You are wrong. See T. Rex and the Crater of Doom. The clearest evidence of an abrupt extinction is the abrupt and total change in the foramintifera.
Actually the clearest evidence against an abrupt extinction is the little change in plankton
a) Diatoms. The K-T event did not much affect the diatoms. Harwood (1988), based on studies from Seymour Island, eastern Antarctic Peninsula, the first to record siliceous microfossil assemblages across a K-T boundary sequence, notes that diatom survivorship across the K-T boundary was above 90 percent. Resting spores increase from 7 percent below to 35 percent across the K-T boundary.
b) Dinoflagellates. Dinoflagellates also were little affected by the K-T event (Bujak and Williams, 1979). Brinkhuis and Zachariasse (1988) record no accelerated rates of extinction across the K-T boundary in Tunisia. Nor does Hultberg (1986) in Scandinavia. Danish dinoflagellates responded more by appearance of new species than by extinctions (Hansen, 1977), as did Seymour Island assemblages (Askin, 1988).
c) Yes other plankton did suffer massive extinctions but it wasn't because of the Asteroid or K-T event.
Marine calcareous microplankton, the coccolithophorids and planktonic foraminifera, were hit hardest of all by the K-T event. Thierstein (1981) proposes that the coccolithophorids extinctions were the most severe plankton extinction event in geologic history; via a "deconvolution" process, Thierstein (1981, 1982) reduced a Cretaceous-Tertiary "transition," in which Cretaceous assemblages were replaced by "new" Tertiary taxa, to an instantaneous catastrophe. Perch-Nielsen et al. (1982) note that the "catastrophic event"at the K-T boundary did not result in geologically instant extinction of the calcareous nannoplankton, and that most Cretaceous species survived the event. At DSDP Site 524, a sample above the K-T boundary contains 90 percent Cretaceous species. Isotopic analyses indicated that the Cretaceous species were not reworked specimens, but represented survivors of the K-T event that continued to reproduce in the earliest Tertiary oceans. The relict species became extinct some tens of thousands of years after K-T boundary time, probably via environmental stresses.
d) Antia and Cheng's (1970) work on survival times of phytoplankton species in complete darkness indicate that 1 month of complete blackout would produce 13 percent extinction, 3 months 68 percent extinction , and 6 months 81 percent. Thus, the 6 month to 1 year global blackout predicted by Wolbach et al. (1985) would have obliterated diatoms, dinoflagellate, and coccolithophorids precisely at the K-T boundary. A blackout event is not reflected in the algal record. The calcareous coccolithophorids and foraminifera were likely affected by pH change of the marine mixed layer via CO2 mantle degassing by the Deccan Traps volcanism.
So please tell me how did photoplankton who depend on sunlight for their very exsistance not only not die out but actually thrive during a global blackout??
e) And the real kicker is, Microfossils are actually found in the Chicxulub crater itself!!! and even though they are essentially at "Ground Zero" they show no ill effects.
Thank you for providing some supporting data. I had not yet pawed through my boxes of paleo papers in the garage. Although I am much more familiar with the Tertiary stratigraphy and micropaleontology of California (for instance, the work of Robert Kleinpell and Manley Natland), I have some experience with the K-T boundary as exposed on the west coast. Needless to say, there is nothing particularly dramatic about it - lithologically or paleontologically. As a matter of fact, the boundary is variable and gradational here.