Autogenic delta progradation during sea-level rise within incised valleys

Using a simple conceptual model of incised-valley evolution, we show that the classic sequence stratigraphic phenomenon of bayhead deltaic systems can be generated by purely autogenic progradation during the late stage of valley flooding. This transient “auto-advance” event occurs under conditions of constant base-level rise and sediment supply, and it results from a strong decrease of in-valley accommodation as base level rises toward the valley apex. We present a laboratory experiment to illustrate the plausibility of this mechanism and apply it to the incised valleys of the Trinity and Brazos Rivers (Texas, USA) as field case studies. Auto-advance can produce out-of-sequence regressive bayhead diastems during highstands similar to a transient change in allogenic forcing. Combined with other recent studies, our findings support the idea that mesoscale autogenic patterns are ubiquitous in the fluviodeltaic record and need to be more extensively incorporated into reconstructions of Earth surface evolution and reservoir models.

Supplemental Material: Autogenic delta progradation during sea-level rise within incised valleys

Three supplemental figures, one table, and supplemental text.<br>

Supplemental Material: Autogenic delta progradation during sea-level rise within incised valleys

Three supplemental figures, one table, and supplemental text.<br>

Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland

The Zackenberg River delta is located in northeast Greenland (74°30′ N, 20°30′ E) at the outlet of the Zackenberg fjord valley. The fjord-valley fill consists of a series of terraced deltaic deposits (ca. 2 km2) formed during relative sea-level (RSL) fall. We investigated the deposits using sedimentological and cryostratigraphic techniques together with optically stimulated luminescence (OSL) dating. We identify four facies associations in sections (4 to 22 m in height) exposed along the modern Zackenberg River and coast. Facies associations relate to (I) overriding glaciers, (II) retreating glaciers and quiescent glaciomarine conditions, (III) delta progradation in a fjord valley, and (IV) fluvial activity and niveo-aeolian processes. Pore, layered, and suspended cryofacies are identified in two 20 m deep ice-bonded sediment cores. The cryofacies distribution, together with low overall ground-ice content, indicates that permafrost is predominately epigenetic in these deposits. Fourteen OSL ages constrain the deposition of the cored deposits to between approximately 13 and 11 ka, immediately following deglaciation. The timing of permafrost aggradation was closely related to delta progradation and began following the subaerial exposure of the delta plain (ca. 11 ka). Our results reveal information concerning the interplay between deglaciation, RSL change, sedimentation, permafrost aggradation, and the timing of these events. These findings have implications for the timing and mode of permafrost aggradation in other fjord valleys in northeast Greenland.

DINAMIKA MORFOLOGI DAERAH SISI LUAR (OUTER) DELTA MAHAKAM KALIMANTAN TIMUR, INDONESIA

Bentuk morfologi bagian luar (outer) delta Mahakam, khususnya Muara Pegah, (Kalimantan Timur) sangat dinamis. Pengukuran batimetri pada dua musim dan tahun berbeda menunjukan proses sedimentasi dan erosi serta progradasi delta meskipun tidak diikuti oleh perubahan garis pantai yang jelas seperti diamati dari citra satelit. Peta batimetri 2005 menunjukan proses sedimentasi yang intensif sedangkan batimetri 2006 menunjukan proses erosi pada delta bagian luar. Secara umum, bila dibandingkan dengan peta batimetri 1989, delta bagian luar Muara Pegah telah mengalami progradasi. Proses progradasi delta bagian luar Muara Pegah dicirikan oleh proses pergeseran garis kedalaman (batimetri) 5 m sampai 20 m telah bergeser ke arah laut atau ke tenggara disebabkan telah terjadinya penimbunan sedimen dalam jumlah yang cukup berarti. Ke arah luar dari delta front, pada kedalaman 20 m atau lebih, bentuk batimetri dipengaruhi oleh arus di Selat Makassar yang mengalir secara kontinu ke arah utara. Pemodelan perubahan batimetri pada kawasan Muara Pegah menggambarkan telah terjadinya erosi dasar sungai secara kontinu sebagai pengaruh dari besarnya debit sungai yang mengalir melalui muara menuju laut lepas. Proses erosi sebagai akibat kondisi arus pasang surut juga terlihat di luar muara Pantai Muara Pegah, akan tetapi besarnya sangat bergantung terhadap kondisi arus pasang surut. Kata Kunci: morfologi delta bagian luar, proses sedimentasi, erosi, progradasi, batimetri, pemodelan, pasang surut The outer delta morphology form of Mahakam delta, e.g. Muara Pegah (East Kalimantan) is very dynamic. The bathymetry of different seasons and times indicate sedimentation, erosion processes and delta progradation although do not followed coastal line changes as shown by satellite image. The bathymetry map in 2005 show the intensive sedimentation process while in 2006 the bathymetry map indicate the erosion process of the outer delta. In general, since it is compared to the 1989’s bathymetry map, the outer delta of Muara Pegah had undergone progradation. The delta progradation of Muara Pegah is characterized by seaward displacement (southeastward) of 5 m and 20 m contour depth as it caused by significance sediment accumulations. To the outer delta front at 20 m depth or more, the bathymetry pattern is influenced by Makassar Strait currents flowing continuously to the North. The dynamics bathymetry modeling of Muara Pegah illustrates a continuous erosion of the river base being influenced by the important river debit that flows via delta to the open sea. The tide erosion process is also observed at the outer part of Muara Pegah coast line, but the intensity is depend on tide condition. Keyword: outer delta morphology, sedimentation processes, erosion, prograde, bathymetry, modeling, tide

INFLUENCIA DEL RÍO ATRATO EN EL GOLFO DE URABÁ DURANTE EL HOLOCENO TARDÍO, MAR CARIBE COLOMBIANO

Sedimentary, geochemical (total organic carbon TOC, total nitrogen TN, total phosphorus TP, biogenic silica BSi and calcium carbonate (CaCO3) and diatoms data of two sediment cores were used to infer general environmental changes in the northern Gulf of Urabá during the late Holocene. The age models (AMS 14C ) suggested that core of the northeastern margin (SP 9) belong to ~960 years BP, while in the core of the northwestern margin (SP 41) the model was adjusted for the last ~2845 years BP. The results indicated that drilling sites are affected by different hydrodynamic processes that, in general, have been maintained during the late Holocene. While in the northwestern margin oceanic processes dominate and there is low input of fluvial sediments to this site, in the northeastern margin there are processes that favor the transport and accumulation of terrigenous sediments, which limit the growth of diatoms. Between 2845 and 2489 year BP, a higher sea level and wet conditions were recorded in the gulf. Since ~2445 years BP a gradual decrease in sea level allowed delta progradation towards the eastern side of the gulf. Apparently, this process would have intensified its presence in the last ~200 year BP, due to natural and anthropogenic factors. Even though the river discharges are channeled predominantly towards the east side of the Gulf, the trend of increasing TOC and diatoms data suggested fluvial input to the northwestern margin from ~800 years BP, which may be associated with a higher activity of Tarenas mouth, the northern branch of the Atrato River.