Showing papers on "Sea-level curve published in 2014"

A late Holocene sea-level curve for the east coast of South Africa

Abstract: South Africa’s extensive and topographically diverse coastline lends itself to interpreting and understanding sea-level fluctuations through a range of geomorphological and biological proxies. In this paper, we present a high-resolution record of sea-level change for the past ~1200 years derived from foraminiferal analysis of a salt-marsh peat sequence at Kariega Estuary, South Africa. A 0.94-m salt-marsh peat core was extracted using a gouge auger, and chronologically constrained using five radiocarbon age determinations by accelerator mass spectrometry, which places the record within the late Holocene period. Fossil foraminifera were analysed at a high downcore resolution, and a transfer function was applied to produce a relative sea- level reconstruction. The reconstructed sea-level curve depicts a transgression prior to 1100 cal years BP which correlates with existing palaeoenvironmental literature from southern Africa. From ~1100 to ~300 cal years BP, sea levels oscillated (~0.5-m amplitudes) but remained consistently lower than present-day mean sea level. The lowest recorded sea level of −1±0.2 m was reached between 800 and 600 cal years BP. After 300 cal years BP, relative sea level has remained relatively stable. Based on the outcomes of this research, we suggest that intertidal salt-marsh foraminifera demonstrate potential for the high-resolution reconstruction of relative sea-level change along the southern African coastline.

The Black Sea Dating Game and Holocene Marine Transgression

Abstract: Dating of major sea-level changes using shells or calcareous microfossils is prone to errors in semi-enclosed marine environments where inputs of seawater and river water vary over time and space. The need to refine mollusc-based age estimates for the rate of the Holocene marine transgression in the Black Sea is the focus of multiple palaeoceanographic and archaeological studies. This ongoing “dating game” seeks to clarify conflicting evidence for a hypothetical catastrophic marine flood that forced the emigration of Neolithic farmers from the shores of a Holocene freshwater lake in the Black Sea. The potential importance of confirming or rejecting this megaflood hypothesis has led to multiple attempts at refining the chronology of the marine transgression and quantifying the palaeosalinity of the Black Sea surface water during the Holocene. Here we report that six new AMS radiocarbon ages of 8890 ± 50 to 8450 ± 40 yr BP were obtained for wood, grass and sedge leaves from peat layers in Core 342 at 33.16 - 32.71 m below present sea level on the Ukrainian Shelf. These plant materials provide critical new ages for quantifying Black Sea carbon reservoir issues. The accuracy of our new AMS wood/peatages is independently supported by palynochronological correlation. The ages of our plant materials have ~100 years precisionandare ~420 - 520 years younger than those previously reported for unsorted detrital peat in Core 342. Paired mollusc—wood ages for brackish—freshwater Dreissena polymorpha shell from detrital peat also shows that an inaccuracy of >1120 yr can arise for shells during times when carbon reservoir values in the semi-isolated, brackish-water Black Sea could depart significantly from global average. Our revised sea level curve shows a gradual early Holocene transgression from water depths of -45.9 to -32.8 m, with initial Mediterranean inflow by 8.9 ka BP.

A Drowning Sunda Shelf Model during Last Glacial Maximum (LGM) and Holocene: A Review

Abstract: DOI: 10.17014/ijog.v1i2.182 Rising sea levels since the Last Glacial Maximum (LGM), some ~20,000 years ago, has drowned the Sunda Shelf and generated the complex coastal morphology as seen today. The pattern of drowning of the shelf will be utilized to assess likely timing of shoreline displacements and the duration of shelf exposure during the postglacial sea level rise. From existing sea level records around Sunda Shelf region, “sea level curve” was assembled to reconstruct the shelf drowning events. A five stage drowning model is proposed, including 1) maximum exposure of the shelf at approximately 20,500 years Before Present (y.B.P.), when sea level had fallen to about -118 m below present sea level (bpl.), 2) melt water pulse (MWP) 1A at ~14,000 y.B.P. when sea level rose to about -80 m bpl., 3) melt water pulse (MWP) 1B at ~11,500 y.B.P., when sea level was predicted around -50 m bpl., 4) Early-Holocene at ~9,700 y.B.P, when sea level was predicted at about-30 m bpl, and 5) sea level high stand at ~4,000 y.B.P., when sea level jumped to approx. +5 m above present sea level (apl.). This study shows that the sea level fluctuated by more than 120 m at various times during LGM and Holocene. Also confirmed that sea level curve of Sunda Shelf seems to fit well when combined with sea level curve from Barbados, although the comparison remains controversial until now due to the considerable distinction of tectonic and hydro-isostatic settings.

