Upper Turonian - lower Campanian planktonic foraminifera from Exmouth Plateau

A planktonic foraminiferal zonal scheme is presented for subdivision of the Upper Cretaceous pelagic carbonate sequence from southern mid-high latitudes. Definition of the zones is based on first and last occurrences of planktonic foraminifera from Ocean Drilling Program Holes 762C and 763B (Leg 122; Exmouth Plateau, south Indian Ocean). During the Late Cretaceous the studied holes were located close to 50°S and for the first time a complete sedimentary record for the mid-high latitudes was obtained. A detailed biostratigraphic analysis has allowed recognition of two new zones (Falsotruncana maslakovae Zone and Marginotruncana marianosi Zone) for the interval extending from the last occurrence of Helvetoglobotruncana helvetica to the first occurrence of Dicarinella asymetrica (upper Turonian - lower Santonian). From this study it is apparent that some low latitude (Globotruncana ventricosa, Hedbergella flandrini, Marginotruncana marianosi) and high latitude (Globigerinelloides impensus and Hedbergella sliteri) marker taxa display a vertical distribution at mid-high latitudes which is different from that known from low latitudes; moreover, one species (Heterohelix papula), overlooked at low latitudes, exhibits a restricted range that seems to be useful for chrono-biostratigraphic correlations: its appearance is suggested to coincide with the Coniacian/Santonian boundary. The proposed biozonation, which is integrated with calcareous nannofossil and magnetostratigraphic data available for the sections studied, is compared with both the low-latitude standard zonation and the planktonic foraminiferal zonal scheme for the circum-Antarctic region, in order to define a bio-chronostratigraphic scale that is useful for mid-high latitudes of the southern oceans.

Mud, sand, heavy and light minerals composition in lower Cretaceous at DSDP Hole 93-603B

During the drilling of Hole 603B on Deep Sea Drilling Project Leg 93, an unexpected series of sand-, silt-, and claystone turbidites was encountered from Cores 603B-45 through -76 (1224-1512 m sub-bottom depth). Complete and truncated Bouma sequences were observed, some indicating deposition by debris flows. Sand emplacement culminated with the deposition of a 30-m-thick, unconsolidated sand unit (Cores 603B-48 through -45). The purpose of this preliminary study is to determine the nature of the heavy mineral suites of this sediment in order to make tentative correlations with onshore equivalents. The heavy mineralogy of Lower Cretaceous North American mid-Atlantic coastal plain sediment has been extensively studied. This sediment is classified as the Potomac Group, which has a varied heavy mineral suite in its lower part (Patuxent Formation), and a limited suite in its upper part (Patapsco Formation). The results of this study reveal a similar trend in the heavy mineral suites of sediment in Hole 603B. Hauterivian through lower Barremian sediment has a heavy mineral suite that is dominated by zircon, apatite, and garnet, with minor amounts of staurolite and kyanite. Beginning in the mid-Barremian, a new source of sediment becomes dominant, one which supplies an epidote-rich heavy mineral suite. The results of the textural analyses show that average grain size of the light mineral fraction increases upsection, whereas sorting decreases. The epidote-rich source may have delivered sediment with a slightly coarser mean grain size. This sediment may represent a more direct continental input at times of maximum turbidite activity (mid-Barremian) and during deposition of the upper, unconsolidated sand unit.

Raw grain-size distributions of the sediment trap time series CB 14 upper, CB 15 lower, CB 16 lower, CBi 1 upper, CBi 2 upper and CBi 3 upper

in preparation