The Cretaceous/Tertiary Boundary at Site 738, Southern Kerguelen Plateau

Abstract

High-resolution stratigraphic evidence of an apparently complete carbonate-rich Cretaceous/Tertiary boundary interval in Section 119-738C-20R-5 from the southern Kerguelen Plateau is summarized and interpreted. The change of the calcareous nannoflora and of the planktonic foraminifers is spread over a laminated interval of about 15 cm thickness. The base of this laminated interval lies in uppermost Maestrichtian chalks, 2 cm below a distinct 2-mm-thick "gray clay" layer, which shows the highest iridium enrichment (18 ppb) measured in this section. No shocked quartz or microspherules, characteristic of an impact, were found. No change in the clay mineralogy, which could be expected for a large volcanic or impact event, could be identified. Elevated metal and iridium concentrations (> 1.6 ppb) occur already in the bioturbated uppermost Maestrichtian chalks several centimeters below the "gray clay" and decrease above the iridium peak gradually over a laminated 12-cm-thick interval to background values of 0.1-0.3 ppb Ir. Application of bio-and magnetochronology shows that the accumulation rates of carbonates and clays, but not of the metals, decreased dramatically at the Cretaceous/Tertiary boundary and thus, the lack of dilution may have led to the observed metal concentrations.

Calcareous nannoplankton mass extinction at the Cretaceous/Tertiary boundary: An update

“…1; Table 1). Studies of these cores have shed much light on the K/T extinction scenario among nannoplankton in the austral realm (Pospichal and Wise, 1990a;Pospichal, 1991;Thierstein et al, 1991;Wei and Thierstein, 1991;Wei and Pospichal, 1991;Ehrendorfer and Aubry, 1992;Pospichal and Bralower, 1992;Pospichal and Huber, 1992;Pospichal and Wise, 1992). A summary of the pertinent lithologic and paleoenvironmental information Scotese and Denham (1988), Terra Mobilis ™ .…”

Multiple factors in the origin of the Cretaceous/Tertiary boundary: the role of environmental stress and Deccan Trap volcanism

“…The pattern of mass extinction at the K/T boundary has been reported by many authors (McLean 1985b;Smit and Romein 1985;Hansen et al 1986;Jaeger 1986;Kauffman 1986;Wiedmann 1986;Raup 1986;Sloan et al 1986;Donovan 1987;Hallam 1987;Hut et al 1987;Jones et al 1987;Wolfe 1987;Officer et al 1987;Albritton 1989;Charig 1989;Keller 1989Keller , 1993Keller , 1994Sahni and Bajpai 1988;Sepkoski 1989;Hansen 1990;Barrera andKeller 1990, 1994;Pandey 1990;Spicer 1989;Ward 1990;Gallagher 1991;Pospichal 1991Pospichal , 1994Raju et al 1991Raju et al , 1995Pospichal and Huber 1992;Thierstein et al 1991;D'Hondt and Herbert 1992;Pospichal and Bralower 1992;Schmitz et al 1992;Sweet and Braman 1992;Ager 1993;Archibald 1993;Keller et al 1993b;Barrera 1994;Kerr 1994;…”

“…It can be calculated that this Ir-rich layer accumulated at an average rate of 5.97 ng Ir/cm 2 /ka over a period of 18 000 years, which is somewhat less than the residence time of Ir in seawater determined by Goldberg et al (1986). Thierstein et al (1991) calculated that the Ir could not have been derived from the oceanic reservoir. However, our calculations suggest that Ir did indeed pass through the hydrosphere and was deposited on the sea floor following hydrolysis, although it had an external source.…”

“…The Ir content of seawater is extremely low, approximately 2!10 -15 g Ir/g seawater with a residence time of 40 000 years (Goldberg et al 1986). Considering data for the "grey clay" at the K/T boundary obtained during ODP Leg 119 Thierstein et al 1991), the zone of maximum Ir enrichment had a thickness of 14.2 cm, an average Ir content of 7.56 ppb and a sedimentation rate of 0.79 cm/ka. It can be calculated that this Ir-rich layer accumulated at an average rate of 5.97 ng Ir/cm 2 /ka over a period of 18 000 years, which is somewhat less than the residence time of Ir in seawater determined by Goldberg et al (1986).…”

Experimental evidence for the global acidification of surface ocean at the Cretaceous–Palaeogene boundary: the biogenic calcite-poor spherule layers

“…The KPB sequences without spherule beds were identified at the following distal oceanic sites worldwide; at Maud Rise (ODP Leg 113, Sites 689 and 690: Michel et al 1990 Schmitz et al 1991;Thierstein et al 1991) in the southern Indian Ocean; and Ontong-Java Plateau (ODP Leg 130, Site 803: Kyte et al 1995) in the central Pacific. The locations of all these sites are also given in Fig.…”