| Abstract: | The Cenomanian succession of the Cauvery Basin, SE India contains an expanded succession of coastal plain deposits which can be dated with precision from the use of cosmopolitan ammonite taxa and thus correlated accurately to marine successions elsewhere. The succession includes palaeosols, fluvial/tidal channels, and offshore sands which provide detailed evidence of sea-level changes. Using high-resolution biostratigraphy it is possible to correlate 11 individual sequences to Europe, 8000km distant. These sequences coincide precisely with the 400 kyr long eccentricity cycle.
In the Mid Cenomanian of NW Europe a short-lived cold event is documented by d18O data (bulk chalks and brachiopods) with a heavy shift of nearly 1.5 ppt, The event is precisely coincident with a rapid sea-level fall of about 25m on the Indian coastal plain which can be identified globally from the use of high-resolution ammonite biostratigraphy (mid Cunningtoniceras inerme Zone, 70ka duration). Orbital tuning of the conspicuously rhythmic succession by time series analysis of greyscale reflectance data provides evidence that the event occurs during a time of maximum eccentricity, characterised by increased contrast between dark marls and light limestones. The cold event represents a cooling of shelf bottom waters of about 5 degrees centigrade during a long eccentricity (400kyr) maximum, and is associated with a brief (c 15 kyr) southerly incursion of a colder water boreal fauna, and the lowest of two global positive excursions of d13C with a heavy shift of 0.7 ppt. Both the rapidity and magnitude of the sea-level fall and cooling are suggestive of glacioeustatic control. |