Geology and geomorphology--Offshore of Carpinteria, California

This part of SIM 3261 presents data for the geologic and geomorphic map (see sheet 10, SIM 3261) of the Offshore of Carpinteria map area, California. The vector data file is included in "Geology_OffshoreCarpinteria.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreCarpinteria/data_catalog_OffshoreCarpinteria.html.
The offshore part of the map area largely consists of a relatively shallow (less than about 45 m deep), gently offshore-dipping (less than 1 degree) shelf underlain by sediments derived primarily from relatively small coastal watersheds that drain the Santa Ynez Mountains. Shelf deposits are primarily sand (unit Qms) at depths less than about 25 m and, at depths greater than about 25 m, are the more fine-grained sediments (very fine sand, silt, and clay) of unit Qmsf. The boundary between units Qms and Qmsf is based on observations and extrapolation from sediment sampling (see, for example, Reid and others, 2006) and camera ground-truth surveying (see sheet 6). It is important to note that the boundary between units Qms and Qmsf should be considered transitional and approximate and is expected to shift as a result of seasonal- to annual- to decadal-scale cycles in wave climate, sediment supply, and sediment transport.
Coarser grained deposits (coarse sand to boulders) of unit Qmsc, which are recognized on the basis of their moderate seafloor relief and high basckscatter (sheet 3), as well as camera observations (sheet 6) and sampling (Reid and others, 2006; Barnard and others, 2009), are found locally in water depths less than about 15 m, except offshore of Rincon Point where they extend to depths of about 21 m. The largest Qmsc deposits are present at the mouths of Rincon Creek and Toro Canyon Creek. The convex seafloor relief of these coarse-grained deposits suggests that they are wave-winnowed lags that armor the seafloor and are relatively resistant to erosion. The sediments may, in part, be relict, having been deposited in shallower marine (or even alluvial?) environments at lower sea levels in the latest Pleistocene and Holocene; this seems especially likely for the arcuate lobe of unit Qmsc that extends 1,700 m offshore from Rincon Point. The Qmsc deposits offshore of Toro Canyon Creek are found adjacent to onshore alluvial and alluvial fan deposits (Minor and others, 2009) and, thus, may have formed as distal-alluvial or fan-delta facies of that system.
Offshore bedrock exposures are assigned to the Miocene Monterey Formation (unit Tm) and the Pliocene and Pleistocene Pico Formation (unit QTp), primarily on the basis of extrapolation from the onshore mapping of Tan and others (2003a,b), Tan and Clahan (2004), and Minor and others (2009), as well as the cross sections of Redin and others (1998, 2004) that are constrained by industry seismic-reflection data and petroleum well logs. Where uncertainty exists, bedrock is mapped as an undivided unit (QTbu). These strata are exposed in structural highs that include the Rincon Anticline and uplifts bounded by the Rincon Creek Fault and by the north and south strands of the Red Mountain Fault.
Bedrock is, in some places, overlain by a thin (less than 1 m?) veneer of sediment, recognized on the basis of high backscatter, flat relief, continuity with moderate- to high-relief bedrock outcrops, and (in some cases) high-resolution seismic-reflection data; these areas, which are mapped as composite units Qms/Tm, Qms/QTbu, or Qms/QTp, are interpreted as ephemeral sediment layers that may or may not be continuously present, whose presence or absence is a function of the recency and intensity of storm events, seasonal and (or) annual patterns of sediment movement, or longer term climate cycles.
Two offshore anthropogenic units also are present in the map area, each related to offshore hydrocarbon production. The first (unit af) consists of coarse artificial fill associated with construction of the Rincon Island petroleum-production facility near the east edge of the map area. The second (unit pd) consists of coarse artificial fill mixed with sediment and shell debris, mapped in outcrops surrounding Rincon Island and at the locations of former oil platforms "Heidi," "Hope," "Hazel," and "Hilda" from the Summerland and Carpinteria oil fields (Barnum, 1998). The Monterey Formation is the primary petroleum-source rock in the Santa Barbara channel, and the Pico Formation is one of the primary petroleum reservoirs.
