科研之友
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摘要
Turonian strata of the Bohemian Cretaceous Basin, Central Europe, preserve a basin-scale record of shoreline transgressions and regressions, previously interpreted to have been strongly influenced by short-term eustatic cycles. Here, nearshore siliciclastic strata in two separate sub-basins are correlated to a multi-stratigraphic dataset generated from a new research core (Bch-1) drilled in offshore marine sediments of the central basin. A high-resolution delta 13C(org), record from Bch-1 is presented along with major- and minor-element proxies, TOC, carbonate content, terrestrial to marine palynomorph ratios, and detailed macro- and microfossil biostratigraphy. The 400 m thick Turonian through Lower Coniacian interval permits correlation to the highest-resolution C-isotope curves available: all carbon-isotope events demonstrated by delta C-13(carb) studies in the British Chalk, NW Germany and other reference sections in Europe are recognized in the delta C-13(corg) curve from Bch-1. A number of short-term, basin-wide regressions in the Bohemian Cretaceous Basin, most likely reflecting eustatic falls, show a recurrence interval of 100 kyr or less. This is an order of magnitude shorter than the timing of sea-level falls inferred from the New Jersey margin and the Apulian platform, interpreted to be driven by glacioeustacy. The estimated magnitude of the Bohemian Basin sea-level falls, typically 10-20 m and generally %26lt;40 m, indicates that the 2.4 Myr period suggested by others to generate 3rd-order cycles, is too long to be the principal cycle generating unconformities in rapidly-subsiding basins, where the rate of eustatic fall must exceed the subsidence rate. Unconformities in low-accommodation settings such as passive margins most likely represent amalgamated records of multiple cycles of sea-level fluctuations of 100 kyr scale, recognizable only in high-resolution datasets from expanded successions. %26lt;br%26gt;Comparison of the delta C-13 excursions to the interpreted sea-level record has not yielded a clear causal link. A longterm %26apos;background%26apos; delta C-13 cycle shows a duration close to the 2.4 Myr long-eccentricity cycle, and shorter-term (1 Myr scale) highs and lows in delta C-13 appear to broadly correspond to intervals characterised by more pronounced short-term sea-level highs and lows, respectively. However, on the scale of intermediate to short-term delta C-13 fluctuations, no systematic relationship between delta C-13 and sea-level change can be demonstrated.
- 出版日期2014-7-1
