Lithogeochemical Character of Near-Surface Bedrock in the New England Coastal Basins

This geographic information system (GIS) data layer shows the generalized
lithologic and geochemical, termed lithogeochemical, character of
near-surface bedrock in the New England Coastal Basins (NECB) study
area of the U.S. Geological Survey's National Water Quality Assessment
(NAWQA) Program. The area encompasses 23,000 square miles in western
and central Maine, eastern Massachusetts, most of Rhode Island,
eastern New Hampshire and a small part of eastern Connecticut.
The NECB study area includes the Kennebec, Androscogginn, Saco,
Merrimack, Charles, and Blackstone River Basins, as well as all
of Cape Cod. Bedrock units in the NECB study area are classified into
38 lithogeochemical units based on the relative reactivity of their
constituent minerals to dissolution and the presence of carbonate or
sulfide minerals. The 38 lithogeochemical units are generalized into 7
major groups: (1) carbonate-bearing metasedimentary rocks; (2)primarily
noncalcareous, clastic sedimentary rocks with restricted deposition in
discrete fault-bounded sedimentary basins of Mississipian or younger age;
(3) primarily noncalcareous, clastic sedimentary rocks at or above
biotite-grade of regional metamorphism; (4) mafic igneous rocks and
their metamorphic equivalents; (5) ultramafic rocks; (6) felsic igneous
rocks and their metamorphic equivalents; and (7) unconsolidated and poorly
consolidated sediments.

本地理信息系统（GIS）数据图层展示了美国地质调查局国家水质评估（NAWQA）计划中新英格兰沿海盆地（NECB）研究区内近地表基岩的概化岩地球化学（lithogeochemical）特征。该研究区覆盖缅因州中西部、马萨诸塞州东部、罗德岛州大部、新罕布什尔州东部以及康涅狄格州东部的小片区域，总面积达23000平方英里。NECB研究区涵盖肯纳贝克河、安德罗斯科金河、萨科河、梅里马克河、查尔斯河与布莱克斯通河流域，以及整个科德角地区。NECB研究区内的基岩单元，依据其组成矿物相对于溶解作用的反应活性，以及碳酸盐或硫化物矿物的赋存状态，被划分为38个岩地球化学单元。上述38个岩地球化学单元被进一步概化为7大类：（1）含碳酸盐变沉积岩；（2）以非钙质碎屑沉积岩为主，且仅局限沉积于密西西比纪或更年轻的、受断层约束的孤立沉积盆地中；（3）以非钙质碎屑沉积岩为主，达到或高于区域变质作用的黑云母级；（4）镁铁质火成岩及其变质等同岩；（5）超镁铁质岩；（6）长英质火成岩及其变质等同岩；（7）未固结及弱固结沉积物。