Sedimentological Study of Sandstone Units in Gutingkeng Formation: A Massive Mudstone Sequence in Southern Taiwan

Tsung-Yi Lin and Peter B. Yuan

Sedimentary structures, ichnofossils and rock composition of sandstone units in a massive mudstone sequence (Gutingkeng Formation, late Miocene- early Pleistocene), in southern Taiwan were studied to interpret depositional environments, sedimentary processes, provenance, and basin evolution.

Sedimentary structures and ichnofossils in the sandstone units indicate that they were probably deposited below storm wave base, in zones ranging from the outer shelf to the slope. Muds were deposited during fair-weather conditions, whereas sands were transported into this basin by storm-induced currents. Strong currents represented by structures such as sharp erosional bases, flute casts, parallel laminations, and ripped-up mud clasts are found. Climbing-ripple laminations, load casts, flame structures, and slump structures are also found when abundant sediment was available and deposited rapidly. These sediments were probably derived from an uplifted terrane composed of low rank metamorphic rocks, based on rock composition and quartz grains characteristics.

From the late Miocene (5 Ma) to the late Pliocene (3-2.5 Ma), sediments were deposited in an outer shelf to slope zone in a foreland basin. From early Pleistocene (2-1.6 Ma), the foreland basin filled up rapidly due to the intensified uplifting of the proto-Central Range during the Penglai orogeny. Consequently as a result of sediment infill, the depositional environment shallowed gradually to the outer shelf. Late in the early Pleistocene (0.4 Ma) the depositional environment deepened to create an outer shelf to slope zone, probably due to global sea level rise and basin subsidence caused by sediment-loading and faulting induced by the orogeny.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California