Continental Margins

The Late Cretaceous tectonic evolution of NE China reflects a complex history of extensional, contractional and strike-slip deformation as a result of the Mesozoic geodynamics of the active margin of East Asia. The NNE–trending, late Jurassic–Cretaceous sedimentary basins in the region display a complete structural record to analyze the nature of deformational events, and a unique stratigraphic archive to discern sediment sources and drainage patterns during their evolution. Here we evaluate the Upper Cretaceous lithostratigraphy and the in-ternal structure of a series of sedimentary basins based on detailed seismic reflection profiles, surface geology and new zircon geochronology, interpret the mode of accommodation space and drainage pattern development in these basins, and present a new tectonic model for their post-rift evolution in the late Cretaceous. The basins occur in three NNE–oriented, subparallel zones, the Eastern (EZ), Central (CZ) and Western (WZ) Zones, in which the distribution, scale and intensity of deformational structures show major variations from the east to the west. The EZ basins include Sanjiang, Boli and Jixi, bounded on the west by the Zhangguangcai range (ZGCR). The CZ is represented by the ~400-km-wide Songliao Basin, which is bounded on the west by the Great Xing'an Range (GXAR). The WZ contains the Genhe, Erlian and Hailar Basins that are delimited by the Mongol–Okhotsk Suture to the north and the west. The Paleozoic Central Asian Orogenic Belt (CAOB), the northern North China Craton (NCC) and the Jiamusi Block (JMB) constitute the basement of these basins. The Early Cretaceous sedimentary record and structural fabric in all the basins resulted from ESE–WNW extension, manifested in NNE- oriented half and full grabens with listric fault geometries and growth fault structures. The Upper Cretaceous stratigraphy in some of these basins display internal unconformities indicating periods of non-deposition, and folds and thrust/reverse faults attesting to contractional deformation episodes in their sedimentary–tectonic records. The Upper Cretaceous basinal strata in the EZ show early Cenomanian–Turonian and early Campanian–Maastrichtian unconformities, consistent with the timing of two discrete episodes of regional contraction in the region. Basement-involved, predominantly E-vergent imbricate thrust faults, positive flower structures, and fault-pro-pagation folds widely occur in the Upper Cretaceous strata of the EZ basins. The dominant drainage direction in these basins was to the W during the late Cenomanian–early Campanian. The nearly 5-km-thick Upper Cretaceous strata of the Songliao Basin in the CZ display a complete depositional record with no unconformity, but with two major episodes of drainage pattern switches. The first switch occurred near the Cenomanian–Turonian boundary with the fluvial systems draining N-NE, instead of W, and carrying sediments derived mainly from NCC. This change coincided with the eastward migration of the main depocenter in the basin. Following the development of a deep, large lake within the basin during the Turonian (92–86 Ma) and then during the Santonian (~86–84.5 Ma), the lacustrine environment experienced rapid shrinking and shal-lowing, and the drainage patterns changed from an axial (NNE–SSW) to a transverse (mainly to the W) system since 84 Ma during Late Cretaceous. The main depocenter migrated to the W within the basin, and the main provenance became ZGCR and JMB to the E–SE. Contractional deformation affected the Songliao depocenter first at the Cenomanian–Turonian boundary and then in the early Campanian-Maastrichtian. The WZ basins experienced non-deposition during much of the late Cretaceous. The uppermost Cretaceous strata in the WZ are represented by fluvial and shallow lacustrine deposits, which show transpressional faults and folds. We infer that the post-rift development of the sedimentary basins and hence the crustal evolution of NE China in the late Cretaceous were mainly controlled by the continental margin tectonics and plate interactions between the Okhotomorsk block (OB), part of the Izanagi oceanic realm, and East Asia. The initial arrival of OB at the East Asia Trench around 100–89 Ma caused the first episode of contractional deformation across the sedimentary basins, and resulted in major shifts in their drainage patterns. The NE translation of OB along the sinistral transform plate boundary during 84–77 Ma exerted a transpressional stress regime, which produced positive flower structures and thrust faults across the basins. The final collision of OB with Siberia–Sakhalin to the north ~70–65 Ma resulted in further shortening and inversion within the CZ–WZ basins, and in reactivation of previously formed normal faults as thrust faults.

