cenomanian, current act
ivity and coastal upwelling were probably strong and radiolarian-rich
sediments accumulated on the distal margin beneath the CCD. Pelagic li
mestones accumulated during the Turonian over the entire margin, possi
bly related to eustatic sea-level rise and consequent reduction in bot
tom current activity. Intense oceanic circulation apparently was renew
ed during the Coniacian-Santonian, as indicated by sedimentary hiatuse
s in the Zanskar shelf succession and accumulation of carbonate-free r
adiolarian ooze in the Karamba Formation.