Showing papers on "Sea-level curve published in 2018"

Sequence architecture and depositional evolution of the northern continental slope of the South China Sea: responses to tectonic processes and changes in sea level

Abstract: The continental slopes of the South China Sea (SCS), the largest marginal sea on the continental shelf of Southeast Asia, are among the most significant shelf-margin basins in the world because of their abundant petroleum resources and a developmental history related to sea floor spreading since Late Oligocene time. Based on integrated analyses of seismic, well-logging and core data, we systematically document the sequence architecture and depositional evolution of the northern continental slope of the SCS and reveal its responses to tectonism, sea-level change and sediment supply. The infill of this shelf-margin basin can be divided into seven composite sequences (CS1‒CS7) that are bounded by regional unconformities. Composite sequences CS3 to CS7 have formed since Late Oligocene time, and each of them generally reflects a regional transgressive–regressive cycle. These large cycles can be further divided into 20 sequences that are defined by local unconformities or transgressive–regressive boundaries. Depositional–geomorphologic systems represented on the continental slope mainly include shelf-edge deltas, prodelta-slope fans, clinoforms of the shelf-margin slope, unidirectionally migrating slope channels, incised slope valleys, muddy slope fans, slope slump-debris-flow complexes, and large-scale soft-sediment deformation of bedding. Changing sea levels, reflected by evidence from sequence architecture in the study area, are generally comparable with those of the Haq (1987) global sea level curve, whereas the regional transgressions and regressions were apparently controlled by tectonic uplift and subsidence. Composite sequences CS3 and CS4 formed from Late Oligocene to Middle Miocene time and represent continental-slope deposition during a time of northwest-northeast seafloor spreading and subsequent development of sub-basins in the southwest-central SCS. The development of composite sequences CS5 to CS7 after Middle Miocene time was obviously influenced by the Dongsha Movement during convergence between the SCS and Philippine Sea plates. Climatic variations and monsoon intensification may have enhanced sediment supply during Late Oligocene‒Early Miocene (25-21 Ma) and Late Pliocene‒Pleistocene (3-0.8 Ma) times. This study indicates that shelf-edge delta and associated slope fan systems are the most important oil/gas-bearing reservoirs in the SCS continental-slope area. This article is protected by copyright. All rights reserved.

Sub-marine Continuation of Peat Deposits From a Coastal Peatland in the Southern Baltic Sea and its Holocene Development

Abstract: Coastal low-lying areas along the southern Baltic Sea provide good conditions for coastal peatland formation. During the Holocene, the transgression of the Littorina Sea has caused coastal flooding, submergence and erosion of ancient coastlines and former terrestrial material. The present Heiligensee & Hutelmoor peatland (located near Rostock in Northern Germany) was found to continue more than 90 m in front of the coastline based on on- and offshore sediment cores and geo-acoustic surveys. The seaward areal extent of the peatland is estimated with 0.16-0.2km2. The offshore limit of the former peatland roughly coincides with the offshore limit of a dynamic coast-parallel longshore bar, with peat deposits eroded seawards. While additional organic-rich layers were found further offshore below a small sand ridge system, no connection to the former peatlands can be established based on 14C age and C/N ratios. The preserved submerged peat deposits with organic carbon contents of 37 % in front of the coastal peatland Heiligensee & Hutelmoor was radiocarbon-dated to 6725 +/- 87 and 7024 +/-73 cal yr BP, respectively, indicating an earlier onset of the peatland as presently published. The formation time of the peat layers gives information about the local sea level rise. The local sea level curve derived from our 14C-dated organic-rich layers is in general agreement to nearby sea level reconstructions (North Rugen and Fischland, Northern Germany), with differences explained by local isostatic movements.

Integrated Sequence Stratigraphy of the Middle Jurassic (Bajocian-Callovian) Chiltan Formation in the Lower Indus Basin, Pakistan

Abstract: Detailed sedimentological analysis of the Jurassic (Bajocian-Callovian) Chiltan Formation has been accomplished from the Middle Indus Basin, Pakistan. We have discriminated six different microfacies that deciphered a carbonate barrier-inlet shelf platform depositional setting. These facies represented the lagoonal tidal inlets (CHF 1 facies), carbonate shoals (CHF 2 facies), fore shore (CHF 3 facies), supra tidal (CHF 4 facies), wash over fans (CHF 5) and near shore (CHF 6 facies) setting. The record of the smaller benthic foraminifera (Lenticulina subalta, lenticulina vobulus and planularia protracta) confirms a middle Jurassic (Bajocian-Callovian) age of the unit. This biostratigraphic calibration suggests that the deposition of the Chiltan Formation correspond to a second order cycle (17 Ma) which encompasses a composite transgressive systems tract and various third order cycles and systems tracts. The long and short term sea level fluctuations show a close match with global sea level curve.