High Frequency Sea-Level Fluctuations in Cretaceous Time: An Emerging Geophysical Problem
- Kenneth J. Hsü
Published Online: 15 MAR 2013
Copyright 1986 by the American Geophysical Union.
Mesozoic and Cenozoic Oceans
How to Cite
Schlanger, S. O. (1986) High Frequency Sea-Level Fluctuations in Cretaceous Time: An Emerging Geophysical Problem, in Mesozoic and Cenozoic Oceans (ed K. J. Hsü), American Geophysical Union, Washington, D. C.. doi: 10.1029/GD015p0061
- Published Online: 15 MAR 2013
- Published Print: 1 JAN 1986
Print ISBN: 9780875905150
Online ISBN: 9781118669914
- Geology, Stratigraphic—Mesozoic—Congresses;
- Geology, Stratigraphic—Cenozoic—Congresses;
- Ocean circulation—Congresses
Refinements in dating and correlation of Cretaceous strata coupled with the mapping of shoreline migrations and determinations of water depths that obtained during deposition of these strata show that from Albian through Maastrichtian time cratonic platforms experienced 6 major marine transgressive pulses. These pulses show a periodicity of ∼5.5±1 Ma. During these marine transgressions water depths on the cratons increased by 100 to 250 m. The global synchroneity of the transgressions implies rates of relative sea-level rise and fall of from 50 to 100 m/my. Recent revisions of geologic time scales show that while changes in ridge-crest spreading rates and global ridge volume and ridge-crest length may account for the general long-term flooding of major cratons from ∼110 to ∼85 Ma, such changes cannot account for the ∼5.5 Ma transgressive-regressive cycles seen in Cretaceous strata. The possibility exists that ridge geometries were highly variable in Mesozoic time but the lack of significant magnetic reversals between chrons 34 and M0 makes it impossible to discern short-term changes in these rates. Other mechanisms such as continent-continent collisions, sediment accumulation in oceanic basins, dessication of marginal seas, hot spot-induced rejuvenation of older sea floor, and stress variations in the lithosphere related to major plate reorganizations also cannot account for the frequency of the Cretaceous transgressive-regressive cycles. If we accept the premise of an ice-free Cretaceous world, and the preponderance of evidence points to the lack of significant glaciation from Albian through Maastrichtian time, we are faced with the challenge of finding a geologically reasonable mechanism capable of affecting major, globally synchronous, short-term changes in the freeboard of the major cratons. The linkage between transgressions and oceanic anoxic events in the Cretaceous ocean adds an economic impulse to the geophysical-geological problem. During oceanic anoxic events large amounts of organic carbon were preserved in marine sediments, sedimentary manganese deposits formed in shallow basins, and sulfide mineral formation was enhanced in axial ridge vent settings.