YU, NENG-TI
National Taiwan University, Taipei, Taiwan

Abstract: Sequence Stratigraphy of the Upper Miocene Estuarine Siliciclastic Strata in Northern Taiwan

Upper Miocene siliciclastic estuarine strata, over 500m thick, continuously outcrop in 3 stratigraphic sections in northern Taiwan. The sequential variations of these tidalites display the relative sea-level changes controlled by Eustatic fluctuations in the tide-influenced coastal plain.

The estuary depositional systems of these tidalites comprise a Tidal Flat dominating in the northern section, and a Barrier-Lagoon with increasing wave influence dominating in the 2 southern sections. In the Tidal Flat deposits, sequence boundary can be identified by the paleosol separating the underlying highstand systems tracts of fining-upward intertidal channel point bars and the overlying lowstand systems tracts of coal-bearing supratidal interbeds. Transgressive systems tracts are composed of the aggradational subtidal sandstones. In the Barrier-Lagoon deposits, sequence boundary can be identified by the erosion surface separating the underlying highstand systems tracts of coarsening-upward, coal-bearing lagoon interbeds and the overlying lowstand systems tracts of barrier sandstones. Transgressive systems tracts are composed of the fining-upward lagoon interbeds with occurrence of nannofossils.

5 sequences are recognized and their relative sea-level changes are synthesized as the initial rise, significant rise and gentle fall. Owing to no significant channel incision or facies change on the sequence boundaries, these sequences evidently belong to Type-2 sequences. Constrained by the N8/9 and NN11/12 in the underlying and overlying shelf strata respectively, the synthesized relative sea-levels appear to be tuned to the 3rd-order fluctuations on the Vail's chart, which indicates the domination of Eustacy in these upper Miocene tidalites in northern Taiwan.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas