Abstract Mechanical stratigraphy exerts a first-order control on deformation at a range of scales from oilfield-scale structural style to deformation (e.g. fracturing) within an individual reservoir stratum. This paper explores an outcrop example where mechanical stratigraphy in a limestone and shale sequence directly influenced the structural style and distribution of deformation related to the propagation of a ‘seismic-scale’ normal fault that has maximum displacement on the order of 100–500 m and extends for more than 10 km. A monocline developed in Cretaceous Buda Limestone above tectonically thinned Del Rio Clay and faulted Santa Elena Limestone is here interpreted as an extensional fault propagation fold. Monocline limb dips reach 59°. The Del Rio Clay is thinned from approximately 36 m to 1.5 m, whereas the underlying Santa Elena Limestone is offset vertically by approximately 74 m along a steep (approximately 80°) normal fault. This large fault displacement of the Santa Elena Limestone is not transferred upward to the Buda Limestone because of ductile flow within the intervening Del Rio Clay. Although upward fault propagation has been inhibited, thinning of the Del Rio Clay and the resultant extreme displacement gradient at the tip of the fault have forced the Buda Limestone into a monoclinal fold. Two competent packstone and grainstone beds, 6 m and 2.7 m thick and separated by 10.5 m of less competent calcareous shale, comprise the Buda Limestone at this location. Deformation features within the competent Buda beds include bed-perpendicular veins that accommodate bed-parallel extension, and bedding plane slip surfaces with an up-dip sense of shear that offset the veins. Deformation is concentrated in the monoclinal limb and not in the monoclinal hinge regions. Consequently, bed-parallel extension and shear strain are associated with monoclinal dip, not with curvature. These results show that for this structure, bed dip is a better proxy for bed-parallel extension and related fracture dilation than is curvature.

Abstract Santa Elena Canyon and the Anguila Fault Zone northwest of the canyon are occupied by the Rio Grande. These features separate Mesa de Anguila, the westernmost part of Big Bend National Park, Brewster County, Texas, from northeastern Chihuahua, Mexico (Fig. 1). The traverse begins on the river at Lajitas (reached by FM 170), southwestern Brewster County, about 2 mi (3.2 km) above the entry to an upper canyon, and ends at the lower end of Santa Elena Canyon, where Terlingua Creek joins the Rio Grande from the northwest. This location is accessible by a paved park road. The canyons are accessible only by river, a trip best made in a sturdy rubber raft. Travel through the canyons is strictly regulated by the Big Bend National Park administration, particularly with respect to safety equipment and camping. Permits may be obtained at a ranger station at Lajitas, or at park headquarters at Panther Junction. The simplest procedure is to arrange a guided tour through businesses in Lajitas, Terlingua Ghost Town 12.5 mi (20.1 km) east of Lajitas on FM 170, or Study Butte (junction of Texas 118 and FM 170) 16.9 mi (27.2 km) east. A permit is necessary to collect rock samples in any national park; even if the intent is to restrict sampling to the Mexican side of the river, it would be best to obtain such a permit. Santa Elena Canyon and the lesser (but still impressive) canyon immediately upstream provide access at and near river level to virtually

Abstract There is a long history of debate over glacial versus non-glacial interpretations of both Quaternary and pre-Quaternary diamicts in various places around the world, and the Spring Mountains in southern Nevada are the site of one such debate. Here the debate focuses not only on Quaternary diamicts, but also on landforms and erosional features. The deposits and geomorphic features in question will be examined on this field trip. The Spring Mountains are developed in a fault block in the southern Basin and Range Province; elevations range from ~4000 ft (1220 m) at the eastern base to 11,918 ft (3634 m) at Charleston Peak. The range is farther south than any other glaciated range in Nevada; however, the glaciated San Gorgonio Mountains on the border of the Basin and Range in California are farther south, though in a much more maritime position. The Spring Mountains lie in the rain shadow of the Sierra Nevada; rainfall increases from ~4 in (10 cm) per year in the Las Vegas Valley to ~20 in (50 cm) per year at the crest of the range. A published interpretation of sedimentary and geomorphic features at the head of Kyle Canyon claims that steep valley heads of Kyle Canyon and Big Falls wash are degraded cirques, that a ridge at the mouth of Big Falls wash is a lateral moraine, and that diamicts exposed in the ridge include glacial till. An alternative view is that the “cirques” are normal valley heads as are found in high-relief desert ranges, that the “lateral moraine” owes some of its ridge character to erosion along Big Falls wash and may originally have been a debris flow levee or a protalus rampart, and that the “till” is actually colluvium. Abundant clast striations constitute a key element of the glacial interpretation, and much rests on whether glacial striations can be distinguished from mass movement striations.