The Offshore of Carpinteria map area is in the Ventura Basin, in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland (Fisher and others, 2009). This province has undergone significant north-south compression since the Miocene, and recent GPS data suggest north-south shortening of about 6 to 10 mm/yr (Larson and Webb, 1992; Donnellan and others, 1993). The active, east-west-striking, north-dipping Pitas Point Fault (a broad zone that includes south-dipping reverse-fault splays), Red Mountain Fault, and Rincon Creek Fault are some of the structures on which this shortening occurs (see, for example, Jackson and Yeats, 1982; Sorlien and others, 2000). This fault system, in aggregate, extends for about 100 km through the Ventura and Santa Barbara Basins and represents an important earthquake hazard (see, for example, Fisher and others, 2009).
References Cited:
Barnum, H.P., 1998, Redevelopment of the western portion of the Rincon offshore oil field, Ventura, California, in Kunitomi, D.S., Hopps, T.E., and Galloway, J.M., eds., Structure and petroleum geology, Santa Barbara Channel, California: American Association of Petroleum Geologists, Pacific Section, and Coast Geological Society, Miscellaneous Publication 46, p. 201-215.
Donnellan, A., Hager, B.H., and King, R.W., 1993, Discrepancy between geologic and geodetic deformation rates in the Ventura basin: Nature, v. 346, p. 333-336.
Fisher, M.A., Sorlien, C.C., and Sliter, R.W., 2009, Potential earthquake faults offshore southern California from the eastern Santa Barbara channel to Dana Point, in Lee, H.J., and Normark, W.R., eds., Earth science in the urban ocean--The Southern California Continental Borderland: Geological Society of America Special Paper 454, p. 271-290.
Jackson, P.A., and Yeats, R.S., 1982, Structural evolution of Carpinteria basin, western Transverse Ranges, California: American Association of Petroleum Geologists Bulletin, v. 66, p. 805-829.
Larson, K.M., and Webb, F.H., 1992, Deformation in the Santa Barbara Channel from GPS measurements 1987-1991: Geophysical News Letters, v. 19, p. 1,491-1,494.
Minor, S.A., Kellogg, K.S., Stanley, R.G., Gurrola, L.D., Keller, E.A., and Brandt, T.R., 2009, Geologic map of the Santa Barbara coastal plain area, Santa Barbara County, California: U.S. Geological Survey Scientific Investigations Map 3001, scale 1:25,000, 1 sheet, pamphlet 38 p., available at http://pubs.usgs.gov/sim/3001/.
Redin, T., Forman, J., and Kamerling, M.J., 1998, Regional structure section across the eastern Santa Barbara Channel, from eastern Santa Cruz Island to the Carpinteria area, Santa Ynez Mountains, in Kunitomi, D.S., Hopps, T.E., and Galloway, J.M., eds., Structure and petroleum geology, Santa Barbara Channel, California: American Association of Petroleum Geologists, Pacific Section, and Coast Geological Society, Miscellaneous Publication 46, p. 195-200, 1 sheet.
Redin, T., Kamerling, M.J., and Forman, J., 2004, Santa Barbara Channel structure and correlation sections--Correlation section no. 34R., N-S structure and correlation section, south side central Santa Ynez Mountains across the Santa Barbara channel to the east end of Santa Cruz Island: American Association of Petroleum Geologists, Pacific Section, Publication CS 32, 1 sheet.
Reid, J.A., Reid, J.M., Jenkins, C.J., Zimmerman, M., Williams, S.J., and Field, M.E., 2006, usSEABED--Pacific Coast (California, Oregon, Washington) offshore surficial-sediment data release: U.S. Geological Survey Data Series 182, available at http://pubs.usgs.gov/ds/2006/182/.
Sorlien, C.C., Gratier, J.P., Luyendyk, B.P., Hornafius, J.S., and Hopps, T.E., 2000, Map restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California: Geological Society of America Bulletin, v. 112, p. 1,080-1,090.
Tan, S.S., and Clahan, K.B., 2004, Geologic map of the White Ledge Peak 7.5' quadrangle, Santa Barbara and Ventura Counties, California--A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm.
Tan, S.S., Jones, T.A., and Clahan, K.B., 2003a, Geologic map of the Pitas Point 7.5' quadrangle, Ventura County, California--A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm.
Tan, S.S., Jones, T.A., and Clahan, K.B., 2003b, Geologic map of the Ventura 7.5' quadrangle, Ventura County, California--A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm.

