Tectonics induced switching of provenance during the Late Quaternary aggradation of the Indus River Valley, Ladakh, India

The Indus River flows through Ladakh, one of the driest and coldest places on earth, in a tectonically active domain. Fluvial, glaciofluvial, lacustrine and debris dominated sequences represent the Late Quaternary sedimentary record along the river course. Karakoram Fault, a major crustal scaled feature reported to be active during the Quaternary, is associated with the Indus River drainage. Linkages between a major, active fault and deposits formed during the activity period of the fault are explored using heavy mineral deduced provenance and Optically Stimulated Luminescence(OSL) chronology.Five deposits in a ~200 km long stretch of the Indus River have been examined for a ~80 ka period to decipher the climate linked aggradation history. Damming of the Indus River at ~79 ka and existence of the Spituk Lake for >30 ka is demonstrated. Using geology of the provenance in relation to the mineralogical attributes of the Quaternary deposits, the major drainage reorganization when the connection of the Tangtse Valley to the Indus was blocked, is inferred at ~73 ka. It is supported by the geologicalgeomorphological evidence. The study demonstrates the application of provenance linked mineralogy in terrestrial aggradation in a tectonically active region.

Quartz grain surface microtextural evidence for provenance of the Quaternary aggradation red earth deposit, southern China

The Quaternary aggradation red earth(QARE)deposit in the middle reaches of the Yangtze River(MRYR)in southern China provides important evidence for understanding the paleoenvironment.However,its provenance remains controversial.In this study,the surface microtextures of grains from the QARE were observed,and compared with those of grains from the loess deposit on the Loess Plateau in northern China.The results show that the surface microtextures and morphologies of the quartz grains in the QARE are distinctly different from those in the northern loess,indicating that the deposits in the two regions have different provenances.The Gobi and deserts in inland northwestern China are not considered as the primary provenance for the QARE in southern China.It is suggested that the large areas of dry and bare river and lake beds and floodplains in the MRYR,which became exposed during glacial periods,provided the dominant source for materials in the QARE.We suggest that against the background of the middle-Pleistocene climate transition(MPT),regional aridification and a strengthened east Asian winter monsoon(driven by global cooling and the rapid uplift of the Tibetan Plateau)were primary drivers for the initiation of the QARE deposit in the MRYR region in southern China.The development of large areas of aeolian red earth deposit is direct evidence of environmental deterioration in the MRYR,indicating a cold and dry environment with frequent aeolian activity,in an area that now experiences a warm and humid subtropical monsoon climate.The results are also evidence of a regional response in the mid-subtropics of southern China to the MPT global cooling event around 1.2 Ma.

Combination Patterns and Depositional Characteristics of Ordovician Carbonate Banks in the Western Tarim Basin,China

The combination patterns and depositional characteristics of the carbonate banks are investigated based on outcrop sections, thin sections, and carbon isotopes of Ordovician in the western Tarim Basin, China. Four carbonate bank combination patterns are deposited in the Ordovician, western Tarim Basin, including： Reef-Bank Complex （RBC）, Algae-Reef-Bank Interbed （ARBI）, Thick-Layer Cake Aggradation Bank （TLCAB）, and Thin-Layer Cake Retrogradation Bank （TLCRB）. All combination patterns show clear periods vertically. The RBC is mainly composed of reefs and bioclastic banks, and the dimension of the RBC depends on the scale of the reefs. Bioclastic banks deposits surround the reefs. The range of the ARBI is determined by the scale of algae-reefs, algae peloid dolomite microfacies and algal dolomite microfacies deposit alternating vertically. TLCAB and TLCRB are deposited as layer-cakes stacking in cycles and extending widely with cross bedding developed. The grains of TLCAB and TLCRB are diverse and multi-source. With the impacting of relative sea level change, biological development and geomorphology, the ARBI, TLCAB or TLCRB, RBC are successively developed from the Lower Ordovician Penglaiba Formation to the Middle Ordovician Yijianfang Formation. The depositional environment analysis of Ordovician indicates that the RBC and ARBI can form effective oil and gas reservoirs, and the TLCAB and TLCRB have the potential to form the huge scale oil and gas reservoirs and to be the crucial targets of exploration for the Ordovician carbonate banks in the future.