Abstract One of the best exposures of the Sierra Madre thrust fault can be seen in the west wall of Santa Anita Canyon in Wilderness Park, city of Arcadia, 15 mi (25 km) northeast of downtown Los Angeles. Figure 1 shows how one can drive to the fault exposure by turning left into the first available parking area in Wilderness Park. The park gates are open 900 am to 5:00 pm daily. The 54-mi-long (90 km) Sierra Madre fault zone forms the southern base of the San Gabriel Mountains along which they have been thrust over the valleys to the south. The 1971 San Fernando M 6.4 earthquake, caused by this fault, created 15 mi (25 km) of surface ruptures beginning 24 mi (40 km) west of this exposure.At the west side of Arcadia’s Wilderness Park (Fig. 2), banded gneiss is thrust over old alluvium containing large boulders. The fault consists of several feet of gouge and crushed rock generated from the gneiss; it dips 35 degrees north. The fault cannot be traced into the upper part of the old alluvium and probably has been inactive since it was deposited, roughly 2,000 to 5,000 years ago (Crook and others,1978). Two of the earliest geologists to describe the San Gabriel Mountains (Davis, 1927; Miller, 1928) believed the range was bounded on the south by normal faults. Mason Hill (1980) was first to show that the western part of the range was not created by the typical basin and range-type faulting. In the late 1930s, John P. Buwalda (1940) mapped portions of the fault zone between La Canada and Monrovia. He was the first to describe the Sierra Madre fault as “a rather wide zone complexly braided as to pattern of fracture lines” rather than a single line trace. It was not until the 1960s that portions of the fault zone were mapped in detail. This mapping was done bya group of Metropolitan Water District (MWD) of Southern California geologists of which the authors were a part. The 1:12,000 scale mapping was carried out between the ArroyoSeco on the west and Sycamore Canyon on the east andestablished 11 localities where crystalline basementrocks could be seen thrust over Quaternary alluvium. The Wilderness Park site was, to our best recollection, discovered during this project by Daniel C. Kalin and isjudged by us to be the best easily accessible example. The first published map showing the fault zone and the Wilderness Park site was produced by Douglas M. Morton(1973). His map shows this fault trace to branch into the interior of the mountain range rather than follow the southern base as does the main fault zone. From 1975–78 the authors, along with C. R. Allen, B. Kamb, and C. M. Payne mapped the fault zone in greater detail, and trenched the fault, as part of a USGS grant to Caltech (Crook and others, 1978). The area mapped is a strip 1.2 to 2.4 mi (2 to 4km) wide extending 24 mi (40 km) from Big Tujanga to San Gabriel Canyons. The 14C dates obtained from the Caltech work reveal that the central part of the Sierra Madre fault has notmoved in 5,000 years. This contrasts with the 1971 earthquake to the west and the recent evidence that the Cucaonga branch to the east has a recurrence interval of about 800 years (Morton and others, 1982). Is the central part of the fault zone truly orders of magnitude less active, or has it accumulated enough strain energyto be currently worrisome?

