秦岭造山带新生代构造隆升与区域环境效应研究

据沉积，构造、地貌并结合地球物理资料综合研究认为，秦岭造山带新生代构造隆升是在中生代白垩纪晚期构造隆升基础上，于晚第三纪中新世迅速隆升，而早更新世早期则是新构造活动最强烈时期。秦岭造山带的新生代构造隆升的方式主要有地垒式、掀斜式、振荡式和翘板式4种。诱发这一地区新构造抬升的主要原因和动力学机制是华北地块自北而南，扬子地块自南而北相向向秦岭造山带之下陆内俯冲和秦岭地块深部软流圈抬升共同作用所致。     

黔南Triticites带旋回层序碳同位素特征及冰川型海平面变化

应用层序地层学理论对黔南独山地区晚石炭世麦粒链带地层进行了详细的沉积层序分析和系统的碳同位素测定，识别出２个三级沉积层序和１７个准层序，其可与北美中大陆同期地层中发现的２个三级沉积层序和１７个亚层序对比，是晚石炭世Ｇｚｈｅｌｉａｎ期存在全球沉积记录同时性的佐证。同时探讨了碳同位素演化与全球海平面变化之间的内在联系，总结出沉积层序内碳同位素演化规律。     

Stratigraphy of the upper cretaceous and lower tertiary strata in the Tethyan Himalayas of Tibet (Tingri area,China)

The 1500-m-thick marine strata of the Tethys Himalaya of the Zhepure Mountain (Tingri, Tibet) comprise the Upper Albian to Eocene and represent the sedimentary development of the passive northern continental margin of the Indian plate. Investigations of foraminifera have led to a detailed biozonation which is compared with the west Tethyan record. Five stratigraphic units can be distinguished: The Gamba group (Upper Albian - Lower Santonian) represents the development from a basin and slope to an outer-shelf environment. In the following Zhepure Shanbei formation (Lower Santonian - Middle Maastrichtian), outer-shelf deposits continue. Pebbles in the top layers point to beginning redeposition on a continental slope. Intensified redeposition continues within the Zhepure Shanpo formation (Middle Maastrichtian - Lower Paleocene). The series is capped by sandstones of the Jidula formation (Danian) deposited from a seaward prograding delta plain. The overall succession of these units represents a sea-level high at the Cenomanian/Turonian boundary followed, from the Turonian to Danian, by an overall shallowing-upward megasequence. This is followed by a final transgression — regression cycle during the Paleocene and Eocene, documented in the Zhepure Shan formation (?Upper Danian - Lutetian) and by Upper Eocene continental deposits. The section represents the narrowing and closure of the Tethys as a result of the convergence between northward-drifting India and Eurasia. The plate collision started in the Lower Maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and uplift. Stronger subsidence and deposition took place from the Middle Maastrichtian to the Lower Paleocene. The final closure of remnant Tethys in the Tingri area took place in the Lutetian.     

~(40)Ar/~(39)Ar dating of shear deformation of the Xianshuihe fault zone in west Sichuan and its tectonic significance

TheNW-SEstrikingXianshuihefaultzoneslicesthesoutheasternTibetanPlateauandconnectssoutheastwardwiththeAnninghe-Zemuhe-Xiaojiangfaultzone,whichformahuge,activesinistralstrike-slipfaultzone(fig.1).ThisfaultzoneisanimportantseismicfaultineastTibet[1-5].EarthquakegeologystudiesandoffsetpatternsofyounggeologicalfeatureshaveshownthatlateQuaternarysinistralsliprateoftheXianshuihefaultzonereaches13mm/a[1,2].TheXianshuhefaultzoneconsistsoftwomainbranches,theDaofufaultbranchinthewestandtheXianshuih…     

Preliminary Study on Cenozoic Group and Fault Activity in the Sea Area Near the Yangtze River Mouth

By shallow seismic prospecting, the Cenozoic Group in the sea area near the Yangtze Rver Mouth can be divided into five seismic sequences. They correspond to the Quaternary,Pliocene, Upper Miocene, Lower Miocene and Eocene respectively. The Quaternary System covers all the detecting area. The Tertiary System overlaps and thins out from NE to SW. The sedimentary basement mainly consists of volcanic rock (J3) and acidic rock (r35). Paleogene or Late Cretaceous basins are not found there. The faults that have been detected are all normal faults. They can be divided into three groups (NE, NW, near EW) by their trend. The NE and NW-trending faults are predominant, and agree with aeromagnetic anomaly. Their length and displacement are larger than that of the EW-trending faults. The activity of the NEtrending faults is different in different segments. The SW segment is a Quaternary fault, the middle segment is a Neogene fault, The NE is Paleogene. But the segment of the NW-trending fault is not obvious. The average vertical displacement rate is about 0.015mm/a.     