Eustatic, tectonic, and climatic signatures in the Lower Cretaceous siliciclastic succession on the Eastern Russian Platform

Abstract: A methodical approach to identifying major abiotic events in the siliciclastic succession accumulated in the shallow epicontinental basin on the Eastern Russian Platform during the Early Cretaceous is presented. On the basis of a reliable chronostratigraphic framework a comparison between global and regional sea level curves was undertaken. The intervals during which the global and regional sea level curve trends are similar correspond to a predominance of eustasy in the particular basin. Alternatively, tectonic activity dominates during intervals when there is no similarity between the trends of the global and regional sea level curves. Three intervals of noncoincidences of trends of these two curves matched with major tectonic events that took place within the Eastern Russian Platform in the Early Cretaceous: the Early Hauterivian tectonic uplift, subsequent Late Hauterivian subsidence and the Late Albian uplift. The main consequences of the tectonic activity were two large regional unconformities and hiati. The comparison of main global and regional sea level trends also reveals major climatic events. “The cold snaps” that occurred during the Early Cretaceous greenhouse world (Hu et al., 2012) coincided with simultaneous global and regional sea level lowstands, peak shallowing of the basin and the almost complete absence of sediments. “The cold snap” is identified in the Late Aptian sedimentary sequences on the Eastern Russian Platform.

Geomorphological evidence for an ongoing transgression on northwestern Svalbard

Abstract: Rise and fall of the global sea level during Pleistocene and Holocene are mainly caused by glacio-isostatic and glacio-eustatic factors directly linked to the cyclic increase and decrease of the Earth’s ice sheets. Apart from the dominating glacio-isostatic and glacio-eustatic factors, several other components have influenced the global sea level, which complicates the regional sea level curves of the world. One place with such a complicated relative sea level curve is northwestern Svalbard, which was covered by ice sheets during the Weichselian glaciations and started to emerge when it was deglaciated around 13 14C ka BP. Since the 1950s numerous authors have argued that there is an ongoing transgression taking place at northwestern Svalbard based upon sedimentary and geomorphological ground and the dating of whale bones. The development of geomorphological features such as lagoons, estuaries and deltas forming in protected areas, are all linked to fluctuations in sea level and can be used to determine whether or not a sea level rise is taking place. A combined map, satellite image and aerial photo analysis has been done to determine whether or not there is an ongoing transgression taking place at northwestern Svalbard and if the coastline can be considered a representative transgressive coast. The study supports the hypothesis of a slow, ongoing transgression but does not offer conclusive evidence for the same. Hence the coastline cannot be considered a typical example of a transgressive coast.

Lithofacies, paleoenvironments and sequence stratigraphic modelling of the Wargal Limestone: Implication for reservoir characterization in the Salt Range, northwest, Pakistan

Abstract: In this paper a detailed stratigraphic analysis of the Middle to Late Permian Wargal Limestone in the Western Salt Range area of the Potwar Basin in north Pakistan is presented. The outcrop data and microfacies analysis suggested that deposition of the Wargal Limestone occurred in the inner shelf to middle shelf-lagoon setting. A regional sequence stratigraphic model of the study unit, with a particular emphasis on the diagenetic fabric of different microfacies has been developed. In this study four, third order depositional sequences (1-4) are recognized. These sequences constituted three Transgressive Systems Tracts (TST 1-3) and four Regressive Systems Tract (RST 1-4). Based on the facies criteria a relative sea level curve is constructed and a comparison with the global sea level curves is made. The relative sea level fall at the 259.6 Ma and 254 Ma in the study area have a global signature, while the 263 Ma fall might be related to the interplay of the local tectonics and sediment supply. The synergy of the diagenetic fabric, results of the XRD, porosity/permeability analysis revealed that best hydrocarbon reservoir qualities exists in the dolomite facies in the middle and upper part of the study unit. The overall hydrocarbon reservoir potential of the Wargal Limestone is moderate to high.

Relict sand waves in the continental shelf of the Gulf of Valencia

Abstract: article i nfo The presence of fossil or relict bedforms is common in the Quaternary fill of modern continental shelf due to sea level oscillations, tectonic subsidence and migration of associated sedimentary facies. The continental margin of the Gulf of Valenciahas beenstronglyinfluenced by glacio-eustasy and neotectonics. High-resolution multibeam bathymetry data, seismic reflection profiles and box core samples were collected across the continental shelf of the Gulf of Valencia during the DERIVA cruises carried out in 2010 and 2011. The integrated analysis of this data set and high-resolution mapping of the relict bedforms on the Valencian continental shelf, ranging between 50 and 90 m allowed the study of previously identified system of sand waves located in front of the present-day Albufera de Valencia lagoon. The system is composed of 27 ridges with a NNE-SSW orientation, i.e. oblique to the present shoreline, in which the lateral horns point backwards. These sand waves can reach 10 m in height and 3 km in length resulting in a maximum slope of 6°. According to seismic stratigraphic and relative sea level curve reconstructions, these sand waves were formed during the Younger Dryas (~12-10 ky BP). Con- sequently, they have been classified as Holocene sand waves associated with coastal sedimentary evolution.