Abstract One of the best exposures of the Sierra Madre thrust fault can be seen in the west wall of Santa Anita Canyon in Wilderness Park, city of Arcadia, 15 mi (25 km) northeast of downtown Los Angeles. Figure 1 shows how one can drive to the fault exposure by turning left into the first available parking area in Wilderness Park. The park gates are open 900 am to 5:00 pm daily. The 54-mi-long (90 km) Sierra Madre fault zone forms the southern base of the San Gabriel Mountains along which they have been thrust over the valleys to the south. The 1971 San Fernando M 6.4 earthquake, caused by this fault, created 15 mi (25 km) of surface ruptures beginning 24 mi (40 km) west of this exposure.At the west side of Arcadia’s Wilderness Park (Fig. 2), banded gneiss is thrust over old alluvium containing large boulders. The fault consists of several feet of gouge and crushed rock generated from the gneiss; it dips 35 degrees north. The fault cannot be traced into the upper part of the old alluvium and probably has been inactive since it was deposited, roughly 2,000 to 5,000 years ago (Crook and others,1978). Two of the earliest geologists to describe the San Gabriel Mountains (Davis, 1927; Miller, 1928) believed the range was bounded on the south by normal faults. Mason Hill (1980) was first to show that the western part of the range was not created by the typical basin and range-type faulting. In the late 1930s, John P. Buwalda (1940) mapped portions of the fault zone between La Canada and Monrovia. He was the first to describe the Sierra Madre fault as “a rather wide zone complexly braided as to pattern of fracture lines” rather than a single line trace. It was not until the 1960s that portions of the fault zone were mapped in detail. This mapping was done bya group of Metropolitan Water District (MWD) of Southern California geologists of which the authors were a part. The 1:12,000 scale mapping was carried out between the ArroyoSeco on the west and Sycamore Canyon on the east andestablished 11 localities where crystalline basementrocks could be seen thrust over Quaternary alluvium. The Wilderness Park site was, to our best recollection, discovered during this project by Daniel C. Kalin and isjudged by us to be the best easily accessible example. The first published map showing the fault zone and the Wilderness Park site was produced by Douglas M. Morton(1973). His map shows this fault trace to branch into the interior of the mountain range rather than follow the southern base as does the main fault zone. From 1975–78 the authors, along with C. R. Allen, B. Kamb, and C. M. Payne mapped the fault zone in greater detail, and trenched the fault, as part of a USGS grant to Caltech (Crook and others, 1978). The area mapped is a strip 1.2 to 2.4 mi (2 to 4km) wide extending 24 mi (40 km) from Big Tujanga to San Gabriel Canyons. The 14C dates obtained from the Caltech work reveal that the central part of the Sierra Madre fault has notmoved in 5,000 years. This contrasts with the 1971 earthquake to the west and the recent evidence that the Cucaonga branch to the east has a recurrence interval of about 800 years (Morton and others, 1982). Is the central part of the fault zone truly orders of magnitude less active, or has it accumulated enough strain energyto be currently worrisome?

Abstract We cannot hope to predict Mesozoic depositional processes and sediment properties well enough to plan effective regional exploration strategies without considering the big picture of Gulf of Mexico deposystem evolution. The two critical big picture elements are the kinematics and timing of the Yucatan Block's detachment and separation from North America and the various major expansions and contractions and the ultimate disappearance of the Western Interior Seaway. Although a number of authors, including this one, have speculated on the timing of separation of Yucatan from North America ( Fillon, 2007a ), no definitive evidence exists: i.e. , drilled samples of the ocean crust and the sediments directly overlying it. Without that unambiguous information we must infer the paleogeographic evolution of the early Gulf of Mexico Basin from deposystem architecture by asking questions such as when do Gulf of Mexico deposystems transition from architectures consistent with deposition in a youthful blockfaulted basin underlain by actively attenuating continental crust to deposition in a mature basin having stable margins surrounding a central region underlain by subsiding ocean crust. An understanding of the paleogeography and paleoceanography of the Gulf of Mexico Basin derived from deposystem architecture can help provide answers to crustal kinematic questions and to more exploration focused questions such as: where, and in section of what age should we look to find facies similar to the organic rich, generative Haynesville Shale facies of eastern Texas and western Louisiana. Although we all know something about the Western Interior Seaway, most of us working on the Mesozoic of the Gulf of Mexico Basin have not spent much time considering what effects it might have had on the prospectivity of Gulf of Mexico deposystems. Through much of Albian and Late Cretaceous time the Western Interior Seaway connected the Gulf of Mexico Basin with the Arctic Ocean Basin. The effects of the establishment and intermittent blocking of this major seaway connecting arctic and tropical