Abstract The Late Cretaceous tectonic evolution of NE China reflects a complex history of extensional, contractional and strike-slip deformation as a result of the Mesozoic geodynamics of the active margin of East Asia. The NNE–trending, late Jurassic–Cretaceous sedimentary basins in the region display a complete structural record to analyze the nature of deformational events, and a unique stratigraphic archive to discern sediment sources and drainage patterns during their evolution. Here we evaluate the Upper Cretaceous lithostratigraphy and the internal structure of a series of sedimentary basins based on detailed seismic reflection profiles, surface geology and new zircon geochronology, interpret the mode of accommodation space and drainage pattern development in these basins, and present a new tectonic model for their post-rift evolution in the late Cretaceous. The basins occur in three NNE–oriented, subparallel zones, the Eastern (EZ), Central (CZ) and Western (WZ) Zones, in which the distribution, scale and intensity of deformational structures show major variations from the east to the west. The EZ basins include Sanjiang, Boli and Jixi, bounded on the west by the Zhangguangcai range (ZGCR). The CZ is represented by the ~ 400-km-wide Songliao Basin, which is bounded on the west by the Great Xing'an Range (GXAR). The WZ contains the Genhe, Erlian and Hailar Basins that are delimited by the Mongol–Okhotsk Suture to the north and the west. The Paleozoic Central Asian Orogenic Belt (CAOB), the northern North China Craton (NCC) and the Jiamusi Block (JMB) constitute the basement of these basins. The Early Cretaceous sedimentary record and structural fabric in all the basins resulted from ESE–WNW extension, manifested in NNE- oriented half and full grabens with listric fault geometries and growth fault structures. The Upper Cretaceous stratigraphy in some of these basins display internal unconformities indicating periods of non-deposition, and folds and thrust/reverse faults attesting to contractional deformation episodes in their sedimentary–tectonic records. The Upper Cretaceous basinal strata in the EZ show early Cenomanian–Turonian and early Campanian–Maastrichtian unconformities, consistent with the timing of two discrete episodes of regional contraction in the region. Basement-involved, predominantly E-vergent imbricate thrust faults, positive flower structures, and fault-propagation folds widely occur in the Upper Cretaceous strata of the EZ basins. The dominant drainage direction in these basins was to the W during the late Cenomanian–early Campanian. The nearly 5-km-thick Upper Cretaceous strata of the Songliao Basin in the CZ display a complete depositional record with no unconformity, but with two major episodes of drainage pattern switches. The first switch occurred near the Cenomanian–Turonian boundary with the fluvial systems draining N-NE, instead of W, and carrying sediments derived mainly from NCC. This change coincided with the eastward migration of the main depocenter in the basin. Following the development of a deep, large lake within the basin during the Turonian (92–86 Ma) and then during the Santonian (~ 86–84.5 Ma), the lacustrine environment experienced rapid shrinking and shallowing, and the drainage patterns changed from an axial (NNE–SSW) to a transverse (mainly to the W) system since 84 Ma during Late Cretaceous. The main depocenter migrated to the W within the basin, and the main provenance became ZGCR and JMB to the E–SE. Contractional deformation affected the Songliao depocenter first at the Cenomanian–Turonian boundary and then in the early Campanian-Maastrichtian. The WZ basins experienced non-deposition during much of the late Cretaceous. The uppermost Cretaceous strata in the WZ are represented by fluvial and shallow lacustrine deposits, which show transpressional faults and folds. We infer that the post-rift development of the sedimentary basins and hence the crustal evolution of NE China in the late Cretaceous were mainly controlled by the continental margin tectonics and plate interactions between the Okhotomorsk block (OB), part of the Izanagi oceanic realm, and East Asia. The initial arrival of OB at the East Asia Trench around 100–89 Ma caused the first episode of contractional deformation across the sedimentary basins, and resulted in major shifts in their drainage patterns. The NE translation of OB along the sinistral transform plate boundary during 84–77 Ma exerted a transpressional stress regime, which produced positive flower structures and thrust faults across the basins. The final collision of OB with Siberia–Sakhalin to the north ~ 70–65 Ma resulted in further shortening and inversion within the CZ–WZ basins, and in reactivation of previously formed normal faults as thrust faults.

The natural radionuclides 210Po and 210Pb were analyzed in samples of surface sea water, rain and dry fallout, and river water collected along the NW Mediterranean coast as well as from a sediment trap moored 3km south of Monaco. Using a box model calculation, the balances and fluxes of 210Po and 210Pb in the coastal waters of the NW Mediterranean

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km2. Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized ...

The concentrations and composition of hydrocarbons in sections from a 210 Pb dated core from Buzzards Bay, Massachusetts are reported. Terrigenous n-alkane concentrations remain constant throughout the 62 cm and 195 years sampled. Gas Chromatographic analysis on SCOT ...

Over the last two decades numerous studies have investigated the structure of the west Iberia continental margin, a non-volcanic margin characterized by a broad continent–ocean transition (COT). However, the nature and structure of the crust of the segment of the margin off SW Iberia is still poorly understood, because of sparse geophysical and geological data coverage. Here we present a 275-km-long multichannel seismic reflection (MCS) profile, line AR01, acquired in E–W direction across the Horseshoe Abyssal Plain, to partially fill the gap of information along the SW Iberia margin. Line AR01 runs across the inferred plate boundary between the Iberian and the African plates during the opening of the Central Atlantic ocean. The boundary separates crust formed during or soon after continental rifting of the SW Iberian margin from normal seafloor spreading oceanic crust of the Central Atlantic ocean. Line AR01 has been processed and pre-stack depth migrated to show the tectonic structure of the crust across the palaeo plate boundary. This boundary is characterized by a 30–40-km-wide zone of large basements highs related to landward-dipping reflections, which penetrate to depths of 13–15 km, and it marks a change in the character of the basement structure and relief from east to west. In this study, we have used pre-stack depth migrated images, the velocity model of line AR01 and magnetic data available in the area to show that the change in basement structure occurs across the fossil plate boundary, separating African oceanic crust of the M series (M21–M16) to the west from the transitional crust of the Iberian margin to the east.