Sequence Stratigraphic Analysis of “XB Field”, Central Swamp Depobelt, Niger Delta Basin, Southern Nigeria

Well logs and biostratigraphic data from six wells in the “XB Field”, central Swamp Depobelt, Niger Delta were integrated to carry out a sequence stratigraphic analysis of depositional systems in the field. The analysis revealed four 3rd order depositional sequences (SEQ1 to 4) bounded by three erosional unconformities interpreted as Sequence Boundaries (SB1 to 3). Transgressive Surfaces of Erosion (TSE1 to 3) that mark the onset of marine flooding and turnarounds from progradational facies to retrogradational facies during sequence build-up were delineated. Three 3rd order Maximum Flooding Surfaces (MFS1, MFS2 and MFS3) characterized by marker shales, high faunal abundance and diversity were also delineated and dated 15.9, 17.4 and 19.4 Ma, respectively. The delineated sequences comprised Lowstand Systems Tracts (progradational packages), Transgressive Systems Tracts (retrogradational packages) and Highstand Systems Tracts (aggradational packages), which reflect depositional systems deposited during different phases of base level changes. The Lowstand Systems Tract (LST) consists of Basin Floor Fans (BFF), Slope Fans and Channel Sands deposited when sea level was low and accommodation space lower than rate of sediment influx. Transgressive Systems Tract (TST) consists of retrogradational marine shales deposited during high relative sea levels and when accommodation space was higher than rate of sediment influx. Highstand Systems Tracts (HST) consisted of shoreface sands displaying mostly aggradational to progradational stacking patterns. The sands of LST and HST show good reservoir qualities while the shales of the TSTs could form potential reservoir seals. The above recognized sequences, were deposited within the Neritic to Bathyal paleoenvironments and are dated mid-Miocene (15.9 - 20.4 Ma) in age.

Depositional Architecture and Evolution of Late Permian Reefs in Ziyun County,Southern Guizhou, China

The uppermost Permian reef complex in Ziyun County, southern Guizhou occurs as a third-order depositional sequence developed in the platform marginal break zone during the Late Permian transgressive period This paper deals with the evolution of the third-order sequence and depositional arthitecture of the sequence stratigraphic units with the analysis of outcrop sequence stratigraphy and chemostratigraphy. Thirteen parasequences which belong to four system tracts are recognized. According to their genetic facies features,three growth strategies of reef accrete from the systems tracts during sea level changes are distinguished as keep-up reefs, give-up reefs and catch-up reefs. In combination with an absolute water depth analysis by chemostratigraphic method, we establish an entire sea level curve of the third-order sequence and discuss its evolution and depositional response.

Anthropogenic impacts to the sediment budget of São Francisco River navigation channel using SWAT

The São Francisco River Basin,located in eastern Brazil,has undergone a significant amount of anthropogenic changes in the last several decades,such as agricultural expansion,irrigation activities,mining,and the construction of large dams.Together,these changes have altered the historic sediment budget and have led to an aggradation of sediments in the navigation channel,impacting the ability to efficiently ship agricultural commodities to regional ports.In an effort to aid decision makers in future waterway navigation planning,an international partnership between the Brazilian government agency CODEVASF and the US Army Corps of Engineers(USACE)was created.Through this partnership a SWAT model of the 630000 km2 São Francisco River basin was developed to better understand both the historic and current sediment budget within the navigation channel.The SWAT model of the São Francisco River Basin was calibrated for hydrology and sediment loads.Monthly discharges were calibrated at 17 Agência Nacional deÁguas(ANA)gages,with Nash-Sutcliffe efficiency(NSE)values ranging from 0.42 to 0.75 for an eleven year simulation.Sediment loads were calibrated to an ANA sediment gage located in the Middle São Francisco River Navigation Channel,with a PBIAS(Percent Bias)of 11.6.Based on model results,the aggradation rate of sediment in the São Francisco River and major tributaries has increased by approximately 20 Mt since Pre-European settlement of the basin(from approximately 7 Mt/a to 27 Mt/a).This increase has contributed to an impaired navigation channel due to shoaling of sandy sediments in the navigation channel.