滇西北新生代逆冲推覆构造

滇西北地区新生代逆冲推覆构造较为发育，从西到东可分出走向NS、相互平行的4带：澜沧江带，云岭带，石钟山带和剑川-洱源带。其中，澜沧江带与云岭带组成对冲格局，云岭带又与石钟山带组成反冲格局，石钟山带与剑川-洱源带又组成对冲格局。参与逆冲推覆的地层主要是中生代三叠系、侏罗系、白垩系及新生代云龙组、宝相寺组，推覆体由石炭系、二叠系、上三叠统岩石组成。逆冲推覆时间为喜马拉雅期。     

P–T–fO2 controls on a partly inverse chromite-bearing ultramafic intrusive: an evaluation from the Sukinda Massif, India

The chromites from the alpine type ultramafic intrusive of Sukinda, India, display a typical partly inverse spinel form and occur in two distinct zones: Brown Ore Zone (BOZ) and Grey Ore Zone (GOZ). The host ultramafites are mostly altered and are represented by the serpentinite, tremolite-talc(chlorite) schist, talc-serpentine schist and chlorite rock. The less altered variants are dunite, harzburgite and websterite. A dyke of orthopyroxenite runs through the main ultramafic body.The composition of olivine (Fo₉₂), orthopyroxene (En_92–89) and Al₂O₃ contents of the parental liquid (10.40–11.45%) determined from chromites, suggest that the parent melt is of boninitic affinity. The chemical plot of TiO₂ content against cr# of chromites corroborates a boninitic parental melt. The Fe–Mg partitioning in olivine and chromite depicts the temperature for chromitites as 1200 °C. A compositional plot of mg# and cr# suggests crystallization at high pressure conditions, corresponding to the kimberlite xenolith field. From the P–T diagram of pyrolite melting and mineral assemblage, the pressure of crystallization is stipulated to be ≥1.2 GPa. The f_O2 values estimated from Fe³⁺/Cr+Al+Fe³⁺ ratios range from 10^−8.3 to 10^−9.3 for the GOZ and 10^−7.1 to 10^−7.3 for the BOZ. The f_O2 values together with the pressure range suggest crystallization at upper mantle conditions. The heterogeneity in chemical composition and f_O2 conditions for the GOZ and BOZ could be linked to heterogeneity in the upper mantle.     

Sedimentology and kinematics of a large, retrogressive growth-fault system in Upper Carboniferous deltaic sediments, western Ireland

Growth faulting is a common feature of many deltaic environments and is vital in determining local sediment dispersal and accumulation, and hence in controlling the resultant sedimentary facies distribution and architecture. Growth faults occur on a range of scales, from a few centimetres to hundreds of metres, with the largest growth faults frequently being under‐represented in outcrops that are often smaller than the scale of feature under investigation. This paper presents data from the exceptionally large outcrops of the Cliffs of Moher, western Ireland, where a growth‐fault complex affects strata up to 60 m in thickness and extends laterally for ≈ 3 km. Study of this Namurian (Upper Carboniferous) growth‐fault system enables the relationship between growth faulting and sedimentation to be detailed and permits reconstruction of the kinematic history of faulting. Growth faulting was initiated with the onset of sandstone deposition on a succession of silty mudstones that overlie a thin, marine shale. The decollement horizon developed at the top of the marine shale contact for the first nine faults, by which time aggradation in the hangingwall exceeded 60 m in thickness. After this time, failure planes developed at higher stratigraphic levels and were associated with smaller scale faults. The fault complex shows a dominantly landward retrogressive movement, in which only one fault was largely active at any one time. There is no evidence of compressional features at the base of the growth faults, thus suggesting open‐ended slides, and the faults display both disintegrative and non‐disintegrative structure. Thin‐bedded, distal mouth bar facies dominate the hangingwall stratigraphy and, in the final stages of growth‐fault movement, erosion of the crests of rollover structures resulted in the highest strata being restricted to the proximity of the fault. These upper erosion surfaces on the fault scarp developed erosive chutes that were cut parallel to flow and are downlapped by the distal hangingwall strata of younger growth faults.     

Caractéristiques et signification d'un niveau coquillier majeur à brachiopodes,marqueur événementiel dans l'évolution dévonienne de la Saoura (Sahara du Nord-Ouest,Algérie)

In the Saoura, the brachiopod shell beds, so-called niveau coralligène, correspond to a major shell deposit dated to the Late Emsian. Brachiopods and crinoids dominate the benthic assemblage that contains also corals, bryozoans, trilobites, goniatites, and orthocones. This major level has a large geographic distribution and it is characterized by a wide brachiopod diversity due to time-averaging, taphonomic feedback and alternate bottom conditions changing from soft to shelly and firm. This kind of brachiopod association is linked to a transgressive onlap system. At regional extent, we can correlate this major shell bed to similar shell deposits from the Ahnet-Mouydir, Tindouf, and Zemmour areas. It indicates an important transgressive event underlined by change in the sedimentation from detritic deposits to carbonate sediments. To cite this article: A. Ouali Mehadji et al., C. R. Geoscience 336 (2004).     

Upper Pleistocene and Holocene paleosalinity and trophic state changes in relation to sea level variation in Rocha Lagoon, southern Uruguay

Paleolimnological data are presented on trophic development in relation to sea level variation in Rocha Lagoon, a 72 km² coastal lagoon in southern Uruguay. Using sediment cores that extended to ∼20,000 yr BP, analyses of grain size, organic matter, carbonate, total carbon, nutrients, and diatoms allowed us to infer changes in trophic state and paleosalinities, which were closely related to Holocene relative sea level variation. Higher trophic states were observed during regressive events, most probably due to increases in runoff and erosion as regressions progressed. Diatom Association Zones (DAZ) were identified in both cores. Those DAZ corresponding to transgressive events were dominated by marine/brackish taxa and relatively low organic matter and nutrient values, while those DAZ corresponding to regressive events showed increases in brackish/freshwater diatoms and both organic matter and nutrients. Although the lagoon formed after the first Holocene marine transgression, our data indicate the existence of a marine/brackish aquatic system during upper Pleistocene (i.e., before 15,000 yr BP), but by ∼20,000 yr BP, the system was still likely to be a semi-arid terrestrial system.