SIM 3261的本部分提供了加利福尼亚州卡平特里亚近海地图区的地质与地貌图数据（详见SIM 3261第10图幅）。矢量数据文件包含于"Geology_OffshoreCarpinteria.zip"压缩包中，可通过http://pubs.usgs.gov/ds/781/OffshoreCarpinteria/data_catalog_OffshoreCarpinteria.html获取。

该地图区的近海主体为相对浅水区（水深约小于45米）、平缓向海倾斜（倾角小于1°）的陆架，其下伏沉积物主要源自汇水入海的圣伊内斯山脉小型沿海流域。陆架沉积在水深约小于25米处以砂为主，对应地层单元Qms；而在水深约大于25米处则为更细粒的沉积物（极细砂、粉砂与黏土），对应地层单元Qmsf。Qms与Qmsf的分界基于沉积物采样（例如Reid等，2006）与相机实地勘测（详见第6图幅）的观测结果外推得到。需注意，Qms与Qmsf的分界应视为过渡且近似的，其位置会随波浪气候、沉积物供给与沉积物搬运的季节-年-十年尺度周期发生变化。

地层单元Qmsc的粗粒沉积（粒度范围从粗砂至巨砾），依据其中等海底起伏与高后向散射强度（第3图幅）、相机观测（第6图幅）与采样数据（Reid等，2006；Barnard等，2009）识别得出，局部分布在水深约小于15米的区域，仅林孔角近海处可延伸至约21米水深。规模最大的Qmsc沉积分布于林孔溪与托罗峡谷溪的河口区域。这些粗粒沉积的凸状海底起伏表明，它们是经波浪淘洗形成的滞留沉积，可覆盖海底并相对抗侵蚀。这些沉积物可能部分为残余沉积，在更新世晚期与全新世时期的低海平面条件下，沉积于更浅的海洋（甚至冲积）环境中；对于从林孔角向海延伸1700米的Qmsc单元弧形叶状体而言，这一推测尤为成立。托罗峡谷溪近海的Qmsc沉积与陆上冲积和冲积扇沉积相邻（Minor等，2009），因此可能形成于该系统的远端冲积或扇三角洲相。

近海基岩露头被归为中新世蒙特雷组（地层单元Tm）以及上新世与更新世皮科组（地层单元QTp），划分依据主要参考Tan等（2003a、b）、Tan与Clahan（2004）以及Minor等（2009）的陆上填图结果，同时结合Redin等（1998、2004）由工业地震反射数据与石油测井资料约束的剖面。存在不确定性的区域，基岩被划分为未分单元（QTbu）。这些地层暴露于构造高地中，包括林孔背斜以及受林孔溪断层和红山断层南北分支控制的抬升地块。

部分区域内，基岩之上覆盖有薄（厚度小于1米？）的沉积物盖层，依据高后向散射强度、平缓起伏、与中-高起伏基岩露头的连续性，以及（部分案例中的）高分辨率地震反射数据识别得出；这些区域被划分为复合地层单元Qms/Tm、Qms/QTbu或Qms/QTp，被解释为暂时性沉积层，可能持续存在也可能不持续，其存在与否取决于风暴事件的新近程度与强度、沉积物运移的季节和（或）年际规律，以及长期气候周期。

地图区内还存在两个近海人为地层单元，均与近海油气生产相关。第一个（单元af）为与地图区东缘附近林孔岛石油生产设施建设相关的粗粒人工填筑物。第二个（单元pd）为混合有沉积物与贝壳碎屑的粗粒人工填筑物，分布在林孔岛周边露头以及萨默兰和卡平特里亚油田的前“海蒂”“霍普”“黑兹尔”和“希尔达”石油钻井平台位置（Barnum，1998）。蒙特雷组是圣巴巴拉海峡的主要烃源岩，而皮科组是主要的油气储集层之一。

卡平特里亚近海地图区位于文图拉盆地，属于西部横断山脉地质省的南部区域，该省位于加利福尼亚大陆边缘带以北（Fisher等，2009）。该省自中新世以来经历了显著的南北向挤压，近期GPS数据显示南北向缩短速率约为6至10毫米/年（Larson与Webb，1992；Donnellan等，1993）。活动的东西走向、北倾的皮塔斯点断层（一个包含南倾逆断层分支的宽缓带）、红山断层与林孔溪断层是该挤压作用发生的部分构造（例如Jackson与Yeats，1982；Sorlien等，2000）。该断层系统整体延伸约100千米，穿过文图拉与圣巴巴拉盆地，是重要的地震危险源（例如Fisher等，2009）。