water masses on global paleoceanography, on global paleoenvironments, and locally on onshore and offshore Gulf Basin deposystems cannot be ignored in our quest to understand the Mesozoic of the Gulf Rim. This paper is a “big picture” review of Gulf of Mexico Basin deposystem evolution within the Late Jurassic (Oxfordian)–Late Cretaceous (Maastrichtian) interval. Seventeen Mesozoic chronosequences are defined therein based on chronostratigraphic data garnered from over 130,000 industry well and pseudowell penetrations of Mesozoic section in the Gulf of Mexico Basin region. Examination of the collected data suggests that grouping the seventeen Gulf of Mexico Mesozoic chronosequences into seven super-chronose-quences optimally distinguishes key phases of deposystem and basin evolution. The oldest super-chronosequence defined in this study, dubbed “MG,” encompasses ca. 16.45 Ma of Norphlet through lowermost Cotton Valley Late Jurassic deposition. Sediment distribution and accumulation rates within the MG interval clearly define the rectilinear configuration of the earliest Gulf of Mexico Basin. This early basin geometry is consistent with fault controlled attenuation and foundering of North American continental crust, associated flooding, and rapid depositional infill concurrent with the earliest detachment of the Mayan (Yucatan) crustal block from North America. The Yucatan block, although showing an affinity with South American (Amazonian) terranes ( Martens, 2009 ), was left attached to the North American plate when North America began pulling away from Gondwana during the initial breakup of Pangea ( Fillon, 2007a ). The next younger super-chronosequence, “MF,” contains a. ca. 13.47 Ma record of Cotton Valley, Bossier, Knowles limestone., Late Tithonian through mid Hauterivian, deposition. The “MF” interval reflects the same rectilinear outline as the “MG,” but is marked by decreased accumulation rates, suggesting that the fault bounded crustal attenuation, rapid sediment infill phase had markedly slowed. The ca. 9.4 Ma of Hosston, Sligo, Sunniland limestone, James limestone, mid-Hauterivian through Early Aptian section contained within the succeeding “ME” super-chronosequence records modification of the early rectilinear basin outline by a temporary reactivation of attenuation and foundering in the western portion of the Gulf of Mexico Basin. “ME” sediment distribution patterns also indicate development of a depositional continental margin and accumulation of true continental margin type deltaic and reef systems. These observations suggest that during this interval a deep continental basin, probably floored by ocean crust, was beginning to form outboard of the attenuated continental crust. Sediment distribution and accumulation rates within the ca. 23.5 Ma Rodessa through lower Washita, Early Aptian through Early Cenomanian “MD” super-chronosequence reflect growth of the Wisconsin interior seaway and a stable phase of relatively low accumulation rates throughout the entire Gulf of Mexico Basin deposystem. During this interval, deposition was very likely influenced by a vigorous tidal and thermohaline current circulation driven by strong temperature contrasts within the Gulf of Mexico–Wisconsin interior seaway–Arctic Ocean connection. The next younger super-chronosequence, “MC,” contains a ca. ca. 16.0 Ma record of Dantzler, Washita, Lower Pine Key, Eutaw, Woodbine, Eagle Ford, Austin, and Early Cenomanian through Late Santonian (Late Cretaceous) deposition. During this phase, there is a marked reduction of accumulation rates in the north-western portion of the basin, attributable perhaps to expansion of the Western interior seaway and continued subsidence of the old Gulf of Mexico Basin margin. Associated small, perhaps tidal submarine delta-like depopods developed, perhaps in response to the regional Western interior seaway transgression ( Blakey, 2014 ). These delta-like depocenters appear to define a new basin margin presaging the modern curved shape of western Gulf of Mexico so familiar to us today. Here also we see the first unambiguous evidence of abyssal deposition in the deepest portion of the Gulf of Mexico Basin underlain by ocean crust. The succeeding ca. 12.82 Ma interval of Late Santonian through Early Maastrichtian upper Pine Key, upper Selma, upper Austin, Taylor, Olmos, Saratoga, and low accumulation rate mainly chalk and marl deposition contained within the “MB” super-chronosequence provides evidence of transgressive onlap associated with an expanding and deepening interior seaway during “MB” time. “MB” onlap has the effect of temporarily reemphasizing structural trends inherited from crustal attenuation that took place during “ME” time. Finally, the ca. 5.4 Ma long terminal Mesozoic “MA” super-chronosequence consists of Maastrichtian, Navarro equivalent, low accumulation rate marls deposited along the basin margin. These low accumulation rate basin rim sediments and low accumulation rate slope sediments are punctuated by high accumulation rate canyon fill and lobe-shaped slope depopods which are probably attributable to sediment reworking, transport and deposition by transitional Cretaceous-Paleogene (K/P) interval mega-tsunami backwash flows immediately following the Chicxulub impact. Higher accumulation rates in the deeper parts of the basin underlain by ocean crust are also consistent with high volume backwash flows.