参考文献
Barnum, H.P., 1998, 加利福尼亚州文图拉市林孔近海油田西区重建，收录于Kunitomi, D.S.、Hopps, T.E. 与Galloway, J.M.编辑，《加利福尼亚州圣巴巴拉海峡构造与石油地质学》：美国石油地质学家协会太平洋分会与海岸地质学会杂刊第46号，第201-215页。
Donnellan, A., Hager, B.H. 与King, R.W., 1993, 文图拉盆地地质与大地测量变形速率之间的差异：《自然》，第346卷，第333-336页。
Fisher, M.A., Sorlien, C.C. 与Sliter, R.W., 2009, 从圣巴巴拉海峡东部至达纳角的南加州近海潜在地震断层，收录于Lee, H.J. 与Normark, W.R.编辑，《城市海洋中的地球科学——南加州大陆边缘带》：美国地质学会特刊第454号，第271-290页。
Jackson, P.A. 与Yeats, R.S., 1982, 加利福尼亚州西部横断山脉卡平特里亚盆地的构造演化：《美国石油地质学家协会通报》，第66卷，第805-829页。
Larson, K.M. 与Webb, F.H., 1992, 1987-1991年GPS测量得到的圣巴巴拉海峡变形：《地球物理新闻通讯》，第19卷，第1491-1494页。
Minor, S.A., Kellogg, K.S., Stanley, R.G., Gurrola, L.D., Keller, E.A. 与Brandt, T.R., 2009, 加利福尼亚州圣巴巴拉县圣巴巴拉沿海平原地区地质图：美国地质调查局科学调查图件3001，比例尺1:25000，1幅图，说明书38页，可通过http://pubs.usgs.gov/sim/3001/获取。
Redin, T., Forman, J. 与Kamerling, M.J., 1998, 圣克鲁兹岛东部至卡平特里亚地区、圣伊内斯山脉的圣巴巴拉海峡东部区域构造剖面，收录于Kunitomi, D.S.、Hopps, T.E. 与Galloway, J.M.编辑，《加利福尼亚州圣巴巴拉海峡构造与石油地质学》：美国石油地质学家协会太平洋分会与海岸地质学会杂刊第46号，第195-200页，1幅图。
Redin, T., Kamerling, M.J. 与Forman, J., 2004, 圣巴巴拉海峡构造与对比剖面——对比剖面第34R号：南北向构造与对比剖面，圣伊内斯山脉中部南侧跨圣巴巴拉海峡至圣克鲁兹岛东端：美国石油地质学家协会太平洋分会出版物CS 32，1幅图。
Reid, J.A., Reid, J.M., Jenkins, C.J., Zimmerman, M., Williams, S.J. 与Field, M.E., 2006, usSEABED——太平洋海岸（加利福尼亚、俄勒冈、华盛顿）近海表层沉积物数据发布：美国地质调查局数据系列182，可通过http://pubs.usgs.gov/ds/2006/182/获取。
Sorlien, C.C., Gratier, J.P., Luyendyk, B.P., Hornafius, J.S. 与Hopps, T.E., 2000, 加利福尼亚州文图拉盆地陆上与近海褶皱断裂晚新生代地层的地图恢复：《美国地质学会通报》，第112卷，第1080-1090页。
Tan, S.S. 与Clahan, K.B., 2004, 加利福尼亚州圣巴巴拉与文图拉县White Ledge Peak 7.5' quadrangle地质图——数字数据库：加利福尼亚地质调查局初步地质图，比例尺1:24000，可通过http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm获取。
Tan, S.S., Jones, T.A. 与Clahan, K.B., 2003a, 加利福尼亚州文图拉县Pitas Point 7.5' quadrangle地质图——数字数据库：加利福尼亚地质调查局初步地质图，比例尺1:24000，可通过http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm获取。
Tan, S.S., Jones, T.A. 与Clahan, K.B., 2003b, 加利福尼亚州文图拉县Ventura 7.5' quadrangle地质图——数字数据库：加利福尼亚地质调查局初步地质图，比例尺1:24000，可通过http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm获取。